SYNTHESIS OF C-LINKED GLYCOSYL AMINO-ACID DERIVATIVES USING ORGANOZINC REAGENTS

Reaction of a range of functionalised zinc/copper reagents, including those derived from alpha-amino acids, with the glucal-derived mesylate 7b leads to a mixture of C-3 and C-1 adducts, in which the former pre dominates. The stereochemistry of the adducts has been firmly establis hed, and in each case the nucleophile was shown to have attacked from the beta-face. By contrast, reaction of the iodohomoalanine-derived zi nc reagent 3a with tri-O-acetyl-D-glucal in the presence of boron trif luoride etherate under sonication gives the alpha-adduct 19 as the maj or isomer. Conversion of this compound into a protected alpha-mannosyl C-linked alpha-amino acid derivative 23 is described.