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Review
10 (
2
); 167-171
doi:
10.1016/j.arabjc.2014.11.053

Synthesis and characterization of a series of novel 2-Schiff base-substituted phenylpyrimidine

, ,
 College of Chemistry and Materials, South-Central University for Nationalities, Wuhan 430074, PR China

⁎Corresponding author. Tel.: +86 2762357762. jianzhangye@gmail.com (Jian Zhang)

Received: , Accepted: ,
© The Author(s) 2014
Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

A new series of pyrimidine derivatives containing Schiff bases structure have been synthesized efficiently by modification of the C-2 position of Biginelli 3,4-dihydropyrimidin-2-(1H)-thiones (DHPMs). Their structures have been characterized by IR, 1H NMR, 13C NMR, MS spectra and elemental analysis.

Keywords

Biginelli
Pyrimidine
Schiff base
Synthesis
1

1 Introduction

Biginelli 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) (Biginelli, 1893; Oliver Kappe, 1993; Kappe, 2000a,b; Dallinger et al., 2004; Gong et al., 2007; Kolosov et al., 2009) are central subunits in a broad range of medicinal agents, which display interesting pharmacological and biological properties, such as calcium channel modulators, α1a-adrenergic receptor antagonists, mitotic kinesin inhibitors and hepatitis B virus replication inhibitors (Kappe, 2000a,b; Deres et al., 2003; Lengar and Kappe, 2004; Singh et al., 2009a,b). The DHPM core was also found in several marine derived natural products, such as Crambine, Batzelladine B (potent HIV gp-120CD4 inhibitors) and Ptilomycalin alkaloids (Aron and Overman, 2004). Additionally, the Biginelli DHPMs are important building blocks in the synthesis of multifunctionalized pyrimidines. DHPMs have attracted our attention because of the fact that several DHPMs have been examined for their antimicrobial properties in the recent years (Chitra et al., 2010; Kumar et al., 2009; Singh et al., 2008). Moreover, pyrimidine derived metal ion complexes have been extensively studied in the recent years owing to their great variety of biological activity ranging from antimalarial, antibacterial, antitumoral, antiviral activities, etc., which have often been related to their chelating ability with trace metal ions (Somnath et al., 2007). Recently, Schiff bases containing pyrimidine derivatives have been synthesized using different methods with modified procedures (Tomma et al., 2014; Parikh and Vyas, 2012; Ray et al., 2012). Pyrimidine derivatives and heterocyclic annulated pyrimidines continue to attract great interest due to the wide variety of interesting biological activities observed in these compounds, such as anticancer (Petrie et al., 1985), antiviral (Nasr and Gineinah, 2002), antitumor (Baraldi et al., 2002), anti-inflammatory (Antre et al., 2011), and antimicrobial activities (Singh and Srivastava, 2013).

In general, DHPMs are readily obtained via three-component Biginelli reaction. With substitution of the C-2 position of DHPMs, we synthesize a series of novel compounds which have potential pharmacological and physiological activities.

2

2 Experimental

2.1

2.1 Materials and methods

All chemicals were of reagent grade, purchased from commercial sources and used without further purification. Aromatic aldehydes, ethylacetoacetate phosphorus oxychloride and hydrazine were purchased from the Alladin Chemical Company, and were used without further purification. All the solvents were dried using standard methods before use. 1H NMR and 13C NMR were recorded on a Bruker 400 for CDCl3 solutions. IR spectra were recorded with an FTIR 1730. X4-digital melting point reader was used to determine the melting points. Mass spectra were obtained on a LCQ DECA XP (Thermo Company). Elemental analyses were performed in a Vario EL cube instrument.

2.2

2.2 Synthesis and characterization of compounds

2.2.1

2.2.1 Synthesis of compounds 1–3

The compound 1 was prepared by the reaction of classical Biginelli reaction (Biginelli, 1893), and the oxidation of compound 1 to compound 2 was readily achieved using nitric acid as reported by Puchala et al. (2001). Subsequently the treatment of compound 2 with phosphorous oxychloride at 105 °C produced compound 3 was described by Singh et al. (2011).

2.2.2

2.2.2 Synthesis of ethyl 2-hydrazinyl-6-methyl-5-carboxylate (4)

Compound 3 (5 mmol) and hydrazine hydrate (10 mmol) were mixed with ethanol in a 25 ml round bottom flask and refluxed at 85 °C for 4 h. The reaction mixture was cooled in ice-bath and the precipitated solid was filtered through a sintered funnel. The crude product was further purified by recrystallization from ethanol to afford pure compound 4.

2.2.3

2.2.3 Synthesis of ethyl 2-(2-benzylidenehydrazinyl)-6-methyl-5-carboxylate (5)

Compound 4 (4 mmol), aromatic aldehydes (6 mmol), acetic acid (0.15 mmol) were mixed with ethanol in a 25 ml round bottom flask and refluxed at 85 °C for 5 h. The reaction mixture was cooled in an ice-bath and the precipitated solid was filtered through a sintered funnel. The crude product was further purified by recrystallization from ethanol to afford pure compound 5 (Scheme 1).

Synthetic route of 2-Schiff base-substituted phenylpyrimidine. Reagents, conditions and yields: (a) AlCl3, EtOH, reflux 3 h, 78–83%; (b) HNO3 (50–60%), ice-bath 1 h, 68–79%; (c) PCl3, EtOH, reflux. 3 h, 69–85%; (d) NH2NH2, EtOH, reflux 4 h, 77–85%; (e) acetic acid, Ar-CHO, EtOH, reflux 5 h.
Scheme 1 Synthetic route of 2-Schiff base-substituted phenylpyrimidine. Reagents, conditions and yields: (a) AlCl3, EtOH, reflux 3 h, 78–83%; (b) HNO3 (50–60%), ice-bath 1 h, 68–79%; (c) PCl3, EtOH, reflux. 3 h, 69–85%; (d) NH2NH2, EtOH, reflux 4 h, 77–85%; (e) acetic acid, Ar-CHO, EtOH, reflux 5 h.

Ethyl 2-(2-benzylidenehydrazinyl)-4-methyl-6-phenylpyrimidine-5-carboxylate (5a). White crystals; yield 65%; mp 152–153 °C; IR (KBr pellet cm−1): 3200 (N—H), 2986 (CH, aromatic), 1720 (C⚌O), 1542 (C⚌N), 1446 (C⚌N) cm−1; 1H NMR (400 MHz, CDCl3) δ 9.07 (s, 1H), 7.82 (s, 1H), 7.75 (dd, J = 7.7, 1.8 Hz, 2H), 7.65 (dd, J = 6.7, 3.0 Hz, 2H), 7.52–7.34 (m, 6H), 4.14 (q, J = 7.1 Hz, 2H), 2.66 (s, 3H), 1.02 (t, J = 7.1 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 168.42, 166.32, 165.07, 158.72, 143.73, 138.25, 134.07, 129.96, 129.62, 128.47, 128.43, 128.12, 127.33, 117.98, 61.40, 23.20, 13.59; ms: m/z 361 (M+1). Anal. Calcd for C21H20N4O2: C, 69.98; H, 5.59; N, 15.55. Found: C, 69.92; H, 5.56; N, 15.58.

Ethyl 2-(2-(4-chlorobenzylidene)hydrazinyl)-4-methyl-6-phenylpyrimidine-5-carboxy-late (5b). White crystals; yield 69%; mp 158–159 °C; IR (KBr pellet cm−1): 3192 (N—H), 3060 (CH, aliphatic), 1710 (C⚌O), 1544 (C⚌N), 1440 (C⚌N) cm−1; 1H NMR (400 MHz, CDCl3) δ 9.39 (s, 1H), 7.71–7.58 (m, 5H), 7.42 (dd, J = 6.5, 4.0 Hz, 3H), 7.07 (t, J = 8.7 Hz, 2H), 4.14 (q, J = 7.2 Hz, 2H), 2.65 (s, 3H), 1.02 (t, J = 7.1 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 168.29, 165.96, 164.76, 162.27, 158.81, 142.48, 138.11, 130.32, 130.08, 129.04, 128.56, 128.08, 117.88, 115.61, 115.39, 61.46, 23.25, 13.58; ms: m/z 379 (M+1). Anal. Calcd for C21H19FN4O2: C, 69.66; H, 5.06; N, 14.81. Found: C, 69.61; H, 5.08; N, 14.83.

Ethyl 2-(2-(4-chlorobenzylidene)hydrazinyl)-4-methyl-6-phenylpyrimidine-5-carboxylate (5c). White crystals; yield 63%; mp 160–161 °C; IR (KBr pellet cm−1): 3198 (N—H), 2981 (CH, aliphatic), 1719 (C⚌O), 1544 (C⚌N), 1439 (C⚌N) cm−1; 1H NMR (400 MHz, CDCl3) δ 9.12 (s, 1H), 7.74 (s, 1H), 7.65 (dd, J = 9.9, 6.0 Hz, 4H), 7.43 (dd, J = 18.2, 14.4 Hz, 4H), 7.36 (s, 1H), 4.14 (q, J = 7.1 Hz, 2H), 2.65 (s, 3H), 1.03 (t, J = 7.1 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 168.41, 166.28, 165.09, 158.62, 144.63, 139.15, 135.08, 129.86, 129.45, 128.55, 128.31, 128.02, 127.53, 117.80, 61.32, 22.31, 13.56; ms: m/z 395 (M+1). Anal. Calcd for C21H19ClN4O2: C, 63.88; H, 4.85; N, 8.98. Found: C, 63.83; H, 4.82; N, 9.03.

Ethyl 2-(2-(4-bromobenzylidene)hydrazinyl)-4-methyl-6-phenylpyrimidine-5-carboxy-late (5d). White crystals; yield 61%; mp 175–176 °C; IR (KBr pellet cm−1): 3197 (N—H), 2981 (CH, aliphatic), 1718 (C⚌O), 1544 (C⚌N), 1437 (C⚌N) cm−1; 1H NMR (400 MHz, CDCl3) δ 9.08 (s, 1H), 7.76 (s, 1H), 7.68–7.58 (m, 4H), 7.53 (d, J = 8.6 Hz, 2H), 7.49–7.41 (m, 3H), 4.14 (q, J = 7.1 Hz, 2H), 2.65 (s, 3H), 1.02 (t, J = 7.1 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ168.39, 166.30, 165.88, 157.60, 146.33, 138.45, 134.10, 128.98, 128.70, 127.95, 127.56, 127.44, 126.98, 118.90, 61.62, 23.31, 13.66; ms: m/z 439 (M+1). Anal. Calcd for C21H19BrN4O2: C, 57.41; H, 4.36; N, 18.19. Found: C, 57.42; H, 4.31; N, 18.12.

Ethyl 2-(2-(4-hydroxybenzylidene)hydrazinyl)-4-methyl-6-phenylpyrimidine-5-carboxylate (5e). White crystals; yield 72%; mp 106–107 °C; IR (KBr pellet cm−1): 3201 (N—H), 2971 (CH, aliphatic), 1720 (C⚌O), 1552 (C⚌N), 1446 (C⚌N) cm−1; 1H NMR (400 MHz, CDCl3) δ 9.36 (s, 1H), 8.76 (s, 1H), 7.63–7.51 (m, 3H), 7.38 (dd, J = 8.6, 5.3 Hz, 4H), 7.36 (s, 1H), 6.68 (d, J = 8.6 Hz, 2H), 4.11 (q, J = 7.1 Hz, 2H), 2.61 (s, 3H), 0.99 (t, J = 7.1 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 168.41, 166.28, 165.68, 158.50, 147.43, 138.45, 134.10, 128.98, 128.70, 127.95, 127.56, 127.44, 126.98, 118.90, 61.62, 23.31, 13.66. ms: m/z 377 (M+1). Anal. Calcd for C21H20N4O3: C, 67.01; H, 5.36; N, 14.88. Found: C, 66.97; H, 5.31; N, 14.81.

Ethyl 4-methyl-2-(2-(4-nitrobenzylidene)hydrazinyl)-4-methyl-6-phenylpyrimidine-5-carboxylate (5f). Yellow crystals; yield 85%; mp 241–242 °C; IR (KBr pellet cm−1): 3330 (N⚌H), 2975 (CH, aliphatic), 1706 (C⚌O), 1545 (C⚌N), 1434 (C⚌N) cm−1; 1H NMR (400 MHz, CDCl3) δ 9.37 (s, 1H), 8.26 (d, J = 8.8 Hz, 2H), 7.93–7.77 (m, 3H), 7.72–7.61 (m, 2H), 7.527.58 (m, 4H), 7.53 (d, J = 8.6 Hz, 2H), 7.49–7.41 (m, 3H), 4.14 (q, J = 7.37 (m, 3H), 4.17 (q, J = 7.1 Hz, 2H), 2.67 (s, 3H), 1.04 (t, J = 7.1 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ168.52, 166.23, 165.12, 157.43, 142.53, 139.11, 133.98, 129.76, 129.42, 128.90, 128.13, 128.02, 127.33, 117.98, 61.40, 23.20, 13.59. ms: m/z 406 (M+1). Anal. Calcd for C21H19N5O4: C, 62.22; H, 4.72; N, 17.27. Found: C, 62.14; H, 4.73; N, 17.30.

Ethyl 4-methyl-2-(2-(4-methylbenzylidene)hydrazinyl)-4-methyl-6-phenylpyrimidine-5-carboxylate (5g). White crystals; yield 79%; mp 156–157 °C; IR (KBr pellet cm−1): 3213 (N⚌H), 2990 (CH, aliphatic), 1719 (C⚌O), 1545 (C⚌N), 1441 (C⚌N) cm−1; 1H NMR (400 MHz, CDCl3) δ 9.20 (s, 1H), 7.64 (m, 5H), 7.517.58 (m, 4H), 7.53 (d, J = 8.6 Hz, 2H), 7.49–7.41 (m, 3H), 4.14 (q, J = 7.38 (m, 3H), 6.90 (d, J = 8.8 Hz, 2H), 4.13 (q, J = 7.1 Hz, 2H), 3.85 (s, 3H), 2.65 (s, 3H), 1.01 (t, J = 7.1 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ168.40, 166.28, 165.02, 158.57, 137.95, 137.78, 137.61, 130.10, 128.97, 128.29, 128.02, 126.85, 125.56, 117.95, 61.38, 23.32, 21.47, 13.60; ms: m/z 375 (M+1). Anal. Calcd for C22H22N4O2: C, 70.57; H, 5.92; N, 14.96. Found: C, 70.49; H, 5.91; N, 14.95.

Ethyl 2-(2-(4-methoxybenzylidene)hydrazinyl)-4-methyl-6-phenylpyrimidine-5-carboxylate (5h). White crystals; yield 70%; mp 130–131 °C; IR (KBr pellet cm−1): 3191 (N⚌H), 2987 (CH, aliphatic), 1715 (C⚌O), 1545 (C⚌N), 1440 (C⚌N) cm−1; 1H NMR (400 MHz, CDCl3) δ 9.31 (s, 1H), 7.717.58 (m, 4H), 7.53 (d, J = 8.6 Hz, 2H), 7.49–7.41 (m, 3H), 4.14 (q, J = 7.53 (m, 5H), 7.527.58 (m, 4H), 7.53 (d, J = 8.6 Hz, 2H), 7.49–7.41 (m, 3H), 4.14 (q, J = 7.37 (m, 3H), 7.18 (d, J = 7.9 Hz, 2H), 4.13 (q, J = 7.1 Hz, 2H), 2.65 (s, 3H), 2.34 (s, 3H), 1.01 (t, J = 7.1 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 168.21, 165.21, 164.76, 164.27, 159.81, 141.68, 136.31, 131.09, 130.89, 129.12, 128.99, 128.28, 127.71, 114.31, 114.09, 61.46, 21.45, 13.28. ms: m/z 391 (M+1). Anal. Calcd for C22H22N4O3: C, 67.68; H, 5.68; N, 14.35. Found: C, 67.71; H, 5.63; N, 13.27.

Ethyl 4-methyl-6-phenyl-2-(2-((Z)-3-phenylallylidene)hydrazinyl)pyrimidine-5-carboxylate (5i). White crystals; yield 81%; mp 191–192 °C; IR (KBr pellet cm−1): 3194 (N⚌H), 3062 (CH, aliphatic), 1711 (C⚌O), 1545 (C⚌N), 1442 (C⚌N) cm−1; 1H NMR (400 MHz, CDCl3) δ 9.49 (s, 1H), 7.64 (dd, J = 6.5, 3.0 Hz, 2H), 7.517.58 (m, 4H), 7.53 (d, J = 8.6 Hz, 2H), 7.49–7.41 (m, 3H), 4.14 (q, J = 7.24 (m, 9H), 7.09 (dd, J = 16.0, 9.3 Hz, 1H), 6.67 (d, J = 16.1 Hz, 1H), 4.14 (q, J = 7.1 Hz, 2H), 2.66 (s, 3H), 1.02 (t, J = 7.1 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 168.38, 166.05, 160.86, 158.79, 143.99, 139.80, 138.28, 131.32, 129.96, 129.15, 128.87, 128.49, 128.11, 127.32, 117.71, 113.89, 61.38, 21.48, 13.59; ms: m/z 387 (M+1). Anal. Calcd for C23H22N4O2: C, 71.48; H, 5.74; N, 14.50. Found: C, 71.42; H, 5.86; N, 14.51.

Ethyl 4-methyl-6-phenyl-2-(2-(thiophen-2-ylmethylene)hydrazinyl)pyrimidine-5-carboxylate (5j). White crystals; yield 60%; mp 140–141 °C; IR (KBr pellet cm−1): 3200 (N⚌H), 2983 (CH, aliphatic), 1720 (C⚌O), 1543 (C⚌N), 1439 (C⚌N) cm−1; 1H NMR (400 MHz, CDCl3) δ 9.27 (s, 1H), 7.90 (s, 1H), 7.64 (dd, J = 6.3, 3.0 Hz, 2H), 7.537.58 (m, 4H), 7.53 (d, J = 8.6 Hz, 2H), 7.49–7.41 (m, 3H), 4.14 (q, J = 7.42 (m, 3), 7.35 (d, J = 4.6 Hz, 1H), 7.427.58 (m, 4H), 7.53 (d, J = 8.6 Hz, 2H), 7.49–7.41 (m, 3H), 4.14 (q, J = 7.15 (m, 1H), 7.117.58 (m, 4H), 7.53 (d, J = 8.6 Hz, 2H), 7.49–7.41 (m, 3H), 4.14 (q, J = 7.00 (m, 1H), 4.13 (q, J = 7.1 Hz, 2H), 2.65 (s, 3H), 1.02 (t, J = 7.1 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ 168.42, 166.30, 165.95, 158.57, 138.98, 138.60, 138.10, 130.07, 128.99, 128.55, 128.08, 127.69, 127.15, 117.75, 61.44, 23.21, 13.60; ms: m/z 367 (M+1). Anal. Calcd for C19H18N4O2S: C, 62.28; H, 4.95; N, 15.29; S, 8.75. Found: C, 62.30; H, 4.89; N, 15.22; S, 8.73.

3

3 Results and discussion

3.1

3.1 Synthesis of compounds

The compound 1 was prepared according to the classical Biginelli reaction in which good yields were obtained by using AlCl3 as an efficient catalyst. The product was isolated from the reaction mixture and the mother liquor containing the catalyst could be directly reused two times and without any loss of activity. The compound 2 was readily prepared according to the procedures reported by Oliver Kappe (Puchala et al., 2001). The method in general provides moderate to good yields of compound 2. However, a fine-tuning of the conditions with respect to HNO3 concentration and reaction time was necessary in every case. Experimental results show that the reaction time will be extended if we use dilute nitric acid and acidic by-products would appear at higher temperature. There are also some reports using N,N-dimethylaniline as solvent in the synthesis of compound 3, but we found that higher yield and shorter reaction time could be achieved by using phosphorus oxychloride as solvent directly. We also improved the post-process procedure. The traditional procedure is that the last traces of phosphorous oxychloride were removed by azeotropic distillation with dry benzene, while we discovered that a good result can be obtained by simply pouring the residue into ice water and extracting with dichloromethane, but column chromatography was still required. Pure compound 4 and compound 5 could be obtained just by recrystallization from ethanol. Different aromatic aldehydes R were used in the final step of the reaction and a series of different compounds 5 were obtained.

3.2

3.2 Structure characterization

The structure of compounds (5a–j) was confirmed by 1H and 13C NMR, IR spectroscopies and MS spectral data. The IR spectra of all the compounds 5a–j showed (C⚌N) and (N—H) stretch at 1542–1552 cm−1 and 3191–3330 cm−1 in accordance with the Schiff bases moiety. The characteristic carbonyl band at around 1720 cm−1 proves the presence of the carboxylate groups. Therefore, informations originating from the IR spectra confirm the structures of all new compounds described in our present paper. In the 13C NMR spectra of the compound 5a, there were 14 signals in the aromatic region. The chemical shift data of carbon atoms C⚌O were around 168 ppm. There were four signals around 165–158 ppm integrating for pyrimidine. And there was one signal at 23 ppm integrating for —CH3. The chemical shift data of —CH2CH3 were around 13 ppm, and —CH2CH3 were around 61 ppm. The rest of the signals belong to benzene. But there were 15 signals instead of 14 signals in the aromatic region in 5b, because there was one carbon coupled with F. And the other compounds’ spectra were same as 5a. In the 400 MHz 1H NMR spectra of the compounds, the N—H proton resonated as a singlet at 9.07–9.49 ppm. The CH proton of —CH⚌N— appeared in the same region with the aromatic protons at 7.64–7.75 ppm because of conjugation. All the other aromatic and aliphatic protons were observed at expected regions. MS showed that found [M+H]-ion peak accorded with calculated value. Elemental analysis was also consistent with the molecular composition of the compounds.

Acknowledgments

The Project was supported by the Nature Science Foundation of Hubei Province of China (No. 2012FFB07410) and the National Nature Science Foundation of China (No. 21302233) for financial support.

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