Incrementally increasing the length of a peptide backbone: effect on macrocyclisation efficiency.

Three novel analogues of the cyclic pentapeptide sansalvamide A have been synthesised in high yield. A leucine residue in the lead compound is replaced with either a glycine, β-alanine or GABA residue, and the corresponding linear precursor peptides are found to cyclise with dramatically improved efficiency. This correlates with an increase in the effective molarity (EM) of the cyclisation reactions.