Synthesis of Antiviral Drug Tecovirimat and Its Key Maleimide Intermediates Using Organocatalytic Mumm Rearrangement at Ambient Conditions.

Tecovirimat is an antiviral agent approved for the treatment of orthopoxvirus infections including smallpox, cowpox and monkeypox. A key challenge in its synthesis lies in the generation of maleimide intermediates, which traditionally requires high-temperature thermal rearrangement and often results in low-to-moderate yields. Classical methods rely on heating in toluene above 70 °C, limiting scalability and efficiency. Herein, we present a mild and efficient organocatalytic approach to the synthesis of tecovirimat intermediates, using a room-temperature Mumm rearrangement of isomaleimide precursors. The reaction is catalyzed by 10 mol% imidazole and N-hydroxysuccinimide. As a representative example for one of the tecovirimat synthesis methods, intermediate N-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-4-(trifluoromethyl)benzamide was synthesized from p-trifluoromethylbenzohydrazide at a 71% yield over two steps. Additionally, N-(2,5-dioxopyrrol-1-yl)(tert-butoxy)formamide was obtained from Boc-hydrazide at a 37% yield. The methodology was sufficiently extended to other benzohydrazide-derived isomaleimides. To support the mechanistic rationale, preliminary PM7 semiempirical computational studies were performed, highlighting the electronic features facilitating the transformation. This work offers a practical and scalable route to tecovirimat intermediates, overcoming key synthetic bottlenecks and enhancing the efficiency of antiviral drug production.