Non‐elastomeric Polypeptide Models of Elastin

The synthesis of two polyhexapeptides is reported. The polyhexapeptides are H‐(Val6‐Ala1‐Pro2‐Gly3‐θ4‐Gly5)n ‐Val‐OMe where θ= Vol or Lys with a mole ratio of 3.5:1 and H‐(Val6‐Ala1‐Pro2‐Gly3‐Lys4‐Gly5)n‐Val‐OMe. The first polymer was utilized with a previously synthesized polyhexapeptide, H‐(Val6‐Ala1 ‐Pro2‐Gly3‐θ‐Gly5)n‐Val‐OMe where θ was either Val4 or Glu4 at a mole ratio of 3.5:1, to obtain an intermolecular cross‐linked matrix by means of primary amide bond formation between the γ‐carboxyls of the Glu residues of one copolymer and the α‐amino groups of the Lys residues of the other copolymer. The cross‐linking reaction was run during a temperature‐elicited phase separation with flow orientation of the polymers. An insoluble, non‐elastomeric, cross‐linked, polyhexapeptide matrix was obtained. The nature of the insoluble polyhexapeptide matrix was well‐demonstrated by the polymer, H‐(Val6‐Ala1‐Pro2‐Gly3‐θ4‐Gly5)n‐Val‐OMe where θ4 is Vol or Lys, which could be formed into cellophane‐like, non‐elastomeric sheets which would tear and which could be shown by microscopy to have sharp edges. This very different property of the polyhexapeptide of tropoelastin as compared to the elastomeric polypentapeptide of tropoelastin is discussed in terms of a different structural role. The purity of key intermediate hexamers and of the polyhexapeptides is demonstrated by carbon‐13 magnetic resonance in addition to the usual analytical methods.