Lignans Lariciresinol

Although structural elucidation of lignans is not a difficult task, the similarities between the structures can create problems. In particular, the determination of stereochemistry at the chiral center requires NOE/ NOESY NMR experiments and/or X-ray analyses. The enantiomeric excesses of the known lignans (+)-lariciresinol, (-)-secoisolariciresinol and (+)-taxiresinol, isolated from Japanese yew T. cuspidata roots, were determined by chiral high-performance liquid chromatographic analyses [78] except for (+)-pinoresinol (77% enantiomeric excess), they were found to be optically pure by Kawamura et al. In an earlier study, the presence of taxiresinol in Taxus species was reported by Mujumdar et al. [69] after they had isolated it from the heartwood of T. baccata, although they did not study its stereochemistry. 

Two lignans (+)-lariciresinol and (-)-siringaresinol. Fig. (8) have also been isolated fi-om the roots of A.mongholicus [255], while... 

Milder I E, Arts I C, van de Putte B, Venema D P and Hollman P C (2005), Lignan contents of Dutch plant foods a database including lariciresinol, pinoresinol, secoisolariciresinol and matairesinol , Br J Nutr, 93, 393-402. 

Hemmati S, Schmidt TJ, Fuss E (2007) (-l-)-Pinoresinol/(-)-lariciresinol reductase from Liman perenne himmelszelt involved in the biosynthesis of justicidin B. FEBS Lett 581 603-610 Umezawa T, Davin LB, Yamamoto E et al (1990) Lignan biosynthesis in Forsythia species. J Chem Soc Chem Commun 1405-1408... 

The morama bean is an excellent source of lignans (Holse et al., 2010). The content of secoisolariciresinol in morama beans (305-406 gg/100 g) is higher than that of soybean (13-273 gg/100 g) and peanut (333 pg/100 g) (Mazur et al., 1998). Likewise, the level of lariciresinol in morama beans (614-825 [tg/100 g) is higher than that of soybeans (287 gg/lOO g), while the level of pinoresinol in morama beans (21-23 gg/lOO g) is lower than the level in soybeans (446 gg/lOO g) (Penalvo et ah, 2004). These lignans can be converted by intestinal bacteria into enterolignans, which possess biological activities such as (anti) estrogenic and antioxidant action. Therefore, they may reduce the risk of certain types of cancers as well as cardiovascular diseases (Adlercreutz, 2007). 

The main lignan in flaxseed is SDG (Figure 2). Also present are a number of other lignans, that is, matairesinol (MAT), lariciresinol, hinokinin,... 

Scheme 10 Four lignans oxidized with the MT0/H202 system lariciresinol (a), isolariciresinol (b), matairesinol (c), and 7-hydroxymatairesinol (d)...

A short and highly stereoselective route to lignan natural products ( )-dihydrosesamin and ( )-lariciresinol using radical methods has been reported [95JCS(P1)927]. These cyclizations proceed in good yields and the stereochemistry at two contiguous chiral centers are established. 

Investigations of gymnosperms and angiosperms showed the existence of a common lignan biosynthetic pathway where it acts as enzymes, particularly pinoresinol/lariciresinol reductase [30] and secoisolariciresinol dehydrogenase [31]. 

Over 40 lignans have been isolated from eight Taxus species to date (Table 1 and 2). a-Conidendrin isolariciresinol, secoisolariciresinol, isotaxiresinol and lariciresinol are found in several species of the genus Taxus. Indeed, isotaxiresinol and secoisolariciresinol are found in all Taxus species. 

Katayama, T., Masaoka, T. and Yamada, H. (1997) Biosynthesis and stereochemistry of lignans in Zanthoxylum ailanthoides. I. (+)—Lariciresinol formation by enzymatic reduction of (+/ —)—pinoresinols. Mokuzai Gakkaishi, 43, 580-8. 

Youn, B., Moinuddin, S.G.A., Davin, L.B., Lewis, N.G. and Kang, C.H. (2005) Crystal structures of apo-form, and binary/ternary complexes of Podophyllum secoiso-lariciresinol dehydrogenase, an enzyme involved in health-promoting and plant defense lignans. /. Biol. Chem., 280, 12917-26. 

Lactases 976 Lamiaceae 967 Langmuir isotherm 944 Lariciresinol, enzymatic formation of 1216 Lead compounds, as oxidants 1292, 1325-1330 Leguminosae 967 Lewis acid catalysis 607-611, 631 Lignans, synthesis of 1158, 1242, 1274 Lignin model compounds 302-306, 867, 868 phosphitylation of 999 Lignins 962, 997, 998... 

LH Xie, T Akao, K Hamasaki, T Deyama, M Hatton. Biotransformation of pinoresinol diglucoside to mammalian lignans by human intestinal microflora, and Isolation of enterococcus faecalis strain PDG-1 responsible for the transformation of (+)-pinoresinol to (+)-lariciresinol. Chem Pharm Bull 51 508-515, 2003. 

The principle pathways of lignan biosynthesis in Forsythia have been elucidated from studies using labelled precursors and cell free extracts. The sequence from coniferyl alcohol (9) to (+)-pinoresinol (10), (+)-lariciresinol (11), (-)-secoisolariciresinol (12) and (-)-matairesinol (13) is now clearly established (scheme 1) [30-33]. Lewis et al. have shown that (+)-pinoresinol (10) is formed via direct stereoselective coupling of the two coniferyl alcohol molecules, a process which requires the complimentary action of a specific protein and an auxiliary oxidase or peroxidase [34,35]. (+)-Lariciresinol (11) and (-)-secoisolariciresinol (12) are then formed by consecutive enantiospecific reduction [36], and (-)-secoisolariciresinol is further metabolised into (-)-matairesinol (13) via enantiospecific dehydrogenation, and into (-)-arctigenin (14) via regioselective 0-methylation [37]. 

Another simple synthesis of lignans of the lariciresinol type (11) involves a straightforward reduction of a functionalised dibenzylbutyrolactone such as (75) or (76) followed by acid-catalysed cyclisation (scheme 24) [77,78]. Cyclisation of the doubly functionalised precursor (77) affords access to the furofuran skeleton (78) (scheme 25). A second synthesis which has also been extended to the furofuran series involves a radical cyclisation step, which proceeds with high stereoselectivity (scheme 26) [79]. This route has been used to synthesise (79) which is a precursor for the synthesis of sesamin and eudesmin [80]. 

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