Synthesis and Functionalization of Novel Quinazoline Scaffolds As

Research & Reviews: Journal of Chemistry e-ISSN:2319-9849 p-ISSN:2322-00 Synthesis and Functionalization of Novel Quinazoline Scaffolds as Antibacterial Agents Shaikha S-Al-Neyadi1, Alaa A Salem1, Akela Ghazawi2, Tibor Pal2 and Ibrahim M Abdou1* 1Department of Chemistry, College of Science, UAE University Al-Ain, 15551 UAE 2Department of Microbiology and Immunology, Faculty of Medicine and Health Sciences, UAE Research Article Received date: 15/08/2018 ABSTRACT Accepted date: 03/08/2018 A new series of Quinazoline derivatives have been designed and Published date: 06/09/2018 synthesized using palladium-catalyzed reactions. The antibacterial activities of the synthesized compounds were screened against four *For Correspondence pathogenic bacteria. Compounds 18b and 9 showed higher sensitivity to S. aureus (gram-positive) with an MIC ≤ 0.25-0.5 μg/ml, respectively. Ibrahim M Abdou, Department of Chemistry, Meanwhile, compounds 13a and 13b were more effective against gram- College of Science, UAE University Al-Ain, negative bacteria, with an MIC<0.25 μg/ml against Escherichia coli, and 15551 UAE, Tel +97137136120. high activities against Pseudomonas aeruginosa, with MIC values of 0.5 and 1.0 μg/ml, respectively. The broadest antibacterial activities were observed with the quinazolines 26a-c, which had MIC value ranging E-mail: [email protected] from<0.25-2 μg/ml. A β-cyclodextrin (β-Cyd) inclusion complex containing quinazolines as a guest was prepared using the kneading method. The Keywords: Quinazoline, Antibacterial synthesis, product was characterized by FTIR and 1H NMR spectrometry, which β-Cyclodextrin, Inclusion complex. proved the formation of the inclusion compound between the host and guest at a molar ratio of 2:1. Based on the results from the present study, some quinazolines could be used as a template for the future development of more potent therapeutic agents through modification or derivatization. INTRODUCTION An alarming, widespread increase in resistance to antimicrobial agents has been observed; thus, the identification of novel structures that will lead to the development of new, potent and less toxic antimicrobial agents is urgently needed. The multiple pharmacological actions of unique synthetic compounds are a prerequisite for classifying a drug as highly potent and efficacious, because these actions offer the possibility of treating various diseases [1]. Therefore, success in designing antimicrobial agents that are distinct from classical antibiotics is the key in treating infectious diseases known for their chronicity and a lack of re- sponse to traditional antibiotics that eventually leads to death. Consequently, the development of novel antibacterial agents with potent activity against drug-resistant microorganisms is urgently needed [2]. Different heterocyclic systems have been explored to develop therapeutically important agents. Among these systems, Quinazolines and Quinazolinones have played significant roles in medicinal chemistry and function as building blocks for the construction of different biologically active molecules [3]. Many substituted quinazoline and quinazolinone derivatives possess a wide range of biological activities, such as antimalarial, anticancer, antimicrobial, antifungal, antiviral, antiprotozoal, anti-inflammatory, diuretic, muscle relaxant, antitubercular, antidepressant, and anticonvulsant activities, among others [4,5]. The quinazoline nucleus has emerged as an area of immense interest because of its broad spectrum of in vitro and in vivo chemotherapeutic efficiencies. Compound A exhibited greater activity against, E. faecalis, and P. aeruginosa. with inhibition zone (16-20 mm) compared to ciprofloxacin (16-21 mm). While Compounds B and C showed comparative activity against K. pneumoniae with inhibition zone (20 mm) as compared to ciprofloxacin (18 mm) [6] (Figure 1). Figure 1. Quinazolinones with antibacterial activity. RRJCHEM | Volume 7 | Issue 3 | September, 2018 14 Research & Reviews: Journal of Chemistry e-ISSN:2319-9849 p-ISSN:2322-00 Quinazolinones have a well-established powerful and broad antimicrobial activity toward different species of pathogenic gram-negative and gram-positive bacteria [7]. Scientific research and clinical studies have already documented the value of Quin- azoline-4-ones in treating various microbial diseases [8]. Based on the importance of these molecules, our attention was focused on the synthesis of novel quinazoline derivatives to identify more potent molecules. We synthesized disubstituted quinazoline derivatives using various synthetic routes and evaluated their biological activities to identify new biologically active pharmacophores that may be specifically applied as antibacterial agents. The synthesized compounds were characterized using IR,1 H and 13C-NMR spectroscopy and elemental analysis. The derivatives were screened against Escherichia coli, Pseudomonas aeruginosa, Staphy- lococcus aureus and Enterococcus. The novel quinazoline derivatives synthesized in the present work might be beneficial in terms of their biological activities; further studies are required to confirm whether these compounds are potential drug candidate. RESULTS AND DISCUSSION Chemistry The aim of the present work was to use the benzoxazinone derivatives as intermediates in the synthesis of 2,3- and/or 2,4-disubstituted quinazolinones and to attach some interesting heterocycles with a quinazolin-4(3H)- one nucleus to identify new biologically active pharmacophores that may be specifically applied as antibacterial agents. Of the various quinazolines that have been reported, the C-2 and N3-disubstituted quinazolines exhibit interesting pharmacological activities [9]. 2,3-Disubstituted quinazolines have been shown to have potent antiviral and antihypertensive acitivities [10]. Based on these findings, the present investigation focused on attaching a pyrimidine moiety to quinazolin-4(3H)-one via azomethine linker (-C=N) at quinazoline N-3 while C-2 remained substituted with a phenyl group to identify new biologically active pharmacophores. The synthetic pathways to the intermediates and final compounds 2-7 are presented in Scheme 1. Briefly anthranilic acid 1 was converted into 3-aminoquinazoline 3 via amination of 4H-benzo[d][1,3]oxazin-4-one 2, followed by a reaction with 5-formyl pyrimidine 6 to afford the target product 7. Anthranilic acid first, reacts with two equivalents of acid chlorides in pyridine solution to give 4H-benzo[d][1,3] oxazin-4-one 2 in 74%. The formation of 4H-benzo[d][1,3]oxazin-4- one 2 is explained by the well-established mechanism in which one mole of an acid chloride acylated the amino group and the second mole reacts with the carboxylic acid group of the anthranilic acid, followed by the loss of one molecule of acid to yield the 4H-benzo[d][1,3]oxazin-4-one 2 [11]. The formation of compound 2 was confirmed 3 by the presence of a sharp band at 1787 cm-1 assigned to C=O, along with a band at 1259 cm-1 for C-O-C, a 1605 cm-1 band for C=N, and a 1306 cm-1 band for C-N. The hydrazinolysis of the benzoxazinone ring system with hydrazine hydrate in boiling ethanol resulted in the production of 3-amino-2-phenylquinazolin-4-one 3 in 87% yield. In production of compound 3, hydrazine hydrate acts as a nucleophile and attacks the carbonyl group of cyclic ester due to its alpha effect. The insertion of ni- trogen atom constructed the quinazoline ring, which was characterized by the disappearance of the C-O-C stretching band at 1259 -1 -1 -1 cm and the appearance of a new carbonyl band at 1668 cm . The presence of a sharp NH2 band at 3307-3217 cm confirmed the formation of 3-amino-2-phenylquinazolin-4-one 3. The structure was further studied by 1H-NMR and the results showed the correct chemical shifts of all protons of the new quinazoline ring. Later, the condensation of aminoquinazoline 3 with pyrimidine aldehydes 6a,b in the presence of acid catalyst to introduce the azomethine linker and produce Schiff base 7a and 7b in 86 and 84% yield respectively (Scheme 1). Scheme 1. Reagents and conditions: i=benzoyl chloride, pyridine, reflux, 4hr; ii=hydrazine hydrate, ethanol, reflux, 12 h; iii=N,N-dimethylamine or 4-chloroaniline, N,N-diisopropyl ethylamine (DIPEA), MW, 150 W, 10 min; iv=DMF-POCl3, 24 h, 25°C; v=ethanol, acetic acid, reflux. The suggested structure of the final product 7a was confirmed based on elemental analysis, IR and NMR spectroscopy data. IR spectroscopy revealed the presence of strong C=N stretching vibration at 1618 cm-1 that was assigned to the new Schiff base linker. In addition, the spectrum showed bands at 1683, 1256 and 1560 cm-1 that corresponded to C=O, C-O-C and C=C. The 1H-NMR spectrum of the final compound showed characteristic signal at δ=8.79 ppm corresponding to methylene protons. The 1H-NMR spectrum of compound 7a showed a signal resonance at δ=8.58 ppm that was attributed to the pyrimidine H-4,6. Formation of the azomethine linker was characterized by the disappearance of the CHO proton at δ=9.71 ppm in compound 6a. Chloroacetyl chloride was used in a simple nucleophilic substitution reaction to extent the linker at quinazoline N-3; the syn- RRJCHEM | Volume 7 | Issue 3 | September, 2018 15 Research & Reviews: Journal of Chemistry e-ISSN:2319-9849 p-ISSN:2322-00 thesis procedure began by reacting 3-amino-2-phenylquinazolin-4(3H)-one 3 with chloroacetyl chloride to yield the corresponding 2-chloro-N-[4-oxo-2-phenylquinazolin-4(3H)-yl]-acetamide 8 in 55% yield. The infrared spectrum of the 3-amino-quinazolin-4(3H)- -1 one 3 showed characteristic absorption bands at 3307 and 3217 cm , attributed to the 3-NH2, which disappeared upon the formation of 2-chloro-N-[4-oxo- substitutedquinazolin-4(3H)-yl]-acetamide 8. Similarly, the 1HNMR spectrum showed two characteristic diastereotopic doublets at δ 4.08-4.18 assigned to CH2 protons. Compound 8 was then reacted with 3,5-bis(trifluoromethyl)aniline in the presence of a catalytic amount of DIPEA to produce compound 9 at a good yield of 71% (Scheme 2).

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