Novel-Type GABAB PAMs: Structure-Activity Relationship in Light of the Protein Structure.

Selecting a known HTS hit with the pyrazolo[1,5-a]pyrimidine core, our project was started from CMPPE, and its optimization was driven by a ligand-based pharmacophore model developed on the basis of published GABAB positive allosteric modulators (PAMs). Our primary goal was to improve the potency by finding new enthalpic interactions. Therefore, we included the lipophilic ligand efficiency (LLE or LipE) as an objective function in the optimization that led to a carboxylic acid derivative (34). This lead candidate offers the possibility to improve potency without drastically inflating the physicochemical properties. Although the discovery of the novel carboxyl feature was surprising, it turned out to be an important element of the GABAB PAM pharmacophore that can be perfectly explained based on the new protein structures. Rationalizing the binding mode of 34, we analyzed the intersubunit PAM binding site of GABAB receptor using the publicly available experimental structures.

N-(4-Substituted-benzoyl)-N'-(ß-d-glucopyranosyl)ureas as inhibitors of glycogen phosphorylase: Synthesis and evaluation by kinetic, crystallographic, and molecular modelling methods.

N-(4-Substituted-benzoyl)-N'-(ß-d-glucopyranosyl) ureas (substituents: Me, Ph, Cl, OH, OMe, NO(2), NH(2), COOH, and COOMe) were synthesised by ZnCl(2) catalysed acylation of O-peracetylated ß-d-glucopyranosyl urea as well as in reactions of O-peracetylated or O-unprotected glucopyranosylamines and acyl-isocyanates. O-deprotections were carried out by base or acid catalysed transesterifications where necessary. Kinetic studies revealed that most of these compounds were low micromolar inhibitors of rabbit muscle glycogen phosphorylase b (RMGPb). The best inhibitor was the 4-methylbenzoyl compound (K(i)=2.3µM). Crystallographic analyses of complexes of several of the compounds with RMGPb showed that the analogues exploited, together with water molecules, the available space at the ß-pocket subsite and induced a more extended shift of the 280s loop compared to RMGPb in complex with the unsubstituted benzoyl urea. The results suggest the key role of the water molecules in ligand binding and structure-based ligand design. Molecular docking study of selected inhibitors was done to show the ability of the binding affinity prediction. The binding affinity of the highest scored docked poses was calculated and correlated with experimentally measured K(i) values. Results show that correlation is high with the R-squared (R(2)) coefficient over 0.9.

Synthesis of new glycosyl biuret and urea derivatives as potential glycoenzyme inhibitors.

O-peracetylated 1-(beta-D-glucopyranosyl)-5-phenylbiuret was prepared in the reaction of O-peracetylated beta-D-glucopyranosylisocyanate and phenylurea. The reaction of O-peracetylated N-beta-D-glucopyranosylurea with phenylisocyanate furnished the corresponding 1-(beta-D-glucopyranosyl)-3,5-diphenyl- as well as 3-(beta-D-glucopyranosyl)-1,5-diphenyl biurets besides 1-(beta-D-glucopyranosyl)-3-phenylurea. O-Peracetylated 1-(beta-D-glucopyranosyl)-5-(beta-D-glycopyranosyl)biurets were obtained in one-pot reactions of O-peracetylated beta-D-glucopyranosylamine with OCNCOCl followed by a second glycopyranosylamine of beta-D-gluco, beta-D-galacto and beta-D-xylo configurations. O-Acyl protected 1-(beta-D-glucopyranosyl)-3-(beta-D-glycopyranosylcarbonyl)ureas were obtained from the reaction of beta-D-glucopyranosylisocyanate with C-(glycopyranosyl)formamides of beta-D-gluco and beta-D-galacto configurations. The O-acyl protecting groups were removed under acid- or base-catalyzed transesterification conditions, except for the N-acylurea derivatives where the cleavage of the N-acyl groups was faster than deprotection. Some of the new compounds exhibited moderate inhibition against rabbit muscle glycogen phosphorylase b and human salivary alpha-amylase.

Assessment of synthetic methods for the preparation of N-beta-d-glucopyranosyl-N'-substituted ureas, -thioureas and related compounds.

Preparation of O-peracetylated N-beta-d-glucopyranosyl-N'-acyl urea derivatives resulted in the formation of anomeric mixtures under the following conditions: acylation of O-peracetylated beta-d-glucopyranosyl urea by acyl chlorides in the presence of ZnCl(2) in refluxing CHCl(3); addition of O-peracetylated beta-d-glucopyranosylamine to acyl isocyanates in acetonitrile at rt; addition of carboxamides to in situ prepared O-peracetylated beta-d-glucopyranosyl isocyanate in refluxing toluene. Deprotection of O-peracetylated N-beta-d-glucopyranosyl-N'-acyl ureas either under base (NaOMe in MeOH at or below rt) or under acid (KHSO(4) or AcCl in MeOH at rt) catalyzed transesterification conditions resulted in unavoidable partial cleavage of the N'-acyl moieties. Reaction of beta-d-glucopyranosylammonium carbamate with an isocyanate, isothiocyanate or isoselenocyanate in dry pyridine at rt appears as a general method for the preparation of the corresponding beta-d-glucopyranosyl ureas, -thio- and -selenoureas, respectively, inclusive N'-acyl derivatives.

Synthesis of N-(beta-D-glucopyranosyl)- and N-(2-acetamido-2-deoxy-beta-D-glucopyranosyl) amides as inhibitors of glycogen phosphorylase.

2,3,4,6-Tetra-O-acetyl-beta-D-glucopyranosyl- and 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-glucopyranosyl azides were transformed into the corresponding per-O-acetylated N-(beta-D-glycopyranosyl) amides via a PMe(3) mediated Staudinger protocol (generation of N-(beta-D-glycopyranosyl)imino-trimethylphosphoranes followed by acylation with carboxylic acids, acid chlorides or anhydrides). The deprotected compounds obtained by Zemplén deacetylation were evaluated as inhibitors of rabbit muscle glycogen phosphorylase b. The best inhibitor of this series has been N-(beta-D-glucopyranosyl) 3-(2-naphthyl)-propenoic amide (K(i)=3.5microM).