SYNTHESIS AND IN-VITRO STUDIES OF SOME NEW QUINOLINE 1 , 3 , 4-THIADIAZOLO PYRIMIDIN DERIVATIVES

A series of eight new quinoline associated 1,3,4-thiadiazolo pyrimidin derivatives (5a-h) have been developed using 4-amino-8-fluoro-quinoline-3-carboxylic acid ethyl ester (1) as raw material and by involving 8-fluoro-4-methylsulfanylthiocarbonylamino-quinoline-3-carboxylic acid ethyl ester (2), 8-fluoro-4hydrazine thiocarbonylamino-quinoline-3-carboxylic acid ethyl ester (3) and 3-amino-7-fluoro-2-mercapto-3Hpyrimido-[5,4-c]quinolin-4-one (4) as intermediates. The title compounds after structure elucidation were used in vitro to find their antibacterial ability towards different micro-organisms.


EXPERIMENTAL
All the reagents and solvents were used as purchased without further purification.Melting points were determined on a Fisher-Johns melting point apparatus and are uncorrected.IR spectra were obtained on a Perkin-Elmer BX serried FTIR 5000 spectrometer using KBr pellet.NMR spectra were recorded on a Varian 300 MHz spectrometer for 1 H-NMR and 100 MHz for 13 C-NMR.The chemical shifts were reported as ppm down field using TMS as an internal standard.Mass spectra were recorded on a VG-Micromass 7070H spectrometer operating at 70 eV.
The antimicrobial studies were conducted by broth method.The broth culture is incubated in non-CO 2 incubator at 35 o C until it achieves or exceeds the turbidity of the 0.5 McFarland standard (usually 2 to 6 hours).By obtaining isolated colonies of bacterial strains to test and combine the colonies and culture in rich media, incubate overnight and count colonies.The turbidity of the actively growing broth culture is adjusted with sterile saline or broth to obtain a turbidity optically comparable to that of the 0.5 McFarland standard and verified cfu/mL count of visible media and the collective results were noted.

Synthesis of 8-fluoro-4-methylsulfanylthiocarbonylamino-quinoline-3-carboxylic acid ethyl ester (2)
To a mixture of 4-amino-8-fluoro-quinoline-3-carboxylic acid ethyl ester (1) (0.01 mol) in dimethyl sulphoxide (10 mL) at room temperature was added carbon disulfide (1.4 mL) and aqueous sodium hydroxide (1.0 mL) solution in drop wise.After 30 min dimethyl sulfate (2.3 g) was added under cold conditions by keeping in an ice bath.The reaction mixture then constantly stirred at room temperature for 1.5 h.After completion of the reaction (monitored by TLC), the resultant solution was poured in ice water.The solid that separated out was filtered, dried and recrystallized from ethanol to get pure 8-fluoro-4-methylsulfanylthiocarbonylamino-quinoline-3-carboxylic acid ethyl ester (2).
The in-vitro antibacterial activity of compounds 5a-h towards different tested bacterial organisms disclosed significant activity with a degree of variation (Table1).It is found that compound 5e displayed considerable activity against B. subtilis.Compounds 5b and 5f are significant active towards M. luteus compared to standard drug.Notable activity is also achieved for compound 5d against S. aureus.All the quinoline based 1,3,4-thiadiazolo pyrimidin derivatives (5a-h) have performed significant to moderate activity against gram-negative bacteria.Derivative 5g has displayed marked activity against S. typhimurium.Remaining derivatives such as, compounds 5a and 5h displayed least activity against all the tested microorganisms.Compounds 5c and 5d were showing significant activity against E. coli.The outstanding properties of this new class of antibacterial substances deserve further investigation in order to clarify the mode of action at molecular level, responsible for the activity observed.

CONCLUSIONS
From the current investigation of anti-microbial and antibacterial screening of all the synthesized compounds, it was proved that all the compounds exhibiting better activity against positive organisms and five gram-negative bacteria.From these results, it was observed that 5e was exhibiting activity more than the slandered drug Benzyl Penicillin against B. subtilis and also considerable active against the second slandered drug Streptomycin.Similarly 5b and 5f are active against M. luteus, makeable activity of compound 5d against S. aureus.Compounds 5c and 5d were showing similar activity against E. coli.Also among 5a-h, it was a common observation that 5a was showed lowest activity against all the bacteria.This was may be because of no substitution on phenyl ring.5a-h exhibited the maximum activity by inhibiting the growth of all the bacteria to a greater extent in comparison with the standard drug Streptomycin.From the structure-activity relationship and to optimize the effectiveness of this series of molecules extensive study is also warranted to determine additional physicochemical and biological parameters.

Table 1 .
The in-vitro antibacterial activity of compounds 5a-h (zone of inhibition in mm).