Niementowski reaction: microwave induced and conventional synthesis of quinazolinones and 3-methyl-1 H -5-pyrazolones and their antimicrobial activity

The Niementowski reaction has been extended to synthesize 3-substituted/2,3-disubstituted-4(3H) quinazolinones instead of the 2-substituted derivatives. The methodology is environmentally benign and completely eliminates the need of solvent for the reaction. Neat reactants were cyclocondensed under microwaves to afford, in good yield, the desired product in less irradiation time as compared to the classical technique. The compared results of microwave and conventional techniques have been discussed. 3-Methyl-1H-pyrazolones were synthesized from substituted hydrazides using various solid supports under microwave irradiation (MWI). The results obtained highlight the versatility of the solid supports. All synthesized compounds were screened for their antibacterial activity against gram positive and gram negative bacteria and showed good to significant activity, as well as demonstrated significant antifungal activity against Candida albicans ATCC 10231 and C. krusei GO3.


Introduction
The present day industrialization has led to immense environmental deterioration.The increasing environmental consciousness throughout the world has put a pressing need to develop an alternate synthetic approach for biologically and synthetically important compounds.This requires a new approach, which will reduce the material and energy intensity of chemical processes and products, minimize or eliminate the dispersion of harmful chemicals in the environment in a way that enhances the industrially benign approach and meets the challenges of green chemisty. 1One of the advances in this area where substantial progress has been made is the microwave-assisted solid-support synthesis. 2Aluminas can be selected as acidic or basic or neutral catalyst depending on the type of organic reaction.The dream of green chemistry has thus come true with the help of the "neat reaction" technology."Neat reaction" is an alternative solvent-free approach in which a mixture of reactants in the absence of solvent is irradiated under microwaves.The striking features are improved yield, shorter reaction time and easier work-up.This justifies the definition of "no solvent" because it completely eliminates the need of a solvent.However, absorption of the conventional heating procedures in the absence of solvent may lead to charring.

Table 1. Observed Yield and Reaction time of compounds 3 (a-l)
Microwave Irradiation (a) (neat Conditions)

Results and Discussion
The amides or amidines generally used in the Niementowski reaction were replaced by formic acid and primary aromatic or heteroaromatic amines, which afforded 3-substituted-4(3H) quinazolinones instead of the corresponding 2-substituted derivative.In continuation of our earlier work on microwave synthesis 16 and with respect to the advantage of coupling, solvent free conditions 17 with microwave irradiation (MWI), equimolar amounts of neat reactants were mixed and irradiated under microwaves.This proved to be a high-yielding protocol (Table 1).
Inspired by the high yields obtained using formic acid, a further study of 4(3H) quinazolinones synthesis, as a possible Niementowski reaction, was carried out using different aromatic and heteroaromatic carboxylic acid, amine and carboxylic acid were mixed and irradiated under microwaves to yield 2,3-disubstituted-4(3H) quinazolinones 1(a-l).Good yields were obtained in less irradiation time (Table 1) compared to the conventional procedure 17  The structures of 3(a-l) were confirmed on the basis of spectral and analytical data.IR spectra showed disappearance of bands at 1710-1720 cm -1 to C=O of carboxylic group and 3400-3300 cm -1 due to NH of amine and appearance of the band at 1685-1699 cm -1 (C=O) and 1590-1615 cm -1 (C=N).In 1 H NMR, appearance of the signal at δ 10.5-12 ppm due to carboxylic proton of amino carboxylic acid and a broad signal at δ 3-4 ppm due to amine confirmed the formation of products 3(a-l).The final structures were established by the appearance of band at 1595 cm -1 and disappearance of band at 1730 cm -1 of carboxylic acid.The disappearance of band at 1720 cm -1 (C=O) of ester and appearance of band at 1660 cm -1 due to the pyrazolone ring. 1 H NMR signal at δ 5.5 due to H-4 proton and at δ 2.3 due to the methyl group protons was present.Elemental analysis is furnished in the experimental section.The reaction pathways are depicted in Scheme 1.

Scheme 1
Where

(b) By microwave heating
Equimolar amounts of 6-bromo-anthranilic acid (2.16 g, 0.01 mol), p-amino benzoic acid (1.37 g, 0.01 mol), and acetic acid (0.60 g, 0.01 mol) were put in an Erlenmeyer flask and irradiated under microwaves in two stages (t 1 = 5 min and t 2 = 4 min) at two different power levels (p 1 = 400 w and p 2 = 500 w) (Table 1) respectively.Reactions progress was monitored by TLC.Upon completion of reaction, the reaction mixture was worked up with an excess of 10% NaHCO 3 solution and recrystallised from ethanol.The % yield is 90%, m.p 175ºC.Similarly 6bromo-2-phenyl-4-oxoquinazolin-3(4H)-yl) benzoic acid 1(b) was also synthesized by using benzoic acid in place of acetic acid.The different 6-substituted compounds have been synthesized by using various amino carboxylic acids by above method.

B) By microwave heating
To the ethanolic solution (20ml) of 2a (0.01 mol) and ethyl acetoacetate (1.30 ml, 0.01mol) in 100 ml beaker, neutral alumina (20 g) was added.The reaction mixture was stirred well and dried in air.It was placed in an alumina bath and subjected to MWI intermittently at an interval of 30s for specified time (Table I).On completion of the reaction, as monitored by TLC examination (at an interval of 30s), the product was extracted with ethanol (3x10 mL).Removal of solvent under reduced pressure gave the desired product (Table 2) which was recrystallised from ethanol.

Conclusions
All compounds were screened for their antifungal against C.albicans ATC and candida krusei and antibacterial against B.subtilis, S.aureus as gram positive and E.coli, P.aeruginosa as gram negative bacteria.Zone of inhibition were measured in millimeters.The antifungal activities of the tested compounds were compared to the standard drug flucanozole (25-28 mm).DMF was used as solvent.All compounds have shown good activity against candida albicans Table 2. Ampicillin (18-20mm), Amoxicillin (19-21mm) and penicillin (17-19mm) were used as standard drugs for antibacterial activity.The compounds 3a, 3b, 3e, 3g and 3h showed significant activity (11-18 mm) against E.Coli and P. aeruginosa (gram-ve) at 100 µg/mL concentration.The compounds 3a, 3c, 3e, 3i and 3l showed good activity (12-19 mm) against S.aureus and B.subtilis (gram +ve) at 100 µg/mL concentration.The 3b, 3c, 3e, 3f and 3i showed good to significant activity against C. albicans ATCC 10231 and C. Krusei G03 at 100 µg/mL concentration.

Table 2 .
Antibacterial Reflux 6-8 hrs, CH 3 COCH 2 COOC 2 H 5 in ethanol as solvent.M' Microwave Method: -MWI 5-7 min, Neutral Alumina CH 3 COCH 2 COOC 2 H 5 in ethanol as solvent and dried in air.All microwave reactions were carried out in a Kenstar microwave oven, model no.OM9925E (2560 MHz, 750 Watts).Melting points were determined in PMP-DM scientific melting point apparatus and were uncorrected.The IR spectra were recorded in KBr on a "Perkin-Elmer RX 1 FT-IR" spectrophotometer (serial No. 51448) and 1 H NMR spectra were recorded on a Bruker A/C 300 F spectrophotometer and chemical shifts (δ) are in ppm relative to internal tetramethylsilane.The mass spectra were run on a Varian model MAT MS-311 spectrometer at 70 eV.Purity of the compounds in addition to elemental analysis was checked by TLC.