Keywords:
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| Chalcones, 2-hydroxy pyrimidines, antibacterial activity, antifungal activity. |
Introduction
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| Chalcones show impressive physiological properties and some of them posses wide range of activities such as antibacterial1 , antiviral2 , antitubercular3 antifungal4, antiinflammatory4 etc. chalcones act as one of the key intermediate for the synthesis of various heterocyclic compounds. |
| Pyrimidine derivatives are reported to possess antiviral5, antileshmanial6, antimicrobial7, anti-inflammatory7, anthelmentic8 etc., Several important sulfa drugs like Sulfadiazine, Sulfamerazine and Sulfadimidine contains Pyrimidine moiety. A variety of natural products such as alkaloids also contain the pyrimidine ring system, these include hypoxanthine and xanthine, which occur in tea, and caffeine and theophylline (the constituents of tea leaves). |
| The key intermediate Chalcones (3a-l) have been synthesized by Claisen-Schmidt condensation reaction by reacting thiophene-2- carbaldehyde and various substituted aromatic ketones in alcohol medium as per the reported procedure9. The resulted Chalcones (3a-l) undergoes selective cyclization with urea in presence of NaOH in alcohol medium to yield the title compounds 2-hydroxy Pyrimidine derivatives. By considering the above facts and in search of small molecules as potential drug candidates, in the present study we have planned to synthesize a novel series of 2-hydroxy pyrimidines followed by their In-vitro antibacterial, antifungal and antitubercular evaluation. The reaction sequence leading to the formation of title compounds is depicted in Scheme-01 |
Experimental
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| Melting pints were recorded in open capillaries with electrical melting point apparatus and were uncorrected. IR spectra (KBr disks) were recorded using Bruker-α IR spectrophotometer. 1H NMR is recorded in Bruker Avance (400 MHz) Spectrometer in CDCl3 solution, with TMS as an internal standard reference. Mass spectra were recorded on a Micromass Q-TOF spectrometer. Elemental analysis was carried out using Vario Elementary Model CHN analyzer instrument. TLC was performed on silica gel coated plates for monitoring the reactions. |
| Synthesis of 2-hydroxy pyrimidines (4a-l) |
| A mixture of Chalcones (3a-l) (0.01 mol) and urea (0.01 mol) was dissolved in ethanol (30 ml) containing few drops of NaOH. The reaction mixture was refluxed on water bath at 70-800C gently for about 8-10 hrs, the progress of the reaction was monitored by TLC (benzene: chloroform 8:2). The hot reaction mixture was then filtered and allowed to cool. The resulting solid so obtained was filtered, washed several times with distilled water, dried and recrystallized from ethanol.The physical data of 2-hydroxy pyrimidines (4a-l) is given in table-1. |
| 4-(4-nitrophenyl)-6-(thiophen-2-yl) pyrimidin- 2-ol (4a) IR (cm-1): 3451 (OH), 3100 (C-H), 1654 (C=N), 1581 (C=C), 1522 & 1343 (NO2), 698 (C-S).1H-NMR (1 PPM): 6.64-7.98 (m, 8H, Ar-H) 10.46 (s, 1H, OH).Mass: 300 (M+1) |
| 4-(4-chlorophenyl)-6-(thiophen-2-yl) pyrimidin-2- ol (4b) IR (cm-1): 3442 (OH), 3105 (C-H), 1671 (C=N), 1588 (C=C), 825 (C-Cl ), 700 (C-S).1H NMR (1 PPM): 7.08- 7.97 (m, 9H, 8H, Ar-H), 11.68 (s, 1H, OH).Mass: 289 (M+1) |
| 4-(thiophen-2-yl)-6-(p-tolyl) pyrimidin-2-ol (4c) IR (cm-1): 3443 (OH), 3097 (C-H), 1658 (C=N), 1593 (C=C), 719 (C-S).1H NMR (1 PPM): 2.43 (s, 3H, CH3), 7.08-7.95 (m, 8H, Ar-H), 9.52 (s, 1H, OH).Mass: 269 (M+1) |
| 4-(4-aminophenyl)-6-(thiophen-2-yl) pyrimidin-2- ol (4d) |
| IR (cm-1): 3317 (OH), 3217 (NH), 3099 ( C-H), 1634 (C=N), 1599 (C=C), 681 (C-S).1H NMR (1 PPM) : 4.9 (s, 2H, NH2). 6.64-7.87 (m, 8H, Ar-H), 9.88 (s, 1H, OH).Mass: 270 (M+1) |
| Biological evaluation |
| Antimicrobial Activity |
| The In-Vitro anti-microbial screening of the newly synthesized 2-hydroxy pyrimidines was carried out against Gram-positive organisms ((E. Fecalis and S. Aureus),Gram-negative organisms (K.pneumoneae and E. Coli) and fungi (C. albicans and A. niger) by conventional tube dilution method10 and compared with that of the standard drug Ciprofloxacin and Flucanazole respectively. |
| Dilutions of each drug were prepared with brain heart infusion broth (BHI) for MIC. A stock solution of drug with concentration 1000 μg/10μl was prepared in DMF. In the initial tube 20 μl of drug was added into the 380 μl of brain heart infusion broth. For dilutions 200 μl of brain heart infusion broth was added into the next 10 tubes separately. Then from the initial tube 200 μl was transferred to the first tube containing 200 μl of brain heart infusion broth. This was considered as 10-1 dilution. From 10-1 diluted tube 200 μl was transferred to second tube to make 10-2 dilution. The serial dilution was repeated up to 10-10 dilution for each drug. From the last tube 200 μl of solution was discarded. From the maintained stock cultures of required organisms, 5 μl was taken and added into 2ml of brain heart infusion broth (Himedia). In each serially diluted tube 200 μl of above culture suspension was added. The tubes were incubated for 24 hrs and observed for turbidity. MIC of each drug was defined as the lowest concentration that produces no visible turbidity after incubation time. |
| In the antibacterial activity, compounds 4c, 4e, 4g and 4h have showed significant activity against gram positive organisms, and most of the synthesized compounds displayed moderate activity aginst K.pneumoneae and compounds 4a and 4g showed good activity aginst E.Coli. In the antifungal activity compounds 4c, 4d, 4k and 4l showed good activity against C.albicans and compounds 4a, 4c, 4d and 4k showed good activity against A.fumigatus. The antimicrobial data of the compounds (4a-l) is given in table-2. |
| Antitubercular activity |
| The antitubercular activity of the synthesized Pyrimidines (4a-l) were carried out by using Middle brook 7H9 agar medium against M. tuberculosis H37Rv strain by Microplate Alamar Blue Assay (MABA)11 method. The Middle brook 7H9 agar medium containing different derivatives, standard drug as well as control was inoculated with M. tuberculosis H37Rv strain. The inoculated plates were incubated at 37O C for four weeks. At the end of four weeks they were checked for growth. |
| The new compounds 4a, 4d, 4e, 4f and 4g have showed significant antitubercular activity with MIC ranging at 12.5 μg. INH was used as standard drug for comparison purpose. The antitubercular data of the compounds (4a-l) is given in table-3. |
Acknowledgements
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| The authors of thankful to authorities of Department of Pharmaceutical Chemistry, SJM College of Pharmacy, Chitradurga and Nitte university, Mangalore for providing necessary facilities. Authors are also thankful to authorities of Department of Microbiology, Maratha Mandal’s NRGH Dental College, Belgaum for antimicrobial and antitubercular studies. The authors are thankful to SAIF, Panjab University, Chandigarh for 1H NMR spectral data and Mass spectral data. |
Tables at a glance
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Figures at a glance
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| Figure 1 |
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