HETEROCYCLES

Paper | Regular issue | Vol. 91, No. 9, 2015, pp. 1763-1773
Received, 21st July, 2015, Accepted, 11th August, 2015, Published online, 24th August, 2015.

■ Synthesis and Antihypertensive α-Blocking Activity Evaluation of Thiazole Derivatives Bearing Pyrazole Moiety

Sobhi M. Gomha,* Khaled Khalil, Hassan Abdel-aziz, and Mohamed Abdalla

Department of Organic Chemistry, Cairo University, Giza-Haram 12613, Egypt

Abstract

A novel, facile reaction for the synthesis of series of thiazole derivatives has been developed from the reaction of the appropriate thiosemicarbazone derivatives and 2-bromo-1-(5-methyl-1-phenyl-1H-pyrazol-4-yl)ethanone in ethanol under reflux. The structures of the newly synthesized products were established on the basis of spectral data (mass, IR, 1H and 13C NMR) and elemental analyses. The pharmacological screening showed that many of the synthesized compounds exhibit a good antihypertensive α-blocking activity and having low toxicity, as compared to Minoxidil.

INTORODUCTION
Thiazoles are a familiar group of heterocyclic compounds possessing a wide variety of biological activities as antimicrobial,1-3 antioxidant,4 antitubercular,5 anticonvulsant,6 anticancer,7 and anti-inflammatory8 agents. Moreover, many derivatives of thiazoles are used as selective cyclooxygenase-2 inhibitors,9 in addition to their use as 5-HT3 receptor antagonists 10 and as potent and selective acetyl Co-A carboxylase-2 inhibitors.11 Furthermore, several pyrazole derivatives received great attention due to their biological and pharmacological activities not only as potential inhibitors of HIV-1,12 pesticides,13 fungicides,14 antihypertensive agents 15 and anticancer activity.16 In addition, thiazoles have attracted more interest not only due to their ability to enhance the lipid solubility but also they can easily metabolize through the normal biochemical reactions.17 As a part of our research interest towards developing new routes for the synthesis of a variety of heterocyclic systems with promising biological and pharmacological activities,18-26 we report in the present article the synthesis of a new series of 1,3-thiazoles bearing pyrazole moiety as anti-hypertensive α-blocking agents and the results were reported against Minoxidil as reference.

RESULTS AND DISCUSSION
The thiosemicarbazones were synthesized by treatment of the corresponding carbonyl compound with thiosemicarbazide in acid medium, unless otherwise indicated, according to the general procedure previously described.
2-Bromo-1-(5-methyl-1-phenyl-1H-pyrazol-4-yl)ethanone (4) was prepared via direct bromination of the acetylpyrazole 3 with bromine in CHCl3 as previously reported in the respective literature.27
The reaction of 2-bromo-1-(5-methyl-1-phenyl-1H-pyrazol-4-yl)ethanone (4) with thiosemicarbazones 2a-r in refluxing ethanol, afforded the corresponding thiazoles 5a-r following Hantzsch thiazole synthesis.28 The reaction proceeded through the reaction of 4 with equivalent amounts of each of thiosemicarbazones 2a-r, to give the S-alkylated intermediates which cyclized in situ under the employed reaction conditions with elimination of water molecule furnished in each case, one isolable product (as tested by TLC). The reaction products were identified as thiazoles 5a-r (Scheme 1). Structures of the final products were elucidated by studying their elemental analyses and spectral data. For example, the 1H NMR spectrum of thiazoles 5a revealed the absence of NH2 protons of compound 2 and showed the signals at δ = 2.58 (s, 3H, CH3), 6.83-7.87 (m, 12H, Ar-H), 8.44 (s, 1H, CH=N), 10.36 (br s, 1H, NH). Also, its mass spectrum showed peaks at m/z = 359 which matches with its molecular formula C20H17N5S.
In the IR spectrum of compounds 5a-r, the characteristic N–H stretching absorption band appeared around the 3299-3092 cm-1 regions. 1H NMR spectra of compounds 5a-r revealed the presence of the –CH=N– proton and the =N–NH– proton as two singlets at δ = 7.66-8.62 and 11.30-11.81 ppm, respectively. The thiazole proton appeared as a multiplet at 6.45-8.14 ppm together with phenyl protons. In addition, EI-MS spectra of 5a-r showed a molecular ion peak with intensities of 95-100%.

Pharmacological screening
Antihypertensive α-blocking activity
The newly synthesized derivatives were subjected to α-blocking activity model screening using α-sympatholytic activity in isolated vascular smooth muscle (Table 1). All the tested compounds showed antihypertensive α-blocking activities and they are arranged in descending order of activities as follows: 5m > 5l > 5e > 5c > 5f > 5g > 5a > 5h > 5q > 5r > 5b > 5d > 5n > 5o > 5p > 5j > 5i > 5k.
It is worth to be mentioned that 5m and 5l compounds are more potent than Minoxidil, while, 5c and 5e are of similar activity.

Structure activity relationship (SAR)
As shown in Table 1, the results of the antihypertensive α-blocking activities exhibited a clear structural activity relation depending on the substitution at either aromatic ring or at the carbonyl carbon of thiosemicarbazone moiety. It has been found that, the dichloro substitution at C-2 and C-6 has been strongly affected the antihypertensive activity (IC50 µg/cm3 = 3.91), even more potent than Minoxidil reference compound, as compared to the dichloro substitution at 2 and 4 carbons (IC50 µg/cm3 = 23.34). On the other hand, mono aromatic substitutions with electron donating or electron withdrawing groups exhibited more antihypertensive activity through aromatic substitution at C-4 (4-OMe; 4.17) rather than at C-2 (2-OMe; 12.65). Moreover, mono substitution at C-4 with Cl and OMe groups led to similar activity to Minoxidil. Interestingly, methyl substitution at carbonyl carbon of thiosemicarbazone, with unsubstituted benzene ring, strongly improved the antihypertensive activity (IC50 µg/cm3 = 3.79) more than the exhibited activity of Minoxidil itself.
CONCCLUSIONS
This paper describes a facile and efficient synthesis of thiazole derivatives via cyclization reaction of 2-bromo-1-(5-methyl-1-phenyl-1H-pyrazol-4-yl)ethanone with thiosemicarbazones. Structures of the final products were elucidated by elemental analyses and FTIR, MS, 1H and 13C NMR spectra. The pharmacological screening of the synthesized products showed potent antihypertensive α-blocking activity.

EXPERIMENTAL
Melting points were determined on a Gallenkamp apparatus and are uncorrected. IR spectra were recorded in KBr using Pye-Unicam SP300 spectrophotometer. 1H and 13C NMR spectra were recorded in deuterated DMSO-d6 using a Varian Gemini 300 NMR spectrometer (300 MHz for 1H NMR and 75 MHz for 13C NMR) and the chemical shifts were related to that of the solvent DMSO-d6. Mass spectra were recorded on a GCMS-Q1000-EX Shimadzu and GCMS 5988-A HP spectrometers, the ionizing voltage was 70 eV. Elemental analyses of the products were carried out at the Microanalytical Centre of Cairo University, Giza, Egypt. The starting thiosemicarbazones 2a-c, 2e-j,29 2d,30 2m, 2p, 2r,31 2n, 2o,32 and 2q33 prepared as previously described.
Synthesis of 2-(2-arylidenehydrazinyl)-4-(5-methyl-1-phenyl-1H-pyrazol-4-yl)thiazole (5a-r).
General procedure: A mixture of thiosemicarbazone derivatives 2a-r (1 mmol) and 2-bromo-1-(5-methyl-1-phenyl-1H-pyrazol-4-yl)ethanone (4) (0.263 g, 1 mmol) in EtOH (30 mL) was refluxed for 2-4 h. (monitored by TLC). The formed precipitate was isolated by filtration, washed with methanol, dried and recrystallized from appropriate solvent to give products 5a–r.
2-(2-Benzylidenehydrazinyl)-4-(5-methyl-1-phenyl-1H-pyrazol-4-yl)thiazole (5a). Yield 67%; pale yellow microcystals; mp 212-214 oC (EtOH); IR (KBr): v 3431 (NH), 1608 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.58 (s, 3H, CH3), 6.83-7.87 (m, 11H, Ar-H and thiazole-H5), 8.19 (s, 1H, pyrazole-H3), 8.44 (s, 1H, CH=N), 10.36 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 12.21(CH3), 113.7, 128.8, 129.1, 129.4, 133.8, 137.4, 137.8, 138.6, 138.9, 139.2, 139.5, 144.1, 145.7, 153.0, 165.9; MS m/z (%): 359 (M+, 27). Anal. Calcd for C20H17N5S (359.45): C, 66.83; H, 4.77; N, 19.48; Found: C, 66.74; H, 4.58; N, 19.29%.
4-(5-Methyl-1-phenyl-1H-pyrazol-4-yl)-2-(2-(4-methylbenzylidene)hydrazinyl)thiazole (5b). Yield 69%; pale yellow microcystals; mp 193-195 oC (EtOH); IR (KBr): v 3412 (NH), 1602 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.18 (s, 3H, CH3), 2.57 (s, 3H, CH3), 6.91-7.97 (m, 10H, Ar-H and thiazole-H5), 8.25 (s, 1H, pyrazole-H3), 8.51 (s, 1H, CH=N), 10.36 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 12.21, 26.3 (CH3), 115.5, 125.2, 125.5, 127.4, 128.6, 129.1, 129.3, 130.7, 137.8, 138.1, 141.9, 144.7, 145.9, 162.0, 167.8; MS m/z (%): 373 (M+, 17). Anal. Calcd for C21H19N5S (373.47): C, 67.53; H, 5.13; N, 18.75; Found: C, 67.42; H, 5.10; N, 18.69%.
2-(2-(4-Methoxybenzylidene)hydrazinyl)-4-(5-methyl-1-phenyl-1H-pyrazol-4-yl)thiazole (5c). Yield 62%; brown microcystals; mp 172-174 oC (EtOH); IR (KBr): v 3417 (NH), 1600 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.57 (s, 3H, CH3), 3.86 (s, 3H, OCH3), 7.00-7.89 (m, 10H, Ar-H and thiazole-H5), 8.03 (s, 1H, pyrazole-H3), 8.52 (s, 1H, CH=N), 9.87 (br s, 1H, NH); MS m/z (%): 389 (M+, 23). Anal. Calcd for C21H19N5OS (389.47): C, 64.76; H, 4.92; N, 17.98; Found: C, 64.69; H, 4.91; N, 17.66%.
2-(2-(2-Methoxybenzylidene)hydrazinyl)-4-(5-methyl-1-phenyl-1H-pyrazol-4-yl)thiazole (5d). Yield 61%; brown microcystals; mp 164-166 oC (EtOH); IR (KBr): v 3411 (NH), 1603 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.58 (s, 3H, CH3), 3.54 (s, 3H, OCH3), 7.51-7.97 (m, 10H, Ar-H and thiazole-H5), 8.14 (s, 1H, pyrazole-H3), 8.44 (s, 1H, CH=N), 9.83 (br s, 1H, NH); MS m/z (%): 389 (M+, 63). Anal. Calcd for C21H19N5OS (389.47): C, 64.76; H, 4.92; N, 17.98; Found: C, 64.55; H, 4.90; N, 17.76%.
2-(2-(4-Chlorobenzylidene)hydrazinyl)-4-(5-methyl-1-phenyl-1H-pyrazol-4-yl)thiazole (5e). Yield 69%; pale yellow microcystals; mp 213-215 oC (dioxane); IR (KBr): v 3436 (NH), 1605 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.74 (s, 3H, CH3), 7.42-7.96 (m, 10H, Ar-H and thiazole-H5), 8.54 (s, 1H, pyrazole-H3), 8.87 (s, 1H, CH=N), 10.06 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 13.2 (CH3), 110.7, 124.6, 124.9, 128.0, 128.9, 129.1, 130.6, 132.0, 137.2, 138.0, 139.1, 142.0, 145.3, 162.7, 164.6; MS m/z (%): 393 (M+, 44). Anal. Calcd for C20H16ClN5S (393.89): C, 60.98; H, 4.09; N, 17.78; Found: C, 60.78; H, 4.03; N, 17.63%.
2-(2-(4-Bromobenzylidene)hydrazinyl)-4-(5-methyl-1-phenyl-1H-pyrazol-4-yl)thiazole (5f). Yield 66%; pale yellow microcystals; mp 251-253 oC (dioxane); IR (KBr): v 3427 (NH), 1603 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.72 (s, 3H, CH3), 7.27-7.94 (m, 10H, Ar-H and thiazole-H5), 8.53 (s, 1H, pyrazole-H3), 8.83 (s, 1H, CH=N), 10.21 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 11.62 (CH3), 110.7, 114.7, 122.5, 125.0, 126.2, 128.2, 129.1, 132.2, 133.4, 137.5, 138.0, 139.1, 145.2,162.8, 165.8; MS m/z (%): 438 (M+, 38). Anal. Calcd for C20H16BrN5S (438.34): C, 54.80; H, 3.68; N, 15.98; Found: C, 54.69; H, 3.62; N, 15.75%.
4-(5-Methyl-1-phenyl-1H-pyrazol-4-yl)-2-(2-(4-nitrobenzylidene)hydrazinyl)thiazole (5g). Yield 66%; brown microcystals; mp 237-239 oC (dioxane); IR (KBr): v 3446 (NH), 1605 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.55 (s, 3H, CH3), 6.98-7.95 (m, 10H, Ar-H and thiazole-H5), 8.12 (s, 1H, pyrazole-H3), 8.49 (s, 1H, CH=N), 10.09 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 12.0 (CH3), 112.6, 115.8, 124.1, 124.9, 126.9, 127.7, 129.1, 135.6, 136.3, 138.8, 139.2, 140.8, 147.0, 162.0, 165.4; MS m/z (%): 404 (M+, 18). Anal. Calcd for C20H16N6O2S (404.45): C, 59.39; H, 3.99; N, 20.78; Found: C, 59.24; H, 3.91; N, 20.58%.
4-(5-Methyl-1-phenyl-1H-pyrazol-4-yl)-2-(2-(3-nitrobenzylidene)hydrazinyl)thiazole (5h). Yield 66%; brown microcystals; mp 184-186 oC (EtOH); IR (KBr): v 3426 (NH), 1603 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.73 (s, 3H, CH3), 7.54-7.96 (m, 10H, Ar-H and thiazole-H5), 8.23 (s, 1H, pyrazole-H3), 8.50 (s, 1H, CH=N), 10.07 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 13.3 (CH3), 110.7, 123.2, 123.7, 124.5, 125.3, 126.9, 128.2, 129.6, 136.3, 137.9, 142.2, 148.7, 164.1, 166.1, 168.4; MS m/z (%): 404 (M+, 72). Anal. Calcd for C20H16N6O2S (404.45): C, 59.39; H, 3.99; N, 20.78; Found: C, 59.32; H, 3.85; N, 20.69%.
N,N-Dimethyl-4-((2-(4-(5-methyl-1-phenyl-1H-pyrazol-4-yl)thiazol-2-yl)hydrazono)methyl)aniline (5i). Yield 66%; brown microcystals; mp 206-208 oC (EtOH); IR (KBr): v 3429 (NH), 1600 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.70 (s, 3H, CH3), 3.15 (s, 6H, 2CH3), 6.77-7.88 (m, 10H, Ar-H and thiazole-H5), 8.30 (s, 1H, pyrazole-H3), 8.62 (s, 1H, CH=N), 9.66 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 11.9, 36.1 (CH3), 110.9, 111.1, 120.3, 124.5, 125.2, 129.4, 131.2, 131.8, 138.1, 138.6, 141.5, 144.3, 153.0, 163.1, 164.8; MS m/z (%): 404 (M+, 72). Anal. Calcd for C22H22N6S (402.52): C, 65.65; H, 5.51; N, 20.88; Found: C, 65.65; H, 5.51; N, 20.88%.
2-((2-(4-(5-Methyl-1-phenyl-1H-pyrazol-4-yl)thiazol-2-yl)hydrazono)methyl)phenol (5j). Yield 66%; yellow microcystals; mp 226-228 oC (EtOH); IR (KBr): v 3447, 3318 (OH and NH), 1606 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.71 (s, 3H, CH3), 5.40 (br s, 1H, OH), 6.94-7.76 (m, 10H, Ar-H and thiazole-H5), 8.26 (s, 1H, pyrazole-H3), 8.51 (s, 1H, CH=N), 10.14 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 13.2 (CH3), 110.8, 116.7, 118.8, 119.8, 125.1, 125.3, 129.1, 129.4, 129.5, 134.4, 138.0, 141.9, 145.1, 158.8, 161.8, 164.2, 167.6; MS m/z (%): 375 (M+, 36). Anal. Calcd for C20H17N5OS (375.45): C, 63.98; H, 4.56; N, 18.65; Found: C, 63.86; H, 4.52; N, 18.48%.
2-(2-(2,4-Dichlorobenzylidene)hydrazinyl)-4-(5-methyl-1-phenyl-1H-pyrazol-4-yl)thiazole (5k). Yield 72%; yellow microcystals; mp 237-239 oC (EtOH); IR (KBr): v 3420 (NH), 1606 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.73 (s, 3H, CH3), 7.40-7.99 (m, 9H, Ar-H and thiazole-H5), 8.17 (s, 1H, pyrazole-H3), 8.54 (s, 1H, CH=N), 10.55 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 13.3 (CH3), 125.0, 125.4, 127.3, 128.2, 128.3, 129.0, 129.5, 130.0, 130.9, 131.6, 131.7, 133.8, 133.9, 135.7, 150.9, 156.4, 169.9; MS m/z (%): 428 (M+, 38). Anal. Calcd for C20H15Cl2N5S (428.34): C, 56.08; H, 3.53; N, 16.35; Found: C, 56.03; H, 3.47; N, 16.25%.
2-(2-(2,6-Dichlorobenzylidene)hydrazinyl)-4-(5-methyl-1-phenyl-1H-pyrazol-4-yl)thiazole (5l). Yield 74%; yellow microcystals; mp 249-251 oC (dioxane); IR (KBr): v 3434 (NH), 1604 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.73 (s, 3H, CH3), 7.47-7.9 (m, 9H, Ar-H and thiazole-H5), 8.21 (s, 1H, pyrazole-H3), 8.50 (s, 1H, CH=N), 10.57 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 13.3 (CH3), 124.1, 124.4, 127.3, 128.0, 128.7, 129.0, 129.9 130.3, 130.9, 132.1, 133.1, 133.8, 134.3, 135.3, 145.0, 156.4, 169.1; MS m/z (%): 428 (M+, 73). Anal. Calcd for C20H15Cl2N5S (428.34): C, 56.08; H, 3.53; N, 16.35; Found: C, 56.01; H, 3.40; N, 16.27%.
4-(5-Methyl-1-phenyl-1H-pyrazol-4-yl)-2-(2-(1-phenylethylidene)hydrazinyl)thiazole (5m). Yield 68%; brown microcystals; mp 162-164 oC (EtOH); IR (KBr): v 3417 (NH), 1602 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.58 (s, 3H, CH3), 2.77 (s, 3H, CH3), 7.47-7.98 (m, 11H, Ar-H and thiazole-H5), 8.51 (s, 1H, pyrazole-H3), 10.63 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 13.3, 15.9 (CH3), 110.7, 124.5, 125.0, 125.4, 125.8, 127.8, 128.1, 128.7, 129.0, 131.5, 136.5, 141.9, 164.1, 166.1, 168.4; MS m/z (%): 373 (M+, 47). Anal. Calcd for C21H19N5S (373.47): C, 67.53; H, 5.13; N, 18.75; Found: C, 67.46; H, 5.06; N, 18.59%.
4-(5-Methyl-1-phenyl-1H-pyrazol-4-yl)-2-(2-(1-(p-tolyl)ethylidene)hydrazinyl)thiazole (5n). Yield 68%; yellowish-brown microcystals; mp 175-177 oC (EtOH); IR (KBr): v 3439 (NH), 1600 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.28 (s, 3H, CH3), 2.54 (s, 3H, CH3), 2.74 (s, 3H, CH3), 6.91-7.88 (m, 10H, Ar-H and thiazole-H5), 8.53 (s, 1H, pyrazole-H3), 10.60 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 13.3, 15.9 (CH3), 110.7, 124.5, 125.0, 125.4, 125.8, 127.8, 128.1, 128.7, 129.0, 131.5, 136.5, 141.9, 164.1, 166.1, 168.4; MS m/z (%): 387 (M+, 30). Anal. Calcd for C22H21N5S (387.50): C, 68.19; H, 5.46; N, 18.07; Found: C, 68.08; H, 5.35; N, 18.01%.
2-(2-(1-(4-Methoxyphenyl)ethylidene)hydrazinyl)-4-(5-methyl-1-phenyl-1H-pyrazol-4-yl)thiazole (5o). Yield 65%; yellowish-brown microcystals; mp 154-156 oC (dioxane); IR (KBr): v 3431 (NH), 1597 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.34 (s, 3H, CH3), 2.73 (s, 3H, CH3), 3.76 (s, 3H, OCH3), 7.23-7.88 (m, 10H, Ar-H and thiazole-H5), 8.53 (s, 1H, pyrazole-H3), 10.12 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 12.3, 21.1, 44.2 (CH3), 110.8, 124.7, 125.4, 126.5, 128.3, 129.7, 131.2, 138.1, 139.6, 142.0, 143.1, 145.8, 153.1, 165.2, 168.1; MS m/z (%): 387 (M+, 30). Anal. Calcd for C22H21N5OS (403.50): C, 65.49; H, 5.25; N, 17.36; Found: C, 65.42; H, 5.19; N, 17.27%.
2-(2-(1-(4-Chlorophenyl)ethylidene)hydrazinyl)-4-(5-methyl-1-phenyl-1H-pyrazol-4-yl)thiazole
(5p). Yield 68%; yellow microcystals; mp 183-185 oC (dioxane); IR (KBr): v 3440 (NH), 1607 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.39 (s, 3H, CH3), 2.76 (s, 3H, CH3), 7.10-7.93 (m, 10H, Ar-H and thiazole-H5), 8.50 (s, 1H, pyrazole-H3), 10.52 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 12.9, 22.0 (CH3), 110.8, 121.4, 125.4, 126.0, 127.2, 129.2, 130.4, 134.6, 137.5, 141.3, 143.6, 141.5, 153.3, 164.2, 169.6; MS m/z (%): 407 (M+, 100). Anal. Calcd for C21H18ClN5S (407.92): C, 61.83; H, 4.45; N, 17.17; Found: C, 61.86; H, 4.39; N, 17.07%. 4-(5-Methyl-1-phenyl-1H-pyrazol-4-yl)-2-(2-(1-(4-nitrophenyl)ethylidene)hydrazinyl)thiazole(5q). Yield 62%; brown microcystals; mp 198-200 oC (dioxane); IR (KBr): v 3421 (NH), 1608 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.32 (s, 3H, CH3), 2.75 (s, 3H, CH3), 7.03-7.89 (m, 10H, Ar-H and thiazole-H5), 8.53 (s, 1H, pyrazole-H3), 10.50 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 13.3, 21.4 (CH3), 110.3, 124.7, 125.4, 125.9, 127.4, 129.2, 131.5, 134.6, 137.6, 142.5, 143.8, 149.4, 150.3, 163.9, 169.0; MS m/z (%): 418 (M+, 63). Anal. Calcd for C21H18N6O2S (418.47): C, 60.27; H, 4.34; N, 20.08; Found: C, 60.21; H, 4.21; N, 19.93%.
4-(1-(2-(4-(5-Methyl-1-phenyl-1H-pyrazol-4-yl)thiazol-2-yl)hydrazono)ethyl)phenol (5r). Yield 66%; brown microcystals; mp 198-200 oC (dioxane); IR (KBr): v 3414 (NH and OH), 1605 (C=N) cm-1; 1H NMR (DMSO-d6): δ 2.30 (s, 3H, CH3), 2.80 (s, 3H, CH3), 4.11 (br s, 1H, OH), 7.02-7.97 (m, 10H, Ar-H and thiazole-H5), 8.51 (s, 1H, pyrazole-H3), 10.38 (br s, 1H, NH); 13C NMR (DMSO-d6): δ 12.6, 26.8 (CH3), 111.2, 115.3, 125.2, 125.8, 129.8, 130.3, 130.9, 138.5, 142.3, 145.2, 162.5, 163.5, 164.1, 166.6, 168.0; MS m/z (%): 389 (M+, 31). Anal. Calcd for C21H19N5OS (389.47): C, 64.76; H, 4.92; N, 17.98; Found: C, 64.71; H, 4.82; N, 17.74%.

Pharmacological assay
Anti-hypertensive α-blocking activity 34–38
Noradrenalin and other sympathomimetic drugs increase vascular smooth muscle tone by stimulation of α-adrenergic receptors. Contractions can be antagonized by adrenergic α-receptor blocking agents, such as phentolamine. Drugs can be tested for their capacity of reducing vascular smooth muscle contractions induced by the adrenergic receptor-activating agent noradrenaline. Moreover, effects of peptides, such as bradykinin, can be tested with strips of aorta or pulmonary artery.
Procedure
As donor animals, white guinea pigs of either sex weighing about 400 g are used. The vessels to be tested are the thoracic aorta or the arteria pulmonalis. The animals are sacrificed by stunning and exsanguinations. The pulmonary artery is quickly removed and cut into helical strips of 1–2 mm width and 15–20 mm length. The strips are mounted in an organ bath with a preload of 1 g. Krebs-Henseleit buffer solution containing 11.5 M glucose is maintained at 37 oC and oxygenated with 95% O2, 5% CO2. Isotonic or isometric registration is performed. Changes in length are recorded isotonically using a lever transducer, isometric force is measured with a force transducer.
Experimental course
Following an equilibration period of 60 min, contractions are induced by repeated administration of (–)-noradrenalin HCl in concentrations of 2 x 10-6 M for testing the contractions of the pulmonary artery and in concentrations of 2 x 10-8 M for testing the contractions of the aorta. After obtaining a state plateau of identically sized contractions, cumulative doses of the test compound are added into the organ bath. Concentrations are given when the response of the previous dose has reached a plateau.
Controls at the end of the experiment
If a compound does not show vaso relating activity at any dose, the sensitivity of the preparation is tested by adding phentolamine (1 x 10-7 M). If a compound shows vaso relating activity, increasing the noradrenalin concentration tests the reversibility of the relaxation.
Evaluation
The contractile force is determined before and after drug administration. Percent inhibition of spas Mogen-induced contraction by test drug is calculated as compared to the maximal contraction with a spas Mogen alone (= 100%). IC50 values are determined from the individual dose response curves. IC50 is defined as the dose of drug leading to a 50% relaxation of noradrenaline induced contraction.
The small values of IC50 for the selected compounds indicate that, for more anticancer effect higher concentrations can be used.

References

1. P. Karegoudar, M. S. Karthikeyan, D. J. Prasad, M. Mahalinga, B. S. Holla, and N. S. Kumari, Eur. J. Med. Chem., 2008, 43, 261. CrossRef
2. A. Cukurovali, I. Yilmaz, S. Gur, and C. Kazaz, Eur. J. Med. Chem., 2006, 41, 201. CrossRef
3. B. F. Abdel-Wahab, H. A. Abdel-Aziz, and E. M. Ahmed, Eur. J. Med. Chem., 2009, 44, 2632. CrossRef
4. M. H. Shih and K. F. Ying, Bioorg. Med. Chem., 2004, 12, 4633. CrossRef
5. M. Shiradkar, G. V. S. Kumar, V. Dasari, S. Tatikonda, K. C. Akula, and R. Shah, Eur. J. Med. Chem., 2007, 42, 807. CrossRef
6. K. M. Amin, A. D. E. Rahman, and Y. A. Al-Eryani, Bioorg. Med. Chem., 2008, 16, 5377. CrossRef
7. S. M. Gomha, S. M. Riyadh, I. M. Abbas, and M. A. Bauomi, Heterocycles, 2013, 87, 341. CrossRef
8. K. M. Dawood, H. A. Gawad, E. A. Rageb, M. Ellithey, and H. A. Mohamed, Bioorg. Med. Chem., 2006, 14, 3672. CrossRef
9. J. S. Carter, S. Kramer, J. J. Talley, T. Penning, P. Collins, M. J. Graneto, K. Seibert, C. Koboldt, J. Masferrer, and B. Zweifel, Bioorg. Med. Chem. Lett., 1999, 9, 1171. CrossRef
10. L. P. Zhu, D. Y. Ye, and Y. Tang, J. Mol. Model, 2007, 13, 121. CrossRef
11. R. F. Clark, T. Zhang, X. Wang, R. Wang, X. Zhang, H. S. Camp, B. A. Beutel, H. L. Sham, and Y. J. Gu, Bioorg. Med. Chem. Lett., 2007, 17, 1961. CrossRef
12. A. M. Kamal El-Dean, A. M. Elkhawaga, S. M. Radwan, and M. M. Ahmed, Phosphorous, Sulfur Silicon Relat. Elem., 2009, 184, 2034. CrossRef
13. M. Ge, E. Cline, and L. Yang, Tetrahedron Lett., 2006, 47, 5797. CrossRef
14. H. A. El-Sherief, A. M. Mahmoud, and A. A. Ismaiel, J. Chem. Res. (S), 1997, 9, 322. CrossRef
15. A. A. Aly, Phosphorous, Sulfur Silicon Relat. Elem., 2006, 181, 2395. CrossRef
16. A. E. Rashad, M. I. Hegab, R. E. Abdel-Megeid, N. F. Fathalla, and M. E. Abdel-Megied, Eur. J. Med. Chem., 2009, 44, 3285. CrossRef
17. G. Saravanan, V. Alagarsamy, C. R. Prakash, P. Kumar, Dinesh and T. P. Selvam, Asian J. Res. Pharm. Sci., 2011, 1, 134.
18. S. M. Gomha and H. A. Abdel-Aziz, Bull. Korean Chem. Soc., 2012, 33, 2985. CrossRef
19. S. M. Gomha, T. M. A. Eldebss, M. M. Abdulla, and A. S. Mayhoub, Eur. J. Med. Chem., 2014, 82, 472. CrossRef
20. S. M. Gomha, Monatsh. Chem., 2009, 140, 213. CrossRef
21. S. M. Gomha and H. A. Abdel-Aziz, J. Serb. Chem. Soc., 2013, 78, 1119.
22. S. M. Gomha, T. A. Salah, and A. O. Abdelhamid, Monatsh. Chem., 2015, 146, 149. CrossRef
23. S. M. Gomha and K. M. Dawood, J. Chem. Res., 2014, 38, 515. CrossRef
24. S. M. Gomha, M. M. Abdulla, and S. M. Abou-Seri, Eur. J. Med. Chem., 2015, 92, 459. CrossRef
25. S. M. Gomha, K. D. Khalil, A. M. El-Zanate, and S. M. Riyadh, Heterocycles, 2013, 87, 1109. CrossRef
26. S. M. Gomha and H. A. Abdel-Aziz, Heterocycles, 2012, 85, 2291. CrossRef
27. C. J. Goddard, J. Heterocycl. Chem., 1991, 28, 1607. CrossRef
28. A. Hantzsch and H. J. Weber, Ber. Dtsch. Chem. Ges., 1987, 20, 3118. CrossRef
29. S. A. Mohammad, L. Lijun, L. Yong-Eok, and L. Dong-Ung, Chem. Pharm. Bull., 2011, 59, 568. CrossRef
30. P. Makam, P. K. Thakur, and T. Kannan. Eur. J. Pharm. Sci., 2014, 52, 138. CrossRef
31. F. Chimenti, B. Bizzarri, A. Bolasco, D. Secci, P. Chimenti, A. Granese, S. Carradori, M. D’Ascenzio, M. M. Scaltrito, and F. Sisto, J. Heterocycl. Chem., 2010, 47, 1269. CrossRef
32. R. R. Saravanan, S. Seshadri, S. R. Gunasekaran, R. Mendoza-Meroño, and S. Garcia-Granda, Spectrochim. Acta, Part A Mol. Biomol. Spect., 2015, 139, 321. CrossRef
33. A. Arshad, H. Osman, M. C. Bagley, C. K. Lam, S. Mohamad, and A. S. M. Zahariluddin, Eur. J. Med. Chem., 2011, 46, 3788. CrossRef
34. R. Rajagopalan, A. V. Ghate, P. Subbarayan, W. Linz, and B. A. Schoelkens, Arzneim. Forsch/Drug Res., 1993, 43, 313.
35. F. J. Hock, K. Wirth, U. Albus, W. Linz, H. J. Gerhards, G. Wiemer, S. Henke, G. Breipohl, W. König, J. Knolle, and B. A. Schölkens, Br. J. Pharmacol., 1991, 102, 769. CrossRef
36. C. A. Winter, E. A. Risley, and G. W. Nuss, J. Pharmacol Exp. Ther., 1963, 141, 369.
37. K. U. Weithmann, S. Jeske, and V. Schlotte, Agent Actions, 1994, 41, 164. CrossRef
38. F. Herrmann, A. Lindemann, J. Gamss, and R. Mertelsmann, Eur. J. Immunol., 1999, 20, 2513. CrossRef