Green synthesis of pyrano [3,2-b]pyran derivatives using nano Si–Mg–fluorapatite catalyst and the evaluation of their antibacterial and antioxidant properties

Abstract

In this study, we synthesize 2-amino-4-alkyl/aryl-6-(hydroxymethyl)-8-oxopyrano[3,2-b] pyran-3-carbonitriles derivatives using a multicomponent reaction featuring aromatic or aliphatic aldehydes, kojic acid, and malononitrile catalyzed by nano fluoroapatite doped with Si and Mg (Si–Mg–FA). All reactions were carried out in EtOH as the solvent under reflux and green condition. The process demonstrates various advantages, including high yields, short reaction times, and simple workup. In addition, toxic organic solvent is not used, nor is chromatographic purification of products required. We characterized the synthesized compounds by Fourier transform infrared, 13CNMR, and 1HNMR spectroscopies. Additionally, the antibacterial properties of the pyrano[3,2-b]pyran derivatives were evaluated by determining the minimum inhibitory concentration on two gram-positive and gram-negative bacteria using the macro dilution method and compared with Penicillin and Tetracycline at the same conditions. The 2-amino-4-(2,4-dichlorophenyl)-4,8-dihydro-6-(hydroxymethyl)-8-oxo-pyrano[3,2-b]pyran-3-carbonitrile and the 2-amino-4-hexyl-4,8-dihydro-6-(hydroxymethyl)-8-oxo-pyrano[3,2-b]pyran-3-carbonitrile show the best antibacterial activity with a MIC value of 62.5 μg/ml against Staphylococcus aureus (ATCC 25923). Moreover, the antioxidant properties of the pyrano[3,2-b] pyrans derivatives were evaluated. It is notable that pyrano[3,2-b] pyrans derivatives, synthesized with substituent groups on benzaldehyde such as-NO2, -COOCH3, -OMe show the best antioxidant activity measured by DPPH radical-scavenging method.