Stereoselective synthesis and 2D NMR study of S-D-glucopyranoside

2, 3, 4-Tri-O-benzyl-6-O trimethylsilyl-α-D-glucopyranosyl bromide reacted with RSH compounds (R = Et, t-Bu, PhCH₂, p-PhBu^t, Ph, 2-benzoxazole, 2-benzothiazole), with diisopropylethylamine as base, to give S-D-glucosides. The α- and β- anomeric ratio was dependent on the pKa. value of the thiol compound. If pKa value was less than or equal to 7, β-anomer was obtained. If pKa value was equal to or more than 11, α anomer was obtained. If pKa value was between 9 and 10.6, a mixture of α- and β-anomer was obtained. The probable mechanism was discussed. The chemical shifts of proton and carbon in these S-D-glucosides were measured and verified by 2D NMR (cosy and hetcor).