Cannabinoid-Inspired Inhibitors of the SARS-CoV-2 Coronavirus 2′-O-Methyltransferase (2′-O-MTase) Non-Structural Protein (Nsp10–16)

The design and synthesis of antiviral compounds were guided by computationally predicted data against highly conserved non-structural proteins (Nsps) of the SARS-CoV-2 coronavirus. Chromenephenylmethanone-1 (CPM-1), a novel biphenylpyran (BPP), was selected from a unique natural product library based on in silico docking scores to coronavirus Nsps with high specificity to the methyltransferase protein (2'-<i>O</i>-MTase, Nsp10-16), which is responsible for viral mRNA maturation and host innate immune response evasion. To target the 2'-<i>O</i>-MTase, CPM-1, along with intermediate BPP regioisomers, tetrahydrophenylmethanones (TPMs), were synthesized and structurally validated via nuclear magnetic resonance (NMR) data and DP4+ structure probability analyses. To investigate the activity of these BPPs, the following in vitro assays were conducted: SARS-CoV-2 inhibition, biochemical target validation, mutagenicity, and cytotoxicity. CPM-1 possessed notable activity against SARS-CoV-2 with 98.9% inhibition at 10 µM and an EC₅₀ of 7.65 µM, as well as inhibition of SARS-CoV-2's 2'-<i>O</i>-MTase (expressed and purified) with an IC₅₀ of 1.5 ± 0.2 µM. In addition, CPM-1 revealed no cytotoxicity (CC₅₀ of >100 µM) or mutagenicity (no frameshift or base-pair mutations). This study demonstrates the potential of computational modeling for the discovery of natural product prototypes followed by the design and synthesis of drug leads to inhibit the SARS-CoV-2 2'-<i>O</i>-MTase.