Conformational Behavior and Absolute Stereostructure of Two Phytotoxic Nonenolides from the Fungus Phoma herbarum

Bioactivity-directed fractionation of extracts from the fungus Phoma herbarum led to the isolation of two new phytotoxic nonenolides: (7S,8S,9R)-7,8-dihydroxy-9-propyl-5-nonen-9-olide (1) and (2R,7S,8S,9R)-2,7,8-trihydroxy-9-propyl-5-nonen-9-olide (2), which were named herbarumins I and II, respectively. The stereostructures were elucidated by spectroscopic methods and a combination of molecular modeling, NOESY and 1H–1H coupling constant data, which revealed that in CDCl3 solution, 1 exists in one preferred conformation, while 2 exhibits a conformational equilibrium. Compounds 1 and 2 caused significant inhibition of radicle growth of seedlings of Amaranthus hypochondriacus.