Exploring Psidium guajava L. Leaf Fractions as a Sustainable Source of Antiviral Compounds for the Inhibition of SARS-CoV-2 Spike–ACE2 Interaction (Wuhan and Omicron) and 3CLpro Activity

The leaves of Psidium guajava L. (guava) are an underutilized resource containing diverse bioactive metabolites. The present study evaluated the inhibitory potential of P. guajava leaf fractions against two SARS-CoV-2 molecular targets: the Spike RBD–ACE2 interaction of the Wuhan and Omicron BA.1 variants, and 3CLpro enzymatic activity. A methanolic extract was fractionated by vacuum liquid chromatography, and fraction F14 was then separated into subfractions F14A–F14D through the use of Sephadex LH-20. The activity was evaluated using colorimetric Spike RBD–ACE2 binding assays and a fluorometric 3CLpro assay. F14 and its subfractions inhibited the Spike RBD–ACE2 interaction of the Wuhan variant, whereas against Omicron BA.1, all fractions showed IC₅₀ values <1.25 mg mL−1. F14, F14C, and F14D also inhibited 3CLpro, with IC₅₀ values <1.25 mg mL⁻¹. F14D demonstrated the most consistent inhibitory profile across all the three targets and was selected for further characterization by LC–HRMS. The three major constituents were tentatively assigned as a myricetin hexoside, a quercetin hexoside, and a quercetin pentoside. Overall, the results of this study suggest that F14D contains bioactive constituents with potential inhibitory activity against SARS-CoV-2 molecular targets, although further studies are required to determine their antiviral activity.