Cycloclavine, a new alkaloid isolated from Ipomoea hildebrandtii seeds is an isomer of agroclavine with the C-atoms 8,9 and 10 forming a 3-membered ring in place of the 8,9-double bond. Its relative and absolute configuration was determined by an X-ray analysis of the methobromide derivative; chiralities: 5R, 8R, 10R. The molecular framework appears to be unusually rigid due to intramolecular forces. NMR deshielding influences of the lone e-pair (free Base) and the N-Me group (methobromide) on the cyclopropylprotons were observed. © 1969.