Paraphaeosphaeride D and berkleasmin F, new circumventors of arbekacin resistance in MRSA, produced by Paraphaeosphaeria sp. TR-022.

Two new compounds, designated paraphaeosphaeride D (1) and berkleasmin F (2) together with a previously known compound, berkleasmin A (3), isolated from a culture broth of the fungus Paraphaeosphaeria sp. TR-022, proved to be new circumventors of arbekacin (ABK) resistance in methicillin-resistant Staphylococcus aureus (MRSA). The structures of 1 and 2 were elucidated by spectroscopic analyses, including various NMR experiments. All compounds showed 10-100 times ABK circumvention activities using the paper disc method and reduced the MIC values of ABK against MRSA from 16 μg ml(-1) to 4 μg ml(-1) (fourfold) using the agar dilution method. These new compounds might be promising lead compounds for developing circumventors of ABK resistance in MRSA.