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Evidence-Based Complementary and Alternative Medicine
Volume 2 (2005), Issue 2, Pages 209-215
Original Article

Inhibition of SARS-CoV 3C-like Protease Activity by Theaflavin-3,3'-digallate (TF3)

1Division of Biotechnology and Pharmaceutical Research, National Health Research Institutes, Taipei, Taiwan
2Institute of Biological Chemistry, Academia Sinica, Taipei, Taiwan
3Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan

Received 30 September 2004; Accepted 11 March 2005

Copyright © 2005 Chia-Nan Chen et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


SARS-CoV is the causative agent of severe acute respiratory syndrome (SARS). The virally encoded 3C-like protease (3CLPro) has been presumed critical for the viral replication of SARS-CoV in infected host cells. In this study, we screened a natural product library consisting of 720 compounds for inhibitory activity against 3CLPro. Two compounds in the library were found to be inhibitive: tannic acid (IC50 = 3 µM) and 3-isotheaflavin-3-gallate (TF2B) (IC50 = 7 µM). These two compounds belong to a group of natural polyphenols found in tea. We further investigated the 3CLPro-inhibitory activity of extracts from several different types of teas, including green tea, oolong tea, Puer tea and black tea. Our results indicated that extracts from Puer and black tea were more potent than that from green or oolong teas in their inhibitory activities against 3CLPro. Several other known compositions in teas were also evaluated for their activities in inhibiting 3CLPro. We found that caffeine, (—)-epigallocatechin gallte (EGCg), epicatechin (EC), theophylline (TP), catechin (C), epicatechin gallate (ECg) and epigallocatechin (EGC) did not inhibit 3CLPro activity. Only theaflavin-3,3′-digallate (TF3) was found to be a 3CLPro inhibitor. This study has resulted in the identification of new compounds that are effective 3CLPro inhibitors.