Antimicrobial peptides (AMPs) are currently being investigated as potential sources of novel therapeutics against an increasing number of microorganisms resistant to conventional antibiotics. The conjugation of an AMP to other bioactive compounds is an interesting approach for the development of new derivatives with increased antimicrobial efficiency and broader spectra of action. In this work, the synthesis of a new peptide−coumarin conjugate via copper(I)-catalyzed azide−alkyne cycloaddition is described. The conjugate was assayed for in vitro cytotoxicity and displayed antifungal activity against Cryptococcus gattii and Cryptococcus neoformans. Additionally, the conjugate exhibited increased antifungal efficacy when compared with the individual peptide, coumarin, or triazole moieties. Treatment of C. gattii with the peptide−coumarin conjugate enhanced the production of reactive oxygen species, suggesting that the oxidative burst plays an important role in the mechanism of action of the conjugate. KEYWORDS: Antimicrobial peptide, copper(I)-catalyzed azide−alkyne cycloaddition, coumarin, cryptococcosis, reactive oxygen species A ntimicrobial peptides (AMPs) are small molecular weight proteins with antimicrobial activity against bacteria, viruses, and fungi. 1 AMPs are currently being investigated as potential sources of novel therapeutic antimicrobial agents because of their broad-spectrum activity and low susceptibility for developing resistance. 2 Ubiquicidin (UBI) is an antimicrobial peptide, which was first isolated from murine macrophages and then found at low concentrations (as a first line of defense) inside human airway epithelial cells, activated macrophages, and in human colon mucosa. UBI is a cationic peptide consisting of 59 amino acid residues. It is not expected to be immunogenic to humans since it is of human origin. 3 UBI 1−59 and some of its fragments have been shown to be microbicidal against a broad spectrum of pathogens. Of particular interest is the fragment UBI 31−38 (Figure 1), which is relatively small, easily synthesized, and exhibits antibacterial activity toward methicillin resistant Staphylococcus aureus. 4 Peptides open up new perspectives in drug design by providing an entire range of highly selective and nontoxic pharmaceuticals. With growing applications of their synthesis and bioactivity, considerable attention has been focused on the research of peptide-based derivatives. 5 Coumarins form an important class of benzopyrones, which are found in nature. Many coumarins and their derivatives possess antimicrobial, anti-inflammatory, and anticancer properties. 6 Research on coumarin compounds as antifungal agents has shown that structural modification of the coumarin skeleton (i.e., the benzene ring, lactone ring, or both) results in derivatives, which possess potent antifungal activity when compared to clinically used antifungal drugs. 7 Therefore, numerous efforts have focused on the development of coumarins as potential drugs. 8 The copper(I)-catalyzed azide−alkyne cyclo...