X-ray crystallography unequivocally shows that protection of the free hydroxyl group of 3,5-O-benzyl-idene-d-xylono-1,4-lactone with diphenyl-diazo-methane proceeded smoothly to give the title compound, C(25)H(22)O(5), with no accompanying epimerization. Unlike the analogously protected lyxono lactone, the isomeric xylono lactone has two mol-ecules present in the asymmetric unit (Z' = 2). The 5...

Four glycoglycerolipids with different head groups have been synthesized and their physicochemical properties studied. The lengths of the head groups from a mono-saccharide to a trisaccharide, in addition to the anomeric stereochemistry for the smaller glycoglycerolipids, have been modified. The synthesis has been optimized to avoid glycerol epimerization and to allow up-scaling. The physicoche...

The aand /?-methyl glycosides (IV and V, respectively) of the antibiotic streptozotocin (I) have been synthesized. In addition, analogs involving epimeric changes at C2 (III) and C4 (II), and of two Q analogs, 3-/?-Dglucopyranosyl-1-methyl-l-nitrosourea (XXIII) and the corresponding Dgalactopyranosyl compound (XXV), together with their tetra-O-acetates (XXII and XXIV, respectively) have been pr...

The cyclic peptide core of the antifungal and antibiotic cyclic depsipeptide LI-F04a was synthesised by using a modified Yamaguchi macrolactonization approach. Alternative methods of macrolactonization (e.g., Corey-Nicolaou) resulted in significant epimerization of the C-terminal amino acid during the cyclization reaction. The D-stereochemistry of the alanine residue in the naturally occurring ...

The crystal structure of D-ribulose 5-phosphate 3-epimerase (RPE) from the cyanobacterium Synechocystis was determined by X-ray crystallography to 1.6 A resolution. The enzyme, which catalyzes the epimerization of D-ribulose 5-phosphate and D-xylulose 5-phosphate, assembles as a hexamer of (beta/alpha)(8)-barrels in the crystallographic asymmetric unit. The active site is highly similar to thos...

An enzyme fraction from the green alga Chlorella pyrenoidosa that catalyzes the reversible epimerization of guanosine B’diphosphate D-mannose to guanosine 5’-diphosphate L-galactose brings about the incorporation of tritium from tritium-labeled water into the hexosyl moieties of those sugar nucleotides. The hexoses were degraded by periodate oxidation whereby the tritium was found to be equally...

6-Amino-3-(2'-deoxy-beta-D-ribofuranosyl)-5-nitro-1H-pyridin-2-one (4), a C-glycoside exhibiting the nonstandard pyDDA hydrogen-bonding pattern, was synthesized via Heck coupling. The nitro group greatly enhances the stability of the nucleoside toward acid-catalyzed epimerization without leading to significant deprotonation of the heterocycle at physiological pH. These results make nucleoside 4...

We consider the APED model (activation-polymerization-epimerization-depolymerization) for describing the emergence of chiral solutions within a non-catalytic framework for chiral polymerization. The minimal APED model for dimerization can lead to the spontaneous appearance of chiral oscillations and we describe in detail the nature of these oscillations in the enantiomeric excess, which are the...