Collagen acts as a scaffolding material to support cells, and it is responsible for the elasticity and strength of the body. Stable polymers based on collagen may have interesting properties as natural collagen replacement biomaterials for use in arthritis, wound, and bone repair. We designed a collagen Gly-Pro-Hyp tripeptide isostere (Figure). Using isostere 1, the amide bond between Gly and Pro in a host-guest peptide 2 was replaced with an (E)-alkene bond to stabilize the collagen triple helix. The alkene bond locks Gly-Pro in the trans conformation to prevent cis-trans isomerization. We expected the Gly-Pro substitution to lead to overall stabilization of the collagen host-guest peptide triple helix.

The synthesis of a Ser-Y[(E)CH=C]-Pro isostere¹ was modified to make the Gly-Y[(E)CH=C]-Pro isostere. A control peptide with 8 tripeptide repeating units, and two peptides with the trans alkene isostere in the middle were synthesized. The stability of the collagen peptides was determined by the melting temperature (T_m) using circular dichroism (CD). The control peptide Ac-(Gly-Pro-Hyp)₈-Gly-Gly-Tyr-NH₂ had a T_m of 50.0 ^oC. One peptide with an alkene isostere in the sequence, Ac-(Gly-Pro-Hyp)₃-Gly-Y[(E)CH=C]-Pro-Hyp-(Gly-Pro-Hyp)₄-Gly-Gly-Tyr-NH₂, had a T_m of 28.3 ^oC. The diastereomeric peptide with the other alkene isostere showed a linear decrease of the ellipiticity at 226 nm with the increase of temperature, which meant that no collagen triple helical structure was formed. From the T_m values, the peptide with alkene isostere 1 forms a less stable triple helical structure than the native-like peptide, however this helix was not nearly as destabilized as the Pro-Gly alkene isostere.

References

(1)       Wang, X. J.; Hart, S. A.; Xu, B.; Mason, M. D.; Goodell, J. R.; Etzkorn, F. A. J. Org. Chem. 2003, 68, 2343-2349.