Conformational behavior and absolute stereostructure of two phytotoxic nonenolides from the fungus Phoma herbarum

Bioactivity-directed fractionation of extracts from the fungus Phoma herbar um led to the isolation of two new phytotoxic nonenolides: (7S,8S,9R)-7,8-d ihydroxy-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, respecti vely. The stereostructures were elucidated by spectroscopic methods and a c ombination of molecular modeling, NOESY and H-1-H-1 coupling constant data, which revealed that in CDCl3 solution, 1 exists in one preferred conformat ion, while 2 exhibits a conformational equilibrium. Compounds 1 and 2 cause d significant inhibition of radicle growth of seedlings of Amaranthus hypoc hondriacus. (C) 2000 Elsevier Science Ltd. All rights reserved.