A2- From concept to market structure that will interact with that target. Such a structure is known as a lead compound(Section E)and is the starting point for drug design. Phase 2-drug Once a lead compound has been identified, the medicinal chemist will devise design synthetic routes that will allow the synthesis of various analogs( Section F) Having produced a series of analogs, the activities of these compounds are compared and certain structural features that are more important to activity than others are identified (structure activity relationships-Section G). These features are retained in the design of further analogs, which will interact more effectively or more selectively with their target(Section H). As well as this, it is necessary to design analogs that have the correct pharmacokinetic properties to reach their Phase 3- drug As soon as a potentially useful drug is discovered, it is patented(Section D).The testing and potential drug must then be thoroughly tested for any side effects or toxicity so carried out to identify wh lites are formed. These metabolites are then tested for activity and side effects. If the drug passes these tests, it is put forward for clinical trials(Section K). Finally the drug can be marketed. At the same time as the pre-clinical and clinical trials are taking place, work is carried out to develop a large-scale synthesis of the compound(section D). The various tests and development work carried out on a new drug must be properly controlled and documented such that they adhere to the requirements laid down by the various regulatory authorities(Section K). Otherwise, the drug may not be allowed to enter clinical trials or the market. The chemlst's Chemists and medicinal chemists make important contributions at various contribution stages of the drug research program. The medicinal chemist is most involved ith drug discovery and drug design. Development chemists are involved in designing a large-scale synthesis for a drug. Organic synthetic chemists are involved in synthesizing radiolabeled drugs for drug metabolism studies, while analytical chemists are involved in quality control, ensuring that the drug satis- fies purity specifications. Many of the practical skills acquired in a chemistry or medicinal chemistry degree are invaluable to the pharmaceutical industry. Practical techniques such as extraction, chromatography, distillation and crystal- lization are vital if a lead compound is to be isolated and purified from a natural extract or a synthetic mixture. Synthetic skills are required in order to synthesize analogs of a lead compound in order to carry out structure activity relation ships. Analytical skills, such as the ability to interpret nuclear magnetic reso- nance (NMR) spectra, are important in determining the structure of a lead compound or a synthetic analog. These skills are just as relevant to the develop ment chemist devising a large-scale synthesis