Heterotrimeric collagen peptides containing functional epitopes. Synthesis of single-stranded collagen type I peptides related to the collagenase cleavage site

Synthetic collagen Peptides containing larger numbers of Gly-Pro-Hyp repeats are difficult to purify by standard chromatographic procedures. Therefore, efficient strategies are required for the synthesis of higher molecular weight collagen-type Peptides. Applying the Fmoc/tBu chemistry, a comparative analysis of the standard stepwise chain elongation procedure on solid support with the procedure based on the use of the synthons Fmoc-Gly-Pro-Hyp(tBu)-OH and Fmoc-Pro-Hyp-Gly-OH was performed. The crude products resulting from the stepwise elongation procedure and from the use of Fmoc-Gly-Pro-Hyp(tBu)-OH clearly revealed large amounts of microheterogeneities that result from incomplete imino acid acylation as well as from diketopiperazine formation with cleavage of Gly-Pro units from the growing peptide chain. Conversely, by the use of the Fmoc-Pro-Hyp-Gly-OH synthon, the quality of the crude products was significantly improved; moreover, protection of the Hyp side chain hydroxyl function is not required using the Fmoc/tBu strategy. With this optimized synthetic procedure, relatively large collagen-type Peptides were obtained in satisfactory yields as highly homogeneous compounds.