ABSTRACT
Several series of benzofurans, benzothiophenes, and benzothiazoles, all featuring the thioamide group, were synthesized and tested as novel K(ATP) channel openers in artificial cell systems: CHO cells transfected with SUR1/Kir6.2, and HEK 293 cells transfected with SUR2B/Kir6.1; these served as model systems for insulin-secreting pancreatic ßâ cells and smooth muscle cells, respectively. All compounds were investigated with respect to their binding affinity for the SUR2B-type K(ATP) channels using [(3)H]P1075 as radioligand. Selected compounds were also tested as agonists in intact cells using DiBAC(4)(3) and DyeB (R7260) as membrane potential dyes. Remarkable affinity for SUR2B/Kir6.1 channels in the single-digit micromolar range was observed. In addition, benzothiazole-derived thioamides with sterically demanding, lipophilic substituents showed >100-fold selectivity in favor of SUR2B/Kir6.1. A one-carbon spacer between the heterocyclic skeleton and the thioamide moiety was observed to be crucial for affinity and selectivity. Two of the most potent and selective compounds were studied by crystal structure analyses.
Subject(s)
Benzofurans/chemistry , Benzothiazoles/chemistry , Potassium Channels, Inwardly Rectifying/agonists , Thioamides/chemistry , Thiophenes/chemistry , Animals , Binding Sites , CHO Cells , Cricetinae , Cricetulus , Crystallography, X-Ray , HEK293 Cells , Humans , KATP Channels , Molecular Conformation , Potassium Channels, Inwardly Rectifying/metabolism , Structure-Activity Relationship , Thioamides/chemical synthesis , Thioamides/pharmacologyABSTRACT
For seventeen 1,4-benzothiazine potassium channel openers, we performed binding studies in rat aortic smooth muscle cells and cardiomyocytes, compared their binding affinities with published relaxation data, and derived 3D-QSAR models using GRIND/ALMOND descriptors. Binding affinities in smooth muscle cells range from a pK(D) of 4.76 for compound 3e to 9.10 for compound 4c. Comparison of data for smooth muscle relaxation and binding shows preferentially higher pEC(50)s for the former. In cardiomyocytes, pK(D) values range from 4.21 for 3e to 8.16 for 4c. 3D-QSAR analysis resulted in PLS models of two latent variables for all three activities with determination coefficients of 0.97 (smooth muscle relaxation) and 0.94 (smooth muscle cells- and cardiomyocytes-binding). Internal validation yielded q(2) values of 0.69, 0.66, and 0.64. The carbonyl on the N-4 substituent, the hydrogen bond acceptor at C-6, the five-membered ring at N-4, and the gem-dimethyls mainly guide strong binding and strong smooth muscle relaxation.
