Synthesis, Antioxidant, and Antihypoxia Activities of 6,7,8,4′-Tetrahydroxyisoflavone and 6,7,8,3′,4′-Pentahydroxyisoflavone

In the present study, 6,8-dihydroxydaidzein (6,8-DHD or 6,7,8,4′-tetrahydroxyisoflavone) and 6,8,3′-trihydroxydaidzein (6,8,3′-THD or 6,7,8,3′,4′-pentahydroxyisoflavone) were synthesized via a facile and efficient way using commercially available formononetin as starting material. Their structures were confirmed using spectroscopic analyses (infrared, nuclear magnetic resonance, and mass spectrometry). The purity was checked by ultra-high performance liquid chromatography. Their antioxidant activities were evaluated via 1,1-diphenyl-2-picrylhydrazyl radical scavenging assay and reducing power assay using ascorbic acid (vitamin C) as a reference compound. The antihypoxia capacity was determined by a hypoxia injury model in PC12 cells. Our study revealed that 6,8-DHD and 6,8,3′-THD exhibited higher antioxidant activities than that of vitamin C and could protect PC12 cells against hypoxia-induced damage. These results indicate that 6,8-DHD and 6,8,3′-THD are excellent antioxidant agents and could be used for alleviating injury induced by hypoxia.

Altering the Regioselectivity of Cytochrome P450 BM3 Variant M13 toward Genistein through Protein Engineering and Variation of Reaction Conditions

The biocatalysts responsible for the enzymatic synthesis of hydroxygenisteins, derivatives of genistein with multiple activities, usually show regioselective promiscuity, hydroxylating genistein to form a mixture of multiple products, which, in turn, results in a cumbersome separation and purification. Hence, it is highly desired to explore the underlying mechanism regulating the regioselectivity of hydroxylases. M13 is a variant of cytochrome P450 BM3 with oxidant activity toward genistein. Herein, genistein was demonstrated to be hydroxylated by M13 to form a mixture of 3'-hydroxygenistein (3'-OHG) and 8-hydroxygenistein (8-OHG), each giving 4% conversion with a ratio of 1:1. Protein engineering toward M13 was thus performed to improve its regioselectivity. When isoleucine at position 86 was mutated into cysteine, the resultant variant M13I86C displayed improved regioselectivity toward 3'-OHG with an increased conversion of 8.5%. The double mutation M13I86CP18W further boosted the conversion of 3'-OHG to 9.6%, and the ratio of 3'-OHG to 8-OHG increased to 12:1. Conversely, both CoCl₂ and glucose 6-phosphate (G6P) could lead to more 8-OHG. When Co²⁺ reached 37.5 mM, M13I86CP18W could give an 8-OHG conversion of 22.4%. The maximal ratio of 8-OHG to 3'-OHG reached 130 when 62.5 mM Co²⁺ was included in the reaction mixture. With the increase of G6P from 10 to 40 mM, the conversion of M13I86CP18W to 8-OHG gradually increased to 22.6%, while the conversion to 3'-OHG decreased to 6%. Thus, both intrinsic residues and external reaction conditions can affect the regiospecificity of M13, which laid the foundation for the selection of suitable biocatalysts for the hydroxylation of genistein.

Synthesis of a novel tannic acid-functionalized polypropylene as antioxidant active-packaging materials

This work focuses on the synthesis of novel tannin-functionalized polypropylene copolymers that are designed to inhibit the oxidation of vegetable oils for potential use as packaging materials. An empty glass Petri dish (control), a chlorinated polypropylene-coated glass Petri dish (control) and a series of the tannin-functionalized polypropylene coated glass Petri dishes overlaid with linseed oil were exposed to air and additional white light. Oligomerization of the oxidized linseed oil was assessed by measuring the flow properties of the exposed oil using a viscometer. The antioxidant effect of the tannic acid grafted polypropylene copolymers (PP-Tann) retarded oligomerization of the linseed oil. The molar mass of the linoleic acid overlaid onto the PP-Tann films was the lowest among the tested samples after each time period indicating that tannin-grafted polypropylene may be a promising packaging material for vegetable oils.