Bioactive natural products from Thai plants

The investigation of Thai medicinal plants for the potential therapeutic agents is surveyed with a particular emphasis on the search for antimalarial agents. The study on Diospyros mollis, Croton sublyratus, and Phyllanthus amarus is described. Thailand is uniquely located to represent the fauna and flora which characterizes the biogeographic province of Indo-Burma. A number of the eastern Himalaya temperate taxa penetrate south into the northern mountains of Thailand while the southern part is evergreen forest thus making this area one of the richest floristic regions of the world (1). It has been estimated that the vascular plants in Thailand are not less than 10,000 species of about 1,763 genera from 245 families (2). The numbers of alkaloidcontaining plants are estimated to be only about 266 species of 176 genera in 67 families based on the Thai plants names and parts of the uncompleted flora of Thailand (3). The potential of natural products as therapeutic agents in the treatment of malaria is enormous. Quinine was introduced as an antimalaiial for more than a century ago. Quinine also served as a prototype as an antimalarial leading to the discovery of synthetic antimalarials based on the quinoline compounds. 4and 8-Aminoquinoline derivatives have proved their efficacy as antimalarials. Mefloquine, a quinoline methanol derivative, has recently been introduced as an antimalarial. The Chinese has a long history of use of a herb called Qing hao (Artemisia annua) for the treatment of malaria. The pure compound was isolated in 1972 and named Qinghaosu (QHS) or Arteannuin meaning the "active principle of Qing hao"(4) In Thailand, interests for the use of herbal medicine for the treatment of malaria has been long standing. Lately many groups of Thai scientists have been working on various plants to scrutinize the validity of these 'claims' as well as searches for new antimalarial agents from plants. During the second world war, Professor Ketusingh attempted to use 30 herbal medicine to treat malaria. The treatments were applied to 543 patients with infections with P. falciparum (255 patients) and P. vivax. (288 patients)(5). From the study the plant of Oroxylum indicum showed the total cure rate as high as 65.7% and it is very interesting to note the definite prefeicnce for the plants of Azadirachta and Nyctanthes arbor-tritis for the treatment of those patients infected with P. vivax