18-Cycloalkyl analogs of enisoprost

By use of standard cuprate methodology, a series of 18-cycloalkyl analogues of enisoprost was prepared in an effort to impede omega chain metabolism and prolong duration of gastric antisecretory activity. An initial product of omega chain oxidation, the C-20 hydroxy analogue, was also synthesized for pharmacological comparison. The cyclopropyl, cyclobutyl, and cyclopentyl analogues were approximately one-fourth as potent as enisoprost in inhibiting gastric acid secretion, while the cyclohexyl and cycloheptyl analogues showed very weak activity, and the 20-hydroxy compound was inactive at a dose 100 times the ED50 of enisoprost. The cyclobutyl compound had a longer duration of antisecretory action than enisoprost and the other cycloalkyl analogues. The cycloalkyl analogues unexpectedly possessed low diarrheogenic activity in rats.