Serpulanines A (1), B (2), and C (3) have been isolated from extracts of the rare Sri Lankan macrofungus Serpula sp. The structures of 1, 2, and 3 were elucidated by a combination of spectroscopic and single-crystal X-ray diffraction analyses. Serpulanines A (1) and B (2) both contain the rare (E)-2-hydroxyimino hydroxamic acid functional group array. A proposed biogenesis for serpulanine B (2) suggests that its (E)-2-hydroxyimino hydroxamic acid moiety arises from a diketopiperazine precursor. Synthetic serpulanine A (1) inhibited class I/II histone deacetylases in murine metastatic lung carcinoma cells with an IC