According to a primary structure proposed for an antibiotic peptide, gratisin, four peptides containing respectively partial sequences, l-Phe–l-Pro–l-Tyr, d-Phe–l-Pro–l-Tyr, l-Phe–l-Pro–d-Tyr, and d-Phe–l-Pro–d-Tyr, were synthesized by a liquid phase method. Among them, cyclo(–l-Val–l-Orn–l-Leu–d-Phe–l-Pro–d-Tyr–)2 showed the strongest activity against the Gram-positive microorganisms tested. The activity toward Bacillus subtilis was similar to that of gramicidin S. Therefore, it is quite possible that natural gratisin is identical to this peptide. To facilitate a further investigation of the structure-activity relationship, four additional analogs were prepared. The results of their antibiotic activities showed that an interchange of d-Phe residues with d-Tyr residues caused the decrease of activity, and that the hydroxyl group of d-Tyr residues had no important role in this activity. The peptides possessing partial sequences, d-Phe–d-Tyr–l-Pro and l-Pro–d-Phe–d-Phe, exhibited strong activity. These facts show that the positions of Pro residues are not restricted to 5 and 5′ for the exhibition of the activity. The CD spectra of these synthetic peptides in an aqueous solution reflected the partial sequences around Pro residues, which affect largely the conformation of these synthetic antibiotics. The temperature dependence of these CD spectra indicated that the conformation of biologically active peptides is more stable than those of less active peptides.
根据为
抗生素多肽格拉亭拟订的一个主要结构,用液相法合成了分别含有部分序列l-
苯丙–l-脯–l-酪、d-
苯丙–l-脯–l-酪、l-
苯丙–l-脯–d-酪和d-
苯丙–l-脯–d-酪的四个
多肽。其中环(–l-缬–l-鸟–l-亮–d-
苯丙–l-脯–d-酪–)2 对所试的革兰氏阳性微
生物表现最强的活性。它对枯草杆菌的活性与
短杆菌肽 S的相似。因此,
天然格拉亭与这个
多肽很可能就是同一个东西。为了便于进一步探讨结构与活性关系,制备了四个别的类似物。从它们的
抗生素活性的结果看出,把 d-
苯丙残基换成d-酪残基会使活性降低,而 d-酪残基的羟基对此活性没有重要作用。具有部分序列 d-
苯丙–d-酪–l-脯和 l-脯–d-
苯丙–d-
苯丙的各个
多肽表现很强的活性。这些情况说明,脯残基的位置并不是非固定在5 及 5'不可才表现出活性。这些合成
多肽在溶液中的圆二色性光谱反映了脯残基周围的部分序列,它们对这些合成
抗生素的构象有很大影响。这些圆二色性光谱的温度依赖关系指出,有
生物活性的
多肽的构象比活性较小的
多肽的构象更稳定些。