Research Article Synthesis and Antimicrobial Studies of Pyrimidine Pyrazole Heterocycles Rakesh Kumar, 1 Jyoti Arora, 1,2 Sonam Ruhil, 3 Neetu Phougat, 3 Anil K. Chhillar, 3 and Ashok K. Prasad 2 1 Department of Chemistry, Bio-organic Laboratory, Kirori Mal College, University of Delhi, Delhi 110 007, India 2 Department of Chemistry, Bio-organic Laboratory, University of Delhi, Delhi 110 007, India 3 Centre for Biotechnology, Maharshi Dayanand University, Rohtak 124 001, India Correspondence should be addressed to Rakesh Kumar; rakeshkp@email.com Received 30 April 2014; Revised 19 July 2014; Accepted 29 July 2014; Published 25 August 2014 Academic Editor: Adriana I. Segall Copyright © 2014 Rakesh Kumar et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Prompted from the diversity of the wider use and being an integral part of genetic material, an efort was made to synthesize pyrimidine pyrazole derivatives of pharmaceutical interest by oxidative cyclization of chalcones with satisfactory yield and purity. A novel series of 1,3-dimethyl-6-hydroxy-2,4-dioxo-5-(1  -phenyl-3  -aryl-1H-pyrazol-5  -yl)-1,2,3,4-tetrahydropyrimidines (5a–d) and 1,3-diaryl-6-hydroxy-4-oxo-2-thioxo-5-(1  -phenyl-3  -aryl-1H-pyrazol-5  -yl)-1,2,3,4-tetrahydropyrimidines (5e–l) has been synthesized. Te structures of these compounds were established on the basis of FT-IR, 1 H NMR, 13 C NMR, and mass spectral analysis. All the synthesized compounds were screened for their antimicrobial activity against bacteria and fungi. Among all the compounds, 5g was found to be the most active as its MIC was 31.25 g/mL against S. aureus and B. cereus. Te compounds 5h, 5c, and 5e also possess antibacterial activity with MIC values as 62.50, 125.00, and 500.00 g/mL, respectively. Te compounds 5c and 5j were found to have antifungal activity against Aspergillus spp. As antifungal drugs lag behind the antibacterial drugs, therefore we tried in vitro combination of these two compounds with standard antifungal drugs (polyene and azole) against Aspergillus spp. Te combination of ketoconazole with 5c and 5j showed synergy at 1 : 8 (6.25 : 50.00 g/mL) and 1 : 4 (25 : 100 g/mL) against A. fumigatus (ITCC 4517) and A. fumigatus (VPCI 190/96), respectively. 1. Introduction Nitrogen heterocycles are of special interest as they constitute an important class of natural and nonnatural products, many of which exhibit useful biological activities. Pyrimidine, being an integral part of DNA and RNA, imparts diverse pharmacological properties, such as bactericide, fungicide, vermicide, insecticide, and anticancer and antiviral agents [1]. Certain pyrimidine derivatives are also known to display antimalarial, antiflarial, and antileishmanial activities [2]. Te pyrazole derivatives are well known to have antimi- crobial [3], antifungal [4], antitubercular [5], anticancer [6], analgesic [7], anti-infammatory [8], antipyretic [9], anticonvulsant [10], antidepressant [11], muscle relaxing [12], antiulcer [13], antiarrhythmic [14], and antidiabetic [15] activities. With growing application of their synthesis and bioactivity, chemists and biologists in recent years have directed considerable attention to the study of pyrazole derivatives. In view of the above mentioned importance of pyrimidines and pyrazoles, we tried to accommodate these moieties in a single molecular framework to synthesize the linked heterocycles for enhancing biological activity. 2. Results and Discussion 2.1. Chemistry. (E)-1-(1  ,3  -Dimethyl-6  -hydroxy-2  ,4  -dioxo- 1  ,2  ,3  ,4  -tetrahydropyrimidin-5  -yl)-3-aryl-prop-2-ene-1- ones (4a–d) and (E)-1-(1  ,3  -diaryl-6  -hydroxy-4  -oxo-2  - thiooxo-1  ,2  ,3  ,4  -tetrahydropyrimidin-5  -yl)-3-aryl-prop- 2-ene-1-ones (4e–l) were synthesized by the Claisen conden- sation of 5-acetyl barbituric/thiobarbituric acid (2a–c) with aromatic aldehydes 3a–d in methanol in the presence of NaOH as a base at 60 ∘ C[16]. Further, cyclocondensation of propenones 4a–l with phenylhydrazine in acidic condition Hindawi Publishing Corporation Advances in Chemistry Volume 2014, Article ID 329681, 12 pages http://dx.doi.org/10.1155/2014/329681