BIOSYNTHESIS AND STEREOCHEMISTRY OF LIGNANS IN ZANTHOXYLUM AILANTHOIDES .1. (-LARICIRESINOL FORMATION BY ENZYMATIC REDUCTION OF (+())-)-PINORESINOLS/

The enzymology and stereochemistry of lignan biosynthesis in Zanthoxyl um ailanthoides Sieb. et Zucc, were investigated. The absolute configu ration of (-)-pinoresinol and (-)-secoisolariciresinol isolated from t he plant by Ishii and others (1983) was (8S, 8'S) and (8R, 8'R), respe ctively, which are the opposites of each other. According to an analog y of the lignan biosynthetic pathway first proposed using Forsythia sp p. plants [coniferyl alcohol-->(8R, 8'R)-(+)-pinoresinol-->(8R, 8'R)-( +)-lariciresinol-->(8R, 8'R)-(-)-secoisolariciresinol], (+)-secoisolar iciresinol should be formed from (-)-pinoresinol, When (+/-)-pinoresin ols were incubated with cell-free extracts from the young shoot in the presence of NADPH, (+)-lariciresinol was detected as a product, Next, ((+/-)-[8,8'-C-14]pinoresinols were incubated for 5, 20, and 60 min w ith 10-80% (NH4)(2)SO4 precipitated protein preparations from the cell -free extracts in the presence of NAD(P)H. This showed that (+)-[8,8'- C-14]lariciresinol formation increased over the time period, whereas t he radioactivity of the (-)-lariciresinol fraction was constant after 5 to. 60 min at almost background level. NAD(P) H was an essential cof actor in the reaction. It was strongly suggested that this (+)-laricir esinol formation was due to an enzyme catalyzing a. stereospecific red uction of the benzyl ether in (+)-pinoresinol. Its absolute configurat ion, (8R, 8'R), was the same as that of naturally occurring (-)-secois olariciresinol.