1. m/e305: M+—side chain plus 42 mass units, 189: 305-C6H12O2, corresponding to the loss of water and the subsequent loss of C6H10O unit through retro-Diels-Alder process in ring A and 171: 189-H2O. H. Budzikiewicz, C. Djerassi and D. H. Williams, “Structure Elucidation of Natural Products by Mass Spectrometry,” Vol. II, Holden-Day Inc., San Francisco, 1964, p. 94.
2. T. Goto and K. Tori,” Jikken Kagaku Kôza, Sup.” Vol. 12, ed. by M. Kotake, Maruzen, Tokyo, 1967, p. 333.