Cyclo(L-Trp-L-Trp) is a diketopiperazine metabolite isolated from an uncharacterised actinomycetes by Korean researchers in 2010 as a broad spectrum antibiotic. Cyclo(L-Trp-L-Trp) is an isomer of the fungal metabolite fellutanine A, which was reported as inactive in antibacterial assays. Cyclo(L-Trp-L-Trp) is highly effective against multidrug-resistant Acinetobacter baumannii, other Gram positive species and the fungi, Saccharomyces cerevisiae, Aspergillus niger and Candida albicans. Cyclo(L-Trp-L-Trp) appears in several recent patents covering a diverse range of diketopiperazines with broad therapeutic claims.