We have completed our investigations on a number of Thai medicinal plants. A number of coumarin (the calanolides) and xanthone derivatives have been found from the tropical rain forest tree in the Calophyllum genus with potential use as novel HIV inhibitors. Manihot esculenta or cassava, commonly known as tapioca, has been studied, and some known and novel cyanogenic glycosides, including linamarin and lotaustralin, have been found, together with flavone derivatives. Seven new flavone derivatives have been isolated and identified from Derris reticulata, locally known as Cha-Aim-Nuea, which is an herb used for relief of thirst. Used as a heart tonic, the hexane extracts of the flowers and twigs of Mammea siamensis, locally known as Sarapee-Ban, have been thoroughly investigated, and some novel coumarins have been isolated together with other compounds. Six new diterpenes, along with four known diterpenes, were isolated from Kaempferia marginata or Tup-Mup. Some of these terpenes exhibited antimalarial, antitubercular, and antifungal activities. Trigonostemon reidioides or Lot-Thanong is widely used in Thai traditional medicine, and a new cytotoxic daphnane, together with two congeners, were isolated from this plant.

     Our interest in colchicine and its derivatives, constituents of Gloriosa superba, lies in their cytotoxicity and anti-cancer activity. Among many cell lines, epidermal and cholangiocarcinoma cancer cells (i.e., KB and HuCCA-1 cells, respectively), are of particular interest since these cancers affect many Thai people. Different modifications of their structures have been studied, and some structure-activity relationships (SAR) have been established. Many modified colchicine derivatives are very potent towards many cancer cell lines and warrant further investigation.

     Recently, methanolic extracts of some eighty plant samples were obtained and partitioned between water and methylene chloride, yielding water- and methylene chloride-soluble materials, which were subjected to biological evaluations for anti-cancer, anti-malarial, anti-oxidant, and anti-invasion activities. Using bioassay-guided procedures, we have selected several bioactive samples for further detailed investigation from various plants, including Calamus acanthophyllus or Whai-Nang, Eurycoma harmandiana or Pla-Lai-Puek-Noi, Zingiber raja (petiolatum) or Put-Nga-Chang, Helixanthera parasitica or Kafak-Ko, Dunbaria longeracemosa or Khang-Krung, and Croton oblongifolius or Plau-Yai.

     In addition to our current interests on the natural products from plants, we have launched an initial study of the natural products from marine organisms. This is, in part, due to the fact that most marine sources in Thailand are relatively unexplored, and an increasing number of marine natural products, possessing interesting and significant biological activities, have been reported. The first phase of our programme has targeted the most abundant species among marine organisms for investigations. About twenty species of tunicates or ascidians, sponges, and soft corals were collected from the East Coast of the Gulf of Thailand, and, after initial extraction, the crude materials have been evaluated for anti-malarial, anti-cancer, and anti-invasion activities, as well as chemoprevention.

     Microorganisms are potential sources of bioactive compounds. Recently, we have isolated fungi from marine organisms, and a few fungi are able to produce diverse arrays of chemicals. The search for new biologically active compounds from fungi is also under active investigation at the Laboratory of Natural Products.

     The Laboratory of Natural Products has collaborated with other laboratories and departments at various universities and governmental organizations, including Mahidol University (the Chulabhorn Research Centre; the Institute of Science and Technology for Research and Development; the Faculty of Pharmacy; and the Departments of Biochemistry and Chemistry, Faculty of Science), Chulalongkorn University (the Department of Chemistry, Faculty of Science), Ramkamhaeng University (the Department of Chemistry, Faculty of Science), Khon Kaen University (Faculty of Pharmaceutical Sciences), Kasetsart University (the Department of Chemistry, Faculty of Science), Srinakharinwirot University (the Department of Chemistry, Faculty of Science), and Ministry of Public Health (the Division of Medicinal Plant Research and Development, Department of Medical Science).