Colletochlorins E and F, New Phytotoxic Tetrasubstituted Pyran-2-one and Dihydrobenzofuran, Isolated from Colletotrichum higginsianum with Potential Herbicidal Activity

A new tetrasubstituted pyran-2-one and a new dihydrobenzofuran, named colletochlorins E and F (1 and 2), were isolated from the culture filtrates of the fungus Colletotrichum higginsianum together with the already known colletochlorin A, 4-chloroorcinol and colletopyrone. Colletochlorins E, the main metabolite, and F were characterized by spectroscopic (NMR, HRESIMS) and chemical methods as 3-[7-chloro-4-hydroxy-2-(1-hydroxy-1-methylethyl)-6-methyl-2,3-dihydro-benzofuran-5-ylmethyl]-4-hydroxy-5,6-dimethyl-pyran-2-one, and 7-chloro-2-(1-hydroxy-1-methylethyl)-6-methyl-2,3-dihydrobenzofuran-4-ol. The absolute configuration 2ꞌS of 1 was deduced by X-ray diffractometric analysis while that 2S of 2 was deduced by comparison of its NMR and CD data with those of 1. When assayed by leaf puncture on Sonchus arvensis and tomato leaves, 2 caused quite large necrosis (wider than 1 cm) while 4-chloroorcinol proved to be the most active compound. These results were confirmed to those obtained in the assay on Lemna minor and on Phelipanche ramosa seed germination. Furthermore, 1, colletochlorin A and colletopyrone were less and modestly active in the last assay, respectively. Interestingly, the phytotoxicity was not associated to an antibiotic activity while only 4-chloroorcinol, colletochlorin F exhibited zootoxic activity.