Inhibition of prostaglandin biosynthesis by 4-O-methylcryptochlorophaeic acid; Synthesis of monomeric arylcarboxylic acids for inhibitory activity testing and X-ray analysis of 4-O-methylcryptochlorophaeic acid.
作者:MASAAKI SHIBUYA、YUTAKA EBIZUKA、HIROSHI NOGUCHI、YOICHI IITAKA、USHIO SANKAWA
DOI:10.1248/cpb.31.407
日期:——
In order to clarify the structure-activity relationship of 4-O-methylcryptochlorophaeic acid (1), which is a lichen meta-depside and a potent inhibitor of prostaglandin (PG) biosynthesis found in our previous screening work, arylcarboxylic acids (5-8) corresponding to the monomeric moieties of 4-O-methylcryptochlorophaeic acid (1) were synthesized and tested for inhibitory effect against PG biosynthesis by an enzyme system prepared from rabbit renal medulla. They were a hundred times less active than 4-O-methylcryptochlorophaeic acid (1), indicating that the dimeric structure of the meta-depside is essential for inhibitory activity against PG biosynthesis. Kinetic studies on the mechanism of inhibition revealed that 4-O-methylcryptochlorophaeic acid (1) inhibits PG biosynthesis competitively with respect to the substrate, arachidonic acid. The three dimensional structure of 4-O-methylcryptochlorophaeic acid (1), which is expected to have a molecular structure able to fit into an active site that accommodates arachidonic acid, was determined by single crystal X-ray analysis with the direct approach. The obtained structure reveals that 4-O-methylcryptochlorophaeic acid (1) maintains a rigid conformation by forming a strong hydrogen bond between a hydroxy group and a methoxy group. Based on these findings, a new active site model of fatty acid cyclooxygenase is proposed in order to explain the inhibition by the meta-depside and acidic non-steroidal antiinflammatory drugs.
4-O-methylcryptochlorophaeic acid (1)是一种地衣元内酯,也是我们之前筛选工作中发现的一种前列腺素(PG)生物合成的强效抑制剂,为了阐明其结构-活性关系,我们合成了与 4-O-methylcryptochlorophaeic acid (1)单体分子相对应的芳基羧酸(5-8),并测试了其对 PG 生物合成的抑制作用、我们合成了与 4-O-甲基隐绿草酸(1)的单体分子相对应的芳基羧酸(5-8),并通过从兔肾髓质制备的酶系统测试了它们对前列腺素(PG)生物合成的抑制作用。它们的活性比 4-O-甲基隐绿草酸(1)低 100 倍,这表明元-二聚体结构是抑制 PG 生物合成活性的关键。对抑制机制的动力学研究表明,4-O-甲基隐绿茶酸(1)与底物花生四烯酸相比,能竞争性地抑制 PG 的生物合成。直接法单晶 X 射线分析测定了 4-O-甲基隐绿茶酸(1)的三维结构,预计其分子结构能够适合花生四烯酸的活性位点。所获得的结构显示,4-O-甲基隐绿茶酸(1)通过在一个羟基和一个甲氧基之间形成强氢键来保持刚性构象。基于这些发现,我们提出了脂肪酸环氧化酶的一个新的活性位点模型,从而解释了元苷和酸性非甾体抗炎药物的抑制作用。