Roubini E, Laufer R, Gilon C, Selinger Z, Roques B P, Chorev M
Department of Pharmaceutical Chemistry, Hebrew University of Jerusalem, Israel.
J Med Chem. 1991 Aug;34(8):2430-8. doi: 10.1021/jm00112a018.
The isosteric methyleneoxy psi (CH2O) function was employed as a novel peptide-bond surrogate and incorporated into sequences of two neuropeptides, substance P (SP) and enkephalin. A pseudopeptide analogue [pGlu6,Phe8 psi(CH2O)Gly9]SP6-11 (7) of SP related C-terminal hexapeptide [pGlu6]SP6-11 and two pseudopeptide analogues of [Leu5]enkephalinamide, [Tyr1 psi (CH2O)Gly2, Leu5] enkephalinamide (11) and [Gly2 psi (CH2O)-Gly3, Leu5]enkephalinamide (17), were synthesized. The N alpha-protected pseudodipeptidic units were incorporated in the appropriate peptide sequences by using conventional coupling methods in solution. Compound 7 was a potent agonist (EC50 = 4.8 nM) of substance P as compared to the parent peptide [pGlu6]SP6-11 (EC50 = 1.2 nM), in stimulating contraction of the isolated guinea pig ileum (GPI). Analogue 7 was more potent on the neuronal (NK-3) than on the muscular (NK-1) tachykinin receptors in the GPI as shown by the ratio of activities, EC50 (NK-1)/EC50 (NK-3) = 3.16, thus displaying an improved selectivity for the NK-3 tachykinin receptor subtype as compared to that of [pGlu6]SP6-11, EC50 (NK-1)/EC50 (NK-3) = 0.44. In the rat vas deferens (RVD) assay, a typical NK-2 system, the pseudopeptide analogue 7 was (EC50 = 2 microM) 10-fold more potent than the parent peptide and 20-fold less potent than eledoisin, an NK-2 selective tachykinin. The pseudopeptide enkephalin analogue 17 had low biological activity when tested in the electrically induced GPI (EC50 = 2.3 microM) and was inactive in the mouse vas deferens (MVD) assay. In the rat brain membrane (RBM) binding assay analogue 17 had low affinity (in the micromolar range) for both the mu and delta binding sites. In contrast, analogue 11 was a potent enkephalin agonist (EC50 = 30 nM), being equipotent to [D-Ala2, Leu5]enkephalinamide (DALE) in the GPI assay. In the MVD, analogue 11 showed a substantially reduced activity (EC50 = 92 nM), being about 10-fold less potent than DALE. In the RBM binding assay analogue 11 showed high affinity (in the nanomolar range) for both mu and delta binding sites with increased selectivity for the delta sites as shown by the ratio of the apparent affinities for both receptors, Ki (delta)/Ki (mu) = 2.1. The contribution of the modified peptide bonds in the mode of interaction of SP and enkephalin at their corresponding receptors is discussed.
等排亚甲基氧基ψ（CH2O）官能团被用作一种新型肽键替代物，并被引入两种神经肽——P物质（SP）和脑啡肽的序列中。合成了与SP相关的C末端六肽[pGlu6]SP6 - 11的假肽类似物[pGlu6，Phe8ψ(CH2O)Gly9]SP6 - 11（7）以及[Leu5]脑啡肽酰胺的两种假肽类似物，即[Tyr1ψ(CH2O)Gly2，Leu5]脑啡肽酰胺（11）和[Gly2ψ(CH2O)-Gly3，Leu5]脑啡肽酰胺（17）。通过在溶液中使用常规偶联方法，将Nα-保护的假二肽单元引入适当的肽序列中。与母体肽[pGlu6]SP6 - 11（EC50 = 1.2 nM）相比，化合物7在刺激豚鼠离体回肠（GPI）收缩方面是P物质的强效激动剂（EC50 = 4.8 nM）。如活性比所示，类似物7在GPI中对神经元（NK - 3）速激肽受体的作用比对肌肉（NK - 1）速激肽受体更强，EC50（NK - 1）/EC50（NK - 3） = 3.16，因此与[pGlu6]SP6 - 11（EC50（NK - 1）/EC50（NK - 3） = 0.44）相比，对NK - 3速激肽受体亚型显示出更高的选择性。在大鼠输精管（RVD）试验（一种典型的NK - 2系统）中，假肽类似物7的效力（EC50 = 2 μM）比母体肽高10倍，比NK - 2选择性速激肽eledoisin低20倍。在电刺激的GPI试验中测试时，假肽脑啡肽类似物17的生物活性较低（EC50 = 2.3 μM），并且在小鼠输精管（MVD）试验中无活性。在大鼠脑膜（RBM）结合试验中，类似物17对μ和δ结合位点的亲和力都很低（在微摩尔范围内）。相比之下，类似物11是一种强效脑啡肽激动剂（EC50 = 30 nM），在GPI试验中与[D - Ala2，Leu5]脑啡肽酰胺（DALE）效力相当。在MVD中，类似物11的活性大幅降低（EC50 = 92 nM），比DALE的效力低约10倍。在RBM结合试验中，类似物11对μ和δ结合位点都显示出高亲和力（在纳摩尔范围内），并且对δ位点的选择性增加，如两种受体的表观亲和力之比所示，Ki（δ）/Ki（μ） = 2.1。讨论了修饰肽键在SP和脑啡肽与其相应受体相互作用模式中的作用。
