Synthesis and Antimicrobial Activity of Some Novel Heterocyclic Candidates via Michael Addition Involving 4-( 4-Acetamidophenyl )-4-oxobut-2-enoic Acid

β-Aroylacrylic acid derivatives showed high biological activity and exhibited a broad spectrum of physiological activities [1] (fungicidal, antitumor, hypotensive, hypolipidemic, and antibacterial). Also, β-aroylacrylic acids were considered as inhibitors for phospholipase [2, 3] and they have antiproliferative activity against human cervix carcinoma (Hela cells) [4, 5]. Besides that, β-aroylacrylic esters are important intermediates in field of medical science and agrochemicals [1]. Chemically, β-aroylacrylic acids are convenient polyelectrophilic reagents in the synthesis of heterocyclic compounds, for which the addition of nitrogen, sulfur, phosphorus, or carbon nucleophiles occurs exclusively at the α-carbon of the electrophilic center of the molecule [6– 13]. On the other hand, aryl and heteroaryl substituted (E)4-oxobut-2-enoic acids and their derivatives represent an important class of compoundswith interesting pharmacological indications including antiulcer and cytoprotective properties [14] and kynurenine-3-hydroxylase [15] and human cytomegalovirus protease inhibiting activity [16]. Also several naturally occurring acylacrylic acids show notable antibiotic activity [17] and they are used as starting materials for the preparation of a novel series of pyridazinones and thiazoles, where many studies have been focused on pyridazinones which are characterized to possess good analgesic and antiinflammatory activities; besides that, these studies have indicated that the heterocyclic ring substitutions at position six and the presence of acetamide side chain that is linked to the lactam nitrogen of pyridazinone ring at position two of the pyridazinone ring improve the analgesic and antiinflammatory activities along with nil or very low ulcerogenicity [18]. The aim of this work is to study the behaviour of azaand carba-Michael addition reactions involving 4-(4-acetamidophenyl)-4-oxobut-2-enoic acid and nitrogen and/or carbon nucleophiles which is considered as a first step to prepare pyridazinones, thiazoles, and other heterocyclic compounds.


Introduction
-Aroylacrylic acid derivatives showed high biological activity and exhibited a broad spectrum of physiological activities [1] (fungicidal, antitumor, hypotensive, hypolipidemic, and antibacterial).Also, -aroylacrylic acids were considered as inhibitors for phospholipase [2,3] and they have antiproliferative activity against human cervix carcinoma (Hela cells) [4,5].Besides that, -aroylacrylic esters are important intermediates in field of medical science and agrochemicals [1].Chemically, -aroylacrylic acids are convenient polyelectrophilic reagents in the synthesis of heterocyclic compounds, for which the addition of nitrogen, sulfur, phosphorus, or carbon nucleophiles occurs exclusively at the -carbon of the electrophilic center of the molecule [6][7][8][9][10][11][12][13].On the other hand, aryl and heteroaryl substituted (E)-4-oxobut-2-enoic acids and their derivatives represent an important class of compounds with interesting pharmacological indications including antiulcer and cytoprotective properties [14] and kynurenine-3-hydroxylase [15] and human cytomegalovirus protease inhibiting activity [16].Also several naturally occurring acylacrylic acids show notable antibiotic activity [17] and they are used as starting materials for the preparation of a novel series of pyridazinones and thiazoles, where many studies have been focused on pyridazinones which are characterized to possess good analgesic and antiinflammatory activities; besides that, these studies have indicated that the heterocyclic ring substitutions at position six and the presence of acetamide side chain that is linked to the lactam nitrogen of pyridazinone ring at position two of the pyridazinone ring improve the analgesic and antiinflammatory activities along with nil or very low ulcerogenicity [18].
The aim of this work is to study the behaviour of azaand carba-Michael addition reactions involving 4-(4-acetamidophenyl)-4-oxobut-2-enoic acid and nitrogen and/or carbon nucleophiles which is considered as a first step to prepare pyridazinones, thiazoles, and other heterocyclic compounds.

Experimental
Melting points were determined on electrothermal apparatus using open capillary method and are uncorrected.Elemental analyses were carried out by the Micro Analytical Center at Cairo University.The IR spectra were recorded on FT/IR-300E Jasco spectrophotometer as potassium bromide discs.The mass spectra were run by a Shimadzu-GC-MS-QP 1000 EX apparatus at 70 eV.( 1 H & 13 C) NMR spectra were recorded 2 Advances in Chemistry on Varian Mercury 300 MHz spectrometer using TMS as internal standard.(1).4-(4-Acetamidophenyl)-4-oxobut-2-enoic acid was prepared according to a published procedure [19].

General
Procedure for the Synthesis of Aza-Michael Adduct (2).A mixture of -aroylacrylic acid 1 (4 mmol) and nitrogen nucleophile (4 mmol) in dry benzene (20 mL) was left for 2 days.The resulting solid formed after concentration was filtered off, dried, and crystallized from ethanol and afforded the desired products.
However the reactions of  and  unsaturated carbonyl compounds with binucleophiles provide a convenient route to interesting heterocycles (Scheme 4).
Recently [38] it was reported that -aroylacrylic acids react with o-phenylenediamine to give quinoxalin-2-ones.Thus when compound 1 was allowed to react with ophenylenediamine in isopropyl alcohol it yielded the quinoxaline derivative compound 6; the reaction takes place via    aza-Michael addition followed by dehydration leading to the desired product; the structure of compound 6 was confirmed by elemental analysis and spectral data.IR spectrum of compound 6 revealed strong absorption bands at 1673, 3107, 3186, 3260, and 3373 cm −1 attributable to  C=O and  NH bonded and nonbonded, respectively.
Furthermore, the reaction of thiazole derivative 9 with hydrazine hydrate and hydroxyl amine was investigated.In this way polynuclear systems containing a thiazole ring fused with another heterocyclic ring are usually formed (Scheme 6).Condensation of 9 with hydrazine hydrate in boiling ethanol yielded N-(4-(6-aminothiazolo [5,4c]pyridazin-3-yl)phenyl)acetamide 10 (Scheme 6).The reaction of the thiazole 9 with hydroxylamine hydrochloride in alcoholic sodium hydroxide affected condensation with carbonyl group and subsequent ring closure, yielding oxazine derivative compound 11.
Furthermore the interaction of Michael adduct compound 13 with hydrazine hydrate gave the diazepine derivative compound 15 (Scheme 8); the structures of compounds 12-15 were confirmed by elemental analysis and spectral data.

Antimicrobial Activity
-Aroylacrylic acid and its derivatives represent one of the most active classes of compounds that possess a wide spectrum of biological activity.Many of these compounds have been used for the treatment of various diseases and exhibit antibacterial activity and a broad spectrum of physiological (fungicidal, antitumor, hypotensive, hypolipidemic, etc.) activities [1].In the present work, synthesis of some aroylacrylic acids and their derivatives was reported.Some of the new synthesized compounds have been tested for their antimicrobial activity evaluation.Antimicrobial activity of the tested samples was determined using a modified Kirby-Bauer disc diffusion method [40].Briefly, 100 l of the test bacteria was grown in 10 mL of fresh media (Mueller-Hinton agar) until they reached a count of approximately 108 cells/mL for bacteria [41].100 l of microbial suspension was spread onto agar plates corresponding to the broth in which they were maintained.The tested organisms were the gram +ve bacteria (Staphylococcus aureus ATCC 25923 and Bacillus subtilis MTCC 121) and the gram −ve bacteria (Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853), by using sterile Whatman-No1 filter paper disks (8.0 mm diameter).Each compound was dissolved in DMSO.Filter paper disks were loaded with certain amount of the tested material (30 g/disk) and then left with care under hot air to complete dryness.The disks were deposited on the surface of agar plates and the disks were incubated at 5 ∘ C for 1 h, to permit good diffusion.All the plates were then incubated for 24 h at 37 ∘ C. The diameter of inhibition zones was measured in mm.Table 1 represents the antibacterial activity of some new synthesized compounds.

Conclusions
Novel pyridazinone, thiazole, diazepine, and other heterocyclic compounds were successfully synthesized through simple methods.The structures for the new synthesized compounds were confirmed by elemental analysis, FTIR, NMR, and mass spectra.These compounds were evaluated for in vitro antibacterial activities against some strains of bacteria.And some of them showed significant activities for both gram positive and gram negative bacteria, where it was found that compounds 2b, 2e, and 3 showed moderate to weak activity against gram +ve and gram −ve bacteria which may be due to the pyridazinone moiety, while compounds 6 and 8 showed moderate to weak activity against gram +ve and gram −ve bacteria because of quinoxaline and pyrazine moiety, and compounds 10 and 11 showed strong to moderate activity against gram +ve and gram -ve bacteria which may be due to thiazole ring; finally compound 15 showed strong activity against gram +ve and gram −ve bacteria because of diazepine moiety.