5,5-Diphenylhydanytoin (phenytoin) is the most widely used anticonvulsant drug, but has many side effects. Although its chemical mode of action is unknown, phenytoin is believed to function primarily by interference with the transport of sodium ions across the neuronal membrane. Structure–activity and lipophilicity–activity studies suggest that the drug interacts with its receptor through hydrogen bonding to the N3—C4 amide bond, and an aromatic–aromatic interaction with the C5 substituent. Since sodium channels are cysteine-rich peptides, whose function depends upon the cysteine[Formula: see text]cystine redox process, it has been hypothesized that the action of the phenytoin receptor may be mimicked by a properly designed cyclodepsipeptide containing a cystinyl moiety, a cavity lined with five oxygen atoms oriented in the trigonal-bipyramidal manner appropriate for selective transport of sodium ions, and a site for the binding of phenytoin. A computer programme and strategy were developed to permit the three-dimensional structures of potential target molecules to be viewed, prior to synthesis. Use of this programme led to the discovery of Boc-L-cystinyl-glycyl-L-prolyl-glycyl-L-prolyl-L-cystine-OCHPh2. This compound, termed phenceptin, was synthesized from a linear precursor containing tert-butoxycarbonyl protection at the N-terminus, benzhydryl ester protection at the C-terminus, and trityl protection at sulfur. Detritylation and cyclization to phenceptin were accomplished with iodine in methanol–pyridine. Using an n-octanol membrane to study the kinetics of ion transport, phenceptin was found to transport sodium ions selectively, but only in its oxidized, cyclic form. This transport was inhibited significantly by one mol-equiv. of phenytoin, and not at all by biologically inactive analogs of the drug. The nature of the binding of phenytoin to phenceptin was examined by nuclear magnetic resonance, in n-C8D17-OH solvent, and found to involve hydrogen bonding of the drug to a glycine residue whose oxygen atom is involved in complexation to sodium ions.
5,5-二苯基肼(苯妥英)是最广泛使用的抗癫痫药物,但具有许多副作用。尽管其化学作用方式尚不清楚,但人们认为苯妥英主要通过干扰神经元膜上钠离子的传输来发挥作用。结构活性和亲脂性活性研究表明,该药物通过氢键与N3—C4酰胺键以及与C5取代基的芳香-芳香相互作用与其受体相互作用。由于钠通道是富含半胱氨酸的肽,其功能取决于半胱氨酸[公式:见文本]半胱氨酸氧化还原过程,有人假设苯妥英受体的作用可能被一个设计良好的环脱氨肽所模拟,其中包含一个半胱氨酸基团、一个以三角双锥方式定向排列的五个氧原子构成的腔,适合选择性地传输钠离子,并且有一个结合苯妥英的位点。开发了一个计算程序和策略,允许在合成之前查看潜在靶分子的三维结构。使用该程序导致发现了Boc-L-半胱氨酰基-L-甘氨酰-L-脯氨酰基-L-甘氨酰-L-脯氨酰-L-半胱氨酸-OCHPh2。这种化合物被称为苯塞普汀,它是从一个线性前体合成的,该前体在N-末端具有叔丁氧羰保护基,在C-末端具有苄基酯保护基,在硫上具有三苄基保护基。用碘在甲醇-吡啶中进行去三苄基化和环化制备苯塞普汀。使用正辛醇膜研究离子传输动力学,发现苯塞普汀只在其氧化的环状形式中选择性地传输钠离子。这种传输受到苯妥英一个当量的显著抑制,而对于该药物的生物非活性类似物则完全没有抑制作用。通过核磁共振在n-C8D17-OH溶剂中研究苯妥英与苯塞普汀的结合性质,发现药物与一个氧原子参与与钠离子络合的甘氨酸残基之间的氢键结合。