Indian Journal of Chemistry Vol. 51B, July 2012, pp 1011-1019 Synthesis, characterization and antimicrobial screening of some quinoline based dihydropyridine and 2-oxo-azetidine derivatives N C Desai* & J P Harsora Division of Medicinal Chemistry, Department of Chemistry, Mahatma Gandhi Campus, Bhavnagar University, Bhavnagar 364 002, India E-mail: dnisheeth@rediffmail.com Received 31 August 2010; accepted (revised) 22 May 2012 2-Chloro-8-methylquinoline-3-carbaldehyde 1 on treatment with 2-cyanoacetohydrazide and thiosemicarbazide yields schiff bases N'-((2-chloroquinolin-3-yl)methylene)-2-cyanoacetohydrazide 2 and 2-((2-chloro-8-methylquinolin-3- yl)methylene)hydrazinecarbothioamide 4, respectively. Compounds 2 and 4 have been used to obtain a series of titled compounds containing azetidinone, thiazole and 2-pyridone scaffolds incorporating quinoline nucleus. The newly synthesized compounds 3a-j and 6a-g have been screened for their antibacterial and antifungal activities and their chemical structures have been elucidated by spectral data. Keywords: Vilsmeier-Haack reaction, quinoline, 2-pyridone, thiazole, azetidinones One of the most frequently encountered heterocycles in Medicinal Chemistry is quinoline with wide applications including antibacterial 1 , antifungal 1,2 , antitumor 3,4 , antimalarial 5 , antiplatelet 6 and anti- depressant 7 activities. Quinoline derivatives are also applied for the preparation of nano- and meso- structures having enhanced electronic and photonic properties 8 . Quinolines and their derivatives are very important compounds because of their wide occurrence in natural products 9 and biologically active compounds 10 . On the other hand, 2-pyridone is a multiple bioactive small molecule and an important pharmacophore that can form hydrogen bonded structures related to the base-pairing mechanism found in DNA and RNA 11,12 . The 2(1H)-pyridone ring system and the corresponding dihydro and tetrahydro derivatives are found abundantly in a wide variety of naturally occurring alkaloids and novel synthetic biologically active molecules 13 . Heterocycles incorporating a 2(1H)-pyridone framework constitute an extensively studied class of compounds owing to their diverse biological activities ranging from anti- HIV, antibacterial and antifungal to free radical scavengers 14 . Pyridin-2(1H)-ones are known to possess a range of biological properties such as analgesic, antimalarial, anti-inflammatory, anti-HIV, phytotoxic, antitumoral and antiviral activities 15-23 . Thiazoles are one of the most intensively investi- gated classes of aromatic five-membered hetero- cycles. The thiazole ring has been extensively studied and it forms a part of Thiamin 24 (Vitamin B 1 ), penicillins and antibacterial thiazoles 25 . Reduced thiazoles serve in the study of polypeptides and proteins and occur as structural units in compounds of biological importance 26 . Thiazole derivatives are found to possess a wide variety of applications ranging from bacteriostatics, antibiotics, CNS regulants to high selling diuretics 27-31 . 2-Azetidinone skeleton is well established as the key pharmacophore of -lactam antibiotics, the most widely employed class of antibacterial agents 32,33 . Being recognized as a potentially useful structural motif, azetidines have included in many studies for aiming at the develop- ment of new drugs, as diverse as antibacterial 34 , anti- convulsant 35 , antitumor 36 , antipsychotic 37 , anti- asthmatic 38 , antihypertensive agents 39 , cocaine antagonists 40 and muscarine agonists 41 in the treatment of Alzheimer’s disease. They also function as enzyme inhibitors and are effective on the central nervous system 42-44 . Results and Discussion The starting compound 2-chloro-8-methylquino- line-3-carbaldehyde 1 was prepared by the Vilsmeier- Haack reaction according to literature method 45 . This quinoline derivative 1 was treated with 2-cyano- acetohydrazide in methanol as a solvent which yielded schiff base N'-((2-chloroquinolin-3-yl)methyl-