Changing an open-chain hydrocarbon to a closed ring. (McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)
The phenomenon whereby compounds whose molecules have the same number and kind of atoms and the same atomic arrangement, but differ in their spatial relationships. (From McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)
The location of the atoms, groups or ions relative to one another in a molecule, as well as the number, type and location of covalent bonds.
Unsaturated hydrocarbons of the type Cn-H2n, indicated by the suffix -ene. (Grant & Hackh's Chemical Dictionary, 5th ed, p408)
Hydrocarbons with at least one triple bond in the linear portion, of the general formula Cn-H2n-2.
Enzymes of the isomerase class that catalyze reactions in which a group can be regarded as eliminated from one part of a molecule, leaving a double bond, while remaining covalently attached to the molecule. (From Enzyme Nomenclature, 1992) EC 5.5.
A chemical element having an atomic weight of 106.4, atomic number of 46, and the symbol Pd. It is a white, ductile metal resembling platinum, and following it in abundance and importance of applications. It is used in dentistry in the form of gold, silver, and copper alloys.
Acetals are chemical compounds formed when a carbonyl group (aldehyde or ketone) reacts with two equivalents of alcohol in the presence of a strong acid, resulting in the formation of a stable carbon-carbon bond and producing water as a byproduct.
The facilitation of a chemical reaction by material (catalyst) that is not consumed by the reaction.
'Ketones' are organic compounds with a specific structure, characterized by a carbonyl group (a carbon double-bonded to an oxygen atom) and two carbon atoms, formed as byproducts when the body breaks down fats for energy due to lack of glucose, often seen in diabetes and starvation states.
Phosphoric or pyrophosphoric acid esters of polyisoprenoids.
The study of the structure, preparation, properties, and reactions of carbon compounds. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)
Acyclic branched or unbranched hydrocarbons having two carbon-carbon double bonds.
'Pyrans' are heterocyclic organic compounds containing a six-membered ring with one oxygen atom and five carbon atoms, which can be found in various natural substances and synthesized compounds, and may have potential applications in medicinal chemistry.
Peptides whose amino and carboxy ends are linked together with a peptide bond forming a circular chain. Some of them are ANTI-INFECTIVE AGENTS. Some of them are biosynthesized non-ribosomally (PEPTIDE BIOSYNTHESIS, NON-RIBOSOMAL).
Alicyclic hydrocarbons in which three or more of the carbon atoms in each molecule are united in a ring structure and each of the ring carbon atoms is joined to two hydrogen atoms or alkyl groups. The simplest members are cyclopropane (C3H6), cyclobutane (C4H8), cyclohexane (C6H12), and derivatives of these such as methylcyclohexane (C6H11CH3). (From Sax, et al., Hawley's Condensed Chemical Dictionary, 11th ed)
Any chemical species which accepts an electron-pair from a LEWIS BASE in a chemical bonding reaction.
Rhodium. A hard and rare metal of the platinum group, atomic number 45, atomic weight 102.905, symbol Rh. (Dorland, 28th ed)
A technology, in which sets of reactions for solution or solid-phase synthesis, is used to create molecular libraries for analysis of compounds on a large scale.
A class of enzymes that catalyze geometric or structural changes within a molecule to form a single product. The reactions do not involve a net change in the concentrations of compounds other than the substrate and the product.(from Dorland, 28th ed) EC 5.
Group of alkaloids containing a benzylpyrrole group (derived from TRYPTOPHAN)
Imines are organic compounds containing a functional group with a carbon-nitrogen double bond (=NH or =NR), classified as azomethines, which can be produced from aldehydes or ketones through condensation with ammonia or amines.
A continuous circle of peptide bonds, typically of 2-3 dozen AMINO ACIDS, so there is no free N- or C-terminus. They are further characterized by six conserved CYSTEINE residues that form CYSTINE KNOT MOTIFS.
Ring compounds having atoms other than carbon in their nuclei. (Grant & Hackh's Chemical Dictionary, 5th ed)
The characteristic three-dimensional shape of a molecule.
A class of organic compounds containing four or more ring structures, one of which is made up of more than one kind of atom, usually carbon plus another atom. The heterocycle may be either aromatic or nonaromatic.
The creation of an amine. It can be produced by the addition of an amino group to an organic compound or reduction of a nitro group.
Enzymes that catalyze the cleavage of a carbon-carbon bond by means other than hydrolysis or oxidation. This subclass contains the DECARBOXYLASES, the ALDEHYDE-LYASES, and the OXO-ACID-LYASES. EC 4.1.
Compounds with a 5-membered ring of four carbons and an oxygen. They are aromatic heterocycles. The reduced form is tetrahydrofuran.
A class of compounds composed of repeating 5-carbon units of HEMITERPENES.
Organic compounds that include a cyclic ether with three ring atoms in their structure. They are commonly used as precursors for POLYMERS such as EPOXY RESINS.
Large enzyme complexes composed of a number of component enzymes that are found in STREPTOMYCES which biosynthesize MACROLIDES and other polyketides.
Cyclic compounds with a ring size of approximately 1-4 dozen atoms.
The excision of in-frame internal protein sequences (INTEINS) of a precursor protein, coupled with ligation of the flanking sequences (EXTEINS). Protein splicing is an autocatalytic reaction and results in the production of two proteins from a single primary translation product: the intein and the mature protein.
A plant genus of the family RUBIACEAE. Some species are used as an ingredient in Chinese and African traditional medicines. Members contain kalata B1, a macrocyclic peptide.
The collective name for the boron hydrides, which are analogous to the alkanes and silanes. Numerous boranes are known. Some have high calorific values and are used in high-energy fuels. (From Grant & Hackh's Chemical Dictionary, 5th ed)
Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures.
Techniques used to synthesize chemicals using molecular substrates that are bound to a solid surface. Typically a series of reactions are conducted on the bound substrate that results in either the covalent attachment of specific moieties or the modification of existing function groups. These techniques offer an advantage to those involving solution reactions in that the substrate compound does not have to be isolated and purified between the reaction steps.
Norbornanes are a class of bicyclic organic compounds consisting of a hydrocarbon skeleton made up of two fused 5-membered rings, where five of the six ring carbons are bonded to hydrogens and one is bonded to two additional carbon atoms, forming a bridge between the rings.
A class of organic compounds containing two ring structures, one of which is made up of more than one kind of atom, usually carbon plus another atom. The heterocycle may be either aromatic or nonaromatic.
A homologous group of cyclic GLUCANS consisting of alpha-1,4 bound glucose units obtained by the action of cyclodextrin glucanotransferase on starch or similar substrates. The enzyme is produced by certain species of Bacillus. Cyclodextrins form inclusion complexes with a wide variety of substances.
'Squalene' is a biologically occurring triterpene compound, naturally produced in humans, animals, and plants, that forms an essential part of the lipid-rich membranes in various tissues, including the skin surface and the liver, and has been studied for its potential benefits in skincare, dietary supplements, and vaccine adjuvant systems.
The internal fragments of precursor proteins (INternal proTEINS) that are autocatalytically removed by PROTEIN SPLICING. The flanking fragments (EXTEINS) are ligated forming mature proteins. The nucleic acid sequences coding for inteins are considered to be MOBILE GENETIC ELEMENTS. Inteins are composed of self-splicing domains and an endonuclease domain which plays a role in the spread of the intein's genomic sequence. Mini-inteins are composed of the self-splicing domains only.
Amino acid sequence in which two disulfide bonds (DISULFIDES) and their connecting backbone form a ring that is penetrated by a third disulfide bond. Members include CYCLOTIDES and agouti-related protein.
Spectroscopic method of measuring the magnetic moment of elementary particles such as atomic nuclei, protons or electrons. It is employed in clinical applications such as NMR Tomography (MAGNETIC RESONANCE IMAGING).
Natural compounds containing alternating carbonyl and methylene groups (beta-polyketones), bioenergenetically derived from repeated condensation of acetyl coenzyme A via malonyl coenzyme A, in a process similar to fatty acid synthesis.
Compounds with a core of 10 carbons generally formed via the mevalonate pathway from the combination of 3,3-dimethylallyl pyrophosphate and isopentenyl pyrophosphate. They are cyclized and oxidized in a variety of ways. Due to the low molecular weight many of them exist in the form of essential oils (OILS, VOLATILE).
A plant genus in the family PINACEAE, order Pinales, class Pinopsida, division Coniferophyta. Balm of Gilead is a common name more often referring to POPULUS and sometimes to COMMIPHORA.
Organic compounds containing a carbonyl group in the form -CHO.
Twenty-carbon compounds derived from MEVALONIC ACID or deoxyxylulose phosphate.
Naphthalene derivatives carrying one or more hydroxyl (-OH) groups at any ring position. They are often used in dyes and pigments, as antioxidants for rubber, fats, and oils, as insecticides, in pharmaceuticals, and in numerous other applications.
A plant genus of the family LOGANIACEAE (classified by some botanists as Strychnaceae).
A group of compounds consisting in part of two rings sharing one atom (usually a carbon) in common.
A genus of bacteria that form a nonfragmented aerial mycelium. Many species have been identified with some being pathogenic. This genus is responsible for producing a majority of the ANTI-BACTERIAL AGENTS of practical value.
Organic nitrogenous bases. Many alkaloids of medical importance occur in the animal and vegetable kingdoms, and some have been synthesized. (Grant & Hackh's Chemical Dictionary, 5th ed)
Synthetic organic reactions that use reactions between unsaturated molecules to form cyclical products.
Inorganic compounds that contain bromine as an integral part of the molecule.
Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.
Sesquiterpenes are a class of terpenes consisting of three isoprene units, forming a 15-carbon skeleton, which can be found in various plant essential oils and are known for their diverse chemical structures and biological activities, including anti-inflammatory, antimicrobial, and cytotoxic properties.
The study of crystal structure using X-RAY DIFFRACTION techniques. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)
A highly toxic gas that has been used as a chemical warfare agent. It is an insidious poison as it is not irritating immediately, even when fatal concentrations are inhaled. (From The Merck Index, 11th ed, p7304)
'Bicyclo compounds' in medicinal chemistry refer to organic molecules containing two fused rings, where each ring shares two common atoms, creating a topological structure that resembles two overlapping circles or bicycle tires.
1,4-alpha-D-Glucan-1,4-alpha-D-glucan 4-alpha-D-glucosyltransferase/dextrin 6 alpha-D-glucanohydrolase. An enzyme system having both 4-alpha-glucanotransferase (EC and amylo-1,6-glucosidase (EC activities. As a transferase it transfers a segment of a 1,4-alpha-D-glucan to a new 4-position in an acceptor, which may be glucose or another 1,4-alpha-D-glucan. As a glucosidase it catalyzes the endohydrolysis of 1,6-alpha-D-glucoside linkages at points of branching in chains of 1,4-linked alpha-D-glucose residues. Amylo-1,6-glucosidase activity is deficient in glycogen storage disease type III.
Semicarbazides are organic compounds containing a functional group with the structure NH2-NH-CO-NH2, which are commonly used as reagents in chemical reactions to form semicarbazones, and can also be found in some pharmaceuticals and industrial chemicals.
Esters formed between the aldehydic carbon of sugars and the terminal phosphate of guanosine diphosphate.
Theoretical representations that simulate the behavior or activity of chemical processes or phenomena; includes the use of mathematical equations, computers, and other electronic equipment.

Do enzymes obey the Baldwin rules? A mechanistic imperative in enzymatic cyclization reactions. (1/1346)

It is commonly assumed that enzymes have evolved to abide by the same energetic and stereoelectronic principles that govern reactions in solution. The principles formulated for organic ring-closure reactions can be used to develop a hypothesis for analysis of enzyme-catalyzed cyclization reactions.  (+info)

Purification and characterization of 2-deoxy-scyllo-inosose synthase derived from Bacillus circulans. A crucial carbocyclization enzyme in the biosynthesis of 2-deoxystreptamine-containing aminoglycoside antibiotics. (2/1346)

The biosynthesis of 2-deoxystreptamine, the central aglycon of a major group of clinically important aminoglycoside antibiotics, commences with the initial carbocycle formation step from D-glucose-6-phosphate to 2-deoxy-scyllo-inosose. This crucial step is known to be catalyzed by 2-deoxy-scyllo-inosose synthase, which has not yet been characterized so far. Reported in this paper is the first purification of 2-deoxy-scyllo-inosose synthase from butirosin-producing Bacillus circulans SANK 72073 to electrophoretic homogeneity. The enzyme was isolated as a heterodimeric protein comprising from a 23 kDa- and a 42 kDa polypeptide chains. The Km of the enzyme for D-glucose-6-phosphate was estimated to be 9.0 x 10(-4) M and that for NAD+ 1.7 x 10(-4) M, kcat for D-glucose-6-phosphate being 7.3 x 10(-2) s(-1). The presence of Co2+ was essential for the enzyme activity, but Zn2+ was totally inhibitory. While the reaction mechanisms are quite similar, 2-deoxy-scyllo-inosose synthase appears to be distinct from dehydroquinate synthase in the shikimate pathway, with respect to the quaternary structure, metal ion requirement, and the kinetic parameters.  (+info)

Elucidating the mechanism of chain termination switching in the picromycin/methymycin polyketide synthase. (3/1346)

BACKGROUND: A single modular polyketide synthase (PKS) gene cluster is responsible for production of both the 14-membered macrolide antibiotic picromycin and the 12-membered macrolide antibiotic methymycin in Streptomyces venezuelae. Building on the success of the heterologous expression system engineered using the erythromycin PKS, we have constructed an analogous system for the picromycin/methymycin PKS. Through heterologous expression and construction of a hybrid PKS, we have examined the contributions that the PKS, its internal thioesterase domain (pikTE) and the Pik TEII thioesterase domain make in termination and cyclization of the two polyketide intermediates. RESULTS: The picromycin/methymycin PKS genes were functionally expressed in the heterologous host Streptomyces lividans, resulting in production of both narbonolide and 10-deoxymethynolide (the precursors of picromycin and methymycin, respectively). Co-expression with the Pik TEII thioesterase led to increased production levels, but did not change the ratio of the two compounds produced, leaving the function of this protein largely unknown. Fusion of the PKS thioesterase domain (pikTE) to 6-deoxyerythronolide B synthase (DEBS) resulted in formation of only 14-membered macrolactones. CONCLUSIONS: These experiments demonstrate that the PKS alone is capable of catalyzing the synthesis of both 14- and 12-membered macrolactones and favor a model by which different macrolactone rings result from a combination of the arrangement between the module 5 and module 6 subunits in the picromycin PKS complex and the selectivity of the pikTE domain.  (+info)

Heterologous expression, purification, reconstitution and kinetic analysis of an extended type II polyketide synthase. (4/1346)

BACKGROUND: Polyketide synthases (PKSs) are bacterial multienzyme systems that synthesize a broad range of natural products. The 'minimal' PKS consists of a ketosynthase, a chain length factor, an acyl carrier protein and a malonyl transferase. Auxiliary components (ketoreductases, aromatases and cyclases are involved in controlling the oxidation level and cyclization of the nascent polyketide chain. We describe the heterologous expression and reconstitution of several auxiliary PKS components including the actinorhodin ketoreductase (act KR), the griseusin aromatase/cyclase (gris ARO/CYC), and the tetracenomycin aromatase/cyclase (tcm ARO/CYC). RESULTS: The polyketide products of reconstituted act and tcm PKSs were identical to those identified in previous in vivo studies. Although stable protein-protein interactions were not detected between minimal and auxiliary PKS components, kinetic analysis revealed that the extended PKS comprised of the act minimal PKS, the act KR and the gris ARO/CYC had a higher turnover number than the act minimal PKS plus the act KR or the act minimal PKS alone. Adding the tcm ARO/CYC to the tcm minimal PKS also increased the overall rate. CONCLUSIONS: Until recently the principal strategy for functional analysis of PKS subunits was through heterologous expression of recombinant PKSs in Streptomyces. Our results corroborate the implicit assumption that the product isolated from whole-cell systems is the dominant product of the PKS. They also suggest that an intermediate is channeled between the various subunits, and pave the way for more detailed structural and mechanistic analysis of these multienzyme systems.  (+info)

Protein aging hypothesis of Alzheimer disease. (5/1346)

Alzheimer disease (AD), the most common form of aging-related neurodegenerative disorders, is associated with formation of fibrillar deposits of amyloid beta-protein (Abeta). While the direct involvement of Abeta in AD has been well documented, the relations between Abeta production, amyloid formation, and neurodegeneration remain unknown. We propose that AD is initiated by a protein aging-related structural transformation in soluble Abeta. We hypothesize that spontaneous chemical modification of aspartyl residues in Abeta to transient succinimide induces a non-native conformation in a fraction of soluble Abeta, rendering it amyloidogenic and neurotoxic. Conformationally altered Abeta is characterized by increased stability in solution and the presence of a non-native beta-turn that determines folding of Abeta in solution and the structure of Abeta subunits incorporated into amyloid fibrils. While the soluble 'non-native' Abeta is both the factor triggering the neurodegenerative cascade and the precursor of amyloid plaques, these two events result from interaction of Abeta with different sets of cellular components and need not coincide in space and time. Extensive literature data and experimental evidence are provided in support of this hypothesis.  (+info)

Site-directed mutagenesis of squalene-hopene cyclase: altered substrate specificity and product distribution. (6/1346)

BACKGROUND: Two regions of squalene-hopene cyclase (SHC) were examined to define roles for motifs posited to be responsible for initiation and termination of the enzyme-catalyzed polyolefinic cyclizations. Specifically, we first examined the triple mutant of the DDTAVV motif, a region deeply buried in the catalytic cavity and thought to be responsible for the initiation of squalene cyclization. Next, four mutants were prepared for Glu45, a residue close to the substrate entrance channel proposed to be involved in the termination of the cyclization of squalene. RESULTS: The DDTAVV motif in SHC was changed to DCTAEA, the corresponding conserved region of eukaryotic oxidosqualene cyclase (OSC), by the triple mutation of D377C/V380E/V381A; selected single mutants were also examined. The triple mutant showed no detectable cyclization of squalene, but effectively cyclized 2,3-oxidosqualene to give mono- and pentacyclic triterpene products. Of the Glu45 mutants, E45A and E45D showed reduced activity, E45Q showed slightly increased activity, and E45K was inactive. A normal yield of pentacyclic products was produced, but the ratio of hopene 2 to hopanol 3 was significantly changed in the less active mutants. CONCLUSIONS: Initiation and substrate selectivity may be determined by the interaction of the DDTAVV motif with the isopropylidene of squalene (for SHC) and of the DCTAEA motif with the epoxide of oxidosqualene (for OSC). This is the first report of a substrate switch determined by a central catalytic motif in a triterpenoid cyclase. At the termination of cyclization, the product ratio may be largely controlled by Glu45 at the entrance channel to the active site.  (+info)

Aureusidin synthase: a polyphenol oxidase homolog responsible for flower coloration. (7/1346)

Aurones are plant flavonoids that provide yellow color to the flowers of some popular ornamental plants, such as snapdragon and cosmos. In this study, we have identified an enzyme responsible for the synthesis of aurone from chalcones in the yellow snapdragon flower. The enzyme (aureusidin synthase) is a 39-kilodalton, copper-containing glycoprotein catalyzing the hydroxylation and/or oxidative cyclization of the precursor chalcones, 2',4',6',4-tetrahydroxychalcone and 2',4',6',3,4-pentahydroxychalcone. The complementary DNA encoding aureusidin synthase is expressed in the petals of aurone-containing varieties. DNA sequence analysis revealed that aureusidin synthase belongs to the plant polyphenol oxidase family, providing an unequivocal example of the function of the polyphenol oxidase homolog in plants, i.e., flower coloration.  (+info)

Intramolecular proton transfer in the cyclization of geranylgeranyl diphosphate to the taxadiene precursor of taxol catalyzed by recombinant taxadiene synthase. (8/1346)

BACKGROUND: The committed step in the biosynthesis of the anticancer drug taxol in yew (Taxus) species is the cyclization of geranylgeranyl diphosphate to taxa-4(5),11(12)-diene. The enzyme taxadiene synthase catalyzes this complex olefin cation cyclization cascade involving the formation of three rings and three stereogenic centers. RESULTS: Recombinant taxadiene synthase was incubated with specifically deuterated substrates, and the mechanism of cyclization was probed using MS and NMR analyses of the products to define the crucial hydrogen migration and terminating deprotonation steps. The electrophilic cyclization involves the ionization of the diphosphate with closure of the A-ring, followed by a unique intramolecular transfer of the C11 proton to the re-face of C7 to promote closure of the B/C-ring juncture, and cascade termination by proton elimination from the beta-face of C5. CONCLUSIONS: These findings provide insight into the molecular architecture of the first dedicated step of taxol biosynthesis that creates the taxane carbon skeleton, and they have broad implications for the general mechanistic capability of the large family of terpenoid cyclization enzymes.  (+info)

Cyclization is a chemical process that involves forming a cyclic structure or ring-shaped molecule from a linear or open-chain compound. In the context of medicinal chemistry and drug design, cyclization reactions are often used to synthesize complex molecules, including drugs, by creating rings or fused ring systems within the molecule's structure.

Cyclization can occur through various mechanisms, such as intramolecular nucleophilic substitution, electrophilic addition, or radical reactions. The resulting cyclized compounds may exhibit different chemical and biological properties compared to their linear precursors, making them valuable targets for drug discovery and development.

In some cases, the cyclization process can lead to the formation of stereocenters within the molecule, which can impact its three-dimensional shape and how it interacts with biological targets. Therefore, controlling the stereochemistry during cyclization reactions is crucial in medicinal chemistry to optimize the desired biological activity.

Overall, cyclization plays a significant role in the design and synthesis of many pharmaceutical compounds, enabling the creation of complex structures that can interact specifically with biological targets for therapeutic purposes.

Stereoisomerism is a type of isomerism (structural arrangement of atoms) in which molecules have the same molecular formula and sequence of bonded atoms, but differ in the three-dimensional orientation of their atoms in space. This occurs when the molecule contains asymmetric carbon atoms or other rigid structures that prevent free rotation, leading to distinct spatial arrangements of groups of atoms around a central point. Stereoisomers can have different chemical and physical properties, such as optical activity, boiling points, and reactivities, due to differences in their shape and the way they interact with other molecules.

There are two main types of stereoisomerism: enantiomers (mirror-image isomers) and diastereomers (non-mirror-image isomers). Enantiomers are pairs of stereoisomers that are mirror images of each other, but cannot be superimposed on one another. Diastereomers, on the other hand, are non-mirror-image stereoisomers that have different physical and chemical properties.

Stereoisomerism is an important concept in chemistry and biology, as it can affect the biological activity of molecules, such as drugs and natural products. For example, some enantiomers of a drug may be active, while others are inactive or even toxic. Therefore, understanding stereoisomerism is crucial for designing and synthesizing effective and safe drugs.

Molecular structure, in the context of biochemistry and molecular biology, refers to the arrangement and organization of atoms and chemical bonds within a molecule. It describes the three-dimensional layout of the constituent elements, including their spatial relationships, bond lengths, and angles. Understanding molecular structure is crucial for elucidating the functions and reactivities of biological macromolecules such as proteins, nucleic acids, lipids, and carbohydrates. Various experimental techniques, like X-ray crystallography, nuclear magnetic resonance (NMR) spectroscopy, and cryo-electron microscopy (cryo-EM), are employed to determine molecular structures at atomic resolution, providing valuable insights into their biological roles and potential therapeutic targets.

Alkenes are unsaturated hydrocarbons that contain at least one carbon-carbon double bond in their molecular structure. The general chemical formula for alkenes is CnH2n, where n represents the number of carbon atoms in the molecule.

The double bond in alkenes can undergo various reactions, such as addition reactions, where different types of molecules can add across the double bond to form new compounds. The relative position of the double bond in the carbon chain and the presence of substituents on the carbon atoms can affect the physical and chemical properties of alkenes.

Alkenes are important industrial chemicals and are used as starting materials for the synthesis of a wide range of products, including plastics, resins, fibers, and other chemicals. They are also found in nature, occurring in some plants and animals, and can be produced by certain types of bacteria through fermentation processes.

Alkynes are a type of hydrocarbons that contain at least one carbon-carbon triple bond in their molecular structure. The general chemical formula for alkynes is CnH2n-2, where n represents the number of carbon atoms in the molecule.

The simplest and shortest alkyne is ethyne, also known as acetylene, which has two carbon atoms and four hydrogen atoms (C2H2). Ethyne is a gas at room temperature and pressure, and it is commonly used as a fuel in welding torches.

Alkynes are unsaturated hydrocarbons, meaning that they have the potential to undergo chemical reactions that add atoms or groups of atoms to the molecule. In particular, alkynes can be converted into alkenes (hydrocarbons with a carbon-carbon double bond) through a process called partial reduction, or they can be fully reduced to alkanes (hydrocarbons with only single bonds between carbon atoms) through a process called complete reduction.

Alkynes are important intermediates in the chemical industry and are used to produce a wide range of products, including plastics, resins, fibers, and pharmaceuticals. They can be synthesized from other hydrocarbons through various chemical reactions, such as dehydrogenation, oxidative coupling, or metathesis.

Intramolecular lyases are a type of enzyme that catalyzes the breakdown of a molecule by removing a group of atoms from within the same molecule, creating a new chemical bond in the process. These enzymes specifically cleave a molecule through an intramolecular mechanism, meaning they act on a single substrate molecule. Intramolecular lyases are involved in various biological processes, such as DNA replication, repair, and recombination. They play a crucial role in maintaining the integrity of genetic material by removing or adding specific groups of atoms to DNA or RNA molecules.

I'm sorry for the confusion, but "Palladium" is not a medical term. It is a chemical element with symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. It's used in various applications, including jewelry, dental work, electronics, and chemical reactions. If you have any medical terms you would like me to define, please let me know!

An acetal is a chemical compound that contains two ether functional groups (-O-) bonded to two carbon atoms, which in turn are bonded to two other carbon atoms forming a six-membered ring. Acetals are formed by the reaction of an aldehyde with two equivalents of an alcohol under acid catalysis, followed by removal of water. They are stable compounds that do not easily hydrolyze back to their starting materials, making them useful in various chemical and industrial applications. In the context of organic chemistry, acetals are a subclass of hemiacetals, which contain only one ether functional group bonded to a carbon atom that is also bonded to another oxygen-containing group.

Catalysis is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst, which remains unchanged at the end of the reaction. A catalyst lowers the activation energy required for the reaction to occur, thereby allowing the reaction to proceed more quickly and efficiently. This can be particularly important in biological systems, where enzymes act as catalysts to speed up metabolic reactions that are essential for life.

Ketones are organic compounds that contain a carbon atom bound to two oxygen atoms and a central carbon atom bonded to two additional carbon groups through single bonds. In the context of human physiology, ketones are primarily produced as byproducts when the body breaks down fat for energy in a process called ketosis.

Specifically, under conditions of low carbohydrate availability or prolonged fasting, the liver converts fatty acids into ketone bodies, which can then be used as an alternative fuel source for the brain and other organs. The three main types of ketones produced in the human body are acetoacetate, beta-hydroxybutyrate, and acetone.

Elevated levels of ketones in the blood, known as ketonemia, can occur in various medical conditions such as diabetes, starvation, alcoholism, and high-fat/low-carbohydrate diets. While moderate levels of ketosis are generally considered safe, severe ketosis can lead to a life-threatening condition called diabetic ketoacidosis (DKA) in people with diabetes.

Polyisoprenyl phosphates are a type of organic compound that play a crucial role in the biosynthesis of various essential biomolecules in cells. They are formed by the addition of isoprene units, which are five-carbon molecules with a branched structure, to a phosphate group.

In medical terms, polyisoprenyl phosphates are primarily known for their role as intermediates in the biosynthesis of dolichols and farnesylated proteins. Dolichols are long-chain isoprenoids that function as lipid carriers in the synthesis of glycoproteins, which are proteins that contain carbohydrate groups attached to them. Farnesylated proteins, on the other hand, are proteins that have been modified with a farnesyl group, which is a 15-carbon isoprenoid. This modification plays a role in the localization and function of certain proteins within the cell.

Abnormalities in the biosynthesis of polyisoprenyl phosphates and their downstream products have been implicated in various diseases, including cancer, neurological disorders, and genetic syndromes. Therefore, understanding the biology and regulation of these compounds is an active area of research with potential therapeutic implications.

Organic chemistry is a branch of chemistry that deals with the study of carbon-containing compounds, their synthesis, reactions, properties, and structures. These compounds can include both naturally occurring substances (such as sugars, proteins, and nucleic acids) and synthetic materials (such as plastics, dyes, and pharmaceuticals). A key characteristic of organic molecules is the presence of covalent bonds between carbon atoms or between carbon and other elements like hydrogen, oxygen, nitrogen, sulfur, and halogens. The field of organic chemistry has played a crucial role in advancing our understanding of chemical processes and has led to numerous technological and medical innovations.

Alkadienes are organic compounds that contain two carbon-carbon double bonds in their molecular structure. The term "alka" refers to the presence of hydrocarbons, while "diene" indicates the presence of two double bonds. These compounds can be classified as either conjugated or non-conjugated dienes based on the arrangement of the double bonds.

Conjugated dienes have their double bonds adjacent to each other, separated by a single bond, while non-conjugated dienes have at least one methylene group (-CH2-) separating the double bonds. The presence and positioning of these double bonds can significantly affect the chemical and physical properties of alkadienes, including their reactivity, stability, and spectral characteristics.

Alkadienes are important intermediates in various chemical reactions and have applications in the production of polymers, pharmaceuticals, and other industrial products. However, they can also be produced naturally by some plants and microorganisms as part of their metabolic processes.

"Pyrans" is not a term commonly used in medical definitions. It is a chemical term that refers to a class of heterocyclic compounds containing a six-membered ring with one oxygen atom and five carbon atoms. The name "pyran" comes from the fact that it contains a pyroline unit (two double-bonded carbons) and a ketone group (a carbon double-bonded to an oxygen).

While pyrans are not directly related to medical definitions, some of their derivatives have been studied for potential medicinal applications. For example, certain pyran derivatives have shown anti-inflammatory, antiviral, and anticancer activities in laboratory experiments. However, more research is needed before these compounds can be considered as potential therapeutic agents.

Cyclic peptides are a type of peptides in which the N-terminus and C-terminus of the peptide chain are linked to form a circular structure. This is in contrast to linear peptides, which have a straight peptide backbone with a free N-terminus and C-terminus. The cyclization of peptides can occur through various mechanisms, including the formation of an amide bond between the N-terminal amino group and the C-terminal carboxylic acid group (head-to-tail cyclization), or through the formation of a bond between side chain functional groups.

Cyclic peptides have unique structural and chemical properties that make them valuable in medical and therapeutic applications. For example, they are more resistant to degradation by enzymes compared to linear peptides, which can increase their stability and half-life in the body. Additionally, the cyclic structure allows for greater conformational rigidity, which can enhance their binding affinity and specificity to target molecules.

Cyclic peptides have been explored as potential therapeutics for a variety of diseases, including cancer, infectious diseases, and neurological disorders. They have also been used as tools in basic research to study protein-protein interactions and cell signaling pathways.

Cycloparaffins, also known as naphthenes or cycloalkanes, are a type of hydrocarbon molecule that contain one or more closed rings of carbon atoms. These rings can be saturated, meaning that they contain only single bonds between the carbon atoms, and may also contain one or more alkyl substituents.

The term "cycloparaffin" is used in the context of organic chemistry and petroleum refining to describe a specific class of hydrocarbons. In medical terminology, cycloparaffins are not typically referenced directly, but they may be relevant in certain contexts, such as in discussions of industrial chemicals or environmental exposures.

Cycloparaffins can be found in various sources, including crude oil and natural gas, and they are often used as feedstocks in the production of various chemicals and materials. They are also found in some foods, such as vegetable oils and animal fats, and may be present in trace amounts in some medications or medical devices.

While cycloparaffins themselves are not typically considered to have direct medical relevance, exposure to certain types of cycloparaffins or their derivatives may be associated with various health effects, depending on the level and duration of exposure. For example, some cycloparaffin-derived chemicals have been linked to respiratory irritation, skin and eye irritation, and potential developmental toxicity. However, it is important to note that these effects are typically associated with high levels of exposure in occupational or industrial settings, rather than with normal environmental or dietary exposures.

I'm sorry for any confusion, but "Lewis acids" is actually a term from the field of chemistry rather than medicine. It was named after Gilbert N. Lewis, who proposed the concept in 1923. A Lewis acid is defined as an electron-pair acceptor in a chemical reaction. In simpler terms, it's a molecule or ion that can accept a pair of electrons from another molecule or ion to form a covalent bond. Common examples of Lewis acids include aluminum chloride (AlCl3), boron trifluoride (BF3), and iron(III) chloride (FeCl3).

I'm sorry for any confusion, but "Rhodium" is not a medical term. It is a chemical element with the symbol Rh and atomic number 45. It is a rare, silvery-white, hard, corrosion-resistant, and chemically inert transition metal. It is found in small quantities in platinum or nickel ores along with some other rare metals.

It's primarily used in industrial applications, such as being a key component in catalytic converters in automobiles, which helps to reduce harmful emissions. It's also used in jewelry, electronics, and scientific instruments due to its properties of resistance to corrosion and heat.

If you have any medical terms or concepts that you would like me to explain, please let me know!

Combinatorial chemistry techniques are a group of methods used in the field of chemistry to synthesize and optimize large libraries of chemical compounds in a rapid and efficient manner. These techniques involve the systematic combination of different building blocks, or reagents, in various arrangements to generate a diverse array of molecules. This approach allows chemists to quickly explore a wide chemical space and identify potential lead compounds for drug discovery, materials science, and other applications.

There are several common combinatorial chemistry techniques, including:

1. **Split-Pool Synthesis:** In this method, a large collection of starting materials is divided into smaller groups, and each group undergoes a series of chemical reactions with different reagents. The resulting products from each group are then pooled together and redistributed for additional rounds of reactions. This process creates a vast number of unique compounds through the iterative combination of building blocks.
2. **Parallel Synthesis:** In parallel synthesis, multiple reactions are carried out simultaneously in separate reaction vessels. Each vessel contains a distinct set of starting materials and reagents, allowing for the efficient generation of a series of related compounds. This method is particularly useful when exploring structure-activity relationships (SAR) or optimizing lead compounds.
3. **Encoded Libraries:** To facilitate the rapid identification of active compounds within large libraries, encoded library techniques incorporate unique tags or barcodes into each molecule. These tags allow for the simultaneous synthesis and screening of compounds, as the identity of an active compound can be determined by decoding its corresponding tag.
4. **DNA-Encoded Libraries (DELs):** DELs are a specific type of encoded library that uses DNA molecules to encode and track chemical compounds. In this approach, each unique compound is linked to a distinct DNA sequence, enabling the rapid identification of active compounds through DNA sequencing techniques.
5. **Solid-Phase Synthesis:** This technique involves the attachment of starting materials to a solid support, such as beads or resins, allowing for the stepwise addition of reagents and building blocks. The solid support facilitates easy separation, purification, and screening of compounds, making it an ideal method for combinatorial chemistry applications.

Combinatorial chemistry techniques have revolutionized drug discovery and development by enabling the rapid synthesis, screening, and optimization of large libraries of chemical compounds. These methods continue to play a crucial role in modern medicinal chemistry and materials science research.

Isomerases are a class of enzymes that catalyze the interconversion of isomers of a single molecule. They do this by rearranging atoms within a molecule to form a new structural arrangement or isomer. Isomerases can act on various types of chemical bonds, including carbon-carbon and carbon-oxygen bonds.

There are several subclasses of isomerases, including:

1. Racemases and epimerases: These enzymes interconvert stereoisomers, which are molecules that have the same molecular formula but different spatial arrangements of their atoms in three-dimensional space.
2. Cis-trans isomerases: These enzymes interconvert cis and trans isomers, which differ in the arrangement of groups on opposite sides of a double bond.
3. Intramolecular oxidoreductases: These enzymes catalyze the transfer of electrons within a single molecule, resulting in the formation of different isomers.
4. Mutases: These enzymes catalyze the transfer of functional groups within a molecule, resulting in the formation of different isomers.
5. Tautomeres: These enzymes catalyze the interconversion of tautomers, which are isomeric forms of a molecule that differ in the location of a movable hydrogen atom and a double bond.

Isomerases play important roles in various biological processes, including metabolism, signaling, and regulation.

Indole alkaloids are a type of naturally occurring organic compound that contain an indole structural unit, which is a heterocyclic aromatic ring system consisting of a benzene ring fused to a pyrrole ring. These compounds are produced by various plants and animals as secondary metabolites, and they have diverse biological activities. Some indole alkaloids have important pharmacological properties and are used in medicine as drugs or lead compounds for drug discovery. Examples of medically relevant indole alkaloids include reserpine, which is used to treat hypertension, and vinblastine and vincristine, which are used to treat various types of cancer.

In the field of organic chemistry, imines are a class of compounds that contain a functional group with the general structure =CR-NR', where C=R and R' can be either alkyl or aryl groups. Imines are also commonly referred to as Schiff bases. They are formed by the condensation of an aldehyde or ketone with a primary amine, resulting in the loss of a molecule of water.

It is important to note that imines do not have a direct medical application, but they can be used as intermediates in the synthesis of various pharmaceuticals and bioactive compounds. Additionally, some imines have been found to exhibit biological activity, such as antimicrobial or anticancer properties. However, these are areas of ongoing research and development.

Cyclotides are a group of naturally occurring cyclic peptides that contain a head-to-tail cyclized structure and a conserved cystine knot motif. They are produced by plants, particularly those in the Rubiaceae family, as a defense mechanism against herbivores and pathogens.

Cyclotides have unique structural features, including a circular arrangement of amino acids and a knotted pattern of disulfide bonds, which contribute to their stability and resistance to degradation. These properties make them attractive candidates for drug development and therapeutic applications.

In addition to their potential use as drugs, cyclotides have also been studied for their potential as insecticides, antimicrobial agents, and anti-cancer therapies. They have been shown to have potent activity against a variety of targets, including cancer cells, bacteria, fungi, and viruses.

Overall, the unique structural and functional properties of cyclotides make them an exciting area of research in the fields of medicinal chemistry, pharmacology, and drug discovery.

Heterocyclic compounds are organic compounds that contain at least one atom within the ring structure, other than carbon, such as nitrogen, oxygen, sulfur or phosphorus. These compounds make up a large class of naturally occurring and synthetic materials, including many drugs, pigments, vitamins, and antibiotics. The presence of the heteroatom in the ring can have significant effects on the physical and chemical properties of the compound, such as its reactivity, stability, and bonding characteristics. Examples of heterocyclic compounds include pyridine, pyrimidine, and furan.

Molecular conformation, also known as spatial arrangement or configuration, refers to the specific three-dimensional shape and orientation of atoms that make up a molecule. It describes the precise manner in which bonds between atoms are arranged around a molecular framework, taking into account factors such as bond lengths, bond angles, and torsional angles.

Conformational isomers, or conformers, are different spatial arrangements of the same molecule that can interconvert without breaking chemical bonds. These isomers may have varying energies, stability, and reactivity, which can significantly impact a molecule's biological activity and function. Understanding molecular conformation is crucial in fields such as drug design, where small changes in conformation can lead to substantial differences in how a drug interacts with its target.

Heterocyclic compounds with 4 or more rings refer to a class of organic compounds that contain at least four aromatic or non-aromatic rings in their structure, where one or more of the rings contains atoms other than carbon (heteroatoms) such as nitrogen, oxygen, sulfur, or selenium. These compounds are widely found in nature and have significant importance in medicinal chemistry due to their diverse biological activities. Many natural and synthetic drugs, pigments, vitamins, and antibiotics contain heterocyclic structures with four or more rings. The properties of these compounds depend on the size, shape, and nature of the rings, as well as the presence and position of functional groups.

Amination is a chemical process or reaction that involves the addition of an amino group (-NH2) to a molecule. This process is often used in organic chemistry to create amines, which are compounds containing a basic nitrogen atom with a lone pair of electrons.

In the context of biochemistry, amination reactions play a crucial role in the synthesis of various biological molecules, including amino acids, neurotransmitters, and nucleotides. For example, the enzyme glutamine synthetase catalyzes the amination of glutamate to form glutamine, an essential amino acid for many organisms.

It is important to note that there are different types of amination reactions, depending on the starting molecule and the specific amino group donor. The precise mechanism and reagents used in an amination reaction will depend on the particular chemical or biological context.

Carbon-carbon lyases are a class of enzymes that catalyze the breaking of carbon-carbon bonds in a substrate, resulting in the formation of two molecules with a double bond between them. This reaction is typically accompanied by the release or addition of a cofactor such as water or a coenzyme.

These enzymes play important roles in various metabolic pathways, including the breakdown of carbohydrates, lipids, and amino acids. They are also involved in the biosynthesis of secondary metabolites, such as terpenoids and alkaloids.

Carbon-carbon lyases are classified under EC number 4.1.2. in the Enzyme Commission (EC) system. This classification includes a wide range of enzymes with different substrate specificities and reaction mechanisms. Examples of carbon-carbon lyases include decarboxylases, aldolases, and dehydratases.

It's worth noting that the term "lyase" refers to any enzyme that catalyzes the removal of a group of atoms from a molecule, leaving a double bond or a cycle, and it does not necessarily imply the formation of carbon-carbon bonds.

Furans are not a medical term, but a class of organic compounds that contain a four-membered ring with four atoms, usually carbon and oxygen. They can be found in some foods and have been used in the production of certain industrial chemicals. Some furan derivatives have been identified as potentially toxic or carcinogenic, but the effects of exposure to these substances depend on various factors such as the level and duration of exposure.

In a medical context, furans may be mentioned in relation to environmental exposures, food safety, or occupational health. For example, some studies have suggested that high levels of exposure to certain furan compounds may increase the risk of liver damage or cancer. However, more research is needed to fully understand the potential health effects of these substances.

It's worth noting that furans are not a specific medical condition or diagnosis, but rather a class of chemical compounds with potential health implications. If you have concerns about exposure to furans or other environmental chemicals, it's best to consult with a healthcare professional for personalized advice and recommendations.

Terpenes are a large and diverse class of organic compounds produced by a variety of plants, including cannabis. They are responsible for the distinctive aromas and flavors found in different strains of cannabis. Terpenes have been found to have various therapeutic benefits, such as anti-inflammatory, analgesic, and antimicrobial properties. Some terpenes may also enhance the psychoactive effects of THC, the main psychoactive compound in cannabis. It's important to note that more research is needed to fully understand the potential medical benefits and risks associated with terpenes.

Epoxy compounds, also known as epoxy resins, are a type of thermosetting polymer characterized by the presence of epoxide groups in their molecular structure. An epoxide group is a chemical functional group consisting of an oxygen atom double-bonded to a carbon atom, which is itself bonded to another carbon atom.

Epoxy compounds are typically produced by reacting a mixture of epichlorohydrin and bisphenol-A or other similar chemicals under specific conditions. The resulting product is a two-part system consisting of a resin and a hardener, which must be mixed together before use.

Once the two parts are combined, a chemical reaction takes place that causes the mixture to cure or harden into a solid material. This curing process can be accelerated by heat, and once fully cured, epoxy compounds form a strong, durable, and chemically resistant material that is widely used in various industrial and commercial applications.

In the medical field, epoxy compounds are sometimes used as dental restorative materials or as adhesives for bonding medical devices or prosthetics. However, it's important to note that some people may have allergic reactions to certain components of epoxy compounds, so their use must be carefully evaluated and monitored in a medical context.

Polyketide synthases (PKSs) are a type of large, multifunctional enzymes found in bacteria, fungi, and other organisms. They play a crucial role in the biosynthesis of polyketides, which are a diverse group of natural products with various biological activities, including antibiotic, antifungal, anticancer, and immunosuppressant properties.

PKSs are responsible for the assembly of polyketide chains by repetitively adding two-carbon units derived from acetyl-CoA or other extender units to a growing chain. The PKS enzymes can be classified into three types based on their domain organization and mechanism of action: type I, type II, and type III PKSs.

Type I PKSs are large, modular enzymes that contain multiple domains responsible for different steps in the polyketide biosynthesis process. These include acyltransferase (AT) domains that load extender units onto the PKS, acyl carrier proteins (ACPs) that tether the growing chain to the PKS, and ketosynthase (KS) domains that catalyze the condensation of the extender unit with the growing chain.

Type II PKSs are simpler enzymes that consist of several separate proteins that work together in a complex to synthesize polyketides. These include ketosynthase, acyltransferase, and acyl carrier protein domains, as well as other domains responsible for reducing or modifying the polyketide chain.

Type III PKSs are the simplest of the three types and consist of a single catalytic domain that is responsible for both loading extender units and catalyzing their condensation with the growing chain. These enzymes typically synthesize shorter polyketide chains, such as those found in certain plant hormones and pigments.

Overall, PKSs are important enzymes involved in the biosynthesis of a wide range of natural products with significant medical and industrial applications.

Macrocyclic compounds are organic compounds containing a large ring structure, typically consisting of 12 or more atoms in the ring. These molecules can be found naturally occurring in some organisms, such as certain antibiotics and toxins, or they can be synthesized in the laboratory for various applications, including pharmaceuticals, catalysts, and materials science.

The term "macrocyclic" is used to distinguish these compounds from smaller ring structures, known as "cyclic" or "small-ring" compounds, which typically contain 5-7 atoms in the ring. Macrocyclic compounds can have a wide range of shapes and sizes, including crown ethers, cyclodextrins, calixarenes, and porphyrins, among others.

The unique structure of macrocyclic compounds often imparts special properties to them, such as the ability to bind selectively to specific ions or molecules, form stable complexes with metals, or act as catalysts for chemical reactions. These properties make macrocyclic compounds useful in a variety of applications, including drug delivery, chemical sensors, and environmental remediation.

Protein splicing is a post-translational modification process that involves the excision of an intervening polypeptide segment, called an intein, from a protein precursor and the ligation of the flanking sequences, called exteins. This reaction results in the formation of a mature, functional protein product. Protein splicing is mediated by a set of conserved amino acid residues within the intein and can occur autocatalytically or in conjunction with other cellular factors. It plays an important role in the regulation and diversification of protein functions in various organisms, including bacteria, archaea, and eukaryotes.

"Oldenlandia" is not a term that has a specific medical definition. It is a genus of flowering plants in the coffee family, Rubiaceae, and it includes over 200 species that are found primarily in tropical and subtropical regions around the world. Some species of Oldenlandia have been used in traditional medicine in various cultures, but there is limited scientific evidence to support their effectiveness or safety.

In modern medical contexts, if "Oldenlandia" is mentioned, it may refer to a specific plant species that has been studied for its potential medicinal properties. For example, Oldenlandia diffusa (also known as Hedyotis diffusa) has been investigated for its anti-inflammatory, antioxidant, and anticancer effects. However, it is important to note that the use of any plant or herbal remedy should be discussed with a qualified healthcare provider, as they can interact with other medications and have potential side effects.

Boranes are a group of chemical compounds that contain only boron and hydrogen. The most well-known borane is BH3, also known as diborane. These compounds are highly reactive and have unusual structures, with the boron atoms bonded to each other in three-center, two-electron bonds. Boranes are used in research and industrial applications, including as reducing agents and catalysts. They are highly flammable and toxic, so they must be handled with care.

Molecular models are three-dimensional representations of molecular structures that are used in the field of molecular biology and chemistry to visualize and understand the spatial arrangement of atoms and bonds within a molecule. These models can be physical or computer-generated and allow researchers to study the shape, size, and behavior of molecules, which is crucial for understanding their function and interactions with other molecules.

Physical molecular models are often made up of balls (representing atoms) connected by rods or sticks (representing bonds). These models can be constructed manually using materials such as plastic or wooden balls and rods, or they can be created using 3D printing technology.

Computer-generated molecular models, on the other hand, are created using specialized software that allows researchers to visualize and manipulate molecular structures in three dimensions. These models can be used to simulate molecular interactions, predict molecular behavior, and design new drugs or chemicals with specific properties. Overall, molecular models play a critical role in advancing our understanding of molecular structures and their functions.

Solid-phase synthesis techniques refer to a group of methods used in chemistry, particularly in the field of peptide and oligonucleotide synthesis. These techniques involve chemically binding reactive components to a solid support or resin, and then performing a series of reactions on the attached components while they are still in the solid phase.

The key advantage of solid-phase synthesis is that it allows for the automated and repetitive addition of individual building blocks (such as amino acids or nucleotides) to a growing chain, with each step followed by a purification process that removes any unreacted components. This makes it possible to synthesize complex molecules in a highly controlled and efficient manner.

The solid-phase synthesis techniques typically involve the use of protecting groups to prevent unwanted reactions between functional groups on the building blocks, as well as the use of activating agents to promote the desired chemical reactions. Once the synthesis is complete, the final product can be cleaved from the solid support and purified to yield a pure sample of the desired molecule.

In summary, solid-phase synthesis techniques are a powerful set of methods used in chemistry to synthesize complex molecules in a controlled and efficient manner, with applications in fields such as pharmaceuticals, diagnostics, and materials science.

Norbornanes are a class of compounds in organic chemistry that contain a norbornane skeleton, which is a bicyclic structure consisting of two fused cyclohexane rings. One of the rings is saturated, while the other contains a double bond. The name "norbornane" comes from the fact that it is a "nor" (short for "norcarene") derivative of bornane, which has a similar structure but with a methyl group attached to one of the carbon atoms in the saturated ring.

Norbornanes have a variety of applications in organic synthesis and medicinal chemistry. Some derivatives of norbornane have been explored for their potential as drugs, particularly in the areas of central nervous system agents and anti-inflammatory agents. However, there is no specific medical definition associated with "norbornanes" as they are a class of chemical compounds rather than a medical term or condition.

Heterocyclic compounds are organic molecules that contain a ring structure made up of at least one atom that is not carbon, known as a heteroatom. These heteroatoms can include nitrogen, oxygen, sulfur, or other elements. In the case of "2-ring" heterocyclic compounds, the molecule contains two separate ring structures, each of which includes at least one heteroatom.

The term "heterocyclic compound" is used to describe a broad class of organic molecules that are found in many natural and synthetic substances. They play important roles in biology, medicine, and materials science. Heterocyclic compounds can be classified based on the number of rings they contain, as well as the types and arrangements of heteroatoms within those rings.

Two-ring heterocyclic compounds can exhibit a wide range of chemical and physical properties, depending on the nature of the rings and the heteroatoms present. Some examples of two-ring heterocyclic compounds include quinoline, isoquinoline, benzothiazole, and benzoxazole, among many others. These compounds have important applications in pharmaceuticals, dyes, pigments, and other industrial products.

Cyclodextrins are cyclic, oligosaccharide structures made up of 6-8 glucose units joined together in a ring by alpha-1,4 glycosidic bonds. They have a hydrophilic outer surface and a hydrophobic central cavity, which makes them useful for forming inclusion complexes with various hydrophobic guest molecules. This property allows cyclodextrins to improve the solubility, stability, and bioavailability of drugs, and they are used in pharmaceutical formulations as excipients. Additionally, cyclodextrins have applications in food, cosmetic, and chemical industries.

Squalene is a organic compound that is a polyunsaturated triterpene. It is a natural component of human skin surface lipids and sebum, where it plays a role in maintaining the integrity and permeability barrier of the stratum corneum. Squalene is also found in various plant and animal tissues, including olive oil, wheat germ oil, and shark liver oil.

In the body, squalene is an intermediate in the biosynthesis of cholesterol and other sterols. It is produced in the liver and transported to other tissues via low-density lipoproteins (LDLs). Squalene has been studied for its potential health benefits due to its antioxidant properties, as well as its ability to modulate immune function and reduce the risk of certain types of cancer. However, more research is needed to confirm these potential benefits.

An intein is a type of mobile genetic element that can be found within the proteins of various organisms, including bacteria, archaea, and eukaryotes. Inteins are intervening sequences of amino acids that are capable of self-excising from their host protein through a process called protein splicing.

Protein splicing involves the cleavage of the intein from the flanking sequences (known as exteins) and the formation of a peptide bond between the two exteins, resulting in a mature, functional protein. Inteins can also ligate themselves to form circular proteins or can be transferred horizontally between different organisms through various mechanisms.

Inteins have been identified as potential targets for drug development due to their essential role in the survival and virulence of certain pathogenic bacteria. Additionally, the protein splicing mechanism of inteins has been harnessed for various biotechnological applications, such as the production of recombinant proteins and the development of biosensors.

Cystine knot motifs are a type of protein structure characterized by the formation of a unique knotted pattern through the linking of three conserved cysteine residues. In this structure, two of the cysteines form a disulfide bond, while the third crosses under and forms an additional disulfide bond with one of the first pair, creating a knot-like shape. This motif is found in a variety of proteins, including some that are involved in important biological processes such as cell signaling, wound healing, and tumor suppression. The cystine knot motif confers stability to these proteins and helps them maintain their function even under harsh conditions.

Magnetic Resonance Spectroscopy (MRS) is a non-invasive diagnostic technique that provides information about the biochemical composition of tissues, including their metabolic state. It is often used in conjunction with Magnetic Resonance Imaging (MRI) to analyze various metabolites within body tissues, such as the brain, heart, liver, and muscles.

During MRS, a strong magnetic field, radio waves, and a computer are used to produce detailed images and data about the concentration of specific metabolites in the targeted tissue or organ. This technique can help detect abnormalities related to energy metabolism, neurotransmitter levels, pH balance, and other biochemical processes, which can be useful for diagnosing and monitoring various medical conditions, including cancer, neurological disorders, and metabolic diseases.

There are different types of MRS, such as Proton (^1^H) MRS, Phosphorus-31 (^31^P) MRS, and Carbon-13 (^13^C) MRS, each focusing on specific elements or metabolites within the body. The choice of MRS technique depends on the clinical question being addressed and the type of information needed for diagnosis or monitoring purposes.

Polyketides are a diverse group of natural compounds that are synthesized biochemically through the condensation of acetate or propionate units. They are produced by various organisms, including bacteria, fungi, and plants, and have a wide range of biological activities, such as antibiotic, antifungal, anticancer, and immunosuppressant properties. Polyketides can be classified into several types based on the number of carbonyl groups, the length of the carbon chain, and the presence or absence of cyclization. They are synthesized by polyketide synthases (PKSs), which are large enzyme complexes that share similarities with fatty acid synthases (FASs). Polyketides have attracted significant interest in drug discovery due to their structural diversity and potential therapeutic applications.

Monoterpenes are a class of terpenes that consist of two isoprene units and have the molecular formula C10H16. They are major components of many essential oils found in plants, giving them their characteristic fragrances and flavors. Monoterpenes can be further classified into various subgroups based on their structural features, such as acyclic (e.g., myrcene), monocyclic (e.g., limonene), and bicyclic (e.g., pinene) compounds. In the medical field, monoterpenes have been studied for their potential therapeutic properties, including anti-inflammatory, antimicrobial, and anticancer activities. However, more research is needed to fully understand their mechanisms of action and clinical applications.

"Abies" is a genus of evergreen trees that are commonly known as firs. They belong to the family Pinaceae and are native to the northern hemisphere, primarily in North America, Europe, and Asia. These trees are characterized by their needle-like leaves, which are flat and shiny, and their conical-shaped crowns.

Firs have been used for various purposes throughout history, including timber production, Christmas tree farming, and ornamental landscaping. Some species of firs also have medicinal properties, such as the use of Abies balsamea (balsam fir) in traditional medicine to treat respiratory ailments and skin conditions. However, it's important to note that the medical use of firs should be done under the guidance of a healthcare professional, as improper use can lead to adverse effects.

Aldehydes are a class of organic compounds characterized by the presence of a functional group consisting of a carbon atom bonded to a hydrogen atom and a double bonded oxygen atom, also known as a formyl or aldehyde group. The general chemical structure of an aldehyde is R-CHO, where R represents a hydrocarbon chain.

Aldehydes are important in biochemistry and medicine as they are involved in various metabolic processes and are found in many biological molecules. For example, glucose is converted to pyruvate through a series of reactions that involve aldehyde intermediates. Additionally, some aldehydes have been identified as toxicants or environmental pollutants, such as formaldehyde, which is a known carcinogen and respiratory irritant.

Formaldehyde is also commonly used in medical and laboratory settings for its disinfectant properties and as a fixative for tissue samples. However, exposure to high levels of formaldehyde can be harmful to human health, causing symptoms such as coughing, wheezing, and irritation of the eyes, nose, and throat. Therefore, appropriate safety measures must be taken when handling aldehydes in medical and laboratory settings.

Diterpenes are a class of naturally occurring compounds that are composed of four isoprene units, which is a type of hydrocarbon. They are synthesized by a wide variety of plants and animals, and are found in many different types of organisms, including fungi, insects, and marine organisms.

Diterpenes have a variety of biological activities and are used in medicine for their therapeutic effects. Some diterpenes have anti-inflammatory, antimicrobial, and antiviral properties, and are used to treat a range of conditions, including respiratory infections, skin disorders, and cancer.

Diterpenes can be further classified into different subgroups based on their chemical structure and biological activity. Some examples of diterpenes include the phytocannabinoids found in cannabis plants, such as THC and CBD, and the paclitaxel, a diterpene found in the bark of the Pacific yew tree that is used to treat cancer.

It's important to note that while some diterpenes have therapeutic potential, others may be toxic or have adverse effects, so it is essential to use them under the guidance and supervision of a healthcare professional.

Naphthols are chemical compounds that consist of a naphthalene ring (a polycyclic aromatic hydrocarbon made up of two benzene rings) substituted with a hydroxyl group (-OH). They can be classified as primary or secondary naphthols, depending on whether the hydroxyl group is directly attached to the naphthalene ring (primary) or attached through a carbon atom (secondary). Naphthols are important intermediates in the synthesis of various chemical and pharmaceutical products. They have been used in the production of azo dyes, antioxidants, and pharmaceuticals such as analgesics and anti-inflammatory agents.

"Strychnos" is a genus of plants, specifically belonging to the Loganiaceae family. While not a medical term itself, certain species of Strychnos contain toxic alkaloids that have been used in medicine and are important to understand from a medical and pharmacological perspective.

The most well-known species is Strychnos nux-vomica, which produces the potent alkaloid strychnine. This alkaloid acts as a competitive antagonist at glycine receptors in the central nervous system, leading to uncontrolled muscle contractions, stiffness, and potentially life-threatening convulsions if ingested or otherwise introduced into the body.

Another important alkaloid found in some Strychnos species is brucine, which also has toxic properties, although it is less potent than strychnine. Both of these alkaloids are used in research and have been employed in the past as rodenticides, but their use in medicine is limited due to their high toxicity.

In a medical context, knowing about Strychnos plants and their toxic alkaloids is essential for understanding potential poisonings, recognizing symptoms, and providing appropriate treatment.

"Spiro compounds" are not specifically classified as medical terms, but they are a concept in organic chemistry. However, I can provide a general definition:

Spiro compounds are a type of organic compound that contains two or more rings, which share a single common atom, known as the "spiro center." The name "spiro" comes from the Greek word for "spiral" or "coiled," reflecting the three-dimensional structure of these molecules.

The unique feature of spiro compounds is that they have at least one spiro atom, typically carbon, which is bonded to four other atoms, two of which belong to each ring. This arrangement creates a specific geometry where the rings are positioned at right angles to each other, giving spiro compounds distinctive structural and chemical properties.

While not directly related to medical terminology, understanding spiro compounds can be essential in medicinal chemistry and pharmaceutical research since these molecules often exhibit unique biological activities due to their intricate structures.

Streptomyces is a genus of Gram-positive, aerobic, saprophytic bacteria that are widely distributed in soil, water, and decaying organic matter. They are known for their complex morphology, forming branching filaments called hyphae that can differentiate into long chains of spores.

Streptomyces species are particularly notable for their ability to produce a wide variety of bioactive secondary metabolites, including antibiotics, antifungals, and other therapeutic compounds. In fact, many important antibiotics such as streptomycin, neomycin, tetracycline, and erythromycin are derived from Streptomyces species.

Because of their industrial importance in the production of antibiotics and other bioactive compounds, Streptomyces have been extensively studied and are considered model organisms for the study of bacterial genetics, biochemistry, and ecology.

Alkaloids are a type of naturally occurring organic compounds that contain mostly basic nitrogen atoms. They are often found in plants, and are known for their complex ring structures and diverse pharmacological activities. Many alkaloids have been used in medicine for their analgesic, anti-inflammatory, and therapeutic properties. Examples of alkaloids include morphine, quinine, nicotine, and caffeine.

A cycloaddition reaction is a type of chemical reaction involving the formation of one or more rings through the coupling of two unsaturated molecules. This process typically involves the simultaneous formation of new sigma bonds, resulting in the creation of a cyclic structure. Cycloaddition reactions are classified based on the number of atoms involved in each component molecule and the number of sigma bonds formed during the reaction. For example, a [2+2] cycloaddition involves two unsaturated molecules, each containing two atoms involved in the reaction, resulting in the formation of a four-membered ring. These reactions play a significant role in organic synthesis and are widely used to construct complex molecular architectures in various fields, including pharmaceuticals, agrochemicals, and materials science.

Bromine compounds refer to chemical substances that contain bromine, a halogen element with the atomic number 35 and symbol Br. Bromine is a volatile, reddish-brown liquid at room temperature that evaporates easily into a red-brown gas with a strong, chlorine-like odor.

Bromine compounds can be formed when bromine combines with other elements or compounds. These compounds have various properties and uses depending on the other elements or groups involved. Some common examples of bromine compounds include:

1. Bromides: These are salts of hydrobromic acid, which contains bromide ions (Br-). They are commonly used as sedatives, anticonvulsants, and in photography.
2. Organobromines: These are organic compounds that contain bromine atoms. They have various uses, including as flame retardants, fumigants, and intermediates in the production of other chemicals.
3. Bromates: These are oxides of bromine that contain the bromate ion (BrO3-). They are used as oxidizing agents in water treatment and bleaching.
4. Bromine pentafluoride (BrF5): This is a highly reactive and corrosive compound that is used as a fluorinating agent in chemical reactions.
5. Bromine trifluoride (BrF3): This is another reactive and corrosive compound that is used as a fluorinating agent, particularly in the production of uranium hexafluoride for nuclear reactors.

It's important to note that some bromine compounds can be toxic, corrosive, or environmentally harmful, so they must be handled with care and disposed of properly.

Molecular sequence data refers to the specific arrangement of molecules, most commonly nucleotides in DNA or RNA, or amino acids in proteins, that make up a biological macromolecule. This data is generated through laboratory techniques such as sequencing, and provides information about the exact order of the constituent molecules. This data is crucial in various fields of biology, including genetics, evolution, and molecular biology, allowing for comparisons between different organisms, identification of genetic variations, and studies of gene function and regulation.

Sesquiterpenes are a class of terpenes that consist of three isoprene units, hence the name "sesqui-" meaning "one and a half" in Latin. They are composed of 15 carbon atoms and have a wide range of chemical structures and biological activities. Sesquiterpenes can be found in various plants, fungi, and insects, and they play important roles in the defense mechanisms of these organisms. Some sesquiterpenes are also used in traditional medicine and have been studied for their potential therapeutic benefits.

X-ray crystallography is a technique used in structural biology to determine the three-dimensional arrangement of atoms in a crystal lattice. In this method, a beam of X-rays is directed at a crystal and diffracts, or spreads out, into a pattern of spots called reflections. The intensity and angle of each reflection are measured and used to create an electron density map, which reveals the position and type of atoms in the crystal. This information can be used to determine the molecular structure of a compound, including its shape, size, and chemical bonds. X-ray crystallography is a powerful tool for understanding the structure and function of biological macromolecules such as proteins and nucleic acids.

Phosgene is not a medical condition, but it is an important chemical compound with significant medical implications. Medically, phosgene is most relevant as a potent chemical warfare agent and a severe pulmonary irritant. Here's the medical definition of phosgene:

Phosgene (COCl2): A highly toxic and reactive gas at room temperature with a characteristic odor reminiscent of freshly cut hay or grass. It is denser than air, allowing it to accumulate in low-lying areas. Exposure to phosgene primarily affects the respiratory system, causing symptoms ranging from mild irritation to severe pulmonary edema and potentially fatal respiratory failure.

Inhaling high concentrations of phosgene can lead to immediate choking sensations, coughing, chest pain, and difficulty breathing. Delayed symptoms may include fever, cyanosis (bluish discoloration of the skin due to insufficient oxygen), and pulmonary edema (fluid accumulation in the lungs). The onset of these severe symptoms can be rapid or take up to 48 hours after exposure.

Medical management of phosgene exposure primarily focuses on supportive care, including administering supplemental oxygen, bronchodilators, and corticosteroids to reduce inflammation. In severe cases, mechanical ventilation may be necessary to maintain adequate gas exchange in the lungs.

Bicyclic compounds are organic molecules that contain two rings in their structure, with at least two common atoms shared between the rings. These compounds can be found in various natural and synthetic substances, including some medications and bioactive molecules. The unique structure of bicyclic compounds can influence their chemical and physical properties, which may impact their biological activity or reactivity.

The Glycogen Debranching Enzyme System, also known as glycogen debranching enzyme or Amy-1, is a crucial enzyme complex in human biochemistry. It plays an essential role in the metabolism of glycogen, which is a large, branched polymer of glucose that serves as the primary form of energy storage in animals and fungi.

The Glycogen Debranching Enzyme System consists of two enzymatic activities: a transferase and an exo-glucosidase. The transferase activity transfers a segment of a branched glucose chain to another part of the same or another glycogen molecule, while the exo-glucosidase activity cleaves the remaining single glucose units from the outer branches of the glycogen molecule.

This enzyme system is responsible for removing the branched structures of glycogen, allowing the linear chains to be further degraded by other enzymes into glucose molecules that can be used for energy production or stored for later use. Defects in this enzyme complex can lead to several genetic disorders, such as Glycogen Storage Disease Type III (Cori's disease) and Type IV (Andersen's disease), which are characterized by the accumulation of abnormal glycogen molecules in various tissues.

Semicarbazides are organic compounds that contain the functional group -NH-CO-NH-NH2. They are derivatives of hydrazine and carbamic acid, with the general structure (CH3)NHCSNH2. Semicarbazides are widely used in the synthesis of various chemical compounds, including heterocyclic compounds, pharmaceuticals, and agrochemicals.

In a medical context, semicarbazides themselves do not have any therapeutic use. However, they can be used in the preparation of certain drugs or drug intermediates. For example, semicarbazones, which are derivatives of semicarbazides, can be used to synthesize some antituberculosis drugs.

It is worth noting that semicarbazides and their derivatives have been found to have mutagenic and carcinogenic properties in some studies. Therefore, they should be handled with care in laboratory settings, and exposure should be minimized to reduce potential health risks.

Guanosine diphosphate sugars (GDP-sugars) are nucleotide sugars that play a crucial role in the biosynthesis of complex carbohydrates, such as glycoproteins and proteoglycans. Nucleotide sugars are formed by the attachment of a sugar molecule to a nucleoside diphosphate, in this case, guanosine diphosphate (GDP).

GDP-sugars serve as activated donor substrates for glycosyltransferases, enzymes that catalyze the transfer of sugar moieties onto various acceptor molecules, including proteins and lipids. The GDP-sugar synthesis pathway involves several enzymatic steps, starting with the conversion of nucleoside triphosphate (NTP) to nucleoside diphosphate (NDP), followed by the attachment of a sugar moiety from a donor molecule, such as UDP-glucose or TDP-rhamnose.

Examples of GDP-sugars include:

1. GDP-mannose: A nucleotide sugar that serves as a donor substrate for the addition of mannose residues to glycoproteins and proteoglycans.
2. GDP-fucose: A nucleotide sugar that is involved in the biosynthesis of fucosylated glycoconjugates, which have important functions in cell recognition, signaling, and development.
3. GDP-rhamnose: A nucleotide sugar that plays a role in the synthesis of rhamnosylated glycoconjugates, found in bacterial cell walls and some plant polysaccharides.
4. GDP-glucose: A nucleotide sugar that is used as a donor substrate for the addition of glucose residues to various acceptors, including proteins and lipids.

Dysregulation of GDP-sugar metabolism has been implicated in several diseases, such as cancer, neurodegenerative disorders, and bacterial and viral infections. Therefore, understanding the synthesis, regulation, and function of GDP-sugars is crucial for developing novel therapeutic strategies to target these conditions.

A chemical model is a simplified representation or description of a chemical system, based on the laws of chemistry and physics. It is used to explain and predict the behavior of chemicals and chemical reactions. Chemical models can take many forms, including mathematical equations, diagrams, and computer simulations. They are often used in research, education, and industry to understand complex chemical processes and develop new products and technologies.

For example, a chemical model might be used to describe the way that atoms and molecules interact in a particular reaction, or to predict the properties of a new material. Chemical models can also be used to study the behavior of chemicals at the molecular level, such as how they bind to each other or how they are affected by changes in temperature or pressure.

It is important to note that chemical models are simplifications of reality and may not always accurately represent every aspect of a chemical system. They should be used with caution and validated against experimental data whenever possible.

Anionic Michael-type cyclization is an alternative to radical cyclization of activated olefins. Metal-catalyzed cyclization ... Radical cyclizations are much faster than analogous anionic cyclizations, and avoid β-elimination side reactions. ... 8) In comparison to cationic cyclizations, radical cyclizations avoid issues associated with Wagner-Meerwein rearrangements, do ... exo cyclization is favored over endo cyclization (macrocyclizations constitute the major exception to this rule). 5-hexenyl ...
The Pschorr cyclization is a name reaction in organic chemistry, which was named after its discoverer, the German chemist ... The Pschorr cyclization has a relatively good atom economy, since essentially only nitrogen is produced as a waste material. ... However, when considering the atom economy it has to be mentioned that the Pschorr cyclization has often only low yields. ... The following reaction scheme shows the Pschorr cyclization for the example of phenanthrene: In the course of the Pschorr ...
The Masamune-Bergman cyclization or Masamune-Bergman reaction or Masamune-Bergman cycloaromatization is an organic reaction and ... In 2015 IBM scientists demonstrated that a reversible Masamune-Bergman cyclisation of diyne can be induced by a tip of an ... Wikimedia Commons has media related to Bergman cyclization. Bergman Cycloaromatization Powerpoint Whitney M. Erwin 2002 (CS1: ... "Reversible Bergman cyclization by atomic manipulation". Nature Chemistry. 8 (3): 220-224. Bibcode:2016NatCh...8..220S. doi: ...
The Nazarov cyclization reaction (often referred to as simply the Nazarov cyclization) is a chemical reaction used in organic ... Diastereoselective cyclizations are also known, in which extant stereocenters direct the cyclization. Almost all of the ... The development of an enantioselective Nazarov cyclization is a desirable addition to the repertoire of Nazarov cyclization ... These are typically referred to as retro-Nazarov cyclization reactions. Nitrogen analogues of the Nazarov cyclization reaction ...
The Volhard-Erdmann cyclization is an organic synthesis of alkyl and aryl thiophenes by cyclization of disodium succinate or ...
... is the central step in Borsche-Drechsel carbazole synthesis, where in the first step ... The Borsche-Drechsel cyclization is a chemical reaction used to synthesize tetrahydrocarbazoles by the acid-catalyzed ... cyclization of cyclohexanone arylhydrazones. The reaction was first described by Edmund Drechsel in 1888 and by Walter Borsche ...
For Bergman cyclization to occur, the epoxide must be removed. Myers-Saito cyclization is another triggering mechanism by which ... The diradicals generated by Bergman and Myers-Saito cyclization are highly reactive.[citation needed] The cyclization of the ... "Bergman Cyclization". Retrieved 2018-05-05. Smith AL, Nicolaou KC (May 1996). "The enediyne ... Enediynes are triggered into a chemically active state via Bergman or Myers-Saito cyclization. The triggering mechanism can be ...
In addition to using a rhodium catalyst, this synthesis features an intramolecular cyclization that results in the normal 5- ... Shambayani, Soroosh; Crowe, William E.; Schreiber, Stuart L. (1990-01-01). "N-oxide promoted pauson-khand cyclizations at room ... Negishi, Eiichi; Holmes, Steven J.; Tour, James M.; Miller, Joseph A. (1985-04-01). "Metal promoted cyclization. 7. Zirconium- ... "Asymmetric Pauson-Khand Cyclization: A Formal Total Synthesis of Natural Brefeldin A". The Journal of Organic Chemistry. 60 (21 ...
"Cyclization of Acetylenic Compounds". Angewandte Chemie International Edition in English. 8 (10): 727-733. doi:10.1002/anie. ...
Cyclization reactions, or intramolecular addition reactions, can be used to form cycloalkenes. These reactions primarily form ... Intramolecular Addition (Cyclization) Reactions". Chemistry LibreTexts. 2015-01-12. Retrieved 2022-11-17. "ELECTROCYCLIC ...
"Cyclization of Acetylenic Compounds". Angewandte Chemie International Edition in English. 8 (10): 727-733. doi:10.1002/anie. ...
"Cyclization of Acetylenic Compounds". Angewandte Chemie International Edition in English. 8 (10): 727-733. doi:10.1002/anie. ...
Trost, B. M.; Greenspan, P. D.; Yang, B. V.; Saulnier, M. G. (1990). "An unusual oxidative cyclization. A synthesis and ...
Reppe, Walter; Kutepow, N; Magin, A (1969). "Cyclization of Acetylenic Compounds". Angewandte Chemie International Edition in ...
Cyclization to Suritozole (6). GABAA receptor negative allosteric modulator GABAA receptor § Ligands Miller JA, Dudley MW, ...
Reppe, Walter; Kutepow, N; Magin, A (1969). "Cyclization of Acetylenic Compounds". Angewandte Chemie International Edition in ...
Trost BM, Greenspan PD, Yang BV, Saulnier MG (November 1990). "An unusual oxidative cyclization. A synthesis and absolute ...
Denmark, S. E.; Jones, T. K. (May 1, 1982). "Silicon-directed Nazarov cyclization". Journal of the American Chemical Society. ... From Polyene Cyclizations to Origin of Biomolecular Homochirality. ETH Zurich (Switzerland). Retrieved November 16, 2019. ... where his laboratory's early work focused on investigation of the Nazarov cyclization reaction and Claisen rearrangement. This ...
This causes cyclization and gives rise to (2S,4S)-4-hydroxy-2,3,4,5-tetrahydrodipicolinate. 4-hydroxy-tetrahydrodipicolinate ... this prevents spontaneous cyclization. The enzyme N-acetylglutamate synthase (glutamate N-acetyltransferase) is responsible for ...
Cyclization with formic acid completed the synthesis of phendimetrazine (5). The reaction between Ephedrine [299-42-3] (1) and ... Cyclization affords phendimetrazine (4). The halogenation of Propiophenone [93-55-0] (1) with bromine gives 2- ...
A more recent example is E.J. Corey's carbenium-mediated cyclization of an engineered linear polyene to provide a tetracyclic ... The key step in Heathcock's synthetic route involves a cyclization of acyclic dialdehydes A or B to form proto-daphniphylline. ... Eschenmoser A, Felix D, Gut M, Meier J, Stadler P (1959). "Some aspects of acid-catalysed cyclizations of terpenoid polyenes". ... Stork G, Burgstrahler AW (1955). "The stereochemistry of polyene cyclization". J. Am. Chem. Soc. 77 (19): 5068-77. doi:10.1021/ ...
The importance of cyclization effects". International Journal of Quantum Chemistry. doi:10.1002/qua.25489. (Chemical pages ...
The use of thiyl radicals as initiators of cyclization has been employed in the synthesis of a number of natural products, ... This section examines intramolecular thiol-ene cyclization reactions, which yields a mixture of 5-exo and 6-endo products in ... The conditions under which these cyclization reactions occur follow Baldwin's rules for ring closure. Given the reversibility ... Lynch, Dylan M.; Scanlan, Eoin M. (2020-07-07). "Thiyl Radicals: Versatile Reactive Intermediates for Cyclization of ...
This cyclization is one of the most complex known enzyme functions and is highly selective. The reaction can be characterized ... Chen N, Zhou J, Li J, Xu J, Wu R (March 2014). "Concerted Cyclization of Lanosterol C-Ring and D-Ring Under Human Oxidosqualene ... Oxidosqualene cyclases (OSC) are enzymes involved in cyclization reactions of 2,3-oxidosqualene to form sterols or triterpenes ... Stork G, Burgstahler AW (October 1955). "The Stereochemistry of Polyene Cyclization". Journal of the American Chemical Society ...
B. E. Maryanoff; H.-C. Zhang; J. H. Cohen; I. J. Turchi; C. A. Maryanoff (2004). "Cyclizations of N-acyliminium ions". Chem. ... Larghi, E. L.; Kaufman, T. S. (2006). "The oxa-Pictet-Spengler Cyclization. Synthesis of Isochromanes and Related Pyran-Type ... Instead of catalyzing the Pictet-Spengler cyclization with strong acid, one can acylate the iminium ion forming the ...
Chamberlin, A. R.; Nguyen, H. D.; Chung, J. Y. L. (1984). "Cationic cyclization of ketene dithioacetals. A general synthesis of ...
Johnson, W.S.; Mathews, F.J. (1944). "Cyclization studies in the benzoquinoline series". J. Am. Chem. Soc. 66 (2): 210-215. doi ... Johnson, W.S.; Mathews, F.J. (1944). "Cyclization studies in the benzoquinoline series". J. Am. Chem. Soc. 66 (2): 210-215. doi ...
Pentacyclic triterpenoids are believed to be synthesized in nature through cyclization of squalene and its derivatives by the ... "Biosynthetic diversity in plant triterpene cyclization". Current Opinion in Plant Biology. 9 (3): 305-314. doi:10.1016/j.pbi. ...
Tang, Man-Cheng; Zou, Yi; Watanabe, Kenji; Walsh, Christopher T.; Tang, Yi (2017-04-26). "Oxidative Cyclization in Natural ...
Youngs, Wiley J.; Djebli, Abdellah.; Tessier, Claire A. (1991-07-01). "Lithium-induced cyclization of tribenzo cyclotriynes". ...
Anionic Michael-type cyclization is an alternative to radical cyclization of activated olefins. Metal-catalyzed cyclization ... Radical cyclizations are much faster than analogous anionic cyclizations, and avoid β-elimination side reactions. ... 8) In comparison to cationic cyclizations, radical cyclizations avoid issues associated with Wagner-Meerwein rearrangements, do ... exo cyclization is favored over endo cyclization (macrocyclizations constitute the major exception to this rule). 5-hexenyl ...
In this article the effect of disulfide cyclization of the polar head of N-palmitoylated USCLs on in vitro biological activity ... In general, disulfide cyclization of the lipopeptides resulted in peptides with reduced cytotoxicity. Disulfide-cyclized USCLs ... Concluding, USCLs are strong membrane disruptors and disulfide cyclization of polar head can have a beneficial effect on its in ... One of these is disulfide cyclization that has been shown to improve drug-like characteristics of peptides. ...
Copper-catalyzed cyclization of steroidal acylaminoacetylenes: Syntheses of novel 11ß-aryl-17,17-spiro[(4H,5-methylene)- ... Copper-catalyzed cyclization of steroidal acylaminoacetylenes: Syntheses of novel 11ß-aryl-17,17-spiro[(4H,5-methylene)- ... Jin, C., Burgess, J., Kepler, J., & Cook, C. (2007). Copper-catalyzed cyclization of steroidal acylaminoacetylenes: Syntheses ...
A CO2/photoredox-cocatalyzed tandem oxidative cyclization of α-bromo ketones and amines enables the preparation of substituted ... CO2/Photoredox-Cocatalyzed Tandem Oxidative Cyclization of α-Bromo Ketones and Amines To Construct Substituted Oxazoles. ...
Reactions involving the cyclization of 1,n-enynes are of high value as they are capable of generating molecular complexity in a ... Reactions involving the cyclization of 1,n-enynes are of high value as they are capable of generating molecular complexity in a ... Part II: In the second part of this thesis, the development of a novel gold(I)-catalyzed cyclization cascade of 1-halo-1,5- ... Part II: In the second part of this thesis, the development of a novel gold(I)-catalyzed cyclization cascade of 1-halo-1,5- ...
Cyclization with a six-residue linker does not perturb the overall structure of RgIA, improves selectivity for the GABAB ... Here, we improved the biopharmaceutical properties of RgIA by backbone cyclization using 3-7 residue peptidic linkers. ... improve the therapeutic properties of RgIA and other conotoxins being considered as drug leads and confirm that cyclization is ... Cyclization with a six-residue linker does not perturb the overall structure of RgIA, improves selectivity for the GABAB ...
McAllister, Laura A (2004) Phase-tag assisted synthesis of N-heterocycles using the Pummerer cyclisation. PhD thesis, ... Oxidation of the linking sulfur atom followed by Pummerer cyclisation and traceless cleavage using SmI2 gives the desired ... Crucially, the sulfur link to resin remains intact throughout the cyclisation leaving the heterocyclic products immobilised. ... based linker which not only links the substrate to resin and allows traceless cleavage but also enables Pummerer cyclisation ...
Cyclization cascade of allenyl azides: Synergy between theory and experiment. Olalla Nieto Faza, Ken S. Feldman, Carlos Silva ... Cyclization cascade of allenyl azides : Synergy between theory and experiment. In: Current Organic Chemistry. 2010 ; Vol. 14, ... Cyclization cascade of allenyl azides: Synergy between theory and experiment. Current Organic Chemistry. 2010;14(15):1646-1657 ... Cyclization cascade of allenyl azides: Synergy between theory and experiment. / Faza, Olalla Nieto; Feldman, Ken S.; López, ...
Cyclization of γ-o-halophenylisocrotonic acids was accomplished by isomerization of the trans acid to cis acid by ultra-violet ... Cyclization of γ-o-halophenylisocrotonic acids was accomplished by isomerization of the trans acid to cis acid by ultra-violet ... Chow, Clark Keelock, "Cyclization Studies Involving the Synthesis of 5-Substituted-1-Naphthol" (1969). Dissertations and Theses ...
Cyclization reactions in confined space. Current Opinion in Colloid & Interface Science 2023, 64 , 101680. ... Cyclizations catalyzed inside a hexameric resorcinarene capsule. Chemical Communications 2019, 55 (25) , 3573-3577. https://doi ... Au‐Cavitand Catalyzed Alkyne‐Acid Cyclizations. European Journal of Organic Chemistry 2019, 2019 (33) , 5678-5684. https://doi. ...
Synthesis of several new uracil and pteridine 6-azaanalogs based on cyclization of arylhydrazones derived from mesoxalic acid ... Synthesis of Several New Uracil and Pteridine 6-azaanalogs Based On Cyclization of Arylhydrazones Derived From Mesoxalic Acid ... Synthesis of several new uracil and pteridine 6-azaanalogs based on cyclization of arylhydrazones derived from mesoxalic acid. ...
For the cyclization of the pyridine derivatives, [RhCl(PPh3)3] showed the highest catalytic activity with respect to efficiency ... Fujii N, Kakiuchi F, Yamada A, Chatani N, Murai S. Transition Metal-Catalyzed Intramolecular Cyclization of 1,5- And 1,6-Dienes ... For the cyclization of the pyridine derivatives, [RhCl(PPh3)3] showed the highest catalytic activity with respect to efficiency ... For the cyclization of the pyridine derivatives, [RhCl(PPh3)3] showed the highest catalytic activity with respect to efficiency ...
... and Regiocontrolled Tandem Cyclization/Cross-Coupling of 2‑Benzyl-3-alkynyl Chromones with Aryl Iodides for the Synthesis of 4H ... pot tandem processbidentate phosphine ligand2 ‑ benzylregiocontrolled tandem cyclization2 ‑<2 -cyclization was reported by this rare ... A novel Pd-catalyzed chemo- and regiocontrolled tandem cyclization/cross-coupling reaction of 3-alkynyl chromone with aryl ...
Citronellal cyclisation over heteropoly acid supported on modified montmorillonite catalyst: effects of acidity and pore ... Dive into the research topics of Citronellal cyclisation over heteropoly acid supported on modified montmorillonite catalyst: ...
Atom Transfer Cyclization with CuSO4 / KBH4: a formal AGET process also applicable to ATRP. A. J. Clark, A. E. C Collis, D. J. ... Ligand Electronic Effects on Rates of Copper Mediated Atom Transfer Radical Cyclisation and Polymerisation. A. J. Clark, G. M. ...
... and Imidazoindoles via Ring-opening Cyclization of Activated Aziridines ...
Hashmi ASK, Loos A, Doherty S, Knight JGK, Robson KJ, Rominger F. Gold Catalyzed Cyclizations: A Comparative Study Between ... Synthesis of highly substituted pyrrolidines via palladium-catalyzed cyclization of 5-vinyloxazolidinones and activated alkenes ...
Project: Total synthesis of Lophirone H via an oxonium-Prins cyclisation. Sponsor: Erasmus student. Whereabouts: EPFL, ...
We report an efficient and environmentally friendly electrochemical approach to perform the bromo cyclization of tryptophol, ...
... this EET taking place instead of the desired photoinduced cyclisation of the DTE. However, no clear evidences of this ...
Raw data for new compounds described in the paper "Catalytic enantioselective arylative cyclizations of alkynyl 1,3-diketones ... Raw data for new compounds described in the paper "Catalytic enantioselective arylative cyclizations of alkynyl 1,3-diketones ... Raw data for new compounds described in the paper "Enantioselective Nickel-Catalyzed anti-Arylmetallative Cyclizations onto ... Raw data for new compounds described in the paper "Enantioselective Nickel-Catalyzed anti-Arylmetallative Cyclizations onto ...
... initiates cyclization from one of the epoxide bonds of bis-oxidosqualene. The cyclization terminates after formation of the A ... Subsequently α-onocerin synthase (LcLCD) carries out the cyclization of the D and E rings from the remaining epoxide ring, to ... A) OSC signature enzymes catalyze the cyclization of 2,3-oxidosqualene, and in more rare cases bis-oxidosqualene, into several ... molecular docking simulation showed that OsONS1 alone produces α-onocerin in two cyclization steps, as opposed to the ...
Intramolecular Cyclization Chemistry 50% * Cinchona Alkaloid Chemistry 50% * Mandelic Acid Chemistry 50% ...
The sequence starts with a Lewis acid-catalyzed cyclization of an epoxyalkene, followed by furan reduction. ...
Synthesis of 1,4-oxazepane-2,5-diones via cyclization of rotationally restricted amino acid precursors and structural ...
In 2014, a diastereoselective SmI2-mediated cyclization was used as a key step by Yang and Chen in the first total synthesis of ... Scheme 23: Domino aza-Reformatsky/cyclization reactions of imines with ethyl dibromofluoroacetate in the presence of chiral 1,2 ... Scheme 24: Domino aza-Reformatsky/cyclization reactions of imines with ethyl bromodifluoroacetate in the presence of a ... Scheme 23: Domino aza-Reformatsky/cyclization reactions of imines with ethyl dibromofluoroacetate in the prese... ...
  • Radical cyclization reactions are organic chemical transformations that yield cyclic products through radical intermediates. (
  • They usually proceed in three basic steps: selective radical generation, radical cyclization, and conversion of the cyclized radical to product. (
  • Radical cyclization reactions produce mono- or polycyclic products through the action of radical intermediates. (
  • The radical cyclization step usually involves the attack of a radical on a multiple bond. (
  • Three conditions must be met for an efficient radical cyclization to take place: A method must be available to generate a radical selectively on the substrate. (
  • Radical cyclization must be faster than trapping of the initially formed radical. (
  • Disadvantages: the relative rates of the various stages of radical cyclization reactions (and any side reactions) must be carefully controlled so that cyclization and trapping of the cyclized radical is favored. (
  • Electrochemically mediated atom transfer radical cyclization (eATRC) has been developed as an easy and clean method allowing the synthesis of halogenated cyclic compounds. (
  • The intramolecular cyclization can be also applied to the C-H/CO/olefin coupling reactions. (
  • This step results from an intramolecular cyclization reaction in which the carbonyl (C=O) group that was a part of the original isocyanate group (-N=C=O), is effectively extracted to yield perimidone and the amine corresponding to the original isocyanate species. (
  • Side reactions are sometimes a problem, and cyclization is especially slow for small and large rings (although macrocyclizations, which resemble intermolecular radical reactions, are often high yielding). (
  • Cyclization of the homologous 6-heptenyl radical is still selective, but is much slower-as a result, competitive side reactions are an important problem when these intermediates are involved. (
  • 2) Cyclization reactions of vinyl, aryl, and acyl radicals are also known. (
  • Reactions involving the cyclization of 1,n-enynes are of high value as they are capable of generating molecular complexity in a minimal number of steps. (
  • These catalytic reactions usually proceed at 120°C. The [RhCl(PPh 3 ) 3 ]-catalyzed cyclization reaction of 2-[(1E)-4,4-dimethyl-1,5-hexadienyl]pyridine smoothly proceeded even at room temperature to give the corresponding cyclized product in 93% yield after 24 h. (
  • Lithium mediated cyclisation reactions. (
  • The first part of this thesis presents the evolution of a novel cationic polyene cyclization cascade for the total synthesis of the meroterpenoid natural product (-)-cyclosmenospongine. (
  • A highly modular and efficient three fragment coupling strategy permitts the facile synthesis of the key cyclization precursor. (
  • Speck, Klaus (2016): The total synthesis of tetracyclic meroterpenoid natural products, Gold(I)-catalyzed cyclizations of 1-Bromo-1,5-Enynes. (
  • A novel Pd-catalyzed chemo- and regiocontrolled tandem cyclization/cross-coupling reaction of 3-alkynyl chromone with aryl iodide was developed for the synthesis of 4 H -furo-[3,2- c ]-chromenes and xanthones. (
  • In many cases, exo cyclization is favored over endo cyclization (macrocyclizations constitute the major exception to this rule). (
  • Although the exo radical is less thermodynamically stable than the endo radical, the more rapid exo cyclization is rationalized by better orbital overlap in the chair-like exo transition state (see below). (
  • Stabilizing the initially formed radical with electron-withdrawing groups provides access to more stable 6-endo cyclization products preferentially. (
  • However, low concentrations of a radical scavenger establish thermodynamic control and provide access to 6-endo products-not via 6-endo cyclization, but by 5-exo cyclization followed by 3-exo closure and subsequent fragmentation (Dowd-Beckwith rearrangement). (
  • The difunctionalization of alkynes through O-attack/5- exo - dig and C-attack/6- endo - dig cyclization was reported by this rare approach, which was selectively controlled by the addition of KF or a bidentate phosphine ligand. (
  • Researchers determine the detailed mechanism of cyclization catalyzed by the cyclization domain of cyclic β-1,2-glucan synthase from Thermoanaerobacter italicus. (
  • Researchers at TUS have proposed a novel mechanism for the cyclization catalyzed by the cyclization domain of cyclic β-1,2-glucan synthase isolated from Thermoanaerobacter italicus (TiCGS Cy ). (
  • CβG biosynthesis is catalyzed by cyclic β-1,2-glucan synthase (CGS), an enzyme that catalyzes the cyclization (closed ring formation) of linear β-1,2-glucan (LβG). (
  • A novel multi-functional sulfur based linker which not only links the substrate to resin and allows traceless cleavage but also enables Pummerer cyclisation chemistry to be carried out at the point of attachment has been developed. (
  • Oxidation of the linking sulfur atom followed by Pummerer cyclisation and traceless cleavage using SmI2 gives the desired oxindole products in good yield and high purity. (
  • Cyclization with a six-residue linker does not perturb the overall structure of RgIA, improves selectivity for the GABAB receptor over the α9α10 nAChR, and improves stability in human serum. (
  • For the cyclization of the pyridine derivatives, [RhCl(PPh 3 ) 3 ] showed the highest catalytic activity with respect to efficiency and selectivity. (
  • The cyclization cascade forms three carbon-carbon bonds and sets four consecutive stereocenters, two of which are tetrasubstituted, to forge the tetracyclic scaffold of cyclosmenospongine in a single step on multi-gram scale. (
  • Part II: In the second part of this thesis, the development of a novel gold(I)-catalyzed cyclization cascade of 1-halo-1,5-enynes in the presence of phenols is described. (
  • Under conditions of kinetic control, 5-exo cyclization takes place preferentially. (
  • A small aliquot of impinger solution (0.5 ml) is mixed with an equal volume of formic acid (a catalyst for cyclization). (
  • Ligand Electronic Effects on Rates of Copper Mediated Atom Transfer Radical Cyclisation and Polymerisation. (
  • It is initially biosynthesized by cyclization of oxidosqualene to lupeol. (
  • The first step of the research involved expressing the cyclization domain alone, TiCGS Cy , as a recombinant enzyme in Escherichia coli . (
  • Effects of cyclization on stability, structure, and activity of α-cono" by Reena Halai, Brid P. Callaghan et al. (
  • Crucially, the sulfur link to resin remains intact throughout the cyclisation leaving the heterocyclic products immobilised. (
  • The results provide insights to further improve the therapeutic properties of RgIA and other conotoxins being considered as drug leads and confirm that cyclization is a readily applicable strategy to improve the stability of peptides with proximate N- and C-termini. (
  • Their 1,6-diene analogues are also applicable to the cyclization reaction to give the corresponding 5- and 6-membered carbocycles. (
  • this EET taking place instead of the desired photoinduced cyclisation of the DTE. (
  • Structural isomerization consists of intramolecular cyclization, resulting in the formation of lumirubin. (
  • This step results from an intramolecular cyclization reaction in which the carbonyl (C=O) group that was a part of the original isocyanate group (-N=C=O), is effectively extracted to yield perimidone and the amine corresponding to the original isocyanate species. (
  • The distinctive characteristic found for pnictogen-bonding catalysis is the breaking of the Baldwin rules, that is selective endo cyclization into the trans -fused ladder oligomers known from the brevetoxins. (
  • Cyclization of sterically hindered enediynes is known to proceed via two competing mechanisms in solution: a classic C1 - C6 or a C1 - C5 cyclization pathway. (
  • Changing protein backbone topology: Structural and dynamic consequences of the backbone cyclization in SH3 domain. (
  • Consequently, the double-coordinating InI2(+) is an especially effective reagent for the selective activation of C≡C and the catalytic initiation of cationic cyclization processes. (
  • nevertheless, incorporation of the d-amino acidity, proline, or an N-alkylated amino acidity facilitates cyclization. (
  • C) Nucleotide alignment of cyclization sequence (D) Nucleotide alignment of upstream AUG region. (
  • On Au(111) we find that the C1 - C5 cyclization is suppressed and that the C1 - C6 cyclization yields a highly strained bicyclic olefin whose surface chemistry was hitherto unknown. (
  • Mutagenesis of aromatic residues in the enzyme active site results in the production of alternative sesquiterpene product arrays due to altered modes of stabilization of carbocation intermediates as well as altered templates for the cyclization of farnesyl diphosphate. (
  • Herein, we report a triflic acid (TfOH)-promoted dehydrative cyclization of N -(2-hydroxyethyl)amides for synthesizing 2-oxazolines. (