Selective vasopressin V1B receptor agonist (Ki values are 0.16, 64, 100 and 3800 nM for V1B, oxytocin, V2 and V1A receptors respectively). Displays weak antidiuretic, vasopressor and in vitro oxytocic activities.
Cyclo(L-Leu-L-Trp) is a diketopiperazine metabolite initially derived from Penicillium, exhibiting antibacterial (MICs = 125-1000 µg/ml) and antifungal activities (MICs = 8-64 µg/ml). It also demonstrates antioxidant properties by reducing the production of hydroxy radicals, as evidenced in an electron spin resonance (ESR) spectroscopy assay (IC50 = 1.8 µM). Additionally, Cyclo(L-Leu-L-Trp) has been identified as a bitter compound capable of quickly crossing rat taste cell membranes ex vivo at a 1 mM concentration. Furthermore, it acts as a melatonin receptor agonist in X. laevis melanophores, suppressing cAMP accumulation at a 20 µM concentration, with this effect being negated by the melatonin receptor antagonist luzindole.