Fusarihexins A and B: Novel Cyclic Hexadepsipeptides from the Mangrove Endophytic Fungus Fusarium sp R5 with Antifungal Activities

Two novel cyclic hexadepsipeptides, fusarihexin A (1) and fusarihexin B (2), and two known compounds, cyclo-(L-Leu-L-Leu-D-Leu-L-Leu-L-Val) (3) and cyclo-(L-Leu-L-Leu-D-Leu-L-Leu-L-Ile) (4), were isolated from the marine mangrove endophytic fungus Fusarium sp. R5. Their chemical structures were elucidated on the basis of spectroscopic data and Marfey's analysis. In an in vitro bioassay, fusarihexin A (1) remarkably inhibited three plant pathogenic fungi: Colletotrichum gloeosporioides (Penz.) Sacc., which causes anthracnose in many fruits and vegetables, Colletotrichum musae (Berk. and M. A. Curtis) Arx, which causes crown rot and anthracnose in bananas, and Fusarium oxysporum Schlecht. f. sp. lycopersici (Sacc.) W. C. Snyder et H. N. Hansen, which causes Fusarium wilt and fruit rot in tomatoes. Fusarihexin B (2) strongly inhibited C. gloeosporioides and C. musae. The compounds were more potent than carbendazim, which is widely used as an agricultural and horticultural fungicide worldwide.