INTRODUCTION:

Non steroidal anti-inflammatory agents continue to be one of the most widely used groups of therapeutic agents. They are used for the treatment of inflammation including pain releasing, antipyretic and rheumatoid arthritis. With the greater life expectancy, it is not surprising that the development of newer NSAIDs continues at a rapid pace. Almost all the NSAIDs under clinical usage are highly acidic in nature and suffer from a common drawback of gastrointestinal toxicity¹.

Indole alkaloids have been proved to be medicinally important natural compounds . Indole ring constitutes an important template for drug design such as the classical NSAIDs indomethacin and indoxole. Indole derivatives have been reported to possess promising biological activities including analgesic², antipyretic³, antifungal⁴, anti-inflammatory^5-7, anthelmintic⁸, cardiovascular⁹, anticonvulsant^10-11, antimicrobial^12-13 and selective COX-2 inhibitory activities^14-17.Thus the efficient synthesis of novel substituted indole derivative compounds still represent highly pursued target.

The area of design and synthesis of novel NSAIDs is being explored for drugs with better efficacy and safety profile. Diarylheterocycle class of compounds has been investigated extensively as COX-2 inhibitors. In contrast, relatively few reports document structural modifications of the existing NSAIDs into better drugs. Thus we decided to explore indole nucleus of indomethacin (NSAID) for structural modifications in order to produce potential anti-inflammatory agents.

Moreover, pyrazoline derivatives have also been reported to possess potent anti-inflammatory activity^18-20. With the view to develop better anti-inflammatory agents we have therefore synthesized some indole derivatives possessing pyrazoline moiety.

EXPERIMENTAL SECTION:

All the melting points were taken in open capillary tubes and the values reported are uncorrected. UV Spectra were recorded on Schimadzu 1700 UV-VIS spectrophotometer. IR Spectra were recorded on Schimadzu FTIR 8400 S using KBr discs. ¹H NMR Spectral study was done using CDCl₃ as solvent on BRUKER Spectrospin 200. Mass Spectral analysis was done in HR Micro Mass QP instrument (Waters).

The purity of the compounds was checked by TLC, using plates coated with Silica gel G. Benzene: toluene (1: 1) mixture was used as mobile phase.

EXPERIMENTAL PROCEDURE:

Synthesis of 3-[(3-chloro-4-fluoro phenyl)-hydrazono]-4-phenyl-butan-2-one (1)

To a vigorously stirred solution of 4.4 gm of ethyl-α-benzylacetoacetate in 5 ml of absolute ethanol, added a solution of 0.9 gm NaOH in 2.5 ml of water. Immediately after precipitation of the gelatinous mass, 50 ml of water was added and stirring was continued for 4 hours. Unreacted ester was removed by extracting with ether. To the above aqueous layer diazonium salt solution was added drop wise and stirring continued maintaining temperature at 0-5 ⁰C. After adding 10 gm of crystalline sodium acetate, stirred for 1 hour. The phenyl hydrazone precipitates quickly with the evolution of carbon dioxide. The solid product was filtered, washed with water, aqueous sodium carbonate solution and then again with water and dried. The crude product (1) is recrystalized from cyclohexane. Melting point was found 115⁰C. Yield was 69%.

Synthesis of 2-acetyl-6-chloro-5-fluoro-3-phenylindole (2)

3.04 gm (0.01 mol) of 3-[(3-chloro-4-fluoro phenyl)-hydrazono]-4-phenyl-butan 2-one was dissolved in absolute ethanol (about 30 ml) and dry HCl was passed for about 2 hours. The resulting solution was heated on a water bath for about 1 hour. Kept aside overnight. Then the product (2) was filtered, dried and recrystallized from ethanol. Melting point was found to be 205⁰C. Yield was 66%.

Synthesis of chalcones of 2-acetyl-6-chloro-5-fluoro-3-phenylindole (3a-g).

2-acetyl-6-chloro-5-fluoro-3-phenylindole (2.87 gm , 0.01 mol) in ethanol (15 ml) was stirred with sodium hydroxide (0.5 gm, in 5 ml water and 5 ml ethanol) for 10 minutes at room temperature. Then appropriate aromatic aldehyde (0.01 mol) (viz. benzaldehyde, furfuraldehyde, m-nitrobenzaldehyde, p-dimethylamino benzaldehyde, p-chloro benzaldehyde, p-anisaldehyde, 3, 4, 5-trimethoxy benzaldehyde) was added to it and stirring was continued for 2 hours. When yellow solid was separated, the product was collected by filtration, washed thoroughly with water until the washings are neutral to litmus and finally washed with little ethanol. It was then recrystallized from ethanol. The physical data of the synthesized compounds (3a-g) are reported in table

Synthesis of dibromo chalcones of 2-acetyl-6-chloro-5-fluoro-3-phenylindole (4a-g).

To a solution of chalcone (3a-g) (0.01mol) in acetic acid (15 ml) was added a solution of bromine in acetic acid (25 % w/v, 6.4 ml) under cooling with stirring. Yellow crystalline which separated after stirring for further 0.5 hour was collected by filtration, washed with acetic acid and finally with petroleum ether. The product was recrystallized from benzene and petroleum ether mixture (1:1 v/v). The physical data of the synthesized compounds (4a-g) are reported in table

Synthesis of 2-(1-phenyl-5-aryl-4, 5-dihydro-3-pyrazolyl)-6-chloro-5-fluoro-3-phenyl indoles (5a-g)

These compounds were synthesized by cyclisation of the appropriate chalcones (3a-g). Triethylamine (10 ml) was added to a mixture of 3a-g (0.01mol) and phenyl hydrazine (0.02mol) in absolute ethanol (50 ml), and the reaction mixture was refluxed for 8 to 10 hours on water bath. The contents were cooled, poured on to crushed ice and kept aside overnight. The resulting precipitate was filtered and recrystallized from ethanol, to give 5a-g (scheme- 1). The physical data of the synthesized compounds (5a-g) are reported in table

Synthesis of 2-(1-phenyl-5-aryl-3-pyrazolyl)-6-chloro-5-fluoro-3-phenyl indoles (6a-g)

Chalcone dibromide 4a-g (0.005 mol) and phenyl hydrazine (0.01 mol) were heated in triethanol amine (15 ml), when solution started bumping (10-15 minutes) heating was stopped. The reaction mixture was cooled, poured into ice cold water and recrystallized from acetic acid to give 6a-g (scheme- 2). The physical data of the synthesized compounds (6a-g) are reported in table

RESULTS AND DISCUSSION:

Phenyl hydrazone of 3-chloro-4-fluoroaniline (1) was synthesized by modified Japp- Klingemann reaction. The IR spectrum (1) has revealed the presence of C=N group exhibiting a strong absorption at 1570 cm^-1, absorption at 3273 cm^-1 due to N-H stretching and a strong absorption band at 1654 cm^-1 due to C=O stretching which were in accordance to the structure of hydrazone. On passing dry HCl gas for 1 hour, the hydrazone underwent Fischer-Indole cyclisation to give 2-acetyl-6-chloro-5-fluoro-3-phenylindole (2) with the disappearance of C=N peak at 1570 cm^-1 in IR spectrum 2. ¹HNMR spectrum 3, revealed N-H proton of indole at δ 9.4, 7 aromatic protons at δ 7.15 -7.57 and 3 aliphatic protons at δ 2.26, confirm the structure of compound 2. The structure of chalcone of 2-acetyl-6-chloro-5-fluoro-3-phenylindole (3a) has been confirmed by ¹HNMR spectrum 6. Appearance of two doublets at δ 6.8 and δ 7.8 characterize olefinic protons of chalcone. Mass spectral analysis of 3a further confirms the structure. Disappearance of these olefinic doublets and appearance of two doublets at δ 5.0 and δ 5.3 in spectrum 9 confirmed the structure of dibromo chalcone (4a). These two signals resonated at deshielding region due to the electronegative effect contributed by bromine attached to these carbons. Mass spectrum 10 further ascertained the structure of compound 4a. The 1HNMR spectrum 12 (compound 5a) exhibit a characteristic ABX pattern for the presence of two diastereotopic protons (non-equivalent) at C-4 and one proton at the C-5 position of pyrazoline. These protons appear as three doublets of doublets. They show double doublet from δ 2.6-2.7 (due to α-CH at C-4), double doublet from δ 3.4-3.5 (due to β-CH at C-4) and double doublet from δ 5.1-5.2 (due to proton present at C-5), each integrating for one proton. The aromatic resonance signal appears as a multiplet from δ 6.8-7.7 and a signal due to N-H proton of indole appears in the region of δ 8.9-9.3.

IR, NMR and Mass spectral data of 5a:

IR- 3440 (N-H str), 3061 (Ar H str), 1597 (C=N str), 1502 (C=C str), 1335 (C-F), 764 & 748 (C-H bending aromatic), 698 (C-Cl str), 550 (C-Br str). NMR- 8.9 (Br s, 1H, N-H), 6.8-7.7 (m, 17H, Ar-H), 5.1-5.2 (dd, 1H, C-5 pyrazoline), 3.4-3.5 (dd, 1H, C-4 pyrazoline), 2.6-2.7 (dd, 1H, C-4 pyrazoline). Mass- 488 (M+Na)

IR, NMR and Mass spectral data of 5b:

IR : 3280(N-H ,str.), 2960 (C-H , str., Alk), 1640 (C=N str.), 1480 (C=C , str.) , 1250 (C-F str.) , 1040 (C-O str.) , 680 (C-Cl str.). NMR- 8.7(s 1H N-H), 6.7-7.6 (m 15 H Ar-H), 5.1-5.2 (dd 1H C-5 pyrazoline), 3.3-3.4 (dd 1H, C-4 pyrazoline), 2.9 -3.0 (dd 1H C-4 pyrazoline). Mass: 456

IR, NMR and Mass spectral data of 5c:

IR: 3300 (N-H , str. ) , 2900 ( C-H , str. ) , 1640 ( C=N , str.), 1500 ( C-NO₂ , str. ) , 1450 ( C=C , str. ) , 1250 (C-F , str. ) , 850 ( C-H , bend , Ar. ) , 700 (C-Cl , str. ). NMR- 8.8 ( s , 1H , N-H ) , 7.3-8.1 (m , 16H ,Ar-H ) , 5.3-5.4 ( dd ,1H, C-5 pyrazoline ) , 3.4-3.5 ( dd , 1H , C-4 pyrazoline ) , 3.0-3.1 ( dd, 1H , C-4 pyrazoline ). Mass : 511

IR, NMR and Mass spectral data of compound 5d:

IR: 3300 ( N-H , str. ) , 3000 ( C-H , str. Ar. ) , 1650 ( C=N, str. ) , 1440 ( C=C , str. ) , 1300 ( C-N , str. , tert. ) , 1260 ( C-F , str. ) , 700 ( C-Cl , str. ). NMR- 9.0 ( s , 1H , N-H ) ,6.6-7.8 ( m ,16H , Ar-H ) , 5.1- 5.2 (dd , 1H ,C-5 pyrazoline ) , 3.3-3.4 (dd , 1H , C-4 pyrazoline ) , 2.8-2.9 ( dd , 1H , C-4 pyrazoline ) , 2.3 ( s , 6Hs , (CH₃ )₂ ). Mass: 509

IR, NMR and Mass spectral data of compound 5e:

IR: 3300 ( N-H , str. ) , 3040 ( C-H , str. , Ar. ) , 1640 ( C=N , str. ) , 1450 ( C=C , str. ) , 1250 ( C-F , str. ) , 700 ( C-Cl , str. ). NMR- 8.9 ( s , 1H , N-H ) , 7.3-7.7 (m , 16H , Ar-H ) , 5.3-5.4 ( dd , 1H , C-5 pyrazoline ) , 3.3-3.4 (dd , 1H , C-4 pyrazoline ) , 2.9-3.0 ( dd , 1H , C-4 pyrazoline ). Mass: 500.

IR, NMR and Mass spectral data of compound 5f:

IR: 3280 ( N-H , str.) , 2960 ( C-H , str. , Ar) , 1680 (C=N , str.), 1480 (C=C , str.) , 1250 ( C-O , str.) , 1010 (C-F , str. ) , 700 (C-Cl , str.). NMR- 8.7 (s , 1H , N-H) , 6.9-7.7 (m , 16Hs , Ar-H) , 5.1-5.2 (dd , 1H , C-5 pyrazoline ) , 3.6 (s , 3Hs , p-o-CH₃) , 3.4-3.5 (dd , 1H , C-4 pyrazoline ) , 3.0-3.1 (dd , 1H , C-4 pyrazoline). Mass : 496

IR, NMR and Mass spectral data of compound 5g:

IR: 3280 ( N-H , str. ) , 3040 ( C-H , str.Ar. ) , 1640 ( C=N , str. ) , 1480 ( C=C , str. ) , 1240 ( C-O , str. ) , 1010 ( C-F , str. ) , 700 ( C-Cl , str. ). NMR ( CDCl₃ , in δ ppm ) ; 8.8 ( s , 1H , N-H ) , 6.7-7.7 ( m , 14Hs , Ar-H ) , 5.2-5.3 ( dd , 1H , C-5 pyrazoline ) , 3.8 ( s , 6Hs , m-(OCH₃ )₂ ) , 3.7 ( s , 3Hs , p-OCH₃ ) , 3.3-3.4 ( dd , 1H , C-4 pyrazoline ) , 2.9-3.0 ( dd , 1H , C-4 pyrazoline ). Mass : 556.

IR, NMR and Mass spectral data of compound 6a:

IR- 3400 (N-H str), 2900 (Ar H str), 1600 (C=N str), 1500 (C=C str), 1340 (C-F), 770 (C-H bending aromatic), 700 (C-Cl str). NMR- 8.8-9.3 (Br s, 1H, N-H), 6.3-7.9 (m, 18H, Ar-H). Mass- 486 (M+Na).

IR, NMR and Mass spectral data of compound 6b:

IR : 3280 ( N-H , str. ) , 3030 ( C-H , str. ,Ar. ) , 1620 ( C=N , str. ) , 1480 ( C=C , str. ) , 1250 ( C-O , str. ) ,1020 ( C-F , str. ) , 710 ( C-Cl , str. ). NMR- 9.0 ( s , 1H , N-H ) , 6.8-8.0 ( m , 16H , Ar-H ). Mass : 454.

IR, NMR and Mass spectral data of compound 6c:

IR : 3300 ( N-H , str. ) , 2900 ( C-H , str. , Ar. ) , 1650 (C=N , str. ) , 1500 ( C-NO₂ , str. ) , 1450 ( C=C , str. ) , 1260 ( C-F , str. ) , 710 (C-Cl , str. ). NMR- 8.9 ( s , 1H , N-H ) , 7.5-8.4 ( m , 17H , Ar-H ). Mass : 509

IR, NMR and Mass spectral data of compound 6d:

IR : 3300 (N-H , str. ) , 3030 ( C-H , str. ) , 1650 ( C=N , str.) , 1420 ( C=C , str. ) , 1360 ( C-N , str. , tert. ) , 1250 ( C-F , str. ) , 700 ( C-Cl , str. ). NMR- 8.7 ( s , 1H , N-H ) , 6.8-7.9 (m , 17Hs ,Ar-H ) , 2.5 (s , 6Hs , N< ). Mass : 507

IR, NMR and Mass spectral data of compound 6e:

IR : 3300 ( N-H , str. ) , 3030 ( C-H , str. Ar. ) , 1640 ( C=N , str. ) , 1480 ( C=C , str. ) , 1250 ( C-F , str. ) , 700 ( C-Cl , str. ). NMR- 9.1 ( s , 1H , N-H ) , 7.3-8.4 (m , 17 Hs , Ar-H ). Mass : 498

IR, NMR and Mass spectral data of compound 6f:

IR : 3280 ( N-H , str. ) , 3050 ( C-H , str. ,Ar.) , 1640 ( C=N , str. ) , 1480 ( C=C , str. ) , 1160 ( C-O , str. ) , 1040 ( C-F , str. ) , 710 (C-Cl , str. ). NMR- 8.9 ( s , 1H , N-H ) , 7.1-8.3 ( m , 17 Hs , Ar-H ) , 3.4 ( s , 3Hs , p-OCH₃ ) . Mass : 494

IR, NMR and Mass spectral data of compound 6g:

IR : 3280 ( N-H , str. ) , 3040 ( C-H , str. Ar. ) , 1640 ( C=N , str. ) , 1480 ( C=C , str. ) , 1300 ( C-O , str. ) , 1240 ( C-F , str. ) , 750 ( C-Cl , str.). NMR- 9.1 ( s , 1H , N-H , str. ) , 6.8-7.9 ( m , 15Hs , Ar-H ) , 3.9 ( s , 6Hs ,m(OCH₃ )₂), 3.7 ( s , 3Hs , p-OCH₃ ). Mass : 554

Table- 1. Physical data of the synthesized compounds (5a-g)

Compound code	R	M.P (⁰C)	Yield (%)	Mol formula	Mol wt.
5a		130	62		466
5b		115	63		456
5c		190	54		511
5d		127	50		509
5e		145	64		500
5f		125	59		496
5g		138	61		556

Table- 2. Physical data of the synthesized compounds (6a-g)

Compound code	R	M.P (⁰C)	Yield (%)	Mol formula	Mol wt.
6a		134	70		464
6b		118	67		454
6c		180	58		509
6d		132	54		507
6e		147	68		498
6f		130	65		494
6g		142	69		554

REFERENCES:

1. Ronald Borne , Mark Levi , Norman Wilson , in :Williams , D.A. , Lemke , T. L. (Eds. ) , Foye’s Principles of Medicinal Chemistry , Lippincott Williams& Wilkins , Baltimore , MD 2008, pp. 954-1003

2. Kameyama , T. , Amanuma , F. , Okuyama , S. , Higuchi , S. , Aihara , H. , J Pharmacobiodyn 1985 , 8 , 477-486

3. Bredt , A. B. , Girey , G. J. , Cacer 1982 , 50 , 1430-1433

4. Sridhar , S. K. , Pandeya , S. N. , Bajpai , S. K. , Manjula , H. , Indian Drugs 1999 , 36, 412-414

5. Kumar , A. , Archana , Sharma , S. , Malik , N. , Sharma , P. , Kushik , K. , Indian J Chem 2004 , 43B , 1532-1536

6. Singh , N., Bhati , S. K. , Kumar , A. , Eur J Med Chem 2008 , 43 , 2597-2609

7. Radwan , M. A. A. , Ragab , E. A. , Sabry , N. M. , El-Shenawy, S. M. , Bioorg Med Chem 2007 , 15 , 3832-3841

8. Danilo Davyt , Walter Entz , Rafael Fernandez , Raŭl Mariezcurrena , Alvaro W. Mombrŭ , Jenny Sadaňa , J Nat Prod 1998 , 61 , 1560-1563

9. Kumar , A. , Saxena , K.K. , Gurtu , S. , Sinha , J.N. , Shanker , K. , Indian Drugs 1986 , 24 , 1-5

10. El-Gendy Adel , A. , Abdou Naida , A. , El-Taber , Z. S. , El-Banna Hosny , A. , Alexandria , J Pharm Sci 1997 , 7 , 99-103

11. Gitto , R. , De Luca , L. , Ferro , S. , Citraro , R. , De Sarro , G. , Costa , L. , Bioorg Med Chem 2009 , 17 , 1640-1647

12. Trivedi , B. , Shah , V. H. , J Indian Chem Soc 1993 , 70 , 645-648

13. Bhusare , S. R. , Shinde , A. B. , Pawar , R. P. ,Vibhute , Y. B. , Indian J Pharm Sci 2004 , 2 , 228-231

14. Guo , W. H. Z. , Yi , X. , Guo , C. , Chu , F. , Cheng , G. , Bioorg Med Chem 2003 , 11 , 5539-5544

15. Kalgutkar , A. S. , Crews , B. C., Rowlinson , S. W. , Marnett , A. B. , Kozak , K. R. , Remmel , R. P. , Proc Natl Acad Sci 2000 , 97 , 925-930

16. Hu , W. , Guo , Z. , Chu , F. , Bai , A. , Yi , X. , Cheng , G. , Li , J. , Bioorg Med Chem 2003 , 11 , 1153-1160

17. Caron , S. , Vazquez , E. , Stevens , R. W. , Nakao , K. , Koike , H. , Murata , Y. , J Org Chem 2003 , 68 , 4104-4107

18. Amir , M. , Kumar , H. , Khan , S. A. , Bioorg Med Chem Letters , 2008 , 18 , 918-922.

19. Amir , M. , Kumar , S. , Indian J Chem 2005 , 44B , 2532-2537

20. Gursoy , A. , Demirayak , S. , Capan , G. , Erol , K. , Vural , K. , Eur J Med Chem 2000 , 35 , 359-364.

Received on 01.09.2014 Modified on 19.09.2014

Asian J. Research Chem. 7(10): October- 2014; Page 882-887

*Corresponding Author E-mail: nirmal_th31@rediffmail.com

INTRODUCTION: