Antihypertensive 9-substituted 1-oxa-4,9-diazaspiro[5.5]undecan-3-ones

Forty-one 9-substituted 1-oxa-4,9-diazaspiro[5.5]undecan-3-ones were prepared for antihypertensive screening in the spontaneously hypertensive rat (SHR). For the 9-(2-indol-3-ylethyl) series, the parent compound, 9-(2-indol-3-ylethyl)-1-oxa-4,9-diazaspiro[5.5]undecan-3-one (21), was the most potent antihypertensive agent. Substitution of lower alkyl groups on the spirolactam ring gave compounds close in activity to 21, while substitution with large alkyl or aryl groups led to a significant decrease in activity. Ring-opened analogues of 21 that contained the same functionality were markedly less active. Several 1-oxa-4,9-diazaspiro[5.5]undecan-3-ones substituted at the 9 position with 1,4-benzodioxan-2-ylmethyl, 1,4-benzodioxan-2-ylhydroxyethyl, and 2-phenylethyl groups also demonstrated significant activity. Compound 21 was chosen for a detailed pharmacological evaluation. Its antihypertensive activity appears to be predominantly due to peripheral alpha 1-adrenoceptor blockade.