Chapter 3: Active Pharmaceutical Ingredients: Structure and Impact on Synthesis

In this chapter the chemical structure of fully synthetic active pharmaceutical ingredients (APIs) are outlined and the relationship with the synthetic methods employed for their construction is discussed. APIs tend to contain multiple nitrogen and oxygen atoms as well as aromatic and heteroaromatic rings. These functional groups aid binding to the desired target and attenuate the physicochemical characteristics needed to achieve bioavailability. API synthesis can generally be covered by the concept of trying to apply simple chemistry on complex substrates. The ideal synthetic sequence should be as short as possible and avoid the use of hazardous reaction conditions or reagents. Clean, high-yielding reactions that form few, if any, impurities are desirable especially towards the end of the synthetic sequence.