Protocatechuic acid methyl ester for COVID-19

Background/Objectives: Since the emergence of the COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the discovery of compounds with antiviral potential from medicinal plants has been extensively researched. This study aimed to investigate plant metabolites with in vitro inhibitory potential against SARS-CoV-2 targets, including 3CLpro, PLpro, Spike protein, and RdRp. Methods: A systematic review was conducted following PRISMA guidelines, with literature searches performed in six electronic databases (Scielo, ScienceDirect, Scopus, Springer, Web of Science, and PubMed) from January 2020 to February 2024. Computational analyses using SwissADME, pkCSM, ADMETlab, ProTox3, Toxtree, and DataWarrior were performed to predict the absorption, distribution, metabolism, excretion, and toxicity (ADMET) profiles as well as other medicinal chemistry parameters of these compounds. Results: A total of 330 plant-derived compounds with inhibitory activities against the proposed targets were identified, with compounds showing IC50 values as low as 0.01 μM. Our findings suggest that several plant metabolites exhibit significant in vitro inhibition of SARS-CoV-2 targets; however, few molecules exhibit drug development viability without further adjustments. Additionally, after these evaluations, two phenolic acids, salvianic acid A and protocatechuic acid methyl ester, stood out for their potential as candidates for developing antiviral therapies, with IC50 values of 2.15 μM against 3CLpro and 3.76 μM against PLpro; respectively; and satisfactory in silico drug-likeness and ADMET profiles. Conclusions: These results reinforce the importance of plant metabolites as potential targets for antiviral drug discovery.