Tibor Docsa

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.

Kinetic and crystallographic studies on 2‐(β‐D‐glucopyranosyl)‐5‐methyl‐1, 3, 4‐oxadiazole, ‐benzothiazole, and ‐benzimidazole, inhibitors of muscle glycogen phosphorylase b. Evidence for a new binding site

In an attempt to identify leads that would enable the design of inhibitors with enhanced affinity for glycogen phosphorylase (GP), that might control hyperglycaemia in type 2 diabetes, three new analogs of β‐D‐glucopyranose, 2‐(β‐D‐glucopyranosyl)‐5‐methyl‐1, 3, 4‐oxadiazole, ‐benzothiazole, and ‐benzimidazole were assessed for their potency to inhibit GPb activity. The compounds showed competitive inhibition (with respect to substrate Glc‐1‐P) with Ki values of 145.2 (±11.6), 76 (±4.8), and 8.6 (±0.7) μM, respectively. In order to establish the mechanism of this inhibition, crystallographic studies were carried out and the structures of GPb in complex with the three analogs were determined at high resolution (GPb‐methyl‐oxadiazole complex, 1.92 Å; GPb‐benzothiazole, 2.10 Å; GPb‐benzimidazole, 1.93 Å). The complex structures revealed that the inhibitors can be accommodated in the catalytic site of T‐state GPb with very little change of the tertiary structure, and provide a rationalization for understanding variations in potency of the inhibitors. In addition, benzimidazole bound at the new allosteric inhibitor or indole binding site, located at the subunit interface, in the region of the central cavity, and also at a novel binding site, located at the protein surface, far removed (∼ 32 Å) from the other binding sites, that is mostly dominated by the nonpolar groups of Phe202, Tyr203, Val221, and Phe252.

Synthesis of 1-(d-glucopyranosyl)-1,2,3-triazoles and their evaluation as glycogen phosphorylase inhibitors

1-(D-Glucopyranosyl)-1,2,3-triazoles were prepared from per-O-acetylated alpha- and beta-D-glucopyranosyl azides as well as per-O-benzoylated (beta-D-gluco-hept-2-ulopyranosylazide)onamide and onic acid methylester by using azide-alkyne cycloaddition catalysed by in situ generated Cu(I) under aqueous conditions. The O-acyl protecting groups were removed by the Zemplén protocol. The test compounds were assayed against rabbit muscle glycogen phosphorylase b to show that the beta-D-glucopyranosyl derivatives were superior inhibitors as compared to the two other series of triazoles.

Synthesis and structure-activity relationships of C-glycosylated oxadiazoles as inhibitors of glycogen phosphorylase

A series of per-O-benzoylated 5-beta-D-glucopyranosyl-2-substituted-1,3,4-oxadiazoles was prepared by acylation of the corresponding 5-(beta-D-glucopyranosyl)tetrazole. As an alternative, oxidation of 2,6-anhydro-aldose benzoylhydrazones by iodobenzene I,I-diacetate afforded the same oxadiazoles. 1,3-Dipolar cycloaddition of nitrile oxides to per-O-benzoylated beta-D-glucopyranosyl cyanide gave the corresponding 5-beta-D-glucopyranosyl-3-substituted-1,2,4-oxadiazoles. The O-benzoyl protecting groups were removed by base-catalyzed transesterification. The 1,3,4-oxadiazoles were practically inefficient as inhibitors of rabbit muscle glycogen phosphorylase b while the 1,2,4-oxadiazoles displayed inhibitory activities in the micromolar range. The best inhibitors were the 5-beta-D-glucopyranosyl-3-(4-methylphenyl- and -2-naphthyl)-1,2,4-oxadiazoles (K(i)=8.8 and 11.6 microM, respectively). A detailed analysis of the structure-activity relationships is presented.

Kinetic and crystallographic studies of glucopyranosylidene spirothiohydantoin binding to glycogen phosphorylase B.

Glucopyranosylidene spirothiohydantoin (TH) has been identified as a potential inhibitor of both muscle and liver glycogen phosphorylase b (GPb) and a (GPa) and shown to diminish liver GPa activity in vitro. Kinetic experiments reported here show that TH inhibits muscle GPb competitively with respect to both substrates phosphate (K(i)=2.3 microM) and glycogen (K(i)=2.8 microM). The structure of the GPb-TH complex has been determined at a resolution of 2.26 A and refined to a crystallographic R value of 0.193 (R(free)=0.211). The structure of GPb-TH complex reveals that the inhibitor can be accommodated in the catalytic site of T-state GPb with very little change of the tertiary structure, and provides a basis of understanding potency and specificity of the inhibitor. The glucopyranose moiety makes the standard hydrogen bonds and van der Waals contacts as observed in the glucose complex, while the rigid thiohydantoin group is in a favourable electrostatic environment and makes additional polar contacts to the protein.

Synthesis of variously coupled conjugates of d-glucose, 1,3,4-oxadiazole, and 1,2,3-triazole for inhibition of glycogen phosphorylase

5-(O-Perbenzoylated-β-D-glucopyranosyl)tetrazole was obtained from O-perbenzoylated-β-D-glucopyranosyl cyanide by Bu(3)SnN(3) or Me(3)SiN(3)-Bu(2)SnO. This tetrazole was transformed into 5-ethynyl- as well as 5-chloromethyl-2-(O-perbenzoylated-β-D-glucopyranosyl)-1,3,4-oxadiazoles by acylation with propiolic acid-DCC or chloroacetyl chloride, respectively. The chloromethyl oxadiazole gave the corresponding azidomethyl derivative on treatment with NaN(3). These compounds were reacted with several alkynes and azides under Cu(I) catalysed cycloaddition conditions to give, after removal of the protecting groups by the Zemplén protocol, β-D-glucopyranosyl-1,3,4-oxadiazolyl-1,2,3-triazole, β-D-glucopyranosyl-1,2,3-triazolyl-1,3,4-oxadiazole, and β-D-glucopyranosyl-1,3,4-oxadiazolylmethyl-1,2,3-triazole type compounds. 5-Phenyltetrazole was also transformed under the above conditions into a series of aryl-1,3,4-oxadiazolyl-1,2,3-triazoles, aryl-1,2,3-triazolyl-1,3,4-oxadiazoles, and aryl-1,3,4-oxadiazolylmethyl-1,2,3-triazoles. The new compounds were assayed against rabbit muscle glycogen phosphorylase b and the best inhibitors had inhibition constants in the upper micromolar range (2-phenyl-5-[1-(β-D-glucopyranosyl)-1,2,3-triazol-4-yl]-1,3,4-oxadiazole 36: K(i)=854μM, 2-(β-D-glucopyranosyl)-5-[1-(naphthalen-2-yl)-1,2,3-triazol-4-yl]-1,3,4-oxadiazole 47: K(i)=745μM).

Effect of glucopyranosylidene-spiro-thiohydantoin on glycogen metabolism in liver tissues of streptozotocin-induced and obese diabetic rats

The major role of liver glycogen is to supply glucose to the circulation in order to maintain normal blood glucose levels. In the muscle and liver, the accumulation and breakdown of glycogen are regulated by the reciprocal activities of glycogen phosphorylase and glycogen synthase. Glycogen phosphorylase catalyses the key step of glycogen degradation and its activity is inhibited by glucose and its analogues. Thus, any readily accessible inhibitor of glycogen phosphorylase may serve as a potential therapy for non-insulin-dependent or type 2 diabetes. Hepatic glycogen phosphorylase has been identified as a novel target for drugs that control blood glucose concentration. Glucopyranosylidene-spiro-thiohydantoin (TH) was found to be one of the most potent glucose derivates, inhibiting the catalytic activity of both muscle and liver glycogen phosphorylase. Here, we demonstrated the co-ordinated regulation of glycogen phosphorylase and synthase by 50 µM TH in liver extracts of Wistar rats, resulting in the activation of synthase by a shortening of the latency compared to control animals. TH was also effective in lowering blood glucose levels and restoring hepatic glycogen content in streptozotocin-induced diabetic rats. Furthermore, intravenous administration of TH to Zucker diabetic fatty rats significantly decreased hepatic glycogen phosphorylase a levels, and the activation of synthase was initiated without any delay.

Gram-scale synthesis of a glucopyranosylidene-spiro-thiohydantoin and its effect on hepatic glycogen metabolism studied in vitro and in vivo

Abstract A high yielding, simple synthesis is described starting from d -glucose to produce gram quantities of a glucopyranosylidene-spiro-thiohydantoin. This compound efficiently inhibited the activity of rat liver glycogen phosphorylase a ; moreover, it also activated phosphorylase phosphatase which, in turn, decreased the amount of glycogen phosphorylase a . Both effects result in the inhibition of glycogen mobilization and the formation of glucose from glycogen.

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

O-Perbenzoylated 5-(β-D-glucopyranosyl)tetrazole was reacted with N-benzyl carboximidoyl chlorides to give the corresponding 4-benzyl-3-(β-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-(β-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.

Glucose-based spiro-heterocycles as potent inhibitors of glycogen phosphorylase.

Glucopyranosylidene-spiro-1,4,2-oxathiazoles were prepared in high yields by NBS-mediated spiro-cyclization of the corresponding glucosyl-hydroximothioates. In an effort to synthesize analogous glucopyranosylidene-spiro-1,2,4-oxadiazolines, with a nitrogen atom instead of the sulphur, attempted cyclizations resulted in aromatization of the heterocycle with opening of the pyranosyl ring. Enzymatic measurements showed that some of the glucose-based inhibitors were active in the micromolar range. The 2-naphthyl-substituted 1,4,2-oxathiazole displayed the best inhibition against RMGPb (K(i)=160 nM), among glucose-based inhibitors known to date.