Process chemistry

Process chemistry is the arm of pharmaceutical chemistry concerned with the development and optimization of a synthetic scheme and pilot plant procedure to manufacture compounds for the drug development phase. Process chemistry is distinguished from medicinal chemistry, which is the arm of pharmaceutical chemistry tasked with designing and synthesizing molecules on small scale in the early drug discovery phase.

Medicinal chemists are largely concerned with synthesizing a large number of compounds as quickly as possible from easily tunable chemical building blocks (usually for SAR studies). In general, the repertoire of reactions utilized in discovery chemistry is somewhat narrow (for example, the Buchwald-Hartwig amination, Suzuki coupling and reductive amination are commonplace reactions). In contrast, process chemists are tasked with identifying a chemical process that is safe, cost and labor efficient, “green,” and reproducible, among other considerations. Oftentimes, in searching for the shortest, most efficient synthetic route, process chemists must devise creative synthetic solutions that eliminate costly functional group manipulations and oxidation/reduction steps.

This article focuses exclusively on the chemical and manufacturing processes associated with the production of small molecule drugs. Biological medical products (more commonly called “biologics”) represent a growing proportion of approved therapies, but the manufacturing processes of these products are beyond the scope of this article. Additionally, the many complex factors associated with chemical plant engineering (for example, heat transfer and reactor design) and drug formulation will be treated cursorily.

Cost efficiency is of paramount importance in process chemistry and, consequently, is a focus in the consideration of pilot plant synthetic routes. The drug substance that is manufactured, prior to formulation, is commonly referred to as the active pharmaceutical ingredient (API) and will be referred to as such herein. API production cost can be broken into two components: the “material cost” and the “conversion cost.” The ecological and environmental impact of a synthetic process should also be evaluated by an appropriate metric (e.g. the EcoScale).

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