**2. Biological applications of benzimidazole-quinoline hybrids**

## **2.1 Anticancer activity**

Hranjec and co-workers developed the synthesis and biological characterisation of novel benzimidazo[1,2-*a*]quinoline-6-carbonitriles derivatives (**Figure 1**). The reaction was initiated by condensing 2-cyanomethylbenzimidazole with heteroaromatic aldehyde yielded acrylic substituted acrylonitriles. The photochemical dehydrocyclisation procedure was utilised to produce benzimidazo[1,2-*a*]quinoline-6-carbonitriles and heteroaromatic fluorenes. All the synthesised compounds were investigated for antiproliferative efficacy against five tumour cell lines such as HeLa, MiaPaCa-2, SW

*Current Development in the Synthesis of Benzimidazole-Quinoline Hybrid Analogues… DOI: http://dx.doi.org/10.5772/intechopen.108949*

620, MCF-7 and H460. Among them, compounds (**I)** and **(II)** showed good antiproliferative activity against all the cell lines with an IC50 range of 2–90 μM [34].

Perin *et al.* synthesised benzimidazo[1,2-*a*]quinolines and benzimidazo[1,2-*a*] quinolines-6-carbonitriles derivatives by the thermal reaction using sulfolane for dehydrohalogenation cyclisation at 280°C followed by UV/Vis spectroscopy (**Figure 2**). Out of all the synthesised compounds **(III), (IV), (V), (VI), (VII)** and **(VIII)** showed strong antiproliferative activity with IC50 range of 2–19 μM [35].

Further, Perin and co-workers have also synthesised amino-substituted cyclic benzimidazo[1,2-*a*]quinoline derivatives and tested *in vitro* for their antiproliferative, antibacterial and antiviral activities (**Figure 3**). Low to moderate yields of amide substituted cyclic derivatives were obtained by condensing acyl halides with an excess quantity of the corresponding amines in absolute dichloromethane. The antiproliferative activity of **(IX), (X)** and **(XI)** was found to be most promising with an IC50 value ranging between 0.48–4.1 μM against HeLa cell line and 0.24–0.69 μM against MCF7 cell line, and it also caused apoptosis in human cervical carcinoma HeLa cells at micromolar doses. Antiviral activity was observed in compounds **(XII), (XIII)** and **(XIV)** having a side chain at position-2 against the herpes simplex virus (HSV) with an EC50 value of 1.8–6.8 μM and human coronavirus with EC50 value of 4–12 μM. In addition, **(IX)** and **(X)** substituting an amide side chain position-6 of the tetracyclic skeleton were efficacious against *S. epidermidis* and *C. albicans* [36]*.*

Perin *et al.* synthesised 2-substituted benzimidazo[1,2-*a*]-quinoline derivatives by microwave-assisted amination of 2-chloro/fluorobenzo[4,5]imidazo[1,2-*a*]quinoline-6-carbonitrile precursors, which were prepared by photochemical dehydrogenation of non-fused *E*-2-(2-benzimidazolyl)-3-(4-halophenyl)acrylonitriles with 4 halobenzaldehyde (**Figure 4**). Furthermore, the antiproliferative efficacy of aminosubstituted derivatives was investigated. Compound **(XV)** showed prominent activity against HCT116 and H460 cells with IC50 values of 0.5 and 0.3 μM, respectively. The compounds **(XVI)** and **(XVII)** with the presence of cyclic tertiary amino substituent displayed excellent antiproliferative action against HCT116 and H460 cell lines with IC50 range of 0.06–0.3 μM [37].

**Figure 2.**

*Amino substituted benzo[4,5]imidazo[1,2-*a*]quinoline derivatives.*

**Figure 3.** *Benzo[4,5]imidazo[1,2-*a*]quinoline amide derivatives.*

#### **Figure 4***.*

*Benzo[4,5]imidazo[1,2-*a*]quinoline-6-carbonitrile derivatives.*

Tantawy *et al.* synthesised novel 2-(1*H*-benzo[*d*]imidazol-2-yl)quinoline-4 carboxylic acid derivatives by the reaction of 2-acetylimidazoles with isatin (**Figure 5**). Compounds **(XVIII), (XIX)** and **(XX)** displayed excellent *in vitro* antitumour activity with IC50 in the range of 12.7–16.13 μg/mL (percentage inhibition of 71.9–74.0%) against MCF7 breast cancer cell lines [38].

Shi and co-workers have designed and synthesised *N*-(2-phenyl-1*H*-benzo[*d*] imidazol-5-yl) quinolin-4-amine derivatives as potent inhibitors of VEGFR-2 (KDR) kinase (**Figure 6**). These derivatives were prepared by the condensation of 4 chloroquinoline with benzimidazole quinoline-4-amines. The synthesised compound **(XXI)** showed the most potent inhibitory activity against VEGFR-2 with IC50 value of 0.03 μM. Moreover, this compound also showed the highest antiproliferative activity against MCF-7 and Hep-G2 cell lines with IC50 values of 1.2 and 13.3 μM, respectively [39].

Brajsa *et al.* prepared 2-Imidazolinyl-substituted triaza-benzo[*c*]fluorenes derivatives from triaza-benzo[*c*]fluorenes using the Pinner reaction and tested for antitumour efficacy in 2D and 3D cell culture (**Figure 7**). The compound **(XXII)** showed the most prominent activity against PANC-1 and MDA-MB-231 cell lines with IC50 values of 1 and 0.2 μM, respectively [40].

Kuang *et al.* prepared a series of 3-(1*H*-benzimidazol-2-yl)quinoline-2(1*H*)-one analogues by coupling reaction of 2-oxo-quinoline-3-carbaldehyde with various *o*-phenylenediamines (**Figure 8**). The HepG2 tumour growth was effectively inhibited by **(XXIII)** with IC50 value of 8.45 μM in an *in vitro* antitumour experiment.

#### **Figure 5.**

*2-(1*H*-benzo[*d*]imidazol-2-yl)quinoline-4-carboxylic acid derivatives.*

*Current Development in the Synthesis of Benzimidazole-Quinoline Hybrid Analogues… DOI: http://dx.doi.org/10.5772/intechopen.108949*

#### **Figure 7.**

*2-(10-Bromopyrido[2*<sup>0</sup> *,3*<sup>0</sup> *4,5]imidazo[1,2-*a*]quinoline-2yl)-4,5-dihydro-1*H*-imidazol-3-ium chloride derivatives.*

**Figure 8.** *3-(1*H*-benzo[*d*]imidazol-2-yl)quinolin-2(1*H*)-one derivatives.*

#### **Figure 9.**

*2-Chloro-3-(5,6-dimethyl-1*H*-benzo[*d*]imidazol-2-yl)quinoline derivatives.*

In addition, the compound **(XXIV)** showed excellent antiproliferative activity against BEL-7402 with IC50 value of 9.06 μM [41].

Similarly, Kuang *et al.* further synthesised 2-chloro-3-(1*H*-benzo[*d*]imidazol-2-yl) quinoline derivatives as potent antitumour agents (**Figure 9**). *In vitro* antitumour assay findings revealed that some compounds had moderate to high inhibitory effects against HepG2, SK-OV-3, NCI-H460 and BEL-7404 tumour cells, as compared to 5-FU and cisplatin. In the HepG2 xenograft model, compound **(XXV)** effectively inhibited tumour growth with IC50 value 7.54 μM [42].

Macan and co-workers prepared 2-Fluoro-5-(1*H*-1,2,3-triazol-1-yl)benzo[4,5] imidazo[1,2-*a*]quinoline-6-carbonitrile derivatives *via* Huisgen 1,3-dipolar cycloaddition of the azide derivatives and the corresponding alkynes using Cu(OAc)2 as a catalyst (**Figure 10**). The presence of 3-chloropropyl functional group in compound **(XXVI)** and 2-hydroxyethyl side-chain in compound **(XXVII)** exhibited the most pronounced growth-inhibitory effect on colon cancer (HCT116) cells with IC50 value of 0.5 μM and 0.6 μM, respectively [43].

#### **Figure 10.**

*2-Fluoro-5-(1*H*-1,2,3-triazol-1-yl)benzo[4,5]imidazo[1,2-*a*]quinoline-6-carbonitrile derivatives.*

#### **Figure 11.**

*(*E*)-3-(5-(3-(4-(3-oxo-3-(pyridin-4-yl)prop-1-en-1-yl)phenyl)-1,2,4-thiadiazol-5-yl)-1*H*-benzo[*d*] imidazol-2-yl)quinoline-2(1*H*)-one derivatives.*

Pragathi and co-workers have synthesised a series of chalcone incorporated 2-quinoline-benzimidazole-1,2,4-thiadiazoles by aldol condensation (**Figure 11**). Synthesised compounds were examined for their anticancer activities against different cancer cell lines such as MCF-7, A549, Colo-205 and A2780. From all the investigated compounds, **(XXVIII)** showed excellent anticancer activities with IC50 range of 0.012–1.46 μM [44].

Gaikwad *et al.* developed a series of 1,2,3-triazole-based quinoline-benzimidazole hybrid scaffolds by a click reaction using the [3+2] azide-alkyne cycloaddition reaction using copper(I)Iodide in DMF (**Figure 12**). Synthesised compounds were screened against a panel of NCI-60 human cancer cell lines for in vitro cytotoxicity evaluation. The compound **(XXIX)** showed an excellent antiproliferative effect with a significant IC50 value of 0.59 μM against the human breast cancer BT-474 cell line [45].

#### **Figure 12.**

*3-(1*H*-benzo[*d*]imidazol-2-yl)-1-((1-(2,3,4-trimethoxybenzyl)-1H-1,2,3-triazol-4-yl)methyl)quinoin-2 (1*H*)-one derivatives.*

*Current Development in the Synthesis of Benzimidazole-Quinoline Hybrid Analogues… DOI: http://dx.doi.org/10.5772/intechopen.108949*

### **2.2 Antimicrobial activity**

Sonar *et al.* synthesised 4-((5-difluoromethoxy)-1*H-*benzo[*d*]imidazol-2-ylthio) methyl)tetrazolo[1,5-*a*]quinoines derivatives (**Figure 13**). These targeted molecules were synthesised by the conversion of 2-chloroquinoline-3-carbaldehyde to tetrazolo [1,5-*a*]quinoline-4-carbaldehyde after treatment with sodium azide, followed by reduction to the corresponding alcohol derivatives and conversion to chloride with thionyl chloride and coupling with 5-(difluoromethoxy)-1*H*-benzo[*d*]-imidazol-2 thiol. The compounds **(XXX), (XXXI), (XXXII), (XXXIII)** and **(XXXIV)** were evaluated for their antibacterial activity against Gram-positive (*B. subtilis* and *S. aureus)* and Gram-negative (*E. Coli* and *S. aboney*) microorganisms. The synthesised compounds demonstrated significant activity against all the bacteria with zone of inhibition ranging from 7 to 17 mm at MIC level of 10 mg/mL [46].

Chaudhari *et al.* synthesised 8-(1-alkyl/alkysulsulphonyl/alkoxycarbonylbenzimidazol-2ylmethoxy)-5-chloroquine derivatives (**Figure 14**). The first step was the reaction of 5-chloro-8-hydroxyquinoline with monochloroacetic acid methyl ester followed by hydrolysis to form 5-chloroquinolin-8-yl)oxy]acetic acid. Which was further reacted with *o*-phenylenediamine to obtain 8-[(1*H*-benzimidazol-2-yl) methoxy]-5-chloroquinoline. The final analogues were synthesised by the reaction of 8-[(1*H*-benzimidazol-2-yl)methoxy]-5-chloroquinoline with different electrophiles in the presence of an appropriate base. Synthesised compounds were tested for their antifungal activity, among them compound **(XXXV), (XXXVI), (XXXVII)** and **(XXXVIII)** showed good antifungal activity against *A. niger* MTCC282 with 18– 19 mm zone of inhibition at 50 μg/mL MIC. In addition, compound **(XXXIX)** showed potent antibacterial activity with 15 mm zone of inhibition (MIC, 25 μg/mL) against *S. aureus* MTCC-96 and *S. typhimurium* MTCC-98 [47].

Gowda *et al.* used one-step method to synthesise 2-(1*H-*benzimidazol-2-yl)-6 substituted thieno[2,3-*b*]quinoline derivatives (**Figure 15**). They introduced nucleophilic substitution reaction of 2-(chloromethyl)-1*H*-benzimidazole 2/2- (mercaptomethyl)-1*H*-benzimidazoles followed by the cyclisation with 2-mercaptoquinoline-3-carbaldehyde 1/2-chloroquinoline-3-carbaldehyde. The antibacterial activity of the synthesised compounds was tested *in vitro* against Gram-positive (*E. coli* and *S. aureus*) and Gram-negative (*P. aeruginosa* and *K. pneumoniae)* pathogens*.*

#### **Figure 13.**

*4-(((5-(Difluoromethoxy)-1*H*-benzo[*d*]imidazol-2-yl)thiomethyl)tetrazolo[1,5-*a*]quinoline derivatives.*

**Figure 14.** *8-((1*H*-benzo[*d*]imidazol-2-yl)methoxy)-5-chloroquinoline derivatives.*

**Figure 15.** *2-(1*H*-benzo[*d*]imidazo-2-yl)thieno[2,3-*b*]quinolines derivatives.*

Compounds **(XL), (XLI), (XLII)** and **(XLIII)** with the substitution of nitro group at the position-5 of benzimidazole ring showed highest MIC at 12.5 μg/mL [48].

Mungra *et al.* synthesised a new class of potent quinoline fused benzimidazole derivatives (**Figure 16**). The final compounds were prepared by the reaction of tetrazolo[1,5-*a*]quinoline-4-carbaldehyde with *o*-phenylenediamine by microwave irradiation. Compounds were further tested for their antimicrobial activity. Among all compounds, **(XLIV)** displayed excellent activity against Gram-positive bacteria *B. subtills* with MIC value of 100 μg/mL [49].

Garudachari *et al.* synthesised quinoline incorporated benzimidazole from aniline and isatin via the multistep process (**Figure 17**). These derivatives were synthesised by multi-component one-pot Doebner and Pfitzinger reaction. Newly synthesised compounds were tested *in vitro* for their antibacterial and antifungal activities. From them, compounds **(XLV), (XLVI), (XLVII)** and **(XLVIII)** showed significant antibacterial activity against *S. aureus* and *E. coli* with a zone of inhibition in the range of 10–16 mm at MIC value of 6.25 μg/mL. Compound **(XLIX)** was showed potent antifungal activity against *A. niger*, and *Penicillium sp.* with 12–15 mm zone of inhibition, and **(L), (LI)** and **(LII)** showed good antifungal activity against *A. niger* and *Penicillium sp.* at 6.25 μg/mL with 12–16 mm zone of inhibition [50].

De Souza *et al.* introduced well-known fluorescent benzoimidazo[1,2-*a*]quinoline derivatives with DNA binding and anticancer properties. Compounds were tested as bifunctional agents that could detect yeast biofilms on stainless steel surfaces and act as biocidal agents (**Figure 18**). The biocidal activity of benzimidazole compound

**Figure 16.**

*4-(1*H*-benzo[*d*]imidazol-2-yl)-7-methyltetrazolo[1,5-*a*]quinoline derivatives.*

**Figure 17.** *4-(1*H*-benzo[*d*]imidazol-2-yl)-2-(4-fluorophenyl)quinoline derivatives.*

*Current Development in the Synthesis of Benzimidazole-Quinoline Hybrid Analogues… DOI: http://dx.doi.org/10.5772/intechopen.108949*

#### **Figure 18.**

*2-((3-(Dimethylamino)propyl)amino)-7*a*,11*a*-dihydrobenzo[4,5]imidazo[1,2-*a*]quinoline-6-carbonitrile derivatives.*

**Figure 19.** *12*H*-benzo[4*<sup>0</sup> *,5*<sup>0</sup> *]imidazo[1*<sup>0</sup> *,2*<sup>0</sup> *:1,2]pyrrolo[3,4-*b*]quinoline derivatives.*

**(LIII)** against yeast cells and biofilms seemed promising. The compound showed significant activity against *C. Albicans* CA01 with MIC value of 4 μg/mL [51].

Villa *et al*. synthesised 12*H*-benzo[4<sup>0</sup> ,50 ]imidazo[1<sup>0</sup> ,20 :1,2]pyrrolo[3,4-*b*]quinoline derivatives using two different pathways (**Figure 19**). In the first path, titled analogues were prepared by the reaction of arylimines and 20 mol% of BF3O(C2H5)2 in dichloroethane. The arylimines were obtained by the reaction of benzimidazole carbaldehyde with arylamine in the presence of InCl3. However, another path was accomplished by a one-pot intramolecular Povarov reaction without isolating the intermediates. Among them, compound **(LIV)** significantly reduced the metabolic activity of *C. albicans* biofilms fungal cells at MIC value of 0.5 μg/mL [52].

El Faydy and co-workers synthesised 8-quinolinol analogues bearing a benzimidazole moiety by condensing 5-(carboxymethyl)-8-quinolinol with substituted *o*phenylenediamines in an acidic medium (**Figure 20**). The synthesised compounds were tested in vitro against two Gram-positive (*B. subtilis and S. aureus)* and two Gram-negative (*E. Ludwigii and E. coli)* microorganisms. The compound **(LV)** showed good antibacterial activity against all the microorganisms, with 28–42 mm zone of inhibition at MIC in the range of 10–20 μg/mL [53].

#### **2.3 Miscellaneous activity**

El-Feky *et al.* investigated the anti-inflammatory potential of several novel *N*-(substituted-phenyl)-2-(2-(6-fluoro-2(4-fluorophenyl)-quinoline-4-yl)-1*H*-

#### **Figure 21.**

*2-(2-(6-Fluoro-2-(4-fluorophenyl)quinolin-4-yl)-1*H*-benzo[*d*]imidazol-1-yl)-*N*-(4-methoxyphenyl) acetamide derivatives.*

benzimidazol-1-yl)acetamides derivatives by the reaction with 4-(1*H-*benzo[*d*]imidazol-2-yl)-6-fluoro-2-(4-fluorophenyl)quinoline with 2-chloro-*N*-arylacetamide (**Figure 21**). Synthesised compounds were investigated for their anti-inflammatory activity. Among them, the compound **(LVI)** showed the highest activity with 55 mg/kg dose (%) [54].

Madawali *et al.* synthesised novel 2-chloro-3-[3-(6-nitro-1*H*-benzimidazol-2-yl)- 1*H*-pyrazol-5-yl]quinolines derivatives from 2-chloro-3-[3-(6-nitro-1H-benzimidazol-2-yl)-4,5-dihydro-1H-pyrazol-5-yl]quinolines by dehydrogenation reaction (**Figure 22**). Among them, compounds **(LVII), (LVIII)** and **(LIX)** showed excellent anti-inflammatory activity with excellent % inhibition of denaturation 82.81, 82.35 and 82.81, respectively [55].

Ukrainets and co-workers synthesised benzimidazo-2-ylamides of 4-hydroxy-2 oxo-1,2-dihydroquinoline-3-carboxylic acids (**Figure 23**). The targeted compounds were prepared by the well-known reaction, which involved heating ethyl esters with 2-aminobenzimidazole. They were tested for their antituberculosis and antithyroid activities. Compounds **(LX)** and **(LXI)** showed the highest activity against *M. tuberculosis H37Rv* ATCC 27294 with MIC value of 1.56 μg/mL. Moreover, the compound **(LXII)** (1.46 nmol/l) showed higher antithyroid activity as compared to the standard drug Mercazolyl (1.63 nmol/l) against the triiodothyronine (T3) hormone [56].

Mantu *et al.* designed and synthesised 2-(1*H*-benzo[*d*]imidazol-1-yl)-*N*-(quinoline-8-yl)acetamide analogues from 2-chloro-*N*-(quinolin-8-yl)acetamide and imidazole

#### **Figure 22.**

*2-Chloro-3-[3-(6-nitro-1*H*-benzimidazol-2-yl)-4,5-dihydro-1*H*-pyrazol-5-yl]quinoline derivatives.*

*Current Development in the Synthesis of Benzimidazole-Quinoline Hybrid Analogues… DOI: http://dx.doi.org/10.5772/intechopen.108949*

**Figure 24.** *2-(1*H*-benzo[*d*]imidazol-1-yl)-*N*-(quinoline-8-yl)acetamide derivatives.*

#### **Figure 25.**

*7-Chloro-*N*-(3-(2-phenyl/ferrocenyl-5-(trifuoromethyl)-1*H*-benzo[*d*]imidazol-1-yl)propyl)quinolin-4-amine derivatives.*

derivatives (**Figure 24**). The synthesised derivatives were tested *in vitro* for anticancer and antimycobacterial activities. Among all hybrid compounds, **(LXIII)** showed good antitumour activity against Renal Cancer A498 (52.92 μM) and Breast Cancer MDA-MB-468 (56.54 μM). This compound also showed antimycobacterial activity against *M. tuberculosis H37Rv* with MIC >100 μM and IC90 value of 77 μg/mL [57].

Baartzes and co-workers synthesised phenyl-benzimidazole and ferrocenylbenzimidazoles fused aminoquinoline derivatives and evaluated their antiplasmodial activity (**Figure 25**). Out of all the synthesised hybrids analogues, phenyl **(LXIV)** and ferrocenyl **(LXV)** showed excellent antiplasmodial activity against multi-drug resistant K1 strains of the human malaria parasite at IC50 values of 0.151 and 0.283 μM, respectively. They were further assessed *in vivo* against *Plasmodium berghei* infected mice. Treatment with either compound decreased parasitemia, with **(LXV)** demonstrating superior activity [58].

Pomel *et al.* synthesised 7-chloro-4-(4-(5-fluoro-1*H*-benzo[*d*]imidazol-2-yl) phenoxy)quinoline derivatives by the reaction of 2-phenol-1*H*-6-fluorobenzimidazole and 4,7-dichloroquinoleine chloride. *T. b. gambiense*, a human parasite, was used *in vitro* to test antitrypanosomal activity (**Figure 26**). The compound **(LXVI)** showed the best *in vitro* activity with IC50 value of 1.98 μM, cytotoxicity CC50 value 10.56 μM and selective index (SI) was 5.3 [59].

Bharadwaj *et al.* synthesised benzimidazole-containing quinolinyl oxadiazoles from quinoline-4-carboxylic acid and benzimidazole hydrazide (**Figure 27**). These

**Figure 27.**

*2-(2-(5-Bromothiophen-2-yl)-1-methyl-1*H*-benzo[*d*]imidazol-5-yl)-5-(2-phenylquinolin-4-yl)-1,3,4 oxadiazole derivatives.*

derivatives were investigated for their antidiabetic, anticoagulant and antiplatelet activity. The anticoagulant activity showed by compound **(LXVII)** and **(LXVIII)** with IC50 values of 0.66 and 0.68 μg/mL, respectively. The compound **(LXVII)** also showed antiplatelet activity [60].

#### **2.4 Summary**

The study summarises the detailed literature review on recent advancements in synthesis and the pharmacological properties of benzimidazole-integrated quinoline hybrids. The most common and efficient approach for the synthesis of benzimidazole derivatives is the condensation reaction between *o*-Phenylenediamine and various carbonyl compounds. However, quinoline derivatives are basically synthesised by the Skraup reaction. It involves a reaction with aniline or a substituted aniline with glycerol in the presence of sulphuric acid, ferrous sulfate, and nitrobenzene. The result and discussion showed that benzimidazole-quinoline hybrids could display various biological activities such as anticancer, antimicrobial, anti-inflammatory, antimycobacterial, antiplasmodial, antitrypanosomal, anticoagulant and antithyroid activities. This established a new level of revolution for the synthesis of hybrid


#### **Table 1.**

*Biological activity of benzimidazole-quinoline hybrids.*

*Current Development in the Synthesis of Benzimidazole-Quinoline Hybrid Analogues… DOI: http://dx.doi.org/10.5772/intechopen.108949*

molecules. The benzimidazole-quinoline hybrids with the highest reported activities are listed in **Table 1**.
