Development Research for Bio-active Cyclic Peptides from Plant Sources

从Rubia cordifolia和R.akane的根中获得的抗肿瘤环六肽RA-VII是抗癌药物的候选物，因为其显示出强的抗肿瘤活性，同时其具有抑制蛋白质合成的独特作用机制，并且期望开发为抗癌药物。在RA-VII的临床试验中，指出了一些改进，例如有效剂量和毒性剂量区域之间的小差异以及作为注射剂的水溶性。为了改善这些问题，制备了各种RA-VII衍生物，并通过各种生物测定对其进行了评价。即，制备Ala-2残基的N-烷基衍生物、由于Tyr-3残基而对酰胺羰基进行的化学修饰以及Tyr-3或-6残基的O-烷基衍生物，并将其用于体外和体内抗肿瘤活性测定。另一方面，通过由14元环和四肽组成的异酪氨酸部分之间的缩合制备的RA类似物建议活性表达位点的拓扑结构和构象与细胞毒活性之间的信息。也就是说，由于Ala-2残基和Tyr-3残基之间的酰胺键而形成的两种构象异构体的反式N-甲基酰胺型被揭示为活性成分。此外，Tyr-3残基上的拓扑结构以及14元环和18元环上的构象是细胞毒性表达的重要因素。为了证实这些范围，我们进一步制备了一些RA类似物，[Gly-1]RA-VII、[Gly-2]RA-VII、[Gly-4]RA-VII、[β-Ala-1]RA-VII、[β-Ala-2]RA-VII和[β-Ala-4]RA-VII及其细胞毒活性进行了研究。除茜草属植物外，还对其它植物源的活性环肽进行了研究，从王不留行中发现了许多新的环肽（石竹科）、亚麻（亚麻科）、繁缕属和益母草属植物。

Antitumor cyclic hexapeptide RA-VII obtained from the roots of Rubia cordifolia and R.akane is a candidate for anticancer drugs from showing the potent antitumor activity, while it has unique action mechanism which inhibits protein synthesis, and the development as an anticancer drug is desired. In the clinical trial of RA-VII, some improvements such as small differences between effective and toxic dose areas and the water solubility as an injection were pointed out. In order to improve these points, various derivatives of RA-VII were prepared and they were estimated by various bio-assay. Namely, the N-alkyl derivatives of the Ala-2 residue, the chemical modifications of the amide carbonyl groups due to the Tyr-3 residue and O-alkyl derivatives of the Tyr-3 or -6 residues were prepared and supplied to in vitro and in vivo assays for antitumor activities. On the other hand, RA analogues prepared by condensing between isodityrosine moieties consisting of 14-membered ring and tetra-peptides suggested the information on the topology of the active expression sites and between the conformations and cytotoxic activities. Namely, a trans N-methyl amide type of two conformers due to the amide bond between the Ala-2 residue and the Tyr-3 residue was revealed to be an active principle. Also, the topology on the Tyr-3 residue and the conformations on 14- and 18-membered rings are important factors in the expression of cytotoxicity. In order to confirm these scope, we prepared further few RA-analogues, [Gly-1]RA-VII, [Gly-2]RA-VII, [Gly-4]RA-VII, [β-Ala-1]RA-VII, [β-Ala-2]RA-VII and [β-Ala-4]RA-VII and their cytotoxic activities were examined.Searching studies for bio-active cyclic peptides from plant sources except for Rubia plants were also carried out and many novel cyclic peptides were found out from Vaccaria segetalis (Caryophyllaceae), Linum usitatissimum (Linaceae), Stellaria and Leonurus plants.