The total synthesis of cyclic hexapeptide dichotomin A from linear peptide precursors containing penicillamine-derived pseudoproline residues is reported. The incorporation of a pseudoproline residue led to a faster reaction and higher head-to-tail cyclization yields in comparison to linear precursors containing the native valine residue. However, deprotection of the pseudoproline resulted in significant amounts of a by-product in which a threonine side chain had undergone dehydration,...