Synthesis of some derivatives of C-(1-deoxy-1-N-substituted-D-glucopyranosyl)formic acid (D-gluco-hept-2-ulopyranosonic acid) as potential inhibitors of glycogen phosphorylase. Per-O-benzoylated derivatives (amide, methyl ester and glycinamide) of C-(1-azido-1-deoxy-alpha-D-glucopyranosyl)formic acid obtained by azide