Novel aminoalkaloids from European mistletoe (Viscum album L.) Bashar Amer a , Ole Johan Juvik a , Fre ´ de ´ ric Dupont b , George W. Francis a , Torgils Fossen a, * a Department of Chemistry and Centre for Pharmacy, University of Bergen, Alle ´gt. 41, N-5007 Bergen, Norway b Department of Botany, Faculty of Pharmacy, University of Lille 2, PO Box 83, 3 Rue du Professeur Laguesse, 59006 Lille Cedex, France 1. Introduction The European white-berry mistletoe (Viscum album L.) (Fig. 1) belongs to the family Loranthaceae (APG III, 2009) within the order Santalales. Originally the plant belonged to Viscaceae (Mabberley, 2008) which has now been included in Loranthaceae. V. album L. is an evergreen dioecious small shrub growing half parasitically on a tree host in temperate Europe and western Asia. Three subspecies are recognised (Mabberley, 2008), one covering the whole range of host species. Two of them grow on conifer hosts: V. album L. subsp. abietis (Wiesb.) Abrom. on fir (Abies Mill.), V. album L. subsp. austriacum (Wiesb.) Vollm. on Scots pine (Pinus sylvestris L.). The best known European mistletoe is V. album L. subsp. album, growing on decidous trees, mostly on apple (Malus Mill.), poplar (Populus L.) and willow (Salix L.), and many other species growing in range but very rarely on oak (Quercus L.) and never on beech (Fagus L.). The species has linear lanceolate leathery leaves which last for several seasons, and whitish, translucent berries that develop in the late fall and early winter from the yellow to green flowers which grow in the sprout axil (Bu ¨ ssing, 2000). According to Mabberley (2008), the name mistletoe is applied not only to the genus Viscum but to any genus of Loranthacae spp. half parasitic on tree or shrub branches. Hypertension, diabetes, arthrosis and cancer are some of the most important illnesses that have been treated by using the white-berry mistletoe as a traditional remedy in Europe. (Bu ¨ ssing, 2000 and references therein). The anticancer activity of mistletoe extracts has been ascribed to the presence of lectins (Franz, 1986), viscotoxins (Romagnoli et al., 2000) and alkaloids (Khwaja et al., 1980, 1986; Park et al., 1998, 1999; Chen et al., 2005 and references therein; Dong et al., 2009; Ge et al., 2009; Zhou et al., 2010). Mistletoe lectins are cytotoxic proteins whose cytotoxic activity results from inhibition of protein synthesis on the ribosomal level (Franz, 1986). Contrary to the viscotoxins and mistletoe alkaloids, mistletoe lectins are not thermally stable and lose their biological activity through heat treatment. Viscotoxins are toxic proteins with relatively low molecular weight (5 kDa) which are produced in stems and leaves of the European mistletoe (V. album L.). The three-dimensional structure of the most important viscotoxin of this species, namely viscotoxin A3, has previously been char- acterised in detail (Romagnoli et al., 2000). Mistletoe alkaloids comprising the third group of anticancer natural products from this species have been scarcely characterised and only limited information about their structure and identities is available. Mistletoe may be able to incorporate alkaloids from the host tree, in agreement with the observation that leaves of mistletoe contained the same alkaloids in similar concentrations to those found in the non-leafy parts of the host (Kanner, 1939; Trautner, 1952; Mortimer, 1957; Martin-Cordero et al., 1989, 1997). Kanner (1939) found caffeine in Loranthaceae spp. growing on coffee trees Phytochemistry Letters 5 (2012) 677–681 A R T I C L E I N F O Article history: Received 27 April 2012 Received in revised form 3 July 2012 Accepted 5 July 2012 Available online 20 July 2012 Keywords: European Mistletoe Viscum album L. Aminoalkaloids Alkaloids 4,5,4 0 -Trihydroxy-3,3 0 -iminodibenzoic acid 4,5,4 0 ,5 0 -Tetrahydroxy-3,3 0 -iminodibenzoic acid 1 H– 15 N HMBC 2D NMR A B S T R A C T The European white-berry mistletoe (Viscum album L.) has remained an important medicinal plant for millennia. Preparations of the plant have found application in the treatment of cancer and the anticancer activity of mistletoe extracts has been ascribed to the presence of lectins, viscotoxins and alkaloids. However, the alkaloids of this species have hitherto remained unidentified because of their claimed extreme lability. Here we report on the isolation and characterisation of the novel aminoalkaloids 4,5,4 0 - trihydroxy-3,3 0 -iminodibenzoic acid (1) and 4,5,4 0 ,5 0 -tetrahydroxy-3,3 0 -iminodibenzoic acid (2) from V. album L. The compounds define a novel group of aminoalkaloids and are the first novel alkaloids ever identified in any mistletoe species. The structures were established using a combination of several 2D NMR spectroscopic techniques and high resolution mass spectrometry. ß 2012 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +47 55 58 34 63; fax: +47 55 58 94 90. E-mail address: torgils.fossen@kj.uib.no (T. Fossen). Contents lists available at SciVerse ScienceDirect Phytochemistry Letters jo u rn al h om ep ag e: ww w.els evier.c o m/lo c ate/p hyt ol 1874-3900/$ – see front matter ß 2012 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.phytol.2012.07.005