Design, Synthesis, and Lead Optimisation of CHVB Series Analogues as Potent Small Molecule Inhibitors of Chikungunya Virus

The worldwide re-emerge of the Chikungunya virus (CHIKV), the high morbidity associated with it, and the lack of an available vaccine or antiviral treatment make the development of a potent CHIKV-inhibitor highly desirable. Therefore, an extensive lead optimisation was performed based on the previously reported CHVB compound 1b and the reported synthesis route was optimised - improving the overall yield in remarkable shorter synthesis and work-up time. 100 CHVB analogues were designed, synthesised, and investigated for their antiviral activity, physiochemistry, and toxicological profile. An extensive structure-activity relationship study (SAR) was performed, which focused mainly on the combination of scaffold changes and revealed the key chemical features for a high anti-CHIKV inhibition. Further, to investigate the druggability of the compound series, a thorough ADMET investigation was carried out: the compounds were screened for their aqueous solubility, lipophilicity, their toxicity in CaCo-2 cells, and possible hERG channel interactions. Additionally, 55 analogues were assessed for their metabolic stability in human liver microsomes (HLMs) which led to a structure-metabolism relationship study (SMR). The compounds showed an excellent safety profile, favourable physicochemical characteristics, and the required metabolic stability. A cross-resistance study confirmed the viral capping machinery (nsP1) to be the viral target of these second-generation CHVB compounds. This study identified five compounds (31b, 31d, 32d, 34, and 35d) as potent, safe, and stable lead compounds for further development as selective CHIKV inhibitors - with 32d as the most promising candidate. Finally, the collected insight led to a successful scaffold hop (64b) for future antiviral research studies.