Tetraprenyltoluquinols from the brown alga Cystophora ﬁbrosa
Damian W. Laird, Ian A. van Altena
Marine Natural Products Group, Chemistry, School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW 2308, Australia Received 13 December 2005; received in revised form 12 March 2006Available online 5 May 2006
Abstract Six cyclised tetraprenyltoluquinols and ﬁve stereoisomers with the previously reported amentol skeleton have been isolated from the lipophilic extract of the South African brown alga Cystophora ﬁbrosa. Structures and relative stereochemistry were determined using spectrometric techniques, particularly 1D and 2D NMR, and molecular modelling experiments. Thecompounds isolated appear to be enantiomeric to compounds with the same skeleton isolated from brown algae of the genus Cystoseira collected in northern Africa and the Mediterranean Sea. The isolation of tetraprenyltoluquinols with the amentol skeleton from this alga suggests that C. ﬁbrosa should be moved from the genus Cystophora into the Cystoseira. Ó 2006 Elsevier Ltd. All rights reserved.Keywords: Cystophora ﬁbrosa; Cystoseiraceae; Brown alga; Isolation; Structure elucidation; Molecular modelling; Chemotaxonomy; Tetraprenyltoluquinol; Meroditerpene; Cystoseira
1. Introduction As part of an ongoing study of metabolites from brown algae of the genus Cystophora and their use as potential intra-generic taxonomic markers, a collection of Cystophora ﬁbrosa (Simons) was made in January2001. C. ﬁbrosa (Cystoseiracea, Fucales, Phaeophyceae) occupies a unique position in the genus as it is the only species of the 26 described to date that occurs outside the cold temperate waters of Australasia (Womersley, 1987). It has only been recorded from Cape Province in South Africa where two disjunct populations, separated by over 100 km, are known (Simons, 1970; Stegenga et al., 1997).Geographic overlap of South African and Australian ﬂora at the generic level is relatively common, especially in terrestrial systems. However, it is unusual that only a single representative of the Cystophora genus has been described from South African waters. As a consequence the taxonomic status of C. ﬁbrosa is still cause for debate and Australian phycologists believe that C. ﬁbrosa should beclassiﬁed in the closely related genus Cystoseira (Womersley, 1987).
Corresponding author. Tel.: +61 2 49215480; fax: +61 2 49215472. E-mail address: Ian.vanAltena@newcastle.edu.au (I.A. van Altena).
As opposed to the restricted geographical range of Cystophora, Cystoseira has a worldwide distribution with a major radiation in the Mediterranean Sea and two species have been recorded from SouthAfrican waters (Silva et al., 1996). A large number of structurally diverse terpenoid secondary metabolites have been isolated from Cystoseira species and have been used as taxonomic markers. In particular, linear and cyclic meroditerpenoids have proven to be very eﬀective tools for discriminating between species of Cystoseira (Amico, 1995; Amico et al., 1990; Valls and Piovetti, 1995) and have evenbeen utilised to identify natural hybrids (Amico et al., 1988a). In contrast to the complexity of secondary metabolites reported from Cystoseira, those produced by species of Cystophora are mostly simple isoprenoid derivatives, acetogenins and polyenes, none exhibiting the complex cyclisations found in the more advanced Cystoseira metabolites (van Altena, 1988 and references therein). Thus far, nocompound common to both Cystoseira and Cystophora genera has been reported. In light of the signiﬁcant structural diﬀerences reported for Cystophora and Cystoseira metabolites it was anticipated that investigation of the secondary metabolites present in C. ﬁbrosa would provide some insight into its taxonomic position.
0031-9422/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved....