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INTRODUCTION
 
1.1 Rationale of the work
Throughout the ages humans have relied on nature for their basic needs for the production of foodstuffs, shelter, clothing, means of transportation, fertilizers, flavours and fragrances, and not least, medicines. Nature has been a source of several medicines for treating various types of diseases in humans and animals for many years (Dev, 1997).
 
 Plants as healing agents was depicted in the cave paintings discovered in France, which have been radiocarbon-dated to between13,000-25,000 BC (Internet I-I).
 
In China, a particular herb called the `Ephedra’ has been known to be used in the treatment of asthma as long as 5000 years ago (Siddique et al., 2003; Ghani, 2003; Wen, 1979). In the same way, various plants have been used as medicines in ancient India, Egypt, Babylon, Greece etc. In India numerous herbal medicines extracted through crude home-made process were widely used in treatment of many diseases (Samira, et al., 2003; Ghani, 1998; Jeans, 1978). Probably, the following two major reasons for widespread use of herbs as medicine through ages: (a) Abundance of the plants and their products, which may be simply extractable in less expensive process, (b) herbal medicines belonging to plant metabolism is well tolerated by human body with less toxic effect.
 
Plants have formed the basis for traditional systems of medicine which have been used for thousands of years in countries such as China (Chang, 1986) and India (Kapoor, 1990). The use of plants in the traditional medicine of many other cultures has been extensively documented (Schultes et al., 1990). These plant-based systems continue to play an essential role in health care, and it has been estimated by the WHO that approximately 80% of the world’s inhabitants rely mainly on traditional medicines for their primary health care. Plant products also play an important role in the health care systems of the remaining 20% of the population, mainly residing in the developed countries. In a study, it has been shown that at least 119 chemical substances, derived from 90 plant species, can be considered as important drugs that are in use in one or more countries (Arvigo et al., 1993). Of these 119 drugs, 74% were discovered as a result of chemical studies directed at the isolation of the active substances from plants used in traditional medicine (Fansworth et al., 1985).
 
Plants are the important source of a diverse range of chemical compounds. Some of these compounds possessing a wide range of pharmacological activity are either impossible or troublesome to synthesize in the laboratory. A phytochemist uncovering these resources is producing useful materials for screening programs for drug discovery. Emergences of newer diseases also lead the scientists to go back to nature for newer and more effective molecules. 
Examples of traditional medicine providing leads to bioactive natural products abound. Artemisinin (qinghaosu) (1) is the antimalarial sesquiterpene from a Chinese medicinal herb Artemisia annua (Wormwood, Fam. Asteraceae) used in herbal remedies since ancient times. Forskolin (2) is the antihypertensive agent from Coleus forskohlii Briq (Fam. Laminaceae), a plant whose use was described in ancient Hindu Ayurvedic texts (Bhatt et al., 1988).

Figure 1.1:  Artemisinin (1)     and        forskolin (2)
Paclitaxel (Taxol) (3)   is a natural product derived from the Taxus baccata (yew tree, Fam. Taxaceae). It is an important natural product that has made an enormous impact on medical history. It interacts with tubulin during the mitotic phase of the cell cycle, and thus prevents the disassembly of the microtubules and thereby interrupts the cell division (Wani et al., 1991). The original target disease for the compound was ovarian and breast cancers, but now it is used to treat a number of other human tissue proliferating diseases as well (Strobel et al., 2004). A case of serendipity is the discovery of the so-called vinca alkaloids, vincristine (4) and vinblastine (5), in Catharanthus roseus. A random screening programme (conducted at Eli Lilly and Company) of plants with antineoplastic activity found these anticancer agents in the 40th of 200 plants examined. Ethnomedicinal information attributed an anorexigenic effect (i.e. causing anorexia) to an infusion from the plant (Tyler, 1986).

                    3

6
Figure 1.2:  Paclitaxal (3)   vincristine (4) and vinblastine (5) ricin (6)
 
Thus, the importance of plants in search of new drugs is not diminishing, and may be increasing. For example, recently ricin (6), a toxin produced by the beans of Ricinus communis, has been found to effectively couple to tumor targeted monoclonal antibodies and has proved to be a very potent antitumor drug (Spalding, 1991; Gupta, 1992). Some researchers have speculated about using ricin in the treatment of cancer, as a so-called ‘magic bullet’ to destroy targeted cells (Lord et al., 2003).
Further, HIV inhibitory activity has been found in some novel coumarins (complex angular pyranocoumarins) isolated from Calophyllum lanigerum (Kashman et al., 1992) such as calophyllolide (7).
                   
                             7                                                                     8
Figure 1.3:  Calophyllolide (7) and andrographolide (8)
 
A recent study conducted at Bastyr University, confirmed the anti-HIV activity of andrographolide (8), a compound isolated from Andrographis paniculata (Otake et al., 1995; Calabrese et al., 2000). Not only do diseases such as AIDS require drugs that target them specifically, but also new therapies are needed for treating ancillary diseases, which are a consequence of a weakened immune system.
 
From early of 20^th century, the research and discovery of hypoglycemic agents in plant kingdom has shown promising results. Allium cepa bulbs are known to hypoglycemic property. Glucokenin, an extract from Cephalandra indica has the property of reducing the amount of sugar in the blood (Collip, 1923). Galegine (9), a guanide isolated from the seeds of Galega officinalis (Fam. Fabaceae) and gymnemic acid (10), a glycosidic acid isolated from Gymnema sylvetre (Fam. Asclepiadaceae)  were found to have a significant blood sugar lowering effect when administered by mouth (Muller, 1925). Bulb of A. cepa as well as Ficus bengalensis and Ficus religiosa extrcts were found to exhibit hypoglycemic activity (Augusty et al., 1961, 1962).
 
 
     
                9                                                                 10
Figure 1.4:  Galegine (9) and gymnemic acid (10)
The use of plant extracts in traditional medicine by old Indian and Chinese people have been going on from ancient time. Herbalism and folk medicine, both ancient and modern, have been the source of much useful therapy (Rashid et al., 1997).
 
It is estimated that there are about 2,500,000 species of higher plants and the majority of these plants have not been investigated in detail for their pharmacological activities. Bangladesh has a vast resource of medicinal plants and majority of our population has to rely upon indigenous systems of medication from economic point of view, extensive investigationof these medicinal plants can lead to the development of new druds for various diseases. 
 
Many higher plants contain novel metabolities with antimicrobial and antiviral properties. However, in the developed world almost all clinically used chemotherapeutics have been produced by in vitro chemical synthesis.
 
1.2 Diabetes and glycemic activity
History of diabetes mellitus dates back to thousands of years. There had been time and discoveries when it appeared that the disease has been conquered but frustration soon followed with reports of further complications and resistant to insulin which is also very expensive treatment. With discovery of insulin by Frederiech Grant Banting and Charles Herbert Best in 1921 and glucose reducing (hypoglycemic) drugs carbutamide (Franke, et al., 1955) in 1955, treatment of diabetes was certainly boosted up. But complications due to this disease still continue. More importantly, it is in the third world countries like Bangladesh that the prevalence of diabetes is raising, partly because of the insulin treatment, lack of knowledge, inadequate medical facilities and insufficient health care.
The treatment of diabetes is, at present, neither simple nor cheap. Insulin (11), the main antidiabetic agent is extracted from animal pancreas is costly for common patients (Figure 1.5, human pancreas). The patients who are immunocompromised (e.g., diabetic, cancer and organ transplant patients) are at risk of infection by opportunistic pathogens,
 

Figure 1.5:  Photograph of human pancreas and β-cell
 
The structure of insulin

 
11
Figure 1.6:  Chemical structure of human insulin (11)
 
such as Aspergillus, Cryptococcus, and Candida, that normally are not major problems in the human population. In addition, more drugs are needed to efficiently treat diabetes. Diabetes, by itself, is more effective in claiming lives each year than any other single disease with the exception of AIDS.
 
Biosynthetic "human" insulin is now manufactured for widespread clinical use by using recombinant DNA technology. More recently, researchers have succeeded in introducing the gene for human insulin into plants and in producing insulin in plants, specifically safflower. It is anticipated that this technique will reduce production costs (Marcial et al., 2007; Internet-I-II).
 
The first genetically-engineered, synthetic "human" insulin was produced in a laboratory in 1977 by Herbert Boyer using E. coli.  Partnering with Genentech founded by Boyer, Eli Lilly went on in 1982 to sell the first commercially available biosynthetic human insulin under the brand name Humulin. The vast majority of insulin currently used worldwide is now biosynthetic recombinant "human" insulin or its analogs.
 
1.3 Objective of the work
Natural products are naturally derived metabolites and/or by-products from microorganisms, plants, or animals (Baker et al., 2000). These substances still play a major role in treatment of diseases either as the drug, or as a ‘forebear’ in the synthesis or design of the agent. The world’s best known and most universally used medicinal agent is aspirin, which is related to salicin (12), having its origins in the plant genera Salix sp. and Populus sp (Strobel et al. 2004). Examples abound of natural product use, especially in small native populations in a myriad of remote locations on Earth. For instance, certain tribal groups in the Amazon basin, the highland peoples of Papua New Guinea, and the Aborigines of Australia each have identified certain plants to provide relief of symptoms varying from head colds to massive wounds and intestinal ailments (Isaacs, 2002).

12
Figure 1.7:  Salicin (12)
 
Even with untold centuries of human experience behind us, and a movement into a modern era of chemistry and automation, it is still evident that natural product-based compounds have had an immense impact on modern medicine. For instance, about 40% of prescription drugs are based on them. Furthermore, well over 50% of the new chemical products registered by the FDA as anticancer, antimigraine, and antihypertensive agents were natural products or derivatives thereof in the time-frame of 1981-2002 (Newman et al., 2003). Excluding biologics, between 1989 and 1995, 60% of approved drugs and pre-new drug application candidates were of natural origin (Grabley et al., 1999). From 1983 to 1994, over 60% of all approved and pre-NDA stage cancer drugs were of natural origin, as were 78% of all newly approved antibacterial agents. At least 21 natural product and natural product-derived drugs have been launched onto the market in the United States, Europe or Japan since 1998 (Beutler, 2005).
 
In recent years, a renewed interest in obtaining biologically active compounds from natural sources has been observed, notwithstanding the impressive progress of new competing methodologies, as for example, combinatorial chemistry (CC) and high throughput screening (HTS) or genetic engineering (GE). By using these techniques it is possible to modify the activity or regulate the properties of the key enzymes responsible for the production of secondary metabolites based on natural products. Thus, by knowing the potential resources it is possible to increase the content of the important active compounds (Owen et al., 1992) and in the future, genes responsible for very specific biosynthetic processes may be encoded into host organisms to facilitate difficult synthetic transformations.
 
There is a general call for new antidiabetic and chemotherapeutic agents that are highly effective and has low toxicity, and produce minor environmental impact. This search is driven by the development of drugs of plant origin like Andrographis paniculata, Anthocephalus chinensis, Sesbania sesban etc. The ingress into the human population of new disease-causing agents such as diabetes, AIDS, ebola, and SARS require the discovery and development of new drugs to combat them.
 
Bangladesh is a good repository of medicinal plants belonging to various families, including Acanthaceae, Rubiaceae, Fabiaceae and Moringaceae. Many of the plants of these families have bee reported to possess medicinal properties including hypoglycemic, anthelminthic, antihepatitic and anti-inflammatory activities etc. which are described in the respective sections. Thus, with this concern, we selected some Bangladeshi plants for chemical investigations (Table 1.1) and evaluate their pharmacological (mainly hypoglycemic, antioxidant, antibacterial and cytotoxic) profiles.
 
These investigations may provide some interesting compounds, which may be pharmacologically active. If significant results are obtained, these can be used as remedies for the treatment of some diseases. Since these plants are available in Bangladesh and as they are used in the folkloric medicines by rural patients, these may be also cost-effective treatment. These prompted us to embark upon their investigation. So, the objective is to explore the possibility of developing new drug candidates from these plants for the treatment of various diseases as with especial emphasis on diabetes. The selected plants are:
 
Table 1.1 List of studied plants and plant parts

 
1.4 The family Acanthaceae
Characteristics-
Plant: Perennial, suffrutescent, armed or unarmed herbs or shrubs.  
Leaves: Leaves exstipulate, usually simple, opposite-decussate.
Flowers: Showy, often colored, bracts and bracteoles, sessile or pedicellate.
Calyx: Usually gamosepalous, persistent, deeply 4-5 lobed, sepals contorted  
Corolla: Gamopetalous, typically 5-lobed, and more usually bilabiate.         
Stamens: Four didynamous or sometimes 2, rarely 5, alternate to the petals.
Anthers: Dorsifixed, usually unequal in a stamen pair, dithecous..
Fruit: Bilocular, more or less stipitate capsule, elastically dehiscent.
Seeds: Non-endospermous, mostly flattened and lenticular or discoid.
 
 
1.4.1 Taxonomy of Acanthaceous plants
The family Acanthaceae consists of 250 genera and 2500 species, widespread in tropical regions, with only a few species in temperate climates. In Bangladesh, this family is represented by 40 genera and 108 species.
The members of Acanthaceae are distributed in Brazil, tropical and subtropical zones of Asia and America.
 
Members of Acanthaceae family
The plants belonging to the family Acanthaceae, which are available in Bangladesh, are shown in Table 1.2.
                      
Table 1.2 List of important Acanthaceous plants available in Bangladesh

 
1.4.2 Medicinal importance of Acanthaceous plants
Among the 108 species of Acanthaceus plants available in Bangladesh, only few are medicinally important. For many years, the indigenous people of many districts have medicinally been used some species of this family are listed below.
 
Table: 1.3. Medicinal importance of Acanthaceous plants                                   

 

 
1.4.3 The Plant Andrographis paniculata
Taxonomic hierarchy: (Wikipedia 2006)
Kingdom:                                         Plantae
     Division:                                     Angiosperms
                Class:                               Eudicots
                      Order:                        Lamiales
                        Unranked:               Asterids
                                Family:            Acanthaceae
                                     Gegus:        Andrographis        
                                         Species:  paniculata           
 
Botanical feature

 
Habitat and distribution: This plant is distributed in Bangladesh, India Sri Lanka and the West Indies. In Bangladesh, A. paniculata is common throughout the country, particularly in Chittagong and the neighbouring hill tracts districts.
 

Figure 1.8 Photograph of A.  paniculata1.4.4 Medicinal uses     
Different parts of A. paniculata are used traditionally as medicine by local people, some of which are mentioned in table 1.4
Table: 1.4: Ethnobotanical uses of different parts of A. paniculata

 
1.4.5 Chemistry
Previous phytochemical investigations of A. paniculata (Figure 1.9-1.11) led to the isolation kalmeghin, the diterpenes andrographolide (13), andrographiside (14), neoandrographolide (15) (Gupta et al., 1996; Madav et al., 1996; Siriong et al., 1992; Pramyothin et al., 1994; Kapil et al., 1993;  Tet. let. 1968). Extract of plant also contains 14-deoxy-11,12-didehydroandographolide (16), 14-deoxy-11,14-didehydroandrographol-ide (17) (JCS 1973; Siripong et al., 1992) 14-deoxy-11-oxoandrographolide, 14-deoxyandrographolide (18) (Matsuda et al., 1998), 14-deoxy-11-hydroxyandrographolide (19) (Matsuda et al., 1994), epigenin ethers, various flavonoids like 7-methyldihydrowogonin (37) (Gupta, at al.,1983),  Skullcapflavone-2´-glycoside (43) (Gupta, at al.,1996); Skullcapflavone-2´-methylether (39) (Jalal et al., 1979); b-sitosterol (27) (Ali et al., 2002), stigmasterol (28), panicolide, phenols,  polyphenols, caffeic acid (23) and chlorogenic acids (22) and a mixture of 3,6-dicaffeoylquinic acids (25) (Sci. Res., 1964; CA, 1961; Leath. Sci.,1978). Roots contain the flavones like 5,7,2´,3´-Tetramethylflavone (33), 5-hydroxy-7, 2´,3´-Trimethoxyflavone (34) (Koteswara at al., 2004)  andrographin and panicolin, 7-methoxywogonin (36); 7-O-Methylwogonin-5-glycoside (42); 5-hydroxy-7, 8,2^´,3^´-tetramethoxy flavone (41) (Kuroyangi et el., 1987), apigenin 4, 7-dimethylethers and monomethoxywightin, and alpha-sitosterol (Sci. Res., 1964; CA, 1965, IJC, 1969; PJSIR, 1972; CA, 1973). The flavonoid glycoside, 2^´,5-dihydroxy-7,8-dimethoxy-flavone-2^´-O-beta-(D)-glucoside and 3-beta-hydroxy-5-stigmata-9(11), 22(23)-diene have also been isolated from the roots (Gupta et al., 1996). Recently some flavonoids like 5-hydroxy-7,2´,6´-trimethoxyflavone (35) (Munta et al., 2003), 5-hydroxy-7,8,2´,5´-tetramethoxyflavone (40) (Mopura et al., 2003) and dihydroskullcapflavone (38) (Hari et al., 2003) have isolated from the plant.  The ash contains considerable quantities of sodium chloride and potassium salts (Said, 1996).

Previously reported compounds from A. paniculata
 

 
Figure 1.9 Structures of compounds reported from A. paniculata (contd)
 

Figure 1.10 Structures of compounds reported from A. paniculata (contd)
 

 
Figure 1.11 Structures of compounds reported from A. paniculata
 
1.5 The family Rubiaceae
Characteristics-
Plant: Trees, shrubs, herbs; evergreen, deciduous trees.
Leaves:  Opposite, sometimes verticillate, simple, inter-or intra-petiolar.
Flowers: 5-merous, rarely 4-merous, hermaphrodite, actinomorphic.
Calyx: Andate to the ovary, with or without distinct lobes..
Corolla: Campanulate, infundibular or salver-shaped, 4-5 lobed.
Stamen: Nunber is as same as corolla lobes, adnate to the throat of corolla tube.              
Anthers: Mostly free, dorsifixedor basifixed, longitudinally dehiscing.
Disc: Annularor cushion-shaped.
Ovary: Inferior, 2 or more locular, styles slender, stigmas bilobed.
Fruit: Usually a capsule, sometimes berry or drupe.
Seeds: Usually with copious endosperm, sometimes winged.              
 
1.5.1 Taxonomy of Rubiaceous plants
The family Rubiaceae consists of about 450 genera and 6500 species, vast majority of which occur in tropical and subtropical regions. In Bangladesh, Rubiaceae family is represented by about 56 genera and 170 species. 
Members of Rubiaceae family
The plants belonging to the family Rubiaceae, which are available in Bangladesh, are listed in table 1.5.
 
Table1.5: List of important Rubiaceous species available in Bangladesh

 
1.5.2 Medicinal importance of Rubiaceous plants
Among the 170 species of Rubiaceae plants available in Bangladesh, only few are medicinally important. For many years some species of this family are being medicinally used by the indigenous people of Bangladesh (Table 1.6).
 
Table: 1.6 Medicinal importances of Rubiaceous Plants

 
1.5.3 The plant Anthocephalus chinensis
Taxonomic hierarchy: (Wikipedia 2006)
Kingdom:                                         Plantae
     Division:                                     Magnoliophyta
                Class:                               Magnoliopsida
                      Order:                        Rubiales
                             Family:              Rubiaceae
                                     Gegus:       Anthocephalus        
                                       Species:    chinensis 
 
Botanical features

 
Habitat and distribution: It is found to grow wild in jungles in almost all areas of the country and also planted as a timber and shade tree (Figure 1.12).
 

 

Figure 1.12 Photograph of A. chinensis (baby tree and flowers)
 
1.5.4 Medicinal uses
Different parts of A. chinensis are used traditionally as medicine by local people, some of which are mentioned in table 1.7.
 
Table: 1.7 Ethnobotanical uses of different parts of A. chinensis

 
1.5.5 Chemistry
Previous phytochemical investigations of A. chinensis (Figure 1.12-1.13) led to the isolation cinchotannic, quinovic and cadambagenic acids, saponins (IJP, 1960 and 1961; IJC, 1974 and 1977), 3^`-O-caffeoylsweroside, kelampayoside A and kelampayoside B (Kitagawa et al., 1996), cadambine (46), cadamine (47),  3-dihydrocadambine (48, 49, 50) and isodihydrocadambine (54), (Brown et al., 1974, 1976) hentriacontanol and beta-sitosterol (27) (Tet Let, 1974 and 1976; Labdev, 1972).
 
Previously reported compounds from A. chinensis

Figure 1.13 Structures of compounds reported from A. chinensis (contd)
 
 
 

 
Figure 1.14 Structures of compounds reported from A. chinensis
 
1.6 The family Fabaceae
Characteistics of the Fabaceous plants
Plant: Trees, shrubs or herbs often twining or climbing by tendrils.
Leaves: Simple, digitately or pinnately compound, very rarely 2-pinnate.
Sepals: 5, united above the middle and beyond the disk.
Calyx: Companulate or tubular with truncate, 5-toothed or 5-lobed limb.
Petals: 5, imbricate, erect or spreading, the upper (standard) outermost.
Stamens: Inserted with petals on the disk within the calyx tube.
Carpel: l, free, style simple, stigmas capitate, terminal.
Flowers: Irregula, hermaphrodite.
Fruit: Usually a dry pod, splitting along bothsutures.
Seeds: Usually exalbuminous.
 
1.6.1 Taxonomy of Fabaceous plants
This family consists of 440 genera and 12000 species, widespread in temperate and cold as well as tropical regions. In Bangladesh, this family has 69 genera and 254 species.
 
Members of Fabaceae family
Table 1.8 List of important Fabaceous species available in Bangladesh
 

 
1.6.2. Medicinal importance of Fabaceous plants
The medicinal uses of Fabaceous plants are listed in Table 1.9.
Table: 1.9 Medicinal importances of Fabaceous plants
 

 
 
1.6.3 The plant Sesbania sesban
Taxonomic hierarchy of the plant S.sesban (Wikipedia 2006)
Kingdom:                                        Plantae
     Phylum:                                      Magnoliophyta
                Class:                               Magnoliopsida
                      Order:                        Fabales
                             Family:               Fabaaceae
                                    Gegus:         Sesbania        
                                        Species:   sesban
 
Botanical features
 

 
Habitat and distribution: It is cultivated throughout the tropics. In Bangladesh, it occurs throughout the country

 
 
 
 
 
 
 
 
 
                                     
 

Figure 1.15 Photograph of S. sesban
 
 
1.6.4 Medicinal uses
Different parts of S. sesban are used traditionally as medicine by local people, some which are mentioned in table 1.10 
Table: 1.10 Ethnobotanical uses of different parts of S. sesban

 
 
1.6.5 Chemistry
Previous chemical investigations of S. sesban (Figure 1.16-1.17) led to the isolation of oleanolic acid (74), drummondol (61), drummondone (62, 63),  sesbanimide (72, 75, 76), sesbanine (77), stigmasta-5,24(28)-dien-3-ol-3-O-b-D galactopyranoside (78), fatty acids and amino acids, (Gupta et al., 1989) various types of lignins composed of guaiacyl, syringyl and p-hydroxyphenylpropane building units (Upadhyaya et al., 1992)  and  also an anti-tumour principle, kaempferol trisaccharide (El-Sayed, 1991).
 
Previously reported compounds from S. sesban

Figure 1.16 Structures of compounds reported from S. sesban (contd)
 

 
Figure 1.17 Structures of compounds reported from S. sesban
 
1.7 The family Moringaceae
Characteristics-
Plant: Deciduous to semi-deciduous trees, generally with gummy bark.
Leaves: Stalked, alternate, 2-3 times pinnately compound, leaflets opposite.      
Flowers: Axillary or mixed panicles, bisexual, usually zygomorphic.
Sepals: 5, spreading or reflexed
Petals: 5, unequal, usually the outermost one the largest.
Stamens: 5, antipetalous and alternating with 5 staminodes.
Ovary: Unilocular, seated on a short gynophore, placentation parietal.
Fruit: An elongated woody capsule.
 
1.7.1 Taxonomy of Moringaceous plants
The family Moringaceae consists of the single genus Moringa with about 10 species of xerophytic trees occurring in Africa and Madagascar and across the Middle East to India. In Bangladesh, the family Moringaceae is represented by 2 species only (Table 1.11).
 
Members of Moringaceae family
Table 1.11: Moringaceous plants available in Bangladesh
 

 

 
1.7.2 Medicinal importance of Moringaceous plants
Both of the Moringaceous plants available in Bangladesh are traditionally used as medicine and vegetables are very promising.
 
Table 1.12 Medicinal importances of Moringaceous plants
 

 

 
1.7.3 The plant Moringa oleifera
Taxonomic hierarchy: (Wikipedia 2006)
Kingdom:                                         Plantae
     Division:                                     Angiosperms
                Class:                               Eudicots
                        Order:                       Brassicales
                             Family:                Morigaceae
                                     Gegus:         Moringa         
                                        Species:    oleifera  
 
 
Botanical feature of M. oleifera
 

               
Habitat and distribution: The plant is well adapted at lower elevations, but grows well upto to 1300 m altitude. It is drought tolerant. Fertile, well-drained soils are suitable for this plant. It is indigenous to Indian subcontinent. It naturalized in many African countries. In Bangladesh, this plant is found all over the country planted mainly for its green fruits.
 

Figure 1.18 Photograph of M. oleifer

1.7.4 Medicinal uses
Table: 1.13 Ethnobotanical uses of different parts of M. oleifera

 

 
1.7.5 Chemistry
Previous chemical investigations on ethanol extract of M.oleifera leaves to the isolation of Niaziminin A,  Niaziminin B, 4-(2´,3´,4´-Tri-O-acetyl-α-L-rhamnosyloxy) benzyl nitr- ile, Niazicinin A, Methyl-4-(2´,3´,4´-Tri-O-acetyl-α-L-rhamnosyloxy) benzyl carbamate, O-Methyl-4-(2´,3´,4´-Tri-O-acetyl-α-L-rhamnosyloxy) benzyl thiocarbamate (E), O-Meth yl-4-(2´,3´,4´-Tri-O-acetyl-α-L-rhamnosyloxy) benzyl  thiocarbamate (Z), Methyl-4-(2´,3´,4´-Tri-O-acetyl-α-L-rhamnosyloxy) benzyl carbamate (Z),  Niazicinin B, Ethyl-4-(2´,3´,4´-Tri-O-acetyl-α-L-rhamnosyloxy) benzyl carbamate (E), Niazicin B, O-ethyl-4-(2´,3´,4´-Tri-O-acetyl-α-L-rhamnosyloxy) benzyl thiocarbamate (Z), Niazinin B, Niazimicin A, Niazinin A, Niazirinin, Niazimin B, 4-(4´-O-Acetyl- α-L-rhamnosyloxy) benzaldehyde, Niazimin A, Niazicin A, 4-(4´-O-Acetyl- α-L-rhamnosyloxy) benzyl isothiocyanate, Niazirin and 4-(α-L-rhamnosyloxy) benzyl isothiocyanate. The petroleum ethar soluble fraction of ethanolic extract of M. oleifera pods afforded 67 compounds. Neutral petroleum insoluble fraction of the ethanolic of M. oleifera pods also afforded 18 compounds (Saleem, 1995). Many more compounds have isolated from the plant by different scintific groups.
 
1.8 Flavonoids: Biogenesis and biosynthesis of flavonoids
Flavonoids and its biogenesis: The flavonoid can be regarded as C₆-C₃-C₆ compounds, in which each C₆ moiety is a benzene ring, the variation in the state of oxidation of the

Fig. 1.19 Scheme of biosynthesis of flavonoids
 
connecting C₃ moiety determines the properties and class of each such compounds.The flavonoids are generally exsist in plants as glycosides, in which one or more of the phenolic hydroxyl groups are combined with sugar residues. The hydroxyl groups are nearly always founds in positions 5 and 7 in ring A, while ring B commonly carries hydroxyalkoxyl groups at the 4^´-position, or at both 3´- and 4´-positions. Glycosides of flavonoid compounds may bear the sugar on any of the available hydoxyl groups.
 
Biosynthesis of flavonoids: In the biosynthesis of flavonoids, trans-cinnamic acid (82) undergoes aromatic hydroxylation to form para-coumaric acid (83) (Figure, 1.19). It is further converted by the enzyme 4-coumarate-CoA ligase into para-coumaroyl-CoA. The later condenses with three molecules of malonyl-CoA (84) to yield naringenin chalcone which is the precursor of different types of flavonoids and other related compounds (Heller et al., 1988; Dewick, 1990). Transformation of the stereospecific action of chalcone isomerase provides a flavone. Two different types of enzyme (dioxygenase and a mixed-function mono-oxygenase) are catalysts for the production of flavone e.g. apigenin (88). Dihydroflavonols are biosynthetic intermediate in the formation of flavonols, catecheins, proanthocyanidins and anthocyanidins. Kaempferol (91) is formed by flavonol synthase and dioxygenase.
 
1.9 Conclusion
 Chemical, hypoglycemic and some biological investigations have been done with the above-listed four plants. Actualy phytochemical investigations have been done with extractives of A. paniculata, A. chinensis and S. sesban. Hypoglycemic, antioxidant, antimicrobial and cytotoxical screening have done with all the four plants. The experimental detailed have been described in the subsiding chapters.