Novel Bithiophene Dimers from Echinops latifoliusas Potential Antifungal and Nematicidal Agents

Three novel dimeric bithiophenes, echinbithiophenedimers A–C (1–3), along with two known thiophenes, 4and 5, were obtained from Echinops latifolius, and their structures were identified through extensive spectroscopic analysis and electronic circular dichroism calculations. Compounds 1–3possessed new carbon skeletons; they are dimeric bithiophenes with 1and 2featuring an unprecedented 1,3-dioxolane ring system and 3featuring an unusual 1,4-dioxane ring. These compounds are the first examples of bithiophene dimers furnished by different cyclic diethers. Dimeric bithiophenes 1–3had good antifungal activities against five phytopathogenic fungi, and compound 3showed excellent activity against Alternaria alternateand Pyricularia oryzae, with a minimal inhibitory concentration value of 8 μg/mL, which was close to or higher than that of carbendazim. Moreover, its effect on the mycelial morphology was observed by scanning electron microscopy. Compounds 1–3, which were demonstrated to be nonphototoxic thiophenes, exhibited better nematicidal activity than the commercial nematicide ethoprophos against Meloidogyne incognita. This study revealed that dimeric bithiophenes containing 1,3-dioxolane or 1,4-dioxane rings could be used as novel antifungal and nematicidal agents for controlling plant fungal and nematode pathogens.