**3. Natural products option**

Plants as a source of medicine Nature, as old as mans' existence, have been a provider of medicines and agents used for the development of medicine. There are other natural sources of medicinal products like marine, but the most prevalent source is a plant [63]. An enormous number of the medications in use today was obtained from a plant. Some medications in use also were developed from a compound originally gotten from a plant. The development of most of these medicines gotten from a plant started from the study of the utilization of the plant in traditional medicinal practice, which gave an insight into the type of pharmacological property or likely pharmacological effect for which the molecules from plants could be developed for.

#### *Therapeutic Inhibitors: Natural Product Options through Computer-Aided Drug Design DOI: http://dx.doi.org/10.5772/intechopen.104412*

The system of traditional medicinal practice keeps on being a very indispensable target in the world's healthcare system because of the dependence of the 80% of the world population on traditional medicinal practice system for their elementary healthcare needs, according to World Health Organization. The remaining 20% of the population who are residents of developed countries also use plant products for healthcare needs or substances developed from plant products [64]. Research has it that between 1959 and 1980 in the United States that about 25% of the dispensed prescription drugs from community pharmacies were products of plant extracts or contained active ingredients obtained from higher plants [65].

Currently in use as medications are at least 119 chemical entities obtained from 90 different plant species. Of all these 119 drug entities, 74% were obtained from plants through direct isolation of active substances from plants that are already in use in traditional medicinal practice systems [66]. It is on record that in all sales made by the leading pharmaceutical industries in the year 1991, most of the sales were made on products derived from natural sources or containing a substance or substances that are natural product-based [67]. It is also on record that in 1993, a total of 57% of the top 150 brand-name products that were prescribed had at least one major active compound from a natural source or derived from a natural source or patterned after substances reflecting biological diversity [68].

Many researchers have taken an interest in discussing and accessing different medicinal plants as a reservoir for new therapeutic agents [63], and some others have persuasively converged their research on the use of specific chemical classes like flavonoids, alkaloids, glycosides, etc. in drug discovery. Recent research has continued to demonstrate and validate the ethnomedicinal drug discovery approach to the initial discovery approaches of pharmaceuticals [69]. Still, some other researchers have estimated that out of about 375 total compounds of pharmaceutical importance in the rain forests, only about one-eight have been explored. Assessing and observing the roles these natural product base medications have played in humanity, there are possibilities that more efficient ones are still in the forest unexplored [70].

This forms the basis for the need for more exploration and research on traditional medicinal plants for the emerging healthcare challenges of humans. Researchers in the field of medicinal plants are no longer only interested in testing plant extracts for pharmacological activities but are also undertaking the isolation of molecules from plant extracts and identifying these molecules. Some has gone further to establish the pharmacological effect of these isolated molecules. For example, in previous research on Vernonia amygdalina, we were able to establish the antidiabetic and antihelminthic effectiveness of methanolic extract Vernonia amygdalina [71, 72], and we went further to isolate six pure molecules from the methanolic extract [73] and then tested the isolated molecules for the antidiabetic and antihelminthic property. From the study, we were able to identify the molecules responsible for the antidiabetic and antihelminthic effects observed in the extract [74].

Likewise, there are thousands of isolated molecules from plants yet to be studied for any pharmacological activity. These molecules form plants are usually deposited in natural product databases from where their structures can be downloaded for studies using Computer-Aided Drug Design. Some of them are also available for purchase for in-vitro and in-vivo studies. Some of the natural product databases include;

• ColleCtion of Open NatUral producTs (COCONUT) [75], containing 406,747 phytocompounds


These isolated and identified natural products can also serve as a primary source for new molecule development through *in-silico* structural modification and synthesis. The existence of these natural products and these databases has provided a vast background for targeted natural product drug design and development. To be able to utilize these natural compounds in receptor/protein/enzyme targeted drug design and development *in-silico*, the receptor/protein/enzyme need to be available in a portable format that will enable its utilization *in-silico*, which is provided in protein databases.
