Untersuchungen über die Konformation des cyclischen Hexapeptids cyclo-Glycyl-L-prolyl-glycyl-glycyl-L-prolyl-glycyl mittels protonenmagnetischer Resonanz und Parallelen zum Cyclodecapeptid Gramicidin S. 14. Mitteilung über homodet cyclische Polypeptide [1] [2]
✍ Scribed by R. Schwyzer; U. Ludescher
- Publisher
- John Wiley and Sons
- Year
- 1969
- Tongue
- German
- Weight
- 416 KB
- Volume
- 52
- Category
- Article
- ISSN
- 0018-019X
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✦ Synopsis
2 I X 69)
SWWYZLW~J. The first proton magnetic resonance observations made with cyclic hexapcptidcs suggested the presence of two types of amide protons : one participating in intramolecular hydrogcn bonds and more strongly shiclded, the other exposed t o thc solvent and less shielded (SCHWYZER et aZ. 1964 [2]). This was taken as evidence for thc @-type structure proposed for homodetic cyclic peptitleswith 2 . (Znf 1) amino acid residues in thc ring (SCHWYZER [4]), n = 1, 2, 3 . . . These conclusions have now been confirmed b y studies on thc solvent dependence of chemical shifts in cycloglycyl-prolyl, cycZo-glycyl-prolyl-glycyl-glyc~l-prolpl-glycyl(III) and gramicidin S. On passing lrom a typical amide proton acceptor solvent (hexadeutcrodimcthylsulfoxide or tetradcuteromethanol) to trifluoroacetic acid the solvsnt-exposed protons become more shiclded and the intraniolccularly hydrogen bonded ones less so (Figure ). The proposed p-structure of the cyclotlecapeptitlc graniicidin S (n = 2 in the above formula; HODGKIN & OLJGHTON [S], crystalline state; SCHWYZER [91, in solution) which 112,s rccently been supported b y siclc-chain interaction studies (using a nuclear magnetic resonance marker) on the biologically active derivative, tliphtha-Iylgraniicidin S (SCHWYZER & LUDESCHER [l]) as well as by other methods [GI [7!, is thus additionally suppoi-tcd. Our experiments, as well as those of KOPPLE [ l l ] , strongly favor a p-structure for simplc cyclohcxapcptjdcs in solutjon ; this is particularly true for compound 111 which is, with respcct to the t\vo prolinc resitluvs, a inotlcl of gramicitlin S.