Cyclo(L-Leu-L-Trp) is a diketopiperazine metabolite originally isolated from
Penicillium.
1 It is active against various bacteria (MICs = 125-1000 μg/ml) and fungi (MICs = 8-64 μg/ml), and it inhibits the production rate of hydroxy radicals in an electron spin resonance (ESR) spectroscopy-based assay (IC
50 = 1.8 μM).
2,3 Cyclo(L-Leu-L-Trp) is a bitter tastant that can rapidly permeate rat taste cell membranes
ex vivo when used at a concentration of 1 mM.
4 It also acts as a melatonin receptor agonist in
X. laevis melanophores, inhibiting cAMP accumulation when used at a concentration of 20 μM, an effect that is blocked by the melatonin receptor antagonist luzindole .
5
