Synthesis, Characterization And Activities Studies Of Phloretin Thiosemicarbazones Schiff Bases

Phloretin [3-(4-hydroxyphenyl)-1-(2,4,6-trihydroxyphenyl)propan-l-one] is a hydrophobic, dihydrochalcone, polyphenolic compound that has been identified in apples and other natural sources. It is suspected to possess a range of pharmacological activities including potent antioxidant activity, antithrombotic properties, hepatoprotective properties. Phloretin has also been correlated with numerous health benefits including reduced risk of cardiovascular disease, asthma, some cancers, and diabetes. Thiosemicarbazones are now well established as an important class of sulphur donor ligands and present a great variety of biological activities ranging from antiviral to anticancer, antitumour, antibacterial, anti-inflammatory and antiamoebic activities.In the present work, three phloretin thiosemicarbazones were achieved through condensation of the phloretin template with thiosemicarbazide,4-methyl thiosemicarbazide, and4-phenyl-3-thiosemicarbazide. Their purity was confirmed by high-performance liquid chromatograph and their structures were determined from their ultraviolet spectra, Fourier-transform infrared,1H and13C NMR, and mass spectra.The solubility of these novel compounds in ultrapure water at25℃was significantly improved compared with that of phloretin in the following order: phloretin thiosemicarbazone (PT,>1.00mg/mL)> phloretin-4-phenyl-3-thiosemicarbazone (PPT,0.52mg/mL)> phloretin-4-methylthiosemicarbazone (PMT,0.24mg/mL)> phloretin (0.02mg/mL). The various antioxidant assays in vitro were evaluated. The results demonstrated that phloretin and its derivates significantly quenched both1,1-diphenyl-2-picryl-hydrazyl and2,2’-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid), the scavenging effects strength follows the order:PPT>PT>PMT>phloretin. They also exhibited strong activity against the lipid peroxidation induced by Fe2+/ascorbic acid. Likewise, these compounds significantly protected against2,2’-azo-bis(2-amidinopropane) dihydrochloride-induced Cu, Zn-superoxide dismutase, and pBR322plasmid DNA damage in a dose-dependent manner, the inhibition strength follows the order:PT>PPT>PMT> phloretin.Tyrosinase plays a central role in biological pigment formation. It catalyzes both the hydroxylation of tyrosine into o-diphenols and the oxidation of o-diphenols into o-quinones that form brown or black pigments. The results in this study showed that all compounds inhibited diphenolase activity dose-dependently, PT possesses potent tyrosinase inhibitory activity (IC50=57.81±1.46μM), which was better than phloretin (IC50=70.08±0.88μM). Kinetic analyses showed that inhibition type by all compounds was reversible and their mechanisms were mixed-type. Their inhibition constants were also determined and compared. Furthermore, phloretin thiosemicarbazones also exhibited potently inhibit monophenolase activity, they could not only lengthen the lag time but also decrease the steady-state rate. The research may inaugurate a new route to further improve phloretin biological activity and application scope.