Neolignans biosynthesis

Neolignans are also compounds composed of two phenylpropanoid units, but linked in a manner other than C8-C8 (Fig. 12.1) [10]. The compounds of this class are often chiral and naturally occurring neolignans are usually optically active, which evokes the involvement of DPs in the biosynthesis of neolignans. 

Herein, we briefly outline the recent advances in the studies of stereoselectivity in the biosynthesis of norlignans, lignans, and neolignans. 

Lourith, N., Katayama, T., and Suzuki, T., 2005, Stereochemistry and biosynthesis of 8-0-4 neolignans in Eucommia ulmoides diastereoselective formation of guaiacylglycerol 8-0-4 -(sinapyl alcohol) ether, J. Wood Sci. 51 370-378. 

Irradiation of 2,2-dimethyl chromene through Pyrex using a 550-W Hanovia lamp initiates a retro 4 + 2 reaction to form the extended quinone methide 4, which reacts with methanol to form a pair of methyl ethers (Scheme 6A).18 Flash photolysis of coniferyl alcohol 5 generates the quinone methide 6 (Scheme 6B) by elimination of hydroxide ion from the excited-state reaction intermediate.19 The kinetics for the thermal reactions of 6 in water were characterized,20 but not the reaction products. These were assumed to be the starting alcohol 5 from 1,8-addition of water to 6 and the benzylic alcohol from 1,6-addition of water (Scheme 6). A second quinone methide has been proposed to form as a central intermediate in the biosynthesis of several neolignans,21a and chemical synthesis of neolignans has been achieved... 

Davin, F.B. and Lewis, N.G. (1992) Phenylpropanoid metabolism biosynthesis of monolignols, lignans and neolignans, lignins and suberins, in Phenolic Metabolism in Plants (eds H.A. Stafford and R.K. Ibrahim). Plenum, New York, pp. 325-75. 

Katayama, T., Suzuki, T., Lourith, N. and Kurita, Y. (2005) Biosynthesis and stereochemistry of lignans and neolignans Stereoselective cross coupling of coniferyl alcohol and sinapyl alcohol in broad-leaved trees. Kami Parupu Kenkyu Happyokai Koen Yoshishu, 72, 84 9. 

Wallis, A. R A. (1998) Structural diversity in lignans and neolignans. In Lewis, N. G., and Sarkanen, S. (eds). Lignin and Lignan Biosynthesis, American Chemical Society, Washington, DC. 

L. B. Davin N. G. Lewis, Phenylpropanoid Metabolism Biosynthesis of Monolignols, Lignans and Neolignans, Lignins and Suberins. In Recent Advances in Phytochemistry] Vol. 26 Phenolic Metabolism in Plants H. A. Stafford, R. K. Ibrahim, Eds. Plenum Press New York, 1992 pp 325-375. 

Composition of Lignin Origin of the Monomeric Units Polymerization of Lignin Lignans Biosynthesis Biological Activity Neolignans... 

The fourth and last example selected refers to a structurally surprising group of neolignans generated by the coupling of allylphenols plus allylphenols (Fig. 7.3.13). The process is initiated by oxidative methoxylation of the precursor 46 to 47. Diels-Alder additions of 47 (as dienophile) -I- 47 (as diene) or of 46 (as dienophile) -l- 47 (as diene) lead respectively to 48 (asatone), and hence to 49, and to 51 (164). Biosynthesis of the sesquineolignan 50 involves both these alternative cycloadditions. Biomimetic synthesis by anodic oxidation of 46 in methanol led to asatone (161). 

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