Four new alkaloids, tsilanine, 13, 10-methoxytsilanine, 14, O-demethyltsilanine, 15, and 10-methoxy-O-demethyltsilanine, 16, have been isolated from Strychnos henningsii. They may be distinguished from the known alkaloids of Strychnos type by the presence, in a seven-membered lactam ring, of an acetal or hemiacetal function. © 1970.