Nitrogenous cyclonerane sesquiterpenes from an algicolous strain of Trichoderma asperellum

Cyclonerins A (1) and B (2) along with seven new congeners, deoxycyclonerins A-D (3-6), cyclonerinal (7), cyclonerizole (8), and cyclonerpyranol (9), were isolated from the culture of a marine algicolous strain (A-YMD-9-2) of Trichoderma asperellum. Their structures and absolute configurations were established by spectroscopic techniques, such as 1D/2D NMR, MS, ECD, and X-ray diffraction. Compounds 1-8, highlighted by the presence of an isoxazole ring in sesquiterpene 8, represent the first occurrence of nitrogenous cyclonerane derivatives, with 1 and 2 belonging to an unprecedented family of hydroxamic acids. The new isolates 1-9 exhibited potent inhibition of one or more marine phytoplankton species tested, and it is interesting that the ferric complexes of 1 and 2 feature higher activities than themselves.