Of lignans

RESEARCH OF LIGNANS AND ESSENTIAL OILS FROM THE ROOT ARCTIUM LAPPA L. 

Heterolignans, synthetic analogs of lignans containing heterocylic fragments 99H(51)1443. 

The most useful of the insertion processes is the intramolecular reactions that occur with high selectivity for the formation of five-membered ring products. The electrophilic nature of the process is suggested by C-H bond reactivity in competitive experiments (3°>20 >1°) [76, 77]. Asymmetric catalysis with Rh2(MPPIM)4 has been used to prepare a wide variety of lignans that include (-)-enterolactone (3) [8], as well as (R)-(-)-baclofen (2) [7],2-deoxyxylolactone (31) [80,81],and (S)-(+)-imperanane (32) [82].Enantioselectivities are 91-96%... 

LiGGiNS J, GRIMWOOD R, BINGHAM s A (2000) Extraction and quantification of lignan ph)doestrogens in food and human samples. naZ Biochem. 287 102-9. 

Recently, some of the specific faecal bacteria involved in the metabolism of dietary isoflavonoids were isolated (Hur et al., 2000). They have been shown to selectively convert genistin and daidzin to their respective aglycones. One of the isolated bacteria, under anoxic conditions, was further shown to metabolise genistein and daidzein to their respective dihydroxy-genistein and dihydroxy-daidzein. In the case of lignans, enterodiol and enterolactone were shown to be excreted in vivo only in rats harbouring a gut microflora (Rowland et al, 1999). 

ADLERCREUTZ H, HONJO H, HIGASHI A, FOTSIS T, HAMALAINEN E, HASEGAWA T and OKADA H (1991) Urinary excretion of lignans and isoflavonoid phyto-oestrogens in Japanese men and women consuming traditional Japanese diet. Am J Clin Nutr. 54 (6) 1093-100. 

The amount of lignans (i.e. secoisolariciresinol) is marked with number 1 in the original phloem sample. 

EtOH extraction was the most efficient way to improve the flavour of the phloem. A solvent/solid ratio of at least 10 1/kg was needed to achieve a significant change in the taste. The loss of catechins was approximately 27% and that of lignans was 35%. All the catechins and lignans were found from the EtOH extract. Losses of lignans and catechins were smaller with other sovents, but either the taste was not modified or the cost of solvent treatment would be too high. Phenolic compounds like lignans and catechins also have a bitter taste and some improvement in flavour may have occurred because of the lower concentration of these. The disappearance of the characteristic... 

Asymmetric catalysis with Rh2(4Y-MPPIM)4 has been used to prepare a wide variety of lignans such as (+)-isodeoxypodophyllotoxin 70 (Equation (62))202,203 and (—)-enterolactone 71 (Equation (63)).194 The chemistry has also been utilized in the synthesis of (A)-(+)-imperanene 72 (Equation (64))197 and (R)-(—)-baclofen 73 (Equation (65)).198 Enantioselectivities of 91-96% ee have been obtained for a broad range of applications. 

C.B.S. Rao, Chemistry of Lignans (Andhra University Press, India, 1978). 

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 of another type, dicarboxylic acid lignans (p-hydroxycinnamate dimers), were isolated from liverworts (Hepaticopsida) and some vascular plants [11, 64]. Little is known about the biosynthesis of this class of lignans, but a feeding experiment demonstrated the conversion of caffeic acid to optically pure epiphyllic acid in a liyerwoTt Lophocolea heterophylla (Fig. 12.9) [65]. 

Moss GP (2000) Nomenclature of lignans and neolignans. Pure Appl Chem 72 1493-1523... 

Suzuki S, Umezawa T (2007) Biosynthesis of lignans and norUgnans. J Wood Sci 53 273-284... 

Beracierta AP, Whiting DA (1978) Stereoselective total syntheses of the ( )-di-0-methyl ethers of agatharesinol, sequirin-A, and hinokiresinol, and of ( )-tri-0-methylsequrin-E, characteristic norlignans of Coniferae. J Chem Soc Perkin Trans 1 1257-1263 Birch AJ, Liepa AJ (1978) Biosynthesis. In Rao CBS (ed) Chemistry of lignans. Andhra University Press, Andhra Pradesh, pp 307-327... 

Okunishi T, Umezawa T, Shimada M (2001) Isolation and enzymatic fomiation of lignans of Daphne genkwa and Daphne odora. J Wood Sci 47 383-388... 

Umezawa T, Davin LB, Lewis NG (1991) Formation of lignans (-)-secoisolariciresinol and (-)-matairesinol with Forsythia intermedia ceU-free extracts. J Biol Chem 266 10210-10217 Okunishi T, Sakakibara N, Suzuki S et al (2004) Stereochemistry of matairesinol formation by Daphne secoisolariciresinol dehydrogenase. J Wood Sci 50 77-81 XiaZ-Q, Costa MA, Pelissier HC et al (2001) Secoisolariciresinol dehydrogenase purification, cloning, and functional expression. J Biol Chem 276 12614-12623... 

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