Isolation of (2S,4R)-2-amino-4-methyl-hex-5-enoic acid, a nonprotein amino acid, as an allelochemical from the fruiting bodies of Boletus fraternus Peck

Abstract

The mushroom Boletus fraternus Peck. shows allelopathy and suppresses the growth of broad leaf plants in nature. According to a bioassay-guided fractionation of the fruiting body of the fungus, a rare nonprotein amino acid was isolated as a major allelochemical. The chemical structure of the compound was determined to be (2S,4R)-2-amino-4-methyl-hex-5-enoic acid (5-dehydrohomoleucine) by analysis of 1 H- and 13 C-nuclear magnetic resonance spectra and comparison with data from the literature. The allelochemical caused 50% inhibition of lettuce seedling radicle growth at a concentration of 34 ppm (w/v). Further, since radicle growth was directed away from the filter paper to prevent contact with the allelochemical at concentrations higher than 300 ppm (w/v), the fungus may use the allelochemical to protect its immediate environment from contamination by other plants. © 2014 The Author(s).