Novel dibenzofuran and biphenyl phytoalexins from Sorbus pohuashanensis suspension cell and their antimicrobial activities

Two novel sulfur-containing dibenzofurans, sorbusins A ( 1 ) and B ( 2 ), two unprecedented biphenyl glycosides, 2′-hydroxyaucuparin 2′- O - ɑ -L-rhamnoside ( 3 ) and noraucuparin 5- O - ɑ -L-rhamnoside ( 4 ), and four known analogues ( 5 – 8 ), were isolated from Sorbus pohuashanensis suspension cell induced by yeast extract. Their structures were elucidated based on spectroscopic analyses and quantum calculation of 13 C NMR data. Structurally, compound 1 possessed a rare naturally occurring benzothiazole moiety and represents the first example of thiazole fused dibenzofuran. A plausible biosynthetic pathway for the sulfur-containing dibenzofurans is proposed. These dibenzofuran and biphenyl phytoalexins were evaluated for their antimicrobial activities against pathogenic fungi and drug-resistant bacteria. Compound 7 exhibited significant antibacterial activity against methicinllin-resistant Staphylococcus aureus with an MIC value of 3.13 μg/mL.