Design, synthesis, and in vitro antitumor activity of 6-aryloxyl substituted quinazoline derivatives

Abstract

Quinazoline derivatives are a class of important antitumor drugs known as small molecule inhibitors that include epidermal growth factor receptor (EGFR) inhibitors. Based on the structure of poziotinib, a series of 6-aryloxyl substituted quinazoline derivatives were designed and synthesized. The in vitro antitumor activities of the compounds were evaluated by the 3-(4,5-dimethyl-thiazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) method using the human gastric cancer N87 (HER2), nonsmall-cell lung cancer H1975 (EGFR^T790M/L858R), and A549 (EGFR^WT) cell lines. The most promising compound 4m exhibited potent antitumoral activities with IC₅₀ values of 6.3 nM and 7.5 nM for N87 and H1975 cell lines, respectively. Meanwhile, it was less potent against A549 cancer cells with an IC₅₀ value of 29.9 μM. The molecular docking results suggested that compound 4m has different binding modes to the wild-type and mutated EGFR.

1. Introduction

Cancer is a common and frequently occurring disease that seriously endangers human health [1]. Therefore, the discovery and development of novel, potent, and less-toxic anticancer reagents are urgent and challenging tasks for medicinal chemists worldwide. Epidermal growth factor receptor (EGFR) is a well-known therapeutic target for anticancer drug discovery [2]. It is a member of the ERBB family receptor tyrosine kinases, which consists of four members: EGFR (also known as ERBB1/HER1), ERBB2/HER2/NEU, ERBB3/HER3, and ERBB4/HER4 [3]. EGFR is a membrane receptor tyrosine kinase that plays an important role in cell proliferation, invasion, metabolism, apoptosis, and survival [4–6]. Its gene overexpression, mutation, or amplification is a driver of many types of human malignancies, including glioblastoma, breast cancer, ovarian cancer, and lung cancer, especially nonsmall-cell lung cancers (NSCLCs) [7–9]. Thus, epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) can be used as antitumoral molecules to inhibit EGFR autophosphorylation and downstream signal transduction. To date, numerous small molecule inhibitors have been discovered, and some have achieved remarkable antitumor efficacies in clinic [10].

Quinazoline is a heterocyclic scaffold that possesses a wide range of biological activities [11–13] and 6-substituted quinazoline derivatives are important antitumor drugs that are used as small molecule inhibitors, especially as EGFR-TKIs [14]. The first-generation drugs, such as gefitinib [15], and erlotinib [16], have significant clinical response rates. However, acquired resistance through mutations such as T790M and T790M/L858R, rapidly arises and causes relapse after 9–14 months posttreatment [17,18]. To overcome this resistance, second and third-generation EGFR-TKIs, such as afatinib [19], osimertinib [20], were developed. The irreversible covalent bound with the Cys 797 confers enhanced sensitivity and selectivity to these TKIs; however, severe side effects are also observed due to their activity against the wild-type (WT) EGFR. Poziotinib (Figure 1, HM 781-36B) is a novel, potent, third-generation, irreversible pan-her inhibitor developed for the prevention and treatment of patients with breast cancer, gastric cancer, and NSCLC, including clinical limitations caused by an acquired mutation (EGFR T790M) [21]. However, severe toxicities, such as diarrhea and skin rash, hampered its clinical administration [22]. Although these side effects are partially ascribed to the toxic de-methyl metabolite, the strong and irreversible inhibition of EGFR is still believed to be the main reason [23]. To further optimize this candidate drug, a series of 6-aryloxyl substituted quinazoline derivatives, were synthesized, and their antitumor activities were screened using the N87 human gastric cancer cell line, and the H1975 and A549 nonsmall-cell lung cancer cell lines.

Figure 1.

Structures and design strategy for 6-aryloxyl substituted quinazolines.

Initially, we reviewed the structures of quinazoline EGFR-TKIs and found that the 6-position of quinazoline is mostly substituted by aliphatic alkanes or cycloalkanes. For instance, gefitinib, erlotinib, icotinib, and vandetanib had the 6,7-dialkyloxyl moieties, but only lapatinib, a rigid aromatic ring (furan), was found in the 6-position. Thus, we presumed that the flexible alkyl chain was crucial for the molecule to have strong interactions with the enzyme. Based on the structures of poziotinib and lapatinib, a series of 6-aryloxyl substituted quinazolines (I, Figure 1) were designed by introducing benzene and pyridine rings. Meanwhile, in order to check the effect of the electron density of these aromatic rings on the antitumoral activity of the drug, an electron-donating methoxy group was also introduced to the 2′- or 4′-position. In previously published studies [24–26], the introduction of small substituents at the end of the acrylamide side chain could change the activity of the reaction between the acrylamide warhead and the amino acid residue Cys 797 in the back pocket. So, four acrylic acid derivatives, including methacrylic acid, but-2-enoic acid, and 3-methylbut-2-enoic acid were used to afford the acrylamides in this article.

2. Results and discussion

2.1. Chemistry

The structures and preparation of compounds 4a–4t are described in Scheme. Starting from a commercially available 6-hydroxyl-7-methoxy-4-arylaminoquinazoline (1), the final target molecules were obtained in three steps. Firstly, treatment of compound 1 with 1- or 2-fluoronitrobenzene at 50 °C generated the intermediates 2a–2e. Secondly, the reduction of the 2a–2e nitro group by the classical Fe/NH₄Cl or H₂/Pd-C method generated the amine compounds 3a–3e. Finally, the amide formation reaction of the compounds 3a–3e with acyl chlorides generated the compounds 4a–4t in a moderate yield.

Scheme.

Synthetic route of target compounds 4a–4t.

2.2 In vitro antitumor activity assay

To determine their antiproliferative activity, all synthesized compounds (4a–4t) were tested on the EGFR overexpressing cell lines, N87 (human gastric cancer), A549 (EGFR^WT), and H1975 (EGFR^L858R/T790M), using the 3-(4,5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide (MTT) assay. The results were expressed as IC₅₀ values and summarized in Table.

Table.

The structure and antiproliferative activities of compounds 4a–4t.

Compound	R	IC50a
		N87(nM)	H1975(nM)	A549(μM)
4a		4.7 ± 1.5	12.3 ± 2.4	36.3 ± 1.5
4b		46.4 ± 6.7	88.5 ± 23.1	40.4 ± 1.7
4c		12.3 ± 2.1	35.4 ± 11.1	38.6 ± 2.8
4d		9.6 ± 1.1	21.3 ± 9.2	30.2 ± 1.6
4e		121 ± 20.5	434 ± 32.5	58.3 ± 2.8
4f		43.4 ± 5.1	63.6 ± 15.3	43.7 ± 1.4
4g		15.7 ± 6.1	8.3 ± 2.1	28.9 ± 1.6
4h		46.7 ± 11.2	98.5 ± 18.5	45.4 ± 2.0
4i		25.2 ± 1.7	53.1 ± 14.4	40.7 ± 2.5
4j		780 ± 45.8	1250 ± 78.0	73.3 ± 1.6
4k		5.3 ± 1.1	9.5 ± 3.5	35.1 ± 1.7
4l		37.5 ± 14.7	24.6 ± 5.8	38.2 ± 3.3
4m		6.3 ± 1.7	7.5 ± 4.4	29.9 ± 2.5
4n		27.3 ± 3.2	41.5 ± 17.3	35.8 ± 1.5
4o		272 ± 27.9	327 ± 25.8	57.4 ± 2.4
4p		16.9 ± 3.7	77.5 ± 12.4	36.3 ± 3.0
4q		74.3 ± 10.6	14.6 ± 5.8	42.3 ± 1.6
4r		83.6 ± 24.3	125.3 ± 27.4	50.6 ± 2.5
4s		97.2 ± 7.9	173.3 ± 45.7	55.3 ± 1.4
4t		567 ± 39.5	870 ± 24.2	68.4 ± 1.3
Poziotinib		1.1 ± 0.03	6.9 ± 0.4	23.5 ± 2.1

^aThe IC₅₀ values represent an average of three experiments ± SD.

The antitumoral activities of these compounds were found to be less potent than those of poziotinib. Meanwhile, they were more potent for N87 and H1975 cancer cells compared to that for A549 cancer cells. Compound 4m showed antitumoral activities against N87 gastric cancer cells with an IC₅₀ value of 6.3 nM, while against H1975 lung cancer cells, the IC₅₀ value was 7.5 nM. A preliminary summary of the structure-activity relationship of the 6-aryloxyl substituted quinazoline derivatives is summarized as follows: 1. Compounds with substitution (R₁) on the acryloyl group generally possessed less antitumoral activity. For example, compound 4d (IC₅₀ = 9.6 and 21.3 nM) was more potent than compound 4i (IC₅₀ = 25.2 and 53.1 nM) when used for the treatment of N87 and H1975 cancer cells. Compound 4n (IC₅₀ = 27.3 and 41.5 nM) was more potent than compound 4s (IC₅₀ = 97.2 and 173.3 nM) when used for the treatment of N87 and H1975 cancer cells; 2. Compounds with benzene substitution at C-6 position exhibited better IC₅₀ values than those with a pyridine substitution. For example, compound 4c (IC₅₀ = 12.3, 35.4 nM and 38.6 μM) was more potent than compound 4r (IC₅₀ = 83.6, 125.3 nM and 50.6 μM) when used for treatment of N87, H1975 and A549 cancer cells, and compound 4d (IC₅₀ = 9.6, 21.3 nM and 30.2 μM) was more potent than compound 4s (IC₅₀ = 97.2, 173.3 nM and 55.3 μM); 3. The methoxyl substitution on the phenyl ring had little effect on the antitumoral activity of the compounds. Compounds 4c (IC₅₀ = 12.3, 35.4 nM and 38.6 μM) and 4d (IC₅₀ = 9.6, 21.3 nM and 30.2 μM) had similar antitumoral activities against N87, H1975 and A549 cancer cells. Compound 4r (83.6, 125.3 nM and 50.6 μM) and 4s (IC₅₀ = 97.2, 173.3 nM and 55.3 μM) exhibited comparable activities. 4. Compounds with para-acrylamide were more potent than those with ortho-acrylamide. For instance, compound 4a (IC₅₀ = 4.7, 12.3 nM) was more potent than compound 4b (IC₅₀ = 46.4, 88.5 nM) when used for the treatment of N87 and H1975 cancer cells, and compound 4k (IC₅₀ = 5.3, 9.5 nM) exhibited a better antitumoral activity than that of compound 4l (IC₅₀ = 37.5, 24.6 nM).

2.3. Molecular docking study

To better understand how these compounds interact with the target proteins, a molecular docking study was performed using the SURFLEX-DOCK module of the SYBYL package version. Poziotinib and compound 4m were selected for the molecular docking study. The proteins selected were EGFR^WT protein (PDB ID code: 4ZAU) and EGFR D770_N771 insNPG protein (PDB ID code: 4LRM). The results of docking analysis were shown in Figure 2. Poziotinib and compound 4m adopted a U-shape in the kinase domain and combined with the EGFR kinase. The amino-pyrimidine group formed a hydrogen bound with the amino acid residue Met 793 in the hinged region and the side chain amine penetrated the solvent region. With the wild-type EGFR, compound 4m formed strong two-dentate hydrogen bounds with Thr 790 because its hydrogen bonds were shorter than those of poziotinib (1.9 Å vs. 2.7 Å). In the mutated EGFR, the amino-pyrimidine group of the compound 4m formed hydrogen bounds with the amino acid residue Met 796 in the hinged region. Poziotinib bound the protein more tightly than compound 4m because the hydrogen bonds were shorter than those of 4m (2.1 Å vs. 2.8 Å). The molecular docking results also suggested that compound 4m had a different binding mode with the wild-type when compared with that of the mutated EGFR. This could be partially explained by its higher potency when used in the treatment of N87 and H1975 cancer cells and when compared with that of A549 cancer cells. Compound 4m was found to have lower binding scores with the wild-type EGFR compared with those with the mutated EGFR. The docking results also showed that the amino-pyrimidine group served as an indispensable anchor for hydrogen bond interactions with Met 793 or Met 796, and that the transformation direction of side chain was of certain significance.

Figure 2.

The results of the molecular docking. A and B are predicted binding model of poziotinib with 4ZAU and 4LRM; C and D are predicted binding model of compound 4m with 4ZAU and 4LRM.

2.4. Conclusion

A series of 6-aryloxyl substituted quinazoline derivatives were designed and synthesized, and their antitumoral activity was screened by the MTT assay using N87, H1975 and A549 cell lines. The most promising compound 4m showed a potent antitumoral activity against N87 and H1975 cells with the IC₅₀ values of 6.3 nM and 7.5 nM. Although it was less potent than the lead compound poziotinib, more investigations on compound 4m toxicity and side effects are required. To the best of our knowledge, the intolerance of poziotinib is due to the toxicity during its clinical usage. We attempted to reduce the toxicity of poziotinib by partially sacrificing its antitumoral activity. Despite that, there is still an unmet medical need to develop novel small molecule EGFR-TKIs or therapeutic approaches to overcome multipoint mutations in EGFR [27].

3. Experiments

3.1. Material and instruments

The chemicals were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. China. The 4-(3,4-dichloro-2-fluorophenylamino)-7-methoxyquinazolin-6-ol (1) was bought from Suzhou NMT Biotech Co., Ltd. China. The NMR spectra of the intermediates and final products in the deuterated solvent were detected on a Bruker 400/101 MHz spectrometer. The high-resolution mass spectra (HRMS) were recorded on an Agilent 6520 ESI/TOF mass spectrometer. The uncorrected melting points (MP) were recorded on a Büchi B-540 melting point apparatus. Flash column chromatographic separation was achieved using a silica gel from Qingdao Ocean Chemical (200–300 mesh) with a particle size from 54 to 74 μm using dichloromethane and methanol (or ethyl acetate) as eluents. The analytical TLC was carried out on a Merck precoated silica gel 60 GF-254 using 0.25-mm-thick TLC plates.

3.2. General experimental procedures and physical data of compounds 4

Sodium carbonate (0.28 g, 2.69 mmol) was added to a solution of compound 3 (0.3 g, 0.67 mmol) in tetrahydrofuran (THF) (8 mL), and under violent stirring. The reaction solution was cooled to 0–5 °C, and a solution of acryloyl chloride (2.34 mmol) in THF (8 mL) was added through an addition funnel within 30 min reaction mixture was stirred for 60 min at room temperature till TLC showed the completion of the reaction. Water (20 mL) was added to the reaction mixture and the aqueous solution was extracted with ethyl acetate. The organic layer was combined, dried, and evaporated. The residue was purified by silica gel column chromatography (dichloromethane/methanol = 50:1 – 10:1) and generated compound 4 as a pale-yellow solid.

N-(4-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy) phenyl)acrylamide (4a)

A pale-yellow solid (187 mg, 56% yield); m.p: 222–224 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 10.14 (s, 1H), 9.76 (s, 1H), 8.46 (s, 1H), 8.05 (s, 1H), 7.66 (d, J = 9.1 Hz, 2H), 7.53 (s, 2H), 7.39 (s, 1H), 6.98 (d, J = 9.1 Hz, 2H), 6.37–6.45 (m, 1H), 6.25 (d, J = 2.1 Hz, 1H), 5.73 (dd, J = 10.1, 2.1 Hz, 1H), 3.94 (s, 3H). ¹³C NMR (101 MHz, DMSO - d₆) δ 162.98, 157.29, 156.22, 154.44, 154.04, 154.01, 153.08, 144.87, 134.49, 131.96, 126.94, 126.50, 125.30, 125.26, 121.00, 119.67, 119.48, 117.27, 113.00, 108.83, 108.40, 56.20. HRMS (ESI): m/z calcd for C₂₄H₁₇Cl₂FN₄O₃: 499.0734 [M+H]⁺; found: 499.0738.

N-(2-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy) phenyl)acrylamide (4b)

A pale-yellow solid (214 mg, 64% yield); m.p: 223–225 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 9.80 (s, 2H), 8.48 (s, 1H), 8.16–8.22 (m, 2H), 7.53 (s, 2H), 7.43 (s, 1H), 7.01–7.10 (m, 2H), 6.70–6.83 (m, 2H), 6.25–6.31 (m, 1H), 5.72–5.76 (m, 1H), 3.94 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 163.71, 157.37, 156.47, 154.46, 151.94, 149.43, 148.48, 144.07, 131.97, 128.35, 128.12, 127.01, 125.37, 125.32, 124.85, 123.13, 122.63, 119.74, 119.55, 115.42, 114.43, 108.87, 108.70, 56.28. HRMS (ESI): m/z calcd for C₂₄H₁₇Cl₂FN₄O₃: 499.0734 [M+H]⁺; found: 499.0730.

N-(4-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)-3-methoxyphenyl)acrylamide (4c)

A pale-yellow solid (184 mg, 52% yield); m.p: 191–193 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 10.22 (s, 1H), 9.64 (s, 1H), 8.40 (s, 1H), 7.67 (d, J = 2.2 Hz, 1H), 7.63 (s, 1H), 7.51 (s, 2H), 7.34 (s, 1H), 7.25 (dd, J = 8.7, 2.3 Hz, 1H), 6.98 (d, J = 8.7 Hz, 1H), 6.43 (dd, J = 17.0, 10.1 Hz, 1H), 6.26 (dd, J = 17.0, 2.1 Hz, 1H), 5.75 (dd, J = 10.1, 2.1 Hz, 1H), 3.98 (s, 3H), 3.77 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 163.06, 157.03, 155.04, 153.51, 150.37, 146.75, 139.65, 136.43, 131.82, 127.26, 126.86, 125.25, 125.21, 120.24, 119.61, 119.42, 111.70, 108.58, 108.09, 107.72, 105.02, 56.09, 55.57. HRMS (ESI): m/z calcd for C₂₅H₁₉Cl₂FN₄O₄: 529.0840 [M+H] ⁺; found: 529.0838.

N-(2-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)-5-methoxyphenyl)acrylamide (4d)

A pale-yellow solid (205 mg, 58% yield) ; m.p: 225–227 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 9.74 (s, 2H), 8.45 (s, 1H), 7.92–7.96 (m, 2H), 7.53 (s, 2H), 7.39 (s, 1H), 6.77 (s, 2H), 6.65 (s, 1H), 6.23–6.27 (m, 1H), 5.73 (d, J = 11.1 Hz, 1H), 3.96 (s, 3H), 3.73 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 163.76, 156.12, 154.80, 154.78, 154.13, 153.61, 145.68, 141.43, 131.92, 129.70, 129.66, 127.14, 127.12, 125.36, 125.33, 125.28, 122.34, 119.19, 117.54, 109.47, 108.54, 108.53, 99.48, 56.21, 55.37. HRMS (ESI): m/z calcd for C₂₅H₁₉Cl₂FN₄O₄: 529.0840 [M+H] ⁺; found: 529.0839.

N-(2-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy) pyridin-4-yl)acrylamide (4e)

A pale-yellow solid (181 mg, 54% yield); m.p: 238–240 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 10.09 (s, 1H), 9.89 (s, 1H), 8.58 (dd, J = 7.9, 1.5 Hz, 1H), 8.50 (s, 1H), 8.34 (s, 1H), 7.76 (dd, J = 4.9, 1.7 Hz, 1H), 7.57 (d, J = 7.7 Hz, 2H), 7.40 (s, 1H), 7.12 (dd, J = 7.9, 4.9 Hz, 1H), 6.85 (dd, J = 17.0, 10.2 Hz, 1H), 6.32 (dd, J = 17.0, 2.1 Hz, 1H), 5.79 (dd, J = 10.2, 2.1 Hz, 1H), 3.87 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 164.26, 157.46, 156.72, 154.57, 153.69, 151.92, 149.91, 142.09, 141.05, 131.53, 130.52, 128.89, 127.60, 126.98, 126.96, 125.33, 125.29, 122.31, 118.90, 116.54, 108.74, 108.26, 56.24. HRMS (ESI): m/z calcd for C₂₃H₁₆Cl₂FN₅O₃: 500.0687 [M+H] ⁺; found: 500.0685.

(E)-N-(4-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl) oxy)phenyl)but-2-enamide (4f)

A pale-yellow solid (175 mg, 51% yield); m.p: 249–251 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 10.14 (s, 1H), 9.86 (s, 1H), 8.45 (s, 1H), 8.09 (s, 1H), 7.69 (s, 1H), 7.67 (s, 1H), 7.53 (s, 2H), 7.38 (s, 1H), 6.97 (s, 1H), 6.95 (d, J = 2.1 Hz, 1H), 6.72–6.81 (m, 1H), 6.16 (dd, J = 15.2, 1.7 Hz, 1H), 3.93 (s, 3H), 1.84 (dd, J = 6.9, 1.6 Hz, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 163.27, 157.24, 156.17, 154.15, 152.77, 149.00, 144.92, 139.36, 134.81, 128.86, 127.16, 127.03, 127.00, 126.97, 126.10, 125.28, 125.24, 120.83, 117.26, 112.78, 108.77, 108.54, 56.17, 17.48. HRMS (ESI): m/z calcd for C₂₅H₁₉Cl₂FN₄O₃: 513.0891 [M+H] ⁺; found: 513.0890.

(E)-N-(2-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl) oxy)phenyl)but-2-enamide (4g)

A pale-yellow solid (158 mg, 46% yield); m.p: 236–238 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 9.81 (s, 1H), 9.55 (s, 1H), 8.47 (s, 1H), 8.18 (d, J = 7.6 Hz, 1H), 8.14 (s, 1H), 7.53 (s, 1H), 7.42 (s, 1H), 6.99–7.08 (m, 3H), 6.81 (dd, J = 15.2, 6.9 Hz, 1H), 6.71 (d, J = 7.9 Hz, 1H), 6.48 (d, J = 15.2 Hz, 1H), 3.95 (s, 3H), 1.85 (dd, J = 6.9, 1.6 Hz, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 169.41, 163.96, 162.36, 156.36, 154.48, 148.29, 144.10, 144.07, 139.89, 132.67, 128.50, 128.34, 125.31, 125.27, 122.71, 122.63, 119.65, 119.47, 117.75, 115.73, 115.56, 108.51, 104.60, 56.26, 17.56. HRMS (ESI): m/z calcd for C₂₅H₁₉Cl₂FN₄O₃: 513.0891 [M+H] ⁺; found: 513.0889.

(E)-N-(4-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl) oxy)-3-methoxyphenyl)but-2-enamide (4h)

A pale-yellow solid (193 mg, 53% yield); m.p: 205–207 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 10.02 (s, 1H), 9.64 (s, 1H), 8.40 (s, 1H), 7.66 (d, J = 2.2 Hz, 1H), 7.61 (s, 1H), 7.51 (t, J = 11.1 Hz, 2 H), 7.34 (s, 6.08–6.12 (m, 1H), 3.99 (s, 3H), 3.76 (s, 3H), 1.86 (d, J = 1.6 Hz, 3H).¹³C NMR (101 MHz, DMSO - d₆) δ 163.40, 157.03, 155.01, 153.50, 150.40, 148.10, 146.90, 139.83, 139.28, 136.81, 128.95, 127.34, 125.98, 125.26, 125.22, 120.36, 119.62, 119.43, 111.57, 108.56, 108.07, 107.42, 104.92, 56.09, 55.56, 17.54. HRMS (ESI): m/z calcd for C₂₆H₂₁Cl₂FN₄O₄: 543.0996 [M+H] ⁺; found: 543.0994.

(E)-N-(2-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl) oxy)-5-methoxyphenyl)but-2-enamide (4i)

A pale-yellow solid (189 mg, 52% yield) ; m.p: 242–244 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 9.74 (s, 1H), 9.47 (s, 1H), 8.44 (s, 1H), 7.94 (d, J = 7.0 Hz, 2H), 7.53 (d, J = 3.4 Hz, 2H), 7.39 (s, 1H), 6.82 (d, J = 6.9 Hz, 1H), 6.76 (s, 1H), 6.62 (dd, J = 9.0, 3.1 Hz, 1H), 6.43–6.46 (m, 1H), 3.97 (s, 3H), 3.72 (s, 3H), 1.84 (dd, J = 6.9, 1.6 Hz, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 164.07, 164.06, 157.20, 156.08, 154.86, 154.06, 148.82, 145.90, 140.20, 130.14, 128.98, 127.12, 127.10, 126.11, 125.34, 125.30, 119.50, 117.73, 111.82, 109.13, 108.68, 108.39, 56.21, 55.35, 17.56. HRMS (ESI): m/z calcd for C₂₆H₂₁Cl₂FN₄O₄: 543.0996 [M+H] ⁺; found: 543.0995.

(E)-N-(2-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl) oxy)pyridin-4-yl)but-2-enamide (4j)

A pale-yellow solid (172 mg, 50% yield); m.p: 226–228 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 10.13 (s, 1H), 9.86 (s, 1H), 8.53 (dd, J = 7.8, 1.6 Hz, 1H), 8.48 (s, 1H), 8.39 (s, 1H), 7.73 (dd, J = 4.9, 1.7 Hz, 1H), 7.55 (s, 2H), 7.38 (s, 1H), 7.09 (dd, J = 7.9, 4.9 Hz, 1H), 6.81–6.85 (m, 1H), 6.54 (dd, J = 15.2, 1.6 Hz, 1H), 3.85 (s, 3H), 1.86 (dd, J = 6.9, 1.6 Hz, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 164.66, 164.65, 157.55, 156.82, 153.73, 142.22, 140.89, 140.81, 132.54, 130.52, 128.99, 128.73, 127.12, 127.07, 125.77, 125.38, 122.64, 119.76, 119.57, 118.98, 116.64, 56.32, 17.73. HRMS (ESI): m/z calcd for C₂₄H₁₈Cl₂FN₅O₃: 514.0843 [M+H] ⁺; found: 514.0842.

N-(4-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy) phenyl)methacrylamide (4k)

A pale-yellow solid (213 mg, 62% yield); m.p: 239–241 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 9.79 (s, 1H), 9.77 (s, 1H), 8.47 (s, 1H), 8.07 (s, 1H), 7.68 (d, J = 9.1 Hz, 2H), 7.53 (s, 2H), 7.40 (s, 1H), 6.97 (s, 2H), 5.79 (s, 1H), 5.49 (s, 1H), 3.94 (s, 3H), 1.94 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 166.59, 157.21, 156.19, 154.15, 153.08, 151.90, 148.99, 144.89, 140.40, 134.37, 128.88, 126.92, 125.29, 125.25, 121.86, 119.75, 119.67, 119.48, 117.05, 112.78, 108.79, 108.57, 56.17, 18.75. HRMS (ESI): m/z calcd for C₂₅H₁₉Cl₂FN₄O₃: 513.0891 [M+H] ⁺; found: 513.0889.

N-(2-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)phenyl)methacrylamide (4l)

A pale-yellow solid (188 mg, 55% yield); m.p: 240–242 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 10.11 (s, 1H), 9.23 (s, 1H), 8.45 (s, 1H), 8.24 (s, 1H), 7.86 (dd, J = 6.0, 3.6 Hz, 1H), 7.53 (s, 2H), 7.38 (s, 1H), 7.09–7.13 (m, 2H), 6.91 (dd, J = 5.8, 3.7 Hz, 1H), 5.83 (s, 1H), 5.48–5.52 (m, 1H), 3.93 (s, 3H), 1.92–1.94 (m, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 166.40, 162.38, 156.05, 156.03, 149.30, 144.36, 144.33, 144.32, 139.90, 128.32, 125.66, 125.33, 125.28, 124.62, 123.19, 120.56, 119.64, 119.45, 116.87, 114.10, 100.69, 99.50, 56.30, 18.57. HRMS (ESI): m/z calcd for C₂₅H₁₉Cl₂FN₄O₃: 513.0891 [M+H] ⁺; found: 513.0888.

N-(4-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)-3-methoxyphenyl) methacrylamide (4m)

A pale-yellow solid (182 mg, 50% yield); m.p: 242–244 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 9.84 (s, 1H), 9.65 (s, 1H), 8.41 (s, 1H), 7.67 (d, J = 2.2 Hz, 1H), 7.62 (s, 1H), 7.51 (t, J = 11.3 Hz, 2H), 7.35 (t, J = 5.5 Hz, 2H), 6.96 (d, J = 8.7 Hz, 1H), 5.79 (s, 1H), 5.51 (s, 1H), 3.99 (s, 3H), 3.76 (s, 3H), 1.95 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 166.76, 157.04, 155.03, 153.52, 152.12, 150.21, 148.12, 146.83, 140.45, 139.52, 136.49, 128.94, 127.31, 125.27, 125.23, 120.05, 119.81, 119.42, 112.34, 108.57, 108.09, 107.56, 105.75, 56.09, 55.58, 18.74. HRMS (ESI): m/z calcd for C₂₆H₂₁Cl₂FN₄O₄: 543.0996 [M+H] ⁺; found: 543.0994.

N-(2-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)-5-methoxyphenyl)acrylamide (4n)

A pale-yellow solid (203 mg, 56% yield); m.p: 180–182 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 9.80 (s, 1H), 9.06 (s, 1H), 8.44 (s, 1H), 7.98 (s, 1H), 7.61 (d, J = 3.0 Hz, 1H), 7.53 (s, 2H), 7.37 (s, 1H), 7.00 (d, J = 9.0 Hz, 1H), 6.73 (dd, J = 9.0, 3.1 Hz, 1H), 5.75 (s, 1H), 5.48 (s, 1H), 3.96 (s, 3H), 3.74 (s, 3H), 1.90 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 166.31, 157.24, 155.64, 155.27, 154.04, 145.71, 141.66, 139.85, 129.75, 126.91, 125.32, 125.28, 120.61, 119.66, 119.47, 119.04, 111.45, 110.18, 109.43, 108.67, 108.35, 99.48, 56.27, 55.43, 18.39. HRMS (ESI): m/z calcd for C₂₆H₂₁Cl₂FN₄O₄: 543.0996 [M+H] ⁺; found: 543.0993.

N-(2-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)pyridin-4-yl)methacrylamide (4o)

A pale-yellow solid (203 mg, 59% yield); m.p: 237–239 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 9.85 (s, 1H), 9.46 (s, 1H), 8.50 (s, 1H), 8.27 (s, 1H), 8.21 (d, J = 9.2 Hz, 1H), 7.84 (d, J = 6.5 Hz, 1H), 7.55 (s, 2H), 7.39 (s, 1H), 7.14 (dd, J = 7.7, 4.9 Hz, 1H), 5.94 (s, 1H), 5.58 (s, 1H), 3.87 (s, 3H), 2.00 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 167.02, 157.45, 156.74, 155.22, 154.52, 149.83, 142.20, 139.55, 132.96, 128.90, 127.01, 126.87, 125.35, 125.31, 121.99, 121.15, 119.71, 119.52, 118.96, 116.31, 108.68, 108.24, 56.23, 18.62. HRMS (ESI): m/z calcd for C₂₄H₁₈Cl₂FN₅O₃: 514.0843 [M+H] ⁺; found: 514.0842.

N-(4-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)phenyl)-3-methylbut-2-enamide (4p)

A pale-yellow solid (190 mg, 54% yield); m.p: 211–213 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 10.03 (s, 1H), 9.92 (s, 1H), 8.45 (s, 1H), 8.12 (s, 1H), 7.66 (d, J = 9.0 Hz, 2H), 7.53 (d, J = 3.9 Hz, 2H), 7.38 (s, 1H), 6.95 (d, J = 9.0 Hz, 2H), 5.91 (s, 1H), 3.93 (s, 3H), 2.13 (s, 3H), 1.83 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 164.48, 157.28, 156.20, 154.49, 154.15, 152.59, 151.99, 150.78, 148.99, 145.00, 135.09, 128.87, 127.21, 127.08, 126.99, 125.29, 125.25, 120.67, 119.29, 117.22, 112.83, 108.82, 108.52, 56.18, 27.02, 19.47. HRMS (ESI): m/z calcd for C₂₆H₂₁Cl₂FN₄O₃: 527.1047 [M+H] ⁺; found: 527.1046.

N-(2-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)phenyl)-3-methylbut-2-enamide (4q)

A pale-yellow solid (201 mg, 57% yield); m.p: 214–216 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 9.81 (s, 1H), 9.35 (s, 1H), 8.48 (s, 1H), 8.14 (s, 1H), 7.54 (d, J = 3.5 Hz, 2H), 7.42 (s, 1H), 6.97–7.08 (m, 3H), 6.72 (dd, J = 8.0, 1.5 Hz, 1H), 6.19 (s, 1H), 3.95 (s, 3H), 2.16 (d, J = 1.0 Hz, 3H), 1.84–1.85 (m, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 164.93, 157.31, 156.40, 154.35, 151.46, 149.31, 148.06, 144.29, 128.93, 128.74, 126.93, 125.32, 125.27, 124.14, 122.61, 119.71, 119.52, 119.30, 115.52, 114.05, 108.82, 108.61, 56.23, 27.02, 19.54. HRMS (ESI): m/z calcd for C₂₆H₂₁Cl₂FN₄O₃: 527.1047 [M+H] ⁺; found: 527.1043.

N-(4-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)-3-methoxyphenyl)-3-methylbut-2-enamide (4r)

A pale-yellow solid (257 mg, 69% yield); m.p: 162–164 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 9.95 (s, 1H), 9.68 (s, 1H), 8.40 (s, 1H), 7.69 (s, 1H), 7.60 (s, 1H), 7.51 (s, 2H), 7.34 (s, 1H), 7.19 (d, J = 7.4 Hz, 1H), 6.95 (d, J = 8.7 Hz, 1H), 5.88 (s, 1H), 3.99 (s, 3H), 3.75 (s, 3H), 2.15 (s, 3H), 1.86 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 164.56, 157.03, 154.99, 153.29, 151.26, 150.38, 146.99, 138.95, 137.16, 128.91, 127.29, 125.25, 125.23, 125.21, 120.35, 119.61, 119.42, 119.16, 111.35, 108.60, 107.38, 104.71, 56.08, 55.54, 27.05, 19.49. HRMS (ESI): m/z calcd for C₂₇H₂₃Cl₂FN₄O₄: 557.1153 [M+H] ⁺; found: 557.1152.

N-(2-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)-5-methoxyphenyl)-3-methylbut-2-enamide (4s)

A pale-yellow solid (227 mg, 61% yield); m.p: 207–209 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 9.75 (s, 1H), 9.25 (s, 1H), 8.43 (s, 1H), 7.92 (s, 2H), 7.52 (s, 2H), 7.37 (s, 1H), 6.76 (s, 1H), 6.60 (dd, J = 8.9, 3.0 Hz, 1H), 6.15 (s, 1H), 3.96 (s, 3H), 3.72 (s, 3H), 2.13 (s, 3H), 1.83 (s, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 165.03, 164.06, 156.12, 154.96, 154.91, 151.87, 146.10, 146.00, 140.22, 130.47, 130.20, 127.06, 126.11, 125.36, 125.30, 119.71, 119.52, 119.28, 117.79, 111.87, 109.17, 108.05, 99.49, 56.23, 55.36, 19.59, 17.56. HRMS (ESI): m/z calcd for C₂₇H₂₃Cl₂FN₄O₄: 557.1153 [M+H] ⁺; found: 557.1152.

N-(2-((4-((3,4-Dichloro-2-fluorophenyl)amino)-7-methoxyquinazolin-6-yl)oxy)pyridin-4-yl)-3-methylbut-2-enamide (4t)

A pale-yellow solid (197 mg, 56% yield); m.p: 246–248 °C; ¹H NMR (400 MHz, DMSO-d₆) δ 9.79 (s, 1H), 9.65 (s, 1H), 8.53 (dd, J = 7.9, 1.6 Hz, 1H), 8.50 (s, 1H), 8.28 (s, 1H), 7.72 (dd, J = 4.9, 1.7 Hz, 1H), 7.56 (s, 2H), 7.40 (s, 1H), 7.09 (dd, J = 7.9, 4.9 Hz, 1H), 6.27 (s, 1H), 3.88 (s, 3H), 2.19 (d, J = 1.1 Hz, 3H), 1.87 (d, J = 1.1 Hz, 3H). ¹³C NMR (101 MHz, DMSO-d₆) δ 165.44, 157.39, 156.79, 154.52, 153.50, 152.51, 151.85, 149.85, 142.24, 140.36, 128.91, 126.90, 125.34, 125.30, 122.81, 119.71, 119.53, 118.92, 118.83, 116.23, 108.67, 108.26, 56.21, 27.13, 19.65. HRMS (ESI): m/z calcd for C₂₅H₂₀Cl₂FN₅O₃: 528.1000 [M+H] ⁺; found: 528.1001.

Design, synthesis, and in vitro antitumor activity of 6-aryloxyl substituted quinazoline derivatives

Table of contents

1.	The general synthetic procedure for intermediates 2a–2e and 3a–3e.	S2–S4
2.	1H and 13C NMR spectra of compounds 4a–4t	S5–S29

1. Experimental procedures and physical data of compounds

1.1 General procedure for the preparation of intermediates 2a–2e

N-(3,4-Dichloro-2-fluorophenyl)-7-methoxy-6-(4-nitrophenoxy)quinazolin-4-amine (2a)

To a solution of compound 1 (5.00 g, 14.1 mmol), potassium carbonate (K₂CO₃) (5.85 g, 42.3 mmol) in N,N-dimethylformamide (DMF) (50.0 mL), was dropwised 1-fluoro-4-nitrobenzene (1.50 mL, 14.1 mmol) slowly at 0 °C. After addition, the reaction mixture was allowed to stir for 6 h at 50 °C and TLC indicated complete consumption of the starting material. The reaction mixture was partitioned between water and ethyl acetate, the organic layers were combined, dried, filtered, and concentrated. The residue was purified by chromatography to afford the compound 2a as yellow powder (5.8 g, 86.6%).¹H NMR (400 MHz, DMSO-d₆) δ 9.78 (s, 1H), 8.48 (s, 1H), 8.30 (s, 1H), 8.21 (d, J = 9.3 Hz, 2H), 7.52 (s, 2H), 7.44 (s, 1H), 7.13 (d, J = 9.3 Hz, 2H), 3.87 (s, 3H).

N-(3,4-Dichloro-2-fluorophenyl)-7-methoxy-6-(2-nitrophenoxy)quinazolin-4-amine (2b)

The synthetic method of compound 2b was the same to compound 2a. Compound 2b as yellow solid (5.5 g, 82.1%). ¹H NMR (400 MHz, DMSO-d₆) δ 9.80 (s, 1H), 8.51 (s, 1H), 8.25 (s, 1H), 8.08 (dd, J = 8.1, 1.6 Hz, 1H), 7.63 (m, 1H), 7.56 (d, J = 4.5 Hz, 2H), 7.45 (s, 1H), 7.32–7.35 (m, 1H), 7.05 (dd, J = 8.4, 1.1 Hz, 1H), 3.93 (s, 3H).

N-(3,4-Dichloro-2-fluorophenyl)-7-methoxy-6-(2-methoxy-4-nitrophenoxy)-quinazolin-4-amine (2c)

The synthetic method of compound 2c was the same to compound 2a. Compound 2c as yellow solid (5.7 g, 85.1%). ¹H NMR (400 MHz, DMSO-d₆) δ 9.69 (s, 1H), 8.46 (s, 1H), 8.11 (s, 1H), 7.91 (d, J = 2.6 Hz, 1H), 7.80 (dd, J = 8.9, 2.7 Hz, 1H), 7.52 - 7.51 (m, 2H), 7.42 (s, 1H), 6.90 (d, J = 8.9 Hz, 1H), 3.95 (s, 3H), 3.90 (s, 3H).

N-(3,4-Dichloro-2-fluorophenyl)-7-methoxy-6-(4-methoxy-2-nitrophenoxy)-quinazolin-4-amine (2d)

The synthetic method of compound 2d was the same to compound 2a. Compound 2d as yellow solid (5.6 g, 83.6%). ¹H NMR (400 MHz, DMSO-d₆) δ 9.72 (s, 1H), 8.46 (s, 1H), 8.00 (s, 1H), 7.66 (d, J = 3.1 Hz, 1H), 7.54 (s, 2H), 7.41 (s, 1H), 7.29 (dd, J = 9.2, 3.1 Hz, 1H), 7.16 (d, J = 9.2 Hz, 1H), 3.95 (s, 3H), 3.85 (s, 3H).

N-(3,4-Dichloro-2-fluorophenyl)-7-methoxy-6-((4-nitropyridin-2-yl)oxy)-quinazolin-4-amine (2e)

The synthetic method of compound 2e was the same to compound 2a. Compound 2e as yellow solid (5.5 g, 82.1%). ¹H NMR (400 MHz, DMSO-d₆) δ 9.82 (s, 1H), 8.63 (dd, J = 8.0, 1.6 Hz, 1H), 8.52 (s, 1H), 8.41 (dd, J = 4.8, 1.7 Hz, 1H), 8.37 (s, 1H), 7.58 (d, J = 8.2 Hz, 2H), 7.43 (d, J = 4.8 Hz, 1H), 7.41 (d, J = 4.8 Hz, 1H), 3.86 (s, 3H).

1.2 General procedure for the preparation of intermediates 3a–3e

6-(4-aminophenoxy)-N-(3,4-dichloro-2-fluorophenyl)-7-methoxyquinazolin-4-amine (3a)

A suspension of 2a (1.00 g, 2.10 mmol), Fe (0.35 g, 6.30 mmol), and NH₄Cl (0.58 g, 10.5 mmol) in CH₃OH/H₂O (10 mL/10 mL) was stirred at 80 °C for 4 h. The mixture was cooled to room temperature, quenched with aqueous Na₂CO₃ solution, and filtered through celite. The aqueous layer was separated and extracted with ethyl acetate. The combined organic layers were washed with water and brine, dried over Na₂SO₄, and concentrated. The residue was purified by chromatography to afford the compound 3a as yellow powder (0.7 g, 75.3 %). ¹H NMR (400 MHz, DMSO-d₆) δ 9.67 (s, 1H), 8.38 (s, 1H), 7.76 (s, 1H), 7.49 (s, 2H), 7.30 (s, 1H), 6.77 (d, J = 8.9 Hz, 2H), 6.59 (d, J = 9.1 Hz, 2H), 4.92 (s, 2H), 3.94 (s, 3H).

6-(2-aminophenoxy)-N-(3,4-dichloro-2-fluorophenyl)-7-methoxyquinazolin-4-amine (3b)

The synthetic method of compound 3b was the same to compound 3a. Compound 3b as yellow solid (0.75 g, 80.6%). ¹H NMR (400 MHz, DMSO-d₆) δ 9.74 (s, 1H), 8.44 (s, 1H), 7.89 (s, 1H), 7.52 (s, 2H), 7.38 (s, 1H), 6.87 (m, 1H), 6.81 (dd, J = 7.9, 1.7 Hz, 1H), 6.65 (d, J = 6.9 Hz, 1H), 6.53–6.49 (m, 1H), 4.97 (s, 2H), 3.97 (s, 3H).

6-(4-amino-2-methoxyphenoxy)-N-(3,4-dichloro-2-fluorophenyl)-7-methoxyquinazolin-4-ami ne (3c)

The synthetic method of compound 3c was the same to compound 3a. Compound 3c as yellow solid (0.8 g, 85.1%). ¹H NMR (400 MHz, DMSO-d₆) δ 9.63 (s, 1H), 8.36 (s, 1H), 7.50 (s, 2H), 7.42 (s, 1H), 7.28 (s, 1H), 6.77 (d, J = 8.5 Hz, 1H), 6.41 (d, J = 2.4 Hz, 1H), 6.18 (dd, J = 8.5, 2.5 Hz, 1H), 5.07 (s, 2H), 3.99 (s, 3H), 3.66 (s, 3H).

6-(2-amino-4-methoxyphenoxy)-N-(3,4-dichloro-2-fluorophenyl)-7-methoxyquinazolin-4-ami ne (3d)

The synthetic method of compound 3d was the same to compound 3a. Compound 3d as yellow solid (0.66 g, 71.0%). ¹H-NMR (400 MHz, DMSO-d₆) δ 9.70 (s, 1H), 8.40 (s, 1H), 7.68 (s, 1H), 7.53 (d, J = 10.1 Hz, 1H), 7.50–7.45 (m, 1H), 7.34 (s, 1H), 6.72 (d, J = 8.7 Hz, 1H), 6.41 (d, J = 2.9 Hz, 1H), 6.13 (dd, J = 8.8, 3.0 Hz, 1H), 4.96 (s, 2H), 3.99 (s, 3H), 3.67 (s, 3H).

6-((4-aminopyridin-2-yl)oxy)-N-(3,4-dichloro-2-fluorophenyl)-7-methoxyquinazolin-4-amine (3e)

To a solution of compound 2e (2.0 g, 4.21 mmol) in 40 mL of methanol was added 1.0 g of 10% Pd on carbon catalyst. The reaction mixture was allowed to stir for 2 h at 40 °C under H₂ atmosphere. The solution was filtered through a pad of celite, dried and concentrated to give compound 3e as yellow powder (0.82 g, 88.2 %). ¹H NMR (400 MHz, DMSO-d₆) δ 9.70 (s, 1H), 8.39 (s, 1H), 8.35 (d, J = 9.4 Hz, 1H), 7.51 (t, J = 7.8 Hz, 1H), 7.29–7.28 (m, 1H), 7.28 (s, 1H), 7.26–7.25 (m, 1H), 7.23 (d, J = 3.2 Hz, 1H), 7.21 (s, 1H), 7.20 (s, 2H), 3.88 (s, 3H).

2. ¹H and ¹³C NMR spectra of compounds 2, 3, and 4

¹HNMR spectrum of 2a

¹HNMR spectrum of 2b

¹HNMR spectrum of 2c

¹HNMR spectrum of 2d

¹HNMR spectrum of 2e

¹HNMR spectrum of 3a

¹HNMR spectrum of 3b

¹HNMR spectrum of 3c

¹HNMR spectrum of 3d

¹HNMR spectrum of 3e

¹H NMR spectrum of 4a

¹³C NMR spectrum of 4a

¹H NMR spectrum of 4b

¹³C NMR spectrum of 4b

¹H NMR spectrum of 4c

¹³C NMR spectrum of 4c

¹H NMR spectrum of 4d

¹³C NMR spectrum of 4d

¹H NMR spectrum of 4e

¹³C NMR spectrum of 4e

¹H NMR spectrum of 4f

¹³C NMR spectrum of 4f

¹H NMR spectrum of 4g

¹³C NMR spectrum of 4g

¹H NMR spectrum of 4h

¹³C NMR spectrum of 4h

¹H NMR spectrum of 4i

¹³C NMR spectrum of 4i

¹H NMR spectrum of 4j

¹³C NMR spectrum of 4j

¹H NMR spectrum of 4k

¹³C NMR spectrum of 4k

¹H NMR spectrum of 4l

¹³C NMR spectrum of 4l

¹H NMR spectrum of 4m

¹³C NMR spectrum of 4m

¹H NMR spectrum of 4n

¹³C NMR spectrum of 4n

¹H NMR spectrum of 4o

¹³C NMR spectrum of 4o

¹H NMR spectrum of 4p

¹³C NMR spectrum of 4p

¹H NMR spectrum of 4q

¹³C NMR spectrum of 4q

¹H NMR spectrum of 4r

¹³C NMR spectrum of 4r

¹H NMR spectrum of 4s

¹³C NMR spectrum of 4s

¹H NMR spectrum of 4t

¹³C NMR spectrum of 4t

Funding Statement

The author would like to thank the financial support by the Doctoral Foundation of Yantai University (No. YX 13B04).