Synthesis, characterization, DFT study and antioxidant activity of (2-hydroxynaphthalen-1-yl) methyl 2-hydroxyphenyl amino phosphonic acid

Abstract

New molecule α-aminophosphonate namely (2-hydroxynaphthalen-1-yl) methyl 2-hydroxyphenyl amino phosphonic acid (HMHP) was synthesized by condensation based on 2-amino phenol and 2-hydroxy naphthaldehyde. During the reaction, imine intermediate namely 2-hydroxyphenyl imino naphthalen-2-ol (HIN) was formed before adding acid phosphorous to the reaction mixture. It can be confirmed the concept of Kabachinik-Fields reaction, which it's perform the attachment of phosphorus atom to the carbon atom of imine function. Both compounds were identified using IR, 1H, 13C and 31P NMR spectroscopic techniques. The evaluation of the antioxidant activity of HMHP and HIN was investigated by utilizing several in vitro assays: scavenging activity against DPPH radical and H2O2 non radical, β-carotene/linoleic acid against linoleic peroxidation, reducing power against ferric oxidation and phosphomolybdate (TAC) against molybdate ion oxidation. Results indicate that HMHP reflects greater antioxidant potency compared to HIN in most tests, where it is apt to offer the hydrogen radical very well at IC50 (37.64 ± 1.43) in DPPH test. For the other tests the inhibition percent at 50 % are relatively closed between them. Except the H2O2 scavenging, while HIN exhibited excellent activity at IC50 (24.7306 ± 0.71785). The quantum chemical calculations were performed using density functional theory (DFT) to study the effects of the transfer electronic and proton transfer on the antioxidant activities of the synthesized compounds. Also, theoretical FT-IR was calculated. The experimental results are in comfort with those calculated theoretically.