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Article

Synthesis and Biochemical Evaluation of 8H-Indeno[1,2-d]thiazole Derivatives as Novel SARS-CoV-2 3CL Protease Inhibitors

by
Jing Wu
1,†,
Bo Feng
2,3,†,
Li-Xin Gao
1,3,
Chun Zhang
1,
Jia Li
2,3,4,
Da-Jun Xiang
5,*,
Yi Zang
3,* and
Wen-Long Wang
1,*
1
School of Life Sciences and Health Engineering, Jiangnan University, Wuxi 214122, China
2
School of Life Science and Biopharmaceutics, Shenyang Pharmaceutical University, Shenyang 110016, China
3
State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China
4
Zhongshan Institute for Drug Discovery, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Zhongshan Tsuihang New District, Zhongshan 528400, China
5
Xishan People’s Hospital of Wuxi City, Wuxi 214105, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Molecules 2022, 27(10), 3359; https://doi.org/10.3390/molecules27103359
Submission received: 19 April 2022 / Revised: 17 May 2022 / Accepted: 17 May 2022 / Published: 23 May 2022
(This article belongs to the Special Issue Synthesis of Heteroaromatic Compounds)
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Abstract

:
The COVID-19 pandemic caused by SARS-CoV-2 is a global burden on human health and economy. The 3-Chymotrypsin-like cysteine protease (3CLpro) becomes an attractive target for SARS-CoV-2 due to its important role in viral replication. We synthesized a series of 8H-indeno[1,2-d]thiazole derivatives and evaluated their biochemical activities against SARS-CoV-2 3CLpro. Among them, the representative compound 7a displayed inhibitory activity with an IC50 of 1.28 ± 0.17 μM against SARS-CoV-2 3CLpro. Molecular docking of 7a against 3CLpro was performed and the binding mode was rationalized. These preliminary results provide a unique prototype for the development of novel inhibitors against SARS-CoV-2 3CLpro.

1. Introduction

The global pandemic of coronavirus disease (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has posted major challenges to public health systems and the economy worldwide [1,2,3,4,5]. There have been 434 million confirmed cases of COVID-19 worldwide as of the end of February 2022, and almost 6 million deaths have been reported [6]. Although multiple effective vaccines against COVID-19 are available, reinfections and breakthrough infections are frequently reported [7,8]. In addition, the virus is continuing to evolve, and a new variant named Omicron enables the virus to evade the immune protective barrier due to a large number of mutations in the receptor binding sites [9,10,11]. Therefore, it is urgent to develop effective drugs and specific treatments for people who are infected by COVID-19 with severe symptoms.
3CLpro (also called Mpro) plays an essential role during replication and transcription of SARS-CoV-2 and has been regarded as an attractive target for treating COVID-19 and other coronavirus-caused diseases [12,13,14]. The development of 3CLpro inhibitors has attracted much attention from medicinal chemists and the pharmaceutical industry. The collective efforts culminated in the recent approval of Paxlovid (nirmatrelvir) by FDA for the treatment of SARS-CoV-2 [15]. As shown in Figure 1, Most known 3CLpro inhibitors are peptidomimetic inhibitors containing a warhead of Michael acceptor, such as nirmatrelvir with nitrile [16], YH-53 with benzothiazolyl ketone [17], compound 1 with α-ketoamide [18], and compound 2 with aldehyde [19]. Others are nonpeptidic inhibitors including covalent and noncovalent inhibitors. Covalent inhibitors, such as Carmofur, Shikonin [20], and 3 [21], are identified by high-throughput screening. Noncovalent inhibitor CCF0058981 [22] and flavonoid analogs (baicalin, baicalein, and 4′-O-Methylscutellarein) [23,24] were obtained through structure-based optimization and from traditional Chinese medicines, respectively.
In pursuit of novel 3CLpro inhibitors, we identified 8H-indeno[1,2-d]thiazole derivative 4 as a novel SARS-CoV-2 3CLpro inhibitor (IC50 = 6.42 ± 0.90 μM) through high-throughput screening of our compound collection (Figure 2). This result provided us with an opportunity to explore novel small molecule inhibitors against SARS-CoV-2 3CLpro. Herein, we designed and synthesized a series of 8H-indeno[1,2-d]thiazole derivatives, evaluated their inhibitory activities against SARS-CoV-2 3CLpro, and elucidated the SARs. Selected compound 7a was subjected to molecular docking to predict the binding mode with SARS-CoV-2 3CLpro.

2. Results and Discussion

2.1. Design and Synthesis of 8H-Indeno[1,2-d]thiazole Derivatives

Based on the structure of compound 4, 14 new 8H-indeno[1,2-d]thiazole derivatives (compounds 7a–7l, and 10a–10b) (shown in Scheme 1 and Scheme 2) were designed and synthesized through a two-step synthesis from the appropriate ketone and thiourea [25,26,27,28]. Adjusting the methoxy group of compound 4 from position 5 to position 6 afforded compound 7a. Considering the effects of steric hindrance and electron withdrawing, compounds 7b–7e were synthesized by substitution of the methoxy group for the butoxy, isobutoxy, and methyl groups and for the chlorine atom. After replacing the 3,5-dimethoxybenzamido moiety in compound 7a with 3,4,5-trimethoxybenzamido, 3,5-diacetoxybenzamido, 3-methoxybenzamido, 3-fluorobenzamido, thiophene-2-carboxamido, and 4-chlorobenzamido, compounds 7f–7k were obtained. To evaluate the effect of ring expansion, compound 7l was synthesized. Finally, ring opening analogues 10a and 10b were synthesized to elucidate the effect of the central ring on the inhibition of 3CLpro.

2.2. SARS-CoV-2 3CLpro Inhibitory Activities and Structure-Activity Relationships

All synthesized compounds were evaluated for inhibitory activity against SARS-CoV-2 3CLpro using PF-07321332 as positive control [29,30,31], and the results were detailed in Table 1. We initially prepared 7a from the commercially available compound 5a by the route outlined in Scheme 1. We noticed that compound 7a with 6-methoxy group on the phenyl ring exhibited inhibitory activity against SARS-CoV-2 3CLpro with 1.28 ± 0.17 μM, about five times more potent than compound 4 with 5-methoxy group on the phenyl ring. The result indicated that the position of the methoxy group on the phenyl ring significantly affected inhibitory activities against SARS-CoV-2 3CLpro. To explore the SAR of this seemingly important position, methoxy group on compound 7a was replaced by butoxy (7b), isobutoxy (7c), methyl groups (7d), and chlorine atom (7e); the inhibitory activities of the corresponding compounds 7b–7e were completely abolished. These results demonstrated that the effect of steric hindrance at this position was detrimental to inhibitory activities. The SAR of R3 was explored next. Replacement of the 3,5-dimethoxybenzamido moiety with 3,4,5-trimethoxybenzamido moiety, 3,5-diacetoxybenzamido moiety, 3-methoxybenzamido moiety, 3-fluorobenzamido moiety, thiophene-2-carboxamido moiety, and 4-chlorobenzamido moiety led to compounds 7f, 7g, 7h, 7i, 7j, and 7k, respectively. The inhibitory activity of compounds 7f and 7g dropped significantly, while compound 7h almost maintained its inhibitory activities. These results indicated that the extra steric hindrance had negative impact on the inhibitory activities. Compared to compound 7h, the inhibitory activities of compounds 7i–7k diminished; these results indicated that introduction of an electron-withdrawing group or heterocyclic ring on the scaffold of 8H-indeno[1,2-d]thiazole took negative roles for inhibitory activities. Expanding the five-membered ring on compound 7a to a six-membered ring led to compound 7l, which unfortunately did not show any inhibitory activity against SARS-CoV-2 3CLpro. Opening the five-membered ring on compound 7a resulted in compounds 10a and 10b, which also lost inhibitory activities. These results indicated that the five-membered ring on compound 7a is important for the inhibitory activity against SARS-CoV-2 3CLpro.

2.3. Predicting Binding Mode of 7a with 3CLpro

To explore the interaction mode between small molecule 7a and 3CLpro (PDB code: 6M2N) [23], we carried out molecular docking by applying AutoDock 4.2 program [31,32,33,34]. Figure 3a showed that 7a docked well into the binding pockets S1 and S2 of 3CLpro, in which the S1, S2 sites play a key role in substrate recognition [35]. As illustrated in Figure 3b, the indene moiety of compound 7a buried deeply into the hydrophobic S2 subsite with π-electrons with Arg188 and hydrophobic interaction with Met165; the 3,5-dimethoxybenzamido moiety of compound 7a formed strong H-bonds with Asn142, Glu166 on S1 subsite, while compounds 4 and 7h escaped from S1 subsite, as shown in Supplementary Materials Figures S1 and S2.

3. Materials and Methods

3.1. Chemistry

All chemical reagents are reagent grade and used as purchased. 1H NMR (400 MHz) spectra were recorded on a Bruker AVIII 400 MHz spectrometer (Bruker, Billerica, MA, USA). The chemical shifts were reported in parts per million (ppm) using the 2.50 signal of DMSO (1H NMR) and the 39.52 signal of DMSO (13C NMR) as internal standards. ESI Mass spectra (MS) were obtained on a SHIMADZU 2020 Liquid Chromatograph Mass Spectrometer (SHIMADZU, Kyoto, Japan).

3.1.1. General Procedure for the Synthesis of Compounds 7a–7k (Exemplified by 7a)

To a solution of 5a (6.2 mmol, 1.0 equiv) in dry ethanol (25 mL) were added thiourea (12.4 mmol, 2.0 equiv) and bromine (6.8 mmol, 1.1 equiv) at room temperature. The reaction solution was stirred at 100 °C for 5–6 h, At the end of the reaction, the solvent was evaporated, and aqueous ammonium hydroxide (25%) was added to the residue. The precipitated solid was collected without purification for the next step. The mixture of 6a (2.2 mmol, 1.1 equiv), aromatic acid (2.0 mmol, 1.0 equiv), HATU (2.0 mmol, 1.0 equiv), and DIPEA (6.0 mmol, 3.0 equiv) in DMF (15 mL) was stirred at room temperature for 2 h. The reaction mixture was quenched with water. The aqueous layer was extracted with EtOAc (30 mL × 2). The combined organic layers were dried over Na2SO4. The residue was purified by column chromatography on silica gel (eluting with DCM) to afford compound 7a as a yellow solid (280.0 mg, yield 37%). 1H NMR (400 MHz, DMSO-d6) δ 12.81 (s, 1H), 7.46 (d, J = 8.4 Hz, 1H), 7.33 (d, J = 2.0 Hz, 2H), 7.22 (d, J = 2.0 Hz, 1H), 6.94 (dd, J = 8.0, 2.4 Hz, 1H), 6.74 (t, J = 2.0 Hz, 1H), 3.87 (s, 2H), 3.84 (s, 6H), 3.80 (s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 164.22, 162.12, 160.52, 157.76, 155.03, 147.98, 133.82, 130.05, 128.39, 118.28, 112.37, 111.83, 105.74, 105.08, 55.60, 55.36, 32.43 ppm. MS (ESI): m/z calcd for C20H19N2O4S [M + H]+ 383.11, found 383.20.
N-(6-butoxy-8H-indeno[1,2-d]thiazol-2-yl)-3,5-dimethoxybenzamide (7b), eluting with DCM, yield = 32%; 1H NMR (400 MHz, DMSO-d6) δ 12.81 (s, 1H), 7.43 (d, J = 8.0 Hz, 1H), 7.33 (d, J = 2.4 Hz, 2H), 7.18 (s, 1H), 6.91 (dd, J = 8.4, 2.4 Hz, 1H), 6.73 (d, J = 2.4 Hz, 1H), 3.99 (t, J = 6.4 Hz, 2H), 3.84 (s, 2H), 3.83 (s, 6H), 1.74–1.67 (m, 2H), 1.49–1.40 (m, 2H), 0.95–0.91 (m, 3H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 164.25, 162.15, 160.54, 157.20, 155.04, 147.96, 133.85, 129.95, 128.32, 118.29, 112.97, 112.39, 105.76, 105.10, 67.48, 55.62, 32.43, 30.89, 18.84, 13.76 ppm. MS (ESI): m/z calcd for C23H25N2O4S [M + H]+ 425.15, found 425.10.
N-(6-isobutoxy-8H-indeno[1,2-d]thiazol-2-yl)-3,5-dimethoxybenzamide (7c), eluting with DCM, yield = 40%; 1H NMR (400 MHz, DMSO-d6) δ 8.27 (s, 1H), 7.43 (dd, J = 8.4, 3.2 Hz, 1H), 7.36–7.32 (m, 2H), 7.19 (d, J = 2.8 Hz, 1H), 6.92 (dd, J = 8.4, 3.2 Hz, 1H), 6.73 (t, J = 2.4 Hz, 1H), 3.85 (s, 2H), 3.83 (s, 6H), 3.78 (d, J = 6.4 Hz, 2H), 2.06–2.00 (m, 1H), 0.99 (d, J = 7.2 Hz, 6H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 164.25, 162.17, 160.50, 157.26, 154.99, 147.94, 133.86, 129.95, 128.31, 118.26, 112.99, 112.45, 105.74, 105.06, 74.11, 55.59, 32.41, 27.78, 19.11 ppm. MS (ESI): m/z calcd for C23H25N2O4S [M + H]+ 425.15, found 425.20.
3,5-dimethoxy-N-(6-methyl-8H-indeno[1,2-d]thiazol-2-yl)benzamide (7d), eluting with DCM, yield = 47%; 1H NMR (400 MHz, DMSO-d6) δ 12.81 (s, 1H), 7.45 (d, J = 7.6 Hz, 1H), 7.39 (s, 1H), 7.34 (d, J = 2.4 Hz, 2H), 7.18 (d, J = 7.6 Hz, 1H), 6.74 (t, J = 2.0 Hz, 1H), 3.87 (s, 2H), 3.84 (s, 6H), 2.38 (s, 3H) ppm; 13C NMR (100 MHz, DMSO-d6) δ 164.26, 162.14, 160.50, 155.22, 146.31, 134.42, 134.30, 133.78, 129.84, 127.40, 126.00, 117.56, 105.73, 105.09, 55.58, 32.16, 21.13 ppm. MS (ESI): m/z calcd for C20H19N2O3S [M + H]+ 367.11, found 366.95.
N-(6-chloro-8H-indeno[1,2-d]thiazol-2-yl)-3,5-dimethoxybenzamide (7e), eluting with DCM, yield = 39%; 1H NMR (400 MHz, DMSO-d6) δ 12.85 (s, 1H), 7.64 (d, J = 1.6 Hz, 1H), 7.54 (d, J = 8.0 Hz, 1H), 7.42 (dd, J = 8.0, 2.0 Hz, 1H), 7.33 (d, J = 2.0 Hz, 2H), 6.74 (t, J = 2.0 Hz, 1H), 3.94 (s, 2H), 3.84 (s, 6H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 164.36, 162.60, 160.48, 154.14, 148.13, 135.82, 133.64, 131.60, 129.72, 126.87, 125.43, 118.83, 105.75, 105.13, 55.57, 32.49 ppm. MS (ESI): m/z calcd for C19H16ClN2O3S [M + H]+ 387.06, found 387.15.
3,5-dimethoxy-N-(5-methoxy-8H-indeno[1,2-d]thiazol-2-yl)benzamide (4), eluting with DCM, yield = 50%; 1H NMR (400 MHz, DMSO-d6) δ 12.80 (s, 1H), 7.44 (d, J = 8.4 Hz, 1H), 7.34 (d, J = 2.4 Hz, 2H), 7.07 (d, J = 2.4 Hz, 1H), 6.81 (dd, J = 8.4, 2.4 Hz, 1H), 6.73 (t, J = 2.4 Hz, 1H), 3.83 (s, 6H), 3.82 (s, 2H), 3.81 (s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 164.32, 162.22, 160.50, 158.81, 138.17, 137.75, 133.77, 132.04, 125.68, 110.29, 105.74, 105.10, 104.65, 103.93, 55.58, 55.20, 31.64 ppm. MS (ESI): m/z calcd for C20H19N2O4S [M + H]+ 383.11, found 383.15.
3,4,5-trimethoxy-N-(6-methoxy-8H-indeno[1,2-d]thiazol-2-yl)benzamide (7f), eluting with DCM, yield = 44%; 1H NMR (400 MHz, DMSO-d6) δ 12.76 (s, 1H), 7.52 (s, 2H), 7.45 (d, J = 8.4 Hz, 1H), 7.21 (d, J = 2.4 Hz, 1H), 6.93 (dd, J = 8.4, 2.4 Hz, 1H), 3.89 (s, 6H), 3.86 (s, 2H), 3.80 (s, 3H), 3.75 (s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 163.94, 162.29, 157.73, 154.98, 152.79, 147.95, 141.00, 130.07, 128.23, 126.73, 118.20, 112.35, 111.81, 105.61, 60.14, 56.11, 55.35, 32.41 ppm. MS (ESI): m/z calcd for C21H21N2O5S [M + H]+ 413.12, found 413.15.
5-((6-methoxy-8H-indeno[1,2-d]thiazol-2-yl)carbamoyl)-1,3-phenylene diacetate (7g), eluting with DCM, yield = 25%; 1H NMR (400 MHz, DMSO-d6) δ 12.91 (s, 1H), 7.86 (d, J = 2.0 Hz, 2H), 7.46 (d, J = 8.4 Hz, 1H), 7.33 (t, J = 2.0 Hz, 1H), 7.22 (d, J = 2.0 Hz, 1H), 6.94 (dd, J = 8.4, 2.0 Hz, 1H), 3.88 (s, 2H), 3.80 (s, 3H), 2.33 (s, 6H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 172.06, 169.05, 164.01, 158.37, 157.74, 151.38, 147.94, 134.01, 130.00, 128.36,119.23, 118.29, 113.15, 112.35, 111.83, 55.35, 32.42, 20.86 ppm. MS (ESI): m/z calcd for C22H19N2O6S [M + H]+ 439.10, found 439.05
3-methoxy-N-(6-methoxy-8H-indeno[1,2-d]thiazol-2-yl)benzamide (7h), eluting with DCM, yield = 47%; 1H NMR (400 MHz, DMSO-d6) δ 12.81 (s, 1H), 7.72–7.70 (m, 2H), 7.48–7.44 (m, 2H), 7.22–7.18 (m, 2H), 6.94 (dd, J = 8.0, 2.4 Hz, 1H), 3.88 (s, 2H), 3.86 (s, 3H), 3.80 (s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 164.43, 162.14, 159.31, 157.73, 155.00, 147.95, 133.25, 130.05, 129.78, 128.32, 120.45, 119.02, 118.26, 112.58, 112.34, 111.80, 55.41, 55.34, 32.40 ppm. MS (ESI): m/z calcd for C19H17N2O3S [M + H]+ 353.10, found 353.15.
3-fluoro-N-(6-methoxy-8H-indeno[1,2-d]thiazol-2-yl)benzamide (7i), eluting with DCM, yield = 34%; 1H NMR (400 MHz, DMSO-d6) δ 12.92 (s, 1H), 8.00–7.94 (m, 2H), 7.65–7.59 (m, 1H), 7.52 (dd, J =8.4, 2.4 Hz, 1H), 7.47 (d, J = 8.0 Hz, 1H), 7.22 (d, J = 2.4 Hz, 1H), 6.94 (dd, J = 8.0, 2.4 Hz, 1H), 3.88 (s, 2H), 3.80 (s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 163.43,163.21, 161.90, 160.77, 157.77, 147.93, 134.26, 130.84 (d, J = 8.0 Hz), 129.95, 128.48, 124.36 (d, J = 3.0 Hz), 119.52 (d, J = 21.0 Hz), 118.30, 114.91 (d, J = 23.0 Hz), 112.36, 111.80, 55.34, 32.42 ppm. MS (ESI): m/z calcd for C18H14FN2O2S [M + H]+ 341.08, found 341.05.
N-(6-methoxy-8H-indeno[1,2-d]thiazol-2-yl)thiophene-2-carboxamide (7j), eluting with DCM, yield = 30%; 1H NMR (400 MHz, DMSO-d6) δ 12.92 (s, 1H), 8.28 (d, J = 8.0 Hz, 1H), 7.98 (d, J = 4.8 Hz, 1H), 7.45 (d, J = 8.0 Hz, 1H), 7.27 (t, J = 4.8 Hz, 1H), 7.22 (d, J = 2.4 Hz, 1H), 6.94 (dd, J = 8.0, 2.4 Hz, 1H), 3.87 (s, 2H), 3.80 (s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 161.76, 159.35, 157.74, 154.97, 147.91, 137.30, 133.61, 130.69, 129.96, 128.64, 128.29, 118.24, 112.34, 111.78, 55.33, 32.43 ppm. MS (ESI): m/z calcd for C16H13N2O2S2 [M + H]+ 329.04, found 329.10.
4-chloro-N-(6-methoxy-8H-indeno[1,2-d]thiazol-2-yl)benzamide (7k), eluting with DCM, yield = 38%; 1H NMR (400 MHz, DMSO-d6) δ 12.90 (s, 1H), 8.14 (dt, J = 8.8, 2.0 Hz, 2H), 7.63 (dt, J = 8.4, 2.0 Hz, 2H), 7.47 (d, J = 8.4 Hz, 1H), 7.22 (d, J = 2.0 Hz, 1H), 6.94 (dd, J = 8.4, 2.4 Hz, 1H), 3.88 (s, 2H), 3.80 (s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 163.77, 162.03, 157.74, 154.90, 147.93, 137.48, 130.82, 130.03, 129.97, 128.73, 128.38, 118.28, 112.34, 111.79, 55.34, 32.41 ppm. MS (ESI): m/z calcd for C18H14ClN2O2S [M + H]+ 357.05, found 356.90.

3.1.2. Procedure for the Synthesis of Compound 7l

To a solution of 5f (528.2 mg, 3.0 mmol) in dry ethanol (10 mL) were added thiourea (456.7 mg, 6.0 mmol) and bromine (0.2 mL, 3.3 mmol) at room temperature. The reaction solution was stirred at 100 °C for 5–6 h. At the end of the reaction, the solvent was evaporated and aqueous ammonium hydroxide (25%) was added to the residue. The precipitated solid 6f was collected without purification for the next step. The mixture of 6f (255.2 mg, 1.1 mmol), 3,5-dimethoxybenzoic acid (182.1 mg, 1.0 mmol), HATU (380.2 mg, 1.0 mmol), and DIPEA (0.5 mL 3.0 mmol) in DMF (6 mL) was stirred at room temperature for 2 h. The reaction mixture was quenched with water. The aqueous layer was extracted with EtOAc (20 mL × 2). The combined organic layers were dried over Na2SO4. The residue was purified by column chromatography on silica gel (eluting with DCM) to afford compound 7l (103.0 mg, yield 26%) as a white solid.
1H NMR (400 MHz, DMSO-d6) δ 12.66 (s, 1H), 7.66 (dd, J = 8.4, 2.0 Hz, 1H), 7.32 (t, J = 2.0 Hz, 2H), 6.88 (s, 1H), 6.85 (dd, J = 8.4, 2.4 Hz, 1H), 6.73 (d, J = 2.4 Hz, 1H), 3.83 (s, 6H), 3.77 (s, 3H), 3.00–2.91 (m, 4H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 164.31, 160.45, 158.42, 156.44, 143.66, 136.68, 133.90, 124.23, 123.33, 121.55, 114.08, 111.82, 105.75, 105.06, 55.59, 55.09, 28.65, 20.74 ppm. MS (ESI): m/z calcd for C21H21N2O4S [M + H]+ 397.12, found 396.95.

3.1.3. General Procedure of Synthesis of 10a–10b (Exemplified by 10a)

A mixture of 8a (10.0 mmol, 1.0 equiv), thiourea (20.0 mmol, 2.0 equiv), and iodine (10.0 mmol, 1.0 equiv) was stirred at 110 °C for 10 h. After the reaction was completed, the residue was triturated with MTBE and adjusted to pH 9–10 with 25% ammonium hydroxide. The precipitated solid was collected and washed with EtOAc (30 mL × 2) and NaHCO3 (15 mL × 2) aqueous solution. The separated organic layer dried over Na2SO4 and evaporated to dryness to afford crude product 9a. The mixture of 9a (3.3 mmol, 1.1 equiv), aromatic acid (3.0 mmol, 1.0 equiv), HATU (3.0 mmol, 1.0 equiv), and DIPEA (9.0 mmol, 3.0 equiv) in DMF (20 mL) was stirred at room temperature for 2 h. Then the reaction mixture was quenched with water. The aqueous layer was extracted with EtOAc (30 mL × 2). The combined organic layers were dried over Na2SO4. The residue was purified by column chromatography on silica gel (eluting with DCM) to afford compound 10a as a white solid (406.7 mg, yield 35%). 1H NMR (400 MHz, DMSO-d6) δ 12.67 (s, 1H), 7.57 (d, J = 8.4 Hz, 1H), 7.32 (d, J = 2.0 Hz, 2H), 7.21 (s, 1H), 6.86 (d, J = 2.4 Hz, 1H), 6.83 (dd, J =8.4, 2.8 Hz, 1H), 6.74 (t, J = 2.4 Hz, 1H), 3.83 (s, 6H), 3.77 (s, 3H), 2.43 (s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 164.74, 160.45, 158.60, 157.76, 149.01, 136.97, 134.22, 130.74, 127.31, 115.96, 111.22, 110.14, 105.80, 104.90, 55.58, 55.04, 21.26 ppm. MS (ESI): m/z calcd for C20H21N2O4S [M + H]+ 385.12, found 385.20.
3,5-dimethoxy-N-(4-(4-methoxy-3-methylphenyl)thiazol-2-yl)benzamide (10b), eluting with DCM, yield = 40%; 1H NMR (400 MHz, DMSO-d6) δ 12.70 (s, 1H), 7.77 (d, J = 2.4 Hz, 1H), 7.75 (s, 1H), 7.49 (s, 1H), 7.33 (d, J = 2.4 Hz, 2H), 6.99 (d, J = 8.8 Hz, 1H), 6.74 (t, J = 2.4 Hz, 1H), 3.84 (s, 6H), 3.82 (s, 3H), 2.20 (s, 3H) ppm. 13C NMR (100 MHz, DMSO-d6) δ 164.59, 160.46, 158.26, 157.15, 149.27, 133.86, 128.07, 126.72, 125.68, 124.62, 110.36, 106.38, 105.79, 105.09, 55.59, 55.31, 16.21 ppm. MS (ESI): m/z calcd for C20H21N2O4S [M + H]+ 385.12, found 385.25.

3.2. Molecule Docking

The protease structure, SARS-CoV-2 3CLpro enzyme (PDB code: 6M2N) with 2.2 Å, was obtained from the the Protein Data Bank at the RCSB site (http://www.rcsb.org (accessed on 6 March 2022)). The molecule docking used the Lamarckian genetic algorithm local search method and the semiempirical free energy calculation method in the AutoDock 4.2 program. Additionally, the charge was added by Kollman in AutoDock 4.2, The docking methold was employed on rigid receptor conformation, all the rotatable torsional bonds of compound 7a were set free, the size of grid box was set at to 10.4 nm × 12.6 nm × 11.0 nm points with a 0.0375 nm spacing and grid center (−33.798 −46.566 39.065), and the other parameters were maintained at their default settings.

3.3. Enzymatic Activity and Inhibition Assays

The enzyme activity and inhibition assays of SARS-CoV-2 3CLpro have been described previously [20,36]. Briefly, the recombinant SARS-CoV-2 3CLpro (40 nM at a final concentration) was mixed with each compound in 50 μL of assay buffer (20 mM Tris, pH 7.3, 150 mM NaCl, 1% Glycerol, 0.01% Tween-20) and incubated for 10 min. The reaction was initiated by adding the fluorogenic substrate MCA-AVLQSGFRK (DNP) K (GL Biochem, Shanghai, China), with a final concentration of 40 μM. After that, the fluorescence signal at 320 nm (excitation)/405 nm (emission) was immediately measured by continuous 10 points for 5 min with an EnVision multimode plate reader (Perkin Elmer, Waltham, MA, USA). The initial velocity was measured when the protease reaction was proceeding in a linear fashion; plots of fluorescence units versus time were fitted with linear regression to determine initial velocity. Plots of initial velocity versus inhibitor concentration were fitted using a four-parameter concentration–response model in GraphPad Prism 8 to calculate the IC50 values. All data are shown as mean ± SD, n = 3 biological replicates.

4. Conclusions

In summary, we synthesized a series of 8H-Indeno[1,2-d]thiazole derivatives and evaluated their biochemical activities against SARS-CoV-2 3CLpro. Among them, the representative compound 7a displayed inhibitory activity with an IC50 of 1.28 ± 0.17 μM against SARS-CoV-2 3CLpro. Molecular docking elucidated that 7a was well-docked into the binding pockets S1 and S2 of 3CLpro. These preliminary results could provide a possible opportunity for the development of novel inhibitors against SARS-CoV-2 3CLpro with optimal potency and improved pharmacological properties.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/molecules27103359/s1, copies of the 1H NMR and 13C NMR spectra for compounds 4, 7a–7l, 10a–10b and Figure S1. surf representation of the compound 4 (bonds representation) in the 3CLpro S1 (red), S2 (blue), S1′ (green), S4 (orange) binding pockets, Figure S2. surf representation of the compound 7h (bonds representation) in the 3CLpro S1 (red), S2 (blue), S1′ (green), S4 (orange) binding pockets.

Author Contributions

Investigation, J.W. (synthesis); B.F. and L.-X.G. (bioassay); C.Z. (molecule docking); Conceptualization, J.L., D.-J.X., Y.Z. and W.-L.W.; writing—original draft preparation, J.W., B.F. and D.-J.X.; writing—review and editing, Y.Z. and W.-L.W.; supervision, Y.Z. and W.-L.W.; project administration, D.-J.X. and W.-L.W.; funding acquisition. All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially supported by the science and technology development foundation of Wuxi (N2020X016) and the Natural Science Foundation of Jiangsu Province (BK20190608).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data are available upon request to the Corresponding Authors.

Acknowledgments

The authors express their gratitude to the BioDuro-Sundia in Wuxi for NMR spectral data and mass spectral data.

Conflicts of Interest

The authors declare no conflict of interest.

Sample Availability

Some of the compounds may be available in mg quantities upon request from the corresponding authors.

References

  1. Zhu, N.; Zhang, D.; Wang, W.; Li, X.; Yang, B.; Song, J.; Zhao, X.; Huang, B.; Shi, W.; Lu, R.; et al. A Novel Coronavirus from Patients with Pneumonia in China, 2019. N. Engl. J. Med. 2020, 382, 727–733. [Google Scholar] [CrossRef] [PubMed]
  2. Zhou, P.; Yang, X.L.; Wang, X.G.; Hu, B.; Zhang, L.; Zhang, W.; Si, H.R.; Zhu, Y.; Li, B.; Huang, C.L.; et al. A pneumonia outbreak associated with a new coronavirus of probable bat origin. Nature 2020, 579, 270–273. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  3. Wang, C.; Horby, P.W.; Hayden, F.G.; Gao, G.F. A novel coronavirus outbreak of global health concern. Lancet 2020, 395, 470–473. [Google Scholar] [CrossRef] [Green Version]
  4. Wu, F.; Zhao, S.; Yu, B.; Chen, Y.M.; Wang, W.; Song, Z.G.; Hu, Y.; Tao, Z.W.; Tian, J.H.; Pei, Y.Y.; et al. A new coronavirus associated with human respiratory disease in China. Nature 2020, 579, 1–8. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  5. Coronaviridae Study Group of the International Committee on Taxonomy of V. The species Severe acute respiratory syndrome-related coronavirus: Classifying 2019-nCoV and naming it SARS-CoV-2. Nat. Microbiol. 2020, 5, 536–544. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  6. WHO. COVID-19 Dashboard with Vaccination Data. Available online: https://covid19.who.int/ (accessed on 28 February 2022).
  7. Abu-Raddad, L.J.; Chemaitelly, H.; Ayoub, H.H.; Tang, P.; Coyle, P.; Hasan, M.R.; Yassine, H.M.; Benslimane, F.M.; Al-Khatib, H.A.; Al-Kanaani, Z.; et al. Relative infectiousness of SARS-CoV-2 vaccine breakthrough infections, reinfections, and primary infections. Nat. Commun. 2022, 13, 532. [Google Scholar] [CrossRef]
  8. CDC COVID-19 Vaccine Breakthrough Case Investigations Team. COVID-19 Vaccine Breakthrough Infections Reported to CDC—United States, January 1–April 30, 2021. MMWR Morb. Mortal. Wkly. Rep. 2021, 70, 792–793. [Google Scholar] [CrossRef]
  9. Chen, J.; Wang, R.; Gilby, N.B.; Wei, G.W. Omicron Variant (B.1.1.529): Infectivity, Vaccine Breakthrough, and Antibody Resistance. J. Chem. Inf. Model 2022, 62, 412–422. [Google Scholar] [CrossRef]
  10. Zhang, L.; Li, Q.; Liang, Z.; Li, T.; Liu, S.; Cui, Q.; Nie, J.; Wu, Q.; Qu, X.; Huang, W.; et al. The significant immune escape of pseudotyped SARS-CoV-2 variant Omicron. Emerg. Microbes. Infect. 2022, 11, 1–5. [Google Scholar] [CrossRef]
  11. Hoffmann, M.; Kleine-Weber, H.; Schroeder, S.; Kruger, N.; Herrler, T.; Erichsen, S.; Schiergens, T.S.; Herrler, G.; Wu, N.H.; Nitsche, A.; et al. SARS-CoV-2 Cell Entry Depends on ACE2 and TMPRSS2 and Is Blocked by a Clinically Proven Protease Inhibitor. Cell 2020, 181, 271–280. [Google Scholar] [CrossRef]
  12. Mody, V.; Ho, J.; Wills, S.; Mawri, A.; Lawson, L.; Ebert, M.; Fortin, G.M.; Rayalam, S.; Taval, S. Identification of 3-chymotrypsin like protease (3CLPro) inhibitors as potential anti-SARS-CoV-2 agents. Commun. Biol. 2021, 4, 93. [Google Scholar] [CrossRef] [PubMed]
  13. V’Kovski, P.; Kratzel, A.; Steiner, S.; Stalder, H.; Thiel, V. Coronavirus biology and replication: Implications for SARS-CoV-2. Nat. Rev. Microbiol. 2021, 19, 155–170. [Google Scholar] [CrossRef] [PubMed]
  14. Pillaiyar, T.; Meenakshisundaram, S.; Manickam, M. Recent discovery and development of inhibitors targeting coronaviruses. Drug Discov. Today 2020, 25, 668–688. [Google Scholar] [CrossRef]
  15. Wen, W.; Chen, C.; Tang, J.; Wang, C.; Zhou, M.; Cheng, Y.; Zhou, X.; Wu, Q.; Zhang, X.; Feng, Z.; et al. Efficacy and safety of three new oral antiviral treatment (molnupiravir, fluvoxamine and Paxlovid) for COVID-19a meta-analysis. Ann. Med. 2022, 54, 516–523. [Google Scholar] [CrossRef] [PubMed]
  16. Chia, C.S.B. Novel Nitrile Peptidomimetics for Treating COVID-19. ACS Med. Chem. Lett. 2022, 13, 330–331. [Google Scholar] [CrossRef]
  17. Konno, S.; Kobayashi, K.; Senda, M.; Funai, Y.; Seki, Y.; Tamai, I.; Schäkel, L.; Sakata, K.; Pillaiyar, T.; Taguchi, A.; et al. 3CL Protease Inhibitors with an Electrophilic Arylketone Moiety as Anti-SARS-CoV-2 Agents. J. Med. Chem. 2022, 65, 2926–2939. [Google Scholar] [CrossRef]
  18. Zhang, L.L.; Lin, D.Z.; Sun, X.Y.Y.; Curth, U.; Drosten, C.; Sauerhering, L.; Becker, S.; Rox, K.; Hilgenfeld, R. Crystal structure of SARS-CoV-2 main protease provides a basis for design of improved α-ketoamide inhibitors. Science 2020, 368, 409–412. [Google Scholar] [CrossRef] [Green Version]
  19. Dampalla, C.S.; Kim, Y.; Bickmeier, N.; Rathnayake, A.D.; Nguyen, H.N.; Zheng, J.; Kashipathy, M.M.; Baird, M.A.; Battaile, K.P.; Lovell, S. Structure-Guided Design of Conformationally Constrained Cyclohexane Inhibitors of Severe Acute Respiratory Syndrome Coronavirus-2 3CL Protease. J. Med. Chem. 2021, 64, 10047–10058. [Google Scholar] [CrossRef]
  20. Jin, Z.; Du, X.; Xu, Y.; Deng, Y.; Liu, M.; Zhao, Y.; Zhang, B.; Li, X.; Zhang, L.; Peng, C.; et al. Structure of M(pro) from SARS-CoV-2 and discovery of its inhibitors. Nature 2020, 582, 289–293. [Google Scholar] [CrossRef] [Green Version]
  21. Xiong, M.; Nie, T.; Shao, Q.; Li, M.; Su, H.; Xu, Y. In silico screening-based discovery of novel covalent inhibitors of the SARS-CoV-2 3CL protease. Eur. J. Med. Chem. 2022, 231, 114130. [Google Scholar] [CrossRef]
  22. Han, S.H.; Goins, C.M.; Arya, T.; Shin, W.J.; Maw, J.; Hooper, A.; Sonawane, D.P.; Porter, M.R.; Bannister, B.E.; Crouch, R.D. Structure-Based Optimization of ML300-Derived, Noncovalent Inhibitors Targeting the Severe Acute Respiratory Syndrome Coronavirus 3CL Protease (SARS-CoV-2 3CLpro). J. Med. Chem. 2022, 65, 2880–2904. [Google Scholar] [CrossRef] [PubMed]
  23. Su, H.X.; Yao, S.; Zhao, W.F.; Li, M.J.; Liu, J.; Shang, W.J.; Xie, H.; Ke, C.Q.; Hu, H.C.; Gao, M.N.; et al. Anti-SARS-CoV-2 activities in vitro of Shuanghuanglian preparations and bioactive ingredients. Acta Pharmacol. Sin. 2020, 41, 1167–1177. [Google Scholar] [CrossRef] [PubMed]
  24. Wu, Q.; Yan, S.; Wang, Y.; Li, M.; Xiao, Y.; Li, Y. Discovery of 4′-O-methylscutellarein as a potent SARS-CoV-2 main protease inhibitor. Biochem. Biophys. Res. Commun. 2022, 604, 76–82. [Google Scholar] [CrossRef] [PubMed]
  25. Goblyos, A.; Santiago, S.N.; Pietra, D.; Mulder-Krieger, T.; von Frijtag Drabbe Kunzel, J.; Brussee, J.; Ijzerman, A.P. Synthesis and biological evaluation of 2-aminothiazoles and their amide derivatives on human adenosine receptors. Lack of effect of 2-aminothiazoles as allosteric enhancers. Bioorg. Med. Chem. 2005, 13, 2079–2087. [Google Scholar] [CrossRef]
  26. Kocyigit, U.M.; Aslan, O.N.; Gulcin, I.; Temel, Y.; Ceylan, M. Synthesis and Carbonic Anhydrase Inhibition of Novel 2-(4-(Aryl)thiazole-2-yl)-3a,4,7,7a-tetrahydro-1H-4,7-methanoisoindole-1,3(2H)-di one Derivatives. Arch. Pharm. 2016, 349, 955–963. [Google Scholar] [CrossRef]
  27. Chordia, M.D.; Murphree, L.J.; Macdonald, T.L.; Linden, J.; Olsson, R.A. 2-Aminothiazoles: A new class of agonist allosteric enhancers of A1 adenosine receptor. Bioorg. Med. Chem. Lett. 2002, 12, 1563–1566. [Google Scholar] [CrossRef]
  28. Chordia, M.D.; Zigler, M.; Murphree, L.J.; Figler, H.; Macdonald, T.L.; Olsson, R.A.; Linden, J. 6-Aryl-8H-indeno[1,2-d]thiazol-2-ylamines: A1 Adenosine Receptor Agonist Allosteric Enhancers Having Improved Potency. J. Med. Chem. 2005, 48, 5131–5139. [Google Scholar] [CrossRef]
  29. Catlin, N.R.; Bowman, C.J.; Campion, S.N.; Cheung, J.R.; Nowland, W.S.; Sathish, J.G.; Stethem, C.M.; Updyke, L.; Cappon, G.D. Reproductive and developmental safety of nirmatrelvir (PF-07321332), an oral SARS-CoV-2 M(pro) inhibitor in animal models. Reprod Toxicol. 2022, 108, 56–61. [Google Scholar] [CrossRef]
  30. Macchiagodena, M.; Pagliai, M.; Procacci, P. Characterization of the non-covalent interaction between the PF-07321332 inhibitor and the SARS-CoV-2 main protease. J. Mol. Graph. Model. 2022, 110, 108042. [Google Scholar] [CrossRef]
  31. Zhao, Y.; Fang, C.; Zhang, Q.; Zhang, R.; Zhao, X.; Duan, Y.; Wang, H.; Zhu, Y.; Feng, L.; Zhao, J.; et al. Crystal structure of SARS-CoV-2 main protease in complex with protease inhibitor PF-07321332. Protein Cell. 2021, 1–5. [Google Scholar] [CrossRef]
  32. Meng, X.D.; Gao, L.X.; Wang, Z.J.; Feng, B.; Zhang, C.; Satheeshkumar, R.; Li, J.; Zhu, Y.L.; Zhou, Y.B.; Wang, W.L. Synthesis and biological evaluation of 2,5-diaryl-1,3,4-oxadiazole derivatives as novel Src homology 2 domain-containing protein tyrosine phosphatase 2 (SHP2) inhibitors. Bioorg. Chem. 2021, 116, 105384. [Google Scholar] [CrossRef] [PubMed]
  33. Morris, G.M.; Huey, R.; Lindstrom, W.; Sanner, M.F.; Belew, R.K.; Goodsell, D.S.; Olson, A.J. AutoDock4 and AutoDockTools4: Automated docking with selective receptor flexibility. J. Comput. Chem. 2009, 30, 2785–2791. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  34. Peralta, J.; Ogliaro, F.; Bearpark, M.; Heyd, J.; Brothers, E.; Kudin, K.; Staroverov, V.; Kobayashi, R.; Normand, J.; Raghavachari, K. Gaussian 09, Revision, D. 01; Gaussian, Inc.: Wallingford, CT, USA, 2013. [Google Scholar]
  35. Yang, H.; Xie, W.; Xue, X.; Yang, K.; Ma, J.; Liang, W.; Zhao, Q.; Zhou, Z.; Pei, D.; Ziebuhr, J.; et al. Design of wide-spectrum inhibitors targeting coronavirus main proteases. PLoS Biol. 2005, 3, e324. [Google Scholar] [CrossRef]
  36. Dai, W.H.; Zhang, B.; Jiang, X.M.; Su, H.X.; Li, J.; Zhao, Y.; Xie, X.; Jin, Z.M.; Peng, J.J.; Liu, F.J. Structure-based design of antiviral drug candidates targeting the SARS-CoV-2 main protease. Science 2020, 368, eabb4489. [Google Scholar] [CrossRef] [Green Version]
Molecules 27 03359 g001 550
Figure 1. SARS-CoV-2 3CLpro inhibitors.
Figure 1. SARS-CoV-2 3CLpro inhibitors.
Molecules 27 03359 g001
Molecules 27 03359 g002 550
Figure 2. Structure of 8H-indeno[1,2-d]thiazole derivatives.
Figure 2. Structure of 8H-indeno[1,2-d]thiazole derivatives.
Molecules 27 03359 g002
Molecules 27 03359 sch001 550
Scheme 1. (a) thiourea, bromine, ethanol, 100 °C, 5–6 h; (b) aromatic acid, HATU, DIPEA, DMF, r t, 2–3 h, 25–50%.
Scheme 1. (a) thiourea, bromine, ethanol, 100 °C, 5–6 h; (b) aromatic acid, HATU, DIPEA, DMF, r t, 2–3 h, 25–50%.
Molecules 27 03359 sch001
Molecules 27 03359 sch002 550
Scheme 2. (a) thiourea, iodine, 110 °C, 10 h; (b) aromatic acid, HATU, DIPEA, DMF, r t, 2–3 h, 35–40%.
Scheme 2. (a) thiourea, iodine, 110 °C, 10 h; (b) aromatic acid, HATU, DIPEA, DMF, r t, 2–3 h, 35–40%.
Molecules 27 03359 sch002
Molecules 27 03359 g003 550
Figure 3. (a) surf representation of the compound 7a (bonds representation) in the 3CLpro S1 (red), S2 (blue), S1′ (green), S4 (orange) binding pocket; (b) the docking results of 7a and 3CLpro (PDB code: 6M2N, active residues in 3.0 Å range around 7a).
Figure 3. (a) surf representation of the compound 7a (bonds representation) in the 3CLpro S1 (red), S2 (blue), S1′ (green), S4 (orange) binding pocket; (b) the docking results of 7a and 3CLpro (PDB code: 6M2N, active residues in 3.0 Å range around 7a).
Molecules 27 03359 g003
Table
Table 1. Inhibitory activities of target compounds against SARS-CoV-2 3CLpro.
Table 1. Inhibitory activities of target compounds against SARS-CoV-2 3CLpro.
Molecules 27 03359 i001
Compd.R1R3nSARS-CoV-2 3CLpro
Inhibition (%) at 20 μMIC50 (μM)
7amethoxy Molecules 27 03359 i002189.5 ± 2.01.28 ± 0.17
7bbutoxy Molecules 27 03359 i00310.5 ± 4.9>20
7cisobutoxy Molecules 27 03359 i0041−3.1 ± 1.7>20
7dmethyl Molecules 27 03359 i005121.7 ± 2.2>20
7echloro Molecules 27 03359 i006127.2 ± 5.3>20
7fmethoxy Molecules 27 03359 i00715.0 ± 5.6>20
7gmethoxy Molecules 27 03359 i008132.6 ± 6.8>20
7hmethoxy Molecules 27 03359 i009172.5 ± 6.12.86 ± 0.11
7imethoxy Molecules 27 03359 i010120.3 ± 4.7>20
7jmethoxy Molecules 27 03359 i011131.9 ± 18.2>20
7kmethoxy Molecules 27 03359 i01211.5 ± 4.5>20
7lmethoxy Molecules 27 03359 i0132−13.1 ± 1.7>20
10a- Molecules 27 03359 i014-1.9 ± 2.1>20
10b- Molecules 27 03359 i015-1.8 ± 3.5>20
PF-07321332
(nirmatrelvir)		 Molecules 27 03359 i01699.5 ± 0.10.012 ± 0.001
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Wu, J.; Feng, B.; Gao, L.-X.; Zhang, C.; Li, J.; Xiang, D.-J.; Zang, Y.; Wang, W.-L. Synthesis and Biochemical Evaluation of 8H-Indeno[1,2-d]thiazole Derivatives as Novel SARS-CoV-2 3CL Protease Inhibitors. Molecules 2022, 27, 3359. https://doi.org/10.3390/molecules27103359

AMA Style

Wu J, Feng B, Gao L-X, Zhang C, Li J, Xiang D-J, Zang Y, Wang W-L. Synthesis and Biochemical Evaluation of 8H-Indeno[1,2-d]thiazole Derivatives as Novel SARS-CoV-2 3CL Protease Inhibitors. Molecules. 2022; 27(10):3359. https://doi.org/10.3390/molecules27103359

Chicago/Turabian Style

Wu, Jing, Bo Feng, Li-Xin Gao, Chun Zhang, Jia Li, Da-Jun Xiang, Yi Zang, and Wen-Long Wang. 2022. "Synthesis and Biochemical Evaluation of 8H-Indeno[1,2-d]thiazole Derivatives as Novel SARS-CoV-2 3CL Protease Inhibitors" Molecules 27, no. 10: 3359. https://doi.org/10.3390/molecules27103359

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