Synthesis and pharmacological evaluation of 4H-1,4-benzothiazine-2-carbonitrile 1,1-dioxide and N-(2-cyanomethylsulfonylphenyl)acylamide derivatives as potential activators of ATP sensitive potassium channels.

1,2,4-Thiadiazine derivatives, like 3-methyl-7-chlorobenzo-4H-1,2,4-thiadiazine 1,1-dioxide, diazoxide and 7-chloro-3-isopropylamino-4H-benzo-1,2,4-thiadiazine 1,1-dioxide, BPDZ 73, are potent openers of Kir6.2/SUR1 K(ATP) channels. To explore the structure-activity relationship of this series of K(ATP) openers, 4H-1,4-benzothiazine-2-carbonitrile 1,1-dioxide and N-(2-cyanomethylsulfonylphenyl)acylamide derivatives were synthesized from 2-acetylamino-5-chloro-benzenesulfonic acid pyridinium salt or 2-aminobenzenethiols. The 4H-1,4-benzothiazine-2-carbonitrile 1,1-dioxide derivatives (e.g., 7-chloro-3-isopropylamino-4H-1,4-benzothiazine-2-carbonitrile 1,1-dioxide, 3f) were found to activate K(ATP) channels as indicated by their ability to hyperpolarize beta cell membrane potential, to inhibit glucose-stimulated insulin release in vitro and to increase ion currents through Kir6.2/SUR1 channel as measured by patch clamp. The potency and efficacy of, for example, 3f is however significantly reduced compared to the corresponding 4H-1,2,4-benzothiadiazine 1,1-dioxide derivatives. Opening of the 4H-1,2,4-thiadiazine ring to get (e.g., 2-cyanomethylsulfonyl-4-fluorophenyl) carbamic acid isopropyl ester (4c) gives rise to compounds, which are able to open K(ATP) channels but with considerable reduced potency compared to, for example, diazoxide. Compound 3a, 7-chloro-3-methyl-4H-1,4-benzothiazine-2-carbonitrile 1,1-dioxide, which inhibits insulin release in vitro from beta cells and rat islets, reduces plasma insulin levels and blood pressure in anaesthetized rats upon intravenous administration.

Arylcyanoguanidines as activators of Kir6.2/SUR1K ATP channels and inhibitors of insulin release.

Phenylcyanoguanidines substituted with lipophilic electron-withdrawing functional groups, e.g. N-cyano-N'-[3,5-bis-(trifluoromethyl)phenyl]-N' '-(cyclopentyl)guanidine (10) and N-cyano-N'-(3,5-dichlorophenyl)-N' '-(3-methylbutyl)guanidine (12) were synthesized and investigated for their ability to inhibit insulin release from beta cells, to repolarize beta cell membrane potential, and to relax precontracted rat aorta rings. Structural modifications gave compounds, which selectively inhibit insulin release from betaTC6 cells (e.g. compound 10: IC(50) = 5.45 +/- 1.9 microM) and which repolarize betaTC3 beta cells (10: IC(50) = 4.7 +/- 0.5 microM) without relaxation of precontracted aorta rings (10: IC(50) > 300 microM). Inhibition of insulin release from rat islets was observed in the same concentration level as for betaTC6 cells (10: IC(50) = 1.24 +/- 0.1 microM, 12: IC(50) = 3.8 +/- 0.4 microM). Compound 10 (10 microM) inhibits calcium outflow and insulin release from perifused rat pancreatic islets. The mechanisms of action of 10 and 12 were further investigated. The compounds depolarize mitochondrial membrane from smooth muscle cells and beta cell and stimulate glucose utilization and mitochondrial respiration in isolated liver cells. Furthermore, 10 was studied in a patch clamp experiment and was found to activate Kir6.2/SUR1 and inhibit Kir6.2/SUR2B type of K(ATP) channels. These studies indicate that the observed effects of the compounds on beta cells result from activation of K(ATP) channels of the cell membrane in combination with a depolarization of mitochondrial membranes. It also highlights that small structural changes can dramatically shift the efficacy of the cyanoguanidine type of selective activators of Kir6.2/SUR2 potassium channels.