engleski

Absolute Configurations of L-Ascorbic Acid Derivatives: Circular Dichroism and X-Ray Crystal Structure Studies

The present study deals with the chiral 2, 3-O, O-dibenzyl derivatives of L-ascorbic acid containing 4-(5, 6-epoxy)- (4), 6-O-tosyl- (8) and 5, 6-O, O-ditosyl- (9) functional groups and it was undertaken to determine the absolute configuration of these compounds which is of importance for elucidation of stereochemical course of their condensation reaction with nucleoside bases and evaluation of their biological properties. X-ray crystal structure analysis using anomalous dispersion gave the exact stereostructures of 2, 3-O, O-dibenzyl-5, 6-isopropylidene-L-ascorbic acid (6) and 8. The comparison of the CD spectra of 4, 8 and 9 with the CD spectra of their synthetic precursors (2-3, 5-7) and L-ascorbic acid (1) itself, as well as crystal structures of 6 and 8 permitted the assignment of the absolute configurations of 4 and 9. Thus, it was found that C-4 and C-5 in 4 and 9 have R- and S- configurations. This means that the syntheses of 4, 8 and 9 proceeded from the starting L-ascorbic acid by retention of configuration.

L-ascorbic acid derivatives ; Single crystal X-ray diffraction ; Circular dichroism spectroscopy ; Cotton effect

nije evidentirano