ISSN: 0973-4945; CODEN ECJHAO
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E-Journal of Chemistry Vol. 3, No.13, pp 307-312, October 2006
Microwave Assisted Synthesis of Some Biologically Active Benzothiazolotriazine Derivatives
PRASHANT KRIPLANI, PAWAN SWARNKAR, RINKU MAHESHWARI and K.G.OJHA* Department of Pure and Applied Chemistry M. D. S. University Ajmer-305 009(India) e-mail: kg_chemistry@rediffmail.com
Received 20 July 2006; Accepted 22 August 2006 Synthesis of some biologically active benzothiazolotriazine derivatives by microwave irradiation is reported. 2-Amino-6-substituted benzothiazoles 1 on treatment with benzaldehyde in anhydrous ethanol afforded 2benzylidenoimino-6-substitutedbenzothiazoles 2 which underwent cyclisation with ammoniumthiocyanate in dioxane to give 2-phenyl benzothiazolo [3,2-]-striazine-4-[3H] thiones 3.These both steps were carried out in microwave. Compound 3 with benzoyl chloride in anhydrous pyridine gave 2-phenyl-3(benzoyl) benzothiazolo [3,2-]-s-triazine-4-thiones 4 in good yields. The structure of all these compounds have been supported by their elemental analysis and their spectral data. All synthesized compounds were tested for their antibacterial activity using standard drug. Keywords: Benzothiazoles, s-triazines, microwave irradiation, antibacterials

Abstract:

Introduction
Heterocyclic compounds containing nitrogen and sulphur possess potential pharmacological activities1-4. Benzothiazole moiety constitute an important class of heterocyclic compounds possessing diverse type of biological activities viz. antibacterial5, fungicidal6, antituberculotic7,antiallergic8,anticancer9etc.Triazine derivatives are also associated with broad spectrum antibacterial10,antifungal11, antiviral activity12-14 against numerous viruses viz. Rauscher viruses, Leukemia Moloney viruses, Leukemia Rhinovirus type-2,influenza virus type-2,Vaccinia viruses, Vasicular stomatitis and Measules viruses. In view of the activities exhibit by benzothiazoles and triazines, we have reported synthesis of some new

K.G.OJHA et al.

benzothiazolotriazine derivatives by conventional method in our earlier paper15.As a part of our continuing interest in biologically active benzothiazolotriazine derivatives, we are reporting a route for synthesis of these compounds by microwave irradiation. Traditional synthesis of compounds suffered from the disadvantages such as long reaction time, low yield and inconvenience of handling. In recent years the use of microwave technology in organic synthesis has received considerable attention. This technology can increase the purity of products, enhance the chemical yield and shorten the reaction time16. All synthesized compounds were tested for their antibacterial activity using standard drug.

Experimental

All the melting points are uncorrected. The purity of synthesized compounds has been checked by thin layer chromatography. IR spectra are recorded on FT-IR Perkin-Elmer (Spectrum RX1) spectrophotometer(max in cm-1) using KBr disc.1H NMR spectra are recorded in CDCl3 on a Bruker DRX-300 MHz using TMS as internal standard. The chemical shifts are reported as parts per million (ppm).Microwave synthesis was carried out in a domestic microwave oven model L.G. MS-194W, 230-50 Hz., 800W.
Microwave synthesis of 2-benzylidenoimino-6-substitutedbenzothiazoles 2
A mixture of 2-amino-6-substitutedbenzothiazole 1 (0.001mol) and benzaldehyde (0.001 mol) in minimum quantity of anhydrous ethanol were taken in Erlen Meyer flask capped with a funnel placed in a microwave oven and irradiated at 160 Watt for 1 to 1.5 minutes. The reaction was monitered by silica gel TLC. (Benzene : Acetone 70 : 30).After completion the reaction , the reaction mixture was allowed to attain room temperature and solid separated was filtered. The crude product was recrystallized from redistilled ethanol.
Microwave synthesis of 2-phenyl benzothiazolo [3,2-]-s-triazine-4-[3H] thiones 3
A mixture of 2-benzylidenoimino-6-substitutedbenzothiazole 2 (0.001mol) and ammoniumthiocyanate (0.002mol) were dissolved in minimum quantity of 1,4-dioxane and were taken in Erlen Meyer flask capped with a funnel placed in a microwave oven and irradiated at 160 Watt for 1.5 to 2 minutes. The reaction was monitered by silica gel TLC.(Hexane : DMF 80 : 20).After completion the reaction , the reaction mixture was allowed to attain room temperature and solid separated was filtered. The crude product was recrystallized from redistilled ethanol.
Synthesis of 2-phenyl-3-(benzoyl) benzothiazolo [3,2-]-s-triazine-4-thiones 4
2-Phenyl benzothiazolo [3,2-]-s-triazine-4-[3H] thiones 3 (0.005mol) was dissolved in minimum quantity of anhydrous pyridine (10ml).To this solution was added benzoyl chloride (0.01mol) dropwise with constant shaking in cold conditions. The reaction mixture was further stirred for 1 hour and poured into acidified icecold water. The solid separated out was filtered and washed repeatedly with water, dried in vacuo and recrystallised from redistilled ethanol.

Results and Discussion

The required 2-amino-6-substitutedbenzothiazoles 1 were prepared by methods reported in literature17,18. The synthesis of compounds 3 starting from 2-amino-6-substituted benzothiazoles 1 from conventional method was reported earlier15 by us. The same reaction scheme was carried out under microwave conditions. It is noteworthy that the reaction which required 4 to 6 hours in conventional methods, was completed within 1 to 2 minutes under microwave conditions and yields have also been improved. Finally compounds 3 on treatment with benzoyl chloride in presence of anhydrous pyridine in acidified cold conditions gave compounds 4(Figure 1). All the synthesized compounds have been characterized on the basis of their physico-chemical data (Table 1) and spectral analysis. Compounds 3 and 4 contain chiral centre and thus exhibit optical activity. The products obtained after purification are dextrorotatory as observed by their optical activity in acetone solution. It seems that the laevo products are obtained in minor quantities and are removed during purification and crystallization.
Figure 1. Reagents and Conditions : (a) Benzaldehyde, Ethyl alcohol, MWI for 1-1.5 minutes (b) NH4SCN,1,4-dioxane, MWI for 1.5-2.0 minutes (c) PhCOCl, Pyridine, in cold conditions. Table 1. Physico-Chemical data of synthesized compounds (C.M.=Conventional M.W.=Microwave) Compound Reaction Period C.M M.W h min 1.5 1.1.2 Yield % C.M M.W M.P. 0 C M.W (C.M.) 161 (160)(190)(260)(120)(110)(125) (285) (165) (136) (105) (298) (130) 15 method,
Elemental Analysis Cald /(Found) % C 61.05 (60.09) 52.99 (51.96) 59.36 (59.23) 68.08 (68.01) 54.29 (55.54) 47.87 (47.79) 52.63 (51.99) 59.82 (56.88) 62.93 (61.74) 56.89 (55.67) 61.39 (60.38) 67.13 (66.78) H 0.03 (0.028) 0.02 (0.018) 0.03 (0.028) 0.04 (0.041) 0.03 (0.027) 0.02 (0.018) 0.03 (0.029) 0.04 (0.039) 0.03 (0.04) 0.03 (0.026) 0.03 (0.031) 0.04 (0.034) N 10.27 (11.11) 8.83 (7.98) 14.84 (15.10) 9.92 (9.98) 12.66 (13.48) 11.17 (11.14) 16.37 (16.23) 12.31 (12.34) 10.01 (9.97) 9.05 (9.10) 13.02 (13.00) 9.79 (9.78)

R Cl Br NO2 OC2H5 Cl Br NO2 OC2H5 Cl Br NO2 OC2H5
2a 2b 2c 2d 3a 3b 3c 3d 4a 4b 4c 4d

Antibacterial Activity

All the synthesized compounds were screened for their antibacterial activity against E.Coli, Pseudomonas aeruginosa and Staphylococcus aureus using Muller Hinton Agar media (Hi Media). The activity was carried out using paper disc method. The zone of inhibition measured in mm. The results of antibacterial activity were tabulated (Table 2) in the form of activity index. Table 2. Antibacterial activity of synthesized compounds S.No. 13 Compd. 2a 2b 2c 2d 3a 3b 3c 3d 4a 4b 4c 4d Ceftazidime E.Coli 0.93 1.00 1.16 0.80 1.00 1.06 1.16 1.00 1.03 1.30 1.33 1.00 1.00 Ps.aeruginosa 0.68 1.00 1.20 0.84 0.84 1.12 1.28 1.04 0.92 1.44 1.40 1.24 1.00 S. aureus 1.11 1.39 1.66 1.22 1.33 1.66 1.89 1.61 1.50 1.94 2.11 1.72 1.00
Zone of inhibition of compound in mm Zone of inhibition of standard drug in mm DMF was used as a solvent. Standard drug Ceftazidime(Ca)(30g/ml) was used for comparison. The compounds were tested at 500g/ml concentration. The observations show that activity index of compound 4c is maximum against E.Coli, activity index of compound 4b is maximum against Pseudomonas aeruginosa, activity index of compound 4c is maximum against Staphylococcus aureus. Activity index =

Conclusion

In above synthetic scheme we use microwave irradiation technique, this leads to considerable saving in the reaction time and energetically profitable. The smaller volume of solvent required contributes to saving in cost and diminishes the waste disposal problem. Compounds 4b and 4c show potential antibacterial activity.

Acknowledgement

Authors are thankful to Head, Department of Pure and Applied Chemistry, M.D.S University, Ajmer India for providing necessary laboratory facilities , to the Director,
CDRI Lucknow India for providing elemental analysis, spectral analysis and Head , Department of Microbiology, J.L.N. Medical College, Ajmer India for providing antibactrial screening facility. Authors also express thanks to CSIR New Delhi India for providing JRF to one of them.(P. Kriplani)

References

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. Katrizky A R,Advances in Heterocylic Chemistry Academic Press, London 1985,135. Proto G and Thomson R H , Endeavour 1976,35, 32. Faria C , Pinza M , Gabma A and Piffen G, Eur.J.Med. Chem.Chim.Ther., 1979,14, 27. Roberts J J and Warwich G P, Biochem. Pharmacol., 1963,12,135. Ansari A S and Banerji J C B, J. Ind. Chem. Soc., 1998,75,108. Sidoova E and Bujdakova H, Pharmazie., 1994,49,375. Waisser K, Dolezal M, Sidoova. E and Odlerova Z, Drasta. J., Chem.Abstr., 1989,110,128063e Uclaf Rousel, Kokai Jpn and Koho, Tokkyo., Chem. Abstr., 1987,106,15649g. Wells G, Bradshaw T D, Diana P, Seaton A, Shi D F, Westwell A D and Stevens M F G, Bioorg. & Med.Chem.lett., 2000,10, 513. Joshua C P, George Abraham and Alaudeen M, J. Indian Chem.Soc., 2004,81,357. Mohan J and Anupama, Indian J.Chem., 2003,42B,2003. Poonian M S, Nowoswiat E F, Blount J F and Karmer M J, J. Med.Chem. 1976,19,1017 Misra V S, Dhar S, Chowdhary B L, Pharmazie, 1976,33 ,790. Chirigos M A, Moloney J B, Humphreys S R, Mantle N, Goldin A, Cancer Res., 1961,21,803. Kriplani P, Swarnkar P and Ojha K G, Heterocyclic Communications 2005, 11(6), 527. (a) Galena S A, Chem.Soc. Rev., 1997,26,233. (b) Sonali R ,Resonance, 2000,5,77. (c) Lindstrom P, Tierney J, Wathey B and Westman J,Tetrahedron,2001,57,9225. (d). More D H, Pawar. N S, Dewang. P M, Patil S L, Mahulikar P P, Rus.J Gen. Chem, 2001, 74(2), 2244. (e) More D H, Pawar N S, Mahulikar P P, J. Sci. Ind.Res. 2003,62,1024. Gupta R R, Jain S K and Ojha K G, Synth.Commun., 1979,9(6), 457. Gupta R R, Ojha K G, Kumar M, J Heterocyclic Chem., 1980, 17,1325.

ISSN: 0973-4945; CODEN ECJHAO
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Vol. 4, No. 2, pp 232-237, April 2007

E-Journal of Chemistry

Microwave Assisted Synthesis Spectral and Antibacterial Investigations on Complexes of Mn(II) With Amide Containing Ligands
N. BHOJAK,* D. D. GUDASARIA, N. KHIWANI and R. JAIN Green Chemistry Research Centre, P.G. Department of Chemistry, Govt. Dungar College (A-Grade), University of Bikaner, Bikaner 334003.
Received 19 November 2006; Accepted 16 December 2006 Abstract: The present research work describes the synthesis, spectral and antibacterial studies on the complexes of Mn(II) with amide group containing ligands. Synthesis of complexes has been carried out by conventional method as well as by microwave method. The complexes have been characterized on the basis of elemental analysis, infrared, electronic spectra and magnetic susceptibility studies. The diffuse reflectance spectrums of the complexes show bands in the region 20,000 cm-1 to 26,000 cm-1 assignable to 6A1g 4 T2g and 6A1g 4E1g transitions. These are also typical of tetrahedral environment around the manganese. The magnetic moment (5.80 BM) of the complex indicates high spin tetrahedral environment. The microwave method of synthesis of complexes have been found easier, convenient and ecofriendly. Keywords: Manganese(II), microwave, amide ligands

Introduction

Manganese is essential to organisms and activates numerous enzymes and for certain enzymes there appears to be a high specificity for manganese(II). Deficiency in soils has led to the infertility in mammals bone malformation in growing chicks.1 The ability of Mn(II) to substitute for Mg(II), a more common physiological cofactor in wide variety of enzymatic reactions has made Mn(II) popular as a spectroscopic probe for the Mg(II) site

N. BHOJAK et al.

in many enzymatic complexes.2 Replacement of Mg(II) by Mn(II) may have different functional consequences with different enzymes. However, there are a number of similarities in the coordination properties of two ions, and in many cases, the maximal rates of enzymatic reaction activated by Mn(II) are nearly equivalent to those obtained with Mg(II). Living organisms can certainly differentiate between the two ions as evidenced by their separate metabolic routes. Thus, Mn(II) still remains one of the best surrogate for Mg(II) in studies of enzymic complexes.3 Investigations on amide ligands is significant due to their biological and analytical importance.4-6 The present research work describes the synthesis, spectral and antibacterial studies on the complexes of Mn(II) with amide group containing ligands. The complexes have been characterized on the basis of elemental analysis, infrared, electronic spectra and magnetic susceptibility studies.

Experimental

All the chemicals and solvents used were of AR grade. Purity of synthesized compounds has been checked by thin layer chromatography. IR spectra are recorded on FT-IR Perkin Elmer spectrophotometer RX1 (max in cm-1) using KBr disc. 1H NMR spectra are recorded in CDCl3 on a Bruker DRX-300 MHz using TMS as internal standard. The chemical shifts are reported as parts per million (ppm). Magnetic susceptibility measurements were carried out on the vibrating sample magnetometer (VSM) model 155 at 5500 Gauss field strength. Microwave synthesis was carried out in domestic microwave oven model L.G. MS-194W, 230-50Hz, 800W. Beck Man DU-64 Spectrophotometer, with quartz cell of 10mm light path was used for absorption measurement.
Microwave Irradiation synthesis of ligands
Four ligands i.e. N, N'-bis-(3-carboxy-1-oxopropanyl)-1,2-ethylenediamine(CPE), N,N'-bis(3-carboxy-1-oxo-propanyl)-1,2-phenylenediamine (CPP), N,N'-bis-(2-carboxy-1oxophenelenyl)-1,2-phenylenediamine(CPPP) N,N'-bis-(3-carboxy-1-oxoprop-2-enyl)-1,2phenylenediamine (CPP-2) were synthesized. In a typical preparation mixture of amine (1.0 mmol) and carboxylic acid (2.1 mmol) were taken in Erlen Meyer flask capped with a funnel placed in a microwave oven and irradiated at 200 watt for 2 minutes. The reaction was monitored by TLC. After completion the reaction, the reaction mixture was allowed to attain room temperature and solid separated was filtered. The crude product was recrystallized from redistilled ethanol.
Microwave Irradiation synthesis of Mn(II) complexes

For the preparation of various complexes, a slurry of ligand (i.e. CPE, CPP, CPPP or CPP-2) (1 mmol) was prepared in water or in water-ethanol mixture. In this a solution of Mn (CH3COO)2.4H2O (1 mmol) was added. The resulting mixture was irradiated in a microwave oven for 2 to 6 minutes at medium power level (600W) maintaining the occasional shaking. The mixture was cooled to room temperature and poured into ice chilled methanol and dried in vacuum over P2O5. In order to synthesize complexes with CPPP prolonged irradiation and cooling was required. Complexes and ligands were also synthesized by conventional method and results were found satisfactory.
Microwave Assisted Synthesis and Antibacterial Investigations

Results and Discussion

Ligands and complexes were identified on the basis of elemental analysis and spectral studies. Colour, yield and elemental analysis data are represented in Table 1.
Vibrational spectra: Few diagnostic IR bands are given in Table 2 (C=O) and (C-O)
stretching frequencies in the region 1595-1535 cm-1 and 1420-1400 cm-1 observed for free ligands and assigned to asymmetric and symmetric modes respectively are shifted in the complexes. These shifts consequently increase the difference between the frequencies of asymmetric and symmetric modes of carboxylate group known as. An increase in the value of has been ascribed to coordination of carboxylate groups to central metal ion in unidentate fashion. The IR bands due to amide (N-H) mode observed at 3397-3209 cm-1 for the free ligands are shifted to higher frequencies indicating non-participation of N of amide group in coordination. Amide I bands due to (C=O) shift negatively opposite to that of (N-H) in the complexes suggesting carbonyl oxygen coordination. Bands observed at 257-224 cm-1 assigned to (Mn - O)7-9 Table 2. IR Spectral assignments of diagnostic bands of ligand and its Mn(II) complexes S.No. Ligand and complexes 1 CPE 2 Mn(II)-CPE 3 CPP 4 Mn(II)-CPP 5 CPPP 6 Mn(II)-CPPP 7 CPP-Mn(II)-CPP2

a = amide I band

N-H C=Oa (C-N+N-H)b (N-H+C-N)c 1280 1288

COO(asym) 1535 1541

COO(sym) 1415 1400
(Mn-O) --247 --257 --224 --248
b = amide II band c = amide III band
Table 1. Physico-Chemical Data of Mn(II) complexes (C.M. = conventional method; M.M. = Microwave method) S.No. Complex Mn(II)CPE Mn(II)CPP Mn(II)CPPP Mn(II)CPP2 Colour Off white Brown Brown Brown Reaction Period C.M. M.M. (h) (min) 1.4 1.5 Yield (%) C.M. M.M. Elemental Analysis Calcd(Found) (%) C 38.25 (38.10) 46.27 (46.29) 56.52 (57.33) 44.6 (46.81) H 5.10 (5.08) 4.30 (4.41) 3.41 (3.48) 3.3 (3.34) N 5.0 (5.08) 4.38 (4.41) 3.41 (3.48) 3.3 (3.34)

Magnetic moments and electronic spectra: Room temperature magnetic moments of the Mn(II) complexes fall in the range 5.6 - 6.02 BM. These values are typical of tetrahedrally coordinated Mn which has five unpaired electrons. The visible spectra of these complexes have been measured in methanol are reported in Table 3. The observed values exhibits bands in the region 20,000 cm-1 to 26,000 cm-1 assignable to 6A1g 4T2g and 6A1g 4E1g,4A1g transitions. These are also typical of tetrahedral environment around the manganese10-11. Antibacterial activity: The antibacterial activity of the compounds against E.coli and S.aureus were carried out using Muller Hinton Agar media (Hi media). The activity was carried out using paper disc method represented in Table 4. Among the various compounds CPPP and its Mn(II) complexes has been found out to be most effective against these microbes showing maximum clarity of zones.
Table 3. Magnetic moments and electronic spectral data of the Mn(II) complexes. S.No. Complex Mn(II)-CPE Mn (II)-CPP Mn (II)- CPPP Mn (II)-CPP-2 eff (BM) 5.58 5.64 5.70 6.00 Electronic Spectral bands max(cm-1) Tentative assignments
Comment Tetrahedral Mn(II) Tetrahedral Mn(II) Tetrahedral Mn(II) Tetrahedral Mn(II)
A1g 4Eg, 4A1g 6 A1g 4T2g 6 A1g 4Eg, 4A1g 6 A1g 4T2g 6 A1g 4Eg, 4A1g 6 A1g 4T2g 6 A1g 4Eg, 4A1g 6 A1g 4T2g E.coli 22 S.aureus 20
Table 4. Antibacterial activity of synthesized compounds S.No. 9 Compound (100 ppm) CPE Mn(II)-CPE CPP Mn(II)-CPP CPPP Mn(II)-CPPP CPP-2 Mn(II)-CPP-2 Chloramphenicol

Conclusions

Mn(II) complexes were found to coordinate through amide oxygen and carboxylate oxygens as revealed by the IR spectroscopy. The magnetic moment for all the complexes recorded corresponds to five unpaired electron. Although we were unable to get single crystals for X-ray studies, magnetic, electronic and vibrational spectroscopic data showed the tetrahedral geometry for all the complexes. Tentative structure of complexes is proposed as Fig 1a Mn(II)-CPE, 1b Mn(II)-CPP, 1c Mn(II)-CPPP, 1d Mn(II)-CPP-2.

Acknowledgements

Authors are thankful to SAIF CDRI Lucknow for spectral Analysis. One of the authors (RJ) is thankful to CSIR for SRF

References

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Gotzias G C Fed. Proc. Supplement, 1961, 10, 98. Sauer K, Accts. Chem. Res., 1980, 1, 32. Coleman W M and Taylor L T, Coord Chem. Rev., 1980,32,1. Pecoraro V L, Baker Li X, Butler M J and Bonadies J A, Recueil Trav. Chim., 1987, 106, 221. Garg B S , Bhojak N, Sharma R K, Bist J S and Mittal S, Talanta 1999, 48, 49. Garg B S , Bhojak N, Nandan D, Ind. J. Chem., 2005, 44A, 1504. Sarojini T A and Ramchandra A, Ind J Chem, 1990, 29A,1174. Beukeleer S D, Desseyn H O, Zoupa E M and Perleps S P, Trans. Met. Chem., 1994, 19,468. Nakamoto K, Infrared and Raman Spectra of Inorganic and Coordination Compounds, Wiley-Interscience Publication, 1977, 3 Singh R, Sharma K and Fahmi N, Trans. Met.Chem., 1999, 24, 562. Paul R C, Chopra R S, Bhambri R K and Singh G, J. Inorg. Nucl. Chem., 1974, 36, 3703.