ISOLATION AND STRUCTURE DETERMINATION OF NATURAL PRODUCTS

Abstract

The present work is concerned with the isolation and characterization of natural products from plants and liverworts which are found in Singapore and Malaysia. Structure elucidation of these compounds was achieved mainly by a combination of chemical and NMR (1H, 13C, COSY, HMQC, HMBC and NOE) studies. Chapter One is dedicated to the chemical investigation of three species of the Guttiferae. The leaves of Calophyllum wallichianum contains four coumarin derivatives, cordatolide A, cordatolide B, cordatolide C and cordatolide D. Cordatolide A and B have the potential inhibitory activity against human imnunodeficiency virus (HIV)-1 reverse transcriplase. Cordatolide C and cordatolide D are new natural products. In addition, two novel lup-20(29)-ene type triterpenoids, 3?,23,28-trihydroxylup-20(29)-ene and 3?,24,28-trihydroxylup-20(29)-ene have been isolated. The leaves of an unidentified Calophyllum species yielded two biflavonoids, amentoflavon and pyranoamentoflavon. Presence of biflavonoids in Calophyllum species is rare. A new oleanane triterpenoid and a novel anthraquinone were isolated from the bark of Ploiarium alternifolium, while the branches of the same species produced two new anthraquinones which are closely related to the one found in the bark. The major constituent found in the leaves of Ploiarium alternifolium was 1,6- dihydroxy-5,7-dimethoxyxanthone, further supporting inclusion of Ploiarium alternifolium in the family Guttiferae. Chapter Two deals with the chemical investigation of an unidentified Lepidozia species. In contrast to previous results which show that the liverwort Lepidozia speices is a rich source of sesquiterpenoids, no sesquiterpenoid was isolated in the investigation of the present Lepidozia species. Instead, five triterpenoids were present.