Cyclo(Leu-Pro) showed antibacterial activity. Yan et al. observed that Cyclo(Leu-Pro) produced by Achromobacter xylosoxidans inhibited aflatoxin production by Aspergillus parasiticus. The diketopiperazine was shown to inhibit catecholamine release in vitro. It could play a role in the hypothalamic modulation of appetite suppressant circuitry.