Pundeer R et al IJARPB: 2013, 3(2), ISSN: Available online on Research Article

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1 Available online on Research Article Received on 15/12/2012; Revised on 23/12/2012; Accepted on 27/12/2012;, -DIBROMOKETOES I THE COVEIET SYTHESIS OF SOME THIAZOLO[3,2-b]-1,2,4- TRIAZOLES AD THEIR ATIMICROBIAL ACTIVITY: ISOLATIO OF EW ITERMEDIATES Rashmi Pundeer a*, Sushma a, Chetan Sharma b, K. R. Aneja b a Department of Chemistry, Kurukshetra University, Kurukshetra, , India. dr.rashmipundeer@gmail.com b Department of Microbiology, Kurukshetra University, Kurukshetra, , India. ABSTRACT An efficient one pot synthesis of 2,6-diaryl thiazolo[3,2-b]-1,2,4-triazoles (5) has been achieved by the reaction of α,α-dibromoacetophenones (1) with 3-aryl-5-mercapto-1,2,4-triazoles (2). The compounds were screened for their in vitro antibacterial and antifungal activity. Compounds 5a and 5d were found to be particularly effective against S. aureus with the zone of inhibition of 25 mm and 24.6 mm respectively; compound 5h was very effective against B. subtilis showing 21.6 mm inhibition-zone. For Gram negative bacteria, compound 5d was found to be best against E. coli (zone of inhibition mm) and P. aeruginosa (zone of inhibition mm). Further, compound 5i showed good antifungal activity; it inhibited the growth of C. albicans with 17.3 mm inhibition-zone (more than the standard drug, amphotericin B having 16.6 mm inhibition-zone) and S. cerevisiae with 16.3 mm inhibition-zone. KEYWORDS: α,α-dibromoacetophenones, thiazolo[3,2-b]-1,2,4-triazoles, antibacterial activity, antifungal activity. ITRODUCTIO -Bromocarbonyl compounds are promising synthons for synthesizing a myriad of - functionalized ketones, carbo- and heterocyclic compounds (Wilhelm et al., 1969; Garcia et al., 1973; Little et al., 1994) in preparative organic chemistry. It is a well explored class of bifunctional compounds readily accessible from the bromination of corresponding ketones. Inspite of their multifaceted utility, there is always a need of exploring the better alternatives because of the lachrymatory properties associated with them. Recently,, -Dibromoketones (, -DK) are attracting increasing attention in view of their (i) high reactivity, (ii) non-lachrymatory nature (iii) convenient preparation under mild conditions and (iv) easy purification. Extensive literature survey reveals that this particular area has not been much explored;, -dibromocarbonyl compounds behave as synthetic equivalents of 2011, IJARPB. All Rights Reserved 102

2 the corresponding -bromocarbonyl compounds in some of their reactions while in others they behave differently (Ahluwalia et al., 1992; Zhandkin et al., 1993; Kolos et al., 2001; Ding et al., 2003; Prakash et al., 2007; Prakash, 2007). Combining different pharmacophoric fragments in a single structure may lead to the compounds with significant biological properties. Earlier it has been demonstrated that the derivatives with 1,2,4-triazole structure have weaker antimicrobial activity than those containing this nucleus condensed with another heterocycles (thiazoles, thiadiazines etc) (Mathew et al., 2007; Amir et al., 2007; Ibrahim, 2009). 1,2,4-triazoles have readymade nucleophilic centres for the synthesis of nitrogen bridged heterocyclic rings. The literature is enriched with progressive findings about the synthesis and pharmacological activities of various condensed heterocycles possessing symmetrical triazole and thiazole nucleus, such as, thiazolo[3,2-b]-1,2,4-trizoles (Roy et al., 1997; Bhat et al., 2004; Kumar et al., 2007; El Bakali et al., 2009; Karthikeyan, 2009; Barbuceanu et al., 2009;). The compounds have engrossed substantial interest because of their utility in synthetic organic chemistry, medicine, agriculture, and industry. In continuation of our work exploring the synthetic utility of, -dibromoketones (Prakash et al., 2007; Pundeer et al., 2012), it was thought of interest to investigate their reaction with 3-aryl- 5-mercapto-1,2,4-triazoles. All the title compounds, thus obtained, were screened for their antibacterial and antifungal activity. MATERIALS AD METHODS Melting points were taken in open capillaries and are uncorrected. IR spectra were recorded on Perkin-Elmer IR spectrophotometer. The 1 H MR spectra were recorded on Bruker 300 MHz instrument. The chemical shifts were expressed in ppm units downfield from an internal TMS standard. Elemental analyses were carried out in Perkin-Elmer 2400 instrument and mass spectra were recorded on Kartos MS-50 mass spectrometer. The α, α-dibromoacetophenones (1) (Boeykens et al., 1994; Paul et al., 2003), 3- phenyl-5-mercapto-1,2,4-triazole (2a) and 3-(4- chlorophenyl)-5-mercapto-1,2,4-triazole (2b) were synthesized according to the reported literature procedure (Dhaka et al., 1974; Tozkoparan et al., 2012). Synthesis of 2-(5-aryl-2H-1,2,4-triazol-3- ylthio)-2-bromo-1-arylethanones (4a-j) General procedure: A mixture of α, α- dibromoacetophenones (1, 0.01 mol) and 3-aryl- 1,2,4-triazole-5-thiones (2, 0.01 mol) in anhydrous ethanol was refluxed for about 2 h. The reaction mixture was cooled to room temperature, neutralized with ammonium hydroxide and 2-(5-aryl-2H-1,2,4-triazol-3-ylthio)- 2-bromo-1-arylethanones (4), thus obtained, were recrystallized from ethanol to give the pure products in good yields (65-75%). 1-phenylethanone (4a) IR (ν cm -1 ): 1682 (C=O), 3410 (H); 1 H MR (CDCl3, 300MHz, ): 4.62 (CHBr), (m, 10H, aromatic); Elemental analysis for C16H12Br3OS: % Calcd. (Found): C, (51.28); H, 3.23 (3.19);, (11.20); DEPT-135: 4.86 (CH, positive peak). 1-p-tolylethanone (4b) IR (ν cm -1 ): 1674(C=O), 3433(H); 1 H MR (CDCl3, 300MHz, ): 2.43 (s, 3H, CH3), 4.66 (CHBr), (m, 9H, aromatic); Elemental analysis for C17H14Br3OS: % Calcd. (Found): C, (52.58); H, 3.63 (3.60);, (10.79); DEPT-135: 4.66 (CH, positive peak). 1-(4-chlorophenyl)ethanone (4c) IR (ν cm -1 ): 1682 (C=O), 3410 (H) 2011, IJARPB. All Rights Reserved 103

3 1 H MR (CDCl3, 300MHz, ): 4.65 (CHBr), (m, 9H, aromatic); Elemental analysis for C16H11BrCl3OS: % Calcd. (Found): C, (47.05); H, 2.71 (2.67);, (10.30). 1-(4-fluorophenyl)ethanone (4d) IR (ν cm -1 ): 1682 (C=O), 3302 (H) 1 H MR (CDCl3, 300MHz, ): 4.60 (CHBr), (m, 9H, aromatic); Elemental analysis for C16H11BrF3OS: % Calcd. (Found): C, (48.93); H, 2.83 (2.86);, (10.74). 1-(4-bromophenyl)ethanone (4e) IR (ν cm -1 ): 1651 (C=O), 3441 (H); 1 H MR (CDCl3, 300MHz, ): 4.68 (CHBr), (m, 9H, aromatic); Elemental analysis for C16H11Br23OS: % Calcd. (Found): C, (42.40); H, 2.45 (2.41);, 9.27 (9.29). 1-(4-nitrophenyl)ethanone (4f) IR (ν cm -1 ): 1643 (C=O), 3364 (H) 1 H MR (CDCl3, 300MHz, ): 4.71(CHBr), (m, 9H, aromatic); Elemental analysis for C16H11Br4O3S: % Calcd. (Found): C, (45.80); H, 2.64 (2.59);, (13.31). DEPT-135: 4.71 (CH, positive peak). 2-(5-(4-chlorophenyl)-2H-1,2,4-triazol-3-ylthio)- 2-bromo-1-phenylethanone (4g) IR (ν cm -1 ): 1690 (C=O), 3425 (H); 1 H MR (CDCl3, 300MHz, ): 4.69 (CHBr), (m, 9H, aromatic); Elemental analysis for C16H11BrCl3OS: % Calcd. (Found): C, (46.09); H, 2.71 (2.68);, (10.19). 2-(5-(4-chlorophenyl)-2H-1,2,4-triazol-3-ylthio)- 2-bromo-1-p-tolylethanone (4h) IR (ν cm -1 ): 1605 (C=O), 3410 (H) 1 H MR (CDCl3, 300MHz, ): 4.74(CHBr), ( 8H, aromatic); Elemental analysis for C17H13BrCl3OS: % Calcd. (Found): C, (48.29); H, 3.10 (3.03);, 9.94 (9.90); DEPT-135: 4.74 (CH, positive peak). 2-(5-(4-chlorophenyl)-2H-1,2,4-triazol-3-ylthio)- 2-bromo-1-(4-fluorophenyl)ethanone (4i) IR (ν cm -1 ): 1682 (C=O), 3418 (H); 1 H MR (CDCl3, 300MHz, ): 4.69(CHBr), ( 8H, aromatic); Elemental analysis for C16H10BrClF3OS: % Calcd. (Found): C, (44.09); H, 2.36 (2.31);, 9.85 (9.80). 2-(5-(4-chlorophenyl)-2H-1,2,4-triazol-3- ylthio)-2-bromo-1-(4-bromophenyl)ethanone (4j) IR (ν cm -1 ): 1682 (C=O), 3410 (H); 1 H MR (CDCl3, 300MHz, ): 4.60 (CHBr), ( 8H, aromatic); Elemental analysis for C16H10Br2Cl3OS: % Calcd. (Found): C, (39.38); H, 2.07 (2.09);, 8.62 (8.69). Synthesis of 2,6-diaryl thiazolo[3,2- b][1,2,4]triazole (5) via cyclization of 2-(5-aryl- 2H-1,2,4-triazol-3-ylthio)-2-bromo-1- arylethanone (4) General Procedure: 2-(5-aryl-2H-1,2,4-triazol-3- ylthio)-2-bromo-1-arylethanones (4) (1 g), was mixed with PPA (P2O5 (4.0 g) and H3PO4 (3 ml)) and heated at C for 2 hr. The reaction mixture was cooled, treated with water and neutralized with K2CO3. The solid, thus obtained, was recrystallized from ethanol to obtain the pure cyclized product 5. One pot synthesis of 2,6-diaryl thiazolo[3,2- b][1,2,4]triazoles (5) General Procedure: The 3-aryl-1,2,4-triazole-5- thiones (2) and α,α-dibromoacetophenones (1) were refluxed in absolute ethanol for 7-8 hr. The reaction mixture was cooled and neutralized with 2011, IJARPB. All Rights Reserved 104

4 aqueous ammonia. The solid product, so obtained, was filtered, washed and recrystallized from ethanol to obtain the pure products (5) in good yield (85-94%). 2,6-diphenylthiazolo[3,2-b][1,2,4]triazole (5a) M.P o C ( o C); Yield 86%. 1 H MR δ (CDCl3, 300 MHz): 7.12 (s, 1H), (m, 6H, aromatic), (d, 2H, aromatic), (d, 2H, aromatic). 2-phenyl-6-p-tolylthiazolo[3,2-b][1,2,4]triazole (5b) M.P o C; Yield 85%. 1 H MR δ (CDCl3, 300 MHz): 2.46 (s, 3H, CH3), 7.06 (s, 1H), (d, 2H, aromatic), (3H, m, aromatic), (d, 2H, aromatic), (d, 2H, aromatic). 6-(4-chlorophenyl)-2-phenylthiazolo[3,2- b][1,2,4]triazole (5c) M.P o C; Yield 89% 1 H MR δ (CDCl3, 300 MHz): 7.10 (s, 1H), (m, 7H, aromatic), (d, 2H, aromatic). 6-(4-fluorophenyl)-2-phenylthiazolo[3,2- b][1,2,4]triazole (5d) M.P o C; Yield 90%. 1 H MR δ (CDCl3, 300 MHz): 7.07 (s, 1H), (m, 5H, aromatic), (m, 4H, aromatic). 6-(4-bromophenyl)-2-phenylthiazolo[3,2- b][1,2,4]triazole (5e) M.P. 179 o C (180 o C); Yield 92%. 1 H MR δ (CDCl3, 300 MHz): 7.15 (s, 1H), (m, 3H, aromatic), (d, 2H, aromatic), (d, 2H, aromatic); (d, 2H, aromatic). 6-(4-nitrophenyl)-2-phenylthiazolo[3,2- b][1,2,4]triazole (5f) M.P o C ( o C); Yield 90%. 1 H MR δ (CDCl3, 300 MHz): 7.06 (s, 1H), (m, 6H, aromatic), (m, 3H, aromatic), (d, 2H, aromatic). 2-(4-chlorophenyl)-6-phenylthiazolo[3,2- b][1,2,4]triazole (5g) M.P o C ( o C); Yield 91%. 1 H MR δ (CDCl3, 300 MHz): (m, 4H, aromatic), 7.96 (s, 1H), (d, 2H, aromatic), (d, 2H, aromatic). 2-(4-chlorophenyl)-6-p-tolylthiazolo[3,2- b][1,2,4]triazole (5h) M.P. 140 o C; Yield 94%. 1 H MR δ (CDCl3, 300 MHz): 2.50 (s, 3H, CH3), (m, 4H, aromatic), (d, 2H, aromatic), (d, 2H, aromatic). 2-(4-chlorophenyl)-6-(4- fluorophenyl)thiazolo[3,2-b][1,2,4]triazole (5i) M.P. 170 o C; Yield 90%. 1 H MR δ (CDCl3, 300 MHz): 7.08 (s, 1H), (m, 4H, aromatic), (d, 2H, aromatic), (d, 2H, aromatic). 6-(4-bromophenyl)-2-(4- chlorophenyl)thiazolo[3,2-b][1,2,4]triazole (5j) M.P o C; Yield 90% 1 H MR δ (CDCl3, 300 MHz): 7.15 (s, 1H), (d, 2H, aromatic), (d, 2H, aromatic), (d, 2H, aromatic), (d, 2H, aromatic). BIOLOGICAL ACTIVITY Antimicrobial activity (bacteria and yeasts) The antimicrobial activity of 10 chemical compounds was evaluated by the agar well diffusion method. All the microbial cultures were adjusted to 0.5 McFarland standard, which is visually comparable to a microbial suspension of approximately cfu/ml. 20 ml of agar medium was poured into each Petri plate and plates were swabbed with 100 µl inocula of the test microorganisms and kept for 15 min for adsorption. Using sterile cork borer of 8 mm diameter, wells were bored into the seeded agar plates and these were loaded with a 100 µl volume with concentration of 4.0 mg/ml of each compound reconstituted in the 2011, IJARPB. All Rights Reserved 105

5 dimethylsulphoxide (DMSO). All the plates were incubated at 37 o C for 24 hr. Antimicrobial activity of each compound was evaluated by measuring the zone of growth inhibition against the test organisms with zone reader (HiAntibiotic zone scale). DMSO was used as a negative control whereas Ciprofloxacin was used as positive control for bacteria and amphotericin-b for yeast. This procedure was performed in three replicate plates for each organism (Ahmad et al., 2001; Andrews, 2001). Determination of Minimum Inhibitory Concentration (MIC) of chemical compounds MIC is the lowest concentration of an antimicrobial compound that will inhibit the visible growth of a microorganism after overnight incubation. MIC of the various compounds against bacterial and yeast strains was tested through a modified agar well diffusion method (Okeke et al., 2001; kere et al., 2005). In this method, a twofold serial dilution of each chemically synthesized compound was prepared by first reconstituting the compound in DMSO followed by dilution in sterile distilled water to achieve a decreasing concentration range of 256 to 0.5 µg/ml. A 100 µl volume of each dilution was introduced into wells (in triplicate) in the agar plates already seeded with 100 µl of standardized inoculum (10 6 cfu/ml) of the test microbial strain. All test plates were incubated aerobically at 37 o C for 24 hr and observed for the inhibition zones. MIC, taken as the lowest concentration of the chemical compound that completely inhibited the growth of the microbe, showed by a clear zone of inhibition, was recorded for each test organism. Ciprofloxacin and amphotericin B were used as positive control while DMSO as negative control. RESULTS AD DISCUSSIO Most of the literature methods available for the synthesis of thiazolo[3,2-b]-1,2,4-triazoles involve the condensation of α-halocarbonyl compounds with 1,2,4-triazoles. The reaction of α- bromoketones with 5-mercapto-3-aryl(1,2,4- triazoles) (2) leads to the formation of 2-(5- phenyl-2h-1,2,4-triazol-3-ylthio)-1- phenylethanone products (3) which on treatment with PPA results in cyclization leading to the formation of 2,6-diaryl thiazolo[3,2-b]-1,2,4- triazoles (5) (Dhaka et al., 1974). In order to compare the reactivity of α,α-dk with α- bromoketone, initially, α,α-dibromoacetophenone (1a) was treated with 5-mercapto-3-phenyl(1,2,4- triazole) (2a) in ethanol under the conditions reported in literature. The reaction was monitored by tlc and showed the formation of single compound. The usual workup of the reaction afforded a solid product. The physical and spectral data of the solid did not show any indication of the formation of expected product 3a, instead the characterization data revealed the formation of a new bromo product, 2-(5-phenyl- 2H-1,2,4-triazol-3-ylthio)-2-bromo-1- phenylethanone (4a). The IR of the compound 4a showed two characteristic peaks at 1682 (C=O) and 3410 (H). The MR showed one singlet at δ 4.86 corresponding to CHBr alongwith the multiplet for deserved number of aromatic protons. In DEPT-135, a positive peak at δ 4.86 clearly indicated the presence of methine proton. To establish the generality of this reaction, various α,α-dibromoacetophenones (1b-f) were treated with triazoles 2a-b in the similar manner. The reaction afforded the corresponding 2-(5- aryl-2h-1,2,4-triazol-3-ylthio)-2-bromo-1-parylethanones (4b-j) in all the cases (Scheme 1). All these products were new and fully characterized with the help of spectral data and elemental analysis. The physical data of the 5- aryl-2h-1,2,4-triazol-3-ylthio)-2-bromo-1-parylethanones (4a-j) is given in Table , IJARPB. All Rights Reserved 106

6 Ar' O H S Ar H H O + Ar CHBr 2 Ar' 1 2 H SH EtOH reflux, 4h Ar' 3 O H S Ar H Br 4 EtOH, reflux 7-8 hr PPA Ar Ar' S H where Ar = C 6 H 5, 4-MeC 6 H 4, 4-ClC 6 H 4, 4-FC 6 H 4, 4-BrC 6 H 4, 4-O 2 C 6 H 4 5 Ar' = C 6 H 5, 4-ClC 6 H 4 Scheme 1: Synthesis of 2,6-diaryl thiazolo[3,2-b]-1,2,4-triazoles by the reaction of α,αdibromoacetophenones with 3-aryl-5-mercapto-1,2,4-triazoles Table 1: Physical data of the 5-aryl-2H-1,2,4-triazol-3-ylthio)-2-bromo-1-p-arylethanones (4a-j) Compounds Ar Ar M.P. ( o C) Yield % 4a C6H5 C6H b C6H5 4-MeC6H c C6H5 4-ClC6H d C6H5 4-FC6H e C6H5 4-BrC6H f C6H5 4-O2C6H g 4-ClC6H4 C6H h 4-ClC6H4 4-MeC6H i 4-ClC6H4 4-FC6H j 4-ClC6H4 4-BrC6H Even after increasing the refluxing time, the compounds 3 were never isolated from this reaction; instead the cyclized products 5 were obtained directly after 7 h of refluxing. It is noteworthy to mention here that the similar products are obtained in the reaction of α-hk after 24 h of refluxing. The reaction further establishes the higher reactivity of α,α-dk than α-hk. All the compounds 5 were characterized by comparing their melting point and 1 H MR with the literature reports (Potts et al., 1971; Dhaka et al., 1974; Ramachandraiah et al., 1985; Britsun et al., 2005;). The newly formed bromo compounds 4 behaved similar to 3 in the reaction with PPA to give the cyclized products, 2,6- diarylthiazolo[3,2-b][1,2,4]triazoles (5) in good yields. The yield of the thiazolotriazoles 5 is better in one-pot rather via intermediate 4. All the 2011, IJARPB. All Rights Reserved 107

7 title compounds were screened for their antibacterial as well as antifungal activities. Biological results A total of six microbial strains were selected on the basis of their clinical importance in causing diseases in humans. Two Gram-positive bacteria (Staphylococcus aureus MTCC 96 and Bacillus subtilis MTCC 121); two Gram-negative bacteria (Escherichia coli MTCC 1652 and Pseudomonas aeruginosa MTCC 741) and two yeasts, Candida albicans (MTCC 227), and Saccharomyces cerevisiae (MTCC 170) were screened for evaluation of antibacterial and antifungal activity of the chemical compounds. All the microbial cultures were procured from Microbial Type Culture Collection (MTCC), IMTECH, Chandigarh. The bacteria were subcultured on utrient agar whereas yeast on Malt yeast agar. Tested chemical compounds possessed variable antibacterial activity against the Gram-positive bacteria (S. aureus and B. subtilis), Gram- negative bacteria (E. coli and P. aeruginosa) and antifungal activity against the yeast (S. cerevisiae and C. albicans). Positive controls produced significantly sized inhibition zones against the tested bacteria and fungi, however, negative control produced no observable inhibitory effect against any of the test organism. On the basis of maximum inhibitory activity shown against Gram positive bacteria, compounds 5a and 5d were found to be most effective against S. aureus with the zone of inhibition of 25 mm and 24.6 mm respectively and compound 5h was very effective against B. subtilis showing the zone of inhibition of 21.6 mm. For Gram negative bacteria, compound 5d was found to be best. It showed the zone of inhibition of 17.3 mm against Escherichia coli and 15.3 mm against P.aeruginosa. In case of fungi, compound 5i was found to be best. It inhibited the growth of C. albicans and S. cerevisiae with the zone of inhibition of 17.3 mm and 16.3 mm respectively (Table 2). Table 2: Antimicrobial activity of the title compounds 5 through agar well diffusion method Compounds Diameter of growth of inhibition zone (mm) a Staphylococcus aureus Bacillus subtilis Escherichia coli Pseudomonas aeruginosa Candida albicans Saccharomyces cerevisiae 5a b c d e f g h i j Ciprofloxacin t t Amphotericin- B t t t t o activity; a Values, including diameter of the well (8mm), are means of three replicates In the whole series, the MIC of various tested chemical compounds ranged between 16 and 256µg/ml against bacteria and between 32 and 128 µg/ml against fungi. Compound 5d was 2011, IJARPB. All Rights Reserved 108

8 found to be best as it exhibited the lowest MIC of 16 µg/ml against S. aureus; compound 5h showed the lowest MIC of 32 µg/ml against B. subtilis (Table 3). Among all the tested compounds, 5d was found to be best against bacterial pathogens and 5j against fungal pathogens. Table 3: Minimum inhibitory concentration (MIC) (µg/ml) of compounds 5 using modified agar well diffusion method Compound o. Staphylococcus aureus Bacillus subtilis Escherichia coli Pseudomonas aeruginosa Candida albicans Saccharomyces cerevisiae 5a t 128 5b t 128 5c d nt t 5e t f t t g t nt nt t 5h nt t 5i t nt j t nt nt t Ciprofloxacin t t Amphotericin- B t t t nt COCLUSIO An efficient α,α-dk mediated method for the synthesis of title compounds 5 is developed. Some new bromo compounds 4 are isolated which can be used as valuable electrophiles to carry out important synthetic transformations with various nucleophiles. REFERECES 1. Ahluwalia VK, Mehta B, Rawat M. An expeditious study of the nature of halogens at a- positions in carbonyl compounds. Synth Commun. 1992; 22: Ahmad I, Beg AJ. Antimicrobial and phytochemical studies on 45 Indian medicinal plants against multidrug resistant human pathogens. J Ethnopharmacol. 2001; 74: Amir M, Kumar H, Javed SA. Synthesis and pharmacological evaluation of condensed heterocyclic 6-substituted- 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazole derivatives of naproxen. Bioorg & Med Chem Lett. 2007; 17: Andrews JM. Determination of minimum inhibitory concentrations. J Antimicrob Chemother. 2001; 48: Barbuceanu SF, Almajan GL, Saramet I, Draghici C, Tarcomnicu AI, Bancescu G. Synthesis, characterization and evaluation of antibacterial activity of some thiazolo[3,2-b][1,2,4]triazole incorporating diphenylsulfone moieties. Eur J Med Chem. 2009; 44: Bhat KS, Holla BS. ovel three component synthesis of 1,2,4- triazolo[3,4-b]thiazoles and their antimicrobial activity. Phosphorus, Sulfur, and Silicon. 2004; 179: , IJARPB. All Rights Reserved 109

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