Terpenoids and Related Compounds. Part XVII : Neutral Constituents of Michelia lanuginosa Wall. Structures, Absolute Configuration and Conformation of Three New Germacranolides. A Novel Rearrangement of Lanuginolide

Department of Chemistry, University College of Science, Calcutta 700 009

Dihydroparthenolide and lanuginolide, two new sesquiterpene iactones of germacrane type, isolated from the trunk bark of Michelia lanuginosa Wall, and 11,13-dehydrolanuginolide­another new gerniacranolide isolated along with parthenolide (4) and a new natural aldehyde sinapaldehyde (17) from the less mature trunk bark of the same plant, are shown to possess stereostructures 1, 5 and 12 respectively on the basis of spectral and chemical evidence. The rela­tive and absolute configurations as well as the molecular conformation of these sesquiterpenes were derived from detailed PMR analyses and substantiated by molecular rotation difference studies. The mass spectral fragmentation patterns of the germacranolides and their derivatives were also rationalised for the first time. The plausible mechanism of a novel rearrangement of lanuginolide (5) under the influence of Adam's catalyst has been discussed. Isolation of sinapaldehyde is biogenetically significant.¹³C NMR signals of acetylsinapaldehyde are also reported.