• Nu S-Au Găsit Rezultate

(1)DOPAMINE D2 RECEPTOR ANTAGONIST ACTIVITY AND MOLECULAR MODELING OF CERTAIN NEW CYCLOHEXANE DERIVED ARYLCARBOXAMIDES STRUCTURALLY RELATED TO METOCLOPRAMIDE MOHAMED N

N/A
N/A
Protected

Academic year: 2022

Share "(1)DOPAMINE D2 RECEPTOR ANTAGONIST ACTIVITY AND MOLECULAR MODELING OF CERTAIN NEW CYCLOHEXANE DERIVED ARYLCARBOXAMIDES STRUCTURALLY RELATED TO METOCLOPRAMIDE MOHAMED N"

Copied!
17
0
0

Text complet

(1)

DOPAMINE D2 RECEPTOR ANTAGONIST ACTIVITY AND MOLECULAR MODELING OF CERTAIN NEW CYCLOHEXANE DERIVED

ARYLCARBOXAMIDES STRUCTURALLY RELATED TO METOCLOPRAMIDE

MOHAMED N. ABOUL-ENEINa*, AIDA A. EL-AZZOUNYa, MOHAMED I.

ATTIAa,b, YOUSREYA A. MAKLADc, MOHAMED ABD EL-HAMID ISMAILd, NASSER M.S. ISMAILd, WALAA H.A. ABDEL-HAMIDe

aMedicinal and Pharmaceutical Chemistry Department (Medicinal Chemistry group), Pharmaceutical and Drug Industries Research Division, National Research Centre, 12622, Dokki, Giza, Egypt

bDepartment of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia

cMedicinal and Pharmaceutical Chemistry Department (Pharmacology group), Pharmaceutical and Drug Industries Research Division, National Research Centre, 12622, Dokki, Giza, Egypt

dPharmaceutical Chemistry Department, Faculty of Pharmacy, Ain Shams University, Cairo, Egypt

eDepartment of Pharmaceutical Chemistry, Faculty of Pharmacy, Misr University for Science & Technology, 6th of October City, Egypt

A series of certain new N-{[1-(4-aralkyl/ethylpiperazine-1- yl)cyclohexyl]methyl}arylcarbox- amides 1a-t structurally related to the antiemetic Metoclopramide (I) was synthesized starting from cyclohexanone, N-aralkyl and/or ethylpiperazine, and KCN in the presence of conc. HCl to furnish the carbonitrile derivatives 3a-d. Subsequent reduction of 3a-d produced the respective amines 4a-d which were elaborated to the desired arylcarboxamides 1a-t through amide coupling reactions. The target compounds 1a-t were evaluated for their dopamine D2 receptor antagonistic activity in vivo by measuring their ability to inhibit apomorphine-induced chewing “Zwansgnagen” in rats. Compound 1h (ED50 = 5.94 µmol/kg) is the most active congener being nearly 2-fold more potent than the previously reported cyclohexane-based dopamine D2 receptor antagonist II (ED50 = 11.66 µmol/kg). Molecular simulation study including fitting to dopamine D2 receptor antagonists 3D-pharmacophore model using Discovery Studio 2.5 programs showed high-fit values. The experimental dopamine D2 receptor antagonistic activity of compounds 1a-t was consistent with the molecular modeling study.

(Received February 6, 2012; Accepted April 7, 2012)

Keywords: Metoclopramide analogues; Arylcarboxamides; 1,1-Disubstituted cyclohexanes; Antiemitcs; D2-Receptor antagonists.

1. Introduction

Metoclopramide (I), the parent arylcarboxamide in the orthopramides family, is clinically used as a gastroprokinetic agent (stimulant of upper gastrointestinal motility) as well as an antiemetic.1 This gastroprokinetic activity is ascribed to the release of acetylcholine upon stimulation of 5-HT4 receptors whereas the antiemetic activity is attributed to the antagonistic

*Corresponding author: [email protected]

(2)

activity at both 5-HT3 serotoninergic and D2 dopaminergic receptors in the chemoreceptor trigger zone (CTZ) in the central nervous system (CNS). Orthopramides possess three common structural elements required for binding to the receptor site: an aromatic moiety, carbonyl function or its bioisosteric group, and a basic nitrogen atom.2-4 Amongst benzamide derivatives, the cyclohexane derivative II was originally reported as Metoclopramide analogue.5 The weak affinity and lack of selectivity of Metoclopramide for dopaminergic and serotoninergic receptors can be explained by the large number of permissible conformers due to the flexibility of its amino chain.6 Accordingly, the intense interest for studying certain molecular modifications of Metoclopramide implies;

change in the substituents of the aromatic ring, structural variations in the amine moiety to obtain a conformationally restricted amino side chain, and increasing the lipophilicity via inclusion of the vicinal carbon atom of the basic nitrogen atom into a cyclohexane ring. This concept will be addressed through the synthesis and biological evaluation of new cyclohexane derived arylcarboxamides 1a-t as potential dopamine D2 receptor antagonists structurally related to Metoclopramide (I).

Fig. 1. Structures of Metoclopramide (I), compound II, and target compounds 1a-t.

2. Experimental

2.1. Chemistry

All melting points were determined using Electrothermal Capillary melting point apparatus and are uncorrected. Infrared (IR) spectra were recorded as thin film (for oils) in NaCl discs or as KBr pellets (for solids) with JASCO FT/IR-6100 spectrometer and values are represented in cm–1. 1H NMR (500 MHz) and 13C NMR (125 MHz) spectra were carried out on Jeol ECA 500 MHz spectrometer using TMS as internal standard and chemical shift values were recorded in ppm on δ scale. The 1H NMR data were represented as follows: chemical shifts, multiplicity (s. singlet, d. doublet, dd. doublet of doublet, t. triplet, m. multiplet, br. broad), number of protons, and type of protons. The 13C NMR data were represented as chemical shifts and type of carbons. Mass spectral data were obtained with electron impact (EI) ionization technique at 70 eV and chemical ionization (CI/CH4) from a Finnigan Mat SSQ-7000 Spectrometer. Elemental analyses were carried out in Microanalytical Unit, National Research Centre and Cairo University. Silica gel TLC (thin layer chromatography) cards from Merck (silica gel precoated aluminum cards with fluorescent indicator at 254 nm) were used for thin layer chromatography. Visualization was performed by illumination with UV light source (254 nm).

Column chromatography was carried out on silica gel 60 (0.063-0.200 mm) obtained from Merck.

2.1.1. General procedure for the synthesis of N-aralkylpiperazines 2b-d

Piperazine dihydrochloride monohydrate (3.54 g, 20.0 mmol) was added to a stirred warmed (65°C) solution of piperazine hexahydrate (3.89 g, 20.0 mmol) in absolute ethanol (9.87 mL). Appropriate aralkyl chloride (20.0 mmol) was added to the reaction mixture dropwise during 5 min with vigorous stirring. Separation of white needles was observed immediately and stirring was further continued for 25 min at 65 °C, then cooling at 0 °C for 30 min. The precipitated piperzine dihydrochloride was filtered off and washed with cold absolute ethanol (10 mL). The combined filtrate and washings were dried (Na2SO4), filtered and evaporated under reduced pressure to afford the respective piperazine derivatives 2b-d as monohydrochloride salts in 66- 95% yields.

O NH

N

N R N N

H H2N

O

C2H5

C2H5

OMe Cl

H2N

O

OMe NH

N C2H5 C2H5 Cl

Metoclopramide (I) 1a-t

R3

R2

R1

II

R4

(3)

2.1.1.1. 1-Benzylpiperazine (2b)7

White solid, m.p. 164 oC of monohydrochloride salt, yield 4.1g (95%).

2.1.1.2. 1-(3,4,5-Trimethoxybenzyl)piperazine (2c)

Buff solid, m.p. 230 oC of dihydrochloride salt(Lit.8 210-211), yield 4.8 g (80%).

2.1.1.3. 1-Benzhydrylpiperazine (2d)

Yellowish white solid, m.p. 70-72 oC of base (Lit. 9 70-72), yield 3.8 g (66%).

2.1.2.General procedure for the Synthesis of [1-(4-aralkyl/ethylpiperazin-1-yl)cyclo- hexyl]acetonitriles 3a-d

Ethylpiperazine 2a and/or the appropriate N-aralkylpiperazine 2b-d as monohydrochloride (100 mmol) were mixed carefully with conc. HCl (0.96 mL, 26.0 mmol) and pH of the reaction mixture was adjusted to 3-4. Cyclohexanone (0.81 mL, 100.0 mmol) was added to the resulting solution followed by addition of potassium cyanide (0.65 g, 100.0 mmol) in H2O (1.72 mL). The reaction mixture was stirred for 2 h at room temperature then was allowed to stand overnight. The reaction mixture was basified (10% NaOH) and the formed precipitate was filtered off and washed with water (10 mL) to afford the corresponding carbonitrile derivatives 3a-d in 50-82% yields.

The crude 3a-d were used in the next step without further purification. Analytical samples of 3a, 3c, and 3d were obtained after recrystallisation from isopropanol.

2.1.2.1. [1-(4-Ethylpiperazin-1-yl)cyclohexyl]acetonitrile (3a)

Yellow solid, m.p. 76-78 oC, yield 5.4 g (50%). IR (KBr, cm-1) exhibited bands at 2217 (CN), 3742, 643. 1H NMR (CDCl3) δ: 1.08-1.84 (m, 15H, 5 x CH2) cyclohexyl, CH2-CH3, CH2- CH3), 2.09-2.86 (m, 8H, (4 x CH2) piperazine). 13C NMR (CDCl3) δ: 11.8 (CH3), 21.9, 24.7, 33.6, 46.2, 51.8, 52.7, 60.5 (6 x CH2), Cq), 116.6 (CN). MS (EI) m/z (%): 221.2 (13.7, M+), 114 (25), 109.1 (10.3), 71 (100). Anal. Calcd. for C14H25N3: C, 71.44; H, 10.71; N, 17.85. Found: C, 71.64;

H, 10.53; N, 17.75.

2.1.2.2. [1-(4-Benzylpiperazin-1-yl)cyclohexyl]acetonitrile (3b)10 White solid, m.p. 94 oC, yield 9.2 g (81.4%).

2.1.2.3. {1-[4-(3,4,5-Trimethoxybenzyl)piperazin-1-yl]cyclohexyl}acetonitrile (3c) Yellowish white solid, m.p. 95 oC, yield 11 g (75%). IR (KBr, cm-1) exhibited bands at 2221(CN), 2931, 2826, 1004.1H NMR (CDCl3) δ: 1.49-1.73 (m, 10H, (5 x CH2) cyclohexyl), 2.46- 2.66 (m, 8H, (4 x CH2) piperazine), 3.50 (s, 2H, CH2-C6H5), 3.81 (s, 3H, OCH3) , 3.82 (s, 6H, 2 OCH3), 6.54 (s, 2H, Har.).13C NMR (CDCl3) δ: 22.0, 22.8, 24.9, 33.9, 46.6, 46.7, 60.8 (6 x CH2), Cq), 53.2, 56.1 (OCH3), 105.7 (CHar.) 122.6 (CN), 129.2, 135.9, 153.1 (Car.). MS (EI) m/z (%): 373 (8.9, M+), 265 (21), 182.2 (38), 181 (100). Anal. Calcd. for C22H33N3O3: C, 68.19; H, 8.58; N, 10.84. Found: C, 67.94; H, 8.82; N, 10.66.

2.1.2.4. [1-(4-Benzhydrylpiperazin-1-yl)cyclohexyl]acetonitrile (3d)

Yellow solid, m.p. 134-136 oC, yield 11.7 g (82%). IR (KBr, cm-1) exhibited bands at 2096 (CN), 3425, 1443, 703. 1H NMR (CDCl3) δ: 1.62-2.14 (m, 10H, (5 x CH2) cyclohexyl), 2.25-2.33 (m, 8H, (4 x CH2), piperazine), 4.20 (s, 1H, CH), 7.23-7.42 (m, 10H, Har.). 13C NMR (CDCl3) δ:

22.2, 25.0, 27.0, 46.9, 52.0, 53.4 (5 x CH2), Cq), 126.9 (CN), 128.0, 128.09, 128.5 (CHar.), 142.8 (Car.). MS (EI) m/z (%): 354 (0.2, M+), 167 (100), 152 (26.5). Anal. Calcd. for C25H31N3: C, 80.39;

H, 8.37; N, 11.25. Found: C, 80.22; H, 8.64; N, 11.46.

2.1.3. General procedure for the synthesis of N-{[1-(4-aralkyl/ethylpiperazin-1- yl)cyclohexyl]- methyl}arylcarboxamides 1a-l

A solution of anhydrous aluminum chloride(2.1 g, 16.0 mmol) in dry THF (5 mL) was added dropwise to a stirred suspension of LiAlH4 (1.9 g, 49.0 mmol) in dry THF (100 mL) at 0 °C.

A solution of the appropriate carbonitrile 3a-d (11.0 mmol) in dry THF (15 mL) was added dropwise to the cooled (0 °C) reaction mixture and stirring was continued for 24 h at room temperature. The reaction was quenched by a slow addition of saturated sodium sulfate solution at 0-5 °C. The formed precipitate was filtered off and washed with THF (10 mL) and ethyl acetate (25 mL). The combined filtrate and washings were dried (Na2SO4), filtered and evaporated under reduced pressure to afford 1-[1-(4-aralkyl/ethylpiperazin-1-yl)cyclohexyl] methanamines 4a-d in 75-85% yields as pale yellow viscous oils which were solidified upon storage. The crude 4a-d were pure enough to be used in the next step without further purification. A solution of the appropriate acyl chloride 5a-c (4.86 mmol) in benzene (20 mL) was added dropwise to a stirred solution of 4a-d (4.42 mmol) and triethylamine (0.04 mL) in benzene (60 mL). The reaction

(4)

mixture was refluxed for 5 h, cooled to room temperature, the formed precipitate was filtered off and washed with benzene (10 mL). The combined filtrate and washings were dried (Na2SO4), filtered and evaporated under reduced pressure to afford the respective arylcarboxamides 1a-l as brown viscous oils. The obtained amides were purified through their dihydrochloride salts which were recrystallised from isopropanol to furnish pure 1a-l.

2.1.3.1. 1-[1-(4-Ethylpiperazin-1-yl)cyclohexyl]methanamine (4a)

Pale yellow viscous oil, yield 2.1 g (87.5%). IR (KBr, cm-1) exhibited bands at 3745, 3677 (NH2), 1458, 612.1H NMR (DMSO-d6) δ: 1.18 (t, 3H, J = 6.9, CH3), 1.21-1.58 (m, 10H, (5 x CH2) cyclohexyl), 3.05 (s, 4H, CH2-CH3 and CH2-NH2), 3.11-3.46 (m, 8H, (4 x CH2) piperazine) 8.09 (br. s, 2H, NH2).13C NMR (DMSO-d6) δ: 9.2 (CH3), 21.9, 26.3, 28.5, 42.3, 45.1, 47.8, 50.9, 50.0 (7 x CH2), Cq). MS (EI) m/z (%): 225.2(0.9, M+), 195.2 (100), 113.1 (6), 83.1 (10.1).

2.1.3.2. 1-[1-(4-Benzylpiperazin-1-yl)cyclohexyl]methanamine (4b)

Pale yellow viscous oil, yield 2.6 g (86.6%). IR (KBr, cm-1) exhibited bands at 3061, 3027 (NH2), 14531, 741. 1H NMR (CDCl3) δ: 1.19-1.93 (m, 10H, (5 x CH2) cyclohexyl), 2.06-2.08 (m, 4H, (2 x CH2) piperazine), 2.47-2.93 (m, 6H, (2 x CH2) piperazine, CH2-C6H5), 3.47 (d, 2H, J = 5 Hz, CH2-NH) 7.26-7.27 (m, 5H, Har.). 13C NMR (CDCl3) δ: 26.2, 28.4, 29.8, 37.7, 52.4, 52.7, 56.1, 66.7 (7 x CH2), Cq), 123.0, 131.2, 132.2, (CHar.), 133.3 (Car.).

2.1.3.3. 1-{1-[4-(3,4,5-Trimethoxybenzyl)piperazin-1-yl]cyclohexylmethanamine (4c) Pale yellow viscous oil, yield 3.8 g (91%). IR (KBr, cm-1) exhibited bands at 3060, 3029 (NH2), 750. 1H NMR (CDCl3) δ: 1.16-1.43 (m, 10H, (5 x CH2) cyclohexyl), 2.33-2.74 (m, 8H, (4 x CH2) piperazine), 3.52 (s, 2H, CH2-NH2), 3.73 (s, 2H, CH2-C6H5), 3.76 (s, 3H, OCH3), 3.76 (s, 2H, 2 OCH3), 6.48 (s, 2H, Har.). 13C NMR (CDCl3) δ: 25.8, 26.2, 29.4, 29.5, 35.6, 45.7, 53.4, 54.5 (7 x CH2), Cq), 58.0, 60.8 (OCH3), 106.0 (CHar.), 133.8, 136.8, 153.0 (Car.). MS (EI) m/z (%): 378.4 (1.8, M+ +1), 167 (100), 181 (99), 196 (7).

2.1.3.4. 1-[1-(4-Benzhydrylpiperazin-1-yl)cyclohexyl]methanamine (4d)

Pale viscous oil, yield 2.7 g (67.5%). IR (KBr, cm-1) exhibited bands at 3060, 3029 (NH2).

1H NMR (CDCl3) δ: 1.31-1.36 (m, 10H, (5 x CH2) cyclohexyl), 2.08 (br.s, 4H, and (2x CH2) piperazine), 3.57-3.65 (m, 6H, CH2-NH2, (2x CH2) piperazine), 5.50 (s, 1H, CH-(C6H5)2), 7.37-7.45 (m, 10H, Har.). 13C NMR (CDCl3) δ: 24.3, 25.6, 30.1, 35.6, 48.8, 51.8, 64.6 (6 x CH2), Cq), 127.3, 127.5, 128.6 (CHar.), 142.7 (Car.).MS (EI) m/z (%): 363.3 (0.23, M+), 333.2 (100), 126.2 (81), 112.1 (47.99).

2.1.3.5. N-{[1-(4-Ethylpiperazin-1-yl)cyclohexyl]methyl}benzamide (1a)

White solid, m.p. 218 °C (dihydrochloride salt), yield 0.58 g (39.9%). IR (KBr, cm-1) exhibited bands at 3064 (NH), 2813, 1644 (C=O). 1H NMR (CDCl3) δ: 1.04 (t, 3H, J = 6.9 Hz, CH2-CH3), 1.39-1.59 (m, 10H, (5 x CH2) cyclohexyl), 2.37 (q, 2H, J = 6.9 Hz, CH2-CH3), 2.40- 2.67 (m, 8H, (4 x CH2) piperazine), 3.49 (d, 2H, J = 9.5 Hz, CH2-NH), 7.39-7.74 (m, 5H, Har.), 7.04 (br. s, 1H, NH). 13C NMR (CDCl3) δ: 12.0 (CH3-CH2), 22.31, 25.98, 29.56, 40.7, 44.35, 52.36, 54.38, 58.05 (7 x CH2), Cq), 126.8, 128.6, 131.3 (CHar.), 134.8 (Car.), 167.1 (C=O). MS (EI) m/z (%): 329.2 (0.05, M+), 195.1 (100), 105.05 (13.74), 77.05 (9.87).

2.1.3.6. N-{[1-(4-Ethylpiperazin-1-yl)cyclohexyl]methyl}-4-chlorobenzamide (1b) White solid, m.p. 230 °C (dihydrochloride salt), yield 0.48 g (30%). IR (KBr, cm-1) exhibited bands at 3254 (NH), 2930, 1641 (C=O). 1H NMR (CDCl3) δ: 1.08 (t, 3H, J = 6.9 Hz, - CH2-CH3), 1.41-1.61 (m, 10H, 5 x CH2) cyclohexyl), 1.88 (br. s, 4H, (2 x CH2) piperazine), 2.38 (q, 2H, J = 6.9 Hz, CH2-CH3), 2.69 (br. s, 4H, (2 x CH2) piperazine), 3.51 (d, 2H, J = 5 Hz, CH2- NH) 7.06 (br. s,1H, NH), 7.40 (d, 2H, J = 10 Hz, Har.), 7.70 (d, 2H, J = 10 Hz, Har.). 13C NMR (CDCl3) δ: 12.0 (CH2-CH3), 22.4, 25.9, 29.6, 40.8, 44.3, 52.4, 54.4, 58.1 (7 x CH2), Cq), 128.3, 128.9 (CHar.), 133.2, 137.5 (Car.), 166.2 (C=O). MS (EI) m/z (%): 364.2 (0.04, M+ + 1), 195.2 (100), 111.05 (10.59), 84.1 (21.52). Anal. Calcd. for C20H30ClN3O.2HCl: C, 54.99; H, 7.38; N, 9.62. Found: C, 54.57; H, 7.76; N, 9.65.

2.1.3.7. N-{[1-(4-Ethylpiperazin-1-yl)cyclohexyl]methyl}-4-nitrobenzamide (1c) Buff solid, m.p. 210 °C (dihydrochloride salt), yield 0.49 g (30%). IR (KBr, cm-1) exhibited bands at 3393 (NH), 2696, 1650 (C=O). 1H NMR (CDCl3) δ: 1.07 (t, 3H, J = 6.9, CH2- CH3), 1.40-1.96 (m, 10H, (5 x CH2) cyclohexyl), 2.38 (q, 2H, J = 6.9, CH2-CH3), 2.68 (br. s, 8H, (4 x CH2) piperazine), 7.22 (br. s, 1H, NH), 7.91 (d, 2H, J = 7.7 Hz, Har.), 8.27 (d, 2H, J = 7.7 Hz, Har.).13C NMR (CDCl3) δ: 12.0 (CH3-CH2), 22.3, 25.8, 29.5, 44.3, 48.9, 52.3, 54.5, 58.0 (7 x CH2),

(5)

Cq), 123.9, 128.0 (CHar.), 140.4, 149.5 (Car.), 165.0 (C=O). MS (EI) m/z (%): 374.2 (0.02, M+), 195.2 (100), 104.05 (4.59), 84.1 (14.58). Anal. Calcd. for C20H30N4O3.2HCl: C, 53.69; H, 7.21; N, 12.52. Found: C, 54.11; H, 7.59; N, 12.43.

2.1.3.8. N-{[1-(4-Benzylpiperazin-1-yl)cyclohexyl]methyl}benzamide (1d)

Buff solid, m.p. 224 °C (dihydrochloride salt), yield 0.64 g (37.1%). IR (KBr, cm-1) exhibited bands at 3265 (NH), 2447, 1673 (C=O), 719. 1H NMR (CDCL3) δ: 1.14-1.62 (m, 10H, (5 x CH2) cyclohexyl), 2.49 (br. s, 4H, (2 x CH2) piperazine), 2.67 (br. s, 4H, (2 x CH2) piperazine), 3.50 (s, 2H, CH2-C6H5), 3.53 (d, 2H, J = 5 Hz, CH2-NH), 7.23-7.51 (m, 10H, Har.), 7.6 (s, 1H, NH). 13C NMR (CDCl3) δ: 21.4, 25.9, 28.9, 33.9, 44.2, 48.9, 54.6, 63.2 (7 x CH2), Cq), 126.9, 128.2, 128.3, 129.1, (CHar., Car.), 167.1 (C=O). MS (EI) m/z (%): 391.9 (0.52, M+), 168 (63), 167 (43), 114 (100). Anal. Calcd. for C25H33N3O.2HCl: C, 64.65; H, 7.60; N, 9.05. Found: C, 64.35; H, 7.45; N, 8.98.

2.1.3.9. N-{[1-(4-Benzylpiperazin-1-yl)cyclohexyl]methyl}-4-chlorobenzamide (1e) White solid, m.p. 226 °C (dihydrochloride salt), yield 1.27 g (67.8%). IR (KBr, cm-1) exhibited bands at 3296 (NH), 2872, 929, 1664 (C=O). 1H NMR (CDCl3 δ: 1.39-1.60 (m, 10H, (5 x CH2) cyclohexyl), 2.46 (br. s, 4H, (2 x CH2) piperazine), 2.67 (br. s, 4H, (2 x CH2) piperazine), 3.51 (s, 4H, CH2-NH, CH2-C6H5), 7.07 (s, 1H, NH), 7.25-7.29 (m, 5H, Har.), 7.4 (d, 2H, J = 8.4 Hz, Har.), 7.7 (d, 2H, J = 8.4 Hz, Har.). 13C NMR (CDCl3) δ: 22.3, 25.9, 29.5, 44.4, 53.1, 54.6, 58.0, 63.14 (7 x CH2), Cq), 127.0, 127.2, 128.2, 128.8, 129.3 (CHar.), 133.2, 137.5, 137.8 (Car.) , 166.0 (C=O). MS (EI) m/z (%): 423 (4.3, M+-2), 257.7 (100), 111 (25), 91 (43.3). Anal. Calcd. for C25H32ClN4O.2HCl: C, 60.18; H, 6.87; N, 8.42. Found: C, 60.49; H, 6.65; N, 8.45.

2.1.3.10. N-{[1-(4-Benzylpiperazin-1-yl )cyclohexyl]methyl}-4-nitrobenzamide (1f) White solid, m.p. 245 °C (dihydrochloride salt), yield 0.51 g (22.6%). IR (KBr, cm-1) exhibited bands at 3250 (NH), 2948, 751, 1658 (C=O). 1H NMR (CDCl3) δ: 1.22-1.60 (m, 10H, (5 x CH2) cyclohexyl), 2.00 (s, 2H,CH2 piperazine), 2.45 (br. s, 2H, CH2 piperazine) 2.66 (s, 4H, (2 x CH2) piperazine), 3.52 (d, 2H, J = 4 Hz, CH2-NH), 7.26 (s, 6H, Har., NH), 7.9 (d, 2H, J = 8 Hz, Har.), 8.26 (d, 2H, J = 8 Hz, Har.). 13C NMR (CDCl3) δ: 25.9, 28.7, 29.6, 40.8, 44.3, 54.5, 58.0, 60.4 (7 x CH2), Cq), 123.0, 128.0, 128.3, 129.3, 137.5, (CHar.), 140.4 ,149.5, 165.0 (Car.), 171.1 (C=O). MS (EI) m/z (%): 434 (5, M+-2), 141.8 (39), 139.9 (46), 91 (100). Anal. Calcd. for C25H32N4O.2HCl: C, 58.94; H, 6.73; N, 11.00. Found: C, 58.67; H, 7.01; N, 10.85.

2.1.3.11. N-({1-[4-(3,4,5-Trimethoxybenzyl)piperazin-1- yl]cyclohexyl}methyl)benzamide (1g)

White solid, m.p. 200 °C (dihydrochloride salt), yield 1.62 g (76.1%). IR (KBr, cm-1) exhibited bands at 3297 (NH), 2498, 1668 (C=O), 754. 1H NMR (CDCl3) δ: 1.16-1.93 (m, 10H, (5 x CH2) cyclohexyl), 2.65-2.79 (br. s, 8H, (4 x CH2) piperazine), 3.39 (d, 2H, J = 5 Hz, CH2-NH), 3.48 (s, 2H, CH2-C6H5), 3.79 (s, 3H, OCH3), 3.81 (s, 6H, 2OCH3), 6.50 (s, 2H, Har.), 7.35-7.73 (m, 5H, Har.), 7.97 (s, 1H, J = 8 Hz, NH). 13C NMR (CDCl3) δ: 22.2, 25.6, 29.6, 40.8, 44.3, 53.0, 54.6, 60.8 (7 x CH2, Cq), 56.13, 58.0 (OCH3), 105.7, 127.0, 128.4, 129.5 (CHar.), 132.9, 133.0, 133.8, 153.1 (Car.), 167.1 (C=O). MS (EI) m/z (%): 482 (0.16, M+), 209 (61), 104 (100), 76 (35). Anal.

Calcd. for C28H39N3O4.2HCl: C, 60.64; H, 7.45; N, 7.58. Found: C, 60.93; H, 7.58; N, 7.47.

2.1.3.12. N-({1-[4-(3,4,5-Trimethoxybenzyl)piperazin-1-yl]cyclohexyl}methyl)-4- chloro- benzamide (1h)

White solid, m.p. 200 °C (dihydrochloride salt), yield 0.85 g (37.1%). IR (KBr, cm-1) exhibited bands at 3027 (NH), 2809, 1627 (C=O), 750. 1H NMR (CDCl3) δ: 1.10-1.66 (m, 10H, (5 x CH2) cyclohexyl), 2.04-2.58 (m, 8H, (4 x CH2) piperazine), 3.34 (d, 2H, J = 10 Hz, CH2-NH), 3.68 (s, 3H, OCH3), 3.72 (s, 8H, 2OCH3, CH2-C6H5), 6.46 (s, 2H, Har.), 7.06 (br.s, 1H, NH), 7.29 (d, 2H, J = 5 Hz, Har.), 7.62 (d, 2H, J = 5 Hz, Har.). 13C NMR (CDCl3) δ: 22.1, 25.8, 28.8, 30.3, 44.2, 48.8, 53.3, 60.8 (7 x CH2, Cq), 56.4, 58.0 (OCH3), 105.8, 128.6, 128.7 (CHar.), 133.4, 134.1, 135.6, 136.9, 153.1 (Car.), 169.1 (C=O). MS (EI) m/z (%): 518 (0.34, M+ + 2), 348 (29.9), 181 (100), 139 (26.5). Anal. Calcd. for C28H38ClN3O4.2HCl: C, 57.10; H, 6.85; N, 7.13. Found: C, 56.88; H, 7.08; N, 6.91.

2.1.3.13. N-({1-[4-(3,4,5-Trimethoxybenzyl)piperazin-1-yl]cyclohexyl}methyl)-4- nitro- benzamide (1i)

Buff solid, m.p. 100 °C (dihydrochloride salt), yield 1.39 g (52.6%). IR (KBr, cm-1) exhibited bands at 3369, 3225 (NH2), 2442, 1597 (C=O), 623. 1H NMR (CDCl3) δ: 1.23-1.48 (m,

(6)

10H, (5 x CH2) cyclohexyl), 1.93-2.26 (m, 8H, (4 x CH2) piperazine), 3.84 (s, 2H, CH2-C6H5), 3.89 (d, 2H, J = 4 Hz, CH2-NH), 3.96 (s, 3H, OCH3), 3.96 (s, 6H, 2OCH3) 6.94 (br.s, 1H, NH), 7.24 (d, 2H, J = 5 Hz, Har.), 8.19 (d, 2H, J = 5 Hz, Har.), 8.27-8.29 (m, 2H, Har.). 13C NMR (CDCl3) δ: 25.9, 26.3, 29.0, 48.9, 51.6, 60.8, 63.4, 63.5 (7 x CH2, Cq), 53.6, 56.1, (OCH3), 105.9, 113.7, 119.4 (CHar.), 131.6, 134.0, 136.8, 151.1, 153.0 (Car.), 167.2 (C=O). MS (EI) m/z (%): 526 (0.01, M+), 123 (57), 84 (100), 78 (47). Anal. Calcd. for C28H38N4O6.2HCl: C, 56.09; H, 6.72; N, 9.34.

Found: C, 56.29; H, 6.62; N, 9.56.

2.1.3.14. N-{[1-(4-Benzhydrylpiperazin-1-yl)cyclohexyl]methyl}benzamide (1j)

White solid, m.p. 222 °C (dihydrochloride salt), yield 0.83 g (40%). IR (KBr, cm-1) exhibited bands at 3058.55 (NH), 1663 (C=O), 699. 1H NMR (CDCl3) δ: 1.28-1.63 (m, 10H, (5 x CH2) cyclohexyl), 2.44-2.69 (m, 8H, (4 x CH2) piperazine), 3.55 (s, 2H, CH2-NH), 4.22 (s, 1H, CH), 7.18-7.46 (m, 15H, Har.), 7.79 (br.s, 1H, NH). 13C NMR (CDCl3) δ: 22.4, 26.0, 29.4, 40.6, 44.6, 48.9, 53.4, (6 x CH2, Cq), 126.9, 127.0, 128.0, 128.5, 128.6, 128.7 (CHar.), 142.4, 142.7 (Car.), 167.1 (C=O). MS (EI) m/z (%): 467.64 (0.42, M+), 333 (93.2), 167 (100), 105 (51.5). Anal. Calcd.

for C31H37N3O.2HCl: C, 68.88; H, 7.27; N, 7.77. Found: C, 68.54; H, 7.47; N, 8.01.

2.1.3.15. N-{[1-(4-Benzhydrylpiperazin-1-yl)cyclohexyl]methyl}-4-chlorobenzamide (1k)

White solid, m.p. 218 °C (dihydrochloride salt), yield 1.27 g (56.9%). IR (KBr, cm-1) exhibited bands at 3409 (NH), 1649.8 (C=O), 1018, 954. 1H NMR (CDCl3) δ: 1.12-1.97 (m, 10H, (5 x CH2) cyclohexyl), 2.23-2.87 (m, 8H, (4 x CH2) piperazine), 3.68 (d, 2H, J = 10 Hz, CH2-NH), 4.24 (s, 1H, CH ), 7.16-7.19 (m, 11H, Har., NH), 7.27 (d, 2H, J = 5 Hz, Har.), 7.44 (d, 2H, J = 5 Hz, Har.). 13C NMR (CDCl3) δ: 26.4, 29.1, 30.4, 49.3, 52.4, 53.5, 63.4 (6 x CH2, Cq), 126.9, 127.0, 128.0, 128.5, 128.6 (CHar.), 128.7, 142.4, 142.7 (Car.), 167.1 (C=O). MS (EI) m/z (%): 502.35 (0.04, M+), 334 (100), 167 (33.26). Anal. Calcd. for C31H36ClN3O.2HCl: C, 64.75; H, 6.66; N, 7.31.

Found: C, 64.85; H, 6.91; N, 7.64.

2.1.3.16. N-{[1-(4-Benzhydrylpiperazin-1-yl)cyclohexyl]methyl}-4-nitrobenzamide (1l) Buff solid, m.p. 222 °C (dihydrochloride salt), yield 2.12 g (93.3%). IR (KBr, cm-1) exhibited bands at 3037 (NH), 1650 (C=O), 698. 1H NMR (CDCl3) δ: 1.09-1.94 (m, 10H, (5 x CH2) cyclohexyl), 2.26-2.42 (m, 8H, (4 x CH2) piperazine), 3.60 (br.s, 2H, CH2-NH), 4.27 (s, 1H, CH ), 7.16-7.48 (m, 14H, Har.), 8.20 (br.s, 1H, NH). 13C NMR (CDCl3) δ: 25.7, 25.9, 34.0, 45.5, 49.1, 51.5, 52.1 (6 x CH2, Cq), 63.5 (CH), 126.9, 127.0, 128.0, 128.5, 128.6, (CHar.) 128.7, 42.4, 142.7 (Car.), 167.8 (C=O). MS (EI) m/z (%): 512.5 (0.6, M+), 167 (100), 150 (35.4). Anal. Calcd. for C31H36N4O3.2HCl: C, 63.59; H, 6.54; N, 9.54. Found: C, 63.25; H, 6.47; N, 9.84.

2.1.4. General procedure for synthesis of 4-amino-N-{[1-(4-aralkyl/ethylpiperazin-1- yl)cyclo- hexyl]methyl}benzamides 1m-p

A solution of the appropriate arylcarboxamide 1c, 1f, 1i, and 1l (2.62 mmol) in 250 mL ethanol (95%) was hydrogenated at room temp and normal pressure for 48 h, using (120 mg) of 10% Pd/C for 1c.HCl and Raney nickel for 1f, 1i, and 1l. The catalyst was filtered off, and ethanol was evaporated under vacuum to afford the corresponding amines 1m-p as viscous oils in 33- 78.7% yields.

2.1.4.1. N-{[1-(4-Ethylpiperazin-1-yl)cyclohexyl]methyl}-4-aminobenzamide (1m) Yellow viscous oil, yield 0.30 g (33.3%). IR (KBr, cm-1) exhibited bands at 3751 and 3422 (NH2), 2927, 1636 (C=O), 1604 (NH bending). 1H NMR (CDCl3) δ: 1.07 (t, 3H, J = 6.9 Hz, CH2- CH3), 1.42-1.58 (m, 10H, (5 x CH2) cyclohexyl), 2.39 (q, 2H, J = 6.9 Hz, CH2-CH3), 2.42-2.69 (m, 8H, (4 x CH2) piperazine), 3.47 (d, 2H, J = 3.4, CH2-NH), 4.01 (s, 1H, NH2), 6.63 (d, 2H, J = 8.4 Hz, Har.), 6.84 (br. s, 1H, NH), 7.58 (d, 2H, J = 8.4 Hz, Har.). 13C NMR (CDCl3) δ: 11.9 (CH3-CH2), 22.9, 26.01, 29.6, 40.6, 44.2, 52.3, 54.3, 58.1 (7 x CH2), Cq), 114.2, 124.3 (CHar.), 128.6, 149.5 (Car.), 167.0 (C=O). MS (EI) m/z (%): 344.25 (0.35, M+), 265.1 (35), 181.05 (100). Anal. Calcd.

for C20H32N4O: C, 69.73; H, 9.36; N, 16.26. Found: C, 69.84; H, 9.49; N, 15.99.

2.1.4.2. N-{[1-(4-Benzylpiperazin-1-yl)cyclohexyl]methyl}-4-aminobenzamide (1n) Colourless viscous oil, yield 0.84 g (78.7%). IR (KBr, cm-1) exhibited bands at 3342 and 3219 (NH2), 2927, 1636 (C=O), 1604 (NH bending), 810. 1H NMR (CDCl3) δ: 1.42-1.59 (m, 10H, (5 x CH2) cyclohexyl), 2.46 (s, 4H, (2 x CH2) piperazine), 2.67 (s, 4H, 2 x CH2) piperazine), 3.50 (d, 2H, J = 8.4 Hz, CH2-NH) 3.97 (br. s, 2H, , CH2-C6H5), 6.7 (d, 2H, J = 8.4 Hz, Har), 7.25-7.30 (m, 6H, Har., NH), 7.6 (d, 2H, J = 8.4 Hz, Har). 13C NMR (CDCl3) δ: 22.36, 25.85, 26.03, 29.61,

(7)

44.41, 48.87, 54.71, 63.21 (7 x CH2), Cq), 114.2, 124.5, 125.6, 127.1, 128.3 (CHar.), 128.6, 137.9, 149.4 (Car.) 167.0 (C=O). MS (EI) m/z (%): 406.1 (0.08, M+), 257 (100), 114.05 (58). Anal. Calcd.

for C25H34N4O: C, 73.85; H, 8.43; N, 13.78. Found: C, 73.65; H, 8.75; N, 13.98.

2.1.4.3. N-({1-[4-(3,4,5-Trimethoxybenzyl)piperazin-1-yl]cyclohexyl}methyl)-4- amino- benzamide (1o)

Yellow viscous oil, yield 0.52 g (40%). IR (KBr, cm-1) exhibited bands at 3369 and 3225 (NH2), 2850, 1636 (C=O), 1604 (NH bending), 847. 1H NMR (CDCl3) δ: 0.79-.1.51 (m, 10H, (5 x CH2) cyclohexyl), 1.97-2.93 (m, 8H, (4 x CH2) piperazine), 3.38 (s, 4H, CH2-NH and CH2-C6H5), 3.78 (s, 3H, OCH3), 3.81 (s, 6H, 2 OCH3), 6.49 (s, 2H, Har.), 6.55 (d, 2H, J = 10 , Har.), 7.16 (d, 2H, J = 10 , Har.), 7.51 (s, 1H, NH). 13C NMR (CDCl3) δ: 22.2, 22.8, 26.0, 31.9, 44.2, 51.2, 53.0, 60.8 (7 x CH2), Cq), 54.5, 56.1 (OCH3), 105.8, 113.7, 124.6 (CHar.), 129.3, 131.5, 133.5, 148.6, 153.1 (Car.), 170.9 (C=O). MS (EI) m/z (%): 495.5 (0.22, M+ -1), 181 (22.84), 114 (100). Anal. Calcd. for C28H40N4O4: C, 67.71; H, 8.12; N, 11.28. Found: C, 67.91; H, 8.46; N, 11.68.

2.1.4.4. N-{[1-(4-Benzhydrylpiperazin-1-yl)cyclohexyl]methyl}-4-aminobenzamide (1p)

Colourless viscous oil, yield 0.56 g (52.6%). IR (KBr, cm-1) exhibited bands at 3059 and 3027 (NH2), 3223 (NH), 1605 (C=O), 920. 1H NMR (CDCl3) δ: 1.20-.1.45 (m, 10H, (5 x CH2) cyclohexyl), 2.30-2.88 (m, 8H, (4 x CH2) piperazine), 3.56 (s, 2H, CH2-NH), 4.21 (s, 1H, CH), 6.53 (d, 2H, J = 10 , Har.), 6.94 (br.s, 1H, NH) 7.24-7.43 (m, 10H, Har.), 7.60 (d, 2H, J = 10 , Har).

13C NMR (CDCl3) δ: 22.8, 29.0, 44.6, 52.4, 53.6, 57.9 (6 x CH2), Cq),128.01, 128.09, 128.5, 128.6, 138.1 (CHar.), 142.3, 148.7, 150.0 (Car.), 170.9 (C=O). MS (EI) m/z (%): 482.45 (0.05, M+), 334 (41.7), 167 (100). Anal. Calcd. for C31H38N4O: C, 77.14; H, 7.94; N, 11.61. Found: C, 77.54; H, 7.65; N, 11.45.

2.1.5. Synthesis of methyl 2-methoxy-4-[(phenylcarbonyl)amino]benzoate (7)

Anhydrous K2CO3 (29.14 g, 211.0 mmol) was added to a stirred solution of 4-benzamido- 2-hyroxybenzoic acid 6 (20.3 g, 79.0 mmol) in acetone (150 mL) and stirring was continued for 5 min at RT, then dimethyl sulphate (19.93 mL, 210.0 mmol) was added dropwise. The reaction mixture was stirred for 1 h at RT then stirring was continued for 18 h at 45 °C. The reaction mixture was filtered, 80% of the filtrate was evaporated under normal pressure, the evaporated solvents were replaced with water, evaporate 40% of this water, cooling (0-5 °C), then add ammonia to adjust pH 9.5-10 and the reaction mixture was stirred for 2 h at 0-5 °C. The precipitated solid was filtered off to afford 13.5 g (60%) of 7 m.p. 148 °C.

2.1.6.Synthesis ofmethyl 5-chloro-2-methoxy-4-[(phenylcarbonyl)amino]benzoate (8) Compound 7 (6 g, 20.0 mmol) was mixed with glacial acetic acid (10.6 mL, 175 mmol), conc. HCl (2.84 mL, 20.0 mmol) and distilled H2O (3.16 mL). The reaction mixture was cooled to 20 °C, and then potassium chlorate was added in four successive portions at 10 min intervals.

During addition, The white color of the reaction mixture changed to canary yellow with evolution of chlorine gas. The temperature of the reaction mixture must be kept between 30-35 °C to avoid loss of chlorine gas. After complete addition, the reaction mixture was stirred at RT for 7 h, then water was added (13.2 mL) and stirring was continued for another 1 h at RT to help complete precipitation of the chlorinated compound 7. The precipitate was filtered off, washed with water several times till neutral to afford 4.9 g (71%) of 8 as buff solid, m.p. 106 °C.

2.1.7. Synthesis of5-chloro-2-methoxy-4-[(phenylcarbonyl)amino]benzoic acid (9) To a stirred solution of 8 (4.0 g, 12 mmol) a solution of 1.7 N lithium hydroxide (13 mL) in THF (13.4 mL) was added. The reaction mixture was stirred overnight at RT, then was evaporated under reduced pressure. The residue was dissolved in H2O (20 mL) and extracted with diethyl ether (2 x 15 mL). The aqueous layer was acidified with conc. HCl under cooling, extracted with ethyl acetate (3 x 15 mL), the organic layer was dried (Na2SO4) and evaporated under reduced pressure to afford 3.20 g (84.2%) of 9 as yellowish white solid m.p. 170 °C.

2.1.8. General procedure for synthesis of 4-amino-N-{[1-(4-aralkyl/ethylpiperazin-1- yl)- cyclohexyl]methyl}-5-chloro-2-methoxybenzamides 1q-t

To a stirred solution of 9 (1.31 g, 4.30 mmol) in CH2Cl2 (10 m), EDCI.HCl (1.3g, 6.79 mmol) was added, then a solution of the appropriate amine 4a-d (4.30 mmol) in CH2Cl2 (5 mL) was added to the reaction mixture. The reaction mixture was stirred overnight at RT, washed with water (2 x 20 mL) then with 10% NaHCO3 (2 x 15 mL). The organic layer was separated, dried

(8)

(Na2SO4) and evaporated under vacuum to afford the corresponding benzamides N-{[1-(4- aralkyl/ethylpiperazin-1-yl)cyclohexyl]methyl}-5-chloro-2-methoxy-4-[(phenylcarbonyl)-

amino]benzamides 10a-d in 44-91% yields which were used in the subsequent hydrolysis step without further purification. A suspension of the appropriate benzamide 10a-d (20.0 mmol) with 10% NaOH (40 mL) was heated to reflux for 24 h. The reaction mixture was cooled, extracted with CH2Cl2 (2 x 25 mL). The organic layer was separated, dried (Na2SO4) and evaporated under reduced pressure to give crude 1q-t as brown viscous oils which were purified through column chromatography to afford the respective pure target compounds 1q-t in 50-62.5% yields.

2.1.8.1. 5-Chloro-N-{[1-(4-ethylpiperazin-1-yl)cyclohexyl]methyl}-2-methoxy-4- [(phenyl- carbonyl)amino]benzamide (10a)

Pale yellow viscous oil, yield 1.98 g (91%). IR (KBr, cm-1) exhibited bands at 3205 (NH), 1644 (C=O), 1532 (C=O), 678. 1H NMR (CDCl3) δ: 1.04-1.55 (m, 13H, CH3 and (5 x CH2) cyclohexyl), 2.15-2.39 (m, 10H, CH2-CH3 and (4 x CH2) piperazine), 3,84 (s, 3H, OCH3,), 7.26- 7.88 (m, 7H, Har.), 8.54 (s, 1H, CH2-NH), 9.29 (s, 1H, NH-C=O). 13C NMR (CDCl3) δ: 14.8 (CH3- CH2), 22.1, 27.0, 35.5, 35.8, 44.6, 45.3, 48.0, 54.2 (7 x CH2, Cq), 56.1 (OCH3), 103.9, 114.0, 126.9, 129.1, 132.7 (CHar.), 134.2, 136.9, 154.7 (Car.), 164.8 (C=O), 165.5 (C=O). MS (EI) m/z (%):

512.7 (0.05, M+), 195 (34.5), 105 (50.7), 58 (100).

2.1.8.2. N-{[1-(4-Benzylpiperazin-1-yl)cyclohexyl]methyl}-5-chloro-2-methoxy-4- [(phenylß carbonyl)amino]benzamide (10b)

Pale yellow viscous oil, yield 1.6 g (65%). IR (KBr, cm-1) exhibited bands at 3391.21 (NH), 1686 (C=O), 1645 (C=O), 699. 1H NMR (CDCl3) δ: 1.42-1.61 (m, 10H, (5 x CH2) cyclohexyl), 2.48 (br.s, 4H, (2 x CH2) piperazine), 2.69 (br. s, 4H, (2 x CH2) piperazine), 3.55 (s, 2H, CH2-C6H5), 3.57 (d, 2H, J = 5, CH2-NH), 3.92 (s, 3H, OCH3), 7.25-7.30 (m, 10H, Har.,), 7.53- 7.62 (m, 2H, Har.), 8.48 (s, 1H, CH2-NH), 8.63 (s, 1H, NH-C6H5). 13C NMR (CDCl3) δ: 25.9, 29.0, 29.7, 44.4, 53.1, 56.5, 57.8, 63.1 (7 x CH2), Cq), 54.1(OCH3), 103.8, 114.0, 127.0, 127.1, 132.2, 157.1, 128.2, 128.4 (CHar.), 129.2, 129.3, 129.4, 129.5, 132.6, 132.7(Car.), 165.5 (C=O), 165.6 (C=O). MS (EI) m/z (%): 579 (0.71, M+ + 4), 175 (4), 91 (15), 63 (100).

2.1.8.3. 5-Chloro-2-methoxy-4-[(phenylcarbonyl)amino]-N-({1-[4-(3,4,5-trimethoxy- benzyl)piperazin-1-yl]cyclohexyl}methyl)benzamide (10c)

Brown viscous oil, yield 1.1 g (44%). IR (KBr, cm-1) exhibited bands at 3409 (NH), 1628 (C=O), 1592 (C=O), 843. 1H NMR (CDCl3) δ: 1.16-1.89 (m, 10H, (5 x CH2) cyclohexyl), 2.48- 2.60 (m, 8H, (4 x CH2) piperazine), 3.42 (s, 4H, CH2-NH, CH2-C6H5), 3.81 (s, 3H, OCH3), 3.81 (s, 9H, 3OCH3), 6.54 (s, 2H, Har), 7.25-8.35 (m, 7H, Har.,), 8.50 (s, 1H, NH-CH2), 8.64 (br. s, 1H, NH- C6H5). 13C NMR (CDCl3) δ: 25.96, 26.1, 29.4, 48.9, 53.2, 53.3, 60.9, 63.4 (7 x CH2), Cq), 56.1 (4 x OCH3), 105.7, 127.1, 114.7, 128.5, 129.1, 132.2, (CHar.), 105.7, 153.2, 132.7, 133.9 134.0, 153.1, 136.9, 157.7 (Car.), 163.6 (C=O), 166.8 (C=O). MS (EI) m/z (%): 663.5 (0.95, M+ -2), 181.1 (37.6), 167.1 (34.3), 57 (100).

2.1.8.4. N-{[1-(4-Benzhydrylpiperazin-1-yl)cyclohexyl]methyl}-5-chloro-2-methoxy-4- [(phenyl- carbonyl)amino]benzamide (10d)

Pale yellow viscous oil, yield 2.15 g (77%). IR (KBr,cm-1) exhibited bands at 3060 (NH), 1600 (C=O), 700. 1H NMR (CDCl3) δ: 1.14-1.84 (m, 10H, (5 x CH2) cyclohexyl), 2.14-2.53 (m, 8H, (4 x CH2) piperazine), 2.79 (s, 2H, CH2-NH), 3.6 (s, 3H, OCH3), 4.29 (s, 1H, CH), 7.31-7.40 (m, 15H, Har.), 7.73 (br.s, 2H, Har.), 7.97 (br.s, 1H, CH2-NH), 8.04 (br.s, 1H, NH-C6H5). 13C NMR (CDCl3) δ: 22.3, 25.3, 25.8, 27.0, 44.8, 48.3, 49.2 (6 x CH2, Cq), 52.5 (OCH3), 127.1, 127.7, 127.9, 128.0, 128.6, 128.7, 128.8, 129.4, (CHar.), 131.0, 134.9, 131.9 136.7, 137.5, 142.3 (Car.), 161.3 (C=O), 166.4 (C=O). MS (EI) m/z (%): 649.2 (2.1, M+ -2), 167 (100), 152 (43.5).

2.1.8.5. 4-Amino-5-chloro-N-{[1-(4-ethylpiperazin-1-yl)cyclohexyl]methyl}-2- methoxybenz- amide (1q)

Colourless viscous oil, yield 5.0 g (62.5%). IR (KBr, cm-1) exhibited bands at 3785 and 3657 (NH2), 2929, 1634 (C=O). 1H NMR (CDCl3) δ: 1.04 (t, 3H, J = 6.9 Hz, CH2-CH3), 1.15-1.54 (m, 10H, (5 x CH2) cyclohexyl), 2.36 (q, 2H, J = 6.9 Hz, CH2-CH3), 2.65 (br.s, 8H, (4 x CH2) piperazine), 3.47 (d, 2H, J = 5, CH2-NH), 3.82 (s, 3H, OCH3), 4.35 (s, 2H, NH2), 6.28 (s, 1H, Har.), 7.94 (s, 1H, Har.), 8.09 (s, 1H, NH). 13C NMR (CDCl3) δ: 11.83 (CH3-CH2), 22.1, 26.0, 29.6, 44.1, 48.5, 52.3, 56.2, 57.8 (7 x CH2) Cq), 53.9 (OCH3), 97.9, 111.3, 112.4, 132.9, 146.8, 157.6 (CHar.,

(9)

Car.) 164.6 (C=O). MS (EI) m/z (%): 408.45 (0.29, M+), 195 (100), 58 (67.95). Anal. Calcd. for C21H33ClN4O2: C, 61.67; H, 8.13; N, 13.70. Found: C, 61.29; H, 7.89; N, 13.45.

2.1.8.6. 4-Amino-N-{[1-(4-benzylpiperazin-1-yl)cyclohexyl]methyl}-5-chloro-2- methoxy

benzamide (1r)

Colourless viscous oil, yield 4.70 g (50%). IR (KBr, cm-1) exhibited bands at 3059 and 3026 (NH2), 2854, 1644 (C=O), 848. 1H NMR (CDCl3) δ: 1.07-1.88 (m, 10H, (5 x CH2) cyclohexyl), 2.19-2.67 (m, 8H, (4 x CH2) piperazine), 3.53 (s, 4H, CH2-NH and CH2-C6H5), 3.72 (s, 3H, OCH3), 4.21 (s, 2H, NH2), 7.25-7.34 (m, 8H, Har., NH). 13C NMR (CDCl3) δ: 22.8, 26.0, 29.0, 29.4, 32.0, 48.9, 53.9, 63.9 (7 x CH2), Cq), 55.7 (OCH3), 98.2, 110.7, 116.5, 128.4, 129.2, 137.7, 138.1, 142.6, 144.8, 153.3 (CHar., Car.), 166.7 (C=O). MS (EI) m/z (%): 472 (0.6, M++1), 153 (47.3), 84 (43.9). Anal. Calcd. for C26H35ClN4O2: C, 66.30; H, 7.49; N, 11.89. Found: C, 65.95;

H, 7.75; N, 11.64.

2.1.8.7. 4-Amino-5-chloro-2-methoxy-N-({1-[4-(3,4,5-trimethoxybenzyl)piperazin-1- yl]cyclo- hexyl}methyl)benzamide (1s)

Colourless viscous oil, yield 3.88 g (40%). IR (KBr, cm-1) exhibited bands at 3854 and 3746 (NH2), 2851, 1629 (C=O), 891.1H NMR (CDCl3) δ: 0.84-2.01 (m, 10H, (5 x CH2) cyclohexyl), 2.40 (br.s, 8H, (4 x CH2) piperazine), 3.42 (s, 4H, CH2-NH and CH2-C6H5), 3.70 (s, 3H, OCH3), 3.70 (s, 9H, OCH3) 6.23 (s, 1H, Har.), 6.52 (br. s, 3H, Har.), 7.10 (s, 1H, NH). 13C NMR (CDCl3) δ: 14.2, 22.7, 29.7, 32.0, 41.9, 47.1, 52.9 (7 x CH2), 53.3 (Cq), 55.7, 56.1,60.9, 63.2 (4 x OCH3), 98.2, 105.7, 110.7, 116.3, 129.1, 133.6, 137.0, 144.9, 153.1, 155.3 (CHar., Car.), 166.9 (C=O). MS (EI) m/z (%): 562 (0.2, M++1), 399 (27.2), 181 (56.5). Anal. Calcd. for C29H41ClN3O5: C, 62.07; H, 7.36; N, 9.98. Found: C, 61.87; H, 7.76; N, 10.08.

2.1.8.8. 4-Amino-N-{[1-(4-benzhydrylpiperazin-1-yl)cyclohexyl]methyl}-5-chloro-2- methoxy- benzamide (1t)

Colourless viscous oil, yield 7.60 g (70%). IR (KBr, cm-1) exhibited bands at 3333, 3203 (NH2), 1619 (C=O), 1249, 752. 1H NMR (DMSO-d6) δ: 1.10-1.96 (m, 10H, (5 x CH2) cyclohexyl), 2.24-2.72 (m, 8H, (4 x CH2) piperazine), 3.29 (br.s, 2H, CH2-NH), 3.75 (s, 3H, OCH3), 4.21-4.42 (m, 3H, CH, NH2), 6.23 (s, 2H, Har.), 7.17-7.41 (m, 10H, Har.), 8.09 (br.s, 1H,NH). 13C NMR (DMSO-d6) δ: 26.0, 28.4, 30.4, 44.7, 47.3, 49.1, 52.2 (6 x CH2, Cq), 55.7 (OCH3), 98.2, 110.7, 116.4, 127.2, 127.9, 128.6, 128.7, 142.3, 144.9, 155.3 (CHar., Car.), 166.8 (C=O). MS (EI) m/z (%):

549 (0.34, M++2), 251.2 (4.6), 181 (100), 167 (84.5). Anal. Calcd. for C32H39ClN4O2: C, 70.25; H, 7.18; N, 10.24. Found: C, 69.92; H, 7.58; N, 10.54.

2.2. Biological evaluation

Adult male albino rats weighing 200-300 g were used in this study. The animals were purchased from Animal House colony of National Research Centre, Cairo, Egypt and were housed under standardized conditions (room temperature 23±2°C, relative humidity 55±5%, 12h- light/12h-dark cycle) .They had free access to tap water and were feeded with commercially available standard rat chow throughout the whole experimental period. All animal procedures were performed after the Ethics Committee of the National Research Centre and in accordance with the recommendations for the proper care and use of laboratory animals "Canadian Council on Animal Care Guidelines, 1984." Tween-80 (Polyoxyethylene-sorbitan monooleate, Sigma USA), apomorphine hydrochloride (Research Biochemicals Inc., Wayland, USA), and Metoclopramide hydrochloride (CID Company, Giza, Egypt).

2.2.1. Dopamine D2 receptor antagonistic activity (Zwangsnagen test)

Groups of 6 rats each were placed individually in cages having shavings of wood on the floor and an observation window and allowed to habituate for 15 minutes before injection of drugs.

A series of doses ranging from 1.5 to 20 mg/kg of the test compounds 1a-t was investigated. Each dose was suspended in tween-80 (7% aqueous solution) as vehicle and administered subcutaneously. A minimum of 4 dose levels per compound and 6 rats per dose were used. One hour later, 0.5% solution of apomorphine hydrochloride (1.25 mg/kg) in saline was injected intravenously, such that the injected solution does not exceed 2 mL/kg. After 5, 10, 20 min., the animals were observed for 1 min. The presence or absence of chewing movement (Zwangsnagen) or compulsory gnawing as well as severity of chewing were noted. The absence of chewing movement 5, 10 or 20 minutes after apomorphine hydrochloride injection is indicative of

(10)

dopamine D2 receptor antagonistic activity and hence antiemetic activity.11 The studied biological activity of the tested compounds was compared with that of Metoclopramide hydrochloride used as reference standard. The ED50 of the most potent compounds were calculated according to the method of Litchfield Wilcoxon.12

2.3. Molecular modeling

Pharmacophore was produced using the Discovery Studio 2.5 software. (Accelrys Inc., San Diego, CA, USA).

2.3.1. Generation of dopamine D2 receptor antagonists pharmacophore

The pharmacophore modeling method has been widely used in lead discovery and optimization as a key tool of computer aided drug design. A hypothesis was formulated using generation common feature pharmacophore model protocol in Discovery studio 2.5. The lead compounds (I-X), which were reported to have dopamine D2 receptor antagonistic activity (Figure 2), were used to generate common feature pharmacophore for the dopamine D2 receptor antagonists.13 A set of conformational models of each structure of the lead compounds was performed and used to generate the common feature hypotheses, where ten hypotheses were generated.14

3. Results and discussion 3.1. Chemistry

The target compounds 1a-l were synthesized as outlined in Scheme 1. Thus, cyclohexanone was allowed to react via Strecker synthesis with N-ethyl and/or aralkylpiperzine 2a-d and KCN in the presence of concentrated HCl to produce the carbonitrile derivatives 3a-d.

Subsequently, the nitrile functionality of 3a-d was subjected to reduction using LiAlH4/AlCl3

reducing mixture15 in dry THF to yield the corresponding amines 4a-d. Compounds 4a-d were then reacted with the appropriate acyl chloride 5a-c in the presence of triethylamine to yield the respective target compounds 1a-l in moderate yields.

Compound Nr. R R1

1a C2H5 H

1b C2H5 Cl

1c C2H5 NO2

1d CH2-C6H5 H

1e CH2-C6H5 Cl

1f CH2-C6H5 NO2

1g CH2-C6H2(OCH3)3 H 1h CH2-C6H2(OCH3)3 Cl 1i CH2-C6H2(OCH3)3 NO2

1j CH(C6H5)2 H

1k CH(C6H5)2 Cl

1l CH(C6H5)2 NO2

Scheme 1: Synthesis of the target compounds 1a-l.

O

NH N +

R NC N

N R H2N N

N R

N N H

N R

R1

O

2a-d 3a-d 4a-d 1a-l

a: R = C2H5 b: R = CH2-C6H5

c: R = CH2-C6H2(OCH3)3

d: R = CH(C6H5)2

i ii iii

(11)

Reagents and conditions: i) KCN, conc. HCl, water, RT, 18 h; ii) LiAlH4/AlCl3, THF, RT, 18 h; iii) appropriate 5a-c, triethylamine, benzene, reflux, 18 h.

Nitro functionality of compounds 1c, 1f, 1i, and 1l was reduced using 10% Pd/C (for 1c) or Raney nickel (for 1f, 1i, and 1l) and molecular hydrogen under normal pressure and room temperature to give the respective amines 1m-p (Scheme 2).

Scheme 2: Synthesis of the target compounds 1m-p.

Reagents and conditions: i) 10% Pd/C (for compound 1c) or Raney nickel (for compounds 1f, 1i, and 1l), H2, RT, 18 h.

The acid 9, which was required to prepare the Metoclopramide analogues 1q-t, was prepared as depicted in Scheme 3. Thus, N-benzoyl-4-aminosalicylic acid 6 was methylated at both phenolic OH and carboxylic acid functionalities using dimethyl sulfate in acetone at 45 °C for 24 hours to give the corresponding methoxybenzoic acid methyl ester 7. Subsequent chlorination of 7 using KClO3 in the presence of concentrated hydrochloric acid at room temperature for 24 h furnished the chlorinated compound 8. The ester functionality of 8 was hydrolyzed by LiOH in THF at room temperature to furnish N-benzoyl-4-aminobenzoic acid derivative 9.

Scheme 3: Synthesis of compound 9.

Reagents and conditions: i) (CH3)2SO4, anhyd. K2CO3, 45 °C, 24 h; ii) KClO3/HCl, RT, 24 h;

iii) LiOH/THF, RT, 24 h.

Metoclopramide analogues 1q-t were synthesized as illustrated in Scheme 4. Thus, the benzoic acid derivative 9 was coupled with the appropriate amine 4a-d using ethyl-3-(3-

N N H

N R

O2N

O

i

N N H

N R

H2N

O

1c, 1f, and 1l 1m-p 1c, 1m: R = C2H5

1f, 1n: R = CH2-C6H5

1i, 1o: R = CH2-C6H2(OCH3)3 1l, 1p: R = CH(C6H5)2

HN

ii HN

i C

O

C O

HN C O iii

COOH OH

COOCH3 OCH3

HN C O COOCH3

OCH3 Cl

COOH OCH3 Cl

6 7 8

9

(12)

dimethylaminopropyl)carbodiimide hydrochloride (EDCI.HCl) in DCM at room temperature to furnish the respective amides 9a-d. Subsequently, the target compounds 1q-t were obtained via refluxing the N-benzoyl derivatives 9a-d in 10% aqueous NaOH solution (Scheme 4).

Scheme 4: Synthesis of the target compounds 1q-t.

Reagents and conditions: i) EDCI.HCl, DCM, RT, 18 h; ii) NaOH, H2O, reflux, 18 h.

The spectral data of the newly synthesized compounds in the present investigation were in accordance with their assigned structures.

3.2. In vivo dopamine D2 receptor antagonistic activity

The newly synthesized compounds 1a-t were evaluated for their dopamine D2 receptor antagonistic activity in vivo by measuring their ability to inhibit apomorphine-induced chewing

“Zwangsnagen” in rats.11 This test measures the inhibition of compulsive stereotyped hyperactivity behavior induced by apomorphine through its stimulation of central dopamine D2 receptors in rats.16 The dopamine D2 receptor antagonistic activity of 1a-t and ED50 values of the selected candidates with potent activity are displayed in Table 1.

Metoclopramide (I) is a relatively weak serotonin-3 (5-HT3) as well as dopamine D2

receptor antagonist. Metoclopramide is one of the most effective agents used intravenously in a high dose to alleviate cisplatin-induced nausea and vomiting.17 Nevertheless, its clinical usefulness is restricted due to its extrapyramidal side effects. Accordingly, Metoclopramide is a ready target for extensive molecular modification to enhance some of its desirable effects and attenuate or abolish side effects. Certain molecular modifications were examined previously in our research group which implied structural variation in the amide side chain through incorporating cyclohexyl moiety in the β-position to the amidic nitrogen to give compound

II.5 Insertion of cyclohexyl moiety increased the lipophilicity of compound II which plays a remarkable role in distribution and binding of drugs to their targets in vivo. Further molecular modifications of compound II were achieved, to improve its dopamine D2 receptor antagonistic profile, through the synthesis of the target compounds 1a-t.

HN C O COOH

OCH3 Cl

9 4a-d +

H2N N

N R N

NH O N R

OCH3 NH

OCl

N N H O N R

OCH3 H2N

Cl

1q-t 10a-d a: R = C2H5

b: R = CH2C6H5

c: R = CH2C6H2(OCH3)3 d: R = CH(C6H5)2

1q: R = C2H5 1r: R = CH2C6H5 1s: R = CH2C6H2(OCH3)3 1t: R = CH(C6H5)2 i

ii

Referințe

DOCUMENTE SIMILARE

e Materials Science Research Center, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.. Zinc oxide microrods were grown on Zn foils by a simple

Fig.7 H 2 absorption results of Mg-Al nano alloys catalyzed by 2mol% Ni nanoparticles at different temperature. Hydrogen absorption rate of Mg-Al alloys catalyzed by 2mol%

The optimized molecular geometry, the length of the covalent bonds, the atomic charges and some electro-optical parameters influencing the bioactivity of the new compounds were

Table 1: List of substituted pyrrole derivatives (ligands) used in docking studies and mean binding energy of compounds (P1-P10) with analgesic receptor... R Mean

The study included the synthesis of silver nanoparticles from the herbal leaves of Ocimum sanctum and Vitex negundo and their antimicrobial activity.. From the study, it was

The correlation of observed activity, in terms of MIC (μg/mL) of reported compounds with different structural parameters, systematic QSAR investigations have been carried out

The low r 2 and q 2 values indicate (data not shown) that the good results in our original model are not due to a chance correlation or structural dependency of the training

In vitro anti-herpes simplex type-1 activity, antioxidant potential and total phenolic compounds of pomegranate (Punica granatum L.) peel extract. Anti-influenza virus activity and