New inhibitors of glycogen phosphorylase as potential antidiabetic agents.

The protein glycogen phosphorylase has been linked to type 2 diabetes, indicating the importance of this target to human health. Hence, the search for potent and selective inhibitors of this enzyme, which may lead to antihyperglycaemic drugs, has received particular attention. Glycogen phosphorylase is a typical allosteric protein with five different ligand binding sites, thus offering multiple opportunities for modulation of enzyme activity. The present survey is focused on recent new molecules, potential inhibitors of the enzyme. The biological activity can be modified by these molecules through direct binding, allosteric effects or other structural changes. Progress in our understanding of the mechanism of action of these inhibitors has been made by the determination of high-resolution enzyme inhibitor structures (both muscle and liver). The knowledge of the three-dimensional structures of protein-ligand complexes allows analysis of how the ligands interact with the target and has the potential to facilitate structure-based drug design. In this review, the synthesis, structure determination and computational studies of the most recent inhibitors of glycogen phosphorylase at the different binding sites are presented and analyzed.

Preparation of acetylated pyranoid glycals from glycosyl halides by chromium(II) complexes under aqueous biphasic conditions.

Reactions of chromium(II) aminocarboxylate complexes (ethylenediamine-tetraacetate, nitrilo-triacetate, imino-diacetate) with acetylated glycopyranosyl chlorides or bromides in liquid-liquid or solid-liquid biphasic media (such as water-diethylether, water-ethyl acetate or halosugar-water) give the corresponding glycals in 75-97% yield.

Synthesis of and a comparative study on the inhibition of muscle and liver glycogen phosphorylases by epimeric pairs of d-gluco- and d-xylopyranosylidene-spiro-(thio)hydantoins and N-(d-glucopyranosyl) amides.

D-Gluco- and D-xylopyranosylidene-spiro-hydantoins and -thiohydantoins were prepared from the parent sugars in a six-step, highly chemo-, regio-, and stereoselective procedure. In the key step of the syntheses C-(1-bromo-1-deoxy-beta-D-glycopyranosyl)formamides were reacted with cyanate ion to give spiro-hydantoins with a retained configuration at the anomeric center as the major products. On the other hand, thiocyanate ions gave spiro-thiohydantoins with an inverted anomeric carbon as the only products. On the basis of radical inhibition studies, a mechanistic rationale was proposed to explain this unique stereoselectivity and the formation of C-(1-hydroxy-beta-D-glycopyranosyl)formamides as byproducts. Enzyme assays with a and b forms of muscle and liver glycogen phosphorylases showed spiro-hydantoin 12 and spiro-thiohydantoin 14 to be the best and equipotent inhibitors with K(i) values in the low micromolar range. The study of epimeric pairs of D-gluco and D-xylo configurated spiro-hydantoins and N-(D-glucopyranosyl)amides corroborated the role of specific hydrogen bridges in binding the inhibitors to the enzyme.

Mass spectrometric studies of anomeric glycopyranosyl azides.

We studied the mass spectrometric behaviour of peracetylated and underivatized anomeric hexopyranosyl azides and 5-thioglucopyranosyl azides by means of different mass spectrometric techniques. The unstable molecular ions fragment predominantly by losing either N3 radical or N2 molecule. Loss of N2 molecule and the protonation of the derived nitrene were characteristic of the studied compounds. The presence of BF3.Et2O in the ion source is favorable for producing the protonated nitrene form. The protonated nitrene shows a new type of ring expansion rearrangement. The abundances of the [M + H - N2]+ ion makes it possible to identify the anomeric configuration of the azido group.

Efficient inhibition of muscle and liver glycogen phosphorylases by a new glucopyranosylidene-spiro-thiohydantoin.

Reaction of C-(1-bromo-1-deoxy-beta-glucopyranosyl)formamide 2 with thiocyanate ions was the key step of a short synthesis of D-glucopyanosylidene-spiro-thiohydantoin 7 which proved to be a potent inhibitor of muscle and liver glycogen phosphorylases.

Evaluation of C-(beta-D-galactosyl) and C-(2-deoxy-D-lyxo-hex-1-enopyranosyl) (D-galactal type) derivatives as inhibitors of beta-D-galactosidase from Escherichia coli.

C-(2-Deoxy-D-lyxo-hex-1-enopyranosyl)formamide was prepared from acetylated C-(beta-D-galactopyranosyl)formamide by a radical-mediated bromination-zinc/N-methylimidazole-induced reductive elimination-Zemplén deacetylation reaction sequence. The preparation of acetylated 5-(2-deoxy-D-lyxo-hex-1-enopyranosyl)tetrazole was improved. Methyl C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formimidate was transformed by benzylamine into N-benzyl-C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formamidine and, after hydrolysis to methyl C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formate, into N-benzyl-C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formamide. A series of C-(beta-D-galactopyranosyl) and C-(2-deoxy-D-lyxo-hex-1-enopyranosyl) derivatives was comparatively investigated for E. coli beta-D-galactosidase inhibitory activity. N-Benzyl-C-(2-deoxy-D-lyxo-hex-1-enopyranosyl)formamidine was the best inhibitor and had K(i) = 6 microM (on the basis of its free base concentration, K(i) = 8.3 nM was obtained). Basicity and hydrophobicity of the aglycon proved to be more important factors for the inhibition than the conformation of the sugar ring.

Preparation of C-(2-deoxyhex/pent-1-enopyranosyl)heterocycles.

Acetylated 1-cyanoglycals (2,6-anhydro-3-deoxyhept/hex-2-enononitriles) were prepared by direct elimination of acetic acid from the appropriate acetylated 2,6-anhydrohept/hexononitriles with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in aprotic solvents. Heterocyclisation of the cyano group of acetylated 1-cyano-D-galactal with 2-aminothiophenol led to 2-(3,4,6-tri-O-acetyl-2-deoxy-D-lyxo-hex-1-enopyranosyl)benz othiazole. Several 2-(per-O-acetylhexo/pentopyranosyl)benzothiazoles also gave 2-(per-O-acetyl-2-deoxyhex/pent-1-enopyranosyl)benzothiazole s with DBU. 3-(Per-O-acetylhexo/pentopyranosyl)-[1,2,4]triazolo[4,3-a] pyrimidines rearranged with DBU to the corresponding acetylated 2-glycosyl-[1,2,4]triazolo[1,5-a]pyrimidines. By the reaction of 1-cyano-D-galactal with ammonium azide, 2-(3,4,6-tri-O-acetyl-2-deoxy-D-lyxo-hex-1-enopyranosyl)tetr azole was prepared and then transformed with carboxylic acid derivatives into 2-(3,4,6-tri-O-acetyl-2-deoxy-D-lyxo-hex-1-enopyranosyl)-5-s ubstituted-1,3,4- oxadiazoles.