A switch in N-terminal capping of β-peptides creates novel self-assembled nanoparticles

Small tripeptides composed entirely of beta 3-amino acids have been shown to self-assemble into fibres following acylation of the N-terminus. Given the use of Fmoc as a strategy to initiate self-assembly in alpha-peptides, we hypothesized that the acyl cap can be replaced by an Fmoc without perturbation to the self-assembly and enable simpler synthetic protocols. We therefore replaced the N-acyl cap for an Fmoc group and herein we show that these Fmoc-protected beta 3-peptides produce regular spherical particles, rather than fibrous structures, that are stable and capable of encapsulating cargo. We then demonstrated that these particles were able to deliver cargo to cells without any obvious signs of cytotoxicity. This is the first description of such regular nanoparticles derived from Fmoc-protected beta 3-peptides. Alteration to the N-terminal cap of beta-peptides switches self-assembly from fibrillar to spherical structures.