Lignans

Literature References: Plant products of low molecular weight formed primarily by the oxidative coupling of p-hydroxyphenylpropene units in which the two units may be linked by an oxygen bridge. The monomeric precursor units are cinnamic acid, cinnamyl alcohol, propenylbenzene and allylbenzene. The term lignan or Haworth lignan is applied to compounds derived by coupling acid and/or alcohol while the compounds derived by coupling propenyl and/or allyl derivatives are called neolignans: O. R. Gottlieb, Fortschr. Chem. Org. Naturst. 35, 1-72 (1978). Lignans occur widely and have been obtained from roots, heartwood, foliage, fruit and resinous exudates of plants. Lignans are optically active compounds. They represent the dimer stage intermediate between monomeric propylphenol units and lignin. Naturally occurring trimers and tetramers have not been reported. Occurrence of lignans, enterolactone, q.v., and enterodiol, in man and animal species: S. R. Stitch et al., Nature 287, 238 (1980); K. D. R. Setchell, ibid. 740. Synthesis of first lignans found in man and animals: G. Cooley et al., Tetrahedron Lett. 22, 349 (1981).