Design, synthesis and in vitro evaluation of 6-amide-2-aryl benzoxazole/benzimidazole derivatives against tumor cells by inhibiting VEGFR-2 kinase

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Abstract

Design, synthesis and in vitro evaluation of 6-amide-2-aryl

benzoxazole/benzimidazole derivatives against tumor cells by inhibiting

VEGFR-2 kinase

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Xu Yuan, Tongyan Liu, Qingyi Yang, , Ke Li,* Yuwen Liu, Changcheng Zhu, ZhiYun

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Zhang, Linghua Li, Conghai Zhang, Mingjin Xie, Jun Lin,* Jihong Zhang* and Yi Jin*

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Design, synthesis and in vitro evaluation of 6-amide-2-aryl

benzoxazole/benzimidazole derivatives against tumor cells by

inhibiting VEGFR-2 kinase

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Xu Yuan, Qingyi Yang, Tongyan Liu, , Ke Li,* Yuwen Liu, Changcheng

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Zhu, Zhiyun Zhang, Linghua Li, Conghai Zhang, Mingjin Xie, Jun Lin,*

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Jihong Zhang* and Yi Jin*

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a. Key Laboratory of Medicinal Chemistry for Natural Resource, Ministry Education

and Yunnan Province, School of Chemical Science and Technology, Yunnan

University, Kunming, 650091, P. R. China.

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b. Laboratory of Molecular Genetics of Aging and Tumor, Medical School, Kunming

University of Science and Technology, Kunming, 650500, P. R. China.

c. Biomedical Department, Yunnan Cancer Hospital, the Third Affiliated Hospital of

Kunming Medical University, Kunming, 650118, P. R. China.

d. Institute of Drug Research and Development, Kunming Pharmaceutical

Corporation, Kunming, 650100, P. R. China.

e. Department of Anorectal, Kunming Municipal Hospital of Traditional Chinese

Medicine, Kunming, 650011, P. R. China.

f. School of Clinical Medicine, Dehong Vocational College, Mangshi, 678400, China

‡ the authors contributed equally to this work.

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Corresponding author. Tel./fax: +86-871-6503-3119. E-mail: likelikelike@126.com

(K. Li), linjun@ynu.edu.cn (J. Lin); zhjihong2000@126.com (JH. Zhang);

jinyi@ynu.edu.cn (Y. Jin).

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Keywords: benzoxazole; benzimidazole; VEGFR-2; angiogenesis; antitumor activity

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Abstract:

Herein, we have carried out a structural optimization campaign to discover the novel

anti-tumor agents with our previously screened YQY-26 as the hit compound. A

library of thirty-seven 6-amide-2-aryl benzoxazole/benzimidazole derivatives has

been designed and synthesized based on the highly conserved active site of VEGFR-2.

Several title compounds exhibited selective inhibitory activities against VEGFR-2

than EGFR kinases, which also displayed selective anti-proliferation potency against

the HUVEC and HepG2 than the A549 and MDA-MB-231 cancer cell lines. The

newly synthesized compounds were evaluated for anti-angiogenesis capability by

chick chorioallantoic membrane (CAM) assay. Among them, compounds 9d showed

the most potent anti-angiogenesis ability (79% inhibition at 10 nM/eggs), the efficient

cytotoxic activities (in vitro against the HUVEC and HepG2 cell lines with IC₅₀

values of 1.47 and 2.57 µM, respectively), and excellent VEGFR-2 kinase inhibition

(IC = 0.051 µM). The molecular docking analysis revealed that compound 9d is a

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Type II inhibitor of VEGFR-2 kinase. These results indicated that the

6-amide-2-arylbenzoxazole and 6-amide-2-aryl benzimidazole derivatives are

promising inhibitors of VEGFR-2 kinase for the potential treatment of

anti-angiogenesis.

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1. Introduction

According to the report published by World Health Organization in 2018, the

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number of cancer cases in the world will increase to 22 million by 2030. Therefore,

continuous exploration and discovery of anti-cancer drugs that are low in toxicity and

highly efficient are still important directions in anti-cancer drug research and

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development. As early as 1971, Dr. Judah Folkman proposed that tumor growth and

metastasis are vascular-dependent, and blocking angiogenesis is an effective strategy

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for inhibiting tumor growth. It has been found that the vascular endothelial growth

factor (VEGF) can promote the proliferation and migration of vascular endothelial

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cells and induce the formation of blood vessels.

There are three main vascular

endothelial growth factor receptors (VEGFR-1, VEGFR-2, and VEGFR-3), which are

key intermediates in tumor angiogenesis and in the formation of new blood vessel

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networks required to supply nutrition and oxygen for tumor growth.

VEGFR-2 is

the main functional receptor of VEGF, and it is involved in the regulation of blood

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vessel formation.

Many studies have shown that the abnormal expression of

VEGFR-2 in tumor cells is related to tumor growth and migration. Therefore,

blocking the VEGF/VEGFR-2 signaling pathway or decreasing its response is a

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practical method in the study of new drugs for cancers

. Recently, numerous small

molecule targeting agents have been approved for inhibiting this critical pathway in

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angiogenesis (Fig. 1),

but the development of novel anti-angiogenic inhibitors to

prevent drug resistance is still necessary.

Up to now, a number of X-ray crystal structures of VEGFR-2 complexed with an

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inhibitor have been reported,

providing a possibility for target-based virtual

screening. In a virtual screening of 200,000 diverse drug-like compounds targeting

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DFG-out pocket

of VEGFR-2 and subsequent phenotypic screen experiments, we

identified a 6-amide-2-arylbenzoxazole derivative, YQY26 (Fig. 2), with

sub-micromolar cytotoxicity against hepatocellular carcinoma cells (HepG2) and

sub-micromolar enzymatic inhibition against the VEGFR-2 protein. Benzoxazoles are

structural isosteres of natural nucleotides that easily interact with bio-macromolecules.

Their derivatives and related fused heterocycles such as benzimidazoles were studied

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for their inflammatory,

antiviral,

antitumor,

antitubercular,

antiprion ,

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and antimicrobial

activities. To further identify new benzoxazole and

benzimidazoles derivatives with potential VEGFR-2 kinase inhibition and anticancer

activities, we synthesized 37 analogs of YQY-26 to establish a structural requirement

for potency. We then carried out anti-angiogenesis assay of chick chorioallantoic

membrane to understand how these compounds can inhibit vascular growth. Our

results demonstrate that our newly synthesized 6-amide-2-arylbenzoxazole and

6-amide-2-arylbenzimidazole derivatives (5 and 9) are a novel class of

small-molecule inhibitors of VEGFR-2.

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Fig. 1. Representative angiogenesis inhibitors currently approved

2. Results and discussion

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2.1 Identification of the hit compound YQY-26 and compound design

Protein kinases have a conserved activation loop consisting of Asp-Phe-Gly amino

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acid residues which is known as a DFG motif. Small molecule kinase inhibitors are

normally divided into Type-I and Type-II groups that differ with their binding

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conformation as DFG-in and DFG-out, respectively. With more favorable kinase

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selectivity and slower off-rates, Type II inhibitors are usually expected to possess

several advantages than Type I inhibitors.

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Fig. 2 Design of novel benzoxazole and benzimidazole derivatives. a) The screening process for hit compound

YQY-26; b) and d) Computational 3D binding pattern of compound YQY-26 with VEGFR-2 kinase; c) 2D binding

pattern of YQY-26 with VEGFR-2.

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To identify novel scaffold of VEGFR-2 inhibitors targeting the catalytic site, a virtual

screening procedure was employed and followed by biological testing of the

identified compound. Publication of the crystal structure (PDB code: 3WZE) of

VEGFR-2 crystallized with sorafenib revealed that sorafenib is a Type II inhibitor

blocking VEGFR-2 DFG-out. Initially, the first step of our study was to evaluate the

reliability of three types of docking methods for the prediction of the binding mode of

sorafenib into the VEGFR-2 protein through GOLD 3.0, MolDock (MVD) and Glide

5.6 software. The docking reliability was evaluated through a comparison of the

root-mean-square deviation (RMSD) between the positions of heavy atoms of the

ligand in the calculated configuration and small molecule in the crystal structure. The

results indicated that all three programs are suitable for virtual screening with RMSD

values (1.1, 1.2, and 1.1, respectively). Then, a total of 200,000 compounds from

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SPECS database were docked and ranked. The selection of the candidate molecules

was based on the following criteria: 1) the ligand can form hydrogen bonding

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interactions with the hinge residues; 2) the ligand should form interaction with

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Asp1046 (a residue important for Type-II inhibitors). Finally, a total of 127

compounds meet the above criteria and were commercially available for in vitro

assay.

In the hepatocellular carcinoma cell line screening (Fig. 2a), we identified eight

compounds with IC₅₀values less than 50µM. These eight compounds were further

tested for VEGFR-2 inhibition in a protein kinase assay. Five compounds

demonstrated potent inhibition (IC < 10 µm), and after confirming the activity with

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re-purchased compound stocks and verifying a dose-dependent response, the most

potent compound 4-chloro-3-fluoro-N-(2-phenylbenzo[d]oxazol-5-yl)benzamide

(YQY-26), was selected for further analysis and optimization. According to the

binding conformation of YQY-26 in VEGFR-2 active pocket, the benzoxazole ring

binds to the hinge region of the kinase protein with two hydrogen bonds. A benzoyl

group occupied the adenosine 5’-triphosphate (ATP) catalytic site with a

hydrogen-halide bond between Cl atom and Lys920, and a phenyl group occupied

another hydrophobic pocket induced by the DFG-out state with an H-π interaction

between phenyl and Leu889 (Fig. 2b-d).

We hypothesized that the unique interactions are important features for Type-II

inhibitors of YQY-26. Meanwhile, benzoxazole and benzimidazole are a highly

significant group of biological molecules that are widely found in agrochemicals,

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pharmaceuticals, synthetic drugs, and bioactive natural products.

As far as we

know, the reports of benzoxazole and benzimidazole derivatives applied to inhibit the

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activity of VEGFR-2 kinase are rare.

Therefore, we planned to investigate the

effects of the designed compounds on the activity through four different ways (Fig.

2a): 1) changing halogen atoms on benzoyl group; 2) replacing benzoyl with phenyl

acetyl group; 3) adding halogen atoms on phenyl group; 4) altering benzoxazole to

benzimidazole.

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2.2 Chemistry

The general preparation methods for 2-arylbenzoxazole derivatives are displayed

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in Scheme 1. The readily available starting material 2,4-diaminophenol 1 was reacted

with different substituted benzoic acids 2 in polyphosphoric acid (PPA) at 170 °C for

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10-18 h to give the 2-arylbenzoxazole intermediate 3. Intermediate 3 and the

substituted aromatic carboxylic acid 4 were subjected to an amidation reaction at

20 °C for 2-4 h with 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDCI) and

hydroxybenzotriazole (HOBt) as a condensing agent and triethanolamine (TEA) as

base to obtain the target compound 5.

Scheme 1. General preparation methods for 2-aryl benzoxazoles derivatives.

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a: R =F, R =Br ,R = X =X =H, n=0

1 2 3 1 2

5t: R =F, R =Cl, R =X =H, X =2-Cl, n=0

1 2 3 1 2

b: R =F, R =Cl, R = X =X =H, n=0

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5u: R =Br, R =Cl, R =X =H, X =2-Cl, n=0

1 2 3 1 2

c: R =Br, R =Cl, R = X =X =H, n=0

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5v: R =R =OMe, R =X =H, X =2-Cl, n=1

1 2 3 1 2

d: R = R =MeO, R = X =X =H, n=1

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5w: R =R =R =OMe, X =H, X =2-Cl, n=1

1 2 3 1 2

e: R = R =R = OMe, X =X =H, n=1

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5x: R =R =X =H, R =OMe, X =2-Cl, n=1

1 3 1 2 2

f: R =F, R =Br, R =X =H, X =Cl, n=0

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5y: R =R =X =H, R =Me, X =2-Cl, n=1

1 3 1 2 2

g: R =F, R =Cl, R =X =H, X =Cl, n=0

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5z: R =F, R =Br, R =X =H, X =2-Br, n=0

1 2 3 1 2

h: R =Br, R =Cl, R =X =H, X =Cl, n=0

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5aa: R =F, R =Cl, R =X =H, X =2-Br, n=0

1 2 3 1 2

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i: R = R =MeO, R = X =H, X =Cl, n=1

5ab: R =Br, R =Cl, R =X =H, X =2-Br, n=0

1 2 3 1 2

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j: R = R =R = OMe, X =H, X =Cl, n=1

5ac: R =R =X =H, R =OMe, X =2-Br, n=1

1 3 1 2 2

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k: R =R =X =H, R =MeO, X =Cl, n=1

5ad: R =R =X =H, R =Me, X =2-Br, n=1

1 3 1 2 2

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l: R =F, R =Br, R =X =H, X =2-F, n=0

5ae: R =F, R =Br, R =H, X = Cl, X =3-Br, n=0

1 2 3 1 2

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m: R =F, R =Cl, R =X =H, X =2-F, n=0

5af: R =Cl, R =F, R =H, X = Cl, X =3-Br, n=0

1 2 3 1 2

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n: R =Br, R =Cl, R =X =H, X =2-F, n=0

5ag: R =Br,R =Cl,R =H,X =Cl,X =3-Br, n=0

1 2 3 1 2

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o: R =R =OMe, R =X =H, X =2-F, n=1

5ah: R =R =OMe, R =H, X =Cl,X =3-Br, n=1

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p: R =R = R =OMe, , X =H, X =2-F, n=1

5ai: R =R =R =OMe, X =Cl, X =3-Br, n=1

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q: R = R = X =H, R =OMe, X =2-F, n=1

5aj: R =R =H, R =OMe, X =Cl, X =3-Br, n=1

1 3 2 1 2

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r: R =R =X =H, R =Me, X =2-F, n=1

5ak: R =R =H, R =Me, X =Cl, X =3-Br, n=1

1 3 2 1 2

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s: R =F, R =Br, R =X =H, X =2-Cl, n=0

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In the above synthetic route, the key step is the condensation between

halobenzoic acid/phenylacetic acid 4 and the 2-arylbenzoxazole structure 3. Factors

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such as reaction temperature, solvent, and condensing agent have great influence upon

the yield of the reaction. Therefore, we used compound 3a as a template to optimize

the reaction conditions. First, we screened for the condensing agent required for the

reaction. When using DCC, 1,1'-carbonyldiimidazole (CDI), and N-methylmorpholine

(NMM) as condensing agents, the reaction did not carry out in CH Cl or

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dimethylformamide (DMF) (Table 1, entry 1, 2). When using EDCI, HOBt, and TEA

as condensing agents, the target product can be obtained in high yield with CH Cl or

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DMF as the solvent at 20°C (Entry 3, 4). In particular, a reaction yield (Entry 4) up to

86.5% was obtained after 4 h reaction with DMF as a solvent. The reaction can also

proceed with CDI and DMAP as a condensing agent and give intermediate yields

(Entry 5, 6). Finally, under optimal conditions, we successfully synthesized

thirty-seven target compounds with good reaction yield (80%-95%), and all the

products were substituted with different electron-withdrawing and electron-donating

substituents of benzoic acid or phenylacetic acid. HPLC analysis also confirmed that

the purity of the compounds was between 95% and 100%.

Table 1. Reaction conditions optimization for the condensation between 3a and 4a.

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Entry

Solvent

Condensation reagent

DCC, CDI, NMM

EDCI, HOBt, TEA

CDI, DMAP

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Yield (%)

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46%

CH Cl₂

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CH Cl₂

CDI, DMAP

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Similarly, the synthesis of 2-arylbenzimidazole derivatives is shown in Scheme 2.

The readily available 4-nitro-1,2-phenylenediamine structure 6 was reacted with

4-chlorobenzoic acid 2 in PPA at 150°C for 10-15 h to give the 2-arylbenzimidazole

structure 7. The nitro group was reduced to generate intermediate structure 8, which

was then reacted with the substituted aromatic acid 4 at 20°C and with EDCI, HOBt,

and TEA as a condensing agent for 2-4 h. Five target compounds of 9 were obtained

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in the 80%-90% yield.

Scheme 2. General preparation methods for 2-arylbenzimidazole derivatives

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a: R =F, R =Cl, R =H, n=0

9d: R =R =H, R =OMe, n=1

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b: R =Br, R =Cl, R =H, n=0

9e: R =R =H, R =Me, n=1

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c: R =R =R =OMe, n=1

1 2 3

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2.3 Biological Activity Evaluation

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2.3.1. Kinase inhibitory activities and structure-activity relationship (SAR) study

The synthesized compounds were evaluated for their inhibitory activities against

vascular Endothelial Growth Factor Receptor 2 (VEGFR-2) and epidermal growth

factor receptor (EGFR) kinase using sunitinib and sorafenib as a positive control.

According to the results (Table 2), it is obvious that all compounds showed selective

inhibition against VEGFR compared with EGFR at 1 µM, although some compounds

exhibited moderate inhibitory activity against EGFR, such as 5i (92.6% against

VEGFR-2 vs. 52.2% against EGFR), 5j (91.5% against VEGFR-2 vs. 58.9% against

EGFR), and 9d (102.8% against VEGFR-2 vs. 51.4% against EGFR). As for the

SARs of 6-amide-2-arylbenzoxazole and 6-amide-2-arylbenzimidazole derivatives

against VEGFR-2 kinase: firstly, compared with YQY-26 (5b, 47.8% inhibition), the

activity of 3-F and 4-Br substituted benzamide (5a, 42.2% inhibition) did not

significantly change, while 3-Br and 4-Cl substituted benzamide (5c, 72.4% inhibition)

contributed to the increased activity. Interestingly, after replacement of benzamide by

phenylacetamide with electron-donating groups, the inhibitory activity of the

compounds against VEGFR-2 was significantly increased, such as 5d (83.5%

inhibition), and 5e (89.3% inhibition), which suggested that the electronic interaction

and the length of aromatic amides had an important effect on the kinase inhibitory

activities.

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Additionally, it is noteworthy that the inhibitory activity of 4-OMe or 4-Me

substituted phenylacetamide is greater than that of 3,4,5-OMe or 3,4-OMe substituted

samples, such as 5o (3,4-OMe, 84.2%), 5p (3,4,5-OMe, 80.3%), 5q (4-OMe, 94.6%),

and 5r (4-Me, 97.3%), which suggested that the position and number of substitutes

also had a certain effect on the kinase inhibitory activities.

Next, we investigated the effects of 2-aryl substituents on the kinase activity (5f to

5ak). The results showed that 4-Cl substituted phenyl provided the best contribution

to activity enhancement. In particular, compound 5k exhibited an inhibitory activity

of 97.3 nM IC against VEGFR-2, while the inhibitory intensity of 2-F, 2-Cl, 2-Br, or

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3-Br substituted phenyl decreased in turn. Intriguingly, electron-donating group (EDG)

substituted phenyl (e.g., 4-Me, 4-OMe) obviously decreased inhibition of VEGFR-2

kinase (5al: 43.2% inhibition, 5am: 38.4% inhibition). Lastly, benzimidazole scaffold

compounds (9a to 9e) showed better VEGFR-2 kinase inhibitory activity than

benzoxazole compounds. Among them, the compound (9d, 51.4 nM IC ) with the

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best activity is basically the same as those of sorafenib (C1, 37.8 nM IC ) and

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sunitinib (C2, 29.2 nM IC ). Noteworthy, introduction of EDG to 2-phenyl also

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reduced the enzyme inhibitory activity (e.g., 9f and 9g). Based on the VEGFR-2

kinase activity evaluation, a preliminary SAR in this work was summarized in Fig. 3.

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Fig. 3 Preliminary structure-activity relationships of synthesized compounds against VEGFR-2 kinase

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2.3.2. Anti-proliferation activity of tumor cells in Vitro

The cell growth inhibitory activities of synthesized compounds were evaluated against

Human umbilical vein endothelial cell (HUVEC) and hepatocellular carcinoma

(HepG2) cell lines highly expressing the VEGFR-2 protein as well as non-small cell

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lung cancer (A549) and human breast cancer (MDA-MB-231) cell lines highly

expressing the EGFR protein by the standard MTT assay, with sorafenib as the

positive control. The anti-proliferative activities were listed in Table 2. Most of the

synthesized compounds showed moderate to high potency against

VEGFR-2-expressing HUVEC and HepG2 cells. Although some of the compounds

displayed anti-proliferative activities similar to those of sorafenib, almost all

compounds failed to inhibit the proliferation of EGFR-expressing A549 and

MDA-MB-231 cells. For example, compounds 5k, 9c, 9d, and 9e displayed

significant potency against HUVEC cell with IC values of 1.47-7.32 µM and against

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HepG2 cell with IC₅₀values of 2.57-8.22 µM, which are similar those of sorafenib

(5.35 and 2.41µM for HUVEC and HepG2 cells, respectively).

Nevertheless, the anti-proliferation activities of some targeted compounds were not

absolutely parallel with the enzymatic assays. For example, although 5q and 5r

exhibited good VEGFR-2 kinase inhibition activity, they displayed moderate

anti-proliferation potency compared to sorafenib. This inconsistency between protein

assay and cell potency could be regarded as the purified kinase domain of VEGFR-2

was being tested in the protein assay, whereas the kinases protein exit as a mixture of

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the cytoskeleton, phosphatases, and chaperones in the cellular assay. In contrast,

compounds 5n and 5v with poor VEGFR-2 protein inhibitions displayed satisfactory

anti-proliferation activities, which may be related to the complicated mechanism of

tumor cell survival, or through alternate cell signaling pathways but not by targeting

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VEGFR-2.

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Table 2 The kinase inhibitory activities and in vitro antiproliferative effects of the synthesized compounds

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a

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kinase inhibitory activities

in vitro anti-proliferative effects (IC50, µM)

Cpd

R

X

n

VEGFR-2

42.2±1.7

EGFR

HUVEC

HepG2

>100

A549

>100

MDA-MB-231

>100

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=Br,

=Cl,

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=F, R

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X

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47.8±2.6

13.9±1.3

27.45±0.62

91.93±3.58

>100

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1

2

1

2

1

2

1

=Br,

=Cl, R

=

X

1

=X

2

=H

0

1

72.4±3.1

32.5±0.7

16.85±1.54

68.15±2.68

16.38±0.76

78.62±3.08

89.2±2.39

>100

3

=H

b

d

83.5±3.6 (578.8±9.5)

37.2±1.7

18.43±0.23

94.34±4.17

=OMe,

=H

b

5

e

=R

2

=OMe

X

1

=X

2

=H

1

0

1

0

1

0

1

0

1

0

89.3±2.56(357.2±6.4)

70.8±2.4

47.3±0.6

35.8±0.7

46.8±2.5

44.1±3.6

52.2±0.9

58.9±2.5

49.4±2.8

32.6±1.2

27.8±1.8

37.1±2.8

32.3±1.4

34.2±2.3

42.8±1.6

39.5±1.3

21.4±2.8

28.5±0.6

25.6±1.4

36.2±0.5

26.5±1.3

43.8±2.8

47.5±2.5

21.8±0.5

22.6±0.7

27.5±1.4

36.2±1.2

39.1±0.5

19.21±1.46

37.23±1.25

22.16±1.33

13.38±0.38

11.36±0.68

13.26±1.07

5.25±0.09

26.35±2.53

54.45±2.71

49.26±1.47

37.02±1.62

24.27±1.27

28.17±0.72

8.22±0.12

16.4±0.79

8.28±0.98

95.13±2.43

>100

93.4±0.68

89.3±2.84

50.8±2.18

>100

79.48±2.79

>100±

=OMe

f

=F, R

=H

2

=Br,

=Cl,

=Cl, X

2

=H

g

=F, R

=H

72.1±1.6

69.21±2.63

>100

h

i

=Br,

90.2±2.8 (338.3±23.5)

b

3

=Cl, R =H

b

=R

=H

=R

2

=OMe,

92.6±2.8(386.4±12.6)

>100

b

j

2

=OMe

91.5±3.1 (258.8±9.7)

>100

=OMe

=R =H,

=OMe

b

k

l

3

101.7±3.1 (97.3±9.2)

74.36±1.37

28.3±1.38

>100

74.26±2.16

>100

=F, R

=H

2

=Br,

=H, X

2

=2-F

63.8±1.7

70.9±2.5

84.2±1.4

84.2±3.6

80.3±0.7

40.21±1.07

20.53±1.04

15.91±1.58

16.23±1.07

21.46±2.16

14.22±0.68

12.75±1.04

50.18±2.07

36.48±1.38

26.86±0.78

20.15±0.67

29.48±1.37

15.38±0.78

16.26±1.28

52.28±2.04

50.57±1.47

37.28±0.27

26.17±1.39

23.58±0.84

75.34±1.65

m

n

o

=F, R

=H

2

=Cl,

2

>100

=Br,

86.3±1.74

>100

83.37±2.17

>100

3

=Cl, R =H

=R

=H

=R

2

=OMe,

p

q

r

2

=OMe

96.36±2.93

37.28±0.93

39.21±1.38

32.95±1.83

16.96±1.73

97.47±2.58

17.27±0.94

48.89±1.07

30.84±1.32

36.27±0.75

31.24±1.47

86.23±1.75

57.32±2.58

46.98±2.06

33.13±0.73

59.21±2.78

96.44±1.36

>100

=OMe

= R =H,

= OMe

=R =H,

b

3

94.6±2.8 (165.9±6.3)

>100

b

3

97.3±0.8 (232.6±5.3)

83.27±1.84

>100

93.68±2.48

>100

= Me

=F, R

=H

s

2

=Br,

=Cl,

=H,

2

=2-Cl

59.5±2.6

71.3±1.3

80.9±2.5

86.4±1.7

75.8±2.6

t

=F, R

=H

62.93±2.45

54.29±3.12

>100

u

v

=Br,

=H,X

2

=2-Cl

66.93±1.19

>100

3

=Cl, R =H

=R

=H

=R

2

=OMe,

=H, X

2

=2-Cl

=2-Br

=3-Br

w

x

2

=OMe

>100

=OMe

=R =H,

=OMe

=R =H,

b

3

90.1±3.1(443.8±12.4)

>100

76.23±2.15

47.67±1.47

>100

b

y

3

93.5±2.8(488.7±16.1)

64.39±1.58

66.22±2.08

74.18±1.85

53.38±1.04

55.24±2.78

40.17±1.26

47.40±1.04

=Me

=F, R

=H

z

2

=Br,

=Cl,

62.3±1.8

59.3±2.6

71.4±0.9

87.3±2.8

aa

ab

ac

ad

ae

=F, R

=H

93.27±2.69

>100

=Br,

=Cl, R

=R =H,

=OMe

=R =H,

3

=H

3

84.33±1.32

74.28±0.63

>100

b

3

89.1±2.5 (842.4±7.4)

= Me

=F, R

2

=Br,

36.5±2.4

18.4±1.3

1

2

ACCEPTED MANUSCRIPT

R

3

1

3

1

2

1

3

1

3

1

2

1

2

1

2

1

2

1

3

1

2

1

3

1

2

1

2

1

2

1

2

=H

5

9

af

ag

ah

ai

aj

ak

al

am

a

=F, R

=H

2

=Cl,

X

1

=H, X

2

=3-Br

0

1

0

1

40.2±1.6

14.6±1.1

19.5±1.7

20.4±1.9

21.5±1.1

36.3±1.6

37.4±1.4

21.6±1.1

19.4±0.5

45.2±0.6

40.8±2.7

43.1±0.7

58.3±1.8

48.3±1.8

31.5±2.1

27.8±0.8

69.31±2.38

53.87±2.86

46.27±1.63

52.38±1.77

38.28±1.05

37.25±2.31

57.48±2.58

63.57±2.31

13.38±0.42

7.61±0.06

7.32±1.26

1.47±0.02

3.21±0.02

26.46±0.16

30.58±0.47

5.35±0.07

52.67±1.63

71.58±2.05

83.79±2.06

>100

46.81±0.96

93.26±2.96

>100

87.8±1.48

>100

=Br,

62.8±0.5

3

=Cl, R =H

=R

=H

=R

2

=OMe,

65.0±1.3

>100

2

=OMe

47.5±2.6

>100

=OMe

=R =H,

= OMe

=R =H,

= Me

=R =H,

= OMe

= R = H,

= OMe

3

79.9±3.8

>100

3

81.7±0.7

64.21±0.56

>100

3

X

1

2

1

2

1

=4-Me,

=H

43.2±1.7

>100

3

=4-OMe,

=H

38.4±1.8

>100

b

=F, R

=H

2

=Cl,

=4-Cl

87.5±2.6 (987.7±4.2)

93.8±3.1 (542.2±6.6)

90.2±2.8 (418.7±5.2)

102.8±2.8 (51.4±1.3)

100.4±3.6 (73.7±4.1)

75.2±2.7

26.26±0.75

11.98±0.17

3.43±0.06

2.57±0.06

5.56±0.08

63.76±1.37

61.38±1.58

36.64±1.03

30.42±1.04

36.76±2.41

73.81±1.06

59.58±1.37

84.38±2.91

76.21±2.16

69.36±1.95

74.38±1.02

75.93±1.92

57.32±1.68

63.25±2.41

>100

b

=Br,

X

1

=4-Cl

=Cl, R

=R =OMe

=OMe

=R =H,

=OMe

=R =H,

=Me

=R =H,

=OMe

=R =H,

=OMe

3

=H

c

2

=4-Cl

d

3

=4-Cl

e

3

=4-Cl

f

3

=4-Me

=4-OMe

g

3

68.3±1.8

>100

b

C1

C2

sorafenib

sunitinib

103.6±3.5(37.8±0.6)

102.3±5.2(29.2±1.7)

57.8±3.1

31.8±1.3

2.41±0.03

NT

7.62±0.05

NT

17.38±0.08

NT

b

d

NT

a

2

65

66

67

68

69

70

71

72

73

74

75

76

77

The kinase inhibition % at 1 µM are the average of two independent experiments.

IC₅₀(nM) values are the average of three independent experiments in the parentheses.

IC₅₀values are the average of three independent experiments.

NT means no test.

b

c

d

2.3.3 Kinase selective inhibitory profile and cytotoxicity on normal cell for 9d

Compound 9d exhibited high inhibitory activity against VEGFR-2 (IC = 0.054

5

0

µM), and effective anti-proliferative potencies against HepG2 cell, which were

comparable to the efficacy of sorafenib. Therefore, we selected 9d for further

investigation. The kinase selectivity profile of 9d was assessed over 5 different

protein kinases and one human normal hepatocellular (LO2) (Table 3). As results

shown, compound 9d had almost poor or no significant inhibitory activity against all

5 tested protein kinases at the concentration of 1 µM and just moderate inhibitory

1

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2

78

79

80

activity against LO2 cell line (inhibition % = 56.4 at 10µM), which revealed that

compound 9d had good selectivity profile and was a VEGFR-2 kinase inhibitor.

Table 3. Kinase selectivity profile and cytotoxicity on normal cell for compound 9d

Kinase tested

Inhibition % at 1 µM

-3.5±0.8

Normal Cell tested

LO2

Inhibition % at 10 µM

56.4±2.4

PDGFRA (PDGFR α)

PDGFRB (PDGFRβ)

FLT1 (VEGFR-1)

FLT4 (VEGFR-3)

MET (c-Met)

2.7±0.9

26.1±1.2

18.5±1.3

-3.6±0.9

2

81

82

83

84

85

86

87

88

89

90

91

92

93

94

2.3.4 Chick chorioallantoic membrane (CAM) studies

The CAM assay was selected to explore angiogenesis, which is an inexpensive,

reliable, simple, and convenient biological method. Thirteen compounds (5e, 5j, 5k,

5q, 5r, 5x, 5y, 5ad, 9a, 9b, 9c, 9d, and 9e) were screened for studying the extent of

new blood vessel formation, which represents the anti-angiogenic strength of the

compounds (Fig. 4a). Compared with the normal saline group as blank control and

the sorafenib as a positive control, the results showed that compound 9d exhibited

greater anti-angiogenic activities than those of sorafenib. In particular, the CAM assay

of 9d at 10 nM/eggs showed a significant decrease in the number of blood vessels and

accompanied by thick ones vanished. The anti-angiogenesis potential of three

concentrations of 9d (0.1, 1, and 10 nM/eggs) reached 28%, 51%, and 79% (Fig. 4b),

respectively. These results confirmed that the anti-angiogenesis ability of 9d on the

CAM assay was concentration dependent.

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95

2

96

97

Fig. 4 a) The effects of thirteen representative compounds on CAM blood vessel growth (10 nM/eggs). b)

Quantification of the effect of 9d on tube formation is displayed in the bar graph. The bars show the mean ±SD

(n =3). Statistical significance: ***P < 0.001.

2

3

98

99

00

01

02

03

04

05

06

07

2.3.5 cell cycle and apoptosis assay by flow cytometric analysis

The cell apoptosis and cell cycle analysis of compound 9d on HepG2 and HUVEC

cells were explored by using Flow Cytometer with dUPT-FITC/PI staining and PI

staining, respectively. Interestingly, very similar changes in cell cycle distribution

were observed. As shown in Fig. 5a, the percent of dUPT-FITC/PI-positive apoptotic

cells was enhancement after HepG2 cells acted with 9d in the concentration of 1 nM

and 10 nM, only 3.3% (blank control), but the apoptotic ratio increased up to 28.1%

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5

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3

08

09

10

after treatment with 9d (10 nM) for 24 h. Similarly, the percent of

dUPT-FITC/PI-positive apoptotic cells was enhancement after HUVEC cells treated

with 9d in the concentration of 1 nM and 10 nM, from 4.9% up to 34.3%.

3

11

3

12

13

Fig. 5 a) The effect of compound 9d on HepG2 cells apoptosis using dUPT-FITC/PI staining; b) the effect of

compound 9d on HepG2 cells cycle using PI staining; c) The effect of compound 9d on HUVEC cells apoptosis

using dUPT-FITC/PI staining; d) the effect of compound 9d on HUVEC cells cycle using PI staining.

3

14

15

16

17

18

19

20

Additionally, HepG2 and HUVEC cell lines were arrested by compound 9d in

G0/G1 phase with a concentration-dependent effect compared to untreated control

cells. As shown in Fig. 5b, 5d and Table 4, the G /G peak in HepG2 cell line

0

1

significantly increased from 47.9% to 55.7% (1 nM), 68.0% (10 nM), and the G /G

0

1

peak of HUVEC significantly increased from 43.2% to 59.3% (1 nM), 71.4% (10 nM)

1

6

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3

21

22

after 24 h of incubation with the compound 9d.

Table 4. Effect of compound 9d on cell cycle distribution in HepG2 and HUVEC cell line.

Concentration

G

0

/G

1

(%)

S (%)

G

2

/M (%)

HepG2 cell

0

1

nM

47.9

55.7

68.0

9.8

8.1

6.7

42.3

36.2

25.3

1

0 nM

HUVEC cell

0

nM

43.2

59.3

71.4

10.4

8.9

46.4

31.8

21.3

1

0 nM

7.3

3

23

24

25

26

27

28

29

30

2.3.6 Effect of 9d on VEGFR-2 phosphorylation

The inhibitory effect of most potent compound 9d on VEGFR-2 was further

determined by assessing the phosphorylation level of VEGFR-2 in VEGFR-2

overexpressed HUVEC cells using western blot. As shown in Fig. 6, 9d was able to

block the phosphorylation of VEGFR-2 significantly compared with control group (*P

< 0.05). However, this inhibition effect of 9d was weaker than that of positive control

sorafenib.

3

31

32

Fig. 6. 9d inhibits the phosphorylation of VEGFR-2 in HUVEC cells. Expression of p-VEGFR-2 and VEGFR-2 in

HUVEC cells were examined by western blots. Densitometric analysis was performed to determine the

phosphorylation rate of VEGFR-2. Values are mean ± SD (n = 3). *P < 0.05, **P < 0.01, ***P < 0.001 vs. Control

group.

3

33

34

35

36

37

2.4 The binding pattern of compound 9d with VEGFR-2 protein

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7

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38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

To better understand the SAR observed in the VEGFR-2 kinases inhibition assay, and

for further guidance of SAR studies, the optimized analog 9d was docked into the

catalytic site of VEGFR-2 protein (PDB code: 3WZE) using Golddock 5.0 with the

default parameters, i.e., pt_crosswt(100), popsiz (100), niche_siz (2), and n_islands

(1). The lowest energy conformation was adopted as the final binding conformation.

As shown in Fig. 7, the binding pattern of 9-4 revealed that the

4-methoxyphenylacetamide moiety was buried in one hydrophobic sub-pocket of the

allosteric site of VEGFR-2, while 2-phenyl imidazole scaffold occupied the adenine

region of the kinase, which assumed the similar binding pattern with the protein as

observed for YQY-26 and sorafenib. The specific binding mode is as follows.

First, four hydrogen-bonding interactions were observed: in the hinge region of the

kinase, amide oxygen and nitrogen atoms of the phenylacetamide moiety H-bonded to

residues Asp1046 and Glu885, respectively; in adenine region, two nitrogen atoms of

the imidazole scaffold formed H-bonds with residues Cys1045 and Cys919,

respectively. Additionally, the imidazole ring and 4-chlorophenyl of 9d were H-π

stacked with the residues Val899, Val916, Val848, and Leu840, respectively, which

enhanced the binding interaction to VEGFR-2 kinase. In particular, the para-methoxy

of phenylacetamide moiety extends to a narrow hydrophobic sub-pocket of the

allosteric site of VEGFR-2, which was embraced by residues Leu1019, Ile892, and

His1026. This result is consistent with the SAR conclusion, indicating that the

presence of substituents in the ortho-, or meta-position of the phenylacetamide moiety

is not conducive to the improvement of kinase inhibition activity. According to these

results, we assumed that compound 9d is a Type II inhibitor of VEGFR-2 kinase.

1

8

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3

62

63

Fig. 7 Putative binding modes of compound 9d in VEGFR-2 kinase were predicted by molecular modeling. The

3D images were prepared with Accelrys Discovery Studio, while the 2D picture was drawn with Molecular

Operating Environment. The key residues within the binding pocket are indicated in green, and the dashed lines

illustrate atom pairs within hydrogen bonds.

3

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

79

80

81

82

83

3．Conclusion

In summary, we designed and synthesized a novel class of 6-amide-2-aryl

benzoxazole and 6-amide-2-aryl benzimidazole compounds that inhibit VEGFR-2

tyrosine kinase. The in-vitro cytotoxic activity assay and chick chorioallantoic

membrane assay showed that these compounds possess anti-tumor and

anti-angiogenesis activity. Compound 9d showed the greatest inhibitory activities

against VEGFR-2 kinase, HUVEC, and HepG2 cells with IC₅₀values of 51.4 nM,

1.47 µM, and 2.57µM, respectively. Molecular docking of the most potent inhibitor

9d into the active site of VEGFR-2 was performed and the result suggested that

compound 9d could bind well with the ATP-binding site of VEGFR-2 kinase. The

above results demonstrated that compound 9d had emerged as a promising candidate

for further development.

4. Experimental

4.1 Chemistry

1

9

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3

84

85

86

87

88

89

90

91

92

93

94

95

96

97

All chemicals and reagents were of commercial grade and were used without

further purification. The reactions were monitored by thin-layer chromatography

(TLC) using silica gel GF . Column chromatography was performed with 200–300

2

54

mesh silica gel. All yields refer to isolated products after purification. The

intermediates and the products synthesized were fully characterized by spectroscopic

data. The nuclear magnetic resonance (NMR) spectra were recorded with a Bruker

1

13

DRX-500 NMR spectrometer ( H: 500 MHz, C: 125 MHz) using CDCl or

3

DMSO-d as solvents. Chemical shifts (δ) are expressed in parts per million (ppm),

6

and J values are given in hertz (Hz). IR spectra were recorded with a Fourier

transform-infrared (FT-IR) Thermo Nicolet Avatar 360 spectroscopy using a KBr

pellet. High-resolution mass spectrometry (HRMS) was performed by liquid

chromatography/mass selective detector time-of-flight (LC/MSD TOF) using an

Agilent instrument. The melting points were measured with an XT-4A melting point

apparatus without correction.

3

4

98

99

00

01

02

03

04

05

06

07

08

09

10

11

12

13

14

4.1.1 General synthesis of 2-phenyl benzoxazole intermediate 3

In a 250-mL round bottom flask, 2,4-diaminophenol-1 (20 mmol) and

halobenzoic acid 2a (20 mmol) were mixed with PPA (100 g). The solution was

stirred under 170°C for 12 h. After the completion of reaction monitored by TLC, the

mixture was neutralized with concentrated KOH solution. A dark brown precipitate

formed, which was filtered to give a dark brown solid. The dark brown solid was

dissolved in 50 mL of ethyl acetate, and the solution was washed twice with water (50

mL) and once with saturated aqueous brine (50 mL). After the organic phase was

dried over anhydrous sodium sulfate, product 3 (yellow solid, yield > 90%) was

obtained by silica gel column chromatography (petroleum ether: ethyl acetate = 3: 1).

4.1.2 General synthesis of target product 5

Substituted benzoic acid or substituted phenylacetic acid 4 (1 mmol) was added

to a 50-mL round bottom flask and dissolved with DMF (20 mL), HOBt (1.5 mmol),

EDCI (1.5 mmol), and TEA (1.5 mmol). Then, the solution was stirred at room

temperature for 10 minutes. DMF was added to dissolve 2-phenyl benzoxazole

2

0

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4

15

16

17

18

19

20

21

22

structure 3, and then the solution was continuously stirred for 2-4 h. The reaction was

monitored by TLC and then stopped after completion was indicated. The resultant

solution was extracted with ethyl acetate (15 mL), washed twice with dilute

hydrochloric acid (50 mL), and the organic phase was dried over anhydrous sodium

sulfate and separated by silica gel column chromatography (petroleum ether: ethyl

acetate = 2: 1). A yellow or white solid product 5 was obtained (yield > 85%).

4.1.3 Spectral data of compounds 5a-5ak

4

23

24

25

26

27

28

29

30

31

4-Bromo-3-fluoro-N-(2-phenylbenzo[d]oxazol-5-yl)benzamide (5a)

Yellow solid; 359mg, 88% yield, Mp 227.9–229.9 °C; IR (KBr): 3334, 3064, 1650,

1

1544, 1483, 1279, 1046, 870, 764, 690; HNMR (500 MHz, DMSO-d ): δ = 10.54 (s,

6

1H), 8.28 (s, 1H), 8.18 (d, J = 7.2 Hz, 2H), 7.96 (d, J = 9.5 Hz, 1H), 7.88 (t, J = 7.7 Hz,

1

3

1H), 7.80 (d, J = 8.8 Hz, 1H), 7.74 (s, 2H), 7.60 (q, J = 7.1 Hz, 3H); CNMR (125

1

MHz, DMSO-d ): δ = 163.66, 163.35, 159.43-157.47 (d, J = 245.00 Hz), 147.21,

6

C-F

141.99, 136.70 (d, J = 6.25 Hz), 136.29, 134.02, 132.26, 129.61, 127.61, 126.78,

125.66 (d, J = 2.50 Hz), 119.21, 116.30 (d, J = 23.75 Hz), 111.84, 110.95; HRMS

+

(TOF ES ): m/z calcd. for C H BrFN O Na [M+Na] , 432.9958; found, 432.9954.

2

0

12

2

4

32

4

33

34

35

36

37

38

39

40

41

4-Chloro-3-fluoro-N-(2-Phenylbenzo[d]oxazol-5-yl)benzamide (5b)

o

Yellow solid; 314mg, 86% yield, Mp 216.9–218.5 C; IR (KBr): 3346, 3064, 1654,

1

1548, 1479, 1426,1058, 812, 694, 637; H NMR (500 MHz, DMSO- d ): δ = 10.57 (s,

6

1H), 8.27 (s, 1H), 8.22 – 8.16 (m, 2H), 8.01 (dt, J = 10.1, 2.0 Hz, 1H), 7.90 – 7.84 (m,

1

3

1H), 7.80 – 7.72 (m, 3H), 7.66 – 7.56 (m, 3H); C NMR (125 MHz, DMSO-d ): δ =

6

1

163.61, 163.37, 158.31-156.34 (d, J_C_-_F= 246.25 Hz), 147.21, 141.97, 136.26, 136.00,

132.29, 131.13, 129.64, 127.61, 126.74, 125.38, 123.41 (d, J = 17.50 Hz), 119.25,

+

116.53 (d, J = 22.50 Hz), 111.86, 110.97; HRMS (TOF ES ): m/z calcd for

+

C H ClFN O Na [M+Na] , 389.0464; found, 389.0466.

20

12

2

4

42

43

44

45

46

3-Bromo-4-chloro-N-(2-Phenylbenzo[d]oxazol-5-yl)benzamide (5c)

o

Yellow solid; 361 mg, 85% yield, Mp 207.8–209.7 C; IR (KBr): 3370, 3269, 3072,

1

2913, 1642, 1540, 1475, 1422,702,617; H NMR (500 MHz, DMSO- d ): δ = 10.56 (s,

6

1H), 8.36 (d, J = 2.1 Hz, 1H), 8.27 (d, J = 1.9 Hz, 1H), 8.22 – 8.16 (m, 2H), 8.00 (dd,

1

3

J = 8.4, 2.1 Hz, 1H), 7.83 – 7.71 (m, 3H), 7.62 (dq, J = 10.6, 6.6 Hz, 3H); CNMR

2

1

ACCEPTED MANUSCRIPT

4

47

48

49

50

(125 MHz, DMSO-d ): δ = 163.44, 147.19, 141.97, 136.80, 136.27, 135.42, 133.12,

6

132.31, 130.91, 129.66, 128.98, 127.62, 126.74, 122.00, 119.22, 111.82, 111.00;

+

HRMS (TOF ES ): m/z calcd for C H BrClN O Na [M+Na] , 448.9663; found,

2

0

12

2

448.9666.

4

51

4

52

53

54

55

56

57

58

59

60

2-(3,4-Dimethoxyphenyl)-N-(2-Phenylbenzo[d]oxazol-5-yl)acetamide (5d)

o

White solid; 349 mg, 90% yield, Mp 170.1–170.6 C; IR (KBr): 3269, 3060, 2991,

1

2835, 1650, 1520,1471, 1266, 1152, 1021, 796, 702, 604; HNMR (500 MHz,

DMSO-d ): δ = 10.33 (s, 1H), 8.25 – 8.13 (m, 3H), 7.71 (d, J = 8.7 Hz, 1H), 7.58 (ddd,

6

J = 13.6, 6.4, 4.4 Hz, 4H), 7.00 (d, J = 1.7 Hz, 1H), 6.90 (d, J = 2.7 Hz, 2H), 3.77 (s,

13

3H), 3.73 (s, 3H), 3.62 (s, 2H); C NMR (125 MHz, DMSO- d ): δ = 169.82, 163.28,

6

148.95, 148.04, 146.67, 142.04, 136.92, 132.25, 129.62, 128.67, 127.58, 126.77,

121.51, 117.90, 113.47, 112.23, 111.05, 110.30, 55.90, 55.83, 43.30; HRMS (TOF

+

ES ): m/z calcd for C H N O Na [M+Na] , 411.1315; found, 411.1312.

2

3

20

2

4

61

4

62

63

64

65

66

67

68

69

70

N-(2-Phenylbenzo[d]oxazol-5-yl)-2-(3,4,5-trimethoxyphenyl)acetamide (5e)

o

White solid; 372 mg, 89% yield, Mp 175.7–177.6 C; IR (KBr): 3252, 3056, 2987,

1

2933, 2835, 1642, 1593, 1540, 1467, 1328, 1242, 1127, 1005, 792, 698, 604; HNMR

(500 MHz, DMSO-d ): δ = 10.35 (s, 1H), 8.43 – 8.11 (m, 3H), 7.72 (d, J = 8.7 Hz,

6

1H), 7.70 – 7.54 (m, 4H), 6.70 (s, 2H), 3.78 (s, 6H), 3.65 (s, 3H), 3.63 (s, 2H);

1

3

CNMR (125 MHz, DMSO-d ): δ = 169.48, 163.29, 153.09, 146.70, 136.86, 132.29,

6

131.83, 129.66, 127.59, 126.77, 117.94, 111.09, 110.34, 106.92, 60.33, 56.20, 43.95;

+

HRMS (TOF ES ): m/z calcd for C H N O Na [M+Na] , 441.1421; found,

2

4

22

2

5

441.1418.

4

71

4

72

73

74

75

76

77

78

79

4-Bromo-N-(2-(4-chlorophenyl)benzo[d]oxazol-5-yl)-3-fluorobenzamide (5f)

o

Yellow solid; 380 mg, 86% yield, Mp 261.0–262.3 C; IR (KBr): 3346, 3068, 1654,

1

1544, 1479, 1099,821, 731, 637, 498; H NMR (500 MHz, DMSO-d ): δ = 10.47 (s,

6

1H), 8.28 (d, J = 7.1 Hz, 1H), 8.17 (d, J = 8.4 Hz, 2H), 7.95 (d, J = 9.8 Hz, 1H), 7.91 –

7.78 (m, 2H), 7.75 (d, J = 8.2 Hz, 1H), 7.70 (d, J = 9.0 Hz, 1H), 7.63 (d, J = 8.3 Hz,

1

3

1

2H); C NMR (125 MHz, DMSO-d ): δ = 163.59, 162.37, 159.45-157.48 (d, J

=

6

C-F

246.25 Hz), 147.22, 141.93, 137.13, 136.60, 136.33, 133.91, 129.67, 129.21, 128.72,

125.63, 125.56 (d, J = 3.63 Hz), 119.33, 116.26 (d, J = 23.75 Hz), 111.86, 110.85;

2

ACCEPTED MANUSCRIPT

+

4

80

81

HRMS (TOF ES ): m/z calcd for C H BrClFN O Na [M+Na] , 466.9569; found,

20 11 2 2

466.9567.

4

82

4

83

84

85

86

87

88

89

90

91

92

4-Chloro-N-(2-(4-chlorophenyl)benzo[d]oxazol-5-yl)-3-fluorobenzamide (5g)

o

Yellow solid; 360 mg, 90% yield, Mp 250.2–250.7 C; IR (KBr): 3350, 1654, 1544,

1

1479, 1099, 817, 739; HNMR (500 MHz, DMSO-d ): δ = 10.52 (d, J = 3.3 Hz, 1H),

6

8.36 (q, J = 2.1 Hz, 1H), 8.25 (s, 1H), 8.17 (td, J = 7.2, 3.7 Hz, 2H), 8.00 (dq, J = 8.7,

1.8 Hz, 1H), 7.83 – 7.78 (m, 1H), 7.77 – 7.72 (m, 2H), 7.66 (td, J = 6.3, 5.2, 3.0 Hz,

1

3

1

2H); CNMR (125 MHz, DMSO-d ): δ = 163.43, 162.41, 158.36-156.40 (d, J

=

6

C-F

245.00 Hz), 147.21, 141.88, 137.08, 136.81, 136.37, 135.40, 133.11, 130.91, 129.80,

129.33, 128.96, 125.59, 121.98, 119.40, 116.50 (d, J = 21.25 Hz), 111.81, 111.04;

+

HRMS (TOF ES ): m/z calcd for C H Cl FN O [M+H] , 401.0254; found,

2

0

12

2

401.0256.

4

93

4

5

94

95

96

97

98

99

00

01

02

3-Bromo-4-chloro-N-(2-(4-chlorophenyl)benzo[d]oxazol-5-yl)benzamide (5h)

o

Yellow solid; 409 mg, 89% yield, Mp 237.2–238.1 C; IR (KBr): 3260, 3072, 2917,

1

1642, 1536, 1471, 829, 727; HNMR (500 MHz, DMSO-d ): δ = 7.6e-7.74 (m, 5H,

6

ArH), 7.98-8.00 (d, J = 8.80 Hz, 1H, ArH), 8.16-8.18 (d, J = 6.70 Hz, 2H, ArH), 8.25

1

3

(s, 1H, ArH), 8.35 (s, 1H, ArH), 10.52 (s, 1H, NH); CNMR (125 MHz, DMSO-d ):

6

δ = 111.04, 111.81, 119.40, 121.98, 125.59, 128.96, 129.33, 129.33, 129.80, 129.80,

130.91, 133.11, 135.40, 136.37, 136.81, 137.08, 141.88, 147.21, 162.41, 163.43,

+

HRMS (TOS ES ): m/z calcd for C H BrCl N O [M+H] , 460.9454; found,

2

0

12

2

460.9452.

5

03

5

04

05

06

07

08

09

10

11

12

N-(2-(4-Chlorophenyl)benzo[d]oxazol-5-yl)-2-(3,4-dimethoxyphenyl)acetamide

(5i)

o

White solid; 367 mg, 87% yield, Mp188.6–190.1 C; IR (KBr): 3256, 3048, 2929,

1

2835, 1642, 1524, 1471, 1266, 1152, 1086, 1025, 850, 723, 608; HNMR (500MHz,

DMSO-d ): δ = 10.29 (s, 1H), 8.23 – 8.10 (m, 3H), 7.69 (dd, J = 8.8, 2.3 Hz, 1H),

6

7.63 (dd, J = 8.7, 2.2 Hz, 2H), 7.57 (d, J = 8.6 Hz, 1H), 7.00 (s, 1H), 6.90 (t, J = 2.6

1

3

Hz, 2H), 3.77 (d, J = 2.3 Hz, 3H), 3.74 (d, J = 2.3 Hz, 3H), 3.62 (s, 2H); CNMR

(125 MHz, DMSO-d ): δ = 169.78, 162.31, 148.97, 148.06, 146.68, 141.96, 137.02,

6

129.76, 129.27, 128.68, 125.62, 121.53, 118.10, 113.54, 112.29, 111.08, 110.30, 55.93,

2

3

ACCEPTED MANUSCRIPT

+

5

13

14

55.86, 43.29; HRMS (TOF ES ): m/z calcd for C H ClN O Na [M+Na] , 445.0926;

23

19

2

4

found, 445.0922.

5

15

5

16

17

18

19

20

21

22

23

24

N-(2-(4-Chlorophenyl)benzo[d]oxazol-5-yl)-2-(3,4,5-trimethoxyphenyl)acetamide

(5j)

o

White solid; 388 mg, 88% yield, Mp 184.9–185.7 C; IR (KBr): 3248, 3085, 2933,

1

2831, 1659, 1561,1471, 1340, 1238, 1127, 1009, 850, 739, 674; H NMR (500 MHz,

DMSO-d ): δ = 10.34 (s, 1H), 8.15 (dd, J = 14.5, 7.3 Hz, 3H), 7.93 – 7.41 (m, 4H),

6

13

6.70 (d, J = 5.6 Hz, 2H), 3.79 (s, 6H), 3.64 (dd, J = 11.9, 5.8 Hz, 5H); CNMR (125

MHz, DMSO-d ): δ = 169.45, 162.33, 153.09, 146.72, 141.97, 137.00, 136.74, 131.79,

6

129.77, 129.28, 125.62, 118.14, 111.10, 110.37, 107.00, 60.32, 56.23, 43.94; HRMS

+

(TOF ES ): m/z calcd for C H ClN O Na [M+Na] , 475.1031; found, 475.1035.

24

21

2

5

25

5

26

27

28

29

30

31

32

33

34

N-(2-(4-Chlorophenyl)benzo[d]oxazol-5-yl)-2-(4-methoxyphenyl)acetamide (5k)

o

White solid; 369mg, 89% yield, Mp 192.6–193.7 C; IR (KBr): 3289, 3072, 2827,

1

1650, 1516, 1246, 817, 731,547; HNMR (500 MHz, DMSO-d ): δ = 10.52 – 10.36

6

(m, 1H), 8.24 (td, J = 9.7, 8.4, 4.3 Hz, 3H), 7.87 – 7.76 (m, 1H), 7.76 – 7.69 (m, 2H),

7.65 (d, J = 8.2 Hz, 1H), 7.39 (d, J = 8.6 Hz, 2H), 7.08 – 6.94 (m, 2H), 3.91 – 3.79 (m,

1

3

3H), 3.70 (d, J = 3.8 Hz, 2H); CNMR (125 MHz, DMSO-d ): δ = 169.89, 162.30,

6

158.42, 146.63, 141.93, 137.01, 130.52, 129.78, 129.27, 128.17, 125.59, 118.01,

+

114.11, 111.12, 110.19, 55.37, 42.81; HRMS (TOF ES ): m/z calcd for

+

C H ClN O Na [M+Na] , 415.0820; found, 415.0816.

22

17

2

3

5

35

5

36

37

38

39

40

41

42

43

44

45

4-Bromo-3-fluoro-N-(2-(2-fluorophenyl)benzo[d]oxazol-5-yl)benzamide (5l)

o

Yellow solid; 391mg, 87% yield, Mp 238.9–239.6 C; IR (KBr): 3273, 3072, 1650,

1

1565, 1479, 1299, 1037, 870, 772, 690; HNMR (500 MHz, DMSO-d ): δ = 10.61 (s,

6

1H), 8.38 (s, 1H), 8.28 (td, J = 7.4, 1.8 Hz, 1H), 8.03 (dd, J = 9.6, 2.1 Hz, 1H), 8.00 –

7.95 (m, 1H), 7.91 – 7.84 (m, 3H), 7.76 (tdd, J = 7.3, 4.8, 1.9 Hz, 1H), 7.59 – 7.48 (m,

1

3

1

2H); CNMR (125 MHz, DMSO-d ): δ = 163.65, 161.30-159.39 (d, J = 238.75

6

C-F

1

Hz), 159.85, 159.25-157.44 (d, J_C_-_F= 226.25 Hz), 146.97, 141.54, 136.60 (d, J =

33.75 Hz), 134.34 (d, J = 10.00 Hz), 134.00, 130.77, 125.61 (d, J = 17.50 Hz), 119.53,

117.61 (d, J = 21.25 Hz), 116.25 (d, J = 23.75 Hz), 114.94 (d, J = 10.00 Hz), 112.28 (d,

+

J = 21.25 Hz), 111.84, 111.01; HRMS (TOF ES ): m/z calcd for C H BrF N O Na

2

0

11

2

4

ACCEPTED MANUSCRIPT

+

5

46

47

[M+Na] , 450.9864; found, 450.9862.

5

48

49

50

51

52

53

54

55

56

57

58

4-Chloro-3-fluoro-N-(2-(2-fluorophenyl)benzo[d]oxazol-5-yl)benzamide (5m)

o

Yellow solid; 358mg, 88% yield, Mp 232.5–233.0 C; IR (KBr): 3432, 3927, 3064,

1626, 1556, 1479, 1422, 1344, 1234, 1046, 817, 756, 559; 1H NMR (500 MHz,

DMSO-d ): δ = 10.51 (s, 1H), 8.28 (d, J = 1.9 Hz, 1H), 8.19 (td, J = 7.7, 1.8 Hz, 1H),

6

7.98 (dd, J = 10.1, 2.0 Hz, 1H), 7.86 (dd, J = 8.3, 2.0 Hz, 1H), 7.82 – 7.73 (m, 3H),

1

3

7.67 (dddd, J = 8.5, 6.9, 5.0, 1.9 Hz, 1H), 7.52 – 7.37 (m, 2H); C NMR (125 MHz,

1

DMSO-d ): δ = 13C NMR (126 MHz, DMSO-d6) δ 163.56, 161.31 (d, J = 256.25

6

C-F

1

Hz), 159.87, 158.30 (d, J_C_-_F= 246.25 Hz), 146.98, 141.55, 136.33, 135.94, 134.33,

131.11, 130.78, 125.49 (d, J = 17.50 Hz), 119.55, 117.62 (d, J = 20.00 Hz), 116.51 (d,

+

J = 22.50 Hz), 114.87, 111.85, 111.04; HRMS (TOF ES ): m/z calcd for

+

C H ClF N O Na [M+Na] , 407.0369; found, 407.0371.

20

11

2

5

59

5

60

61

62

63

64

65

66

67

68

69

3-Bromo-4-chloro-N-(2-(2-fluorophenyl)benzo[d]oxazol-5-yl)benzamide (5n)

o

Yellow solid; 400mg, 86% yield, Mp 312.3–314.0 C; IR (KBr): 3428, 3248, 3081,

2970, 2917, 2848, 1630, 1548, 1475, 1295, 1246, 743, 629; 1H NMR (500 MHz,

DMSO-d ): δ = 10.55 (s, 1H), 8.35 (d, J = 2.1 Hz, 1H), 8.29 (d, J = 1.9 Hz, 1H), 8.20

6

(t, J = 7.5 Hz, 1H), 7.99 (dd, J = 8.2, 2.1 Hz, 1H), 7.82 – 7.73 (m, 3H), 7.67 (td, J =

1

3

7.8, 3.5 Hz, 1H), 7.51 – 7.39 (m, 2H); C NMR (125 MHz, DMSO-d ): δ = 163.44,

6

1

161.27 (d, J = 243.50 Hz), 159.88, 146.99, 141.55, 136.80, 136.36, 134.36,

C-F

133.11, 130.89, 130.81, 128.97, 125.52, 121.98, 119.58, 117.64 (d, J = 20.00 Hz),

+

111.88, 111.06; HRMS (TOF ES ): m/z calcd for C H BrClFN O Na [M+Na] ,

20

11

2

466.9569; found, 466.9567.

5

70

71

72

73

74

75

76

77

2-(3,4-Dimethoxyphenyl)-N-(2-(2-fluorophenyl)benzo[d]oxazol-5-yl)acetamide

(5o)

o

White solid; 345mg, 85% yield, Mp172.3–174.9 C; IR (KBr): 3273, 3068, 2995,

1

2831, 1646, 1524, 1471, 1270, 1152, 1025, 870, 772, 604; HNMR (500 MHz,

DMSO-d ): δ = 10.33 (s, 1H), 8.21 (s, 2H), 7.74 (d, J = 8.8 Hz, 1H), 7.65 (q, J = 7.3,

6

6.7 Hz, 1H), 7.59 (d, J = 9.0 Hz, 1H), 7.52 – 7.36 (m, 2H), 7.01 (d, J = 9.5 Hz, 1H),

13

6.91 (d, J = 9.1 Hz, 2H), 3.77 (s, 3H), 3.73 (s, 3H), 3.62 (s, 2H); CNMR (125 MHz,

2

5

ACCEPTED MANUSCRIPT

1

5

6

78

79

80

81

82

83

84

85

86

87

88

89

90

91

92

93

94

95

96

97

98

99

00

01

02

03

04

05

DMSO-d ): δ = 169.82, 161.31 (d, J = 257.50 Hz), 159.80, 148.97, 148.07, 146.48,

6

C-F

141.64, 137.02, 134.31, 130.79, 128.67, 125.50, 121.53, 118.28, 117.62 (d, J = 21.25

+

Hz), 115.00, 113.53, 112.28, 111.13, 110.35, 55.89, 43.31; HRMS (TOF ES ): m/z

+

calcd for C H FN O [M+H] , 407.1402; found, 407.1397.

2

3

20

2

4

N-(2-(2-Fluorophenyl)benzo[d]oxazol-5-yl)-2-(3,4,5-trimethoxyphenyl)acetamide

(5p)

o

Yellow solid; 388mg, 89% yield, Mp 173.8–175.2 C; IR (KBr): 3248, 3077, 2987,

1

2938, 2831, 1642, 1589, 1540, 1471, 1326, 1238, 1127, 1001, 772, 608; HNMR (500

MHz, DMSO-d ): δ = 10.34 (s, 1H), 8.20 (t, J = 4.3 Hz, 2H), 7.75 (d, J = 8.8 Hz, 1H),

6

7.71 – 7.64 (m, 1H), 7.58 (dd, J = 8.8, 2.1 Hz, 1H), 7.50 – 7.39 (m, 2H), 6.69 (s, 2H),

1

3

3.78 (s, 6H), 3.64 (s, 3H), 3.62 (s, 2H); CNMR (125 MHz, DMSO-d ): δ = 169.46,

6

1

161.29 (d, J = 253.75 Hz), 159.81, 153.09, 151.01, 146.52, 141.64, 136.95, 136.75,

C-F

134.32, 131.78, 130.80, 125.53, 118.34, 117.64 (d, J = 21.25 Hz), 111.16, 110.41,

+

106.99, 60.33, 56.23, 43.94; HRMS (TOF ES ) : m/z calcd for C H FN O [M+H] ,

2

4

22

2

5

437.1507; found, 437.1503.

N-(2-(2-Fluorophenyl)benzo[d]oxazol-5-yl)-2-(4-methoxyphenyl)acetamide (5q)

o

White solid; 350mg, 93% yield, Mp 169.6–170.2 C; IR (KBr): 3297, 3064, 2958,

1

2904, 1663, 1536, 1246, 1033, 817, 768, 698; HNMR (500 MHz, DMSO-d ): δ =

6

10.36 (s, 1H), 8.20 (td, J = 3.8, 1.8 Hz, 2H), 7.74 (d, J = 8.8 Hz, 1H), 7.70 – 7.63 (m,

1H), 7.58 (dd, J = 8.8, 2.1 Hz, 1H), 7.50 – 7.39 (m, 2H), 7.29 (d, J = 8.6 Hz, 2H), 6.96

1

3

– 6.86 (m, 2H), 3.73 (d, J = 1.2 Hz, 3H), 3.62 (s, 2H); CNMR (125 MHz,

1

DMSO-d ): δ = 169.91, 161.29 (d, J = 255.00 Hz), 159.80, 158.44, 146.46, 141.62,

6

C-F

137.02, 134.36 (d, J = 8.75 Hz), 130.80, 130.52, 128.19, 125.52, 118.24, 117.64 (d, J

+

= 21.25 Hz), 114.94, 114.13, 111.15, 110.28, 55.38, 42.81; HRMS (TOF ES ): m/z

+

calcd for C H FN O [M+H] , 377.1296; found, 377.1297.

2

18

2

3

6

06

07

N-(2-(2-Fluorophenyl)benzo[d]oxazol-5-yl)-2-(P-tolyl)acetamide (5r)

o

White solid; 328mg, 91% yield, Mp 169.6–170.2 C; R (KBr): 3269, 3081, 2917,

2

6

ACCEPTED MANUSCRIPT

1

6

08

09

10

11

12

13

14

15

1669, 1561, 1479, 1340, 821, 764; HNMR (500 MHz, DMSO-d ): δ = 10.38 (s, 1H),

6

8.20 (dd, J = 4.7, 2.1 Hz, 2H), 7.74 (d, J = 8.8 Hz, 1H), 7.70 – 7.63 (m, 1H), 7.58 (dd,

J = 8.9, 2.1 Hz, 1H), 7.50 – 7.39 (m, 2H), 7.26 (d, J = 7.9 Hz, 2H), 7.14 (d, J = 7.8 Hz,

1

3

2H), 3.64 (s, 2H), 2.27 (s, 3H); CNMR (125 MHz, DMSO-d ): δ = 169.72, 161.30

6

1

(d, J = 256.25 Hz), 159.80, 159.25, 146.48, 141.63, 137.00, 135.95, 134.36 (d, J=

C-F

10

.

00 Hz), 133.21, 130.80, 129.37, 129.24, 125.52, 118.26, 117.63 (d, J = 21.25 Hz),

+

115.00, 111.14, 110.32, 43.32, 21.00; HRMS (TOF ES ): m/z calcd for C H FN O

22

18

2

+

[M+H] , 361.1347; found, 361.1347.

6

16

6

17

18

19

20

21

22

23

24

25

26

4-Bromo-N-(2-(2-chlorophenyl)benzo[d]oxazol-5-yl)-3-fluorobenzamide (5s)

o

White solid; 396mg, 855 yield, Mp 187.5–186.7 C; IR (KBr): 3420, 3309, 3077,

1

1646, 1565, 1475, 1422, 1033, 821, 735, 637; H NMR (500 MHz, DMSO-d ): δ =

6

10.52 (s, 1H), 8.32 (s, 1H), 8.16 (d, J = 7.7 Hz, 1H), 7.98 (dd, J = 9.6, 2.1 Hz, 1H),

7.91 (t, J = 7.7 Hz, 1H), 7.81 (d, J = 12.0 Hz, 3H), 7.72 (d, J = 8.0 Hz, 1H), 7.64 (t, J

1

3

= 7.7 Hz, 1H), 7.58 (t, J = 7.5 Hz, 1H); CNMR (125 MHz, DMSO-d ): δ = 163.80,

6

1

161.33, 159.43 (d, J = 243.75 Hz), 147.10, 141.54, 136.69, 136.34, 134.10,

C-F

133.27, 132.52, 132.28, 131.65, 128.10, 125.68, 119.83, 116.32 (d, J = 23.75 Hz),

+

112.14, 111.18; HRMS (TOF ES ): m/z calcd for C H BrClFN O Na [M+Na] ,

2

0

11

2

466.9569; found, 466.9565

6

27

6

28

29

30

31

32

33

34

35

36

37

4-Chloro-N-(2-(2-chlorophenyl)benzo[d]oxazol-5-yl)-3-fluorobenzamide (5t)

o

Yellow solid; 367mg, 85% yield, Mp 184.5–185.6 C; IR (KBr): 3428, 3072, 1667,

1

1552, 1479, 1037, 821, 739,563; HNMR (500 MHz, DMSO-d ): δ = 10.54 (s, 1H),

6

8.32 (s, 1H), 8.16 (d, J = 7.9 Hz, 1H), 8.01 (d, J = 10.1 Hz, 1H), 7.88 (d, J = 8.6 Hz,

1H), 7.79 (q, J = 8.8 Hz, 3H), 7.71 (d, J = 8.2 Hz, 1H), 7.64 (t, J = 7.8 Hz, 1H), 7.57 (t,

1

3

J = 7.5 Hz, 1H); CNMR (125 MHz, DMSO-d ): δ = 13C NMR (126 MHz,

6

1

DMSO-d6) δ 163.65, 161.29, 158.33 (d, J_C_-_F= 246.25 Hz), 147.06, 141.53, 136.33,

135.95, 133.24, 132.51, 132.25, 131.64, 131.16, 128.07, 125.77, 125.38, 123.31,

+

119.77, 116.55 (d, J = 22.50 Hz), 112.08, 111.16, 40.38; HRMS (TOF ES ): m/z calcd

+

for C H Cl FN O Na [M+Na] , 423.0074; found, 432.0069.

2

0

11

2

6

38

39

3-Bromo-4-chloro-N-(2-(2-Chlorophenyl)benzo[d]oxazol-5-yl)benzamide (5u)

2

7

ACCEPTED MANUSCRIPT

o

6

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

White solid; 395mg, 86% yield, Mp 189.4–191.3 C; IR (KBr): 3444, 3252, 3077,

1

2917, 2852, 1638, 1552, 1471, 1426, 1029, 809, 735; HNMR (500 MHz, DMSO-d ):

6

δ = 10.61 (s, 1H), 8.42 – 8.35 (m, 1H), 8.33 (s, 1H), 8.17 (d, J = 7.8 Hz, 1H), 8.06 –

7.97 (m, 1H), 7.83 (d, J = 8.2 Hz, 2H), 7.78 (d, J = 9.4 Hz, 1H), 7.73 (d, J = 8.0 Hz,

1

3

1H), 7.65 (t, J = 7.7 Hz, 1H), 7.59 (t, J = 7.6 Hz, 1H); CNMR (125 MHz, DMSO-d ):

6

δ = 188.89, 163.56, 161.32, 147.08, 141.53, 136.83, 136.35, 135.44, 133.30, 133.15,

132.52, 132.30, 131.66, 130.97, 129.01, 128.13, 125.80, 122.01, 119.82, 112.12,

+

111.21; HRMS (TOF ES ): m/z calcd for C H BrCl N O [M+H] , 460.9554; found,

2

0

12

2

460.9451.

N-(2-(2-Chlorophenyl)benzo[d]oxazol-5-yl)-2-(3,4-dimethoxyphenyl)acetamide

(5v)

o

White solid; 384 mg, 91% yield, Mp 153.4–153.9 C; IR (KBr): 3277, 3064, 2991,

1

2635, 1646, 1524, 1471, 1266, 1148, 1025, 792, 727, 604; HNMR (500 MHz,

DMSO-d ): δ = 10.36 (s, 1H), 8.25 (d, J = 2.0 Hz, 1H), 8.13 (dd, J = 7.8, 1.7 Hz, 1H),

6

7.75 (d, J = 8.8 Hz, 1H), 7.69 (dd, J = 8.1, 1.3 Hz, 1H), 7.61 (ddd, J = 9.3, 6.9, 1.8 Hz,

2H), 7.55 (td, J = 7.6, 1.3 Hz, 1H), 7.00 (d, J = 1.7 Hz, 1H), 6.90 (d, J = 3.8 Hz, 2H),

1

3

3.77 (s, 3H), 3.74 (s, 3H), 3.63 (s, 2H); CNMR (125 MHz, DMSO-d ): δ = 169.84,

6

161.20, 148.98, 148.07, 146.53, 141.60, 137.01, 133.17, 132.48, 132.23, 131.62,

128.66, 128.04, 125.83, 121.53, 118.44, 113.54, 112.30, 111.20, 110.52, 55.93, 55.86,

+

43.30; HRMS (TOF ES ): m/z calcd for C H ClN O [M+H] , 423.1106; found,

2

3

20

2

4

423.1103.

N-(2-(2-Chlorophenyl)benzo[d]oxazol-5-yl)-2-(3,4,5-trimethoxyphenyl)acetamide

(5w)

o

White solid; 389mg, 86% yield, Mp 155.4–156.7 C; IR (KBr): 3236, 3032, 2933,

1

2831, 1646, 1593, 1467, 1238, 1127, 996, 817, 735, 608; HNMR (500 MHz,

DMSO-d ): δ = 10.35 (s, 1H), 8.23 (d, J = 2.0 Hz, 1H), 8.13 (dd, J = 7.8, 1.8 Hz, 1H),

6

7.75 (d, J = 8.8 Hz, 1H), 7.69 (dd, J = 8.0, 1.3 Hz, 1H), 7.64 – 7.58 (m, 2H), 7.55 (td,

J = 7.5, 1.3 Hz, 1H), 6.69 (s, 2H), 3.78 (s, 6H), 3.65 (d, J = 1.2 Hz, 3H), 3.63 (s, 2H);

2

8

Article Doi

Design, synthesis and in vitro evaluation of 6-amide-2-aryl benzoxazole/benzimidazole derivatives against tumor cells by inhibiting VEGFR-2 kinase

DOI: 10.1016/j.ejmech.2019.06.054

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Article abstract of DOI:10.1016/j.ejmech.2019.06.054

Full text of DOI:10.1016/j.ejmech.2019.06.054

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