Identification, optimization, and biological evaluation of 3-O-β-chacotriosyl ursolic acid derivatives as novel SARS-CoV-2 entry inhibitors by targeting the prefusion state of spike protein.

The COVID-19 pandemic generates a global threat to public health and continuously emerging SARS-CoV-2 variants bring a great challenge to the development of both vaccines and antiviral agents. In this study, we identified UA-18 and its optimized analog UA-30 via the hit-to-lead strategy as novel SARS-CoV-2 fusion inhibitors. The lead compound UA-30 showed potent antiviral activity against infectious SARS-CoV-2 (wuhan-HU-1 variant) in Vero-E6 cells and was also effective against infection of diverse pseudotyped SARS-CoV-2 variants with mutations in the S protein including the Omicron and Delta variants. More importantly, UA-30 might target the cavity between S1 and S2 subunits to stabilize the prefusion state of the SARS-CoV-2 S protein, thus leading to interfering with virus-cell membrane fusion. This study offers a set of novel SARS-CoV-2 fusion inhibitors against SARS-CoV-2 and its variants based on the 3- O -β-chacotriosyl UA skeleton. [Display omitted] • A set of 3-O-β-chacotriosyl UA saponins were synthesized and characterized. • These saponins showed potent inhibition toward diverse pseudotyped SARS-CoV-2 variants with mutations in S. • Intensive structure-activity relationships were conducted. • Lead compound UA-30 displayed improved anti-SARS-CoV-2 activity in vitro and SI. • UA-30 was shown to bind to SARS-CoV-2 S2 protein directly and block the prefusion state of spike protein. [ABSTRACT FROM AUTHOR]