Cyclization: Changing an open-chain hydrocarbon to a closed ring. (McGraw-Hill Dictionary of Scientific and Technical Terms, 5th ed)Stereoisomerism: 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)Molecular Structure: 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.Alkenes: Unsaturated hydrocarbons of the type Cn-H2n, indicated by the suffix -ene. (Grant & Hackh's Chemical Dictionary, 5th ed, p408)Alkynes: Hydrocarbons with at least one triple bond in the linear portion, of the general formula Cn-H2n-2.Intramolecular Lyases: 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.Palladium: 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.AcetalsCatalysis: The facilitation of a chemical reaction by material (catalyst) that is not consumed by the reaction.KetonesPolyisoprenyl Phosphates: Phosphoric or pyrophosphoric acid esters of polyisoprenoids.Chemistry, Organic: The study of the structure, preparation, properties, and reactions of carbon compounds. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)Alkadienes: Acyclic branched or unbranched hydrocarbons having two carbon-carbon double bonds.PyransPeptides, Cyclic: 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).Cycloparaffins: 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)Lewis Acids: Any chemical species which accepts an electron-pair from a LEWIS BASE in a chemical bonding reaction.Rhodium: Rhodium. A hard and rare metal of the platinum group, atomic number 45, atomic weight 102.905, symbol Rh. (Dorland, 28th ed)Combinatorial Chemistry Techniques: 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.Isomerases: 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.Indole Alkaloids: Group of alkaloids containing a benzylpyrrole group (derived from TRYPTOPHAN)IminesCyclotides: 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.Heterocyclic Compounds: Ring compounds having atoms other than carbon in their nuclei. (Grant & Hackh's Chemical Dictionary, 5th ed)Molecular Conformation: The characteristic three-dimensional shape of a molecule.Heterocyclic Compounds with 4 or More Rings: 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.Amination: 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.Carbon-Carbon Lyases: 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.Furans: Compounds with a 5-membered ring of four carbons and an oxygen. They are aromatic heterocycles. The reduced form is tetrahydrofuran.Terpenes: A class of compounds composed of repeating 5-carbon units of HEMITERPENES.Epoxy Compounds: 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.Polyketide Synthases: Large enzyme complexes composed of a number of component enzymes that are found in STREPTOMYCES which biosynthesize MACROLIDES and other polyketides.Macrocyclic Compounds: Cyclic compounds with a ring size of approximately 1-4 dozen atoms.Protein Splicing: 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.Oldenlandia: 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.Boranes: 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, Molecular: Models used experimentally or theoretically to study molecular shape, electronic properties, or interactions; includes analogous molecules, computer-generated graphics, and mechanical structures.Solid-Phase Synthesis Techniques: 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.NorbornanesHeterocyclic Compounds, 2-Ring: 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.Cyclodextrins: 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.SqualeneInteins: 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.Cystine Knot Motifs: 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.Magnetic Resonance Spectroscopy: 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).Polyketides: 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.Monoterpenes: 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).Abies: 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.Aldehydes: Organic compounds containing a carbonyl group in the form -CHO.Diterpenes: Twenty-carbon compounds derived from MEVALONIC ACID or deoxyxylulose phosphate.Naphthols: 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.Strychnos: A plant genus of the family LOGANIACEAE (classified by some botanists as Strychnaceae).Spiro Compounds: A group of compounds consisting in part of two rings sharing one atom (usually a carbon) in common.Streptomyces: 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.Alkaloids: 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)Cycloaddition Reaction: Synthetic organic reactions that use reactions between unsaturated molecules to form cyclical products.Bromine Compounds: Inorganic compounds that contain bromine as an integral part of the molecule.Molecular Sequence Data: 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.SesquiterpenesCrystallography, X-Ray: The study of crystal structure using X-RAY DIFFRACTION techniques. (McGraw-Hill Dictionary of Scientific and Technical Terms, 4th ed)Phosgene: 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 CompoundsGlycogen Debranching Enzyme System: 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.SemicarbazidesGuanosine Diphosphate Sugars: Esters formed between the aldehydic carbon of sugars and the terminal phosphate of guanosine diphosphate.Models, Chemical: Theoretical representations that simulate the behavior or activity of chemical processes or phenomena; includes the use of mathematical equations, computers, and other electronic equipment.