Structural insight into the active site of mushroom tyrosinase using phenylbenzoic acid derivatives

So far, many inhibitors of tyrosinase have been discovered for cosmetic and clinical agents. However, the molecular mechanisms underlying the inhibition in the active site of tyrosinase have not been well understood. To explore this problem, we examined here the inhibitory effects of 4′-hydroxylation and methoxylation of phenylbenzoic acid (PBA) isomers, which have a unique scaffold to inhibit mushroom tyrosinase. The inhibitory effect of 3-PBA, which has the most potent inhibitory activity among the isomers, was slightly decreased by 4′-hydroxylation and further decreased by 4′-methoxylation against mushroom tyrosinase. Surprisingly, 4′-hydroxylation but not methoxylation of 2-PBA appeared inhibitory activity. On the other hand, both 4′-hydroxylation and methoxylation of 4-PBA increased the inhibitory activity against mushroom tyrosinase. In silico docking analyses using the crystallographic structure of mushroom tyrosinase indicated that the carboxylic acid or 4′-hydroxyl group of PBA derivatives could chelate with cupric ions in the active site of mushroom tyrosinase, and that the interactions of Asn260 and Phe264 in the active site with the adequate-angled biphenyl group are involved in the inhibitory activities of the modified PBAs, by parallel and T-shaped π-π interactions, respectively. Furthermore, Arg268 could fix the angle of the aromatic ring of Phe264, and Val248 is supposed to interact with the inhibitors as a hydrophobic manner. These results may enhance the structural insight into mushroom tyrosinase for the creation of novel tyrosinase inhibitors.     

树豆叶二苯乙烯类成分的甲醚化和体外抗肿瘤活性

为获得具有抗肿瘤活性的甲醚化先导化合物,对树豆(Cajanus cajan)叶中的二苯乙烯类成分进行甲醚化,并测定其对人肿瘤细胞的细胞毒性。将木豆素C、树豆酮酸A、Cajanotone和木豆素与碘甲烷-碳酸钾反应制备O-甲基产物,通过波谱数据分析产物结构分别鉴定为:2-异戊烯基-3,5-二甲氧基二苯乙烯(1)、树豆酮酸A甲醚(2)、5-O-methylcajanotone(3)和3-O-甲基木豆素(4),其中化合物3是新化合物。肿瘤细胞增殖抑制实验(CCK-8法)结果表明,木豆素C对乳腺癌MDA-MB-231、宫颈癌HeLa、肝癌Hep G2、结肠癌SW480及3种非小细胞肺癌细胞(A549, NCI-H460和NCI-H1299)的半数抑制浓度IC50分别为14.4、16.1、19.6、17.4和25.7～29.6μmol L~(–1);木豆素对宫颈癌和结肠癌之外的5种肿瘤细胞有弱抑制作用,IC50为44.9～78.3μmol L~(–1);而对照的3,4′,5-三甲氧基二苯乙烯(三-O-甲基白藜芦醇)对乳腺癌MDA-MB-231、宫颈癌HeLa、结肠癌SW480和肝癌Hep G2细胞有较强抑制作用(IC50为3.0～14.5μmol L~(–1))。树豆叶二苯乙烯甲醚化衍生物1～4对7种肿瘤细胞系无明显细胞毒活性。