Exploring 2-methyl-substituted vitamin K3 derivatives with potent inhibitory activity against the 3CL protease of SARS-CoV-2.

Since the outbreak of the pandemic, various anti-SARS-CoV-2 drugs have been developed. In particular, 3CL protease (3C-like protease, 3CLpro) is an attractive drug target because it is an essential enzyme for viral multiplication and is present only in viruses, not in humans. To date, 3CLpro inhibitors against SARS-CoV-2 such as nirmatrelvir and ensitrelvir have been launched as oral drugs in Japan, but there is still no potent drug against SARS-CoV-2, due to issues of in vivo absorption and stability. Recently, vitamin K3 was reported to show inhibitory activity against 3CLpro of SARS-CoV-2, and the mechanism of action was predicted to be the formation of a covalent bond between the thiol group of cysteine 145, the active center of 3CLpro, and the C-3 position of vitamin K3. Therefore, we synthesized derivatives in which the 2-methyl group of the vitamin K3 was systematically converted to other substituents and examined their inhibitory activity against 3CLpro of SARS-CoV-2. The results showed that the compounds with the sulfide structure showed an approximately 4-fold increase in activity over vitamin K3. These results indicated the possibility of creating new inhibitors based on vitamin K3 and its derivatives.

Exploring Novel Vitamin K Derivatives with Anti-SARS-CoV-2 Activity.

From our compound library of vitamin K derivatives, we found that some compounds exhibited anti-SARS-CoV-2 activity in VeroE6/TMPRSS2 cells. The common structure of these compounds was menaquinone-2 (MK-2) with either the m-methylphenyl or the 1-naphthyl group introduced at the end of the side chain. Therefore, new vitamin K derivatives having more potent anti-SARS-CoV-2 activity were explored by introducing various functional groups at the ω-position of the side chain. MK-2 derivatives with a purine moiety showed the most potent antiviral activity among the derivatives. We also found that their mechanism of action was the inhibition of RNA-dependent RNA polymerase (RdRp) of SARS-CoV-2. The chemical structures of our compounds were completely different from those of nucleic acid derivatives such as remdesivir and molnupiravir, clinically approved RdRp inhibitors for COVID-19 treatment, suggesting that our compounds may be effective against viruses resistant to these nucleic acid derivatives.

Effect of lonidamine derivatives on the inhibition of transformed cell area expansion.

Expansion of transformed cell area is regulated by the surrounding nontransformed cells. Lonidamine (LND) was recently found to regulate transformed cell area expansion through suppressing the cell motility of nontransformed cells; however, the structure-activity relationship between LND and this inhibitory activity has yet to be elucidated. We synthesized several LND derivatives and evaluated their inhibitory activity against the expansion of transformed cell area and found that the halogenation pattern on the benzene ring moiety, the carboxylic acid moiety, and the overall hydrophobicity of the molecule were correlated with inhibition activity. We also found that the localization of the tight junction protein, zonula occludens-1 (ZO-1), in nontransformed cells was significantly altered after treatment with the LND derivatives that displayed inhibitory activity. Further studies with LND derivatives and monitoring the localization of ZO-1 may help to develop more active compounds for suppressing transformed cell area expansion and lead to new anticancer treatments.