Incorporation of Unprotected Heterocyclic Side Chains into Peptoid Oligomers via Solid-Phase Submonomer Synthesis

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Abstract
Peptoids (N-substituted glycines) are an important class of biomimetic oligomers that have made a significant impact in the areas of combinatorial drug discovery, gene therapy, drug delivery, and biopolymer folding in recent years. Sequence-specific peptoid oligomers are easily assembled from primary amines by the solid-phase submonomer method. However, most amines that contain heterocyclic nitrogens in the side chain do not incorporate efficiently. We present here a straightforward revision of the submonomer method that allows efficient incorporation of unprotected imidazoles, pyridines, pyrazines, indoles, and quinolines into oligomers as long as 15 monomers in length. This improved method uses chloroacetic acid instead of bromoacetic acid in the acylation step of the monomer addition cycle, and allows for the incorporation of new side chains that should enable the synthesis of peptoids with entirely new properties.