Modulation of the 6-position of benzopyran derivatives and inhibitory effects on the insulin releasing process

Abstract

The synthesis of different series of 4- and 6-substituted R/S-3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans is described. All of these new benzopyran derivatives were bearing, at the 4-position, a phenylthiourea moiety substituted on the phenyl ring by a meta or a para-electron-withdrawing group such as Cl or CN. The study aimed at exploring the influence of the nature of the substituent at the 6-position in order to develop new benzopyran-type K(ATP) channel activators exhibiting an improved selectivity towards the insulin secreting cells. The original compounds were examined in vitro on rat pancreatic islets (inhibition of insulin release) as well as on rat aorta rings (vasorelaxant effect) and their activity was compared to that of the reference K(ATP) channel activators (±)-cromakalim, (±)-pinacidil, diazoxide and to previously synthesized cromakalim analogues. Structure-activity relationships indicated that the inhibitory effect on the insulin secreting cells was related to the lipophilicity of the molecules and to the size of the substituent located at the 6-position. A marked inhibitory activity on the insulin secretory process was obtained with molecules bearing a bulky tert-butyloxycarbonylamino group at the 6-position (20-23). The latter compounds were found to have the same efficacy on the pancreatic endocrine tissue than some previously described molecules. Lastly, radioisotopic experiments further identified R/S-N-4-chlorophenyl-N'-(6-tert-butyloxycarbonylamino-3,4-dihydro-2,2-dimethyl-2H-1-benzopyran-4-yl)thiourea (23) as a K(ATP) channel opener.