Covering: 2005 to 2008 Lignans are a class of secondary metabolites derived from the oxidative dimerization of two phenylpropanoid units. This review covers the source, chemistry and bioactivities of natural lignans, and highlights the total syntheses of some lignans and asymmetric syntheses of their motifs.

The molluscicidal activity of leaf and rhizome extracts of Iris germanica L. (var. alba) against Biomphalaria alexandrina snails was evaluated and the rhizome extracts were found to be the most potent. Activity-guided fractionation revealed that the chloroform extract showed the highest molluscicidal activity (LC₉₀ = 1.26 mg/l) among the tested extracts of the rhizomes. Fraction B prepared from the chloroform extract was the most potent molluscicide (LC₉₀ = 0.96 mg/l) in addition, it showed a significant heart rate reduction in the snail after a 6- to 24-h exposure period. It also displayed a significant level of cercaricidal potential in a time-concentration relationship pattern. Chromatographic fractionation and purification of fraction B resulted in the isolation of two novel compounds: 5,2′-dihydroxy-3-methoxy-6,7- methylenedioxyflavone and 5,7,2′-trihydroxy-6-methoxyflavanone. Their structures were established by one- and two-dimensional NMR methods and mass spectrometry