Cyclic dipeptides exhibit potency for scavenging radicals

Twenty kinds of cyclic dipeptides containing l-leucine were synthesized, and their antioxidant activity against OH and O2·- was investigated. Compounds possessing polar amino acid residues, such as Asp, Cys, Glu, Lys, Pro, Ser, and Trp, exhibited higher antioxidant activity against OH than vitamin E. However, only cyclo(l-Cys-l-Leu) scavenged O2·-.