Indian Journal of Chemistry Vol. 438 , January 2004 , pp. 174-179

Synthesis and antimicrobial activities of some imidazole substituted indoles

Kadriye Benkl i 1*, Seref Demirayakl, Nalan Gundogdu-Karaburun I, Nuri Kiraz2, Gokalp Iscan3 & Umit Ucucu 1

'Anadolu University, Faculty of Pharmacy, Department of Pharmaceutical Chemistry, 26470 Eskisehir, Turkey 20smangazi University, Faculty of Medicine, Department of Microbiology, 26100 Eskisehir. Turkey

3Anadolu Univers ity , Faculty of Pharmacy, Department of Microbio logy , 26470 Eski sehir, Turkey E-mail: kbenkli @anado lu .edu.tr

Received 22 No velliber 2002; accepted (revised) 6 October 2003

The compounds I -substituted 2-( imidazo l- I-yl )-3 -(4,5-diary limidazo l-2-y l) indo les 2, I-substituted 2-<imidazol-I-y l)-3-(phenal1lhro[9, I 0-dJimidazol-2-yl )indoles 3 and I-substituted 2-(imidazol-l-yl)-3-(be nzimidazol-2-yl)indo les 4 have been synthesized from I-substitllted 2-(imidazol-I-yl)-3-formy lindole 1. The structural e lucidation of the synthesi sed compounds has been performed by IR. IH NMR and mass spectroscopic data and ele mental analyses. Antimicrobial activities of the compounds are examined and notable antifungal activity is obtained fro m some o f the co mpounds as expected in compari­son with the control agent ketoconazole.

Imidazole and indole residues are probably the most well-known heterocycles which are common and im­pOl·tant feature of a variety of natural products and medicinal agents l

-6

. Compounds, carrying indole resi­due, exhibiting antibacterial and antifungal activity have been severally reported7

. '6 . Mitomycines are natural antibiotics bearing indole residue that are also anticancer compounds as DNA cross-linking agents l7

•

Also, there are many compounds in the literature bearing imidazole residue and possessing antibacterial and antifungal activities 18-26. Among those a group which is called azole group antifungals, takes atten­tion with its clinical usage and forms an important antifungal drug group effecting via aromatase inhibi­tion pathway i.e. k1etoconazole, c1otrimazole, micona­zole, tioconazole27 etc.

In consideration of these data, the goal of this study is to combine the two main structures, i.e. aforemen­tioned indole and imidazole residues, in order to de­velop a hybrid molecule and to test the antibacterial and antifungal activities of the newly synthesised compounds.

The compound I-substituted 2-(imidazol-I-yl)-3-(4,5-diarylimidazol-2-yl) 2/(phenanthro[9, 10- d]imid­azol-2-yl) 3/(benzimidazol-2-yl)indole 4 derivatives were prepared using the synthetic methods outlined in Scheme 1 Synthesis of the imidazole 2 and phenan­throimidazole 3 derivatives using I-substituted 2-(imidazol-l-yl)-3-formylindoles and appropriate 1,2-dicarbonyl compound have been performed according to the general method described in the literature28

. In

this method, an aldehyde and 1,2-dicarbonyl com­pounds in acetic acid were heated in the presence of ammonium acetate. Benzimidazole d .... rivatives 4 were prepared by reacting the I-substituted 2-(imidazol-l­yl)-3-formylindoles and 1,2-phenylenediamine. In this general method, 1,2-phenylenediamine and aldehyde bisulphite adducts were heated in melhanol 29

.

Spectroscopic methods confirmed the structures of the compounds. The characteristic stretching bands at about 3290-2460 cm- I originated from imidazoles ' N­H group were observed in the IR spectra of all com­pounds. Also this N-H group resonated in the I H NMR spectra at about 11.44-12.80 ppm as broad singlets. All the other IR absorption bands and NMR peaks characterising the compounds were obtained as expected.

Results and Discussion The ill vitro antibacterial activity results showed

that the most sensitive microorganism to the control antibiotic, chloramphenicol succinate, are all bacterial strains except Pseudomonas aeruginosa, and to the control antifungal, ketoconazole, sensitive organisms are Calldida albicans and Candida parapsilosis. In consideration of the results, we may conclude that some of the tested products have noticeable antifungal activities. The compound 2j with a MIC value equiva­lent to that of the standard, i.e. 32 /Jg/mL against E. coli, is the most significant compound when our compounds' antibacterial activity is concerned . How­ever, in known classic azole antifungals, imidazole

BENKLI el al.: SYNTHESIS OF IMIDAZOLE SUBSTITUTED INDOLES 175

Q + CICOCH2C1 a Q CI b W c .. ~ ) .. ..

N-H N-C N 0 I I \\ I R R 0 R

Q:JCCHO + [~ d .. W

CHO

§ N CI N § N N~ I I I lJN R H R

1

R'

R' N

0 eoc\ e 1 + ~

§ H

0 N N~ R'

I lJN R ~ R' 2

1 + e ca(~

~ N I § I ~

N N~ I I N R ~ 3

N~

~I'N~ I I I

§ H N N~ I I N R ~

f

4 1,3 and 4 R

a CH3

b C2HS

c C6HS

R R' R R' R R' 2a CH3 H 2e C2HS H 2i C6Hs H 2b CH, CH3 2f C2HS CH) 2j C6HS CH3

2c CH3 OCH 3 2g C2HS OCH) 2k C6Hs OCH3

2d CH1 CI 2h C2HS CI 21 C6HS CI

a: TrielhylaminerrHF b: AICI,/l60-170 a Ce: DMF/POCI 3 d: K 2CO)IDMF e: NH40Ac/AcOH f: (i) NaHSOiCHJOH/reflux, ( ii ) C6HsNOireflux

176 INDIAN J. CHEM .. SEC B. JANUARY 2004

residue is attached to another aromatic ring system via an alkyl chain to form the biofunctional group; appre­ciable activity should be obtained from our com­pounds although imidazole residue is directly attached to the indole ring system.

In our work COl/dido albical/s, COl/dido krusei al/d Calldida parapsilosis were used as fungi and the MIC values obtained against these fungi for the standard compound ketoconazole is found to be 2, 8 and 2 /Jg/mL respectively. As expected, the antifungal activ­ity results are much noteworthy than the antibacterial activity results , as it canies a I-substi tuted imidazole residue. Compound 4a, is found to be active as the standard compound ketoconazole against fungi tested. When this compound's structure is examined, (2-benzimidazolyl) residue is attached to 3rd position of l-methyl-2-(l-imidazolyl)indole nucleus, it can be seen that it has the smallest structure of its series.

The other compounds which should be considered as effective are 2a, 2f, 2k and 3b, i.e. 4,5-di(phenyl , 4-methylphenyl or 4-methoxyphenyl)imidazoles. On the other hand, phenanthroimidazole residue on com­pound 3b, should be considered as the ring isostere of 4,5-diphenylimidazole. It is also noteworthy that, our

compounds carrying chlorophenyl group are ineffec­tive in tautology with the chloroaryl group's role in azole group antifungals .

Experimental Section Melting points were determined by usi ng an Elec­

trothermal 9100 digital melting point: apparatus and are uncorrected. IR spectra were recorded on a Schi­madzu 435 lR spectrophotometer; and lH NMR spec­tra on a Bruker DPX 400 NMR spectrometer at 400 MHz in DMSO-ch using TMS as in ternal standard . Analyses for C, H, N were within 0.4 % of the theo­retical values. I-Substituted 2-chloro-3-formylindoles and I-substituted 2-(imidazol-I-yl)-3-formylindoles were prepared according to the literature method2

1.22

.

Some characteristics of the compounds are given in Table I.

I-Substituted 2-(imidazol-I-yl)-3-( 4,5-diarylimid­azol-2-yl)indoles 2 and I-substituted 2-(imidazol-I­yl)-3-(pbenanthro[9,IO-d]imidazol-2-yl)indoles 3. General procedure. The suitable I-substituted 2-(imidazol-l-yl)-3-formylindole I (5 mmoles), an ap­propriate benzil or 9, IO-phenanthrenequinone (5 mmoles) and ammonium acetate (5 mmoles) were

Table I -Some characteristics and antimicrobial activity testing results (as ~g/mL) of the compounds

Compd m.p. Yield Mol. formula A B C 0 E F G DC (0/0 )

2a 236 48 C27H2,Ns 250 250 250 500 500 16 15 8

2b 152 55 C29H2sNs 125 125 250 250 250 125 125 125

2c 245 62 C29H2SNs02 64 125 250 125 250 32 32 32

2d 227 56 C27H'9Ci2NS 64 500 250 250 250 64 125 125

2e 201 64 C2sH23NS 250 250 500 500 500 125 125 125

2f 101 70 C30HnNs 250 250 250 125 250 16 (; 16

2g 234 48 C30HnNs0 2 250 250 250 250 250 64 32 32

2h 217 52 C28H2,CI2Ns 125 125 125 250 250 125 250 250

2i 253 61 C32H23NS 250 250 250 500 250 125 250 250

2j 112 72 C34H27NS 32 64 250 64 250 64 125 125

2k 130 70 CJ4HnNs02 125 125 250 250 250 64 16 64

21 188 68 CJ2H2,Ci2Ns 250 250 250 250 250 125 250 250

3a 281 44 C27H'9NS 125 125 250 250 250 125 250 250

3b 317 60 C28H2,Ns 250 250 500 250 250 32 16 32

3c 178 58 C32Hz,Ns 250 250 250 250 250 250 250 250

4a 264 72 C'9H,sNs 125 250 250 250 250 2 4 I

4b 160 65 CzoH17Ns 250 500 250 250 250 16 16 16

4c 282 56 C24 H17Ns 125 500 250 250 250 16 16 16

Chloramphenicol succinate 32 4 125 16 32 Ketoconazole 2 4 4 A: E. coli B: S. aI/reus C: P. aerogillosa 0: P. vulgaris E: S. ryphimuriulll F: C. albicalls H: C. krusei G: C. parapsi-losis

BENKLI el al.: SYNTHESIS OF IMIDAZOLE SUBSTITUTED INDOLES 177

refluxed in acetic acid for 2 hr. The mixture was poured in ice-water and neutralised with ammonium hydroxide. The precipitate was filtered and washed with water and crystallised from ethanol.

2a: IR(KSr, em-I): 3210-2S12(N-H), 1608-ISI3(C=N, C=C); IH NMR : 8 3.2S(3H, s, N-CH) , 6.8S-7.42(15H , m, Ar-H and imidazole-H), 7.78(1 H, s, imidazole-H), 8.4S( 1 H, d, 1=7.78 Hz, imidazole­H), 11.43(1 H, s, N-H).

2b: IR(KSr, em-I): 3200-2S10(N-H), 160S-1518(C=N, C=C); IH NMR: 8 1.64(6H, s, CHJ ) ,

3.6S(3H, s, N-CH), 6.SS(4H, d, 1=8.45 Hz, Ar-H), 7.16-7.49(9H, m, Ar-H and imidazole-H), 7.78(1 H, s, imidazole-H), 8.73(1 H, d, 1=7.71 Hz, imidazole-H) , 11.39(1H, s, N-H).

2c: IR(KSr, em-I) : 3190-2S24(N-H), 1600-IS08(C=N, C=C); IH NMR: 8 3.8S(6H, s, OCH3) ,

3.98(3H, s, N-CH ) , 6.87(4H, d, 1=8.75 Hz, Ar-H) , 7.23-7.46(9H, m, Ar-H and imidazole-H), 7.84(1 H, s, imidazole-H), 8.66(IH, d, 1=7.7S Hz, imidazole-H), 11.44( I H, s, N-H).

2d: lR(KSr, em-I): 3220-2490(N-H), 160S­ISOO(C=N, C=C); IH NMR: 8 3.88(3H, s, N-CH J ) ,

6.89(4H, d, 1=8.77 Hz, Ar-H), 7.33-7.47(9H, m, Ar-H and imidazole-H), 7.86(lH , s, imidazole-H), 8.57(IH, d, 1=7.76 Hz, imidazole-H), 11.47(IH, s, N-H) .

2e: lR(KSr, em-I): 3208-2S06(N-H), 160S-ISIS (C=N, C=C); IH NMR: 8 1.36(3H, t, N-CH2-CH3), 3.91(2H, g, N-CH2-CH) , 6.79-7.48(1SH, m, Ar-H and imidazole-H), 7.81 (I H, s, imidazole-H), 8.S2( I H, d, 1=7.78 Hz, imidazole-H), 11.45(IH, s, N-H).

2f: IR(KSr, em-I): 3220-2516(N-H), 1608-IS04(C=N, C=C); IH NMR: 8 1.36(3H, t, N-CHr CH), 1.84(6H , S, CH3), 3.97(2H, g, N-CHrCH3), 6.79(4H, d, 1=8.70 Hz, Ar-H), 7.26-7.44(9H, m, Ar-H and imidazole-H), 7.78(1 H, s, imidazole-H), 8.68( I H, d, 1=7.76 Hz, imidazole-H) , 11.38(1 H, s, N-H) .

2g: IR(KSr, em-I) : 3200-2S00(N-H), 160S­ISOO(C=N, C=C); IH NMR: 8 1.3S(3H, t, N-CHr CH3), 3.84(6H, s, OCH3), 3.99(2H, g, N-CH2-CH3), 6.88(4H, d, 1=8.70 Hz, Ar-H), 7.28-7.44(9H, m, Ar-H and imidazole-H), 7.80(1 H, s, imidazole-H), 8.6S(1 H, d, 1=7.78 Hz, imidazole-H), II.4S(1H, s, N-H) .

2h: IR(KSr, em-I): 3200-2S10(N-H), 1605-ISOO(C=N, C=C); IH NMR: 8 1.35(3H, t, N-CHr CH3), 3.93(2H, g, N-CHrCH3), 6.88(4H, d, 1=8.84 Hz, Ar-H), 7.28-7 .48(9H, m, Ar-H and imidazole-H), 7.86(1H, s, imidazole-H), 8.7S(1 H, d, 1=7.68 Hz, imi­dazole-H), 11.46( 1 H, s, N-H).

2i: lR(KSr, em-I) : 3210-242S(N-H), 1610-1538(C=N, C=C); IH NMR: 8 6.63-7.2S(19H, m, Ar-

H), 8.10(1 H, s, imidazole-H), 8.57(2H, d, 1=7.22 Hz, imidazole-H), 11.39( I H, s, N-H) .

2j: IR(KBr, em-I): 3250-2455(N-H), 1600-1530(C=N, C=C); I H NMR: 8 1.56 and I.S8(6H , two S, -CH3), 6.66-7.44(17H, m, Ar-H), 8.16(IH, s, imida­zole-H) , 8.69(2H, d, 1=7.34 Hz, imidazole-H), 11.49( I H, s, N-H) .

2k: IR(KSr, em-I): 32S0-2460(N-H), 1615-IS40(C=N, C=C); IH NMR: 83 .73 and 3.7S(6H, two s, OCH3), 6.76-7.58(17H, m, Ar-H), 8.13(1 H, s, imi­dazole-H), 8.6S(2H, d, 1=7.23 Hz, imidazole-H), 11.46(1 H, s, N-H).

21: IR(KSr, em-I): 32S0-2460(N-H), 161S-IS40(C=N, C=C); IH NMR: 8 6.74-7.SS(l7H, m, Ar­H), 8.16(1H, s, imidazole-H), 8.67(2H, d, 1,=7.42 Hz, imidazole-H), II.4S( I H, s, N-H).

3a: IR(KSr, em-I): 3240-2460(N-H), IS8S­IS80(C=N, C=C); IH NMR: 8 3.34(3H, s, N-CH3), 7.15-7 .66(9H , m, Ar-H , imjdazole-H), 7.88(1H, s, imidazole-H), 8.33-8.60(3H, m, phenanthrene-H, imi­dazole-H), 8.71-8.86(2H, m, phenanthrene-H, imida­zole-H), 11.4S(1 H, s, N-H).

3b: lR(KBr, em-I): 32S0-2460(N-H), 161S-1575(C=N, C=C); IH NMR: 8 1.23(3H, t, N-CH2-CH3), 3.99(2H, g, N-CH2-CH3) , 7.16-7.64(9H, m, Ar­H, imidazole-H), 8.10-8.12(2H, m, phenanthrene- H, imidazole-H), 8.38-8.47(2H, m, phenanthrene-H, imi­dazole-H) , 8.69-8.75(2H, m, phenanthrene-H, imida­zole-H), 12.80(1 H, s, N-H) ; EI-MS: mlz 427.22(M+), 40.99( 100%).

3c: IR(KSr, em-I): 3278-2470(N-H), 1615-IS83(C=N, C=C); IH NMR : 8 6.86-7.64(14H, m, Ar­H, imidazole-H), 8.10-8.12(2H, m, phenanthrene-H , imidazole-H), 8.38-8.47(2H, m, phenanthrene-H, imi­dazole-H), 8.69-8 .7S(2H, m, phenanthrene-H, imida­zole-H), 12.80( I H, s, N-H) .

I-Substituted 2-Cimidazol-I-yl)-3-(benzimidazol-2-yl)indoles 4. The suitable I-substituted 2-(imidazol­l-yl)-3-formylindoles I (S mmoles), 1,2-phenylene­diamine (7 mmoles) and sodium bisulphite (7 mmoles) were refluxed in methanol for 6 hr. The sol­vent was evaporated and nitrobenzene was added to the medium and refluxed for 30 min . Diluted HCI was added to the mixture and extracted with diethyl ether. Water-phase was neutralised by NH3 and the residue was filtered and crystallised from toluene.

4a: IR(KSr, em-I) : 3180-2496(N-H). 1617-lS7S(C=N, C=C); IH NMR: 8 2.S8(3H. s, N -CH,). 7.22-7.4S(8H, m, Ar-H), 7.S7(1H, bs, imidazole-H ), 7.88(1H, s, imidazole-H) , 8.8S(lH, d, 1=7.S8 Hz, imi­dazole-H), II.S4(lH, s, N-H) .

178 INDIAN J. CHEM., SEC B, JANUARY 2004

4b: IR(KBr, cm" ): 3200-2500(N-H), 1615-1575(C=N, C=C); 'H NMR: 0 1.39(3H, t, N-CHr CII), 3.99(2H, g, N-CHr CH ), 7.24-7.48(8H, m, Ar­H), 7 .53(1 H, bs, imidazole-H), 7.85(1 H, s, imidazole­H), 8.81 (I H, d, J=7.5 8 Hz, imidazole-H) , 11.50(1 H, s, N-H).

4c: IR(KBr, cnf'): 3290-2500(N-H), 1615-1575(C=N, C=C); ' H NMR: 0 6.90-7.43(13H, m, Ar­H), 7.68(1 H, s, imidazole-H), 7.70(1 H, s, imidazole­H), 8.23(1 H, d , J=6.83 Hz, imidazole-H) , 11.44( I H, s, N-H) ; EI-MS: mlz 374.54(M+), 77 .02(100%).

Antimicrobial activity Antimicrobial susceptibilty tests were done using

micro- and macro-broth dilution methods. The follow­ing were used as test bacteria in microdilution meth­ods: Escherichia coli (ATCC 25922), Staphylococcl/s aureus (ATCC 6538), Pseudolllollas aerugillosa (ATCC 27853), Proteus vulgaris (N RRL B-123) and Sa 1111 011. ella typhillluriulII (NRRL B-4420). The com­pounds were evaluated against Calldida albicolIs , Calldida krusei and Candida parapsilosis (Clinical Isolate, Osmangazi University , Facul ty of Medicine, Eskisehir, Turkey) using macrobroth d iluti on method

and results are given in Table I as Ilg/mL. Microbroth Dilutioll Methods. Micro-diluti on broth

susceptibility assaio was used for the antibacterial evaluation of the compounds. Stock solutions of com­pounds 2a-4c were prepared in DMSO (Carlo-Erba). Dilution series were prepared from I mg/mL to 0.5 ).lg/mL in steril e di stilled water in micro-test tubes fro m where they were transferred to 96-well mi cro­titer plates (Brand). O verni gh t grown bacterial sus­pensions in double strength Mueller-Hinton broth (Merck) was standard ized to approx imately 108

CFU/mL (using Mc Farland No: 0.5) . 100)1L of each bacterial suspension was then added to each well. The last row containing only the serial dilutions of antim­icrobial agent without microorgani sm was used as

negative control. After incubation at 37°C for 24 hr the first well without turbidity was determined as the minimal inhibition concentration (M IC). Chloram­phenicol succinate was used as standard antibacterial agent.

Macrobroth Dilution Method. Testing was per­formed according to the gu idelines of NCCLS docu­ment M27-A. Candida strai ns were subcultured twice on Sabouraud dextrose agar (Oxoid) plates and were incubated at 35°C for 24 hr to ensure optimal growth prior to testing. Stock solutions of compounds were prepared in 100% dimethyl sulphoxide. Stock solu-

tions of the compounds were then diluted with RPM I 1640 medium (with I-glutamine but without bicarbon­ate; Sigma Chemical Co., St. Louis, Mo.) buffered to pH 7.0 with 0.165 M morpholinopropanesulfonic ac id (M OPS ; Sigma) . The final concentration ranges used

were 0 .25 to 250 Ilg/mL for all compounds. Testing was performed in 96-well round-bottom microtitrat ion plates. Yeast inocula were prepared in sterile water and were diluted in RPMl 1640 medium to give a fi­nal inoculum concentration of approximately 5x I 0" to

2.5x I 03 blastoconidiaimL. The plates were incubated at 35°C, and end-points were read visually after 48 hr. The MIC of the compounds was defined , as the low­est concentration at which there was 80% inhibiti on of growth compared with the g row th for a drug-free contro l 3'.

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