We describe the development of the practical manufacturing of Ensitrelvir, which was discovered as a SARS-CoV-2 antiviral candidate. Scalable synthetic methods of indazole, 1,2,4-triazole and 1,3,5-triazinone structures were established, and convergent couplings of these fragments enabled the development of a concise and efficient scale-up process to Ensitrelvir. In this process, introducing a meta -cresolyl moiety successfully enhanced the stability of intermediates. Compared to the initial route at the early research and development stage, the overall yield of the longest linear sequence (6 steps) was improved by approximately 7-fold. Furthermore, 9 out of the 12 isolated intermediates were crystallized directly from each reaction mixture without any extractive workup (direct isolation). This led to an efficient and environmentally friendly manufacturing process that minimizes waste of organic solvents, reagents, and processing time. This practical process for manufacturing Ensitrelvir should contribute to protection against COVID-19.

We describe the development of the practical manufacturing of Ensitrelvir, which was discovered as a SARS-CoV-2 antiviral candidate. Scalable synthetic methods of indazole, 1,2,4-triazole and 1,3,5-triazinone structures were established, and convergent couplings of these fragments enabled the development of a concise and efficient scale-up process to Ensitrelvir. In this process, introducing a meta-cresolyl moiety successfully enhanced the stability of intermediates. Compared to the initial route in the medicinal synthetic stage, the overall yield of the longest linear sequence (six steps) was improved by approximately 7-fold. Furthermore, nine out of the twelve isolated intermediates were crystallized directly from each reaction mixture without any extractive work-up (direct isolation). This led to an efficient and environmentally friendly manufacturing process that minimizes waste of organic solvents, reagents, and processing time. This practical process for manufacturing Ensitrelvir should contribute to protection against COVID-19.

An efficient and robust method was developed to introduce the triazole unit of Ensitrelvir, a COVID-19 therapeutic agent. One of the key steps is introducing the triazole unit in the triazinone with Cs2CO3 and KI in a heterogeneous system. Detailed reaction screening revealed that addition of LiCl allowed the reaction to proceed quantitatively in the presence of inexpensive Et3N, and the selectivity of the N-alkylation was greatly improved. The key to promoting the reaction is the mild formation of the lithium triazinolate accompanied by precipitation of Et3NHCl (the only insoluble matter in this reaction). Dissolving all the substrates and reagents should contribute to further improvement of the process robustness.

An efficient and robust method was developed to introduce the triazole unit of Ensitrelvir, a COVID-19 therapeutic agent. One of the key steps is introducing the triazole unit in the triazinone with Cs2CO3 and KI in a heterogeneous system. Detailed reaction screening revealed that addition of LiCl allowed the reaction to proceed quantitatively in the presence of inexpensive Et3N, and the selectivity of the N-alkylation was greatly improved. The key to promoting the reaction is the mild formation of the lithium triazinolate accompanied by precipitation of Et3N∙HCl (the only insoluble matter in this reaction). Dissolving all the substrates and reagents should contribute to further improvement of the process robustness.