The epigeal part of Thermopsis lanceolata has yielded a new alkaloid — dithermamine — which is the first representative of a bimolecular series of quinolizidine alkaloids. As the result of a study of the NMR and mass spectra of dithermamine and its reaction products, and also by its conversion into thermopsine, its structure has been established as 3-(Δ5′-dehydro-α-isolupan-5′-yl)thermopsine. © 1974, Consultants Bureau, a division of Plenum Publishing Corporation. All rights reserved.