molecules Article Cytotoxicity and Antioxidant Potential of Novel 2-(2-((1H-indol-5yl)methylene)-hydrazinyl)-thiazole Derivatives Adriana Grozav 1, Ioan-Dan Porumb 2, Luiza Ioana G˘ain˘a 2,*, Lorena Filip 3,* and Daniela Hanganu 4 1 Department of Organic Chemistry, Faculty of Pharmacy, “Iuliu Ha¸tieganu”University of Medicine and Pharmacy, 8 Victor Babes, Cluj-Napoca RO-400012, Romania; [email protected] 2 Research Center on Fundamental and Applied Heterochemistry, Faculty of Chemistry and Chemical Engineering, “Babe¸s-Bolyai”,University, M. Kogalniceanu 1, Cluj-Napoca RO-400028, Romania; [email protected] 3 Department of Bromatology, Hygiene, Nutrition, Faculty of Pharmacy, “Iuliu Ha¸tieganu”University of Medicine and Pharmacy, 8 Victor Babes, Cluj-Napoca RO-400012, Romania 4 Department of Pharmacognosy Faculty of Pharmacy, “Iuliu Ha¸tieganu”University of Medicine and Pharmacy, 8 Victor Babes, Cluj-Napoca RO-400012, Romania; [email protected] * Correspondences: [email protected] (L.I.G.); lfi[email protected] (L.F.); Tel.: +40-264-593-833 (L.I.G.); Fax: +40-264-590-818 (L.I.G.) Academic Editor: Wim Dehaen Received: 4 January 2017; Accepted: 7 February 2017; Published: 9 February 2017 Abstract: Newly synthesized 2-(2-((1H-indol-5yl)methylene)-hydrazinyl)-thiazole derivatives were evaluated for their in vitro cytotoxicity on two carcinoma cell lines A2780 and HeLa. Significant cytotoxic activity for 2-(2-((1H-indol-5-yl)methylene)hydrazinyl)-4-methylthiazole (1) and 2-(2-((1H-indol-5-yl)methylene)hydrazinyl)-4-phenylthiazole (3), on both A2780 [IC50: 11.6 µM(1), and 12.4 µM(3)] and HeLa [IC50: 22.4 µM(1) and 19.4µM(3)] cell lines is reported. Their antioxidant potential was evaluated by spectrophotometric method, using DPPH radical or Fe (TPTZ)3+ complex, and EPR spectroscopy, therefore the compounds 1 and 3 showed remarkable antioxidant activity simultaneously with a cytotoxic effect on A2780 and HeLa cell lines. Furthermore, based on theoretical quantum chemical calculation, the present study analyzed the chemoselectivity of the hydrogen extraction from the indolyl-hydrazinil-thiazoles in reaction with free radicals. Keywords: cytotoxic activity; antioxidant activity; DFT calculation; indol; thiazole 1. Introduction The heterocyclic derivatives with thiazole or indole units can be found in a variety of biologically active compounds that makes them some of the most extensively studied heterocycles. An example of a natural compound in which both indole and thiazole rings are linked is 3-thiazol-20-yl-indole known as Camalexin, a phytoalexin produced in different plant leaves [1,2] or synthetic derivatives based on thiazolyl-1H-indols with antiproliferative activity in peritoneal mesothelioma or MiaPaCa-2 cell line [3,4], HIV-1 RT inhibitors based on thiazolyl-hydrazinyl-1H-indol-2-one derivatives [5] and isomer analogs of our compounds acting as inhibitors for Mycobacterium tuberculosis [6]. The recent investigations are focused to develop new molecules based on indole scaffolds because of their biological potential, essential amino acid like tryptophan, psychoactive substances [7] like synthetic alkaloids, Sumatriptan for migraine treatment, Vincristine and other indole derivatives as antiproliferative agents [8], Delavirdine anti-HIV drug, Doleasetron antiemetic drug [9], and Molecules 2017, 22, 260; doi:10.3390/molecules22020260 www.mdpi.com/journal/molecules Molecules 2017, 22, 260 2 of 12 Molecules 2017, 22, 260 2 of 11 antioxidantcompounds compounds[10] but the [10 examples] but the examplesof biologically of biologically active compounds active compounds bearing bearingindole indolering are ring in arecontinuous in continuous expansion. expansion. TheThe thiazole can be identifiedidentified in the structure of different drugs, epothilone a microbial product andand theirtheir syntheticsynthetic analogsanalogs havinghaving anti-canceranti-cancer properties,properties, thiaminethiamine isis vitaminvitamin B1,B1, sulfathiazolansulfathiazolan isis antimicrobialantimicrobial agent,agent, abafunginas is fungicide, tiazofurin an antineoplastic, ritonavir is anti-HIV, andand fanetizole,fanetizole, meloxicam,meloxicam, andand fentiazacarefentiazacare areare anti-inflammatoryanti-inflammatory agentsagents [[11,12].11,12]. ThiazolesThiazoles bearing bearing hydrazine hydrazine moieties moieties have have gained gained a special a special attention attention because becauseof their biological of their biologicaland pharmacological and pharmacological properties as properties inhibitors as on inhibitors human monoamine on human oxidase monoamine (hMAO) oxidase [13], (hMAO)antimicrobial [13], antimicrobialagents [14], histone agents [14acetyltransferase], histone acetyltransferase inhibitors [15], inhibitors anti-inflammatory [15], anti-inflammatory agents [16], agents as well [16], asas wellantiproliferative as antiproliferative activity activity highlighted highlighted by our byprevious our previous studies studies [17–19]. [17 –19]. ConsideringConsidering the the biological biological potential potential of heterocyclic of heterocyclic derivatives derivatives bearing bearing thiazole thiazole and indole and scaffolds, indole scaffolds,the objectives the objectivesof this study of this were study to identify were to ne identifyw possible new antiprol possibleiferative antiproliferative agents and agents the study and the of studytheir antioxidant of their antioxidant potential. potential.For a better For understand a better understandinging of the antioxidant of the antioxidant properties propertieson molecular on molecularlevel, the level,structure the structure of 2-(2-((1 of 2-(2-((1H-indol-5-yl)methylene)-hydrazinyl)-thiazoleH-indol-5-yl)methylene)-hydrazinyl)-thiazole derivatives derivatives and andthe thechemoselectivity chemoselectivity of the of the radical radical generation generation reactions reactions have have been been studied studied using using molecular modelingmodeling toolstools asas DensityDensity FunctionalFunctional TheoryTheory (DFT) using hybrid B3LYP, 6-31G*,6-31G*, andand Hartree-FockHartree-Fock 3-21G3-21G modelsmodels [[20–22]20–22] offeredoffered byby SpartanSpartan 0606 software.software. 2.2. Results and DiscussionDiscussions 2.1.2.1. Synthesis of the New 2-(2-((1H-Indol-5-yl)methylene)hydrazinyl)thiazole2-(2-((1H-Indol-5-yl)methylene)hydrazinyl)thiazole DerivativesDerivatives TheThe synthesissynthesis ofof newlynewly 2-(2-((12-(2-((1HH-indol-5-yl)methylene)-hydrazinyl)-thiazole-indol-5-yl)methylene)-hydrazinyl)-thiazole derivativesderivatives werewere performedperformed byby the the Hantzsch Hantzsch protocol protocol in twoin two steps, steps, the condensationthe condensation of 1H of-indole-5-carbaldehyde 1H-indole-5-carbaldehyde with hydrazinecarbothioamidewith hydrazinecarbothioamide yielding yielding (E)-2-[(1 (HE-indol-3-yl)methylene])-2-[(1H-indol-3-yl)methylene] thiosemicarbazone thiosemicarbazone [23] followed [23] byfollowed its cyclocondensation by its cyclocondensation with α-halocarbonyl with α-halocarbonyl derivatives, derivatives, Scheme1. Scheme 1. Scheme 1. Synthesis of 2-(2-((1H-indol-5-yl)methylene)hydrazinyl)thiazole-indol-5-yl)methylene)hydrazinyl)thiazole derivatives.derivatives. TheThe structure structure of indolyl-hydrazinyl-thiazole of indolyl-hydrazinyl-thiazole derivatives derivatives 1–6 were1 –confirmed6 were confirmedby NMR, spectroscopy by NMR, 1 13 spectroscopy( H-NMR and (1H-NMRC-NMR, andCOSY,13 C-NMR,HMQC and COSY, HMBC) HMQC and andmass HMBC) spectrometry. and mass The spectrometry.characteristic Thesinglet characteristic for imine proton singlet (HC=N) for imine can proton be identified (HC=N) around can be 8.06–8.41 identified ppm, around while 8.06–8.41 the NH proton ppm, while from theindole NH ring proton appears from around indole ring10.6 appearsppm in acetone around 10.6but more ppm indeshielded, acetone but around more 11.5 deshielded, ppm, in arounda more 11.5polar ppm, solvent in a like more dimethyl polar solvent sulfoxide like. dimethyl sulfoxide. 2.2.2.2. Cytotoxic Activity TheThe new indolyl-hydrazinyl-thiazoles 1–6 were tested in vitrovitro,, by colorimetric method MTT, for theirtheir cytotoxiccytotoxic activityactivity onon twotwo tumortumor cellcell lines:lines: HeLa (human cervical cancer cells) and A2780 (human ovarianovarian cancercancer cells).cells). The The inhibitory inhibitory activity activity of of the the compounds compounds was was measured measured and and quantified quantified using using the the mathematic parameter IC50, (Figure 1). Cisplatin, a metal-based drug currently used in cancer therapy, was used as control (Figure 1). Molecules 2017, 22, 260 3 of 12 mathematic parameter IC50, (Figure1). Cisplatin, a metal-based drug currently used in cancer therapy, Moleculeswas used 2017 as, 22 control, 260 (Figure1). 3 of 11 IC50 (μM) Compounds HeLaIC50 (µ A2780M) Compounds Cisplatin 20.10HeLa ± 0.22 12.30 ± 0.22 A2780 Cisplatin1 20.1022.42± ± 0.220.24 11.65 12.30 ± 0.21± 0.22 1 2 22.4228.55± ± 0.240.25 26.49 11.65 ± 0.21± 0.21 2 3 28.5519.42± ± 0.250.22 12.99 26.49 ± 0.50± 0.21 3 19.42 ± 0.22 12.99 ± 0.50 4 33.98 ± 0.31 28.08 ± 0.23 4 33.98 ± 0.31 28.08 ± 0.23 5 5 19.84 ± ± 0.33 19.66 19.66 ± 0.50± 0.50 6 6 34.72 ± ± 0.25 20.15 20.15 ± 0.26± 0.26 Figure 1. Cytotoxic activity of in vitro of Compounds 1–6 against HeLa and A2780 tumor cells. * Data Figure 1. Cytotoxic activity of in vitro of Compounds 1–6 against HeLa and A2780 tumor cells. are reported as IC50 values determined by MTT assay after 24 h of continuous exposure