Synthesis of 2-(β-d-glucopyranosyl)-5-(substituted-amino)-1,3,4-oxa- and -thiadiazoles for the inhibition of glycogen phosphorylase

• Preparation of new anhydro-aldose semicarbazones and thiosemicarbazones.
• Synthesis of 2-acylamino- or 2-arylamino-5-(β-d-glucopyranosyl)-1,3,4-oxa- and -thiadiazoles.
• Low micromolar inhibitor of glycogen phosphorylase.

O-Perbenzoylated 4-phenyl-[C-(β-d-glucopyranosyl)formaldehyde]semicarbazone was prepared in the reaction of O-perbenzoylated β-d-glucopyranosyl cyanide and 4-phenylsemicarbazide in the presence of Raney-Ni. Acylation of O-perbenzoylated C-(β-d-glucopyranosyl)formaldehyde semicarbazone furnished the corresponding 4-acyl-[C-(β-d-glucopyranosyl)formaldehyde]semicarbazones. The reaction of O-perbenzoylated C-(β-d-glucopyranosyl)formaldehyde semicarbazone with the corresponding thiosemicarbazide resulted in O-perbenzoylated C-(β-d-glucopyranosyl)formaldehyde thiosemicarbazone and its 4-phenyl derivative. Acylation of O-perbenzoylated C-(β-d-glucopyranosyl)formaldehyde thiosemicarbazone provided the corresponding 4-acyl-2-acylamino-5-(β-d-glucopyranosyl)-Δ2-1,3,4-thiadiazolidines. Oxidative transformations of these precursors gave O-protected 2-(β-d-glucopyranosyl)-5-substituted-amino-1,3,4-oxa- and -thiadiazoles. The O-benzoyl protecting groups were removed under base-catalysed transesterification conditions. The C-glucopyranosyl heterocyclic compounds proved inactive against rabbit muscle glycogen phosphorylase b, however, the semicarbazones showed moderate inhibition (best inhibitor was 4-phenyl-[C-(β-d-glucopyranosyl)formaldehyde]semicarbazone (Ki = 29 μM).

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