Synthesis, Characterization and Antimicrobial Evaluation of Pyrimido Cyclohept[B] Indole Derivatives

Introduction

On the basis of the interesting structures and biological ativities exhibited several heterocyclic systems possessing indole nucleus, we have chosen the indole nucleus fused with seven membered ring cyclohept [b] indole as the core subject matter for investigation in this synthetic study. In continuation of our study in 2-(4′-methyl)benzylidene-1-oxo-3,4,5,10-tetrahydrocyclohept [b] indole(3a)we became interested in developing novel methods to prepare some novel systems containing pyrazino-,isoxazolo-, pyrimido-, thiopyrimido-, aminopyrimido- and pyrano-rings annelated to carbazole skeleton. Our interest in such compounds has been further increased by the recent discovery of pyrido-carbazoles as an appropriate skeleton to design DNA intercalating drugs [1-3]. Besides this, many tetracyclic compounds have been synthesized by the replacement of pyridine ring by other heterocyclic rings and their effects on biological properties [4-12] were studied. Tetrahydrocarbazoles and its derivatives were examined as an antidepressant drugs [13]. Tetrahydrocyclohept [b] indole derivatives are associated with various potential biological activities such as anti-inflammatory, bactericidal, analgesic, antibiotic, insecticidal and fungicidal studies [14-19].

Nitrogen heterocycles bearing amino substituent are of broad pharmaceutical interest leading to continuous efforts in the study of their structure activity relationship. In particular, these compounds show remarkable antitumor characteristics and have good prospects for future medicinal uses. However, a major drawback in using these classes of compounds as drugs is their insolubility in water, which makes it extremely difficult to administer it in intravenous form, limiting its practical application. Incorporation of amino group into these systems was found to enhance the hydrophilicity and water solubility of these molecules. Amino carbazoles derivatives have showed potential activities to both Alzheimer’s disease and cancer [20,21].

Materials and Methods

Melting points were determined on a Boetius micro heating table or on a Raga heating block and are uncorrected. Thin Layer Chromatography [TLC] was performed using glass plates coated with silica gel G [incorporating CaSO₄ (13%) as binder]. Petroleum ether and ethyl acetate were used as irrigant. Spots were visualized with iodine. Purification of the crude samples was carried out using chromatographic columns packed with silica gel (60-120 mesh). IR Spectra were recorded on Shimadzu FT IR 8201(PC)S spectrometer model spectrometer, using KBR discmethod and the absorption frequencies quoted in reciprocal centimeters (cm^-1).¹H-NMR spectra were taken on BRUKER-400 (400 MHz), BRUKER-500 (500 MHz) spectrometer using trimethylsilane (TMS) as internal reference. The chemical shifts are quoted in parts per million (ppm) (s=singlet; d=doublet; t=triplet; q=quardret; bs=broad singlet and m=multiplet). Elemental analysis was performed on Vario EL III CHNS analyzer and Perkin-Elmer analyzer. Microanalysis was obtained (C, H, N, ± 0.4%).

General procedure for preparation of 2-(4′-methyl)benzylidine-1-oxo-3,4,5,10-tetrahydrocyclohept [b] indole (2a)

A mixture of the 1-oxo-2,3,4,5-tetrahydrocyclohept [b] indole (1a) (0.001 mol) and 4-methylbenzaldehyde (2)0.001 mol was treated with 4% alcholic potassium hydroxide and stirred for 24 h at room tempterature. The product 2-(4′-methyl)-benzylidine-1-oxo-3,4,5,10-tetrahydro-cyclohept [b] indole (3a-3d) precipitated as crystalline mass was filtered off and dried.

2-(4′-methyl)benzylidine-7-methyl-1-oxo-3,4,5,10-tetrahydrocyclohept [b] indole (3a)

Yellow solid, Yield: 0.182 g(85.44%), M.p: 202ºC; IR (KBr) [v_maxcm^-1]: 3326, 1620, 1943, 1435, 1350, 1234, 802, 709, 671 cm^-1; ¹H-NMR (CDC1₃) δ (ppm)=2.35(s, 3H,C₇-CH₃)2.38(s, 3H, C₄-CH₃), 2.79-3.12(m,6H, C₄-H₂, C₅-H₂ C₆-H₂),7.12- 7.54 (m, 8H, C₆-H, C₈-H,C₉-H, benzylic -H, C₂′-H, C₃′-H, C₅′-H, C₆′-H) and 11.28(s, 1H, -NH). Anal. calcd for C₂₂H₂₁NO:C, 83.778%, H,6.710%, N, 4.440%, Found: C,83.75%, H,6.70%, N, 4.40%.

2-(4′-methyl)benzylidine-8-methyl-1-oxo-3,4,5,10-tetrahydrocyclohept [b] indole (3b)

Yellow solid, Yield: 0.163 g (76.52%), M.p: 202ºC; IR (KBr) [v_max cm^-1]: 3322,2918,1632,1560,1526,1432,1341,1271,1230,1182, 1160, 1034, 985, 911,873, 796, 761, 700 cm^-1; ¹H-NMR (CDC1₃) δ (ppm): 2.35(s, 3H,C₇-CH₃)2.38(s, 3H, C₄-CH₃), 2.79-3.12(m,6H, C₄-H₂, C₅-H₂ C₆-H₂),7.12-7.54 (m, 8H, C₆-H, C₈-H, C₉-H, benzylic -H, C₂′-H, C₃′-H, C₅′-H, C₆′-H) and11.28(s, 1H, -NH). Anal. calcd for C₂₂H₂₁NO:C, 83.778%, H,6.710%, N, 4.440%. Found: C,83.756%, H,6.65%, N, 4.340%.

2-(4′-methyl)benzylidine-9-methyl-1-oxo-3,4,5,10-tetrahydrocyclohep [b] indole (3c)

Yellow solid, Yield: 0.179 g (76.52%); M.p: 202ºC; IR (KBr) [v_maxcm^-1]: 3315, 2923, 2858, 1630, 1579,1529,1435, 1382, 1328,1252, 1160, 984, 910, 810,695 cm^-1; ¹H-NMR (CDC1₃) δ (ppm)=2.35(s, 3H,C₇-CH₃) 2.38(s, 3H, C₄-CH₃), 2.79-3.12(m,6H, C₄-H₂, C₅-H₂ C₆-2),7.12- 7.54 (m, 8H, C₆-H, C₈-H,C₉-H, benzylic -H, C₂′-H, C₃′-H, C₅′-H, C₆′-H) and11.28(s, 1H, -NH). Anal. calcd for C₂₂H₂₁NO:C, 83.778%, H,6.710%, N, 4.440%. Found: C,83.776%, H,6.721%, N, 4.410%.

2-(4′-Methyl)benzylidine-1-oxo-3,4,5,10-tetrahydrocyclohept [b] indole (3d)

Yellow solid, Yield: 0.194 g (64.66%), M.p: 202ºC; IR (KBr) [v_maxcm^-1]: 3292, 2923, 1630, 1588, 1522, 1460, 1334, 1260, 1183, 981, 812, 744cm^-1; ¹H-NMR (CDC1₃) δ (ppm)=2.35(s, 3H,C₇-CH₃), 2.38(s, 3H, C₄-CH₃), 2.79-3.12(m,6H, C₄-H₂, C₅-H₂ C₆-2), 7.12-7.54 (m, 8H, C₆-H, C₈-H,C₉-H, benzylic -H, C₂′-H, C₃′-H, C₅′-H, C₆′-H) and 11.28(s, 1H, -NH). Anal. calcd for C₂₁H₁₉NO:C, 83.778%, H,6.710%, N, 4.440%. Found: C,83.776%, H,6.712%, N, 4.420%.

General procedure for preparation of 2-hydroxy-5,6,7,12-tetrahydro-4(4′-ethyl)-phenyl-pyrimido[3′,4′:5,4]cyclo-hept- [b] indole (4a-4d)

A mixture of respective 2-(4′-methyl)benzylidine-1-oxo-3,4,5,10-tetrahydro cyclohept [b] indole(3a) (0.001 mol) and urea (0.001 mol) in presence of sodium methoxide in dry ethanol (10 ml) was refluxed on water bath for 18 h. The excess solvent was removed by evaporation and the reaction mixture was poured into an ice. The precipitate obtained was filtered off, dried and purified by passing through silica gel column and eluting with petroleum ether and ethyl acetate mixture (65:35) to yield the respective 2- hydroxy-5,6,7,12-tetrahydro-4(4′-methyl)phenylpyrimido [3′,4′:5,4]cyclohept [b] indole(4a).

2-hydroxy-9-methyl-5,6,7,12-tetrahydro-4(4′-methyl)phenylpyrimido[3′,4′:5,4] cyclohept [b] indole (4a)

Yield: 0.220 g [70%], Mp: 248ºC;IR (KBr) [v_maxcm^-1]: 3325,3757,2924,1620,1543,1435,1350,1237, 1141,918, 802, 763, 671, 524; ¹H-NMR (CDC1₃) δ (ppm): 2.38(s,3H, C₉CH₃) 2.50(s,3H, C₄-CH₃) 2.07-3.13(m, 6H, C₅-H₂, C₆-H₂,C₇-H₂) 7.09-759 (m, 7H, C₈H,C₁₀-H, C₁₁-H C₂′-H, C₃′-H, C₅′-H, C₆′-H ) 7.37 (s, 1H, C₂-OH), 11.30(s, 1H indole NH). Anal. calcd for C₂₃H₂₁N₃O:C, 77.720%, H,5.955%; N, 11.82%.Found: C,77.70%, H,5.75%, N,11.62%.

2-hydroxy-9-methyl-5,6,7,12-tetrahydro-4(4′-methyl)phenylpyrimido[3′,4′:5,4] cyclohept [b] indole (4b)

Yield: 0.204 g [65%], Mp: 250ºC; IR (KBr) [v_maxcm^-1]: 3412, 2923, 1706, 1620, 1517, 1443, 1331, 1230, 802; ¹H-NMR (CDC1₃) δ (ppm)=2.26 s, 3H, C₁₀ -CH₃) 2.10 (s, 3H, C₄-CH₃) 2.05-2.99 (m, 6H, C₅-H₂, C₆-H₂, C₇-H₂) 6.96-7.52 (m, 7H, C₈H,C₉-H, C₁₁-H C₂′-H, C₃′-H, C₅′-H, C₆′-H) 7.260 (s, 1H, C₂-OH), 8.78 (s, 1H indole NH). Anal. calcd for C₂₃H₂₁N₃O: C, 77.720%, H, 5.955%, N, 11.82%. Found: C, 77.70%, H, 5.75%, N, 11.52%.

2-hydroxy-9-methyl-5,6,7,12-tetrahydro-4(4′-methyl)phenylpyrimido[3′,4′:5,4] cyclohept [b] indole (4c)

Yield:0.208 g [65%], Mp: 248ºC; IR (KBr) [v_maxcm^-1]: 3447, 2924, 1621, 1444, 1330, 1211, 802, 743, 620; ¹H-NMR (CDC1₃) δ (ppm)=2.35 (s,3H, C₁₁ -CH₃) 2.20 (s,3H, C₄-CH₃) 2.10-2.99 (m, 6H, C₅-H₂, C₆-H₂, C₇-H₂) 7.02-7.86 (m, 7H, C₈H, C₉-H, C₁₀-H C₂′-H, C₃′-H, C₅′-H, C₆′-H) 6.310 (s,1H, C₂-OH), 9.22 (s, 1H indole NH). Anal. calcd for C₂₃H₂₁N₃O: C, 77.720%, H, 5.955%, N, 11.82%. Found: C, 77.70%, H, 5.75%, N, 11.62%.

2-hydroxy-4(4′-methyl)phenyl-5,6,7,12-tetrohydropyrimidocyclohept [b] indole (4d)

Yield:0.205 g [65%], Mp: 252ºC; IR (KBr) [v_maxcm^-1]: 3308, 3152, 2289, 1617, 1545, 1445, 1328, 1206, 1051, 984, 802, 582, ¹H-NMR (CDC1₃) δ (ppm)=2.38 (s, 3H, C₄CH₃) 2.163-2.98 (m, 6H, C₅-H₂, C₆-H₂, C₇-H₂) 6.27 (s, 1H, C₂-OH), 6.91-7.64, (m, 7H, C₈-H, C₉-H, C₁₀-H, C₁₁-H,C₂′-H, C₃′-H, C₅′-H, C₆′-H) 8.23 (s, 1H indole NH). Anal. calcd for C₂₃H₁₉N₃O, C, 77.720%, H, 5.955%, N, 11.82%. Found: C, 77.70%, H, 5.75%, N, 11.62%.

General procedure for preparation of 2-amino-5,6,7,12-tetra-hydro-4(4′-methyl)phenyl-pyrimido-[3′,4′:5,4]-cyclohept [b] indole (5a-5d)

A mixture of respective 2-(4′-methyl)benzylidine-1-oxo-3,4,5,10-tetrahydrocyclohept [b] indole (0.001 mol) and guanidine nitrate (0.001 mol) in presence of sodium methoxide in dry ethanol was refluxed on water bath for 18 hours. The excess solvent was removed by evaporation and the reaction mixture was poured into anice. The precipitate obtained was filtered, dried and purified by column, eluting with petroleum ether and ethyl acetate mixture (65: 35) to yield the respective 2-amino-5,6,7,12-tetrahydro-4-(4′-methyl)phenylpyrimido[3′,4′:5,4] cyclohept [b] indole(5a-5d).

2-amino-9-methyl-5,6,7,12-tetrahydro-4(4′-methyl)phenylpyrimido[3′,4′:5,4]cyclohept [b] indole (5a)

Yield:0.225g [65%], Mp: 248ºC;IR (KBr) [v_maxcm^-1]: 3325,3324,1620,1541,1427,1257, 802; ¹H-NMR (CDC1₃) δ (ppm)= 2.38(s,3H, C₉-CH₃), 2.35(s,3H, C₄′-CH₃), 2.08-3.13 (m, 6H, C₅-H₂, C₆-H₂, C₇-H₂) 7.08-7.59(m, 7H, C₈-H, C₁₀-H, C₁₁-H,C₂′-H, C₃′-H, C₅′-H, C₆′-H) 7.26 (s, 2H,C₂-NH₂) 11.31 (s, 1H indole NH).Anal. calcd for C₂₃H₂₂N₄: C, 77.965%, H, 6.2604%, N, 15.817%. Found: C, 15.817%, H,6.10%, N, 15.71%.

2-amino-10-methyl-5,6,7,12-tetrahydro-4(4′-methyl)phenylpyrimido[3′,4′:5,4]cyclohept [b] indole (5b)

Yield: 0.225 g [62%], Mp: 246ºC;IR (KBr) [v_max cm^-1]: 3441,2920,1617,1544,1443,133, 1213,1040, 803. ¹H-NMR (CDC1₃) δ (ppm)=2.38 (s,3H,C₁₀CH₃) 2.73 (s, 3H, C₄-CH₃) 2.81-2.87(m, 2H, C₅-H₂,) 3.11-316(m, 2H, C₆-H₂),3.42-347 (m,2H, C₇-H₂)6.79-7.48(m, 7H, C₈-H, C₉-H, C₁₁-H, C₂′-H, C₃′-H, C₅′-H, C₆′-H),7.26 (s, 2H, C₂-NH₂),9.57(s, 1H-C₁₂, indole NH). Anal. calcd for C₂₃H₂₂N₄: C,77.965%, H, 6.2604%, N, 15.817%. Found: C, 15.817%, H, 6.10%, N, 15.71%.

2-amino-11-methyl-5,6,7,12-tetrahydro-4(4′-methyl)phenylpyrimido[3′,4′:5,4]cyclohept [b] indole (5c)

Yield: 0.225 g [62%], Mp: 244ºC; IR (KBr) [v_maxcm^-1]: 3432,2920,1617,1542,1444, 1333, 1201,1038,939,819,739,576;¹H-NMR (CDC1₃) δ (ppm)=22.42(s,3H, C₁₁CH₃), 2.57(s,3H, C₄-CH₃), 2.02(m, 2H, C₅-H₂), 2.85-2.89(m, 2H,C₆-H₂),3.142-318(m, 2H, C₇-H₂),7.26 (s, 2H, C₂-NH₂), 7.01-7.61(m, 7H, C₈-H, C₉-H, C₁₁-H, C₂′-H, C₃′-H, C₅′-H, C₆′-H ), 9.52 (s, 1H, C₁₂ indole NH). Anal. calcd for C₂₃H₂₂N₄: C,77.965%, H, 6.2604%, N, 15.817%. Found: C, 77.817%, H, 6.10%\;N, 15.761%.

2-amino-4(4′-methyl)phenyl-5,6,7,12-tetrohydropyrimidocyclohept [b] indole (5d)

Yield: 0.260 g [63%], Mp: 243ºC;IR (KBr) [v_maxcm^-1]: 3291,2929,1618,1541,1444,1329, 1203,1100,1041,802,740,628,584; ¹H-NMR (CDC1₃) δ (ppm)=2.42(s,3H, C₄ ′-CH₃),2.03-2.10 (m,2H, C₅-H₂),2.86-2.90(m, 2H, C₆-H₂),3.15-3.19(m,2H, C₇-H₂),7.26 (s 2H, C₂NH₂)7.09-7.61 (m,7H, C₈-H, C₉-H,C₁₀-H, C₁₁-H C₂′-H, C₃′-H, C₅′-H,C₆′-H) 9.51(s, 1H,C₁₂ indole NH). Anal. calcd for C₂₂H₂₀N₄: C, 77.620%, H, 5.9291%, N, 16.458%. Found:C, 77.52%, H, 5.89%, N, 16.34%.

Conclusion

In conclusion 2-hydroxy-4-(4′-methyl)phenyl-5,6,7,12-tetrahydrocyclohept [b] indole(4a-d)and 2-amino-4-(4′-methyl)phenyl-5,6,7,12-tetrahydrocyclohept [b] indole(5a-d)have beensynthesized from the newly developed synthon 2-(4′-methyl)benzylidene-7-methyl-1-oxo-3,4,5,10-tetrahydrocyclohept [b] indole(3a -d) by reacting with the reagent urea and guanidine nitrate.

From our results on the biological activity of the cyclohept [b] indole derivatives, it was found that the compound (I) 2-hydroxy-4-(4′-methyl)phenyl-5,6,7,12-tetrahydropyrimidocyclohept [b] indole(4d) found better activity against the organism.

A. baumanii and compound(2) 2-amino-4-(4′-methyl)-phenyl-5,6,7,12-tetrahydrocyclohept [b] indole(5d) showed better activity against the organism Aeromonas hydrophilla and A. baumanii,moderate activity against Thiobacillus thidurane.

2-amino-4(4′-methyl)phenyl-5,6,7,12-tetrahydropyrimidocyclohept [b] indole(5d) were found better activity against the organism A. hydrophilla.

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