Secondary Metabolites of the Sponge-Derived Fungus Acremonium persicinum
This study reports the isolation and characterization of six new acremine metabolites, 5-chloroacremine A (4), 5-chloroacremine H (5), and acremines O (6), P (7), Q (8), and R (9), together with the known acremines A (1), F (2), and N (3) from the fungus Acremonium persicinum cultured from the marine sponge Anomoianthella rubra. The relative configuration of acremine F (2) was determined by analyses of proton coupling constant values and NOESY data, and the absolute configuration confirmed as (1S, 4S, 6R) by X-ray crystallographic analysis of the borate ester derivative 15. Acremines O, P, and R were each shown to be of 8R configuration by 1H NMR analyses of MPA esters. The relative configurations suggested for acremines P and Q were each deduced by molecular modeling together with NOESY and coupling constant data. The 3JH–C values in acremine P were measured using the pulse sequence EXSIDE, and the observed 3JH8–C4 of 5.4 Hz and small 3JH–C values (<1.5 Hz) from H-8 to C-10 and C-11 were fully consistent with stereoisomer 7a. For acremine Q, NOESY data combined with molecular modeling established the preferred diastereomer 8a.