Probing the ß-pocket of the active site of human liver glycogen phosphorylase with 3-(C-ß-d-glucopyranosyl)-5-(4-substituted-phenyl)-1, 2, 4-triazole inhibitors.

Human liver glycogen phosphorylase (hlGP), a key enzyme in glycogen metabolism, is a valid pharmaceutical target for the development of new anti-hyperglycaemic agents for type 2 diabetes. Inhibitor discovery studies have focused on the active site and in particular on glucopyranose based compounds with a ß-1 substituent long enough to exploit interactions with a cavity adjacent to the active site, termed the ß-pocket. Recently, C-ß-d-glucopyranosyl imidazoles and 1, 2, 4-triazoles proved to be the best known glucose derived inhibitors of hlGP. Here we probe the ß-pocket by studying the inhibitory effect of six different groups at the para position of 3-(ß-d-glucopyranosyl phenyl)-5-phenyl-, 1, 2, 4-triazoles in hlGP by kinetics and X-ray crystallography. The most bioactive compound was the one with an amine substituent to show a Ki value of 0.43 µM. Structural studies have revealed the physicochemical diversity of the ß-pocket providing information for future rational inhibitor design studies.

New synthesis of 3-(ß-D-glucopyranosyl)-5-substituted-1,2,4-triazoles, nanomolar inhibitors of glycogen phosphorylase.

O-Perbenzoylated 5-(ß-D-glucopyranosyl)tetrazole was reacted with N-benzyl carboximidoyl chlorides to give the corresponding 4-benzyl-3-(ß-D-glucopyranosyl)-5-substituted-1,2,4-triazoles. Removal of the O-benzoyl and N-benzyl protecting groups by base catalysed transesterification and catalytic hydrogenation, respectively, furnished a series of 3-(ß-D-glucopyranosyl)-5-substituted-1,2,4-triazoles with aliphatic, mono- and bicyclic aromatic, and heterocyclic substituents in the 5-position. Enzyme kinetic studies revealed these compounds to inhibit rabbit muscle glycogen phosphorylase b: best inhibitors were the 5-(4-aminophenyl)- (Ki 0.67 µM) and the 5-(2-naphthyl)-substituted (Ki 0.41 µM) derivatives. This study uncovered the C-glucopyranosyl-1,2,4-triazoles as a novel skeleton for nanomolar inhibition of glycogen phosphorylase.

Synthesis of 2-(ß-D-glucopyranosylamino)-5-substituted-1,3,4-oxadiazoles for inhibition of glycogen phosphorylase.

Aromatic aldehyde 4-(2,3,4,6-tetra-O-acetyl-ß-d-glucopyranosyl)semicarbazones were synthesized by the addition of different hydrazones onto O-peracetylated ß-d-glucopyranosyl isocyanate. Oxidative transformations of these precursors gave O-protected 2-(ß-d-glucopyranosylamino)-5-substituted-1,3,4-oxadiazoles. Removal of the O-acetyl protecting groups under Zemplén conditions gave test compounds to show low micromolar inhibition against rabbit muscle glycogen phosphorylase b. Best inhibitors of these series were 4-(ß-d-glucopyranosyl)semicarbazones of 4-nitrobenzaldehyde (Ki=4.5µM), 2-naphthaldehyde (Ki=5.5µM) and 2-(ß-d-glucopyranosylamino)-5-(4-methylphenyl)-1,3,4-oxadiazole (Ki=12µM).

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

O-Perbenzoylated 4-phenyl-[C-(ß-d-glucopyranosyl)formaldehyde]semicarbazone was prepared in the reaction of O-perbenzoylated ß-d-glucopyranosyl cyanide and 4-phenylsemicarbazide in the presence of Raney-Ni. Acylation of O-perbenzoylated C-(ß-d-glucopyranosyl)formaldehyde semicarbazone furnished the corresponding 4-acyl-[C-(ß-d-glucopyranosyl)formaldehyde]semicarbazones. The reaction of O-perbenzoylated C-(ß-d-glucopyranosyl)formaldehyde semicarbazone with the corresponding thiosemicarbazide resulted in O-perbenzoylated C-(ß-d-glucopyranosyl)formaldehyde thiosemicarbazone and its 4-phenyl derivative. Acylation of O-perbenzoylated C-(ß-d-glucopyranosyl)formaldehyde thiosemicarbazone provided the corresponding 4-acyl-2-acylamino-5-(ß-d-glucopyranosyl)-Δ(2)-1,3,4-thiadiazolidines. Oxidative transformations of these precursors gave O-protected 2-(ß-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-(ß-d-glucopyranosyl)formaldehyde]semicarbazone (Ki=29µM).

Suberoylanilide hydroxamic acid, a potent histone deacetylase inhibitor; its X-ray crystal structure and solid state and solution studies of its Zn(II), Ni(II), Cu(II) and Fe(III) complexes.

Reaction of the potent hydroxamate-based histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid (SAHA), with hydrated metal salts of Fe(III), Cu(II), Ni(II) and Zn(II) yielded a tris-hydroxamato complex in the case of Fe(III) and bis-hydroxamato complexes in the case of Cu(II), Ni(II) and Zn(II) both in the solid state and in solution. Reaction of the secondary hydroxamic acid, N-Me-SAHA, also yielded a tris-hydroxamato complex in the case of Fe(III) and bis-hydroxamato complexes in the case of Cu(II), Ni(II) and Zn(II) in solution. These metal complexes have the hydroxamato moiety coordinated in an O,O'-bidentate fashion. Stability constants of the metal complexes formed with SAHA and N-Me-SAHA in a DMSO/H(2)O 70/30%(v/v) mixture are described. A novel crystal structure of SAHA together with a novel synthesis for N-Me-SAHA are also reported.