Plants are gifted naturally for the synthesis of medicinal compounds, whose characterization has led to discovery of new, cheap drugs with high therapeutic potential. Medicinal plants contribute significantly to rural livelihoods. Apart from the  traditional healers practicing  herbal  medicine, many  people  are involved  in  collecting  and  trading  medicinal plants. This has resulted in an increased demand for herbal remedies worldwide leading to realization of enhanced new drugs. Despite the fact that medicinal plant use has  been an  old habit  in most communities, the emergence of drug and multi drug resistant strains of microorganisms have even opened a more wider window for continued research and discoveries on medicinal plants. Also most communities in  developing nations are  deep into medicinal plant use due to the alarming rates of poverty  rates  and  therefore  this  needs  scientific backing  especially  in  deducing  their  efficacies  to treatment  of  such  ailments.  Either in their pure compounds or as standardized plant extracts, they provide unlimited opportunities for new drug leads because of the unmatched availability of chemical diversity.  The bioactivity of natural products is associated with the effects of various phytochemicals such as tannins, cardiac glycosides, saponins, flavonoids among others. The World Health Organization (WHO) estimates that 80% of the world’s population depends on medicinal plants for their primary health care. Herbal remedies are cheap alternative to conventional medicine.

Phytochemicals can have complementary or overlapping mechanisms of action in the  body,  including  antioxidant effects, modulation of enzyme actions, stimulation of the immune  system,  modulation of  hormone metabolism, anti-bacterial  and antiviral  effect, interference with DNA replication and physical action  whereby some may bind physically to cell walls thus preventing the adhesion of pathogens to human cell  walls.

An Alkaloid is a plant-derived compound that is toxic or physiologically active. Some alkaloids such  as  isopteropodine,  pteropopine  have anti-microbial  activity  whereby  they  act  by promoting white blood cells to dispose harmful micro-organisms and cell debris.

Tannins are astringent, bitter plant polyphenols that either bind and precipitate or shrink proteins. They have physiological role by acting as antioxidants through free radical scavenging activity, chelation of transition metals, inhibition of pro-oxidative enzymes and lipid peroxidation, hence modulating oxidative stress and preventing degenerative diseases. They also inhibit tumour growth by inducing apoptosis.

Flavonoids are structural derivatives of flavones, containing conjugated aromatic systems, often bound to sugars as glycosides, and they are phenolic and water soluble in nature. They exert their roles as anti-oxidants, and hence protecting against degenerative diseases.  Flavonoids such as quercetin, act as chain breaking anti-oxidants, and by preventing oxidation of low-density lipoprotein by macrophages and metal ions like copper. This reduces the oxidative stress.

Saponins are service active agents with soap-like properties and can be detected by their ability to cause foaming and to haemolyse blood cells.  They have a host of biological roles including boosting respiratory system as expectorant, and hence activity against cough.  They also  have  anti-protozoa activity  whereby  they  act  by  reacting  with cholesterol  in  the  protozoal  cell  membranes causing  cell  lysis.

CONCLUSION

Natural products are still a major part in supporting the primary health systems. Their bio-activity is mainly associated with secondary metabolites which often elaborated for the plant defence.  Some of these phytochemicals accidentally protect humans against pathogens and that is why they are a main target for drug prospecting programs. Phytochemicals are known to have several important properties to cells including; prophylactic, therapeutic, nutritive and immune-modulative properties.