CHEMICAL STUDIES ON PLANTS OF MEDICINAL AND ECONOMIC IMPORTANCE

Abstract

This thesis consists of two chapters and deals with the isolation and characterization of the constituents of three tree species found in Papua New Guinea and Singapore. Structure elucidation was performed using a combination of NMR (COSY, HMQC, HMBC, NOE, 1H and 13C) and chemical methods. Chapter One begins with a general introduction to the chemistry of the Guttiferae and covers such topics as the types of metabolite present, the chemotaxonomic uses of Guttiferae xanthones and the occurrence of biologically active compounds. The Chapter continues with a study of the constituents of the bark of an unidentified Calophyllum species from Papua New Guinea. Seven tocotrienol derivatives were obtained, three of which [2,7 ,8-trimethyl-2-( 4' ,8' -dimethyl-3' ,7' -nonadienyl )-chroman-6-ol, 2,7,8-trimethyl2-( 4',8' -climethyl-3', 7' -nonadienyl )-5-(?-tocotrienol-5" -yl)-chroman-6-ol and 5-( 8-tocotrienol5" -yl )-?-tocotrienol are novel. The bark also contains four polyisoprenylated benzophenone derivatives. Of these, 13-O-methylcambogin are described here for the first time. Finally, a new xanthone derivative, 1,7-dihydroxy-3,5-dimethoxy-2-(3-methylbut-2-enyl )-xanthone, was isolated. Chapter One concludes with a study of the bark of Mesua ferrea L. which was also obtained from Papua New Guinea. Two compounds were isolated and shown to be vanillin and the novel xanthone, 2-hydroxy-1,5-dimethoxyxanthone. The latter compound was identified using NMR spectroscopic methods and was chemically correlated with the corresponding known trimethoxyxanthone . Chapter Two initially deals with the chemistry of the Meliaceae and an overview of the chemistry of this family is presented. The chapter continues with the results of an investigation of the constituents of the fresh fruits of Dysoxylum cauliflorum Hiern from Singapore. Five known dammarane triterpenoids were isolated along with one novel triterpenoid. Extensive 1H , 13C NMR studies revealed this compound to have a novel 23(24 ?25)abeo-dammarane skeleton. A pathway for the biogenesis of this skeleton is proposed.