Abstract
Six N-glycosyl benzofuran derivatives were synthesized by the catalysis of organic bases and condensation agents. The benzofuran derivatives were obtained by the reaction of various salicylaldehydes in acetone, and then hydrolyzed to the corresponding carboxylic acids. Finally, the target compounds were synthesized by acylation and the reaction conditions were optimized. The acetylcholinesterase (AChE) inhibitory activity of the desired compounds was tested using Ellman’s method. Most of the compounds showed acetylcholinesterase-inhibition activity; N-(2,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-3-yl)benzofuran-2-carbxamide (5a) showed the best acetylcholinesterase inhibition, with an inhibitory rate of 84%.
Introduction
Benzofurans are an important family of oxygen-containing heterocycles. Natural benzofuran compounds have anti-tumor, anti-fungal, anti-senile dementia and anti-inflammatory activity and thus provide important heterocyclic active molecule for the development of new drugs [1, 2, 3, 4]. The main clinical drugs containing a benzofuran skeleton are the anti-arrhythmic amiodarone (I), the anti-hypertensive bufuralol (II) and the anti-fungal griseofulvin (III) [5,6], whose structures are shown in Figure 1. Some studies have shown that many compounds containing a benzofuran skeleton can be used as monoamine oxidase inhibitors, potent acetylcholinesterase (AChE) inhibitors or potent Multitarget-Directed Ligands in the treatment of Alzheimer’s disease [7, 8, 9, 10].
Drugs containing a benzofuran skeleton.
D-glucosamine is an important natural monosaccharide with many kinds of biological activity, such as anti-inflammatory, anti-cancer and anti-bacterial [11, 12, 13]. The synthesis of glucosamine derivatives has recently become of interest with respect to increasing their biological activity, as many studies have shown that glucosamine derivatives have strong biological properties, including anti-oxidant and anti-AChE [14, 15, 16, 17].
Due to the excessive lipid-water partition coefficient and poor water solubility of benzofuran, it cannot easily reach the anticipated site of action of the drug. Glucosamine is an active molecule with multi-hydroxyl groups and has strong water solubility. Therefore, unprotected glucosamine was linked to benzofuran via an amide bond in order to increase the water solubility of the coumarin molecule and improve its bioavailability and activity. The synthesized derivatives were tested for AChE inhibitory activity by Ellman’s method, and glycosylated heterocyclic compounds with better AChE-inhibitory activity were identified.
Results and Discussion
Chemistry
In our experiment, ethyl benzofuran-2carboxylate 1 was synthesized from substituted salicylaldehyde in acetone solution catalyzed by potassium carbonate, and hydrolyzed to benzofuran-2-carboxylic acid 3. Then, under the catalysis of N,N-diisopropylethylamine and HATU, 3 and glucosamine 4 were reacted in acetonitrile solution to produce N-glycosyl benzofuran derivatives 5a–5f in high yield (Scheme 1).
Synthetic pathways of the N-glycosyl benzofuran derivatives.
In the second stage, coumarilic acid 3a and the condensation agent HATU were used as representatives to select the best reaction conditions. Table 1 summarizes the molar ratio, solvent, temperature and duration of the various reactions.
Optimizing the conditions for the synthesis of 5a
| Entry | n(3a) : HATU | Time (min) | Temp. (°C) | Solvent | Yield (%) |
|---|---|---|---|---|---|
| 1 | 1:1.0 | 50 | 30 | ACN | 56 |
| 2 | 1:1.2 | 50 | 30 | ACN | 77 |
| 3 | 1:1.3 | 50 | 30 | ACN | 85 |
| 4 | 1:1.4 | 50 | 30 | ACN | 85 |
| 5 | 1:1.3 | 50 | 20 | ACN | 66 |
| 6 | 1:1.3 | 50 | 30 | ACN | 85 |
| 7 | 1:1.3 | 50 | 40 | ACN | 85 |
| 8 | 1:1.3 | 50 | 30 | DCM | NR |
| 9 | 1:1.3 | 50 | 30 | MeOH | 38 |
| 10 | 1:1.3 | 50 | 30 | EtOH | 46 |
| 11 | 1:1.3 | 50 | 30 | ACN | 85 |
| 12 | 1:1.3 | 20 | 30 | ACN | 32 |
| 13 | 1:1.3 | 40 | 30 | ACN | 73 |
| 14 | 1:1.3 | 50 | 30 | ACN | 85 |
| 15 | 1:1.3 | 60 | 30 | ACN | 85 |
Biological activity
The AChE inhibition activity of the newly synthesized compounds was evaluated in vitro by Ellman’s method, using AChE extracts from Electric eel [18,19]. Table 2 summarizes the compounds’ inhibitory potency (‘inhibition rate’).
In vitro inhibitory activity of target compounds against AChE.
| Compound | Inhibition rate (%)a |
|---|---|
| 5a | 84 |
| 5b | 53 |
| 5c | 65 |
| 5d | 77 |
| 5e | 58 |
| 5f | 64 |
| mb | 1.79 |
a Inhibitory activity at a concentration of 1mg/mL.
bm stands for D-glucosamine hydrochloride.
As shown in Table 2, the inhibitory activity of all the compounds to AChE is higher than that of the precursor compound, D-glucosamine hydrochloride m, and the inhibitory rate of the optimum compound 5a is 84%, indicating that the presence of benzofurans enhances the inhibitory activity.
Conclusion
Six N-glycosyl benzofuran derivatives were designed and synthesized by a green, efficient and convenient method. Optimum reaction conditions were identified and all yields were above 60%. The compounds were determined by NMR, IR and HRMS. Most of the compounds demonstrated acetylcholinesterase inhibition activity and compound 5a showed the best acetylcholinesterase inhibition with an inhibition rate of 84%.
Experimental
Chemistry
All chemicals were purchased from commercial sources and used without further purification unless otherwise stated. Melting points were determined on a Yanaco melting point apparatus and were uncorrected. IR spectra were recorded on a Bruker Tensor 27 spectrometer with KBr pellets. 1H NMR spectra were recorded on a Bruker Avance 500 MHz at ambient temperature using DMSO-d6 as solvent and TMS as an internal standard. Chemical shifts were reported in ppm. HRMS (ESI) analysis was performed on an Agilent 6230 mass spectrometer.
General procedure for synthesis of ethyl benzofuran-2carboxylate (1)
Potassium carbonate, anhydrous (10 mmol) was added to an acetone solution of various salicylaldehydes (8 mmol) and stirred sufficiently. Ethyl chloroacetate (20 mmol) was added to the solution and the reaction mixture was stirred under reflux for 8 h. After removing the solvent, adding H2O and extracting with ethyl acetate, product 1 was obtained, yield 70%.
General procedure for synthesis of benzofuran-2-carboxylic acid (3)
A sodium hydroxide (4 mmol) water (10 mL) solution was added to 20 mL ethanol containing 1 (3 mmol). After dropping, the reaction liquid was heated to 40°C and stirred for 1 h. After the reaction, the pH was adjusted to 1 by 5 mol/L HCl and the precipitate was filtered, washed with H2O and ice ethanol, and dried. Product 3 was obtained, yield 90%.
Synthesis of Glucosamine (4)
Glucosamine hydrochloride (2 mmol) and N,N-diisopropylethylamine (2 mmol) were added to a 50 ml flask and stirred for 3 h to obtain compound 4, yield 99%.
General procedure for Synthesis of 5a–5f
3 (2 mmol) was added to 15 ml Na2SO4 dried acetonitrile, and N,N-diisopropylethylamine (4 mmol) was added after stirring and dissolving. HATU (2.6 mmol) was dissolved in 5 ml acetonitrile and slowly dripped. When the solution turned yellow, 4 (2.6 mmol) was added. The reaction was complete after 50 minutes’ continuous stirring at 30°C. The mixture was filtered and washed with acetonitrile to give 5a–5f.
N-(2,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-3-yl)benzofuran-2-carboxamide (5a)
Yield 85%; mp 212–214°C; IR (cm−1): 3401, 3065, 2360, 1593, 1447, 1215, 795; 1H NMR: 7.97 (d, J = 8.5 Hz, 1H, NH), 7.79 (d, J = 7.5 Hz, 1H, ArH), 7.71 (d, J = 8.5 Hz, 1H, ArH), 7.64 (s, J = 8.5 Hz, 1H, ArH), 7.51 (m, 1H, ArH), 7.36 (t, J = 10.0 Hz, 1H, ArH), 6.61 (d, J = 4.0 Hz, 1H, HGlu), 5.10 (t, J = 4.0 Hz, 1H, HGlu), 5.02 (d, J = 5.5 Hz, 1H, HGlu), 4.85 (d, J = 6.0 Hz, 1H, HGlu), 3.84–3.80 (m, 1H, HGlu), 3.75–3.71 (m, 1H, OH), 3.67–3.64 (m, 2H, OH), 3.55–3.50 (m, 1H, OH), 3.23–3.17 (m, 1H, HGlu); ESI-HRMS (m/z): calcd for C15H17NO8Na+ [M+Na]+: 346.0896; Found: 346.0907.
5-Methyl-N-(2,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-3-yl)benzofuran-2-carboxamide (5b)
Yield 77%; mp 189–190°C; IR (cm−1): 3403, 3060, 2345, 1588, 1437, 1201, 792; 1H NMR: 7.92 (d, J = 8.0 Hz, 1H, NH), 7.56 (m, 2H, ArH), 7.30 (d, J = 8.5 Hz, 1H, ArH), 7.17 (d, J = 4.0 Hz, 1H, ArH), 6.61 (d, J = 4.0 Hz, 1H, HGlu), 5.09 (t, J = 3.5 Hz, 1H, HGlu), 5.02 (d, J = 5.5 Hz, 1H, HGlu), 4.85 (d, J = 5.5 Hz, 1H, HGlu), 3.84−3.80 (m, 1H, HGlu), 3.75−3.71 (m, 1H, OH) 3.67−3.64 (m, 2H, OH), 3.53–3.49 (m, 1H, OH), 3.22−3.16 (m, 1H, HGlu), 2.42 (s, 3H, C-H); ESI-HRMS (m/z): calcd for C16H20NO7+ [M + H]+: 338.1234; Found: 338.1244.
7-Methoxy-N-(2,4,5-trihydroxy-6-(hydroxymethyl) tetrahydro-2H-pyran-3-yl)benzofuran-2-carboxamide (5c)
Yield 64%; mp 265–266°C; IR (cm−1): 3412, 3050, 2344, 1583, 1424, 1254, 780; 1H NMR: 8.07 (d, J = 6.5 Hz, 1H, NH), 7.20 (s, 1H, ArH), 7.12 (m, 2H, ArH), 6.94 (d, J = 8.5 Hz, 1H, ArH), 6.56 (d, J = 4.0 Hz, 1H, HGlu), 5.09 (t, J = 3.5 Hz, 1H, HGlu), 5.02 (d, J = 5.5 Hz, 1H, HGlu), 4.85 (d, J = 5.5 Hz, 1H, HGlu), 3.94 (s, 3H, −OCH3) 3.84−3.80 (m, 1H, HGlu), 3.75−3.71 (m, 1H, OH) 3.67−3.64 (m, 2H, OH), 3.53–3.49 (m, 1H, OH), 3.22−3.16 (m, 1H, HGlu); ESI-HRMS (m/z): calcd for C16H19NO8Na+ [M+Na]+: 376.1003; Found: 376.1009.
6-Methoxy-N-(2,4,5-trihydroxy-6-(hydroxymethyl) tetrahydro-2H-pyran-3-yl)benzofuran-2-carboxamide (5d)
Yield 68%; mp 168–169°C; IR (cm−1): 3377, 3010, 2340, 1606, 1437, 1197, 812; 1H NMR: 8.30 (d, J = 9.0 Hz, 1H, NH), 7.73 (d, J = 8.5 Hz, 1H, ArH), 7.56 (s, 1H, ArH), 7.27 (d, J = 1.5 Hz, 1H, ArH), 6.98 (m, 1H, ArH), 6.61 (d, J = 6.0 Hz, 1H, HGlu), 5.09 (t, J = 4.0 Hz, 1H, HGlu), 5.07 (d, J = 5.5 Hz, 1H, HGlu), 4.85 (d, J = 5.5 Hz, 1H, HGlu), 3.84 (s, 3H, −OCH3) 3.83−3.80 (m, 1H, HGlu), 3.75−3.71 (m, 1H, OH) 3.67−3.64 (m, 2H, OH), 3.53–3.49 (m, 1H, OH), 3.22−3.16 (m, 1H, HGlu); ESI-HRMS (m/z): calcd for C16H19NO8Na+ [M+Na]+: 376.1003; Found: 376.1015.
5-Methoxy-N-(2,4,5-trihydroxy-6-(hydroxymethyl) tetrahydro-2H-pyran-3-yl)benzofuran-2-carboxamide (5e)
Yield 72%; mp 181–182°C; IR (cm−1): 3420, 3017, 2360, 1579, 1436, 1208, 780; 1H NMR: 7.90 (d, J = 3.5 Hz, 1H, NH), 7.60 (d, J = 9.0 Hz, 1H, ArH), 7.55 (s, 1H, ArH), 7.27 (d, J = 3.0 Hz, 1H, ArH), 7.07 (m, 1H, ArH), 6.60 (d, J = 4.5 Hz, 1H, HGlu), 5.09 (t, J = 3.5 Hz, 1H, HGlu), 5.01 (d, J = 5.5 Hz, 1H, HGlu), 4.84 (d, J = 5.5 Hz, 1H, HGlu), 3.81 (s, 3H, −OCH3) 3.73−3.70 (m, 1H, HGlu), 3.68−3.63 (m, 2H, OH) 3.54−3.50 (m, 1H, OH), 3.46– 3.42 (m, 1H, OH), 3.22−3.18 (m, 1H, HGlu); ESI-HRMS (m/z): calcd for C16H19NO8Na+ [M+Na]+: 376.1003; Found: 376.1015.
5-Fluoro-N-(2,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-3-yl)benzofuran-2-carboxamide (5f)
Yield 76%; mp 132–133°C; IR (cm−1): 3421, 3009, 2401, 1573, 1438, 1213, 791; 1H NMR : 8.06 (d, J = 8.0 Hz, 1H, NH), 7.63 (s, 1H, ArH), 7.61 (d, J = 8.0 Hz, 1H, ArH), 7.21 (s, 1H, ArH), 7.10 (m, 1H, ArH), 6.61 (d, J = 4.0 Hz, 1H, HGlu), 5.09 (t, J = 4.0 Hz, 1H, HGlu), 5.02 (d, J = 5.5 Hz, 1H, HGlu), 4.85 (d, J = 6.0 Hz, 1H, HGlu), 3.85−3.81 (m, 1H, HGlu), 3.74−3.70 (m, 1H, OH), 3.65−3.62 (m, 2H, OH), 3.53–3.46 (m, 1H, OH), 3.24−3.18 (m, 1H, HGlu); ESI-HRMS (m/z): calcd for C15H16FNO8Na+ [M+Na]+: 364.0803; Found: 364.0811.
Acknowledgments
This work was supported by the Postgraduate Research and Practice Innovation Program of Jiangsu Province (KYCX18-2580, KYCX19-2277, KYCX19-2281), Open-end Funds of Jiangsu Key Laboratory of Marine Biotechnology (HS2014007), Project 521 Funded by Lianyungang (LYG52105-2018023), A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD) and Public Science and Technology Research Funds Projects of Ocean (201505023).
References
[1] Hayakawa, I.; Shioya, R.; Agatsuma, T.; Furukawa, H.; Naruto, S.; Sugano, Y. 4-Hydroxy-3-methyl-6-phenylbenzofuran-2-carboxylic acid ethyl ester derivatives as potent anti-tumor agents. Bioorg. Med. Chem. Lett. 2004, 14, 455-458.10.1016/j.bmcl.2003.10.039Search in Google Scholar PubMed
[2] Zhao, S.Z.; Wei, P.; Wu, M.Y.; Zhang, X.Q.; Zhao, L.Y.; Jiang, X.L.; Hao, C.Z.; Su, X.; Dongmei Zhao, D.M.; Cheng, M.S. Design, synthesis and evaluation of benzoheterocycle analogues as potent antifungal agents targeting CYP51. Bioorgan. Med. Chem. 2018, 26, 3242-3253.10.1016/j.bmc.2018.04.054Search in Google Scholar PubMed
[3] Sethi, P.; Bansal, Y.; Bansal, G. Synthesis and PASS-assisted evaluation of coumarin–benzimidazole derivatives as potential anti-inflammatory and anthelmintic agents. Med. Chem. Res. 2018,27, 61-71.10.1007/s00044-017-2036-1Search in Google Scholar
[4] Kushwaha, P.; Fatima, S.; Upadhyay, A.; Gupta, S.; Bhagwati, S.; Baghel, T.; Siddiqi, B.T.; Nazir, A.; Sashidhara, K.V. Synthesis, biological evaluation and molecular dynamic simulations of novel Benzofuran-tetrazole derivatives as potential agents against Alzheimer’s disease. Bioorgan. Med. Chem. 2018, 29, 66-72.10.1016/j.bmcl.2018.11.005Search in Google Scholar PubMed
[5] Gill, J.; Heel, R.C.; Fitton, A. Amiodarone. Drugs. 1992, 43, 69-110.10.2165/00003495-199243010-00007Search in Google Scholar PubMed
[6] Dağlı, Ö.; Köse, D. A.; Avcı, G.A.; Şahin, O. Novel mixed-ligand complexes of coumarilate/N, N’-diethylnicotinamide with some transition metals. J. Therm. Anal. Calorim. 2017, 129, 1389-1402.10.1007/s10973-017-6373-6Search in Google Scholar
[7] Mostofi, M.; Ziarani, G.M.; Mahdavi, M.; Moradi, A.; Nadri, H.; Emami, S.; Alinezhad, H.; Foroumadi, A.; Shafiee, A. Synthesis and structure-activity relationship study of benzofuran-based chalconoids bearing benzylpyridinium moiety as potent acetylcholinesterase inhibitors. Eur. J. Med. Chem. 2015, 103, 361-369.10.1016/j.ejmech.2015.08.061Search in Google Scholar PubMed
[8] Joubert, J.; Foka,G.B.; Repsold, B.P.; Oliver, D.W.; Kapp, E.; Malan, S.F. Synthesis and evaluation of 7-substituted coumarin derivatives as multimodal monoamine oxidase-B and cholinesterase inhibitors for the treatment of Alzheimer’s disease. Eur. J. Med. Chem. 2017, 125, 853-864.10.1016/j.ejmech.2016.09.041Search in Google Scholar PubMed
[9] Hiremathad, A.; Chand, K.; Keri, R.S. Development of coumarinbenzofuran hybrids as versatile multitargeted compounds for the treatment of Alzheimer’s Disease. Chem. Biol. Drug. Des. 2018, 92, 1497-1503.10.1111/cbdd.13316Search in Google Scholar PubMed
[10] Zha, X.M.; Lamba, D.; Zhang, L.L.; Lou, Y.H.; Xu, C.X.; Kang, D.; Samez, S. Novel tacrine-benzofuran hybrids as potent multitarget-directed ligands for the treatment of Alzheimer’s disease: design, synthesis, biological evaluation, and X-ray crystallography. J. Med. Chem. 2015, 59, 114-131.10.1021/acs.jmedchem.5b01119Search in Google Scholar PubMed
[11] Azuma, K.; Osaki, T.; Kurozumi, S.; Kiyose, M.; Tsuka, T.; Murahata, Y.; Okamoto, Y. Anti-inflammatory effects of orally administered glucosamine oligomer in an experimental model of inflammatory bowel disease. Carbohyd. Polym. 2015, 115, 448-456.10.1016/j.carbpol.2014.09.012Search in Google Scholar
[12] Karagozlu, M.Z.; Kim, S.K. Anti-cancer effects of chitin and chitosan derivatives. In Handbook of anticancer drugs from marine origin. Springer, Cham. 2015, pp 413-42110.1007/978-3-319-07145-9_20Search in Google Scholar
[13] Skarbek, K.; Gabriel, I.; Szweda, P.; Wojciechowski, M.; Khan, M.A.; Görke, B.; Milewski, S.; Milewska, M.J. Synthesis and antimicrobial activity of 6-sulfo-6-deoxy-D-glucosamine and its derivatives. Carbohyd. Res. 2017, 448, 79-87.10.1016/j.carres.2017.06.002Search in Google Scholar
[14] Wang, L.; Wu, Y.R.; Ren, S.T.; Yin, L.; Liu, X.J.; Cheng, F.C.; Liu, W.W.; Shi, D.H.; Cao, Z.L.; Sun, H.M. Synthesis and bioactivity of novel C2-glycosyl oxadiazole derivatives as acetylcholinesterase inhibitors. Heterocycl. Commun. 2018, 24, 333-338.10.1515/hc-2018-0166Search in Google Scholar
[15] Yin, L.; Wang, L.; Liu, X.J.; Cheng, F.C.; Shi, D.H.; Cao, Z.L.; Liu, W.W. Synthesis and bioactivity of novel C2-glycosyl triazole derivatives as acetylcholinesterase inhibitors. Heterocycl. Commun. 2017, 23, 231-236.10.1515/hc-2016-0163Search in Google Scholar
[16] Liu, W.W.; Li, Q.X.; Shi, D.H. Synthesis, characterization, and biological evaluation of some novel glycosyl 1,3,4-thiadiazole derivatives as acetylcholinesterase inhibitors. Heterocycles. 2015, 91, 275-286.10.3987/COM-14-13134Search in Google Scholar
[17] MubarakAli, D.; LewisOscar, F.; Gopinath, V.; Alharbi, N.S.; Alharbi, S.A.; Thajuddin, N. An inhibitory action of chitosan nanoparticles against pathogenic bacteria and fungi and their potential applications as biocompatible antioxidants. Microb. Pathogenesis. 2018, 114, 323-327.10.1016/j.micpath.2017.11.043Search in Google Scholar
[18] Ellman, G.L.; Courtney, K.D.; Andres Jr, V.; Featherstone, R.M. A new and rapid colorimetric determination of acetylcholinesterase activity. Biochem. Pharmacol. 1961, 7, 88-95.10.1016/0006-2952(61)90145-9Search in Google Scholar
[19] Shetab-Boushehri, S.V. Ellman’s method is still an appropriate method for measurement of cholinesterases activities. EXCLI. J. 2018, 17, 798-799.Search in Google Scholar
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