Mosberg H I, Omnaas J R, Medzihradsky F, Smith C B
College of Pharmacy, University of Michigan, Ann Arbor 48109.
Life Sci. 1988;43(12):1013-20. doi: 10.1016/0024-3205(88)90547-4.
Tetrapeptides of primary sequence Tyr-X-Phe-YNH2, where X is D-Cys or D-Pen (penicillamine) and where Y is D-Pen or L-Pen, were prepared and were cyclized via the side chain sulfurs of residues 2 and 4 to disulfide or dithioether-containing analogs. These peptides are related to previously reported penicillamine-containing pentapeptide enkephalin analogs but lack the central glycine residue of the latter and were designed to assess the effect of decreased ring size on opioid activity. Binding affinities of the tetrapeptides were determined to both mu and delta opioid receptors. Binding affinity and selectivity in the tetrapeptide series were observed to be highly dependent on primary sequence. For example, L-Pen4 analogs displayed low affinity and were nonselective, while the corresponding D-Pen4 diastereomers were of variable affinity and higher selectivity. Among the latter compounds were examples of potent analogs in which selectivity shifted from delta selective to mu selective as the ring size was increased. The relatively high binding affinity and delta receptor selectivity observed with one of the carboxamide terminal disulfide analogs led to the synthesis of the corresponding carboxylic acid terminal, Tyr-D-Cys-Phe-D-PenOH. This analog displayed delta receptor binding selectivity similar to that of the standard delta ligand, [D-Pen2,D-Pen5]enkephalin (DPDPE), and was found to have a 3.5-fold higher binding affinity than DPDPE. All the tetrapeptides were further evaluated in the isolated mouse vas deferens (mvd) assay and all displayed opioid agonist activity. In general, tetrapeptide potencies in the mouse vas deferens correlated well with binding affinities but were somewhat lower. Receptor selectivity in the mvd, assessed by examining the effect of opioid antagonists on the tetrapeptide concentration-effect curves, was similar to that determined in the binding studies.
制备了一级序列为Tyr-X-Phe-YNH2的四肽，其中X为D-半胱氨酸（D-Cys）或青霉胺（D-Pen），Y为D-青霉胺或L-青霉胺，并通过第2位和第4位残基的侧链硫原子环化形成含二硫键或二硫醚的类似物。这些肽与先前报道的含青霉胺的五肽脑啡肽类似物有关，但缺少后者的中心甘氨酸残基，其设计目的是评估环大小减小对阿片样物质活性的影响。测定了这些四肽对μ和δ阿片受体的结合亲和力。观察到四肽系列中的结合亲和力和选择性高度依赖于一级序列。例如，L-Pen4类似物显示出低亲和力且无选择性，而相应的D-Pen4非对映异构体具有可变的亲和力和更高的选择性。在后者的化合物中，有一些强效类似物的例子，随着环大小的增加，选择性从δ选择性转变为μ选择性。观察到一种羧酰胺末端二硫键类似物具有相对较高的结合亲和力和δ受体选择性，从而合成了相应的羧酸末端类似物Tyr-D-Cys-Phe-D-PenOH。该类似物显示出与标准δ配体[D-Pen2,D-Pen5]脑啡肽（DPDPE）相似的δ受体结合选择性，并且发现其结合亲和力比DPDPE高3.5倍。所有四肽在分离的小鼠输精管（mvd）试验中进一步评估，均显示出阿片样激动剂活性。一般来说，小鼠输精管中四肽的效力与结合亲和力相关性良好，但略低。通过检查阿片拮抗剂对四肽浓度-效应曲线的影响来评估的mvd中的受体选择性与结合研究中确定的相似。
