Small Head-to-Tail Macrocyclic α‑Peptoids

A convenient
and efficient methodology for the head-to-tail macrocyclization
of small 3-mer, 4-mer, and 5-mer α-peptoid acids (9-, 12-, and
15-atom N-substituted glycine oligomers) is described.
The cyclic trimer has a ccc amide sequence in the
crystal structure, whereas the tetramer has ctct and
the pentamer has ttccc stereochemistry. NMR analysis
reveals rigid structures in solution. These synthetic macrocycles
may prove useful in medicinal and materials applications.