Biologically active vallesamine, strychnan, and rhazinilam alkaloids from Alstonia: Pneumatophorine, a nor-secovallesamine with unusual incorporation of a 3-ethylpyridine moiety

Four alkaloids comprising two vallesamine, one strychnan, and pyranopyridine alkaloid were isolated from two Malayan Alstonia species, A. pneumatophora and A. rostrata. Several of the isolated alkaloids show antiproliferative (e.g., rhazinicine) and vasorelaxation (e.g., pneumatophorine, undulifoline) effects.