Green and sustainable metrics: Charting the course for green-by-design small molecule API synthesis

Sustainable small molecule Active Pharmaceutical Ingredient (API) manufacturing starts at the onset of route development by employing a Green-by-Design strategy. Reliable metrics are imperative for setting targets and measuring process improvements throughout the development cycle. This article reviews some of the many tools and methods established to analyze and assess the greenness and sustainability of a process, each of which highlights different aspects of process efficiency, waste formation or overall environmental impact reduction. Most calculations, such as process mass intensity (PMI), are mass-based and do not consider the types of raw materials used. In contrast, a full life cycle assessment (LCA) offers detailed information about the “cradle to grave” environmental impact of a manufacturing route and its specific resources, but the high data requirements and long timelines are not conducive for multiple processes or repeated assessments during process optimization. To address these challenges, we introduce a Streamlined PMI-LCA Tool, developed in collaboration with the ACS Green Chemistry Institute Pharmaceutical Roundtable (ACS GCIPR), that combines PMI with a “cradle to gate” approach to include the environmental footprint of the synthesis’ raw materials. The frequent re-evaluation of a process continuously highlights areas for improvement and guides the prioritization of process development activities to effectively and rapidly achieve a Green-by-Design commercial synthetic route. The utility of this approach to Green-by-Design is demonstrated with the reduction of PMI for MK-7264 from 366 to 88 over the course of process development.