Alkaloid naturally occurring in the d-form; found in Dicentra cucullaria (L.) Bernh., Adlumia fungosa (Ait.) Greene, Fumariaceae, and several Corydalis species: Manske, Can. J. Res. 7, 265 (1932); 8, 210, 407 (1933); 9, 436 (1933); Edwards, Handa, Can. J. Chem. 39, 1801 (1961). Synthesis of dl-form: Groenewoud, Robinson, J. Chem. Soc. 1936, 199. Resolution of isomers: Haworth et al., Nature 165, 529 (1950). Stereoisomer of adlumidine, q.v., and of capnoidine: Manske, J. Am. Chem. Soc. 72, 3207 (1950). Preliminary stereochemical studies: Safe, Moir, Can. J. Chem. 42, 160 (1964). Revised stereochemistry: Blaha et al., Collect. Czech. Chem. Commun. 29, 2328 (1964); Snatzke et al., Tetrahedron 25, 5059 (1969). Crystal and molecular structure: Gorinsky, Moss, J. Cryst. Mol. Struct. 3, 299 (1973). Shows GABA (q.v.) antagonist activity: Curtis et al., Nature 226, 1222 (1970).