Septanose carbohydrates. I. Acid-catalysed reaction of D-glucose with acetone

Abstract

Two septanose derivatives of D-glucose, 1,2:3,4-di-O-isopropylidene-α-D-glucoseptanos(e4 a) and 2,3:4,5-di-O-isopropylidene-D-glucoseptanos(e5 a), have been isolated from the mixture of products formed by treating D-glucose with acidified acetone. Acid hydrolysis of (4a) yielded 1,2-O-isopropylidene- α-D-glucoseptanose which has been converted into a mixture of (4a) and a third D-glucoseptanose derivative, 1,2:4,5-di-O-isopropylidene-α-D-glucoseptanose (8a). Methylation of (5a) yielded the two D-glucoseptanoside derivatives, methyl 2,3:4,5-di-O-isopropylidene-α-D-glucoseptanoside and methyl 2,3:4,5-di-O-isopropylidene-β-D-glucoseptanosiwde, which have been selectively hydrolysed to give methyl α (and β-)-D-glucoseptanosides. Conformations of these various septanose compounds are proposed on the basis of n.m.r. parameters and these conformations are compared with those found in the solid state by X-ray analysis.