NOVEL BENZYLIC ETHER REDUCTIONS IN LIGNAN BIOGENESIS IN FORSYTHIA-INTERMEDIA

Forsythia intermedia cell-free preparations catalyse the stepwise conv ersion of pinoresinol into secoisolariciresinol via lariciresinol; to our knowledge, this represents the first documented example of the red uction of benzylic ethers (or their quinone methide analogues) in plan ts. In this study, the specificity of the reductive steps was establis hed: with (+)- and (-)-pinoresinols as substrates, it was found that t heir overall conversion into lariciresinol was highly enantioselective [i.e.> 99:1 in favour of the (+)-antipode], whereas (-)-secoisolarici resinol formation was more strictly enantioselective with only reducti on of (+)-lariciresinol being observed. Under the conditions examined to date, it was not possible to demonstrate the NADP-dependent back re action using (+/-)-lariciresinols as substrates. Interestingly, neithe r (+)- nor (-)-epipinoresinols [i.e. the diastereomers of (+/-)-pinore sinols] underwent similar reduction to afford lariciresinol, epilarici resinol or secoisolariciresinol.