What is "lignan"

n. (context organic chemistry English) Any of a class of phenylpropanoid (propylbenzene) type of molecules found in essentially all plants, generally dimeric or higher order, and produced by secondary metabolic pathways branching off of aromatic amino acid biosynthesis, in some cases having associated antioxidant or estrogenic (phytoestrogenic) activities; having in common with lignin the phenylpropanoid monomers, where lignin is a random oxidative polymerization of the same

The lignans are a group of chemical compounds found in plants. 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, known as phenylpropanoids, 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, a structure formed by joining the two propylbenzene residues at other than the β-carbon atom of the propyl side chain.

Some examples of lignans are pinoresinol, podophyllotoxin, and steganacin.

When a part of the human diet, some plant lignans are metabolized by intestinal bacteria to mammalian lignans enterodiol (1) and enterolactone (2). Lignans that can be metabolized to mammalian lignans are pinoresinol, lariciresinol, secoisolariciresinol, matairesinol, hydroxymatairesinol, syringaresinol and sesamin. 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 isoflavones and coumestans.