Synthesis and Antimicrobial Activity of Some New Pyrazoles, Fused Pyrazolo[3,4-d]-pyrimidine and 1,2-Dihydroimidazo-[2,1-c][1,2,4]triazin-6-one Derivatives

A novel series of 7,7-diphenyl-1,2-dihydroimidazo[2,1-c][1,2,4]triazin-6(7H)-one 6a–h, were easily prepared via reactions of novel 2-hydrazinyl-4,4-diphenyl-1H-imidazol-5(4H)-one (2) with hydrazonoyl halides 3a–h. In addition, we also examined the reaction of compound 2 with commercially available active methylene compounds to afford new pyrazoles containing an imidazolone moiety, expected to be biologically active. The structures of the synthesized compounds were assigned on the basis of elemental analysis, IR, 1H-NMR and mass spectral data. The antifungal and antibacterial activities of the newly synthesized compounds were evaluated.


Introduction
Imidazoles are reported to have broad biological activities [1][2][3][4]. On the other hand, over the past two decades; pyrazole-containing compounds have received considerable attention owing to their diverse chemotherapeutic potential, including antineoplastic activities. Our literature survey revealed that some pyrazoles have been implemented as antileukemic [5,6], antitumor [7,8] and anti-proliferative [9] agents, in addition to their capability to exert remarkable anticancer effects through inhibiting different types of enzymes that play important roles in cell division [10]. Moreover, they have emerged as
The structural elucidation of compounds 6a-h was based on spectral evidence and microanalytical data. The mass spectra of them showed the molecular ion peaks at the expected m/z values. Their IR spectra indicated the disappearance of the NH 2 group, and revealed in each case a C=O band in the region 1734-1710 cm −1 and two bands at 3430-3220 cm −1 assignable to 2NH groups. Also, their 1 H-NMR spectra showed the presence of two signals for two NH groups at δ = 8.28-8.41 and 9.28-9.36 ppm. These two signals disappeared upon exchange with deuterium oxide. The 13 C-NMR spectrum of 6a, taken as an example for the series of compounds 6, revealed a signal for the C=O group at δ = 166.7 ppm. This chemical shift value suggested that the N-1 near C=O is sp 3 hybridized nitrogen atom pyrrole type, similar to that of compounds of type A (δ 164-167) and different from the sp 2 hybridized nitrogen that of their isomers having structure B (δ 170-175) ppm ( Figure 1). Based on the above finding we conclude that the isolated products have structures 6 and not the isomeric structure 7. Finally, the suggestion that the site of cyclization of the intermediates 4 involves N-1 to give 6 is consistent with literature reports [33]. Our study was extended to the reaction of 2 with a variety of active methylene compounds, namely acetyl acetone (8), ethyl acetoacetate (9), diethyl malonate (10) and malononitrile (11) in order to synthesize compounds 12-15, respectively (Scheme 2). These compounds have a pyrazole moiety and were anticipated to be biologically active. The structures of 12-15 were confirmed on the basis of spectroscopic data and elemental analyses (see Experimental section).
In addition, reaction of the hydrazine derivative 2 with acetophenone (16) gave the hydrazone 19, which was converted further into the 1-(imidazol-2-yl) pyrazole-4-carbaldehyde 20 by treatment with Vilsmeier-Haack reagent (prepared by dropwise addition of phosphorus oxychloride in ice cooled DMF) [34]. The structure of the isolated aldehyde was confirmed on the basis of MS, IR, 1 H-NMR spectra and elemental analysis. For example, the IR spectrum revealed absorption bands at 1681, 1724, 3166 cm −1 corresponding to 2 C=O and NH groups, respectively. The 1 H-NMR spectra showed the presence of the NH and aldehyde groups at δ = 9.33, 9.88 ppm, respectively (Scheme 3). We also examined the reaction of 2 with ethoxymethylenemalononitrile (17). The isolated product was identified as the pyrazole derivative 21 on the basis of its elemental analysis and spectral data (Scheme 3). For example, the IR spectra of compounds 21 showed v CN and v CO near 2240 and 1724 cm −1 , respectively (see Experimental section). The reaction of carbonitrile 21 with formic acid gave the corresponding 1-imidazol-2-yl-1H-pyrazolo [3,4-d]pyrimidin-4(5H)-one 22. The lack of v CN in the IR spectrum of the isolated product supported the formation of structure 22 (Scheme 3).

EtOH
Furthermore, 1-(1H-pyrazol-1-yl)-1H-imidazol-5(4H)-one 23, was prepared by reaction of 2 with chalcone 18 (Scheme 3). The structure of 23 was established based on its spectral data. The IR spectrum showed strong bands at 1722, 3169 cm −1 for C=O and NH, respectively. Also, the 1 H-NMR spectra of 23 revealed no signal assignable to the NH 2 group, while it revealed the presence of three characteristic signals due to the diasterotopic H atoms of a CH 2 group coupled with H atom (Hx) next to it (HA, HB and HX). The HA proton which is cis to HX resonates upfield at δ 2.91 ppm as doublet of doublets (dd, J = 17.2 and 6.5 Hz), while HB which is trans to HX resonates downfield at δ 4.14 ppm (dd, J = 17.3 and 12.6 Hz). HX appeared as double of doublet at δ of 5.98 (dd, J = 12.8 and 6.5 Hz) (see Experimental section).

Antimicrobial Activity
The compounds were tested for their activities against Gram +ve bacteria (Staphylcoccus aureus) and Gram -ve bacteria (Escherichia coli), in addition to the pathogenic fungi Aspergillus flavus and Candida albicans. The antimicrobial screening results were measured by the average diameter of the inhibition zones, expressed in mm, and are depicted in Table 1. The results showed that, all the tested compounds displayed significant activities against E. coli and S. aureus, while, only compounds 6c, 6h and 20 were moderately active against A. flavus and C. albicans. However, the activities of the tested compounds are much less than those of standard antifungal and antibacterial agents used. Table 1. Antimicrobial activity of the tested compounds.

General
All melting points were measured on Electrothermal IA 9000 series digital melting point apparatus. The IR spectra were recorded in potassium bromide discs on a Pye Unicam SP 3300 or Shimadzu FT IR 8101 PC infrared spectrophotometers. The NMR spectra were recorded at 270 MHz on a Varian Mercury VX-300 NMR spectrometer. 1 H-NMR (300 MHz) and 13 C-NMR (75.46 MHz) were run in deuterated chloroform (CDCl 3 ) or dimethylsulphoxide (DMSO-d 6 ). Chemical shifts were related to those of the solvent. Mass spectra were recorded on a Shimadzu GCMS-QP1000 EX mass spectrometer at 70 eV. Elemental analyses and the biological evaluation of the products were carried out at the Microanalytical Centre of Cairo University, Giza, Egypt. All reactions were followed by TLC (Silica gel, Aluminum Sheets 60 F254, Merck). Hydrazonoyl chlorides 3a-g [35,36] were prepared as reported in the literature.

Conclusions
We have established a new and efficient synthesis of a novel series of 7,7-diphenyl-1,2dihydroimidazo[2,1-c][1,2,4]triazin-6(7H)-ones. We could also extend this technique to the synthesis of new pyrazole containing imidazolone moieties. The antifungal and antibacterial activities of the newly synthesized compounds were evaluated.