Synthesis and biological evaluation of (3-arylisoxazol-5-yl) methyl 6-fluoro-4-oxo-4H-chromene-2-carboxylates as antioxidant and antimicrobial agents

J. Serb. Chem. Soc. 82 (1) 1–12 (2017) JSCS–4942 UDC 547.786/.787+547.814.1: 615.279–188:615.28–188 Original scientific paper Synthesis and biological evaluation of (3-arylisoxazol-5-yl)methyl 6-fluoro-4-oxo-4H-chromene-2-carboxylates as antioxidant and antimicrobial agents KUMARASWAMY BATTULA1, SIRASSU NARSIMHA1, VASUDEVA REDDY NAGAVELLI1* and MUTHENENI SRINIVASA RAO2 1 Department of Chemistry, Kakatiya University, Warangal-506009, Telangana, India and 2 Chemical Biology Laboratory, Indian Institute of Chemical Technology, Hyderabad-500007, India (Received 22 December 2015, revised 6 September, accepted 27 September 2016) Abstract: A series of novel (3-arylisoxazol-5-yl)methyl 6-fluoro-4-oxo-4H-chromene-2-carboxylate derivatives (C1–C12) were synthesized by the Cu(I)-catalyzed reaction of in situ generated nitrile oxides with prop-2-ynyl 6-fluoro-4-oxo-4H-chromene-2-carboxylate in good yields and their antioxidant and antimicrobial activities were investigated. Among all the synthesized compounds, C1 (IC50: 16.43±0.57 µM) and C12 (IC50:15.98±0.72 µM) registered good antioxidant activity as compared to the standard drug trolox. Compounds C1, C3 and C6 registered very good inhibition against all the tested Gram-positive and Gram-negative bacterial strains with MIC values ranging from 9.375 to 37.5 µg mL-1. Compounds C7–C11 registered good inhibition against Bacillus subtilis and Staphylococcus aureus with MIC values ranging from 18.75 to 37.5 µg mL-1. Compounds C10 and C11 against Pseudomonas aeroginosa showed more prominent activity than the standard drug penicillin (MIC: 12.5 µg mL-1) with an MIC value of 9.375 µg mL-1 (≈1.33-fold more potent than penicillin). Compounds C7–C9 registered good to moderate antifungal activity against the four tested fungal strains with MIC values ranging from 18.75 to 37.5 µg mL-1. Keywords: isoxazole; chromene; antioxidant; antimicrobial activity. INTRODUCTION Isoxazole and its derivatives have attracted much awareness because of their unique structure and applications.1 The isoxazole ring system is a five-membered heterocyclic ring structure composed of nitrogen and oxygen atoms at the 1,2 positions and is used in the synthesis of pharmaceuticals.2,3 The isoxazole moiety is a versatile lead molecule in pharmaceutical development and has a wide range * Corresponding author. E-mail: doi: 10.2298/JSC151222088B 1 2 BATTULA et al. of biological activities. In the past few years, the therapeutic interest of isoxazole derivatives in the pharmaceutical and medicinal fields has been given great attention by medicinal chemist.4,5 A literature survey revealed that isoxazole derivatives are well known to exhibit antibacterial,6 GABAA antagonist,7 anticancer,8 antidiabetic9 and anti-HIV activities.10 The synthesis of isoxazole derivatives is obviously an important assignment in modern medicinal chemistry research. Isoxazole is the basic moiety for several drugs, such as zonisamide (Z, an anti-convulsant), leflunomide (L, a disease-modifying antirheumatic drug, DMARD) and valdecoxib (V, a COX-2 inhibitor), Fig. 1. Although a number of synthetic methods are available,11 the copper(I)-catalyzed union of terminal alkynes and oximes to give 3,5-disubstituted isoxazole exhibits a remarkably broad scope and exquisite selectivity.12 In recent years, extensive studies have been focused on isoxazole derivatives because of their diverse chemical reactivity, accessibility and wide range of biological activities. Fig. 1. Structures of isoxazole-congaing drugs. Chromone and its derivatives are reported to be physiologically and pharmacologically active and find applications in the treatment of several diseases. Chromone derivatives are a broad class of chemical compounds with many important pharmacological properties.13,14 Substituted chromone derivatives play a significant role in the medical field with many pharmacological activities, such as anti-HIV,15 antimicrobial,16 anticancer,17,18 antiviral,19 antioxidant,20 cytotoxic activities21 and anti-inflammatory activity.22 Based on the above considerations and in continuation of ongoing research on biologically potent azole derivatives,23–31 herein, the synthesis of (3-arylisoxazol-5-yl)methyl 6-fluoro-4-oxo-4H-chromene2-carboxylate hybrids and their antioxidant and antimicrobial activities are reported. EXPERIMENTAL All the reagents and solvents were purchased from Sigma–Aldrich or S.D. Fine Chemicals and used without further purification. Thin-layer chromatography (TLC) was performed using Merck silica gel 60 F254 pre-coated plates (0.25 mm) and silica gel (particle size 60–120 mesh) was used for column chromatography. Melting points were determined using a Cintex apparatus and are uncorrected. FTIR spectra were recorded using a Bruker spectrometer and are reported on the frequency of absorption (cm-1). Elemental analysis was performed using a CHROMENE-DERIVED ISOXAZOLES AS ANTIOXIDANT AND ANTIMICROBIAL AGENTS 3 Perkin Elmer 2400 CHN elemental analyzer. The 1H-NMR spectra were recorded on a Varian Gemini 400 MHz spectrometer and the 13C-NMR spectra on a Bruker 100 MHz spectrometer. CDCl3 was used as the solvent. The 1H-NMR spectra are reported relative to Me4Si (δ 0.0 ppm). Coupling constants (J) values are presented in Hz and spin multiples are given as s (singlet), d (doublet), t (triplet), dd (doublet of doublets) and m (multiplet). The mass spectral analysis was recorded on a Bruker HCT mass spectrometer using the electrospray ionization mass spectrometry (ESI-MS) technique. Analytical and spectral data of the synthesized compounds are given in Supplementary material to this paper. Synthesis of ethyl 6-fluoro-4-oxo-4H-chromene-2-carboxylate (2) To a stirred solution of 1-(5-fluoro-2-hydroxyphenyl)ethanone (10 g, 64.93 mmol, 1 eq) and diethyl oxalate (194.79 mmol, 3 eq) in ethanol (200 mL) was added Na metal (389.58 mmol, 6 eq) and the reaction mixture was refluxed under a nitrogen atmosphere for 4 h. After completion of the reaction (TLC), the reaction mixture was cooled, 6 M HCI (100 mL) was added and the product was extracted with CH2CI2 (3×200 mL). The combined organic layer was washed with brine, dried over anhydrous Na2SO4 and evaporated under reduced pressure to afford the crude compound. Recrystallization of the crude compound from ethyl acetate and diethyl ether afforded compound 2 (13.5 g, 88 %) as a light yellow solid. Synthesis of 6-fluoro-4-oxo-4H-chromene-2-carboxylic acid (3) Ethyl 6-fluoro-4-oxo-4H-chromene-2-carboxylate (10 g, 42.37 mmol) was dissolved in 50 % aqueous NaOH solution and stirred at room temperature for 5 h. After completion of the reaction (TLC) the reaction mixture was neutralized with dilute HCl and extracted with ethyl acetate (3×50 mL). The combined organic layer was washed with brine, dried over anhydrous Na2SO4 and evaporated under reduced pressure to afford compound 3 (6.34 g, 72 %) as a light yellow powder. Synthesis of prop-2-ynyl 6-fluoro-4-oxo-4H-c (...truncated)