Analysis of the alkaloids of three Annonaceae from Malaya has led to the isolation of several isoquinoline compounds: (-)-asimilobine, (-)-anonaine, (-)-norliridine, liriodenine and (-)-scoulerine from Disepalum pulchrum; (-)-oliveroline, (-)-N-oxyoliverine, liriodenine and (-)-coclaurine from Polyalthia macropoda; liriodenine, oxostephanine, (-)-discretamine, isoursuline and a new alkaloid, (-)-thaipetaline, from Polyalthia stenopetala. (-)-Thaipetaline belongs to the very small group of the C-4 substituted tetrahydroprotoberberines. © 1990.