GC-MS on the Viking 1976 Mars missions did not detect organic molecules on the Martian surface, even those expected from meteorite bombardment. This result suggested that the Martian regolith might hold a potent oxidant that converts all organic molecules to carbon dioxide rapidly relative to the rate at which they arrive. This conclusion is influencing the design of Mars missions. We reexamine this conclusion in light of what is known about the oxidation of organic compounds generally and the nature of organics likely to come to Mars via meteorite. We conclude that nonvolatile salts of benzenecarboxylic acids, and perhaps oxalic and acetic acid, should be metastable intermediates of meteoritic organics under oxidizing conditions. Salts of these organic acids would have been largely invisible to GC-MS. Experiments show that one of these, benzenehexacarboxylic acid (mellitic acid), is generated by oxidation of organic matter known to come to Mars, is rather stable to further oxidation, and would not have been easily detected by the Viking experiments. Approximately 2 kg of meteorite-derived mellitic acid may have been generated per m(2) of Martian surface over 3 billion years. How much remains depends on decomposition rates under Martian conditions. As available data do not require that the surface of Mars be very strongly oxidizing, some organic molecules might be found near the surface of Mars, perhaps in amounts sufficient to be a resource. Missions should seek these and recognize that these complicate the search for organics from entirely hypothetical Martian life. (+info)
A novel histone deacetylase inhibitor identified by high-throughput transcriptional screening of a compound library.
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Libraries of compounds are increasingly becoming commercially available for the use of individual academic laboratories. A high-throughput system based on a stably integrated transcriptional reporter was used to screen a library of random compounds to identify agents that conferred robust augmentation of a signal transduction pathway. A novel histone deacetylase (HDAC) inhibitor, termed scriptaid, conferred the greatest effect, a 12- to 18-fold augmentation. This facilitation of transcriptional events was generally applicable to exogenous gene constructs, including viral and cellular promoters, different cell lines and reporter genes, and stably integrated and transiently introduced sequences. Scriptaid did not interfere with a further induction provided by stimulation of the cognate signal transduction pathway (transforming growth factor beta/Smad4), which implied the functional independence of ligand-stimulated transcriptional activation and histone acetylation states in this system. Additional insights into this and other signal transduction systems are likely to be afforded through the application of compound screening technologies. (+info)
Selective permeation and organic extraction of recombinant green fluorescent protein (gfpuv) from Escherichia coli.
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BACKGROUND: Transformed cells of Escherichia coli DH5-alpha with pGFPuv, induced by IPTG (isopropyl-beta-d-thiogalactopyranoside), express the green fluorescent protein (gfpuv) during growth phases. E. coli subjected to the combination of selective permeation by freezing/thawing/sonication cycles followed by the three-phase partitioning extraction (TPP) method were compared to the direct application of TPP to the same culture of E. coli on releasing gfpuv from the over-expressing cells. MATERIAL AND METHODS: Cultures (37 degrees C/100 rpm/ 24 h; mu = 0.99 h(-1)-1.10 h(-1)) of transformed (pGFP) Escherichia coli DH5-alpha, expressing the green fluorescent protein (gfpuv, absorbance at 394 nm and emission at 509 nm) were sonicated in successive intervals of sonication (25 vibrations/pulse) to determine the maximum amount of gfpuv released from the cells. For selective permeation, the transformed previously frozen (-75 degrees C) cells were subjected to three freeze/thaw (-20 degrees C/ 0.83 degrees C/min) cycles interlaid by sonication (3 pulses/6 seconds/25 vibrations). The intracellular permeate with gfpuv in extraction buffer (TE) solution (25 mM Tris-HCl, pH 8.0, 1 mM beta-mercaptoethanol beta-ME, 0.1 mM PMSF) was subjected to the three-phase partitioning (TPP) method with t-butanol and 1.6 M ammonium sulfate. Sonication efficiency was verified on the application to the cells previously treated by the TPP method. The intra-cell releases were mixed and eluted through methyl HIC column with a buffer solution (10 mM Tris-HCl, 10 mM EDTA, pH 8.0). RESULTS: The sonication maximum released amount obtained from the cells was 327.67 microg gfpuv/mL (20.73 microg gfpuv/mg total proteins-BSA), after 9 min of treatment. Through the selective permeation by three repeated freezing/thawing/sonication cycles applied to the cells, a close content of 241.19 microg gfpuv/mL (29.74 microg gfpuv/mg BSA) was obtained. The specific mass range of gfpuv released from the same cultures, by the three-phase partitioning (TPP) method, in relation to total proteins, was higher, between 107.28 microg/mg and 135.10 microg/mg. CONCLUSIONS: The selective permeation of gfpuv by freezing/thawing/sonication followed by TPP separation method was equivalent to the amount of gfpuv extracted from the cells directly by TPP; although selective permeation extracts showed better elution through the HIC column. (+info)
Asymmetric conjugate addition of arylthiols to enoates and its application to organic synthesis of biologically potent compounds.
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As a part of our studies aimed at asymmetric catalytic reactions by using an external chiral ligand, we have developed a catalytic asymmetric addition reaction of an arylthiol to alpha,beta-unsaturated esters under the control of an external chiral ligand. The characteristic of our technology is a double activation of a thiol by lithiation and chelate formation with a chiral tridentate amino diether ligand, which simultaneously and effectively controls a stereochemistry of the reaction. One significant feature of an arylthiol is a bulky 2-substitution on aryl group, which enables the formation of a really reactive monomeric thiolate species. s-Cis conformation and capability of electron lone pair-differentiating coordination of a carbonyl oxygen to lithium are structural requirements of the substrates for high enantioselectivity. The enantioselectivity came up to 97% under the cited conditions. Asymmetric protonation of a transient enolate, generated by conjugate addition of a lithium thiolate to an enoate, was also realized. The stereochemistry of the protonation was controlled by the conformation of initially formed transient enolate in a 1,2-asymmetric induction manner. This technology enabled the asymmetric synthesis of (S)-naproxene. Stereoselective tandem C-S and C-C bond-forming reaction was developed as a logical extension by trapping the transient enolate intermediate with an aldehyde as a carbo-electrophile in the presence of phenylthiotrimethylsilane as an equilibrium-shift reagent. This tandem reaction was extended to a stereoselective cyclization of omega-oxo-alpha,beta-unsaturated esters initiated by a lithium thiolate. Stereoselectivity of both tandem inter- and intramolecular reaction is predictable by an allylic strain-controlled conformation model of the enolate, in which an approach of aldehyde takes place anti to C-S bond through coordination of an aldehyde oxygen to lithium. Total synthesis of (-)-neplanocin A was achieved by using the tandem cyclization as a key tool for the direct construction of a five-membered carbocycle where every carbon is functionalized. (+info)
A structure-activity relationship study was performed on cyclic RGD peptides using a combination of multisubstituted alkene dipeptide isosteres. To clarify the effects on bioactivity of a valine N-methyl group in the cyclo(-Arg-Gly-Asp-D-Phe-MeVal-) peptide developed by Kessler's group, novel D-Phe-Val-type isosteres with methyl-substituting groups on the olefin were designed and synthesized. Syntheses of D-Phe-psi[(E)-CH=CMe]-Val-type isosteres were carried out in essentially identical fashion to the previously reported preparation of psi[(E)-CH=CH]-type congeners. Alternatively, D-Phe-psi[(E)-CMe=CX]-Val-type isosteres (X=H or Me) were synthesized via stereoselective alkylation of beta-(1,3-oxazolidin-2-on-5-yl)-alpha,beta-enoates using organocopper reagents. The resulting four isosteres were utilized in either solution- or solid-phase peptide synthesis to afford the cyclic RGD peptidomimetics, cyclo(-Arg-Gly-Asp-D-Phe-psi[(E)-CX=CX]-Val-) (X=H or Me). alpha(V)beta(3) and alpha(IIb)beta(3) integrin antagonistic activities of the peptidomimetics along with Kessler's peptides were comparatively evaluated. In addition, structural calculations of these compounds by simulated annealing/energy minimization using dihedral and distance restraints derived from (1)H-NMR data in DMSO gave insight into the effects of the valine N-methyl group as well as the D-phenylalanine carbonyl oxygen. (+info)
A direct synthesis of hyperolactone C.
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Hyperolactone C is prepared from furan 4. The key transformation is a tandem Claisen rearrangement/lactonization. (+info)
Development of useful reactions based on the novel reactivities of allenic compounds and their application to tandem cyclizations.
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This review highlights a recent study on allenic compounds by the author's group. In the first section, the organocopper-mediated ring-opening reaction of ethynylaziridines and palladium-catalyzed reductive synthesis of allenes are described. In the second section, palladium-catalyzed stereoselective cyclization of allenes, including the tandem reaction, leading to aziridines, pyrrolidines, benzoisoindoles, and cyclopropanes is presented. The final section reviews aziridination and medium-ring formation due to the intramolecular reaction of bromoallenes. The latter reaction is based on the author's recent discovery that bromoallenes can act as allylic dication equivalents in the presence of a palladium catalyst and alcohol. (+info)
Reverse vesicles as a new system for studying enzymes in organic solvents.
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A new approach to the study of enzyme activity in organic solvents has been developed by using optically transparent reverse vesicles. Polyphenol oxidase was incorporated in an active form into the above ternary system formed by the non-ionic surfactant tetra(ethylene glycol) dodecyl ether/n-dodecane/water. The enzyme in this microenvironment, surprisingly, showed an apparent positive co-operativity which has never before been described either in aqueous solution or in reverse micelles. In addition, the Vmax. expressed was similar to that in water and twice that displayed in reverse micelles. (+info)