Rationale and Objective of the Work

Phytochemistry is a branch of Pharmacognosy, with chemical and biological characters, which study the obtaining of medicaments by natural or semi synthesis methods? The subject “Phytochemstry” deals with the chemical structures of secondary metabolites, their metabolism, and their distribution and biological functions [1] (Figure 1).

a. Unmodified natural products of which the therapeutic efficacy was only remotely suggested by folk medicine use e.g. vincristine.

b. Modified natural or synthetic substances based on a natural product used in traditional medicine e.g. aspirin [5].

c. Terrestrial plants, especially higher plants, have a long history of use in the treatment of human diseases [6]. Fossil records date human use of plants as medicines at least to the Middle Paleolithic age some 60,000 years ago [7]. Several well-known species, including licorice (Glycyrrhiza glabra) myrrh (Commiphoraspecies), and poppy capsule latex (Papaver somnjferum), were referred to by the first known written record on clay tablets from Mesopotamia in 2600 BC, and these plants are still in use today for the treatment of various diseases as ingredients of official drugs or herbal preparations used in systems of traditional medicine. Furthermore, morphine, codeine, noscapine (narcotine), and papaverine isolated from P. somnferum were developed as single chemical drugs and are still clinically used. Hemisuccinate carbenoxolone sodium, a semi-synthetic derivative of glycyrrhetic acid found in licorice, is prescribed for the treatment of gastric and duodenal ulcers in various countries [6].

A careful selection of plants is conditioned by success in the research of natural products, based on various criteria such as chemotaxonomic data, ethnomedical information, field observations or even discrete collection [8]. Historical encounters with plants as therapeutic instruments helped to introduce particular chemical entities into modem medicine. Plants, especially those with ethno- pharmacological have been the primary sources of medicines for early drug discovery. In fact, a recent sis by Fabrican and Farnsworth showed that the uses of 80% of 122 plant-derived drugs were related to their original ethno pharmacological purposes. Current drug development from terrestrial plants has relied mainly on bioactivity-guided isolation methods which have led, for example, to the discovery of essential anticancer agents, Taxus brevifolia paclitaxel and Camptotheca acuminate camptothecin [6]. The goals of using plants as sources of therapeutic agents are a) to isolate bioactive compounds for direct use as drugs, e.g. digoxin, digitoxin, morphine, reserpine, taxol, vinbiastine, vincristine; b) to produce bioactive compounds of novel or known structures as lead compounds for semisynthesis to produce patentable entities of higher activity and/or lower toxicity, e.g., metformin, nabilone, oxycodon (and other narcotic analgesics), taxotere, teniposide, verapamil, and miodarone, which are based, respectively, on galegine, 9- tetrahydrocannabinol, morphine, taxol, podophyllotoxin, and khellin; c) to use agents as pharmacologic tools, e.g., lysergic acid diethlamide (LSD), mescaline, yohimbine; and d) to use the whole plant or part of it as a herbal remedy, e.g., cranberry, echinacea, feverfew, garlic, etc [9].The number of higher plant species (angiosperms and gymnosperms) on this planet is estimated at 250,000[10].with a lower level at 215,000 [11].and an upper level as high as 500,000[12].Of these, only about 6% have been screened for biologic activity, and a reported 5% have been evaluated phytochemically [13].

It was estimated that in 1991 in the United States, for every 10,000 pure compounds most likely those based on synthesis) that arebiologically evaluated (primarily in vitro), 20 would be tested in animal models, and 10 of these would be clinically evaluated, and only one would reach U.S. Food and Drug administration approval for marketing. The time required for this process was estimated at 10 years at a cost of $231 million (U.S.) [14]. The major drawback of this strategy is the frequent isolation of known metabolites. Therefore, hyphenated techniques (LC-UV, LC-MS, and LC-NMR have been developed; in order to detect is early as possible potential original structures. These compounds can then be tested in various bioassays [8]. More recently combinatorial chemistry and high throughput robotic screening techniques have been employed as viable strategies for drug discovery programs [15]. Chemical diversity of secondary plant metabolites that results from plant evolution is superior to at found in synthetic combinatorial chemical libraries [14]. Medicinal plants have played an essential role in the development of human culture, for example religions and different ceremonies. (E.g. Dutura has long been associated with the worship of Shiva, the Indian God). Plants are directly used as medicines by a majority of cultures around the world, for example Chinese medicine and Indian medicine. Many food crops have medicinal effects, for example garlic. Medicinal plants are resources of new drugs. Studying medicinal plants helps to understand the plant toxicity and protect human and animals from natural poisons. Cultivation and preservation of medicinal plants protect biological diversity, for example metabolic engineering of plants [16]. The medicinal plants are used in the pharmaceutical, cosmetic, agricultural, and food industries. With the onset of scientific research into herbals, it becomes increasingly clear that medicinal herbs have potential in today's synthetic era, as numbers of medicines become resistant. According to one estimate only 20% of the plant flora has been studied and 60% of synthetic medicines owe their origin to plants. Ancient knowledge coupled with scientific principles can come to the forefront and provide us with powerful remedies to eradicate the diseases. In real sense, coupling of ancient knowledge and scientific principle is essential-

       1. To identify alternative and complementary medicine.

       2. To reduce the toxicity of drug therapy especially toxicity reduction of synthetic and semi synthetic drugs.

       3. To find the lead compound diversification to treat various diseases [17].

       History of Traditional Herbal Medicine in Bangladesh

Traditional Medicine is the medicine or treatment based on traditional uses of plants, animals or their products, other natural substances (including some inorganic chemicals), religious verses, cultural practices, and physical manipulations including torture. As this system of medicine has been in use almost unchanged generation after generation throughout the ages for the treatment of various physical and psychological diseases, it is called traditional. Most of the times, the type, preparation, and uses of traditional medicines are largely influenced by folklore customs and the cultural habits, social practices, religious beliefs and, in many cases, superstitions of the people who prescribe or use them [18]. The earliest mention of traditional medicine is found in “Rigveda”, the oldest repository of knowledge in this subcontinent. Later “Ayurveda”, developed from the Vedic concept of life, became the important source of all systems of medical sciences. In course of time it became a part of culture and heritage of the people of the Indian subcontinent Traditional medicine involves the use of both material and non-material components. The material components invariably comprise parts or organs of plants and their products. They also consist of animal organs, minerals and other natural substances.

The non-material components, which constitute important items of religious and spiritual medicines, include torture, charms, magic, incantations, religious verses, amulets and rituals like sacrifices, appeasement of evil spirits, etc. [18]. Treatments in traditional medicine involve internal and external use of medicinal products, physical manipulation of different parts of the body, performing rituals, psychological treatment, and also minor surgery. Ayurvedic medicinal preparations consist mainly of powdered plant materials, semi-solid preparations, decoctions, elixirs, and distillate. Many of these also contain inorganic chemical substances, minerals, and products for animals. Ayurvedic medicine also uses alcoholic extracts and alcoholic solutions of the ingredients, tinctures and elixirs [18]. The major constituents of Unani medicine are whole plants or their powders or pastes or products and their extracts, infusions, decoctions and distillates. In the preparation of these medicines, minerals, inorganic chemicals, and animal products are also frequently used. The Indian subcontinent's medical knowledge is termed Ayurveda for hundreds of years. Plant alkaloids are the primary active ingredients of Ayurvedic drugs. Toda’ the pharmacologically active ingredients of many Ayurvedic medicines are being identified and their usefulness in drug therapy being determined. As only a certain percentage of plants are used in traditional medicines, it is roughly estimated that of the discovered 17,000 species, nearly 3,000 species are used in medicinal field [19]. Some crude drugs used as medicine in Bangladesh are reported in following (Table 1).