Colletopyrandione, a new phytotoxic tetrasubstituted indolylidenepyran-2,4-dione, and colletochlorins G and H, new tetrasubstituted chroman- and isochroman-3,5-diols isolated from Colletotrichum higginsianum

A new tetrasubstituted indolylidenpyrandione named colletopyrandione (1), together with a tetrasubstituted chroman- and a tetrasubstituted isocroman-3,5-diol, named colletochlorins G and H (2, 3), respectively, were isolated from the culture filtrates of the fungus Colletotrichum higginsianum together with the already known colletochlorin A, 4-chloroorcinol, colletopyrone and colletochlorins E and F. Colletopyrandione and the two new colletochlorins (G and H) were characterized as (Z)-3-(3-hydroxy-3-methylindolin-2-ylidene)-5,6-dimethyl-pyran-2,4-dione, 8-chloro-2,2,7-trimethyl-chroman-3,5-diol and 8-chloro-1,1,7-trimethyl-isochroman-3,5-diol, respectively, by spectroscopic (NMR and HRESIMS) methods. The relative configuration of 1 was assigned by X-ray diffractometric analysis. Colletopyrandione was isolated as scalemic mixture and the absolute configuration of the most abundant enantiomer was assigned by ECD and VCD spectra combined with quantum-mechanical calculations. Assayed in several biological systems, colletopyrandione showed a modest phytotoxic activity, associated to a complete lack of toxicity towards off-target organisms.