Enterolactone, structure

Fig. 2.86. Chemical structures of the iosflavones daidzein, genistein, O-desmethylangolensin, equol, and the lignans enterolactone and enterodiol. Reprinted with permission from Z. Kuklenyik el al. [209].

NM Saarinen, A Smeds, SI Makela, J Ammala, K Hakala, JM Pihlava, EL Ryhanen, R Sjohohn, R Santti. Structural determination of plant lignans for the formation of enterolactone in vivo. J Chromatogr B 25 311-319, 2002. 

FIGURE 25.1 Structures of nonsteroidal phytoestrogens. The most prevalent classes of phytoestrogens are (1) flavones apigenin (2) kaempferol (3) isoflavones daidzein (4) genistein (5) formononetin (6) biochanin A (7) lignans enterolactone (8) coumestans coumestrol (9) flavanones 8-prenylnaringenin. 

The structures of the lignoids 1, 2 and 3 illustrate some common and some different features. All three compounds comprise two C6-C3-moieties, numbered 1 to 9 and V to 9, and hence their monomers are presumably metabolites of the shikimate pathway. Since this pathway is restricted to plants, the biosynthesis of 3 is a mystery. Could enterolactone be a bacterial degradation product of lignins ingested with plant food, or is it synthesized ex novo (133) If so, what are its precursors - a pertinent question since enterolactone lacks oxy-functions at the 4- and 4 -positions of the aryls, a structural particularity not shared with any other naturally occurring C6-C3-dimer known. Indeed free p-hydroxyls are essential for the oxidative coupling of the monomers regardless of the mechanism of the reaction. 

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