Branched-chain sugars. Part III. Synthesis of D-nogalose (6-deoxy-3-C-methyl-2,3,4-tri-o-methyl-D-mannopyranose)

Abstract

D-Nogalose [D-(1)], the enantiomer of a sugar component of the antibiotic nogalamycin, has been synthesized in seventeen steps from methyl α-D-glucopyranoside. The C-methyl substituent was introduced by addition of methylmagnesium iodide to 1,2:5,6-di-O-isopropylidene-β-D-arabino-hexofuranos-3-ulose (15). A related attempt to prepare L-nogalose (1) from 1,2:5,6-di-O-isopropylidene-α-D-xylo-hexofuranos-3-ulose (2) was unsuccessful, since configurational inversion at C-5 could not be achieved at a later stage of the synthesis.