Ethylidene-Tethered Chromene-Pyrone Hybrids as Potential Plant-Growth Regulators from an Endolichenic Species.

sp., a lichen-associated fungus, produced six skeletally new dimeric spiciferones (-) and four known metabolites (-). The new structures were elucidated by spectroscopic analysis, and their absolute configurations were determined by electronic circular dichroism calculations. Compounds and - represent the first examples of ethylidene-bridged dimers from the building blocks 4-chromene-4,7(8)-dione and α-pyrone, and is a unique homodimer of spiciferone. Compounds , , and - significantly inhibited the growth of weed-like dicot at 100.0 μM. Notably, showed the strongest inhibitory activity against the fresh weight and root elongation of with the IC values of 32.04 and 26.78 μM, respectively, whereas , , and stimulated the growth of at lower concentrations. Meanwhile, compounds and exhibited weak inhibitory effects on the root elongation of monocot rice, while and exhibited growth-promoting effects on the shoot and root elongation of rice in a roughly dose-dependent manner.