Exploring new catechin derivatives as SARS-CoV-2 Mpro inhibitors from tea by molecular networking, surface plasma resonance, enzyme inhibition, induced fit docking, and metadynamics simulations.

SARS-CoV-2 Mpro (Mpro) is the critical cysteine protease in coronavirus viral replication. Tea polyphenols are effective Mpro inhibitors. Therefore, we aim to isolate and synthesize more novel tea polyphenols from Zhenghedabai (ZHDB) white tea methanol-water (MW) extracts that might inhibit COVID-19. Through molecular networking, 33 compounds were identified and divided into 5 clusters. Further, natural products molecular network (MN) analysis showed that MN1 has new phenylpropanoid-substituted ester-catechin (PSEC), and MN5 has the important basic compound type hydroxycinnamoylcatechins (HCCs). Thus, a new PSEC (1, PSEC636) was isolated, which can be further detected in 14 green tea samples. A series of HCCs were synthesized (2-6), including three new acetylated HCCs (3-5). Then we used surface plasmon resonance (SPR) to analyze the equilibrium dissociation constants (KD) for the interaction of 12 catechins and Mpro. The KD values of PSEC636 (1), EGC-C (2), and EC-CDA (3) were 2.25, 2.81, and 2.44 µM, respectively. Moreover, compounds 1, 2, and 3 showed the potential Mpro inhibition with IC50 5.95 ± 0.17, 9.09 ± 0.22, and 23.10 ± 0.69 µM, respectively. Further, we used induced fit docking (IFD), binding pose metadynamics (BPMD), and molecular dynamics (MD) to explore the stable binding pose of Mpro-1, showing that 1 could tightly bond with the amino acid residues THR26, HIS41, CYS44, TYR54, GLU166, and ASP187. The computer modeling studies reveal that the ester, acetyl, and pyrogallol groups could improve inhibitory activity. Our research suggests that these catechins are effective Mpro inhibitors, and might be developed as therapeutics against COVID-19.

Discovery of honokiol thioethers containing 1,3,4-oxadiazole moieties as potential α-glucosidase and SARS-CoV-2 entry inhibitors.

Honokiol, isolated from a traditional Chinese medicine (TCM) Magnolia officinalis, is a biphenolic compound with several biological activities. To improve and broaden its biological activity, herein, two series of honokiol thioethers bearing 1,3,4-oxadiazole moieties were prepared and assessed for their α-glucosidase and SARS-CoV-2 entry inhibitory activities. Among all the honokiol thioethers, compound 7l exhibited the strongest α-glucosidase inhibitory effect with an IC50 value of 18.9 ± 2.3 µM, which was superior to the reference drug acarbose (IC50 = 24.4 ± 0.3 µM). Some interesting results of structure-activity relationships (SARs) have also been discussed. Enzyme kinetic study demonstrated that 7l was a noncompetitive α-glucosidase inhibitor, which was further supported by the results of molecular docking. Moreover, honokiol thioethers 7e, 9a, 9e, and 9r exhibited potent antiviral activity against SARS-CoV-2 pseudovirus entering into HEK-293 T-ACE2h. Especially 9a displayed the strongest inhibitory activity against SARS-CoV-2 pseudovirus entry with an IC50 value of 16.96 ± 2.45 µM, which was lower than the positive control Evans blue (21.98 ± 1.98 µM). Biolayer interferometry (BLI) binding and docking studies suggested that 9a and 9r may effectively block the binding of SARS-CoV-2 to the host ACE2 receptor through dual recognition of SARS-CoV-2 spike RBD and human ACE2. Additionally, the potent honokiol thioethers 7l, 9a, and 9r displayed relatively no cytotoxicity to normal cells (LO2). These findings will provide a theoretical basis for the discovery of honokiol derivatives as potential both α-glucosidase and SARS-CoV-2 entry inhibitors.