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). |