Lignans compounds biosynthesis

Using this system, (Z)-hinokiresinol isolated from cultured cells of A. officinalis was determined to be the optically pure (75 )-isomer, while ( )-hinokiresinol isolated from cultured cells of C. japonica had 83.3% e.e. in favor of the (7S)-enantiomer (Table 12.1). The enzymatically formed (Z)-hinokiresinol obtained following incubation of p-coumaryl p-coumarate with a mixture of equal amounts of recZHRSa and recZHRSf) was found to be the optically pure (75)-isomer, which is identical to that isolated from A. officinalis cells (Table 12.1). A similar result was obtained with the crude plant protein from A. officinalis cultured cells, where the formed (Z)-hinokiresinol was almost optically pure, 97.2% e.e. in favor of the (75)-isomer (Table 12.1). In sharp contrast, when each subunit protein, recZHRSa or recZHRSP, was individually incubated with p-coumaryl p-coumarate, ( )-hinokiresinol was formed (Table 12.1). The enantiomeric compositions of ( )-hinokiresinol thus formed were 20.6% e.e. (with recZHRSa) and 9.0% e.e. (with recZHRSP) in favor of the (7S)-enantiomer (Table 12.1). Taken together, these results clearly indicate that the subunit composition of ZHRS controls not only cis/trans selectivity but also enantioselectivity in hinokiresinol formation (Fig. 12.3). This provides a novel example of enantiomeric control in the biosynthesis of natural products. Although the mechanism for the cis/trans selective and enantioselective reaction remains to be elucidated, for example by x-ray crystallography, the enantioselective mechanism totally differs from the enantioselectivity in biosynthesis of lignans, another class of phenylpropanoid compounds closely related to norlignans in terms of structure and biosynthesis. 

Lignans represent an extremely diverse group of compounds. This is the result of both structural diversity and stereo-selective biosynthesis. One particular plant species generally makes only one enantiomer of a particular compound. The other enantiomer may be synthesized by a different species. As a consequence, it is virtually impossible to summarize the biosynthesis of lignans in general. Instead, the focus here will be on the biosynthesis of the lignan podophyllotoxin in a number of different plant species, as an illustration of the different biosynthetic routes that can be used to synthesize the same compound. 

Phenylpropenes are derived from cinnamic acid and share the first steps of lignin/lignan biosynthesis. Shortening of the cinnamic acid side chain by two carbons leads to compounds with a C -C skeleton called benzenoids. Other volatile... 

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