The Scientific World Journal

Volume 2014 (2014), Article ID 581737, 10 pages

http://dx.doi.org/10.1155/2014/581737

Research Article

A Mini Library of Novel Triazolothiadiazepinylindole Analogues: Synthesis, Antioxidant and Antimicrobial Evaluations

Jaiprakash Sharanappa Biradar,¹ Parveen Rajesab,1,2 Naveen Jaiprakash Biradar,¹ and Sasidhar Balappa Somappa1,3

¹Central Research Lab, Department of Chemistry, Gulbarga University, Gulbarga, Karnataka State 585 106, India

² Smt. V.G. Degree College for Women, Gulbarga, Karnataka State 585 102, India

³Organic Chemistry Section, Chemical Science and Technology Division, National Institute for Interdisciplinary Science and Technology (CSIR), Thiruvanthapuram-695 019, Kerala, India

Received 23 August 2013; Accepted 4 December 2013; Published 20 February 2014

Academic Editors: L. Previtera and M. Wujec

Copyright © 2014 Jaiprakash Sharanappa Biradar et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

A new series of novel triazolothiadiazepinylindole analogues were synthesized with an aim to examine possible antioxidant and antimicrobial activities. The titled compounds (3a–z) were obtained in good yield by reacting 5-(5-substituted-3-phenyl-1H-indol-2-yl)-4-amino-4H-1,2,4-triazole-3-thiols 1a–c with 3-(2,5-disubstituted-1H-indol-3-yl)-1(4-substituted phenyl)prop-2-en-1-ones 2a–i. All the newly synthesized compounds were characterized by IR, ¹H NMR, mass spectroscopic and analytical data. The synthesized analogues were tested for antioxidant and antimicrobial potency. Among the tested compounds 3a–c and 3j–l have shown very promising free radical scavenging activity and total antioxidant capacity. Compounds 3d–f, 3m–o, and 3s–z have shown excellent ferric reducing antioxidant activity. An outstanding antimicrobial activity is observed with compounds 3a–c and 3j–l.

1. Introduction

Antioxidants [1–3] act as “free radical scavengers” hence to prevent or slow the damage done by the free radicals [4–6]. Free-radical-induced oxidative stress associated with several cellular toxic processes including oxidative damage to protein, and DNA, membrane lipid oxidation, enzyme inactivation, and gene mutation leads to carcinogenesis [7]. Antioxidants are involved in processes such as immunity, protection against tissue damage, and reproduction and prevent growth or development caused by free radicals [8–10]. Antioxidants are useful in the prevention and treatment of Parkinson’s and Alzheimer’s disease [11–13].

Heterocycles constitute one of the major areas of organic chemistry and play important roles in drug discovery. Many of the best selling drugs currently in use contain one or more heterocyclic rings. Several fused heterocycles as well as biheterocycles are referred to as privileged structures [14]. Among them, sulfur- and nitrogen-containing heterocyclic compounds have maintained the interest of researchers and their unique structures led to several applications in different areas [15]. Triazoles and their derivatives constitute an important class of heterocyclic compounds and their analogues have been reported to possess various biological activities such as antimicrobial [16], anti-inflammatory [17], antihypertensive, anti-HIV [18], anticancer, and antitumor [19, 20]. Several compounds containing 1,2,4-triazole rings known as drugs like fluconazole, posaconazole, alprazolam, [21] and triazolothiadiazepine analogues represent a well-known class of drug substances at different stages of research, which possess antiviral [22] and antimicrobial properties [23].

Indole is a heterocycle of great importance in biological systems [24, 25]. The indole moiety is present in a number of drugs currently [26] in the market; in our previous approaches, we have described some new indole analogues with highly potent antioxidant, DNA cleavage and antimicrobial activities [27–30].

Interestingly, we have developed a new green protocol for the synthesis of rapid and clean synthetic route towards mini library of triazolothiadiazepinylindole analogues, which showed in vitro antioxidant and antimicrobial activities.

2. Materials and Methods

2.1. Chemistry

All chemicals used in this investigation were of analytical grade and were purified whenever necessary. Melting points of the synthesized compounds were measured in open capillaries and are uncorrected. Reactions were monitored by thin-layer chromatography (TLC) on silica gel 60 F₂₅₄ aluminium sheets (MERCK). Iodine vapour was used as detecting agent. IR spectra were recorded in KBr on PerkinElmer and FTIR spectrophotometer ( in cm⁻¹). ¹H NMR and ¹³C NMR spectra on BRUKER AVENCE II 400-MHz NMR spectrometer and the chemical shifts were expressed in ppm ( scale) downfield from TMS as an internal reference. The mass spectra were recorded on LC-MSD-Trap-SL instrument. The elemental analysis was performed by using FLASH EA 1112 SERIES instrument.

2.1.1. General Procedure for the Synthesis of Compounds 1a–c

The precursors 5-(5-substituted-3-phenyl-1H-indol-2-yl)-4-amino-4H-1,2,4-triazole-3-thiols) (1a–c) were obtained from 3,5-disubstituted indol-2-carboxyhydrazides by reported method [31].

2.1.2. General Procedure for the Synthesis of Compounds 2a–i

3-(2,5-disubstituted-1H-indol-3-yl)-1(4-substituted phenyl) prop-2-en-1-one 2a–i were prepared by reported method [29] by reacting disubstituted indole aldehydes with substituted acetophenone in the presence of piperidine in good yields.

2.1.3. General Procedure for the Synthesis of Compounds 3a–z

(1) Conventional Method. To a solution of substituted indolyl- triazole 1a–c (0.01 mol) in acetic acid substituted chalcones 2a–i (0.01 mol) were added. The reaction mixture was refluxed 3-4 hrs. The completion of the reaction was monitored by TLC. After the completion, the reaction mixture was poured to a beaker containing 100 mL of ice-cold water. The crude products thus separated were filtered and recrystallized from ethanol to yield target compounds 3a–z.

(2) Microwave Oven Method. A mixture of substituted indolyl triazole 1a–c (0.01 mol) and substituted chalcones 2a–i (0.01 mol) was powdered, mixed, and introduced to borosil sample crucible containing few drops of acetic acid. This was subjected to microwave irradiation for 10 minutes with 70% microwave power. After the completion (TLC), reaction mixture was brought to room temperature, washed with ethanol, and recrystallized to get the title compounds 3a–z which were found to be in good purity (TLC) and excellent yield.

8-(5-Chloro-2-phenyl-1H-indol-3-yl)-3-(5-chloro-3-phenyl-1H-indol-2-yl)-6-(4-chlorophenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3a). IR (KBr) (cm⁻¹): 3180, 3090, 1654, 1624, 1546; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 12.47 (s, 1H, indole NH), 11.63 (s, 1H, indole NH), 7.31–8.23 (m, 20H, Ar-H), 5.65 (s, 1H, –CH=); ¹³C NMR (DMSO-d₆+ CDCl₃) (ppm): 108, 111, 113, 117, 118, 118, 118, 120, 123, 125, 126, 126, 126, 128, 128, 128, 128, 129, 129, 129, 130, 132, 133, 134, 135, 138, 138, 144, 145, 166. MS: m/z = 712 , 714 [M+2], 718 [M+4], 720 [M+6]; Anal. calcd. for (C₃₉H₂₃N₆Cl₃S): C, 65.60; H, 3.25; N, 11.77%. Found: C, 65.59; H, 3.21; N, 11.75%.

8-(5-Chloro-2-phenyl-1H-indol-3-yl)-3-(5-chloro-3-phenyl-1H-indol-2-yl)-6-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3b). IR (KBr) (cm⁻¹): 3189, 3049, 1608, 1579, 1553; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.15 (s, 1H, indole NH), 10.25 (s, 1H, indole NH), 7.29–8.72 (m, 21H, Ar-H), 4.95 (s, 1H, –CH=); MS: m/z = 678 , 680 [M+2], 682 [M+4]; Anal. calcd. for (C₃₉H₂₄N₆Cl₂S): C, 68.92; H, 3.56; N, 12.37%. Found: C, 68.81; H, 3.52; N, 12.31%.

8-(5-Chloro-2-phenyl-1H-indol-3-yl)-3-(5-chloro-3-phenyl-1H-indol-2-yl)-6-(4-methylphenyl[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3c). IR (KBr) (cm⁻¹): 3108, 3053, 1606, 1574, 1553; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.03 (s, 1H, indole NH), 10.03 (s, 1H, indole NH), 7.29–8.14 (m, 20H, Ar-H), 5.35 (s, 1H, –CH=), 2.44 (s, 3H, CH₃); MS: m/z = 692 , 694 [M+2], 696 [M+4]; Anal. calcd. for (C₄₀H₂₆N₆Cl₂S): C, 69.26; H, 3.78; N, 12.12%. Found: C, 69.15; H, 3.69; N, 12.21%.

3-(5-Chloro-3-phenyl-1H-indol-2-yl)-6-(4-chlorophenyl)-8-(5-methyl-2-phenyl-1H-indol-3-yl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3d). IR (KBr) (cm⁻¹): 3391, 3265, 1601, 1540, 1519; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.43 (s, 1H, indole NH), 10.85 (s, 1H, indole NH), 6.40–9.13 (m, 20H, Ar-H), 4.91 (s, 1H, –CH=), 2.66 (s, 3H, CH₃); MS: m/z = 692 , 694 [M+2], 696 [M+4]; Anal. calcd. for (C₄₀H₂₆N₆Cl₂S): C, 69.26; H, 3.78; N, 12.12%. Found: C, 69.15; H, 3.69; N, 12.21%.

3-(5-Chloro-3-phenyl-1H-indol-2-yl)-8-(5-methyl-2-phenyl-1H-indol-3-yl)-6-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3e). IR (KBr) (cm⁻¹): 3106, 2996, 1650, 1590, 1560; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.01 (s, 1H, indole NH), 10.12 (s, 1H, indole NH), 6.40–8.58 (m, 21H, Ar-H), 4.91 (s, 1H, –CH=), 2.55 (s, 3H, CH₃); MS: m/z = 658 , 660 [M+2]; Anal. calcd. for (C₄₀H₂₇N₆ClS): C, 72.88; H, 4.13; N, 12.75%. Found: C, 72.75; H, 4.09; N, 12.64%.

3-(5-Chloro-3-phenyl-1H-indol-2-yl)-8-(5-methyl-2-phenyl-1H-indol-3-yl)-6-(4-methylphenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3f). IR (KBr) (cm⁻¹): 3443, 3133, 1602, 1578, 1558; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.31 (s, 1H, indole NH), 10.25 (s, 1H, indole NH), 7.11–8.18 (m, 20H, Ar-H), 5.29 (s, 1H, –CH=), 2.54 (s, 3H, CH₃), 2.43 (s, 3H, CH₃); MS: m/z = 672 , 674 [M+2]; Anal. calcd. for (C₄₁H₂₉N₆ClS): C, 73.15; H, 4.34; N, 12.48%. Found: C, 73.02; H, 4.29; N, 12.37%.

3-(5-Chloro-3-phenyl-1H-indol-2-yl)-6-(4-chlorophenyl)-8-(1H-indol-3-yl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3g). IR (KBr) (cm⁻¹): 3239, 3098, 1607, 1578, 1553; ¹H NMR (DMSO-d₆+ CDCl₃) δ (ppm): 11.78 (s, 1H, indole NH), 10.51 (s, 1H, indole NH), 6.40–8.56 (m, 17H, Ar-H), 4.94 (s, 1H, –CH=); MS: m/z = 602 , 604 [M+2], 606 [M+4]; Anal. calcd. for (C₃₃H₂₀N₆Cl₂S): C, 65.67; H, 3.34; N, 13.92; Found: C, 65.57; H, 3.28; N, 13.85%.

3-(5-Chloro-3-phenyl-1H-indol-2-yl)-8-(1H-indol-3-yl)-6-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3h). IR (KBr) (cm⁻¹): 3404, 3104, 1608, 1558, 1505; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 10.61 (s, 1H, indole NH), 10.01 (s, 1H, indole NH), 6.43–8.91 (m, 18H, Ar-H), 5.15 (s, 1H, –CH=); MS: m/z = 568 , 570 [M+2]; Anal. calcd. for (C₃₃H₂₁N₆ClS): C, 69.65; H, 3.72; N, 14.77%. Found: C, 69.55; H, 3.65; N, 14.71%.

3-(5-Chloro-3-phenyl-1H-indol-2-yl)-8-(1H-indol-3-yl)-6-(4-methylphenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3i). IR (KBr) (cm⁻¹): 3160, 3096, 1645, 1603; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.97 (s, 1H, indole NH), 11.39 (s, 1H, indole NH), 6.80–7.85 (m, 17H, Ar-H), 5.59 (s, 1H, –CH=), 2.64 (s, 3H, CH₃); MS: m/z = 582 , 584 [M+2]; Anal. calcd. for (C₃₄H₂₃N₆ClS): C, 70.03; H, 3.98; N, 14.41%. Found: C, 69.91; H, 3.95; N, 14.31%.

3-(5-Bromo-3-phenyl-1H-indol-2-yl)-8-(5-chloro-2-phenyl-1H-indol-3-yl)-6-(4-chlorophenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3j). IR (KBr) (cm⁻¹): 3148, 3098, 1643, 1589, 1551; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 12.48 (s, 1H, indole NH), 11.99 (s, 1H, indole NH), 7.07–8.23 (m, 20H, Ar-H), 5.60 (s, 1H, –CH=); MS: m/z = 756 , 758 [M+2], 760 [M+4], 762 [M+6]; Anal. calcd. for (C₃₉H₂₃N₆BrCl₂S): C, 61.75; H, 3.06; N, 11.08%. Found: C, 61.69; H, 3.01; N, 10.91%.

3-(5-Bromo-3-phenyl-1H-indol-2-yl)-8-(5-chloro-2-phenyl-1H-indol-3-yl)-6-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3k). IR (KBr) (cm⁻¹): 3158, 3068, 1590, 1576, 1551; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.15 (s, 1H, indole NH), 10.05 (s, 1H, indole NH), 7.29–8.72 (m, 21H, Ar-H), 5.45 (s, 1H, –CH=); MS: m/z = 722 , 724 [M+2], 726 [M+4]; Anal. calcd. for (C₃₉H₂₄N₆BrClS): C, 64.69; H, 3.34; N, 11.61%. Found: C, 65.21; H, 3.51; N, 11.45%.

3-(5-Bromo-3-phenyl-1H-indol-2-yl)-8-(5-chloro-2-phenyl-1H-indol-3-yl)-6-(4-methylphenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3l). IR (KBr) (cm⁻¹): 3108, 3029, 1644, 1606, 1553; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.03 (s, 1H, indole NH), 10.33 (s, 1H, indole NH), 7.2–8.1 (m, 20H, Ar-H), 5.05 (s, 1H, –CH=), 2.44 (s, 3H, CH₃); MS: m/z = 736 , 738 [M+2], 740 [M+4]; Anal. calcd. for (C₄₀H₂₆N₆BrClS): C, 65.09; H, 3.55; N, 11.39%. Found: C, 64.89; H, 3.51; N, 11.28%.

3-(5-Bromo-3-phenyl-1H-indol-2-yl)-6-(4-chlorophenyl)-8-(5-methyl-2-phenyl-1H-indol-3-yl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3m). IR (KBr) (cm⁻¹): 3176, 3048, 1623, 1584, 1509; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 12.20 (s, 1H, indole NH), 11.15 (s, 1H, indole NH), 6.32–8.13 (m, 20H, Ar-H), 5.60 (s, 1H, –CH=), 1.74 (s, 3H, CH₃); MS: m/z = 736 , 738 [M+2], 740 [M+4]; Anal. calcd. for (C₄₀H₂₆N₆BrClS): C, 65.09; H, 3.55; N, 11.39%. Found: C, 64.09; H, 3.51; N, 11.28%.

3-(5-Bromo-3-phenyl-1H-indol-2-yl)-8-(5-methyl-2-phenyl-1H-indol-3-yl)-6-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3n). IR (KBr) (cm⁻¹): 3240, 3198, 1604, 1558, 1553; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.01 (s, 1H, indole NH), 9.90 (s, 1H, indole NH), 6.40–8.58 (m, 21H, Ar-H), 4.31 (s, 1H, –CH=), 2.55 (s, 3H, CH₃); MS: m/z = 702 , 704 [M+2]; Anal. calcd. for (C₄₀H₂₇N₆BrS): C, 68.28; H, 3.87; N, 11.94%. Found: C, 68.18; H, 3.82; N, 11.83%.

3-(5-bromo-3-phenyl-1H-indol-2-yl)-8-(5-methyl-2-phenyl-1H-indol-3-yl)-6-(4-methylphenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3o). IR (KBr) (cm⁻¹): 3117, 3047, 1641, 1606, 1573; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 10.25 (s, 1H, indole NH), 9.95 (s, 1H, indole NH), 7.11–8.18 (m, 20H, Ar-H), 5.15 (s, 1H, –CH=), 2.54 (s, 3H, CH₃), 2.43 (s, 3H, CH₃); MS: m/z = 716 , 718 [M+2]; Anal. calcd. for (C₄₁H₂₉N₆BrS): C, 68.62; H, 4.07; N, 11.71%. Found: C, 68.52; H, 4.05; N, 11.59%.

3-(5-Bromo-3-phenyl-1H-indol-2-yl)-6-(4-chlorophenyl)-8-(1H-indol-3-yl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3p). IR (KBr) (cm⁻¹): 3167, 3047, 1648, 1589, 1558; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 10.61 (s, 1H, indole NH), 10.23 (s, 1H, indole NH), 6.83–8.19 (m, 17H, Ar-H), 5.19 (s, 1H, –CH=); MS: m/z = 646 , 648 [M+2], 650 [M+4]; Anal. calcd. for (C₃₃H₂₀N₆BrClS): C, 61.17; H, 3.11; N, 12.97%. Found: C, 61.12; H, 3.09; N, 12.85%.

3-(5-Bromo-3-phenyl-1H-indol-2-yl)-8-(1H-indol-3-yl)-6-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3q). IR (KBr) (cm⁻¹): 3097, 2998, 1606, 1578, 1551; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.01 (s, 1H, indole NH), 10.01 (s, 1H, indole NH), 6.83–8.91 (m, 18H, Ar-H), 5.15 (s, 1H, –CH=); MS: m/z = 612 , 614 [M+2]; Anal. calcd. For (C₃₃H₂₁N₆BrS): C, 64.60; H, 3.45; N, 13.70%. Found: C, 64.56; H, 3.41; N, 13.51%.

3-(5-Bromo-3-phenyl-1H-indol-2-yl)-8-(1H-indol-3-yl)-6-(4-methylphenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3r). IR (KBr) (cm⁻¹): 3104, 3049, 1608, 1598, 1558; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.07 (s, 1H, indole NH), 10.19 (s, 1H, indole NH), 6.80–7.85 (m, 17H, Ar-H), 5.39 (s, 1H, –CH=) 2.64 (s, 3H, CH₃); MS: m/z = 626 , 628 [M+2]; Anal. calcd. for (C₃₄H₂₃N₆BrS): C, 65.07; H, 3.69; N, 13.39%. Found: C, 64.95; H, 3.65; N, 13.28%.

8-(5-Chloro-2-phenyl-1H-indol-3-yl)-6-(4-chlorophenyl)-3-(5-methyl-3-phenyl-1H-indol-2-yl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3s). IR (KBr) (cm⁻¹): 3219, 3196, 1641, 1589, 1552; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.01 (s, 1H, indole NH), 10.25 (s, 1H, indole NH), 6.40–8.59 (m, 20H, Ar-H), 4.95 (s, 1H, –CH=), 2.56 (s, 3H, CH₃); MS: m/z = 692 , 694 [M+2], 696 [M+4]; Anal. calcd. for (C₄₀H₂₆N₆Cl₂S): C, 69.26; H, 3.78; N, 12.12%. Found: C, 69.14; H, 3.72; N, 12.02%.

8-(5-Chloro-2-phenyl-1H-indol-3-yl)-3-(5-methyl-3-phenyl-1H-indol-2-yl)-6-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3t). IR (KBr) (cm⁻¹): 3244, 3189, 1641, 1604, 1552; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 12.39 (s, 1H, indole NH), 11.09 (s, 1H, indole NH), 6.80–7.85 (m, 21H, Ar-H), 5.15 (s, 1H, –CH=), 2.76 (s, 3H, CH₃); MS: m/z = 658 , 660 [M+2]; Anal. calcd. for (C₄₀H₂₇N₆ClS): C, 72.88; H, 4.13; N, 12.75%. Found: C, 72.78; H, 4.10; N, 12.59%.

8-(5-Chloro-2-phenyl-1H-indol-3-yl)-3-(5-methyl-3-phenyl-1H-indol-2-yl)-6-(4-methylphenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3u). IR (KBr) (cm⁻¹): 3248, 3198, 1606, 1579, 1552; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 12.20 (s, 1H, indole NH), 11.98 (s, 1H, indole NH), 7.05–8.13 (m, 20H, Ar-H), 4.37 (s, 1H, –CH=), 2.57 (s, 3H, CH₃), 2.01 (s, 3H, CH₃); MS: m/z = 672 , 674 [M+2]; Anal. calcd. for (C₄₁H₂₉N₆ClS): C, 73.15; H, 4.34; N, 12.48%. Found: C, 73.28; H, 4.31; N, 12.36%.

6-(4-Chlorophenyl)-8-(5-methyl-2-phenyl-1H-indol-3-yl)-3-(5-methyl-3-phenyl-1H-indol-2-yl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3v). IR (KBr) (cm⁻¹): 3248, 3198, 1604, 1574, 1552; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.39 (s, 1H, indole NH), 10.39 (s, 1H, indole NH), 6.43–8.91 (m, 20H, Ar-H), 4.55 (s, 1H, –CH=), 2.58 (s, 3H, CH₃); MS: m/z = 672 , 674 [M+2]; Anal. calcd. for (C₄₁H₂₉N₆ClS): C, 73.15; H, 4.34; N, 12.48%. Found: C, 73.28; H, 4.31; N, 12.36%.

8-(5-Methyl-2-phenyl-1H-indol-3-yl)-3-(5-methyl-3-phenyl-1H-indol-2-yl)-6-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3w). IR (KBr) (cm⁻¹): 3248, 3179, 1604, 1574, 1556; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.05 (s, 1H, indole NH), 10.10 (s, 1H, indole NH), 6.32–8.13 (m, 21H, Ar-H), 5.60 (s, 1H, –CH=), 2.23 (s, 6H, CH₃); MS: m/z = 638 ; Anal. calcd. For (C₄₁H₃₀N₆S): C, 77.09; H, 4.73; N, 13.16%. Found: C, 77.06; H, 4.68; N, 13.03%.

8-(5-Methyl-2-phenyl-1H-indol-3-yl)-3-(5-methyl-3-phenyl-1H-indol-2-yl)-6-(4-methylphenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3x). IR (KBr) (cm⁻¹): 3184, 3148, 1606, 1574, 1553; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 11.05 (s, 1H, indole NH), 10.07 (s, 1H, indole NH), 6.40–8.77 (m, 20H, Ar-H), 4.15 (s, 1H, –CH=), 2.54 (s, 6H, CH₃), 2.31 (s, 3H, CH₃); MS: m/z = 652 ; Anal. calcd. for (C₄₂H₃₂N₆S): C, 77.27; H, 4.94; N, 12.87%. Found: C, 77.17; H, 4.91; N, 12.96%.

8-(1H-Indol-3-yl)-3-(5-methyl-3-phenyl-1H-indol-2-yl)-6-phenyl-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3y). IR (KBr) (cm⁻¹): 3354, 3258, 1674, 1595, 1554; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 10.61 (s, 1H, indole NH), 10.01 (s, 1H, indole NH), 6.40–8.91 (m, 18H, Ar-H), 4.85 (s, 1H, –CH=), 2.54 (s, 3H, CH₃); MS: m/z = 548 ; Anal. calcd. for (C₃₄H₂₄N₆S): C, 74.43; H, 4.41; N, 15.32%. Found: C, 74.39; H, 4.39; N, 15.25%.

6-(4-Chlorophenyl)-8-(1H-indol-3-yl)-3-(5-methyl-3-phenyl-1H-indol-2-yl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine (3z). IR (KBr) (cm⁻¹): 3391, 3244, 1667, 1601, 1540; ¹H NMR (DMSO-d₆+ CDCl₃) (ppm): 12.23 (s, 1H, indole NH), 10.11 (s, 1H, indole NH), 6.76–7.61 (m, 17H, Ar-H), 4.37 (s, 1H, –CH=), 2.08 (s, 3H, CH₃); MS: m/z = 582 584 [M+2]; Anal. calcd. For (C₃₄H₂₅N₆S): C, 70.03; H, 3.98; N, 14.41%. Found: C, 69.98; H, 3.95; N, 14.35%.

2.2. Biological Activities

2.2.1. Antioxidant Activities

(1) Free Radical Scavenging Activity. Free radical scavenging activity was done by DPPH method [32]. Different concentrations (25 μg, 50 μg, and 100 μg) of samples and butylated hydroxy anisole (BHA) were taken in different test tubes. The volume was adjusted to 100 μL by adding MeOH. Five milliliters of 0.1 mM methanolic solution of DPPH was added to these tubes and shaken vigorously. The tubes were allowed to stand at 27°C for 20 min. The control was prepared as above without any samples. The absorbances of samples were measured at 517 nm. Radical scavenging activity was calculated using the following formula:

(2) Total Antioxidant Capacity. Various concentrations of samples (25 μg, 50 μg, and 100 μg) were taken in a series of test tubes. To this, 1.9 mL of reagent solution (0.6 M sulfuric acid, 28 mM sodium phosphate, and 4 mM ammonium molybdate) was added. The tubes were incubated at 95°C for 90 min and allowed to cool. The absorbance of each aqueous solution was measured at 695 nm against a blank. Antioxidant capacities are expressed as equivalents of ascorbic acid. Ascorbic acid equivalents were calculated using standard graph of ascorbic acid. The values are expressed as ascorbic acid equivalents in μg per mg of samples.

(3) Ferric Reducing Antioxidant Power. Various concentrations of samples (25 μg, 50 μg, and 100 μg) were mixed with 2.5 mL of 200 mmol/L sodium phosphate buffer (pH 6.6) and 2.5 mL of 1% potassium ferricyanide. The mixture was incubated at 50°C for 20 min. Next, 2.5 mL of 10% trichloroacetic acid (w/v) was added. From this solution, 5 mL was mixed with 5 mL of distilled water and 1 mL of 0.1% ferric chloride and absorbance was measured spectrophotometrically at 700 nm. BHA was used as standard.

2.3. Antimicrobial Activity

Series of novel indole analogues are tested for in vitro antimicrobial activity against gram-negative bacteria Escherichia coli ATCC 25922 and Klebsiella pneumoniae ATCC 33499 and gram-positive bacteria Staphylococcus aureus ATCC 6538 and antifungal activity against Candida tropicalis ATCC 8302 and Candida albicans ATCC 60193by applying the agar plate diffusion technique [33]. Dilution process was adopted at 25 μg, 50 μg, and 100 μg/mL concentrations, respectively. The activity is compared with reference drugs gentamycin for antibacterial and fluconazole for antifungal activity. The zone of inhibition after 24 hr of incubation at 37°C in case of antibacterial activity and 48 hr in case of antifungal activity was compared with that of standards.

3. Results and Discussion

3.1. Chemistry

Molecules were designed with the aim of exploring their antioxidant and antimicrobial activities. The target compounds were synthesized as outlined in (Scheme 1). 3,5-Disubstitutedindole-2-carboxyhydrazides were reacted with carbon disulphide in the presence of base and hydrazine hydrate to get 5-(5-substituted-3-phenyl-1H-indol-2-yl)-4-amino-4H-1,2,4-triazole-3-thiols 1a–c. Claisen-Schmidt condensation of 2,5-disubstituted indole-3-carboxaldehydes with substituted acetophenones produced 3-(2,5-disubstituted-1H-indol-3-yl)-1-(4-substituted-phenyl)prop-2-en-1-one 2a–i. The synthesized compounds 3a–z were obtained in good yield by cyclocondensation of 5-(5-substituted-3-phenyl-1H-indol-2-yl)-4-amino-4H-1,2,4-triazole-3-thiol 1a–c with 3-(2,5-disubstituted-1H-indol-3-yl)-1(4-substituted phenyl)prop-2-en-1-one 2a–i. The formation of products was monitored by TLC. All the newly synthesized compounds were characterized by IR, ¹H NMR, ¹³C NMR, mass spectroscopic and analytical data. The IR spectrum of 8-(5-chloro-2-phenyl-1H-indol-3-yl)-3-(5-chloro-3-phenyl-1H-indol-2-yl)-6-(3-chlorophenyl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazepine 3a showed a strong absorption at 3180 cm⁻¹ and 3090 cm⁻¹ corresponding to indole NH, absorption at 1654 and 1624, corresponding to triazole C=N, and absorption at 1546 cm⁻¹ corresponding to thiadiazepine C=N stretching, respectively. The ¹H NMR spectrum of 3a has exhibited a singlet at 12.47 ppm due to indole NH and peak at 11.63 ppm is due to indole NH which is also D₂O exchangeable. A multiplet between 7.31–8.47 ppm corresponds to twenty aromatic protons present in the molecule and a peak at 5.65 ppm is assigned for the –CH= of thiadiazepine ring proton. The ¹³C NMR spectrum of compound 3a has shown peaks at δ 108, 111, 113, 117, 118, 118, 118, 120, 123, 125, 126, 126, 126, 128, 128, 128, 128, 129, 129, 129, 130, 132, 133, 134, 135, 138, 138, 144, 145, and 166. The mass spectrum of compound 3a has shown molecular ion peak at m/z 712 which is corresponding to molecular weight of the compound. The above spectral data supports the formation of compound 3a.

Scheme 1: Schematic representation for the formation of novel triazolothiadiazepinylindole 3a–z.

Various new triazolothiadiazepinylindole analogues synthesized during the present investigation are listed in (Table 1).

Table 1: Comparative data of conventional and microwave methods for the synthesis of novel triazolothiadiazepinylindole 3a–z.

Compda Number
Substituents
Conventional method
Microwave method
    m.p.c 

     (°C)

R
R′
R′′
R′′′
Time (min)
Yieldb (%)
Time (min)
Yieldb (%)

3a
Cl
Cl
Cl
Ph
180–240
85
10
95
200–02

3b
Cl
Cl
H
Ph
180–240
80
10
93
142–43

3c
Cl
Cl
Me
Ph
180–240
75
10
95
194–96

3d
Cl
Me
Cl
Ph
180–240
80
10
95
160–62

3e
Cl
Me
H
Ph
180–240
70
10
93
190–92

3f
Cl
Me
Me
Ph
180–240
65
10
95
158–60

3g
Cl
H
Cl
H
180–240
60
10
85
195–97

3h
Cl
H
H
H
180–240
60
10
80
168–70

3i
Cl
H
Me
H
180–240
70
10
90
155–57

3j
Br
Cl
Cl
Ph
180–240
80
10
98
210–12

3k
Br
Cl
H
Ph
180–240
85
10
96
195–97

3l
Br
Cl
Me
Ph
180–240
85
10
95
140–42

3m
Br
Me
Cl
Ph
180–240
75
10
90
180–82

3n
Br
Me
H
Ph
180–240
65
10
85
165–67

3o
Br
Me
Me
Ph
180–240
60
10
80
168–70

3p
Br
H
Cl
H
180–240
60
10
85
210–12

3q
Br
H
H
H
180–240
60
10
75
218–20

3r
Br
H
Me
H
180–240
60
10
80
120–22

3s
Me
Cl
Cl
Ph
180–240
75
10
85
183–85

3t
Me
Cl
H
Ph
180–240
75
10
85
201–02

3u
Me
Cl
Me
Ph
180–240
80
10
87
181–83

3v
Me
Me
Cl
Ph
180–240
65
10
85
190–92

3w
Me
Me
H
Ph
180–240
60
10
80
161–62

3x
Me
Me
Me
Ph
180–240
65
10
86
172–74

3y
Me
H
H
H
180–240
60
10
75
158–60

3z
Me
H
Cl
H
180–240
60
10
70
149–51

Products were characterized by IR, ¹H NMR,¹³C NMR, MS, and elemental analysis. Isolated yield. Melting points are uncorrected.

3.2. Biological Activities

The compounds 3a–z were screened for their antioxidant (free radical scavenging, total antioxidant capacity, and ferric reducing antioxidant power) and antimicrobial activities.

3.2.1. Antioxidant Activities

(1) Free Radical Scavenging Activity. The target compounds were screened for free radical scavenging activity by DPPH method [32]. The samples were prepared at concentrations of 25, 50, and 100 μg/100 μL and butylated hydroxy anisole (BHA) was taken as standard. DPPH is a stable free radical in a methanolic solution. Because of the unpaired electron of DPPH, it gives a strong absorption maxima at 517 nm in the visible region (purple color). In addition, the unpaired electron of the radical becomes paired in the presence of a hydrogen donor (a free radical scavenging antioxidant), decreasing the absorption. Among the compounds tested 3a–c and 3j–l have shown very promising free radical scavenging activity. The increased activity is due to the existence of halogen substitution at the five positions of both indoles. The hydrogen of indole NH could be donated to the DPPH to form DPPH free radical; by the presence of phenyl ring at the third position of indole, the DPPH free radical will be stabilized by the resonance. Compounds 3d–f, 3m–o, and 3s–x containing halogen atom at five positions of indole and a methyl group at another indole ring have shown moderate activity, whereas compounds 3g–i, 3p–r, and 3y–z have shown the least activity compared with the standard. The bar graph representation of percentage of free radical scavenging activity is displayed in Figures 1 and 2.

Figure 1: Free radical scavenging activity of 3a–m.

Figure 2: Free radical scavenging activity of 3n–z.

(2) Total Antioxidant Capacity. Total antioxidant activity was performed to all the newly synthesized compounds [34]. Antioxidant capacities are expressed as equivalents of ascorbic acid. Among the tested compounds 3a–c and 3j–l which are halogen substituted triazolothiadiazepinylindole have shown very strong total antioxidant capacity. Compounds with methyl substitution at the fifth position of the indole ring and no substitution at the second and fifth positions have shown the least total antioxidant capacity compared with the standard. The increased activity is due to the presence of halogen at the fifth position and a phenyl ring at the third position of indole. The results of total antioxidant activity are shown in Figures 3 and 4.

Figure 3: Total antioxidant capacity of 3a–m.

Figure 4: Total antioxidant capacity of 3n–z.

(3) Ferric Reducing Antioxidant Power Activity. The novel compounds were screened for ferric reducing antioxidant activity [35]. Butylated hydroxy anisole (BHA) was used as standard. All the tested compounds have shown positive tendency towards the ferric reducing activity. The presence of reducer (i.e., antioxidant) causes the reduction of the Fe⁺³/ferricyanide complex to the Fe⁺² form after the addition of trichloroacetic acid and ferric chloride. The reducing power of test compounds increases with increase in concentration. Compounds 3d–f, 3m–o, and 3s–z have shown excellent ferric reducing antioxidant activity and other analogues of indole have shown moderate to high activity. The presence of methyl group at the fifth position of the indole ring plays an important role as a better electron donor which enhances reducing power activity of the compounds. The results are presented in Figures 5 and 6.

Figure 5: Ferric reducing antioxidant power activity of 3a–m.

Figure 6: Ferric reducing antioxidant power activity of 3n–z.

3.3. Antimicrobial Activity

Applying the agar plate diffusion technique [33], series of novel triazolothiadiazepinylindole analogues were screened for in vitro antibacterial activity against (Table 2) gram-negative bacteria Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae) and gram-positive bacteria Staphylococcus aureus (S. aureus) at 25 μg/mL, 50 μg/mL, and 100 μg/mL concentrations, respectively. Gentamycin was used as standard. The zone of inhibitions was measured in mm for each concentration. Most of the screened compounds were found to have significant antibacterial activity. Compounds 3a–c and 3j–l have shown very good activity against all the three bacterial strains. Compounds 3d–f, 3m–o, and 3s–x have shown moderate activity and compounds 3g–i, 3p–r, and 3y–z have shown the least activity. Antifungal screening of the compounds was carried out in vitro against two fungi strains Candida tropicalis and Candida albicans at 25 μg/mL, 50 μg/mL, and 100 μg/mL concentrations using fluconazole as standard. Among the tested indole analogues the majority of compounds exhibited moderate to significant antifungal activity.

Table 2: Zone of inhibition in mm at 25, 50, and 100 µg/mL concentrations.

Compd name
Antibacterial activity
Antifungal activity

S.  aureus
E. coli
K. pneumoniae
C. tropicalis
C.  albicans

25
50
100
25
50
100
25
50
100
25
50
100
25
50
100

3a
13
17
20
15
20
22
16
22
25
14
18
20
13
15
18

3b
14
16
20
16
19
24
15
21
24
15
17
21
14
17
19

3c
15
15
19
14
21
25
14
23
26
13
16
20
15
16
20

3d
11
12
17
12
15
16
09
14
15
10
12
15
10
12
14

3e
10
13
15
11
16
17
08
15
18
09
11
14
09
11
12

3f
09
12
16
09
14
16
09
13
14
09
12
13
09
10
10

3g
02
06
08
05
07
08
05
07
09
02
04
06
03
04
05

3h
03
04
09
03
05
07
04
08
10
01
03
05
03
06
09

3i
05
07
08
04
06
08
03
06
08
03
04
06
05
06
08

3j
14
18
21
18
18
23
15
21
23
15
18
21
13
15
17

3k
13
19
20
17
20
22
17
23
24
16
19
21
15
17
18

3l
12
18
21
16
19
25
16
22
26
12
15
21
13
16
19

3m
10
10
15
10
12
15
09
15
16
10
12
15
09
11
12

3n
08
11
14
08
13
14
10
13
18
09
11
14
09
09
11

3o
08
10
14
09
14
16
09
13
19
08
10
12
10
10
12

3p
03
04
09
04
05
08
06
08
12
04
06
08
03
05
07

3q
03
05
07
03
05
08
05
09
11
03
05
07
05
06
08

3r
04
06
08
06
08
09
04
08
10
02
05
06
03
06
07

3s
10
10
15
10
12
15
09
14
15
10
12
14
11
12
13

3t
09
11
13
11
14
17
10
15
18
08
11
15
09
10
12

3u
08
11
14
08
13
14
10
13
14
09
13
13
08
12
14

3v
09
09
16
10
12
15
11
12
17
10
12
15
09
13
15

3w
08
10
14
09
14
16
09
12
15
09
11
16
10
11
12

3x
09
12
12
09
11
14
08
14
16
08
10
17
09
10
12

3y
04
06
09
05
08
10
05
09
10
05
09
10
04
05
06

3z
05
05
08
04
09
11
04
10
12
04
08
11
04
04
05

Std.1
15
19
22
18
21
25
17
23
27
—
—
—
—
—
—

Std.2
—
—
—
—
—
—
—
—
—
15
19
22
16
19
21

Std.1: gentamycin, Std.2: fluconazole.

The bold font refers to the compounds which have shown more potent antimicrobial activities.

4. Conclusions

We have synthesized titled compounds 3a–z by economic, better yield, and safer methods through the formation of compounds 1a–c and 2a–i under thermal and microwave condition. The compounds 3a–z were subjected for their antioxidant and antimicrobial screening. Very potent antimicrobial, scavenging and antioxidant activity was observed with compounds containing halogens at the fifth position of indoles. Excellent ferric reducing activity was observed with compounds containing electron donor group at five positions of one/both indoles. Therefore, the findings will provide a great impact on chemists and biochemists for further investigations in the indole field in search of molecules possessing potent antioxidant and antimicrobial activities.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

The authors thank the Department of Chemistry, Gulbarga University, Gulbarga. The authors are also thankful to the director of IISc (Bangalore) and IIT (Madras) for spectroscopic analysis. They also extend their sincere thanks to BIOGENICS, Hubli, and Department of Microbiology, Gulbarga University, Gulbarga, for their assistance in carrying out biological activities.

References

S. V. Lennon, S. J. Martin, and T. G. Cotter, “Dose-dependent induction of apoptosis in human tumour cell lines by widely diverging stimuli,” Cell Proliferation, vol. 24, no. 2, pp. 203–214, 1991.

H. Shirinzadeh, B. Eren, H. Gurer-Orhan, S. Suzen, and S. Özden, “Novel indole-based analogs of melatonin: synthesis and in vitro antioxidant activity studies,” Molecules, vol. 15, no. 4, pp. 2187–2202, 2010.

M. L. Circu and T. Y. Aw, “Reactive oxygen species, cellular redox systems, and apoptosis,” Free Radical Biology and Medicine, vol. 48, no. 6, pp. 749–762, 2010.

Y. Hangun-Balkir and M. L. McKenney, “Determination of antioxidant activities of berries and resveratrol,” Green Chemistry Letters and Reviews, vol. 5, no. 2, pp. 147–153, 2012.

F. Regoli and G. Principato, “Glutathione, glutathione-dependent and antioxidant enzymes in mussel, Mytilus galloprovincialis exposed to metals under field and laboratory conditions: implications for the use of biochemical biomarkers,” Aquatic Toxicology, vol. 31, no. 2, pp. 143–164, 1995.

N. Topalca, E. Yegin, and I. Celik, “Influence of indole-3-butyric acid on antioxidant defense systems in various tissues of rats at subacute and subchronic exposure,” Food and Chemical Toxicology, vol. 47, no. 10, pp. 2441–2444, 2009.

H. E. Poulsen, H. Prieme, and S. Loft, “Role of oxidative DNA damage in cancer initiation and promotion,” European Journal of Cancer Prevention, vol. 7, no. 1, pp. 9–16, 1998.

M. Liu, X. Q. Li, C. Weber, C. Y. Lee, J. Brown, and R. H. Liu, “Antioxidant and antiproliferative activities of raspberries,” Journal of Agricultural and Food Chemistry, vol. 50, no. 10, pp. 2926–2930, 2002.

B. Halliwell, “Role of free radicals in the neurodegenerative diseases: therapeutic implications for antioxidant treatment,” Drugs & Aging, vol. 18, no. 9, pp. 685–716, 2001.

K. Sudha, A. Rao, S. Rao, and A. Rao, “Free radical toxicity and antioxidants in Parkinson's disease,” Neurology India, vol. 51, no. 1, pp. 60–62, 2003.

G. S. Yossi, M. Eldad, and O. Daniel, “Oxidative stress induced-neurodegenerative diseases: the need for antioxidants that penetrate the blood brain barrier,” Neuropharmacology, vol. 40, no. 8, pp. 959–975, 2001.

K. Asplund, “Antioxidant vitamins in the prevention of cardiovascular disease: a systematic review,” Journal of Internal Medicine, vol. 251, no. 5, pp. 372–392, 2002.

K. N. Prasad, W. C. Cole, and B. Kumar, “Multiple antioxidants in the prevention and treatment of Parkinson's disease,” Journal of the American College of Nutrition, vol. 18, no. 5, pp. 413–423, 1999.

C. Li-Hsun, C. Chia-Mao, B. S. Deepak, and S. Chung-Ming, “Divergent synthesis of unsymmetrical annulated biheterocyclic compound libraries: benzimidazole linked indolo-benzodiazepines/quinoxaline,” ACS Combinatorial Science, vol. 13, no. 4, pp. 391–398, 2011.

M. García-Valverde and T. Torroba, “Special issue: sulfur-nitrogen heterocycles,” Molecules, vol. 10, no. 2, pp. 318–320, 2005.

T. Karabasanagouda, A. V. Adhikari, and N. S. Shetty, “Synthesis and antimicrobial activities of some novel 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles and 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazines carrying thioalkyl and sulphonyl phenoxy moieties,” European Journal of Medicinal Chemistry, vol. 42, no. 4, pp. 521–529, 2007.

M. D. Mullican, M. W. Wilson, D. T. Connor, C. R. Kostlan, D. J. Schrier, and R. D. Dyer, “Design of 5-(3,5-di-tert-butyl-4-hydroxyphenyl)-1,3,4-thiadiazoles, -1,3,4-oxadiazoles, and -1,2,4-triazoles as orally-active, nonulcerogenic antiinflammatory agents,” Journal of Medicinal Chemistry, vol. 36, no. 8, pp. 1090–1099, 1993.

T. Wen-Jie and H. Yong-Zhou, “Simple and efficient one-pot synthesis of 2,4-diaryl-1,2,3-triazoles,” Synthetic Communications, vol. 36, no. 17, pp. 2461–2468, 2006.

Y. A. Al-Soud, N. A. Al-Masoudi, and A. R. Ferwanah, “Synthesis and properties of new substituted 1,2,4-triazoles: potential antitumor agents,” Bioorganic & Medicinal Chemistry, vol. 11, no. 8, pp. 1701–1708, 2003.

B. S. Holla, B. Veerendra, M. K. Shivananda, and B. Poojary, “Synthesis characterization and anticancer activity studies on some Mannich bases derived from 1,2,4-triazoles,” European Journal of Medicinal Chemistry, vol. 38, no. 7-8, pp. 759–767, 2003.

S. F. Barbuceanu, G. L. Almajan, I. Saramet, C. Draghici, R. Socoteanu, and F. Barbuceanu, “New S-alkylated 1,2,4-triazoles incorporating diphenyl sulfone moieties with potential antibacterial activity,” Journal of the Serbian Chemical Society, vol. 74, no. 10, pp. 1041–1049, 2009.

A.-R. Farghaly, E. De Clercq, and H. El-Kashef, “Synthesis and antiviral activity of novel [1,2,4]triazolo[3,4-b][1,3,4] thiadiazoles, [1,2,4]triazolo[3,4-b][1,3,4] thiadiazines and [1,2,4]triazolo[3,4-b] [1,3,4] thiadiazepines,” Arkivoc, vol. 2006, no. 10, pp. 137–151, 2006.

M. Kidwai, P. Sapra, P. Misra, R. Saxena, and M. Singh, “Microwave assisted solid support synthesis of novel 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazepines as potent antimicrobial agents,” Bioorganic & Medicinal Chemistry, vol. 9, no. 2, pp. 217–220, 2001.

E. R. Abbey, L. N. Zakharov, and S.-Y. Liu, “Boron in disguise: the parent fused BN indole,” Journal of the American Chemical Society, vol. 133, no. 30, pp. 11508–11511, 2011.

F.-R. Alexandre, A. Amador, S. Bot et al., “Synthesis and biological evaluation of aryl-phospho-indole as novel HIV-1 non-nucleoside reverse transcriptase inhibitors,” Journal of Medicinal Chemistry, vol. 54, no. 1, pp. 392–395, 2011.

A. J. Kochanowska-Karamyan and M. T. Hamann, “Marine indole alkaloids: potential new drug leads for the control of depression and anxiety,” Chemical Reviews, vol. 110, no. 8, pp. 4489–4497, 2010.

B. S. Sasidhar and J. S. Biradar, “Synthesis of some bisindolyl analogs for in vitro cytotoxic and DNA cleavage studies,” Medicinal Chemistry Research, vol. 22, no. 7, pp. 3518–3526, 2013.

J. S. Biradar and B. S. Sasidhar, “Solvent-free, microwave assisted Knoevenagel condensation of novel 2,5-disubstituted indole analogues and their biological evaluation,” European Journal of Medicinal Chemistry, vol. 46, no. 12, pp. 6112–6118, 2011.

J. S. Biradar, B. S. Sasidhar, and R. Parveen, “Synthesis, antioxidant and DNA cleavage activities of novel indole derivatives,” European Journal of Medicinal Chemistry, vol. 45, no. 9, pp. 4074–4078, 2010.

J. S. Biradar, R. Parveen, B. S. Sasidhar, and S. M. Praveen, “Synthesis of new indolyl benzodiazepines and their DNA cleavage and antimicrobial activities,” Indian Journal of Heterocyclic Chemistry, vol. 20, pp. 181–182, 2010.

J. S. Biradar, Studies in the indole field [Ph.D. thesis], Gulbarga University, Gulbarga, India, 1982.

R. P. Singh, K. N. C. Murthy, and G. K. Jayaprakasha, “Studies on the antioxidant activity of pomegranate (Punica granatum) peel and seed extracts using in vitro models,” Journal of Agricultural and Food Chemistry, vol. 50, no. 1, pp. 81–86, 2002.

C. Praveen, A. Ayyanar, and P. T. Perumal, “Practical synthesis, anticonvulsant, and antimicrobial activity of N-allyl and N-propargyl di(indolyl)indolin-2-ones,” Bioorganic & Medicinal Chemistry Letters, vol. 21, no. 13, pp. 4072–4077, 2011.

K. Mruthunjaya and V. I. Hukkeri, “In vitro antioxidant and free radical scavenging potential of Parkinsonia aculeata Linn,” Pharmacognosy Magazine, vol. 4, no. 13, pp. 42–51, 2008.

J. C. M. Barreira, I. C. F. R. Ferreira, M. B. P. P. Oliveira, and J. A. Pereira, “Antioxidant activity and bioactive compounds of ten Portuguese regional and commercial almond cultivars,” Food and Chemical Toxicology, vol. 46, no. 6, pp. 2230–2235, 2008.