Three New Fatty Acid Esters from the Mushroom Boletus pseudocalopus

A bioassay‐guided fractionation and chemical investigation of a MeOH extract of the Korean wild mushroom Boletus pseudocalopus resulted in the identification of three new fatty acid esters, named calopusins A–C ( 1–3 ), along with two known fatty acid methyl esters ( 4–5 ). These new compounds are structurally unique fatty acid esters with a 2,3‐butanediol moiety. Their structures were elucidated through 1D‐ and 2D‐NMR spectroscopic data and GC–MS analysis as well as a modified Mosher's method. The new compounds 1–3 showed significant inhibitory activity against the proliferation of the tested cancer cell lines with IC 50 values in the range 2.77–12.51 μM.