Pyrogallol B-ring enhances catechin binding to the SARS-CoV-2 spike receptor-binding domain to inhibit interaction with ACE2.

Severe acute respiratory syndrome coronavirus 2 infects host cells through binding of the spike protein receptor-binding domain (RBD) to the human angiotensin-converting enzyme 2 receptor. In this study, the antiviral activity of 14 catechin derivatives was evaluated using a pseudovirus assay that emulates spike-mediated cell fusion. Of these, gallocatechin gallate, epigallocatechin gallate, epigallocatechin 3-(3″-O-methyl) gallate, and epigallocatechin exhibit strong inhibitory effects on infection. A structural comparison of the compounds revealed that catechins with a pyrogallol-type B-ring configuration exhibited greater inhibitory effects than their catechol-type counterparts. Docking simulations demonstrated that the hydroxyl group at the 5-position of the B-ring forms a hydrogen bond with Gln493 on the spike RBD, thereby facilitating additional stabilizing interactions with adjacent residues, such as Tyr453. Although catechin bioavailability is low, the results of this study suggest that regular consumption or gargling may offer localized antiviral activity at mucosal surfaces, such as those found in the oral or nasal cavity, because the catechin concentrations used in the cell assays are similar to those observed in green tea (100 µM). This study underscores the potential of pyrogallol-type catechins to act as antiviral agents.