Synthesis of octanoyl[8-leucyl]angiotensin II, a lipophilic angiotensin antagonist.

Octanoyl[8-leucyl]angiotensin II (oct-LAT) was synthesized with the aim of obtaining a longer acting angiotensin (AT) inhibitor. The new compound, with a partition coefficient K=7.00 in n-BuOH-HOAc-H2O, was compared with [Leu8]angiotensin II (LAT, K=0.18) as an AT antagonist in two isolated smooth muscle preparations and in the rat blood pressure assay. The two compounds were equally potent in the rat uterus, but LAT was more effective in the guinea pig ileum and the in vivo assay. LAT's effect was longer lasting in the smooth muscles, but the duration of in vivo inhibition was the same for the two compounds. It is concluded that partitioning between external medium and biophase is not a limiting factor for antagonistic potency and permanence of effects of 8-substituted AT derivatives.