Synthesis and Antimicrobial Activity of Novel Series of Diversely Substituted Acetyl Pyrazoline Bearing Biphenyl Carbonitrile Motif

. Novel series of diversely substituted acetyl pyrazoline having biphenyl carbonitrile motif have been synthesized. The reaction of 2-cyno-4’-bromomethyl biphenyl with1-(4-hydroxy-phenyl)-ethanone resulted in acetophenone derivative of biphenyl-2-carbonitrile. This acetophenone derivative was condensed with substituted aromatic aldehyde in mixed solvent resulted in various substituted chalcones. These chalcones were further cyclized using hydrazine hydrate in presence of glacial acetic acid to produce titled compound derivatives. The chemical structures of synthesized compounds were elucidated by 1 H-NMR, 13 C-NMR FT-IR and mass spectra. Synthesized compounds were screened for their antimicrobial activity by broth dilution method. Out of twelve newly synthesized compounds, eight compounds are found to be equipotent to Ampicillin.

Medicinally important heterocyclic compounds are widely distributed in the nature and known to mankind since early of 18th century. After the 2 nd world war, significant efforts were made to develop novel drugs with improved efficiency and to fight against new diseases. Among all, pyrazoline is one of the important classes of heterocyclic compound possessing various therapeutic values. Pyrazoline is a five member ring with two adjacent Nitrogen atoms in a ring. Many synthetic medicinal compound possessed pyrazoline motif functionalized with various groups. Besides this, significant researches have been continued on pyrazoline derivatives around the world. Pyrazoline compounds are acquiring more importance because of their immense biological and pharmacological potential. This class of compound possesses wide spectrum of biological activities such as antimicrobial [1,2,3], anti-inflammatory and analgesic [4,5], anticancer [6,7], antidepressant [8], anti-tuberculosis [9,10], antiamoebic [11] antioxidant [12,13], antihyperglycemic [14], anti-epileptic [15,16], anti-parkinson and anti-alzheimer [17].
Though significant research efforts have been made to develop drugs which can be used to cure diseases born out of microbial infections, still it is required to develop novel drugs with improved efficiency against resistant microbes [18,19]. Literature survey reveals that the pyrazoline class compounds possesses various therapeutic properties and can be further explored to have better drug molecule. Such numerous biological and medicinal values of pyrazoline compounds prompted us to develop novel acetyl pyrazoline molecules having biphenyl carbonitrile.
In the present work, novel series of acetyl pyrazoline functionalized with biphenyl carbonitrile have been synthesized by reaction of chalcon with hydrazine hydrate in the presence of acetic acid. The easy work up and purification methods produced almost pure compounds. All synthesized compounds were screened for their potential antibacterial and antifungal activity using standard drugs and stains.

Materials:
All key raw materials, reagents and solvents were of commercial grade and used after further purification. All melting points were measured using open capillaries in a liquid paraffin bath and were uncorrected. The completion of reaction was monitored by thin layer chromatography using silica gel-G as absorbent and Toluene: Ethyl acetate was employed as mobile phase. The visualization of TLC was accomplished by UV light and Iodine. IR spectra (KBr pallet) were recorded on FT-IR, Perkin Elmer RX1 spectrophotometer and NMR spectra on BRUKER AVANCE II (400 MHz) using TMS as internal standard (chemical shifts in δ ppm).

Methods:
In the present work, novel acetyl pyrazoline derivatives were prepared by following general reaction scheme as shown in figure 1.1. The physical constants of synthesized compounds are mentioned in Table 1

Biological Evaluation
Selected synthesized compounds were screened for their in vitro antibacterial and antifungal activity using representative strains of Gram-negative bacteria (Escherichia Coli, Pseudomonas Aeruginosa) and Gram-positive bacteria (Staphylococcus Aureus, Streptococcus Pyogenus). For antifungal activity, Candida Albicans, Aspergillus Niger and Aspergillus Clavatus were used as representative stains. The Ampicillin, Chloramphenicol, Ciprofloxacin and Norfloxacin were used as standard antibacterial drugs for the comparison, while, Nystatin and Greseofulvin were used as standard antifungal drugs. The broth dilution test method was followed for screening antimicrobial activity.

Results and discussion:
The present study describes the synthesis of twelve novel acetyl pyrazoline having biphenyl carbonitrile motif. The presence of characteristic peaks at 1657 and 1259 cm -1 in FT-IR confirmed the presence of carbonyl group. The characteristic bands present at 1604 cm -1 support the presence of pyrazoline ring. The characteristic peak observed at 2223 cm -1 confirmed the presence of nitrile group. Further, the presence of characteristic peaks observed in 1 H-NMR and 13 C-NMR confirms the structure of synthesized compounds.

Conclusion:
Total twelve derivatives of substituted acetyl pyrazoline having biphenyl carbonitrile motif has been synthesized in reasonably good yield. The spectral analysis; FT-IR, 1 H-NMR, 13 C-NMR and Mass spectral data confirmed the structures of synthesized compounds. Synthesized compounds were evaluated for biological property. Compounds APC-1, APC-2, APC-4, APC-5, APC-9, APC-