1.1 INTRODUCTION OF NATURAL PRODUCTS
As the term implies, natural products are those chemical compounds which are derived from living organisms including plants, animals, insects, and microorganisms, while the research on natural products includes the investigation of their structures, formation, uses and purpose in the organism. Compounds which occurred naturally may be classified into three categories.
Primary metabolites- the compounds which occurred in all cells and it plays a central role in metabolism and reproduction of those cells.
Secondary metabolites-They are high molecular weight polymeric materials. Most of the primary metabolites make use of their biological effects within the cell or organism that is responsible for their production.
Chemotaxonomy- Chemotaxonomy provides another reason for examining the constituents of plants.
Phytochemical survey can reveal natural products that are “markers” for botanical and evolutionary relationships (10).
A brief account of type of the phytochemicals distributed in plant flora is given below:
Phenolic compounds (11) are plant metabolites, which was widely distributed in plant kingdom. It is also identified as polyphenols which is found in fruits of some plants, they were naturally occurring coloured pigments and it is also responsible for the colour of fruits .
Flavonoids (12) are important group of polyphenols, widely distributed in plant flora 4,000 flavonoids are known to exist and some of them are pigments in higher plants. Quercetin, kaempferol and quercitrin are common. Soya flavones have recently gained importance due to variety of pharmacological activities.
Acylphloroglucinols (13) are group of phenolic compounds having significant antidepressant activity.
Alkaloids (14) are basically nitrogen containing bases and the most important class of phytochemicals. The amino acids act as building blocks for the biosynthesis of alkaloids. More than 10,000 different alkaloids have been discovered in species from over 300 plant families.
First identified in 1820s, coumarin (15) is an oxygen heterocycle that is famous for its vanilla-like or freshly-mowed hay fragrance. Coumarin is a chemical compound (benzopyrone); a toxin found in many plants, notably in high concentration in the tonka bean, vanilla grass, woodruff, mullein, and bison grass. Coumarin and its derivatives are principal oral anticoagulants.
Coumarins are competitive inhibitors of vitamin K in the biosynthesis of prothrombin (16).
Furanocoumarins (17) are photosensitizing agents used in the treatment of pigment disorders. Ayurveda, the ancient science of India, has described the use of bawachi (Psoralia corylifolia) for the treatment of leucoderma.
Furochromones (18) are group of coumarins, derived from benzopyrone. They are related to furano coumarins. Hydroxycoumarins represent another group of coumarins.
Glycosides are water-soluble constituents, found in the cell sap. They are colourless, crystalline substanes containing carbon, hydrogen and oxygen. Some glycosides are peculiar in having nitrogen and sulphur.
The glucosinolates (19) are a class of organic compounds that contain sulfur and nitrogen and are derived from glucose and an amino acid. Glucosinolates are water-soluble anions and belong to the glucosides. About 120 different glucosinolates are known to occur naturally in plants. They are synthesized from certain amino acids.
Resins (20) are brittle, non-volatile, solid substances. Oleoresins are natural products of resin mixed with volatile oils. Gum-resins are plant exudates and are mixtures of gum and resin and often volatile oils. Balsams are combinations of resins or oleoresins with aromatic acids.
Saponins (21) are glycosides found in number of plants. they are amphipathic glycosides grouped phenomenologically by the soap-like foaming they produce when shaken in aqueous solutions, and structurally by their being composed of one or more hydrophilic glycoside moieties combined with a lipophilic triterpene derivative Some are poisonous.
Terpenoids (22) may be defined as a group of molecules whose structure is based on a various but definite number of isoprene units (methylbuta-1,3-diene, named hemiterpene, with 5 carbon atoms). Terpenoids are extraordinarily diverse but they all originate through the condensation of the universal phosphorylated derivative of hemiterpene, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) giving geranyl pyrophosphate (GPP). Plant terpenoids are used extensively for their aromatic qualities. They play a role in traditional herbal remedies.Sesquiterpene lactones constitute significant group of phytochemicals. They are formed by condensation of three isoprene molecules followed by oxidation.
Sterols (23) are derivatives of steroids. Modern clinical studies have supported their role as anti-inflammatory and analgesic agents. Sterols are also known as steroid alcohols. They are a subgroup of steroids with a hydroxyl group at the 3-position of the A-ring. They are amphipathic lipids synthesized from acetyl-coenzyme A via the HMG-CoA reductase pathway.
Tannins (24) are astringent, bitter plant polyphenols that either bind and precipitate or shrink proteins. They are phenolic compounds of high molecular weight. Tannins are widely distributed in plant flora. Tannins have shown potential antiviral (25), antibacterial (26) and antiparasitic effects (27). In the past few years tannins have also been studied for their potential effects against cancer through different mechanisms.
1.2. FAMILY RUBIACEAE
Family Rubiaceae (28) is cosmopolitan in distribution. This plant family comprises 630 genera and 1300 species. In India, it comprises about 74 genera and 450 species. It is available almost worldwide though it is most rich in the tropical regions of both hemispheres. Coffee (Coffea), quinine (Cinchona), madder (Rubia), ipecac (Carapichea Aublet) and various horticultural plants, notably Gardenia, Ixora, Mussaenda, and Pentas. Several genera include pantropical weeds, notably Mitracarpus, Richardia, and Spermacoae, of neotropical origin, and Oldenlandia (Hedyotis) were the important members of the family.
1.2.1 IMPORTANCE OF THE FAMILY RUBIACEAE
The chemical constituents of Rubiaceae species used as timber, ornamental purposes ,etc., The species of this family is used for their high -quality timber (e.g., Nauclea diderichii) ,ornamentals (Ixora, Gardenia). Additionally they have medicinal value as well.
The root extract (Mussaenda frondosa) was used for blemishes on the tongue, sepals for diuretic. (ref) The fruit extract of the Randia echinocarpa was used for the treatment of kidney ailments. Various species of this family were used,such as abortifacient, cancer of the stomach and small intestine, circulatory problems, coughs, diabetes, diarrhoea, injuries and wounds happened by accidents,diuretic,etc.,
Rubiaceae species have been a treasured supply of latest secondary metabolites for scientific functions. Plant drugs, consequently, retain to represent an important a part of the medicines, especially the areas of present day medicine and additionally in conventional scientific structures like in our conventional ayurveda, siddha and Unani as an immunomodulator. But the potential use of higher vegetation as a source of recent pills remains poorly explored of the anticipated 2,50,000-5,00,000 plant species, only a small percentage has been investigated phytochemically and even a smaller percentage has no longer been well studied in phrases of their pharmacological houses. In maximum cases, best pharmacological screening or preliminary research were performed and it is also predicted that only 8000 species had been studied for medicinal use82.
Phytochemical analysis discovered the presence of secondary metabolites like alkaloids, flavonoids, tannins, steroids, saponins, terpenoids, sanranetin-4-o-glycoside fatty chain acids and cardiac glycosides within the extracts of the Rubiaceae circle of relative species83.In conventional medication, Rubiaceae species are used as an antioxidant84-86,anticancer87,88,89,90,antimicrobial91,92,antidiabetic93,antiinflammatory94,hypocholesteromic95,woundhealing96,antimalarial97,antipyretic and analgesic98-100etc.,
1.3.1 GENUS RANDIA
Randia is a large genus contains more than 100 species in the coffee or bedstraw family (Rubiaceae).The genus include small trees, trunk with short simple, branched thorns, young branchlets. It is present in peninsular India and SriLanka. The leaves are simple, opposite, lamina 3.5-7.5 x1.3-3. The flowers were inflorescence umbel, white-cream with 0.5cm long.
1.3.2 GENUS TARENNATarenna is a large evergreen shrub which belongs to Ixora family (Rubiaceae), the genus of about 370 species which was distributed in tropical and subtropical Africa, Asia, Madagascar. The flowers are short, creamy white,fragrant. The leaves are simple, broad length with a width 3.2-9.x2.3-5.
1.4 BENKARA MALABARICA (LAM.) TIRVENG.
Benkara malabarica is an erect woody, gray, velvety and shrubby plant. Medicinally it is very important plant.
Synonym Randia malabarica Lam.
Kingdom PlantaePhylum TracheophytaClass MagnoliopsidaFamily Rubiaceae
Genus BenkaraVERNACULAR NAMES
Malayalam ben-karaTamil PudanTelugu Pedalli
Peninsular India and Sri Lanka; throughout-western ghats.
Small trees; Trunk with short straight forward or branched thorns; bark gray, lenticellate; blaze yellow; Young branchlets subterete, glabrous. Leaves straightforward, opposite, decussate; plant structure linear, interpetiolar, deciduous and exploit scar; stalk ca. 0.8 cm long, bulging in cross section, glabrous; plate three.5-7.5 x 1.3-3, obovate, apex obtuse to shortly acuminate with blunt tip, base attenuate, margin entire, coriaceous, hairless beneath; midvein raised above; secondary nerves ca. 6 pairs, domatia gift at axils; tertiary nerves obscure.Inflorescence like corymbs, axillary; flowers white-cream; pedicle ca. 0.5 cm long. Berry, globos, with crown of persistent gyre lobes; seeds several.
1.5.1 TARENNA ASIATICA (L.)KUNTZE EX K.SCHUM
The plant is used to treat skin diseases, in wound pain,etc.,
Synonym Canthium corymbosum (Willd.) Pers.
Kingdom PlantaePhylum TracheophytaClass MagnoliopsidaFamily Rubiaceae
Genus Tarenna1.5.2. VERNACULAR NAMES
Malayalam kuppipoovuTamil TharaniOthers Tharani,Thaerani
Indo-Malaysia , Kerala, All Districts in Tamil Nadu
In terminal inflorescence cymes, 3-chotomous; cream, fragrant. Flowering from December-April. Fruit-a circular berry, with a crown of curl lobes, dark brown once dry. mature throughout the year. Field tips-leaves dark shiny inexperienced on top of, uninteresting at a lower place; leaf arrangement-opposite-decussate; Leaf type-Simple; leaf shape-oblong-oblanceolate; Leaf Apex-Acute; Leaf Base-Truncate; Leaf margin entire.
Antimicrobials (53) are chemicals that kill microbes. Antimicrobial is the name for a chemical that either kills or prevents the growth of microbes (‘bugs’ or ‘germs’) such as bacteria, viruses, fungi or protozoa. Some antimicrobials are produced by bugs themselves (e.g. penicillin is produced by the penicillium mould), others are designed in the laboratory. Different bugs are susceptible to different antimicrobials e.g. the penicillium mould is not killed by the penicillin it produces, but some bacteria are susceptible to penicillin. Antiviral are drugs that kill or prevent the growth of viruses. Viral infections are much harder to treat than bacterial infections because viruses live inside our cells, making it harder for the immune system to see them and attack them .
A large number of human, animal and plant disease are caused by pathogenic microbes (fungi bacteria and algae). Infections due to fungi and bacteria have been a major cause of death in higher organisms. The discovery of antibiotic penicillin by Fleming is therefore considered to be one of the most important discoveries in the world. Historically many of the new antibiotics were isolated from natural sources (soil microbes, plants etc). Many more were later synthesized and introduced in clinical practices. Several antibiotics, which have been found to be clinically effective as antibacterial, antifungal and antiprotozoal agents are found to inhibit carcinomas in experimental animals and are used as antitumor agents for the control of malignant diseases. However the toxic side effects of bone marrow changes, kidney and liver damage have precluded extensive therapeutic applications of these agents for cancer treatment.
Unfortunately human struggle against pathogenic microbes is far from over due to many reasons. Most important of them time to time discovery of new pathogens, remarkable abilities of microbes to develop resistance against used antibiotic. The discovery and development of new antimicrobial agent is therefore a going process. Remarkable diversity of chemicals present in biological samples has tremendous potential in search of new antimicrobial agents.
There is no single all embracing bioassay to evaluate the antimicrobial activity of a sample. Therefore, the evaluation process generally involves the use of a number of bioassay methods and careful comparison of all the data in order to arrive at an appropriate conclusion (54).
There are three major methods for antimicrobial testing:
(a) Agar diffusion method.
(b) Agar dilution method.
(c) Bioautographic method.
In the agar diffusion method, wells are cut in seeded agar and the sample is then introduced directly into these wells. After incubation the diameter of the clear zone around the well is measured and compared against zones of inhibition produced by the solutions of known concentrations of standard antibiotics. In samples where the presence of suspended particle matter (or precipitation of water insoluble substances on the disc or cylinder) interferes with the diffusion of the antimicrobial substance, warming on a hot plate may be advantageous. Five or six samples may be tested simultaneously by the diffusion method.
In the agar dilution method, the medium is inoculated with the test organism and the samples to be tested are mixed with the inoculated medium. The material is inoculated and the growth of the microorganisms is viewed and compared with a control culture which does not contain the test sample. The experiment is repeated at various dilutions of the test sample in the culture medium and the highest dilution at which the sample just prevents the growth of microorganism (MIC) is determined.
The bioautographic procedure for screening for antimicrobial activity involves localizing the antibacterial activity on a chromatogram. The antimicrobial agent is transferred from the TLC plate or paper chromatogram to an inoculated agar plate by diffusion and zones of inhibition visualized.
Spoilage of foods due to the presence of bacterial and fungal infection has been a major concern for decades and it causes a considerable loss world wide. The demand for non toxic, natural preservatives has been rising with increased awareness and reports of ill effects of synthetic chemicals present in foods. Further more emergence of food borne pathogens has lately become a major public health concern. Many compounds present in the plants have been reported to be biologically active, antimicrobial, allopathic, antioxidants and have bio regulatory properties. There is a need to discover new antimicrobial compounds in view of many plant and human microbial diseases.