Mycenaaurin A, an Antibacterial Polyene Pigment from the Fruiting Bodies of Mycena aurantiomarginata

A new polyene pigment, mycenaaurin A (1), was isolated from fruiting bodies of Mycena aurantiomarginata. Mycenaaurin A consists of a tridecaketide that is flanked by two amino acid moieties. These are likely to be derived biosynthetically from S-adenosylmethionine. The tridecaketide itself contains an alpha-pyrone, a conjugated hexaene, and an isolated alkenyl moiety. The structure of the new pigment was established by 2D NMR spectroscopic methods and APCIMS. The absolute configuration of the four stereogenic centers was determined by degradation of 1 by ozonolysis and GC-MS comparison of the resulting fragments, after appropriate derivatization, with authentic synthetic samples. Mycenaaurin A (1) might act as a constitutive defense compound, since it exhibits antibacterial activity against the gram-positive bacterium Bacillus pumilus.