SynopsisVariations I-XVIII of a trimerlike cross-linked collagen model peptide were synthesized and used to investigate the cooperation of different neighboring Gly-X-Y tripeptides. The carboxyterminal decapentapeptide of the triple-helical part of collagen type I was chosen as the starting point of sequentially modified elongations. The transition temperatures determined by CD measurements show that the incorporation of the imino acid free tripeptides Gly-Ala-Ala and Gly-Ile-Ala results in a weakening of the triple-helical structure. I t is demonstrated that the desired thermal stability of the collagen triple helix requires the "clustered" arrangement of helix-promoting tripeptides, especially of Gly-Pro-Hyp.

SynopsisA collagen model peptide comprising three covalently cross-linked chains (Ala-GlyProIg with a stable triple-helix conformation was utilized as the constant part of elongated model peptides of different composition. The tripeptides Gly-Prc-Hyp, Gly-ProAla, Gly-Pro-Pro, Gly-Pro-Ser, Gly-Afa-Hyp, Gly-Phe-Hyp, Gly-Glu-Hyp, Gly-Ma-Lys, and Gly-Pro-Phe were coupled at the N-terminal to the cross-linked peptide. The transition temperatures determined by CD measurements are higher for the peptides containing the Gly-X-Hyp sequences followed by those with the Gly-Prc-Y sequences. In experiments with combinations of two different tripeptides coupled to the constant part of the cross-linked model peptides higher transition temperatures were observed if the sequence of helix-promoting tripeptides was not interrupted.

Some tri-and hexapeptides containing hydroxyproline and serine were synthesized using the 2-methoxyethoxymethyl group for the protection of the hydroxyl function. For N-protection not only the NpS and the Z group but also the Boc group can be used. As compared to the But group the Mem group is much more stable towards TFA. Application of Mem protection allows a complete deblocking of the Boc group without affecting the Mem group.