Isolation and structure determination of a new depsipeptide crocapeptin C from the myxobacterium <i>Melittangium boletus</i>

A new cyclic depsipeptide, crocapeptin C (1), containing 3-amino-6-hydroxy-2-piperidone (Ahp) was isolated from the methanol extract of the myxobacterium Melittangium boletus. The chemical structure of crocapeptin C (1) was determined through NMR and ESI-MS analysis. The stereochemistries of the constituent amino acids in crocapeptin C (1) were determined using the advanced Marfey’s method and ROESY spectrum data. Crocapeptin C (1) exhibited potent inhibitory activity against chymotrypsin with an IC50 value of 0.5 µM.</p

Synthesis and Antimicrobial Activity of Novel 4-Hydroxy-2-quinolone Analogs

Alkyl quinolone has been proven to be a privileged scaffold in the antimicrobial drug discovery pipeline. In this study, a series of new 4-hydroxy-2-quinolinone analogs containing a long alkyl side chain at C-3 and a broad range of substituents on the C-6 and C-7 positions were synthesized. The antibacterial and antifungal activities of these analogs against Staphylococcus aureus, Escherichia coli, and Aspergillus flavus were investigated. The structure-activity relationship study revealed that the length of the alkyl chain, as well as the type of substituent, has a dramatic impact on the antimicrobial activities. Particularly, the brominated analogs 3j with a nonyl side chain exhibited exceptional antifungal activities against A. flavus (half maximal inhibitory concentration (IC50) = 1.05 &micro;g/mL), which surpassed that of the amphotericin B used as a positive control. The antibacterial activity against S. aureus, although not as potent, showed a similar trend to the antifungal activity. The data suggest that the 4-hydroxy-2-quinolone is a promising framework for the further development of new antimicrobial agents, especially for antifungal treatment