A stereochemical study of a potentially prebiotic peptide-forming reaction was carried out as the first part of a systems chemistry investigation of potential paths for symmetry breaking. Substantial diastereomeric excesses result from a fast epimerization of the 5(4H)-oxazolone intermediate in aqueous solution.

Cloned immortalized MC615 mouse chondrocytic cells were used to examine their capability to produce multiple types of matrix proteoglycans. Immunofluorescence staining indicated a uniform expression of aggrecan, biglycan and decorin by all cells. After culture with [35S]sulphate, proteo[35S]glycans secreted by the cells were found to elute in two peaks from a Sepharose CL-4B column. The first p...

We tested bile acid oxazoline derivatives of chenodeoxycholic (CDC-OX), 7-ketolithocholic (7-KLC-OX), ursodeoxycholic (UDC-OX), and deoxycholic (DC-OX) as inhibitors of the 7-epimerization of the primary bile acids cholic acid (CA) and CDC in cultures of four species of bacteria and the human fecal flora. The organisms tested elaborate a 7 alpha- and/or 7 beta-hydroxysteroid dehydrogenase (HSDH...

New DKR type: An N-heterocyclic carbene (NHC)-catalyzed dynamic kinetic resolution of racemic α-substituted β-keto esters has been developed. This method relies on the epimerization of an NHC-enol intermediate before subsequent aldol/acylation events. Highly substituted β-lactones are produced in good yield with good to excellent selectivities (see scheme).

An approach to the intramolecular Diels-Alder reaction has led to a cascade synthesis of complex carbocycles composed of three fused rings and up to five stereocenters with complete stereocontrol. Computational analysis reveals that the reaction proceeds by a Michael/Michael/cyclopropanation/epimerization cascade in which size and coordination of the counterion is key.

[formula: see text] A novel pentacyclic polyhydroxylated sterol, xestobergsterol A (1a), has been synthesized in 24 steps and in good overall yield from stigmasterol 17. The key steps of the synthesis are the Breslow remote functionalization of the polyoxygenated steroid derived from 25 and the base-catalyzed epimerization-aldol condensation of the dione derived from 27.

position 6,1-4) the preparation of 7-epi-aminocephalosporanic 'acid (7a-ACA) has thus far not been reported. Some 7-epi-cephalosporins have been prepared by base-catalyzed epimerization of cephalosporin sulfoxidesu or acidcatalyzed ring expansion of 6-epi-penicillins.e) Both procedures, however, are not convenient for the preparation of 7-epi-cephalosporin derivatives. We wish to report the direct

An adaptable approach: The first highly convergent stereoselective synthesis of feglymycin (see structure) and its enantiomer is based on the coupling of repeating peptide fragments. The use of weakly basic conditions throughout the synthesis suppressed the epimerization of sensitive aryl glycine units. Feglymycin has strong anti-HIV activity as well as potent (previously identified as weak) an...