48 Available online at www.derpharmachemica.com ISSN 0975-413X CODEN (USA): PCHHAX Der Pharma Chemica, 2017, 9(9):48-56 (http://www.derpharmachemica.com/archive.html) An Efficient One-pot Synthesis of some New Pyrazolyl Appended 1,3,4-Oxadiazole Derivatives as Antibacterial and Antioxidant agents Ajay N Ambhore 1 , Rahul D Kamble 2 , Pratima P Mogle 1 , Shrikant V Hese 1 , Shuddhodan N Kadam 1 , Madhav J Hebade 1 , Sonali S Kamble 3 , Rajesh N Gacche 3 , Bhaskar S Dawane 1 * 1 School of Chemical Sciences, Swami Ramanand Teerth Marathwada University, Nanded, Maharashtra, India 2 Department of Chemistry, Amruteshwar Arts, Commerce and Science College, Pune, Maharashtra, India 3 School of Life Sciences, Swami Ramanand Teerth Marathwada University, Nanded (MS) India ABSTRACT Synthesis of 2(3,5-disubstituted)-1H-pyrazol-4-yl-thio-5-(pyridin-4-yl)1,3,4-oxadiazoles was achieved via one pot multi-component reaction of 1-(4-substitutedphenyl)-2-((5-(pyridin-4-yl)-1,3,4-oxadiazol-2-yl)thio)ethanone, substituted benzaldehydes and hydrazine hydrate by using Bleaching earth clay (pH 12.5, 10 wt%) and Polyethyleneglycol (PEG-400) as a green reaction media. The method is found an efficient, eco- friendly and catalyst recycled for five times with no significant loss in the yield of product. All the synthesized compounds were characterized by spectral data and screened in vitro for their antibacterial and antioxidant activities. The compounds 5s and 5l have shown considerable antioxidant and antimicrobial activity, however all other synthesized compounds demonstrated moderate activities. Keywords: PEG-400, Bleaching Earth Clay (BEC), 1,3,4 Oxadiazole, Antibacterial, Antioxidant INTRODUCTION The chemistry of heterocyclic compounds has attracted researchers in recent times owing to its increasing significance in the field of pharmaceuticals and industrial applications [1,2]. In fact, the development of simple, elegant and facile methodologies for the synthesis of heterocycles is one of the most essential aspects in organic synthesis. Oxadiazoles are very well inevitable class of heterocyclic compounds with assorted pharmaceutical applications. The 1,3,4-oxadiazoles have emerged as an important class of compound with resourceful applications in the meadow of pharmaceutical, pesticide and polymer sciences. The synthesis of 1,3,4-oxadiazole and its derivatives have established scrupulous attention for a long time because of its outstanding biological and pharmacological properties such as, antitubercular [3], antimicrobial, anti-HIV [4], antiviral [5], anti-inflammatory [6], antimalarial [7], antioxidant [8-10], antineoplastic [11] and hypoglycemic activity [12]. Thus the synthesis of oxadiazole offers a great impulsion to research on development of bioactive compounds of therapeutic importance. On the other hand pyrazole and their derivatives have acknowledged a standing attention in heterocyclic chemistry and captivate substantial interest because of its versatile biological activities including antimalarial [13], antifungal [14,15], anti-inflammatory [16-21]. In recent times, some pyrazoles have been reported for their potential therapeutic bioactivities like antimicrobial, antiviral and anticancer [22-28]. In view of the above observations and considering the significant structural diversity in pharmaceutical chemistry, herein we design and develop some new compounds predicting significant biological activities based on molecular hybridization. It includes the hybridization of two important pharmacophores i.e., pyrazole and 1,3,4-oxadiazole into a single molecular skeleton leading to new prototype as a better drug candidate possibly having improved biological activities [29] and combat drug resistance [30]. Development of eco-friendly route for the synthesis of bioactive compounds is one of the prime goals of medicinal chemist. The classical method adapted for the synthesis of bioactive hybrid molecules suffers from many serious disadvantages like prolonged reaction time, use of toxic solvents and reagents, expensive ligands, poor yields and one or more side products. So as to overcome such issues and to make synthesis ideal, the principle of green chemistry attracted the attention of synthetic chemist. The use of green solvent is one of the important aspects of green chemistry. The PEG-400 is frequently used as a green solvent because of its one or more advantages over conventional solvent such as commercial availability, nonvolatile, thermal stability, miscibility with organic solvents and reusability. With these points of view we use PEG- 400 as a green solvent to reduce the toxic effect of conventional solvents on the environment [31-35].