Pestalotic acids A-I, antibacterial ambuic acid analogues, from a mycoparasite (Pestalotipsis sp. cr014) of Cronartium ribicola.

The white pine blister rust caused by Cronartium ribicola is a severe disease of Pinus armandii Franch in Sichuan Province, China. A mycoparasite was isolated from aeciospore piles of C. ribicola and identified as Pestalotipsis sp. The chemical constituents were investigated and nine new polyketides, named pestalotic acids A-I (1-9), were isolated from solid fermentation products of Pestalotiopsis sp. cr014. Their structures were elucidated by extensive spectroscopic methods, including 1D- and 2D- NMR, HR-MS experiments. Compounds 2-5 and 7-9 exhibited strong antibacterial activities in vitro against five plant pathogens, with minimum inhibitory concentration values of 0.78-100 µg/mL.