New Access to Pyrano[2,3-c]pyrazole-3-carboxylates via Domino Four-Component Reaction and Their Antimicrobial Activity

60 Indones. J. Chem., 2020, 20 (1), 60 - 71 New Access to Pyrano[2,3-c]pyrazole-3-carboxylates via Domino Four-Component Reaction and Their Antimicrobial Activity Muhammad Siddiq Maarop1, Fatin Nur Ain Abdul Rashid1, Mohd Fazli Mohammat2,*, Zurina Shaameri2, Saiful Azmi Johari3, Mazurah Mohamed Isa3, and Anis Low Muhammad Low4 Department of Chemistry, Faculty of Applied Sciences, Universiti Teknologi MARA, UiTM Shah Alam, 40450 Shah Alam, Selangor, Malaysia 1 Organic Chemistry Laboratory, Institute of Science, Universiti Teknologi MARA, Kampus Puncak Alam, 42300 Bandar Puncak Alam, Selangor, Malaysia 2 Antimicrobial Laboratory, Anti-Infective Branch, Bioactivity Programme, Natural Products Division, Forest Research Institute Malaysia (FRIM), 52109 Kepong, Selangor, Malaysia 3 Atta-ur-Rahman Institute (AURINS), Universiti Teknologi MARA, Kampus Puncak Alam, 42300 Bandar Puncak Alam, Selangor, Malaysia 4 Abstract: A library of some novel classes of pyrano[2,3-c]pyrazole-3-carboxylates was synthesized by employing uncatalyzed domino four-component reaction using diethyloxaloacetate, hydrazine hydrate, aldehydes and malononitrile in refluxing of ethanol-acetic acid solvent systems. Series of domino reactions involving of pyrazolone formation, Michael addition, and Thorpe-Ziegler cyclization reaction managed to produce the cyclized products from moderate to excellent yield. This protocol provides a reliable, general and salient procedure for the title compound using a one-pot approach. Preliminary biological screening unveiled limited potentials of this class of compounds for antimicrobial lead compound due to its limited solubility properties. * Corresponding author: email: Received: October 10, 2018 Accepted: April 4, 2019 DOI: 10.22146/ijc.39566 Keywords: four-component diethyloxaloacetate ■ INTRODUCTION Isomeric pyranopyrazole structure includes pyrano[2,3-c]pyrazole, pyrano[4,3-c]pyrazole, pyrano[3, 2-c]pyrazole and pyrano[3,4-c]pyrazole (Fig. 1). Functionalized pyrano[2,3-c]pyrazoles are the most explored and widely studied and displayed significant roles in pharmaceutical fields. It possesses many interesting biological activities varying from antimicrobial [1], analgesic [2], vasodilator [3], anticancer [4], anti-inflammatory [5], inhibitors of human Chkl N N H N O Pyrano[2,3-c]pyrazole O N Pyrano[4,3-c]pyrazole reactions; kinase [6], antifungicidal [7] and also as biodegradable agrochemicals [8]. The construction of pyrano[2,3-c]pyrazole structures has been established through different modes of multicomponent reactions (MCRs) either in two-, three- or four-component reactions [9-11]. MCRs are considered convergent one-pot reaction protocol involving two or more of simple yet different starting materials to provide highly complex materials or archetypical molecules with high variability. In addition, O N N N N O Pyrano[3,2-c]pyrazole Pyrano[3,4-c]pyrazole Fig 1. Structures of isomeric pyranopyrazole Muhammad Siddiq Maarop et al. pyrano[2,3-c]pyrazole-3-carboxylate; Indones. J. Chem., 2020, 20 (1), 60 - 71 MCR approaches also offered multiple advantages including the elimination of complicated purification operations, the use of readily available flexible building blocks as well as solvent and reagent economical purposes [12]. Currently, most MCRs toward constructing the pyranopyrazole ring skeleton involved the reagents of hydrazines, β-ketoesters, aldehydes, and the active methylene nitriles. Interestingly, with regards to our literature searches, there is only a single report that successfully employed diethyl oxaloacetate as the source of the active methylene group. This one-pot reaction was successfully performed by Gein et al. during the synthesis of ethyl 6-amino-4-aryl-5cyano-1,4-dihydropyrano[2,3c]pyrazole-3-carboxylates, using a four-component twoparallel reaction manner [13]. Previously, diethyl oxalacetate was reported as a non-common source of the active methylene group in most of the MCRs for bearing two active ester groups that prone to undergo different multiple substitution reactions [14]. Initially, replicating four-component two-parallel reaction manner as reported by Gein et al. [13], we managed to synthesize a library of some novel dihydropyrano[2,3-c]pyrazoles-3-carboxylates, but in reasonable yield. Nevertheless, upon changing the original reaction protocol to domino type reaction manner furnished the title compounds and their derivatives from moderate to excellent yields. This library of compounds was then subjected to antimicrobial study as part of our endeavor on the screening of biologically active heterocyclic type compounds [15-18]. ■ EXPERIMENTAL SECTION Materials All reagents and starting materials were purchased from Sigma-Aldrich Co. and Merck Chemical Co. Thin layer chromatography (TLC) was performed using aluminum precoated sheets (Merck Kieselgel 60 GF254, 0.25 mm thick) and was visualized with an ultraviolet lamp (254 and 365 nm). Bacterial species for in vitro antibacterial test were Escherichia coli (E.C), Salmonella typhimurium (S.T), and Proteus vulgaris (P.V) as Gramnegative (-ve) and Staphylococcus aureus (S.A), Muhammad Siddiq Maarop et al. Staphylococcus cohnii (S.C) and haemolyticus (S.H) as Gram-positive. 61 Staphylococcus Instrumentation Melting points were determined on an automatic FP62 melting point apparatus from Mettler Toledo and are uncorrected. 1H and 13C-NMR spectra were recorded on JOEL NMR Spectrometer instrument operating at 400 MHz at room temperature, in CDCl3 or DMSO solutions. Chemical shift values are given in δ units (ppm) relative to TMS as an internal standard. IR spectra (4000–400 cm–1) were recorded on Varian Excalibur 3100 FT-IR spectrometer, using ATR. CHNS was performed on Flash Elemental Analyzer 110 series. The antimicrobial test were performed using Well Diffusion Method, Sample concentration: 5.0 mg/mL (50% DMSO prepared in 2 mL), Incubation temperature: 37 °C, Positive Control: Streptomycin, Chloramphenicol (500 μg/mL), Negative Control: 50% DMSO. Procedure General procedure for the synthesis of pyranopyrazole 5a-5t. (Method A) To a solution of diethyloxalacetate sodium salt (5.5 mmol) in 20 mL ethanol, 35% hydrazine solution (5.5 mmol) and 1 mL of acetic acid were added and refluxed for 15 min. Then, carbonyl compound (5 mmol) and malononitrile (5 mmol) were added to the reaction mixture, and the reflux continued for an additional 15 min. The reaction mixture was left to cool, and the resulting solid was filtered off, washed with water. (5a) Ethyl 6-amino-5-cyano-4-phenyl-1,4-dihydro pyrano[2,3-c]pyrazole-3-carboxylate. Following the above mentioned procedure, 5a was isolated as a white solid (82%). m.p 226–227 °C. IR spectrum, v, cm–1: 3388 (NH2), 3218 (NH), 2199 (CN), 1716 (COOEt), 1651 (C=C). 1H-NMR (400 MHz, DMSO): 7.26–7.22 (m, 2H), 7.17–7.13 (m, 1H), 7.06 (m, 2H), 6.99 (s, 2H), 4.71 (s, 1H), 4.06–4.01 (m, 2H), 1.01–0.98 (t, 3H). 13C-NMR (1 (...truncated)