α‑Pyrone and Sterol Constituents of <i>Penicillium aurantiaco­brunneum</i>, a Fungal Associate of the Lichen <i>Niebla homalea</i>

Four new metabolites, 4-epi-citreoviridin (1), auransterol (3), and two analogues (2 and 4) of paxisterol (6), together with two known metabolites (15R*,20S*)-dihydroxy­episterol (5) and (6), were isolated from cultures of the fungal associate, Penicillium aurantiaco­brunneum, of the lichen Niebla homalea, endemic to California and Baja California. The structures of all compounds were determined by comprehensive spectroscopic and spectrometric methods, as well as single-crystal X-ray diffraction for the determination of the absolute configuration of 3. Compound 1 showed selective cytotoxicity toward MCF-7 breast and A2780 ovarian cells with IC50 values of 4.2 and 5.7 μM, respectively.