From ancient time, the belief has been that the plants contain some biologically active compounds with therapeutic properties useful for treatment of various ailments, including asthma, gastro-intestinal problems, skin disorders, respiratory and urinary complications, hepatic and cardiovascular disease etc. The medicinal value of these plants signifies a great potential for the discovery and development of new pharmaceuticals due to its chemical substances that produce a positive physiological action on the human body [1].Different parts of the plants, such as in the roots, stems, leaves, flowers, fruits or seeds are the deposited areas of phytochemical and are often seen as pigmented molecules in the outer layer of plant tissue [3]. Medicinally important plants having its pharmacological benefits due to accumulation of bioactive phytochemicals in the plant tissue considered as primary and secondary metabolites. Primary metabolites as organic compounds that comprises of glucose, starch, polysaccharide, protein, lipids and nucleic acid which are helpful for growth and development of the human body. Plants produce secondary metabolites which include alkaloids, flavonoids, saponins, terpenoids, steroids, glycosides, tannins, volatile oils etc [1,4].
Secondary metabolites due to its therapeutic value which includes phytochemicals, a pharmacological active compounds plays an important role towards curing many diseases. Phytochemical includes
(a) Alkaloids, having the characteristics of antispasmodic, antimalarial, analgesic, diuretic activities, (b)Terpenoids, having the properties of antiviral, anthelmintic, antibacterial, anticancer, antimalarial, anti-inflammatory
(c) Glycosides are known for its antifungal and antibacterial properties
(d) Phenols and flavonoids are reported to have an antioxidant, anti-allergic, antibacterial properties etc.
(e)Saponins have the properties of anti-inflammatory, antiviral, plant defence activities[19,20].In India, a numerous studies have been conducted to validate the traditional use of medicinal plants by investigating the phytochemicals ingredients present. Based on the study from current works such as published literature, book etc effort has been made to maintain & manage the collected records and informations in consolidated form towards summarizing on the phytochemicals activity of the medicinal plants widely used in India.

Phytochemical profile

Phytochemicals are secondary plant metabolites can be classified based on the chemical composition (containing nitrogen or not), chemical structure (for example, having rings, containing a sugar), the biosynthetic pathway (e.g., phenylpropanoid, which produces tannins) or their solubility in various solvents[17]. Investigative studies have demonstrated that many of plants contain secondary metabolites can be divided into three chemically distinct namely alkaloids, terpenes and phenolics that could be potential sources for several effective drugs.

Alkaloid

Alkaloids are generally present in higher plants, particularly in dicots, whereas only a few have been noted in lower plants. The alkaloids can occur in the whole plant or in the specific plant organ. Alkaloids are derived from amino acid mostly contain one or more carbon rings which usually contain nitrogen. The type of Alkaloids and plant families depend upon the position of nitrogen atom in the carbon ring. Alkaloids play important roles in plants as it checks the feeding of herbivores, protects from pathogenic hit, and inhibitions of competitors Alkaloids have several pharmacological importance like antihypertensive (many indole alkaloids) and antiarrhythmic (quinidine, spareien) effects, antimalarial activity (quinine) and anticancer actions (dimeric indoles, vincristine,vinblastine). A few alkaloids contains caffeine, nicotine, and morphine etc possessing the stimulant property used as the analgesic and quinine as the anti-malarial drug .

Fig.1: Chemical Structure of Nitrogen atom in heterocyclic rings

Phenol

Plant synthesizes another secondary product that contain a phenol group is basically a hydroxyl functional heterogeneous group present on an aromatic ring. The phenolic compounds are present in medicinal plants that are important secondary metabolites and show a wide range of pharmacological activities like anticancer, antiinflammatory. The polyphenols consisted of nine compounds, namely gallic acid, quercitrin, quercetin, kaempferol-3-O-glucoside, 3-O-geraniin, 1-Ogalloyl-4,6-trihydroxy-3,4,31-trimethoxydiphenoylβ-D-glucose, 2,3-di-O-galloyl-β-D-glucose, and 1,2,3-tri-O-galloyl-β-D-glucose.[1].Phenol compounds include flavanoid and tannin, details of which are given below.

Flavonoids

Flavonoids, a group of plant secondary metabolites, where the molecular framework is catagorised by variable phenolic structures, and possess anticancer activity[1]. Flavonoids are diveded into two classes due to position of the benzenoid substituent such as flavone (2-position) and isoflavone (3- position). Flavanoids generally are produce naturally and linked with sugars in conjugated form falls under any one class, may be categorized as monoglycosidic, diglycosidic, etc. The glycosidic linkage is normally located at position 3 or 7 and the carbohydrate unit can be L-rhamnose, Dglucose, glucorhamnose, galactose or arabinose[3].Flavanoids be active ingredients of numerous herbal medicines[2].

Tannin

A common characteristics of phenolic compounds is the presence of at least one hydroxyl-substituted aromatic ring system.On the other hand when a compound contain 10 hydroxyl groups ,these compounds referred as Tannin. Hydrolysable is another important group of tannins represent Esters lies between gallic acid and sugars. Tannins posses antioxidants, with anti-inflammatory, antidiarrhoeal, cytotoxic, antiparasitic, antibacterial, antifungal and antiviral activities. Tannins are a heterogeneous group of high molecular weight polyphenolic compounds with the capacity to form reversible and irreversible complexes with proteins(mainly), polysaccharides (cellulose, hemicellulose, pectin, etc.), alkaloids, nucleic acids and minerals, etc. Based of their structural characteristics it is therefore possible to divide the tannins into four major groups: Gallotannins, ellagitannins, complex tannins, and condensed tannins.
(1) Gallotannins are all those tannins in which galloyl units or their meta-depsidic derivatives are bound to diverse polyol-, catechin-, or triterpenoid units. These gallotannins are widely distributed in plants, often in bark, leaves and fruits.
(2) Ellagitannins are those tannins in which atleast two galloyl units are C–C coupled to each other, and do not contain a glycosidically linked catechin unit.
(3)Complex tannins are tannins in which a catechin unit is bound glycosidically to a gallotannin or an ellagitannin unit.
(4) Condensed tannins are all oligomeric and polymeric proanthocyanidins formed by linkage of C-4 of one catechin with C-8 or C-6 of the next monomeric catechin.

Fig. 2: Chemical Structure of Aromatic aliphatic ring containing phenols.

Terpenes

Terpenes are the largest class of secondary metabolites having hydrocarbons and the combination of several five-carbon isoprene units, resulting from hydrocarbons. Terpenes interact with biomembranes and membrane proteins and most of the terpenoids are lipophilic. In general, terpenes show cytotoxic activities against a wide range of organisms, ranging from bacteria and fungi to insects and vertebrates have been widely used in herbal medicine against infections. The word Terpens and terpenoids are increasingly used interchangeable and their main differences between them is that Terpens are hydrocarbons where is Terpenoids have been denatured by oxidation or chemically modified [23]. Terpenoids can be thought as modified terpenes in which methyl groups have been moved or removed, or oxygen atoms added. The followings are the classification of Terpenoid according to the number of isoprene unit.
(a) Hemiterpenoids: Consist of a single isoprene unit. The only hemiterpene is the Isoprene itself, but oxygen-containing derivatives of isoprene such as isovaleric acid and prenol is classify as hemiterpenoids.
(b) Monoterpenoids: Biochemical modifications of monoterpenes such as oxidation or rearrangement produce the related monoterpenoids. Monoterpenoids have two isoprene units. Monoterpenes may be of two types i.e linear (acyclic) or contain rings e.g.Geranyl pyrophosphate, Eucalyptol, Limonene,Citral, Camphor and Pinene.
(c) Sesquiterpenes: Sesquiterpenes have three isoprene units e.g. Artemisinin, Bisabolol and Fernesol, oil of flowers, or as cyclic compounds, such as Eudesmol, found in Eucalyptus oil.
(d) Diterpenes: It composed for four isoprene units. They derive from geranylgeranyl pyrophosphate. There are some examples of diterpenes such as cembrene, kahweol, taxadiene and cafestol. Retinol, retinal, and phytol are the biologically important compounds while using diterpenes as the base.
(e) Triterpenes: It consists of six isoprene units e.g. Lanosterol and squalene found in wheat germ, and olives.steroidal glycosides, the cucurbitacins (occurring in members of the Cucurbitaceae and a few other families) express substantial cytotoxic activities; they inhibit tumor growth in vitro and in vivo.

Fig. 2: Chemical Structure of Aromatic aliphatic ring containing phenols.

Saponin

Saponins are a group of secondary metabolites found widely distributed in the families of monocots, and are less frequent in dicots (Araliaceae, Fabaceae, Plantaginaceae, Scrophulariaceae, Solanaceae). Triterpene saponins are abundant in several dicot families, such as Ammaranthaceae (formerly Chenopodiaceae), Caryophyllaceae, Phytolaccaceae, Poaceae, Primulaceae, Ranunculaceae, and Sapotaceae. They are absent in gymnosperms Saponin act upon wounding-induced decompartmentation ,as it stored as bidesmosidic (containing two sugar chains one attached to the C-3 and one at C-22compounds ) in the vacuole, which are cleaved to the active monodesmosidic (C-3 position) compounds by a β-glucosidase or an esterase.Saponin are chemically classified as a glycosylated steroids,triterpenoids, and steroid alkaloids.An agylone is the compound remaining after the glycosyl group on a glycoside is replaced by hydrogen atom.Steroid aglycones have two derivatives known as spirostan and furostan. Another important feature of sapogenin (aglycone) is the linkage with the carbohydrate part that consists of one or more sugar moieties containing glucose, galactose, xylose, arabinose, rhamnose, or glucuronic acid glycosidically.

Glycoside

Glycoside is a class of natural products composed of two molecules consists of
(1) sugar which is primarily D-glucose, sometimes it can be Lrhamnose and L-fructose
(2) aglycone composed of flavonoid or a terpene.
Aglycone is a part of cardiac glycosides which is highly toxic and found in number of plants. Aglycone of cardiac glycosides which can be categorized in two chemical groups cardenolide and bufadienolide. Cardenolide plays a important role in cardiac activity. The most important phenomenon of transport activities of cells and neuronal signalling depends on the Na+-, K+ATPase, building up Na+ and K+ gradients which is inhibited by cardiac glycosides causes death through cardiac and respiratory arrest.

Essential oil

Essential oil are hydrophobic liquids that can be extracted from many plants.It is also known as volatile oils,ethereal oils. Essential oil associated constituents characterized by low molecular weight with the plant material from which the oil is components,such as terpenes, terpenoids, and other extracted, is a complex mixture of volatile plant aromatic and aliphatic chemical compounds.

Table 1-A: Phytochemical activities of Medicinal Plant on some Diseases

Table 1-B: Phytochemical activities of Medicinal Plant on some Diseases