Anti-bacterial cyclic dipeptides from Hormonema dematioides, an endophytic fungus of Juniperus communis.

Hormonema sp., an endophytic fungi found in the medicinal plant of Juniperus communis leaves, was reported to possess antimicrobial compounds from its unidentified species. In this study, 21 cyclic dipeptides (1-21) were isolated and identified from H. dematioides. All the 21 isolated cyclic dipeptides were reported for the first time from the genus Hormonema. The antimicrobial activity by the disc diffusion method showed that five compounds including cyclo(Pro-Gly) (9), cyclo(Phe-Ile) (11), cyclo(Ile-Val) (12), cyclo(Val-Ala) (17), and cyclo(Ala-Phe) (20) inhibited the growth of Staphylococcus aureus with inhibition zone diameters ranging from 12 to 30 mm. Further bioassay demonstrated that four cyclic dipeptides (9, 12, 17, and 20) showed significant antibacterial activity against S. aureus with MIC values of 0.04, 0.39, 0.01, and 0.10 µg/mL, respectively, as compared to the positive control (ciprofloxacin, MIC = 0.08 µg/mL). However, none of these cyclic dipeptides showed obvious anti-fungal activity against Candida albicans.