Azetidine-2-carboxylic acid is a non proteinogenic amino acid homologue of proline found in common beets. Azetidine-2-carboxylic acid can be misincorporated into proteins in place of proline in many species including humans. It is a toxic and teratogenic agent.

[D-Arg0,Hyp2,3,D-Phe7]-Bradykinin

Retrocyclin-1 is a kind of Theta-defensin. Retrocyclin-1 recognizes and binds to carbohydrate-containing surface molecules, to protect cells from HIV-1 infection. Retrocyclin-1 exhibits high affinity to fetuin, gp120 (Kd=35.4 nM), CD4 (Kd=31 nM), and galactosylceramide (Kd=24.1 nM).