Isolation and structures of virescenosides from the marine-derived fungus Acremonium striatisporum

Four new diterpene glycosides, virescenosides R1 (1), R2 (2), R3 (3) and Z (4) were isolated from a marine strain of Acremonium striatisporum KMM 4401 associated with the holothurian Eupentacta fraudatrix. Structures of 1–3 were determined as the corresponding biosides having isopimaradiene-type aglycons with additional oxidation and unsaturation patterns. Virescenosides Z (4) was structurally identified as altroside, containing 7-en-6-one group in the tricyclic aglycon moiety. The compounds 1–4 were examined for inhibition of non-specific esterase activity in mouse lymphocytes.