Syntheses of pseudodipeptides H-Tyrψ[CH2O]Ile-OH and H-Tyrψ[CH2O]Phe-OH were carried out using the intramolecular Williamson reaction of O-benzyltyrosinol with ethyl chloroacetate followed by N-protection and aldol reaction of the corresponding morpholin-3-one in position C2 with butanone or benzaldehyde, elimination of the hydroxy group to give derivatives with a double bond either as the E/Z (1 : 1) diastereomeric mixture in the case of the former derivative or as the Z-isomer only in the case of the latter one. Stereoselective hydrogenation and hydrolysis of both the lactams yielded the corresponding pseudodipeptides lacking the carbonyl group as a hydrogen bond donor. The introduction of the pseudodipeptides into positions 2 and 3 of oxytocin and vasopressin caused total absence of all biological activities in the formed analogues. The results of the bioassay and NMR study confirmed the importance of the H-bond between the backbone carbonyl of the Tyr2 and NH proton of the Asn5 residues for stabilization of the β-turn in the cyclic hexapeptide part of both the hormones and for their biological activity.
采用O-苄基酪氨醇与氯乙酸乙酯的分子内Williamson反应,随后对相应的吗啉-3-酮在C2位进行N-保护和醛醇反应,与丁酮或苯甲醛反应,消除羟基得到双键衍生物,前者衍生物为E/Z(1:1)非对映异构体混合物,后者衍生物仅为Z-异构体。对两种内酰胺进行立体选择性氢化和水解,得到相应的缺乏羰基作为氢键供体的假二肽。将这些假二肽引入催产素和加压素的位置2和3,导致形成的类似物完全丧失所有生物活性。生物测定和NMR研究结果证实,Tyr2骨架羰基与Asn5 NH质子之间的氢键对于稳定两种激素环状六肽部分的β-转角及其生物活性至关重要。