High‐Throughput Experimentation (HTE) Applied to the Synthesis of API Impurities: A Case Study in Oxidative Decarboxylation of Aryl Acetic Acids

Abstract High‐throughput experimentation (HTE) has dramatically impacted experimental reaction development by enabling the rapid exploration of a diverse set of reaction conditions. During the past few decades, HTE has evolved as a tool to expedite reaction discovery and optimization. This work details the application of HTE to synthesize impurities of active pharmaceutical ingredients (APIs) with ketone/aldehyde functionality, specially focusing on ibuprofen impurity E. Initial experiments using K 2 S 2 O 8 as oxidant yielded moderate results. Subsequent HTE screens identified cerium ammonium nitrate (CAN) and RuCl 3 ‐NaIO 4 as new effective decarboxylative oxidants, with RuCl 3 ‐NaIO 4 in the presence of tetrabutylammonium bromide (TBAB) achieving the highest yield of 65 %. This optimized method was successfully applied to synthesize ibuprofen impurity E on a gram scale. Additionally, the applicability of these methods to obtain other API related substances, such as naproxen impurity L and ketoprofen impurity A, was demonstrated. This research highlights the potential of HTE to streamline the synthesis of API impurities, making them widely accessible for pharmaceutical development purposes.