A Facial Synthesis and Antimicrobial Activity of Some Pyrazole Derivatives Carrying Indole

The title compounds (7a-h) were prepared by esterification of indole-5-carboxylic acid (1) and subsequent treatment with hydrazine hydrate in methanol via the hydrazide (3). Finally hydrazide (3) condensed with different substituted aldol (6) in acetic acid / PTSA catalytic media produced (3,5-subsituted-4,5-dihydropyrazol-1-yl)(1H-indol-5-yl)methanone (7a-h) in good yields. All the newly synthesized compounds are by elemental analysis and spectral studies and evaluated for antimicrobial activities.


Experimental
The melting points were determined in open capillaries.The purity of the compound was checked by the thin layer chromatography (TLC) on a silica-coated aluminum sheet (silica gel 60F 254 ) using dichloromethane and methanol (8:2, v/v).The IR spectra were recorded on a Nicolet Avatar 330-FTIR spectrometer.The 1 H-and 13 C NMR (5a) spectra was recorded on a Varian 300 MHz NMR spectrometer using TMS as the internal standard the chemical shift (δ) are reported in ppm and the signals are described as singlet (s), doublet (d), triplet (t), quartet (q), broad (br) and multiplet (m).The FAB mass spectra were recorded on Jeol SX 102/DA-6000 spectrophotometer/data system using argon/xenon (6 KV, 10 mA) FAB gas, at 70 eV.Elemental analysis was carried out a flash EA 1112 Series, CHNSO analyzer (Thermo).The solvent and reagents were purchased from commercial venders in the appropriate grade and were used without purification.

Procedure for the preparation of methyl or ethyl 1H-indole-5-carboxylate (2)
To a solution of indole-5-carboxylic acid (1) (0.0015 mol), dry DMF and ethyl (or) methyl iodide (0.0015 mol) was added drop wise in 500 mL round bottom flask.Flask provided with a mechanical stirrer.The reaction mixture was stirred for 2-3 h at 20-25 o C, reaction monitored by TLC technique up to completion.After the reaction completed, ice water was added and stirred for 30 min.The crude indole ester isolated by filtration technique was purified by silica column chromatography technique with methanol and dichloromethane with good yield (96%).The 1 H NMR (300 MHz) spectra of methyl ester (2) recorded in DMSO-d 6 shows 1.33 ppm (t, 3H, -CH 3 ), 4.3ppm (q, 2H, -CH 2 ).

Procedure for the preparation of 1H-indole-5-carbohydrazide (3)
To a solution of methyl or ethyl 1H-indole-5-carboxylate 2 (0.001 mol) in a dry methanol in 500 mL round bottom flask, hydrazine hydrate (0.0015 mole) was added.Flask provided with a mechanical stirrer.The reaction mixture was stirred for 3-4 h at 55-60 o C temperature, reaction monitored by TLC technique up to completion.After the reaction completed, methanol was removed by vacuum into that ice cold water was charged, solids collected by filtration technique, purified by silica column chromatography technique with methanol and dichloromethane with good yield (96%).The 1 H NMR (300 MHz) spectra of 1H-Indole-5-carbohydrazide (3) recorded in DMSO-d 6 shows disappearance of ester peaks and appearance of 4.4 ppm (2H, -NH 2 ), 9.5 ppm (1H, -CO-NH).

General procedure for the preparation of arylideneacetophenones (Chalkones)(6a-k)
To solution of 3 g of sodium hydroxide in 30 mL of water and 18 mL of ethyl alcohol in 500 mL round bottom flask.Flask provided with a mechanical stirrer, 7 mL of acetophenone was added.The reaction mixture cooled to 0-5 o C, into that 6 mL of pure aryl aldehyde was added.Stirred the reaction mixture for 3 h at 20-25 o C temperature, reaction was monitored by TLC technique up to completion.After the reaction completed, pH 6-7 was adjusted by using diluted hydrochloric acid.The reaction mixture washed with ether, ether layer was separated.The organic layer was dried by anhydrous Na 2 SO 4 and stiff of the solvent using vacuum.The isolated crude chalkone was purified by silica column chromatography technique with methanol and dichloromethane with good yield (96%).The same procedure was followed for the preparation of all chalkones (6a-h).

General procedure for the preparation of (3,5-diphenyl-4,5-dihydropyrazol-1yl)(1H-indol-5-yl)methanone (7a-h)
A mixture of compound (3) (0.01 mole) and benzylideneacetophenone (6a) (0.01 mole) taken in 500 mL round bottom flask.Flask provided with a mechanical stirrer, into that acetic acid (30 mL) and catalytically amount of p-tolunesulphonic acid (PTSA) was added.The reaction mixture was stirred for 6-8 h at 105-108 o C temperature, reaction monitored by TLC technique up to completion.After the completion of reaction, the mass cooled to room temperature and poured into ice cold water.The precipitate was collected by filtration technique, wet cake washed with water and recrystallized from ethanol to afford 7a.The same procedure was followed for the preparation of all pyrazol derivatives of indoles (7b-h).The structure of 7a was conformed by the analytical data given below.

Results and Discussion
The reaction sequences employed for the synthesis of title compound is shown in Scheme 1.The key intermediates 1-(1H-indole-5-yl) propan-1-one (2), 1H-indole-5-carbohydrazide (3), Chalkones (6), required for the preparation of the target compounds was obtained by the indole-5-carboxylic acid (1) treated with alkyl halides in presence of base in polar solvents afforded ester (2) in a very good yields (96%).The ester compound (2) treated with the hydrazine hydrate in presence of alcohol (methanol, ethanol, etc.) gave acid hydrazide compound (3) in good yields (86%).The Compound (3) was reacted with chalkones (6) in presence of acetic acid / PTSA at reflux temperature to give target compound (7a-h) in good yields (79%).The structural elucidation of new compounds were based on their elemental analysis and spectral (IR, 1 H NMR, mass) data.The characterization data of all the new compounds and their spectral data are given below.

Biological screening
The in vitro antimicrobial activity was carried out against 24 h old cultures of three bacteria and three fungi by cup-plate method.Compounds (7a-h) has been tested for their antimicrobial activity against E. coli, P. aeruginosa and S. aureus and antifungal activity against A. niger, A. flavus and A. terrus at a concentration of 1000 µg/mL in distilled DMSO using cup plate diffusion method.Nutrient agar and potato dextrose agars were used to culture the bacteria and fungus respectively.The solution of getamycine 1000 µg/mL and fluconazole 1000 µg/mL were prepared in sterilized water and used for standards for comparison of antibacterial and antifungal activities respectively the results were discussed in Table 1.The Compounds 7a and 7d exhibiting good activity against E. coli and compounds 7c and 7f show good activity of against P. aeruginosa, and compounds 7b, 7e and 7h showing good activity against S. aureus.All remaining compounds exhibited moderate activity Scheme 1.