Structure and Cytotoxic Activity of Enzymatic Hydrolysis Products of Secoiridoid Glucosides, Isoligustroside and Isooleuropein

Hydrolysis of isoligustroside ( 1 ) and isooleuropein ( 2 ), secoiridoid glucosides, in the presence of β ‐glucosidase provided 2‐(4‐hydroxyphenyl)methyl (2 R ,3 S ,4 S )‐3‐formyl‐3,4‐dihydro‐4‐(2‐methoxy‐2‐oxoethyl)‐2‐methyl‐2 H ‐pyran‐5‐carboxylate ( 3 ) and 2‐(3,4‐dihydroxyphenyl)methyl (2 R ,3 S ,4 S )‐3‐formyl‐3,4‐dihydro‐4‐(2‐methoxy‐2‐oxoethyl)‐2‐methyl‐2 H ‐pyran‐5‐carboxylate ( 4 ), respectively. The structures of 3 and 4 were elucidated on the basis of extensive spectral analyses, including 2D‐NMR experiments. Compounds 3 and 4 were found to be new rearrangement products of the aglycones of 1 and 2 . The cytotoxic activities of 3 and 4 were evaluated using a disease‐oriented panel of 39 human cancer cell lines and showed moderate cytotoxic activity for 4 , while 3 exhibited weaker activity compared to that of 4 .