Two new cyclopeptides from the co‑culture broth of two marine mangrove fungi and their antifungal activity

Background: The strategy that co‑cultivation two microorganisms in a single confined environment were recently developed to generate new active natural products. In the study, two new cyclic tetrapeptides, cyclo (D‑Pro‑L‑Tyr‑L‑Pro‑L‑Tyr) (1) and cyclo (Gly‑L‑Phe‑L‑Pro‑L‑Tyr) (2) were isolated from the co‑culture broth of two mangrove fungi Phomopsis sp. K38 and Alternaria sp. E33. Their antifungal activity against Candida albicans, Gaeumannomyces graminis, Rhzioctonia cerealis, Helminthosporium sativum and Fusarium graminearum was evaluated. Materials and Methods: Different column chromatographic techniques with different solvent systems were used to separate the constituents of the n‑butyl alcohol extract of the culture broth. The structures of compounds 1 and 2 were identified by analysis of spectroscopic data (one‑dimensional, two‑dimensional ‑ nuclear magnetic resonance, mass spectrometry) and Marfey’s analytic method. Dilution method was used for the evaluation of antifungal activity. Results: Compounds 1 and 2 were identified as cyclo (D‑Pro‑L‑Tyr‑L‑Pro‑L‑Tyr) and cyclo (Gly‑L‑Phe‑L‑Pro‑L‑Tyr), respectively. Compounds 1 and 2 showed moderate to high antifungal activities as compared with the positive control. Conclusions: Compounds 1 and 2 are new cyclopeptides with moderate antifungal activity being worthy of consideration for the development and research of antifungal agents.