SESQUITERPENES FROM SOUTHERN MAGNOLIA-VIRGINIANA

A chemical study of the leaves of the southern evergreen Magnolia virg iniana provided, besides the known sesquiterpene lactones costunolide, parthenolide and trifloculoside, two new sesquiterpenes, costunolact- 12 beta-ol and its acetal dimer. The molecular structure of the acetal dimer of costunolact-12 beta-ol was determined by single crystal X-ra y diffraction. An annual study of the relative ratios of the major ses quiterpenes in leaves of M. virginiana showed <10% of costunolide over the 12 month period. In contrast, parthenolide and costunolact-12 bet a-ol varied markedly over the same time period with a maximum of >90% of parthenolide in July/August and a minimum of < 20% in January. Howe ver, no lignans typical of the northern variety Of M. virginiana could be detected in the annual study of the southern variety of this taxon . (C) 1997 Elsevier Science Ltd.