Cyclo(L-Leu-L-Trp)

Cyclo(L-Leu-L-Trp) is a diketopiperazine metabolite originally isolated from Penicillium. It is active against various bacteria (MICs = 125-1000 ug/ml) and fungi (MICs = 8-64 ug/ml), and it inhibits the production rate of hydroxy radicals in an electron spin resonance (ESR) spectroscopy-based assay (IC50 = 1.8 uM). 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. It also acts as a melatonin receptor agonist in X. laevis melanophores, inhibiting cAMP accumulation when used at a concentration of 20 uM, an effect that is blocked by the melatonin receptor antagonist luzindole .