A trifunctional template, derived by formal coupling of (S)-aspartic acid and (2S,3R,4R)-diaminoproline (available from vitamin C) as a diketopiperazine, was incorporated by solid-phase peptide synthesis into a protein loop mimetic containing the sequence -Ala-Asn-Pro-Asn-Ala-Ala-; this was shown by NMR analysis to adopt a stable β-hairpin conformation in DMSO.