Water Mediated Synthesis of N′-Arylmethylene-4,5,6,7-tetrahydro-2H-indazole-3-carbohydrazide Library

A novel two-step synthesis of 4,5,6,7-tetrahydro-2H-indazole-3-carbohydrazide has been developed. The library of N′-arylmethylene-4,5,6,7-tetrahydro-2H-indazole-3-carbohydrazide was generated by coupling of hydrazide to various aromatic and heterocyclic aldehydes in water media at ambient temperature with great flexibility regarding reaction time and yield. 1. Introduction Derivatives of indazole and other pyrazole-containing condensed systems are attracting attention because of their biological activity and the possibilities of further conversions. Anti-inflammatory, analgesic, antipyretic, and antirheumatic activity has been reported for pyrazole derivatives [1–3]. One of these derivatives, 2-(1-phenyl-pyrazole-4-yl)propionic acid I (Figure 1), has been shown to be clinically active in the treatment of rheumatic disorders. In addition, it has been reported that pyrazole corticoids III, IV (Figure 1) are more active than parent corticoids. One of these derivatives, 17α,21-dihydroxy-20-oxopregn-4-eno[3,2-c]-2′-(4-fluorophenyl) pyrazole II (Figure 1) [4], has been used clinically as a topical anti-inflammatory agent. However, literature reveals that 4,5,6,7-tetrahydro-2H-indazole derivatives exhibit dopaminergic [5], anti-inflammatory [6], herbicidal [7], and antitumor [8] activity and cannabinoid modulators [9], as HMG-COA reductase inhibitors [10]. Hydrazide analogues also possess other biological activities like anticonvulsant [11], antidepressant [12], anti-inflammatory [13], antimalarial [14], antimycobacterial [15], anticancer [16], and antimicrobial [17–21] activities. Figure 1 Our Continuous efforts for the synthesis of various novel heterocycles for biological interest using various catalyst and green approaches [22–26] and the remarkable pharmaceutical importance of fused hydrazide and pyrazole derivatives, prompted us to design and synthesize a scaffold 4,5,6,7-tetrahydro-2H-indazole-3-carbohydrazide using water as a green solvent. 2. Materials and Methods Melting points were determined on electrothermal apparatus using open capillaries and are uncorrected. Thin-layer chromatography was accomplished on 0.2？mm precoated plates of silica gel G60 F254 (Merck). Visualization was made with UV light (254 and 365？nm) or with an iodine vapor. IR spectra were recorded on a FTIR-8400 spectrophotometer using DRS prob. 1H NMR spectra were recorded on a Bruker AVANCE II (400？MHz) spectrometer in DMSO. Chemical shifts are expressed in δ？ppm downfield from TMS as an internal standard. Mass spectra were determined using direct inlet probe on a GCMS-QP 2010