Stereoelectronic factors in the stereoselective epoxidation of glycals and 4-deoxypentenosides.

Glycals and 4-deoxypentenosides (4-DPs), unsaturated pyranosides with similar structures and reactivity profiles, can exhibit a high degree of stereoselectivity upon epoxidation with dimethyldioxirane (DMDO). In most cases, the glycals and their corresponding 4-DP isosteres share the same facioselectivity, implying that the pyran substituents are largely responsible for the stereodirecting effect. Fully substituted dihydropyrans are subject to a "majority rule", in which the epoxidation is directed toward the face opposite to two of the three groups.

Probing osmotic effects on invertase with L-(-)-sucrose.

L-(-)-sucrose was efficiently synthesized using intramolecular aglycon delivery and used to elucidate osmotic effects on the activity of invertase, which catalyzes the hydrolysis of D-(+)-sucrose. The osmotic effect imposed by L-sucrose was responsible for more than 30% of the activity loss ascribed otherwise to "substrate inhibition."

Cryoprotection with L- and meso-trehalose: stereochemical implications.

Two unnatural stereoisomers of alpha,alpha-trehalose (L- and meso-trehalose) were synthesized and evaluated as cryoprotectants in order to determine the functional consequences of relative or absolute stereochemistry on their physicochemical properties. Adherent yeast cell cultures were frozen in 10% solutions of D-, L-, and meso-trehalose for periods of 7-28 days, then evaluated by a MTT viability assay. D- and L-trehalose were equally effective in maintaining high rates of cell survival, thus demonstrating the absence of chiral discrimination at the carbohydrate-lipid interface, whereas meso-trehalose was inferior in cryoprotection efficacy.