Microwave Assisted Synthesis of Some Biologically Active Benzothiazolotriazine Derivatives
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Microwave Assisted Synthesis of Some Biologically Active Benzothiazolotriazine Derivatives
PRASHANT KRIPLANI 0
PAWAN SWARNKAR 0
RINKU MAHESHWARI 0
K.G.OJHA 0
0 Department of Pure and Applied Chemistry M. D. S. University Ajmer-305 009(India)
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-α]-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-α]-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.
Benzothiazoles; s-triazines; microwave irradiation; antibacterials
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
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(νmax 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-α]-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-α]-s-triazine-4-thiones 4
2-Phenyl benzothiazolo [3,2-α]-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.
Spectral Analysis of compounds 2a-2d,3a-3d,4a-4d.
Compound 2a: M.F.C14H9N2SCl, IR (KBr) ν max in cm-1859(C-Cl),1349(C-S),1597(C=N),
1447,1535(ArC=C), 1HNMR (300MHz, (...truncated)