Utilization of the p-nitrobenzyloxycarbonyl (pNZ) amine protecting group and pentafluorophenyl (Pfp) esters for the solid phase synthesis of spiroligomers

Non-Covalent Interactions Enforce Conformation in Switchable and Water-Soluble Diketopiperazine-Pyridine Foldamers

To reach their potential as mimics of the dynamic molecules present in biological systems, foldamers must be designed to display stimulus-responsive behavior. Here we report such a foldamer architecture based on alternating pyridine-diketopiperazine linkers. Epimerization is conveniently prevented through a copper-catalyzed coupling protocol. The compounds' native unswitched conformation is first discovered in the solid and solution state. The foldamers can be solubilized in DMSO and pH 9.5 buffer, retaining conformational control to a large degree. Lastly, dynamic switching is demonstrated through treatment with acid, leading to behaviour we describe as stimulus-responsive sidechain reconfiguration.

A spirocyclic backbone accesses new conformational space in an extended, dipole-stabilized foldamer

Most aromatic foldamers adopt uniform secondary structures, offering limited potential for the exploration of conformational space and the formation of tertiary structures. Here we report the incorporation of spiro bis-lactams to allow controlled rotation of the backbone of an iteratively synthesised foldamer. This enables precise control of foldamer shape along two orthogonal directions, likened to the aeronautical yaw and roll axes. XRD, NMR and computational data suggest that homo-oligomers adopt an extended right-handed helix with a pitch of over 30 Å, approximately that of B-DNA. Compatibility with extant foldamers to form hetero-oligomers is demonstrated, allowing greater structural complexity and function in future hybrid foldamer designs.

Development of Fmoc-Protected Bis-Amino Acids toward Automated Synthesis of Highly Functionalized Spiroligomers

We report the fluorenylmethoxycarbonyl (Fmoc) protection of functionalized bis-amino acid building blocks using a temporary Cu²⁺ complexation strategy, together with an efficient multikilogram-scale synthesis of bis-amino acid precursors. This allows the synthesis of stereochemically and functionally diverse spiroligomers utilizing solid-phase Fmoc/tBu chemistry to facilitate the development of applications. Four tetramers were assembled on a semiautomated microwave peptide synthesizer. We determined their secondary structures with two-dimensional nuclear magnetic resonance spectroscopy.