New Synthetic Methods towards the Nucleobase Moiety of Remdesivir

Snead et al. and the groups of Sarpong and Garg have reported new synthetic methods towards pyrrolo[2,1-f][1,2,4]-triazin-4-amine (1), the nucleobase moiety of Remdesivir. Snead’s work¹⁾ involved the use of pyrrole as a starting material to give 2 by cyanation at the 2-position and subsequent amination at the 1-position. Afterwards, 2 is treated with formamidine to obtain 1 through the formation of a 1,2,4-triazine ring. On the other hand, Sarpong and Garg et al.²⁾ chose a different approach by synthesizing the formamide 3 in two steps using 2,5-dimethoxytetrahydrofuran as a starting material and converting it into the cyanoamidine 4 by addition of cyanamide. Upon treatment of 4 with Lewis acid the synthesis of 1 is completed with the formation of a 1,2,4-triazine. 3 can also be synthesized from 1-aminopyrrole.
Remdesivir has been approved as a drug for COVID-19 in Japan and the US. In addition, other drug candidates also include the pyrrolotriazine moiety. Both methods show premise to be widely used in medicinal chemistry as new approaches to synthesize 1.