Beta-peptoid "foldamers"--why the additional methylene unit?

The field of peptoid (i.e., N-alkylglycine) research has been thriving since the first publications on this molecular design appeared in 1992. A highly efficient and modular synthetic platform, which is compatible with automation and ready generation of combinatorial libraries, was published the same year. This has enabled the investigation of numerous compounds with this architecture, and ligands with a wide variety of interesting biological targets have thus been discovered. Furthermore, detailed biophysical and structural studies focusing on the investigation of the conformational space adopted and three-dimensional folding of these peptide mimics have been undertaken. The same is true for beta-peptides (i.e., oligomers composed of beta-amino acids). Since the first publication describing peptide mimics combining these two structural modifications [the N-alkyl-beta-alanines (beta-peptoids)] in 1998, on the other hand, the application of this backbone construct has appeared much more sparsely in the literature. The present perspective article will provide an overview of the data obtained for beta-peptoid-containing peptide mimics as well as a discussion of the future challenges associated with this type of backbone modification.