Lignan
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A lignan is a group of chemical compounds found in plants. Lignans are one of the major classes of phytoestrogens, which are estrogen-like chemicals and also act as antioxidants. The other classes of phytoestrogens are the isoflavones, and coumestans. Plant lignans are polyphenolic substances derived from phenylalanine via dimerization of substituted cinnamic alcohols (see cinnamic acid), known as monolignols, to a dibenzylbutane skeleton 2. This reaction is catalysed by oxidative enzymes and is often controlled by dirigent proteins.
Many natural products are built up of C6C3 units (a propylbenzene skeleton 1) derived from cinnamyl units just as terpene chemistry builds on isoprene units. Structure 3 is a neolignan.
Some examples of lignans are pinoresinol, podophyllotoxin, and steganacin.
When part of the human diet, lignans are converted into the mammalian lignans known as enterodiol (1) and enterolactone (2) by intestinal bacteria.
[edit] Food Sources
Flax seed is among the highest sources of lignan (~301129 µg/100 g); the principal lignan precursor found in flaxseed is secoisolariciresinol diglucoside. Other sources of lignans include pumpkin seeds, sesame seeds, rye, soybeans, broccoli, beans, and some berries.
