Structural Optimizations of Thieno[3,2‑b]pyrrole Derivatives for the Development of Metabolically Stable Inhibitors of Chikungunya Virus

Chikungunya virus (CHIKV) is a re-emerging vector-borne alphavirus, and there is no approved effective antiviral treatment currently available for CHIKV. We previously reported the discovery of thieno­[3,2-b]­pyrrole 1b that displayed good antiviral activity against CHIKV infection in vitro. However, it has a short half-life in the presence of human liver microsomes (HLMs) (T1/2 = 2.91 min). Herein, we report further optimization studies in which potential metabolically labile sites on compound 1b were removed or modified, resulting in the identification of thieno­[3,2-b]­pyrrole 20 and pyrrolo­[2,3-d]­thiazole 23c possessing up to 17-fold increase in metabolic half-lives in HLMs and good in vivo pharmacokinetic properties. Compound 20 not only attenuated viral RNA production and displayed broad-spectrum antiviral activity against other alphaviruses and CHIKV isolates but also exhibited limited cytotoxic liability (CC50 > 100 μM). These studies have identified two compounds that have the potential for further development as antiviral drugs against CHIKV infection.