Isolation of lignans as seed germination and plant growth inhibitors from Mediterranean plants and chemical synthesis of some analogues Marina DellaGreca • Simona Zuppolini • Armando Zarrelli Received: 30 November 2012 / Accepted: 6 July 2013 / Published online: 18 July 2013 Ó Springer Science+Business Media Dordrecht 2013 Abstract Lignans and lignins are among the main metabolic products of phenylpropanoid metabolism in vascular plants. They are compounds representing the building blocks of plant cell walls. Moreover they have a broad range of biological activities such as antitumoral, antimitotic, antiviral and cytotoxic and are thought to be involved in the plant defense against pathogens and pests. In this paper we report a survey of the past and current literature about lignans and neolignans and their germination inhibitory activity on cultivated and wild species from plants of the Med- iterranean area. Some examples of synthetic method- ologies of these molecules have also been reported. Keywords Lignan Á Neolignan Á Phytotoxicity Á Mediterranean plants Introduction In 1927 Robinson recognized that a common feature of many natural products was a C6C3 unit (i.e. a phenyl- propanoid skeleton) perhaps derived from cinnamyl units. In a review of natural resins Haworth (1936) proposed that the class of compounds derived from two C6C3 units b,b 0 -linked should be called lignans. Lignans and lignins are the main metabolic prod- ucts of the phenylpropanoid metabolism in vascular plants. In woody ones, they typically account for more than 20 % of the weight of Angiosperms and over 25 % of that of the Gymnosperms. Together, they constitute some of the most expensive metabolic products generated by plants (Lewis and Yamamoto 1989), and are derived from the shikimate–chorismate pathway (Campbell et al. 1993; Dewick 1995) which produces the aromatic amino acids, phenylalanine and tyrosine (Jensen 1986). Extension of the phenylprop- anoid pathway in vascular plants, from phenylalanine onwards, ultimately leads to both the dimeric/oligo- meric lignans as well as the polymeric lignins. The biosynthesis of lignans has recently been revised based on the discovery of the dirigent proteins that guide phenolic radical coupling (Davin et al. 1997; Davin and Lewis 2000). Lignans are derived mainly via differential partitioning of the monolignol, coniferyl alcohol, to yield the lignan pinoresinol, which in turn represents the precursor of both seco- isolariciresinol and matairesinol. They are biosynthe- sized in the cell cytoplasm through the action of enzymes of the phenylpropanoid pathway, in which Phenylalanine Ammonia Lyase (PAL) catalyzes the initial step of the secondary metabolism and Pinores- inol Lariciresinol Reductases (PLR) accelerates the final steps of biosynthesis of lignans. M. DellaGreca (&) Á S. Zuppolini Á A. Zarrelli Chemical Sciences Department, University Federico II, Complesso Universitario Monte Sant’Angelo, 80126 Naples, Italy e-mail: dellagre@unina.it 123 Phytochem Rev (2013) 12:717–731 DOI 10.1007/s11101-013-9311-7