Bitter principle from Jamaica quassia, Picrasma excelsa (Sw.) Planch., Simaroubaceae. Isoln: Clark, J. Am. Chem. Soc. 60, 1146 (1938). Identity of isoquassin and picrasmin: Adams, Whaley, ibid. 72, 375 (1950). Isomer of quassin, q.v.: Valenta et al., Tetrahedron 18, 1433 (1962).