Deamination of 2-amino-2-deoxyhexitols and of their per-O-methylated derivatives with nitrous acid

The products of nitrous acid deamination of per-O-methylated 2-amino-2-deoxy-d-glucitol and $\text{2-}\text{amino}\text{-2-}\text{deoxy}\text{-3-O-β-}\text{d}\text{-galactopyranosyl-}\text{d}\text{-glucitol}$ and its per-O-methylated derivative have been characterized by g.l.c.—mass spectrometry after treatment with sodium borodeuteride and further substitution by acetylation, methylation, or (trideuteriomethyl)ation. The results confirm that the most important reaction pathway (1) involves a 1 → 2-hydride shift to give $\text{2-}\text{deoxy-}\text{d}\text{-arabino-}\text{hexoses}$, but that significant side-reactions include (2) solvolytic displacement at C-2, (3) a 3 → 2-hydride shift, to give $\text{2-}\text{deoxy-}\text{d}\text{-erythro-3-}\text{hexuloses}$, and (4) a C-4→C-2 migration to give $\text{2-}\text{deoxy}\text{-2-C-}\text{(hydroxymethyl)-}\text{d}\text{-ribose}$ and -d-arabinose. Reactions (3) and (4) result in elimination of the original 3-O-substituents, with the exposure of new reducing groups, from oligosaccharides terminated by 3-O-substituted 2-amino-2-deoxyhexitols.