The Dominant Secondary Metabolite of Caulerpa Genus Caulerpenyne CYN

Caulerpa spp. contain several linear terpenoid secondary metabolites and especially caulerpenyne (CYN, Fig. 1) has been associated with anti-cancer, anti-proliferative, anti-microbial, anti-herpetic and anti-viral properties in many reports. Both invasive Caulerpa spp. contain the dominant sesquiterpenoid metabolite CYN, which can be found in high concentrations up to 1.3% of the dry weight of the alga (Amade and Lemée, 1998; Dumay et al., 2002). CYN contents of invasive and non-invasive Caulerpa species of the Mediterranean are similar, suggesting that this molecule is not the key for the success of rapidly spreading species but rather a wider distributed metabolite of Caulerpa spp. in general (Jung et al., 2002).

Purified CYN is a feeding inhibitor against sea urchins (Erickson et al., 2006). But in the natural context, this compound might be considered to be rather a storage form for more reactive metabolites, which are formed enzy-matically after wounding the giant algal cells (Weissflog et al., 2008). CYN contains an unusual bis-enoyl acetoxy functionalisation that is transformed rapidly by esterases once the algal cells are disrupted. This enzymatic transformation results in the formation of the highly reactive 1,4-bis-aldehyde oxytoxin-2 (Jung and Pohnert, 2001). The transformation is relevant for the activated chemical

Figure 1. Caulerpenyne, the major terpenoid metabolite produced by C. taxifolia and C. racemosa.

OAc defence and the survival of the unicellular macroalga after mechanical wounding (Adolph et al., 2005). Oxytoxin-2 is central for the rapid sealing of the giant cells after wounding, which enables survival and reproduction of Caulerpa spp. (Adolph et al., 2005). Once a cell is injured, a plug is formed around the wound by protein cross-linking with this activated secondary metabolite. The polymer material seals the cells and prevents leakage of the cytoplasm into the surrounding sea water (Dreher et al., 1982).

In general, terpenes from Caulerpales are known for their icthytoxic, antibacterial, anti-fungal and anti-proliferative properties (Paul and Fenical, 1986, 1987). Nevertheless, some specialised herbivores such as the sea slugs Lobiger serradifalci and Oxynoe olivacea have adapted to this defensive reaction and do not only consume Caulerpa spp. but also exploit their chemistry for their own chemical defence by sequestration (Gavagnin et al., 1994; Cimino et al., 1999).

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