Synthesis, characterization and antimicrobial evaluation of some novel 1,2,4-triazolo[3,4-b][1,3,4]thiadiazine bearing substituted phenylquinolin-2-one moiety

Swagatika Ghosh; Amita Verma; Alok Mukerjee; Milan Kumar Mandal

doi:10.1016/j.arabjc.2015.07.003

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ORIGINAL ARTICLE

12 (

); 3046-3053

doi:

10.1016/j.arabjc.2015.07.003

Synthesis, characterization and antimicrobial evaluation of some novel 1,2,4-triazolo[3,4-b][1,3,4]thiadiazine bearing substituted phenylquinolin-2-one moiety

Swagatika Ghosh^{^a}, Amita Verma^{^a,⁎}, Alok Mukerjee^{^b}, Milan Kumar Mandal^{^a}

a Department of Pharmaceutical Sciences, Faculty of Health Sciences, Allahabad, Uttar Pradesh 211007, India

b Department of Pharmaceutical Chemistry, United Institute of Pharmacy, UPSIDC, Naini, Allahabad, Uttar Pradesh 211010, India

⁎Corresponding author. Tel.: +91 9919698663; fax: +91 9236524622. amitaverma.dr@gmail.com (Amita Verma)

Received: 2014-4-3, Accepted: 2015-7-7, Published: 2015-12-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Pathogenic microbes have mutated and developed resistance to the latest range of antibiotics, which has kept synthetic chemist hunting for better and least toxic antimicrobial agents. Cyclocondensation of substituted anilines with 3-phenyl-2-propenoic acid yielded Phenyl-(substituted)-quinolin-2-one derivatives (1a–1t). In the next step phenylquinolin-2-one acetic acid derivatives (2a–2t) were prepared by the treatment of (1a–1t) with chloroacetic acid. Further (2a–2t) derivatives were reacted with thiocarbohydrazide to obtain a series of 4-amino-5-sulfanyl-4,5-dihydro-1,2,4-triazolo-4-pheny-(substituted)-quinolin-2-one derivatives (3a–3t). Then condensation of (3a–3t) with phenacyl bromide provided series of fused heterocyclic derivatives of 4-phenyl-1-({6-phenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl}methyl)-(substituted)-1,2-dihydro quinolin-2-one (4a–4t). Structures of these newly synthesized derivatives were established by elemental analysis, FT-IR, ¹H NMR and Mass spectroscopy. Final derivatives (4a–4t) were screened for their in vitro antibacterial and antifungal activities against the standard drugs Ampicillin and Fluconazole respectively. The compounds 4d, 4g and 4j showed potent activity against all the studied microbes. Particularly compounds substituted with halogen groups at para position of phenylquinoline ring exhibited significant antimicrobial activity against studied microbes.

Keywords

Antimicrobial

Cyclocondensation

Phenylquinoline

Triazolothiadiazine

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1 Introduction

Rapid increase in pathogenic fungi and bacteria that are multi resistant to antibiotics has become major threat in treatment of infectious diseases. Heterocyclic compounds having 1,2,4-triazolo ring system substituted with nitrogen and sulfur exhibit a wide range of biological activities such as antibacterial (Guzeldemirci and Kucukbasmac, 2010; Karegoudar et al., 2008), antifungal (Fang et al., 2010; Banday and Rauf, 2009), antitubercular (Bhat et al., 2004) properties. Also a number of Quinoline derivatives have been well known to possess a variety of pharmacological activities like antibacterial (Zitouni et al., 2005), antifungal (Purohit et al., 2011) and anti-inflammatory (Tozkoparan et al., 2000; Amir et al., 2008; Chen et al., 2006; Abdel-Megeed et al., 2009 ). Literature survey reveals that heterocyclic compounds containing halogen atoms have attracted attention due to ability of halogens to act as hydroxy mimic agent. So substitution of hydrogen by halogens and other substituents plays an important role in designing new pharmacophores for biological studies. Various compounds containing 1,2,4-Triazolo nucleus are well known as powerful antibacterial (Varvaresou et al., 2000), antifungal and antimycobacterial agents (Sridharaa et al., 2010; Karegoudar et al., 2008). Moreover the use of heterocyclic compounds containing 1,3,4-Thiadiazoles and 1,3,4-Thiadiazines is widely known due to their therapeutic effects against pathological conditions such as pain, inflammation, and hypertension (Ahmad et al., 2012; Clerici et al., 2001). The synthesis of heterocyclic rings containing both 1, 2, 4-Triazolo nucleus and 1, 3, 4- Thiadiazine ring has attracted attention due to their antimicrobial (Goksen et al., 2007), analgesic (Turan-Zitouni et al., 1999), antiviral and anti-inflammatory properties (Isloor et al., 2009; Abadi et al., 2005). The problem of drug resistance of the pathogenic strains of microbes to the older derivatives of triazoles is a well-known fact for the researchers. Therefore it was planned to synthesize a new series of 4-phenyl-1-({6-phenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl}methyl)-(substituted)-1,2-dihydroquinolin-2-one (4a–4t) derivatives by linking (substituted)-4-phenylquinolin-2(1H)-one with 1,2,4-triazolo[3,4-b][1,3,4]thiadiazine moiety (Fig. 1) and to evaluate their in vitro antimicrobial activity.

General structure of final synthesized derivatives.

2 Materials and methods

2.1

2.1 General

The entire chemicals required for the synthesis and other experimental work were purchased from Merck, Sigma Aldrich and Rankem chemical company. Melting points of all synthesized compounds were determined in open capillaries by Temp Star apparatus and are uncorrected. The purity of the compounds was routinely checked in each step by TLC using Silica Gel 60G and the developed plates were visualized by UV light. Spectroscopic data were recorded by the following instruments; IR spectra were recorded on FT-IR-8400S, Schimadzu, Japan, ¹H NMR spectra were recorded by Bruker DRX – 300 MHz FT NMR with low and high temperature facility (−90 °C to +80 °C) in the solvents CDCl₃. Chemical shifts are reported in parts per million (δ) and signals are described as singlet (s), doublet (d), triplet (t), quartet (q) and multiplet (m). The Mass spectra were obtained by Agilent 6520 Q-TOF (ESI-MS) and Elemental analysis was done by Elemental Analyzer: Vario EL-III.

2.2

2.2 Chemistry

In the present work twenty novel derivatives of phenylquinoline-1,2,4-triazolothiadiazines were synthesized, following the synthetic route given in Scheme 1. The starting material phenylquinoline-2-one derivatives (1a–1t) for the synthesis of desired compounds were obtained by cyclocondensation (Lipson et al., 2000) of Aniline derivatives with 3-phenyl-2-propenoic acid (Cinnamic acid) in the presence of ethanol, conc. H₂SO₄ and Nitrobenzene. In this step conc. H₂SO₄ acts as condensing reagent and catalyst to favor forward reaction. Then the compounds (1a–1t) on the treatment with chloroacetic acid in the presence of alkaline medium provided 2-oxophenyl-(substituted)-quinolin-1-ylacetic acid derivatives (2a–2t). In the next step (2a–2t) on heating with thiocarbohydrazide gave 4-amino-5-sulfanyl-4,5-dihydro-1,2,4-triazol-4-phenyl-(substituted)-quinolin-2-one (3a–3t) in good yield. Then cyclization of (3a–3t) with phenacyl bromide in the presence of anhydrous ethanol provided the desired product 4-phenyl-1-({6-phenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazol-3-yl}methyl)-(substituted)-1,2-dihydroquino line-2-one (4a–4t). The synthesized compounds were purified and recrystallized using ethanol and acetone. The characterization of these new derivatives was done by their Elemental analysis and spectroscopic (FT-IR, ¹H NMR and MASS) data.

Synthetic Scheme for 1,2,4-triazolo[3,4-b][1,3,4]thiadiazine bearing substituted phenylquinolin-2-one (4a–4t). Where R = H, 2-Br, 3-Br, 4-Br, 2-Cl, 3-Cl, 4-Cl, 2-F, 3-F, 4-F, 2-NO2, 3-NO2, 4-NO2, 2-CH3, 3-CH3, 4-CH3, 2-OCH3, 3-OCH3, 4-OCH3, 3,4,5-t-OCH3. Reagents and conditions: (a) C2H5OH, Nitrobenzene, Con. H2SO4, reflux, 80 °C, 4 h; (b) chloroacetic acid, NaHCO3, water, CuO, reflux, 80 °C, 5 h; (c) thiocarbohydrazide, Δ, 2 h; (d) phenacyl bromide, anhydrous ethanol, NH4OH, 50 °C, 6 h.

2.3

2.3 General procedure for the synthesis of Phenyl-(substituted)- quinolin-2-one derivatives (1a–1t)

Equimolar quantity of aniline derivatives (0.1 mol) and 3-phenyl-2-propenoic acid (14.8 g, 0.1 mol) were refluxed for 4 h using 20 ml of ethanol in the presence of 2–4 drops of conc. Sulfuric acid and 2–3 drops of nitrobenzene. After refluxing the resulting product was kept at room temperature and then filtered. The filtered product was left for overnight to dry in hot air oven by maintaining temperature 40 °C and then the product was recrystallized from ethanol.

2.4

2.4 General procedure for the synthesis of 2-oxo-4-phenyl-(substituted)- quinolin-acetic acid derivatives (2a–2t)

In this step the compounds (1a–1t) 0.01 mol refluxed with Chloroacetic acid (0.94 g, 0.01 mol) in the presence of NaHCO₃, CuO and water for 2 h. The resulting solution was filtered and allowed to cool at room temperature. To the filtrate dilute HCl was added. The solid thus separated out was dried and recrystallized from ethanol.

2.5

2.5 General procedure for the synthesis of 4-amino-5-sulfanyl-4,5-dihydro-1,2,4-triazolo-4-phenyl-(substituted)- quinolin-2-one (3a–3t)

Mixture of 2a–2t (0.03 mol) and thiocarbohydrazide (3.18 g, 0.03 mol) was heated till all the contents melted. A homogenous reaction mixture was obtained during reaction process. Then the product was treated with dilute sodium carbonate solution. The white solid separated out was filtered, washed twice with cold water. Then the product was recrystallized from Acetone.

2.6

2.6 General procedure for the synthesis of 4-phenyl-1-({6-phenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl}methyl)-(substituted)-1,2-dihydroquinolin-2-one (4a–4t)

The synthesized compounds 3a–3t (0.003 mol) were refluxed with Phenacylbromide (0.597 g, 0.003 mol) in the presence of anhydrous ethanol (30 ml) with continuous stirring for 6 h. The resulting reaction mixture was allowed to attain room temperature and was neutralized with 20% NH₄OH solution. The separated precipitate was the filtered and recrystallized from ethanol to obtain the final derivatives (4a–4t).

2.6.1

2.6.1 4-Phenyl-1-({6-phenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4a)

White Solid Crystal; IR (KBr, cm⁻¹): 3040 (Ar C—H str), 1702 (C⚌O str), 1610 (C⚌N str), 1577 (C⚌C str), 1306 (Ar C—N str), 650 (C—S—C); ¹H NMR (CDCl₃, 300 MHz): δ (ppm): 4.61 (s, 2H, S—CH₂—), 5.97 (s, 2H, CH₂), 6.98 (s, 1H, CH⚌), 7.41–7.42 (m, 2H, Ar—H), 7.45 (q, 2H, J = 8.0 Hz, Ar—H), 7.46 (t, 6H, J = 8.0 Hz, Ar—H), 7.53 (q, 1H, Ar—H), 7.73–7.75 (m, 3H, Ar—H). ESI-MS (m/z) calcd. is 449.5, found 450.5 [M + H]⁺; anal. calcd. for C₂₆H₁₉N₅OS (449.52): C 69.47, H 4.26, N 15.58; found: C 69.43, H 4.20, N 15.53.

2.6.2

2.6.2 8-Bromo-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4b)

Brown amorphous Solid; IR (KBr, cm⁻¹): 3042 (Ar C—H str), 1710 (C⚌O str), 1640 (C⚌N str), 1550(C⚌C str), 1320 (Ar C—N str), 650 (C—S—C), 740 (C—Br); ¹H NMR (CDCl₃, 300 MHz): δ (ppm): 4.52 (s, 2H, S—CH₂—), 5.94 (s, 2H, CH₂), 6.78 (s, 1H, CH⚌), 7.21 (t, 1H, J = 7.5 Hz, Ar—H), 7.42–7.44 (m, 3H, Ar—H), 7.46 (d, 4H, J = 8.0 Hz, Ar—H), 7.48 (q, 2H, J = 8.0 Hz, Ar—H), 7.75 (q, 3H, Ar—H). ESI-MS (m/z) calcd. is 528.4, found 529.5 [M + H]⁺; anal. calcd. for C₂₆H₁₈BrN₅OS (528.42): C 59.10, H 3.43, N 13.25; found: C 59.09, H 3.48, N 13.28.

2.6.3

2.6.3 7-Bromo-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4c)

Brown amorphous Solid; IR (KBr, cm⁻¹): 3041 (Ar C—H str), 1709 (C⚌O str), 1632 (C⚌N str), 1535 (C⚌C str), 1325 (Ar C—N str), 648 (C—S—C), 742 (C—Br); ¹H NMR (CDCl₃, 300 MHz): δ (ppm) : 4.53 (s, 2H, S—CH₂—), 6.05 (s, 2H, CH₂), 7.18 (s, 1H, CH⚌), 7.41 (m, 2H, Ar—H), 7.46 (t, 4H, J = 8.0 Hz, Ar—H), 7.73 (q, 5H, J = 8.0 Hz, Ar—H), 8.08 (d, 2H, J = 8.0 Hz, Ar—H). ESI-MS (m/z) calcd. is 528.4, found 529.2 [M + H]⁺; anal. calcd. for C₂₆H₁₈BrN₅OS (528.42): C 59.10, H 3.43, N 13.25; found: C 59.09, H 3.48, N 13.28.

2.6.4

2.6.4 6-Bromo-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4d)

Brown amorphous Solid; IR (KBr, cm⁻¹): 3039 (Ar C—H str), 1706 (C⚌O str), 1635 (C⚌N str), 1539 (C⚌C str), 1328 (Ar C—N str), 647 (C—S—C), 744 (C—Br); ¹H NMR (CDCl₃, 300 MHz): δ (ppm) : 4.52 (s, 2H, S—CH₂—), 5.98 (s, 2H, CH₂), 6.78 (s, 1H, CH⚌), 7.41–7.45 (m, 2H, Ar—H), 7.46 (t, 4H, J = 8.0 Hz, Ar—H), 7.47 (q, 3H, J = 8.5 Hz, Ar—H), 7.73 (q, 2H, J = 8.0 Hz, Ar—H) 8.01 (d, 2H, J = 8.5 Hz, Ar—H). ESI-MS (m/z) calcd. is 528.4, found 529.6 [M + H]⁺; anal. calcd. for C₂₆H₁₈BrN₅OS (528.42): C 59.10, H 3.43, N 13.25; found: C 59.13, H 3.39, N 13.28.

2.6.5

2.6.5 8-Chloro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4e)

White Solid Crystal; IR (KBr, cm⁻¹): 3038 (Ar C—H str), 1700 (C⚌O str), 1611 (C⚌N str), 1549 (C⚌C str), 1338 (Ar C—N str), 665 (C—S—C), 758 (C—Cl); ¹H NMR (CDCl₃, 300 MHz): δ (ppm): 4.54 (s, 2H, S—CH₂—), 6.04 (s, 2H, CH₂), 6.78 (s, 1H, CH⚌), 7.19 (t, 1H, J = 7.5 Hz, Ar—H), 7.36–7.40 (m, 3H, Ar—H), 7.46 (d, 4H, J = 8.0 Hz, Ar—H), 7.48 (q, 2H, J = 8.5 Hz, Ar—H), 7.75 (q, 3H, J = 8.0 Hz, Ar—H), ESI-MS (m/z) calcd. is 483.9, found 484.8 [M + H]⁺; anal. calcd. for C₂₆H₁₈ClN₅OS (483.97): C 64.52, H 3.75, N 14.47; found: C 64.51, H 3.77, N 14.43.

2.6.6

2.6.6 7-Chloro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4f)

White Solid Crystal; IR (KBr, cm⁻¹): 3035 (Ar C—H str), 1748 (C⚌O str), 1608 (C⚌N str), 1538 (C⚌C str), 1340 (Ar C—N str), 662 (C—S—C), 750 (C—Cl); ¹H NMR (CDCl₃, 300 MHz): δ (ppm): 4.53 (s, 2H, S—CH₂—), 6.02 (s, 2H, CH₂), 7.18 (s, 1H, CH⚌), 7.41–7.45 (m, 2H, Ar—H), 7.46 (t, 4H, J = 8.0 Hz, Ar—H), 7.73 (q, 5H, J = 8.5 Hz, Ar—H), 8.08 (d, 2H, J = 8.0 Hz, Ar—H). ESI-MS (m/z) calcd. is 483.9, found 484. [M + H]⁺; anal. calcd. for C₂₆H₁₈ClN₅OS (483.97): C 64.52, H 3.75, N 14.47; found: C 64.50, H 3.71, N 14.42.

2.6.7

2.6.7 6-Chloro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4g)

White Solid Crystal; IR (KBr, cm⁻¹): 3032 (Ar C—H str), 1745 (C⚌O str), 1609 (C⚌N str), 1530 (C⚌C str), 1332 (Ar C—N str), 668 (C—S—C), 755 (C—Cl); ¹H NMR (CDCl₃, 300 MHz): δ (ppm): 4.52 (s, 2H, S—CH₂—), 5.98 (s, 2H, CH₂), 6.78 (s, 1H, CH⚌), 7.31–7.36 (m, 2H, Ar—H), 7.46 (t, 4H, J = 8.0 Hz, Ar—H), 7.52 (q, 3H, J = 8.5 Hz, Ar—H), 7.73 (q, 2H, J = 2.5 Hz, Ar—H), 8.38 (d, 2H, J = 8.5 Hz, Ar—H). ESI-MS (m/z) calcd. is 483.9, found 484.6 [M + H]⁺; anal. calcd. for C₂₆H₁₈ClN₅OS (483.97): C 64.52, H 3.75, N 14.47; found: C 64.55, H 3.79, N 14.45.

2.6.8

2.6.8 8-Fluoro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4h)

White flakes of Solid Crystal; IR (KBr, cm⁻¹): 3020 (Ar C—H str), 1720 (C⚌O str), 1640 (C⚌N str), 1536 (C⚌C str), 1322 (Ar C—N str), 645 (C—S—C), 747 (C—F); ¹H NMR (CDCl₃, 300 MHz): δ (ppm): 4.56 (s, 2H, S—CH₂—), 6.05 (s, 2H, CH₂), 6.78 (s, 1H, CH⚌), 7.24 (t, 1H, J = 7.5 Hz, Ar—H), 7.41–7.43 (m, 3H, Ar—H), 7.46 (d, 4H, J = 8.5 Hz, Ar—H), 7.48 (q, 2H, J = 8.0 Hz, Ar—H), 7.92 (q, 3H, J = 2.5 Hz, Ar—H). ESI-MS (m/z) calcd. is 467.5, found 468.4 [M + H]⁺; anal. calcd. for C₂₆H₁₈FN₅OS (467.51): C 66.79, H 3.88, N 14.98; found: C 66.73, H 3.85, N 14.99.

2.6.9

2.6.9 7-Fluoro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4i)

White flakes of Solid Crystal; IR (KBr, cm⁻¹): 3019 (Ar C—H str), 1721 (C⚌O str), 1642 (C⚌N str), 1537 (C⚌C str), 1326 (Ar C—N str), 649 (C—S—C), 749 (C—F); ¹H NMR (CDCl₃, 300 MHz): δ (ppm): 4.55 (s, 2H, S—CH₂—), 6.05 (s, 2H, CH₂), 7.18 (s, 1H, CH⚌), 7.41–7.43 (m, 2H,Ar—H), 7.48 (t, 4H, J = 2.5 Hz, Ar—H), 7.89 (q, 5H, J = 8.0 Hz, Ar—H), 8.08 (d, 2H, J = 8.0 Hz, Ar—H). ESI-MS (m/z) calcd. is 467.5, found 468.6 [M + H]⁺]⁺; anal. calcd. for C₂₆H₁₈FN₅OS (467.51): C 66.79, H 3.88, N 14.98; found: C 66.73, H 3.84, N 14.96.

2.6.10

2.6.10 6-Fluoro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4j)

White flakes of Solid Crystal; IR (KBr, cm⁻¹): 3017 (Ar C—H str), 1730 (C⚌O str), 1643 (C⚌N str), 1539 (C⚌C str), 1318 (Ar C—N str), 667 (C—S—C), 756 (C—F); ¹H NMR (CDCl₃, 300 MHz): δ (ppm): 4.58(s, 2H, S—CH₂—), 5.98 (s, 2H, CH₂), 6.80 (s, 1H, CH⚌), 7.44–7.45 (m, 2H, Ar—H), 7.48 (t, 4H, J = 2.5 Hz, Ar—H), 7.52 (q, 3H, J = 8.0 Hz, Ar—H), 7.78 (q, 2H, J = 8.0 Hz, Ar—H), 8.38 (d, 2H, J = 8.0 Hz, Ar—H). ESI-MS (m/z) calcd. is 467.5, found 468.4 [M + H]⁺; anal. calcd. for C₂₆H₁₈FN₅OS (467.51): C 66.79, H 3.88, N 14.98; found: C 66.77, H 3.84, N 14.99.

2.6.11

2.6.11 8-Nitro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4k)

Yellow flakes of Solid Crystal; IR (KBr, cm⁻¹): 3045 (Ar C—H str), 1735 (C⚌O str), 1620 (C⚌N str), 1540 (C⚌C str), 1300, 890 (Ar C—N str), 670 (C—S—C); ¹H NMR (CDCl₃, 300 MHz): 4.41 (s, 2H, S—CH₂—), 5.89 (s, 2H, CH₂), 6.78 (s, 2H, CH⚌), 7.43–7.45 (m, 2H, Ar—H), 7.46 (t, 4H, J = 8.0 Hz, Ar—H), 7.48 (q, 2H, J = 8.0 Hz Ar—H), 7.58 (t, 1H, Ar—H), 8.13 (q, 3H, Ar—H). ESI-MS (m/z) calcd. is 494.5, found 495.3 [M + H]⁺; anal. calcd. for C₂₆H₁₈N₆O₃S (494.52): C 63.15, H 3.67, N 16.99; found: C 63.19, H 3.63, N 16.98.

2.6.12

2.6.12 7-Nitro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4l)

Yellow flakes of Solid Crystal; IR (KBr, cm⁻¹): 3046 (Ar C—H str), 1731 (C⚌O str), 1622 (C⚌N str), 1541 (C⚌C str), 1303, 882 (Ar C—N str), 672 (C—S—C); ¹H NMR (CDCl₃, 300 MHz): 4.42 (s, 2H, S—CH₂—), 6.26 (s, 2H, CH₂), 7.18 (s, 1H, CH⚌), 7.30 (d, 2H, J = 7.5 Hz, Ar—H), 7.45–7.46 (t, 5H, J = 8.0 Hz, Ar—H), 7.49 (q, 2H, J = 8.0 Hz, Ar—H), 8.01 (q, 3H, J = 7.5 Hz, Ar—H), 8.75 (d, 1H, J = 8.5 Hz, Ar—H). ESI-MS (m/z) calcd. is 494.5, found 495.6 [M + H]⁺; anal. calcd. for C₂₆H₁₈N₆O₃S (494.52): C 63.15, H 3.67, N 16.99; found: C 63.12, H 3.65, N 16.95.

2.6.13

2.6.13 6-Nitro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4m)

Yellow flakes of Solid Crystal; IR (KBr, cm⁻¹): 3040 (Ar C—H str), 1732 (C⚌O str), 1624 (C⚌N str), 1543 (C⚌C str), 1306, 875 (Ar C—N str), 673 (C—S—C); ¹H NMR (CDCl₃, 300 MHz): 4.42 (s, 2H, S—CH₂—), 6.21 (s, 2H, CH₂), 6.80(s, 1H, CH⚌), 7.43–7.45 (m, 2H, Ar—H), 7.46 (t, 4H, J = 8.0 Hz, Ar—H), 7.49 (q, 2H, J = 8.0 Hz, Ar—H), 7.73 (q, 2H, Ar—H), 8.05 (d, 2H, J = 8.5 Hz, Ar—H), 9.04 (d, 1H, J = 8.0 Hz, Ar—H). ESI-MS (m/z) calcd. is 494.5, found 495.5 [M + H]⁺; anal. calcd. for C₂₆H₁₈N₆O₃S (494.52): C 63.15, H 3.67, N 16.99; found: C 63.10, H 3.69, N 16.95.

2.6.14

2.6.14 8-Methyl-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4n)

White Solid Crystal; IR (KBr, cm⁻¹): 3010 (Ar C—H str), 2895 (Aliphatic C—H str), 1704 (C⚌O str), 1605 (C⚌N str), 1560 (C⚌C str), 1304 (Ar C—N str), 662 (C—S—C); ¹H NMR (CDCl₃, 300 MHz): δ (ppm): 2.61 (s,3H,CH₃), 4.53 (s, 2H, S—CH₂—), 5.95 (s, 2H, CH₂), 6.78 (s, 1H, CH⚌), 7.29–7.32 (m, 1H, Ar—H), 7.45 (q, 3H, J = 8.0 Hz, Ar—H), 7.49 (t, 5H, J = 8.0 Hz Ar—H), 7.46–7.48 (t, 5H, J = 8.0 Hz, Ar—H), 7.50–7.59 (q, 4H, J = 8.0 Hz, Ar—H). ESI-MS (m/z) calcd. is 463.5, found 464.5 [M + H]⁺; anal. calcd. for C₂₇H₂₁N₅OS (463.55): C 69.96, H 4.57, N 15.11; found: C 69.93, H 4.56, N 15.14.

2.6.15

2.6.15 7-Methyl-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4o)

White Solid Crystal; IR (KBr, cm⁻¹): 3009 (Ar C—H str), 2885 (Aliphatic C—H str), 1706 (C⚌O str), 1606 (C⚌N str), 1558 (C⚌C str), 1305 (Ar C—N str), 664 (C—S—C); ¹H NMR (CDCl₃, 300 MHz): δ (ppm): 2.43 (s, 3H, CH₃), 4.53 (s, 2H, S—CH₂—), 5.99 (s, 2H, CH₂), 7.18 (s, 1H, CH⚌), 7.41–7.44 (m, 2H, Ar—H), 7.46 (t, 4H, J = 8.0 Hz, Ar—H), 7.49 (q, 2H, J = 2.5 Hz, Ar—H), 7.64–7.65 (m, 2H, Ar—H), 7.75 (q, 2H, J = 8.5 Hz, Ar—H), 8.18 (d, 1H, J = 8.0 Hz, Ar—H). ESI-MS (m/z) calcd. is 463.5, found 464.7 [M + H]⁺; anal. calcd. for C₂₇H₂₁N₅OS (463.55): C 69.96, H 4.57, N 15.11; found: C 69.95, H 4.59, N 15.14.

2.6.16

2.6.16 6-Methyl-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4p)

White Solid Crystal; IR (KBr, cm⁻¹): 3004 (Ar C—H str), 2898 (Aliphatic C—H str),1705 (C⚌O str), 1603 (C⚌N str), 1559 (C⚌C str), 1307 (Ar C—N str), 665 (C—S—C); ¹H NMR (CDCl₃, 300 MHz): 2.46 (s, 3H, CH₃), 4.51 (s, 2H, S—CH₂—), 5.98 (s, 2H, CH₂), 6.45 (d, 1H, J = 8.5 Hz, Ar—H), 6.78 (s, 1H, CH⚌), 7.43–7.45 (m, 3H, Ar—H), 7.46 (t, 4H, J = 8.0 Hz, Ar—H), 7.74 (q, 4H, J = 8.0 Hz, Ar—H), 8.16 (m, 1H, Ar—H). ESI-MS (m/z) calcd. is 463.5, found 464.6 [M + H]⁺; anal. calcd. for C₂₇H₂₁N₅OS (463.55): C 69.96, H 4.57, N 15.11; found: C 69.98, H 4.53, N 15.15.

2.6.17

2.6.17 8-Methoxy-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4q)

White needle Crystal; IR (KBr, cm⁻¹): 3012 (Ar C—H str), 2870 (Aliphatic C—H str), 1708 (C⚌O str), 1608 (C⚌N str), 1566 (C⚌C str), 1302 (Ar C—N str), 680 (C—S—C); ¹H NMR (CDCl₃, 300 MHz): δ (ppm): 4.09 (s, 3H,OCH₃), 4.50 (s, 2H, S—CH₂—), 5.98 (s, 2H, CH₂), 6.78 (s, 1H, CH⚌), 7.09 (q, 1H, J = 7.5 Hz, Ar—H), 7.41 (m, 3H, Ar—H), 7.46 (t, 5H, J = 8.0 Hz, Ar—H), 7.73 (q, 4H, J = 8.0 Hz, Ar—H). ESI-MS (m/z) calcd. is 479.5, found 480.6 [M + H]⁺; anal. calcd. for C₂₇H₂₁N₅O₂S (479.55): C 67.62, H 4.41, N 14.60; found: C 67.62, H 4.46, N 14.68.

2.6.18

2.6.18 7-Methoxy-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4r)

White needle Crystal; IR (KBr, cm⁻¹): 3013 (Ar C—H str), 2890 (Aliphatic C—H str), 1703 (C⚌O str), 1607 (C⚌N str), 1565 (C⚌C str), 1309 (Ar C—N str), 682 (C—S—C); ¹H NMR (CDCl₃, 300 MHz): 3.86 (s, 3H, OCH₃), 4.51 (s, 2H, S—CH₂—), 5.98 (s, 2H, CH₂), 7.04 (d,2H, J = 8.0 Hz,Ar—H), 7.18 (s, 1H, CH⚌), 7.41 (m, 2H, Ar—H), 7.46 (t, 4H, J = 8.0 Hz Ar—H), 7.73 (q, 4H, J = 8.0 Hz, Ar—H), 8.35 (d, 1H, J = 8.0 Hz, Ar—H). ESI-MS (m/z) calcd. is 479.5, found 480.6 [M + H]⁺; anal. calcd. for C₂₇H₂₁N₅O₂S (479.55): C 67.62, H 4.41, N 14.60; found: C 67.64, H 4.45, N 14.58.

2.6.19

2.6.19 6-Methoxy-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4s)

White needle Crystal; IR (KBr, cm⁻¹): 3014 (Ar C—H str), 2875 (Aliphatic C—H str), 1707 (C⚌O str), 1624 (C⚌N str), 1563 (C⚌C str), 1332 (Ar C—N str), 681 (C—S—C); ¹H NMR (CDCl₃, 300 MHz): δ (ppm): 3.82 (s, 3H, OCH₃), 4.51 (s, 2H, S—CH₂—), 5.98 (s, 2H, CH₂), 6.79 (s, 1H, CH⚌),7.02 (q, 1H, J = 8.0 Hz, Ar—H), 7.46 (m, 2H, Ar—H),7.48 (t, 6H, J = 8.0 Hz, Ar—H), 7.68–7.69 (d, 3H, J = 8.0 Hz, Ar—H), 7.89 (d, 1H, J = 8.0 Hz, Ar—H). ESI-MS (m/z) calcd. is 479.5, found 480.4 [M + H]⁺; anal. calcd. for C₂₇H₂₁N₅O₂S (479.55): C 67.62, H 4.41, N 14.60; found: C 67.61, H 4.45, N 14.56.

2.6.20

2.6.20 6,7,8-Trimethoxy-4-phenyl-1-({6-phenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4t)

White needle Crystal; IR (KBr, cm⁻¹): 3023 (Ar C—H str), 2901 (Aliphatic C—H str),1706 (C⚌O str), 1620 (C⚌N str), 1564 (C⚌C str), 1330 (Ar C—N str), 683 (C—S—C); ¹H NMR (CDCl₃, 300 MHz): δ (ppm): 3.84 (s, 9H, 3xOCH₃), 4.51 (s, 2H, S—CH₂—), 5.98 (s, 2H, CH₂), 6.85 (s, 1H, CH⚌), 7.45(d, 2H, J = 8.5 Hz, Ar—H), 7.48(m,5H, Ar—H), 7.74 (q, 4H, Ar—H). ESI-MS (m/z) calcd. is 539.6, found 540.7 [M + H]⁺; anal. calcd. for C₂₉H₂₅N₅O₄S (539.60): C 64.55, H 4.67, N 12.98; found: C 64.54, H 4.63, N 12.95.

2.7

2.7 In-vitro antimicrobial assay/studies

2.7.1

2.7.1 Minimal Inhibitory Concentrations

Minimal Inhibitory Concentrations (MICs, μg/mL) were determined on different microbes using Broth Micro Dilution procedure according to the recommendations of National Committees for Clinical Laboratory Standards (NCCLS) (Barry, 1991; CLSI Document, 2006; NCCLS Document, 2002 ). MIC was defined as the lowest conc. of compound that inhibited visible growth of microbes after incubation at 35 °C for 24 h. for bacteria and 48 h for fungi. Strains of gram −ve bacteria Pseudomonas aeruginosa (MCCB 0035), Escherichia coli (ATCC 8739) and gram +ve bacteria Staphylococcus aureus (ATCC 29213) and fungal strains Aspergillus fumigatus (NCIM 2081), Aspergillus niger (NCIM 2191), Candida albicans (NCIM 2087) were used for testing antibacterial and antifungal activities. Bacterial strains were grown in Mueller–Hinton Broth and fungal strains were grown in Sabouraud Liquid medium. The inoculum densities of 5 × 10⁵ CFU/mL for bacteria and 0.5–2.5 × 10³ CFU/mL for fungi were prepared. Ampicillin Anhydride and fluconazole were used as standard antibiotic powder. The synthesized compounds were dissolved in DMSO and further dilutions were prepared in sterile distilled water of various concentrations by twofold serial dilution method to obtain the required concentration 512, 256, 128, 64, 32, 16, 8, 4, 2, 1, 0.5, 0.25 μg/mL. Ampicillin anhydride and fluconazole were diluted in sterile distilled water. Twofold dilutions of the compound and standards were prepared as 512–0.5 μg/mL and 64–0.25 μg/mL concentrations respectively. After dilution was completed, microbe suspensions were inoculated into each well of row. MIC values were given as μg/mL. The turbidity was monitored visually and spectrophotometrically and the lowest concentration, at which no growth was seen, recorded and considered as MIC of that particular compound. The MIC of the synthesized compounds and standard drug has been summarized in Table 2.

2.7.2

2.7.2 Agar Disk Diffusion

Agar Disk Diffusion testing technique was used as per CLSI guidelines for evaluating antimicrobial potentials of synthesized derivatives with suitable modification. Mueller–Hinton Agar (MHA) petri plates was prepared, standardized and then inoculated with standardized test organism suspension. Stock solution of synthesized compounds was prepared in DMSO and further diluted with distilled water to get concentration of test compounds 100 μg/ml, ampicillin (100 μg/ml) and Clotrimazole (100 μg/ml). Disk of 8 mm diameter was prepared from Whatman filter paper and sterilized by keeping in hot air oven at 140 °C for 1 h. Further the standard and test solution were added to each disk (100 μg/8 mm disk) and then with the help of sterile forceps placed on agar plates one at a time. In a plate three disks were applied by triplicate manner and it was ensured that disk made complete contact with agar layer. Bottom of the agar plates was labeled and incubated at temperature 35 °C for 24 h and 48 h for bacterial and fungal strains in BOD incubator. Measurement of zone of inhibition produced by test compounds and standard drug against microbial growth was done using a scale. Final data of zone of inhibition obtained by different test compounds as compared with that of standard have been enumerated in (Table 3).

3 Results and discussion

3.1

3.1 Chemistry

In the present work twenty derivatives of phenylquinoline-1,2,4-triazolothiadiazines were synthesized. The structures of the synthesized compounds were established by spectral data. According to IR spectroscopic data compounds (4a–4t) showed peaks at 1306–1330 cm⁻¹, 650–682 cm⁻¹ due to -N⚌C and C—S—C stretching vibrations respectively and no absorption peaks at 3140–3280 cm⁻¹, 3050–3090 cm⁻¹ due to -NH₂ and -SH groups respectively indicated smooth cyclization of triazoles leading to the formation of thiadiazine ring. Further, ¹H NMR spectra of the synthesized compounds were confirmed by the appearance of S—CH₂ proton of 1,3,4-thiadiazine ring at 4.40–4.54 ppm and —CH₂ proton at 5.97–6.20 ppm as broad singlet. All other aromatic protons were observed at expected region. Mass spectra (ESI-MS) of all the synthesized compounds showed molecular ion [M + H]⁺ peak in agreement with their molecular formula. Physical and elemental analyses are listed in Table 1.

Table 1 Physical and analytical data of synthesized compounds (4a–4t).

Comp.	R	Molecular formula	m.p. (°C)	Yield	Analysis of C, H, N (%), (cal./found)
Comp.	R	Molecular formula	m.p. (°C)	Yield	C	H	N
4a	H	C₂₆H₁₉N₅OS	202–203	69	69.47(69.43)	4.26(4.20)	15.58(15.53)
4b	2-Br	C₂₆H₁₈BrN₅OS	194–195	61	59.10(59.09)	3.43(3.48)	13.25(13.28)
4c	3-Br	C₂₆H₁₈BrN₅OS	180–181	69	59.10(59.12)	3.43(3.44)	13.25(13.19)
4d	4-Br	C₂₆H₁₈BrN₅OS	185–186	67	59.10(59.13)	3.43(3.39)	13.25(13.28)
4e	2-Cl	C₂₆H₁₈ClN₅OS	160–161	62	64.52(64.51)	3.75(3.77)	14.47(14.43)
4f	3-Cl	C₂₆H₁₈ClN₅OS	175–176	60	64.52(64.50)	3.75(3.71)	14.47(14.42)
4g	4-Cl	C₂₆H₁₈ClN₅OS	150–152	65	64.52(64.55)	3.75(3.79)	14.47(14.45)
4h	2-F	C₂₆H₁₈FN₅OS	140–142	59	66.79(66.73)	3.88(3.85)	14.98(14.99)
4i	3-F	C₂₆H₁₈FN₅OS	130–131	68	66.79(66.73)	3.88(3.84)	14.98(14.96)
4j	4-F	C₂₆H₁₈FN₅OS	115–116	60	66.79(66.77)	3.88(3.84)	14.98(14.99)
4k	2-NO₂	C₂₆H₁₈N₆O₃S	146–147	72	63.15(63.19)	3.67(3.63)	16.99(16.98)
4l	3-NO₂	C₂₆H₁₈N₆O₃S	155–156	76	63.15(63.12)	3.67(3.65)	16.99(16.95)
4m	4-NO₂	C₂₆H₁₈N₆O₃S	165–166	75	63.15(63.10)	3.67(3.69)	16.99(16.95)
4n	2-CH₃	C₂₇H₂₁N₅OS	123–124	62	69.96(69.93)	4.57(4.56)	15.11(15.14)
4o	3-CH₃	C₂₇H₂₁N₅OS	132–133	59	69.96(69.95)	4.57(4.59)	15.11(15.14)
4p	4-CH₃	C₂₇H₂₁N₅OS	110–112	63	69.96(69.98)	4.57(4.53)	15.11(15.15)
4q	2-OCH₃	C₂₇H₂₁N₅O₂S	210–211	56	67.62(67.62)	4.41(4.46)	14.60(14.68)
4r	3-OCH₃	C₂₇H₂₁N₅O₂S	230–231	57	67.62(67.64)	4.41(4.45)	14.60(14.58)
4s	4-OCH₃	C₂₇H₂₁N₅O₂S	225–226	62	67.62(67.61)	4.41(4.45)	14.60(14.56)
4t	3,4,5-t-OCH₃	C₂₉H₂₅N₅O₄S	215–217	51	64.55(64.54)	4.67(4.63)	12.98(12.95)

3.2

3.2 In-vitro antimicrobial assay/studies

3.2.1

3.2.1 Antibacterial activity

All the synthesized derivatives (4a–4t) were tested for their in vitro antimicrobial activity against gram positive (S. aureus) and gram negative (E. coli, P. aeruginosa) bacteria and results have been presented in Tables 2 and 3. The resultant MIC value of synthesized compounds was found in good agreement with the results of zone of inhibition. Compounds 4d, 4g and 4j having substitution at sixth position of phenyl quinolone ring showed highest activity against all studied bacterial strains. Highest activity was shown by compound 4d at MIC value 1 μg/mL against S. aureus, 2 μg/mL against E. Coli and 4 μg/mL P. aeruginosa. Other derivatives 4c, 4f, and 4i showed comparable activity as compared with standard drug as these had substitution by halogen atoms at seventh position of core pharmacophore phenylquinoline ring. Compounds 4b, 4e, 4h, 4m and 4r also possessed some activity against tested bacterial strains. Further replacement of halogen groups with methyl, nitro, methoxy and tri-methoxy groups reduced antibacterial potentials and compounds 4a, 4k, 4l, 4n, 4o, 4p, 4q, 4s and 4t showed least activity as revealed from MIC study from Table 2.

Table 2 Minimum Inhibitory Concentration (MIC) in μg/mL of 1,2,4-triazolo thiadiazines (4a–4t)^a,b against Bacterial and Fungal strains.

Comp. code	R	Bacterial strains			Fungal strains
Comp. code	R	EC	PA	SA	AF	AN	CA
4a	H	256	128	256	128	256	64
4b	2-Br	64	128	64	128	64	32
4c	3-Br	64	32	64	64	32	8
4d	4-Br	2	4	1	32	4	2
4e	2-Cl	256	256	128	>256	32	16
4f	3-Cl	128	128	64	128	16	16
4g	4-Cl	2	4	2	8	2	1
4h	2-F	128	128	64	64	32	8
4i	3-F	64	64	32	32	16	4
4j	4-F	8	8	2	4	4	2
4k	2-NO₂	256	256	128	128	128	64
4l	3-NO₂	128	256	64	128	32	16
4m	4-NO₂	32	64	16	32	16	32
4n	2-CH₃	>256	256	>256	>256	>256	128
4o	3-CH₃	256	>256	>256	128	>256	256
4p	4-CH₃	>256	128	128	128	256	128
4q	2-OCH₃	128	64	32	64	32	16
4r	3-OCH₃	64	32	16	32	16	32
4s	4-OCH₃	64	128	64	128	64	32
4t	3,4,5-t-OCH₃	64	128	64	64	32	16
AA	Stand. drug	1	4	2	–	–	–
CL	Stand. drug	–	–	–	16	4	1

a Minimum inhibitory concentration was determined by micro-broth dilution method.

b E. coli, Escherichia coli ATCC 8739; P. aeruginosa, Pseudomonas aeruginosa MCCB 0035; S. aureus, Staphylococcus aureus ATCC 29213; A. fumigatus, Aspergillus fumigatus NCIM 2081; A. niger, Aspergillus niger NCIM 2191; C. albicans, Candida albicans NCIM 2087.

Table 3 Zone of inhibition of 1,2,4-triazolo thiadiazines (4a–4t)^a,b against Bacterial and Fungal strains at concentration of 100 μg/8 mm disk compared with broad spectrum antibacterial standard drug Ampicillin (AA) and Clotrimazole (CL) 100 μg/8 mm disk.

Comp. code	R	Diameter of growth inhibition zone^⁎ (mm)
Comp. code	R	EC	PA	SA	AN	CA
4a	H	10	12	13	10	11
4b	2-Br	13	15	16	13	14
4c	3-Br	14	16	17	15	16
4d	4-Br	16	17	19	18	20
4e	2-Cl	12	13	15	17	18
4f	3-Cl	15	14	17	17	18
4g	4-Cl	16	17	19	20	23
4h	2-F	14	15	17	16	19
4i	3-F	12	15	16	18	20
4j	4-F	15	16	18	20	22
4k	2-NO₂	12	15	16	16	17
4l	3-NO₂	14	16	17	17	19
4m	4-NO₂	12	14	15	15	16
4n	2-CH₃	07	09	10	07	09
4o	3-CH₃	07	08	11	09	10
4p	4-CH₃	05	06	08	08	11
4q	2-OCH₃	10	11	12	13	14
4r	3-OCH₃	11	09	10	12	15
4s	4-OCH₃	12	10	08	10	12
4t	3,4,5-t-OCH₃	13	15	16	15	16
AA	Stand. drug	18	17	21	–	–
CL	Stand. drug	–	–	–	22	24

⁎ Average of triplicate.

a Zone of inhibition of compounds was determined by micro-broth dilution method.

b Ec: Escherichia coli; Pa: Pseudomonas aeruginosa; Sa: Staphylococcus aureus; An: Aspergillus niger; Ca: Candida albicans; AA: Ampicillin anhydride; CL: Clotrimazole.

3.2.2

3.2.2 Antifungal activity

Compounds 4d, 4g and 4j showed highest activity against tested fungal strains in comparison with clotrimazole. Both MIC and Zone of Inhibition data from Tables 2 and 3 reveal that halogen substitution at sixth position of phenylquinoline ring. Compounds 4d and 4j showed nearly equipotent activity as compared with standard drug at MIC concentration of 2 μg/mL and 4 μg/mL against A. niger and C. albicans whereas compound 4g was the most potent at 1 μg/mL concentration against C. albicans. Compounds 4b, 4c, 4e, 4f, 4h and 4i showed moderate activity as hydrogen was substituted with bromo, chloro and fluro atoms at seventh and eighth position of phenylquinoline ring. Antifungal activity further decreased in compounds 4k, 4l, 4m, 4o, 4p, 4q, 4r and 4s having methyl, nitro and methoxy groups at various position of phenylquinoline ring. Least activity was seen in 4a and 4n against all studied fungal strains.

3.2.3

3.2.3 Structure activity relationship of antimicrobial study

MIC and Zone of Inhibition data showed and clarified Structure–activity relationship analysis of final synthesized derivatives. The study suggested that compounds having substitution on sixth, seventh and eight position of phenylaquinoline ring by halogen atom possessed good activity. Specially having substitution at sixth position by halogen group, compounds 4d, 4g and 4j emerged to be most useful as they were having highest activity against both studied fungal and bacterial strains, whereas substitution by electron donating groups, like compounds 4k, 4l, 4m, 4n, 4o, 4p, 4q, 4r, 4s and 4t having methyl, nitro, methoxy and trimethoxy groups was not as effective as halogen substituents.

4 Conclusion

In this study we have successfully synthesized and reported synthesis of novel 1,2,4-triazolo[3,4-b][1,3,4]thiadiazine bearing substituted phenylquinolin-2-one hybrids. This study showed some 1,2,4-triazolo thiadiazines derivatives bearing phenyl quinoline moiety possessed moderate to good antibacterial and antifungal activities. The antimicrobial study suggested that compounds (4a–4t) by halogen substitution on sixth position of phenylquinoline ring (4d, 4g and 4j) showed highest activity against all studied microbial strains. Other compounds also possessed some activity but failed to attract more attention in comparison with standard drugs. The authors are working further to optimize compounds with good activity and findings will be reported in further publications.

Acknowledgments

The authors are thankful to the Head, Department of Microbiology and Department of Biotechnology, SHIATS for providing microbial strains and to Deputy Director & Head, SAIF, CDRI Lucknow for Elemental Analysis, NMR and Mass spectroscopic data of the compounds. The authors will welcome valuable comments and suggestions from reviewers, for which they shall be highly grateful.

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Clinical and Laboratory Standards Institute, 2006. Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically Approved Standard, Seventh ed. CLSI document M7-A7. Wayne, Pennsylvania, USA, p. 1–49.
Fang B., Zhou C.H., Rao X.C., . Eur. J. Med. Chem.. 2010;45(9):4338-4398.
Goksen U.S., Kelekci N.G., Goktas O., Koysal Y., Kilic E., Isik S., Aktay G., Ozalp M., . Bioorg. Med. Chem.. 2007;15(17):5738-5751.
Guzeldemirci N.U., Kucukbasmac O., . Eur. J. Med. Chem.. 2010;45(1):63-68.
Isloor A.M., Kalluraya B., Shetty P., . Eur. J. Med. Chem.. 2009;44(9):3784-3787.
Karegoudar P., Prasad D.J., Ashok M., Mahalinga M., Poojary B., Holla B.S., . Eur. J. Med. Chem.. 2008;43(4):808-815.
Lipson V.V., Desenko S.M., Orlov V.D., Shishkin O.V., Shirobokova M.G., Chernenko V.N., Znioveve L.I., . Chem. Hetrocyc. Comp.. 2000;36:1329-1335.
Purohit D.H., Dodiya B.L., Ghetiya R.M., Vekariya P.B., Joshi H.J., . Acta Chim. Slov.. 2011;58:53-59.
Sridharaa A.M., Reddy K.R.V., Keshavayya J., Chidananda B., Prasad Y., Kumar G.S., Vadiraj S.G., Bose P., Goud S.K., Peethambar S.K., . Der. Pharma. Chemica. 2010;2(5):201-211.
Tozkoparan B., Gokhan N., Aktay G., Yeşilada E., Ertan M., . Eur. J. Med. Chem.. 2000;35(12):743-750.
Turan-Zitouni G., Kaplancikli Z.A., Erol K., Kilic F.S., . Farmaco. 1999;54(4):218-223.
Varvaresou A., Tsantili-Kakoulidou A., Siatra-Papastaikoudi T., Tiligada E., . Arzneimittelforschung. 2000;50(1):48-54.
Zitouni G.T., Kaplancikli Z.A., Yildiz M.T., Chevallet P., Kaya D., . Eur. J. Med. Chem.. 2005;40(6):607-613.

Introduction

Materials and methods

General
Chemistry
General procedure for the synthesis of Phenyl-(substituted)- quinolin-2-one derivatives (1a–1t)
General procedure for the synthesis of 2-oxo-4-phenyl-(substituted)- quinolin-acetic acid derivatives (2a–2t)
General procedure for the synthesis of 4-amino-5-sulfanyl-4,5-dihydro-1,2,4-triazolo-4-phenyl-(substituted)- quinolin-2-one (3a–3t)
General procedure for the synthesis of 4-phenyl-1-({6-phenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl}methyl)-(substituted)-1,2-dihydroquinolin-2-one (4a–4t)
In-vitro antimicrobial assay/studies

Results and discussion

Chemistry
In-vitro antimicrobial assay/studies

Conclusion

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[9] Clerici F., Pocar D., Guido M., Loche A., Perlini V., Brufani M., . J. Med. Chem.. 2001;44(60):931-936.

[10] Clinical and Laboratory Standards Institute, 2002. Reference Method for Broth Dilution Antifungal Susceptibility Testing of Yeasts; Approved Standard-Second Edition. NCCLS document M27-A2. Wayne, Pennsylvania, USA, p. 1–29.

[11] Clinical and Laboratory Standards Institute, 2006. Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria That Grow Aerobically Approved Standard, Seventh ed. CLSI document M7-A7. Wayne, Pennsylvania, USA, p. 1–49.

[12] Fang B., Zhou C.H., Rao X.C., . Eur. J. Med. Chem.. 2010;45(9):4338-4398.

[13] Goksen U.S., Kelekci N.G., Goktas O., Koysal Y., Kilic E., Isik S., Aktay G., Ozalp M., . Bioorg. Med. Chem.. 2007;15(17):5738-5751.

[14] Guzeldemirci N.U., Kucukbasmac O., . Eur. J. Med. Chem.. 2010;45(1):63-68.

[15] Isloor A.M., Kalluraya B., Shetty P., . Eur. J. Med. Chem.. 2009;44(9):3784-3787.

[16] Karegoudar P., Prasad D.J., Ashok M., Mahalinga M., Poojary B., Holla B.S., . Eur. J. Med. Chem.. 2008;43(4):808-815.

[17] Lipson V.V., Desenko S.M., Orlov V.D., Shishkin O.V., Shirobokova M.G., Chernenko V.N., Znioveve L.I., . Chem. Hetrocyc. Comp.. 2000;36:1329-1335.

[18] Purohit D.H., Dodiya B.L., Ghetiya R.M., Vekariya P.B., Joshi H.J., . Acta Chim. Slov.. 2011;58:53-59.

[19] Sridharaa A.M., Reddy K.R.V., Keshavayya J., Chidananda B., Prasad Y., Kumar G.S., Vadiraj S.G., Bose P., Goud S.K., Peethambar S.K., . Der. Pharma. Chemica. 2010;2(5):201-211.

[20] Tozkoparan B., Gokhan N., Aktay G., Yeşilada E., Ertan M., . Eur. J. Med. Chem.. 2000;35(12):743-750.

[21] Turan-Zitouni G., Kaplancikli Z.A., Erol K., Kilic F.S., . Farmaco. 1999;54(4):218-223.

[22] Varvaresou A., Tsantili-Kakoulidou A., Siatra-Papastaikoudi T., Tiligada E., . Arzneimittelforschung. 2000;50(1):48-54.

[23] Zitouni G.T., Kaplancikli Z.A., Yildiz M.T., Chevallet P., Kaya D., . Eur. J. Med. Chem.. 2005;40(6):607-613.

Synthesis, characterization and antimicrobial evaluation of some novel 1,2,4-triazolo[3,4-b][1,3,4]thiadiazine bearing substituted phenylquinolin-2-one moiety

Abstract

Keywords

Antimicrobial

Cyclocondensation

Phenylquinoline

Triazolothiadiazine

1 Introduction

2 Materials and methods

2.1 General

2.2 Chemistry

2.3 General procedure for the synthesis of Phenyl-(substituted)- quinolin-2-one derivatives (1a–1t)

2.4 General procedure for the synthesis of 2-oxo-4-phenyl-(substituted)- quinolin-acetic acid derivatives (2a–2t)

2.5 General procedure for the synthesis of 4-amino-5-sulfanyl-4,5-dihydro-1,2,4-triazolo-4-phenyl-(substituted)- quinolin-2-one (3a–3t)

2.6 General procedure for the synthesis of 4-phenyl-1-({6-phenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl}methyl)-(substituted)-1,2-dihydroquinolin-2-one (4a–4t)

2.6.1 4-Phenyl-1-({6-phenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4a)

2.6.2 8-Bromo-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4b)

2.6.3 7-Bromo-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4c)

2.6.4 6-Bromo-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4d)

2.6.5 8-Chloro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4e)

2.6.6 7-Chloro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4f)

2.6.7 6-Chloro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4g)

2.6.8 8-Fluoro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4h)

2.6.9 7-Fluoro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4i)

2.6.10 6-Fluoro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4j)

2.6.11 8-Nitro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4k)

2.6.12 7-Nitro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4l)

2.6.13 6-Nitro-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4m)

2.6.14 8-Methyl-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4n)

2.6.15 7-Methyl-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4o)

2.6.16 6-Methyl-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4p)

2.6.17 8-Methoxy-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4q)

2.6.18 7-Methoxy-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4r)

2.6.19 6-Methoxy-4-phenyl-1({6-phenyl-7H-[1,2,4]triazolo[3,4b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4s)

2.6.20 6,7,8-Trimethoxy-4-phenyl-1-({6-phenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazin-3-yl}methyl)-1,2-dihydroquinolin-2-one (4t)

2.7 In-vitro antimicrobial assay/studies

2.7.1 Minimal Inhibitory Concentrations

2.7.2 Agar Disk Diffusion

3 Results and discussion

3.1 Chemistry

3.2 In-vitro antimicrobial assay/studies

3.2.1 Antibacterial activity

3.2.2 Antifungal activity

3.2.3 Structure activity relationship of antimicrobial study

4 Conclusion

Acknowledgments

References

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