No abstract

An efficient, practical, and commercially viable manufacturing process was developed with ≥99.7% purity and 31% overall yield (including four chemical reactions and one recrystallization) for an active pharmaceutical ingredient, called Metopimazine (1), an antiemetic drug used to prevent emesis during chemotherapy. The development of two in situ, one-pot methods in the present synthetic route helped to improve the overall yield of 1 (31%) compared with earlier reports (<15%). For the first time, characterization data of API (1), intermediates, and also possible impurities are presented. The key process issues and challenges were addressed effectively and achieved successfully.

Rebamipide (1) is a superior drug compared to existing drugs for use in healing of peptic ulcers, gastrointestinal bleeding, and dyspepsia. It is also useful as an ophthalmic drug for the treatment of dry eye syndrome. Process intensification for its synthesis was achieved by (i) averting uncontrollable frothing using Krapcho decarboxylation instead of conventional acid hydrolysis, where uncontrollable frothing became chaotic, (ii) minimizing organic waste generation by using a single organic solvent, and (iii) avoiding anti-foaming agents (n-octanol, acetophenone) and acetic acid. With these trifling modifications, the overall yield of active pharmaceutical ingredient (API) was ≥83% with excellent purity (≥99.89%), and the process meets the metrics of “green” chemistry with an E-factor = 11.5. The developed hassle-free commercial process is viable for multi-kilogram synthesis of Rebamipide (1) as the key step, Krapcho decarboxylation is safe to run at 130–140 °C in DMSO, and it was proved to be effective by differential scanning calorimetry thermal screening studies. The characterization data of intermediates, process-related impurities, and API are reported. The carryover and process-related impurities were controlled efficiently. The present work can enhance the scope and worldwide adoptability of Rebamipide (1), which is currently limited to Asian countries.

Nefopam hydrochloride is extensively used in most of the European countries until today as an analgesic because of its non-opiate (non-narcotic) and non-steroidal action with fewer side effects compared with opioid and other analgesics, which cause more troublesome side effects. A multikilogram synthesis of nefopam hydrochloride has been achieved in one pot using a single solvent (toluene). A ≥99.9% purity of the active pharmaceutical ingredient (API) was achieved in excellent overall yield (≥79%). The one-pot, five-step synthetic process involves formation of an acid chloride (3) from benzoylbenzoic acid (2) followed by amidation (4), reduction (5), cyclization (6), and formation of the hydrochloride salt (1). The major advantages include (i) use of a single solvent, (ii) >90% conversion in each step, (iii) a cost-effective and operationally friendly process, (iv) averting the formation of genotoxic impurities, and (v) improved overall yield (≥79%) provided by the one-pot operation. For the first time, we report the characterization data of API 1, intermediates 3, 4, and 5, and also a possible impurity (5a).