Vinylogous polypeptides

8 Other Examples of Synthetic Oligomers 7.8.1 Vinylogous Polypeptides 

The planar structure of the peptide bond may be extended as represented by the vinylogous polypeptides which contain an (E)-ethenyl unit inserted between the carbonyl carbon and the a-carbon (Fig. 7.16). 

Some vinylogous peptides have been synthesized in solution and shown to possess novel secondary structures. They can adopt a hairpin turn and a novel helical sheet conformation, stabilized by two intramolecular hydrogen bonds of 10- and 12-membered rings, respectively [77,78]. 

The monomers are prepared by the homologation of N-protected amino acid aldehydes. Boc-protected amino aldehyde was synthesized in solution via Weinreb amide reduction with LiAlH4.Then, using a Wittig reaction, it was transformed into an olefin bearing an ethyl ester group, which was subsequently saponified. 

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