Lomatia tasmanica, W. M. Curtis

Deans, Bianca J., Tedone, Laura, Bissember, Alex C. & Smith, Jason A., 2018, Phytochemical profile of the rare, ancient clone Lomatia tasmanica and comparison to other endemic Tasmanian species L. tinctoria and L. polymorpha, Phytochemistry 153, pp. 74-78 : 75

2.1. Lomatia tasmanica

Maceration of L. tasmanica provided the naphthoquinone juglone (1) (0.34% w/w) ( Fig. 1 ). The 1 H and 13 C NMR spectroscopic and MS data (see: Supporting Information) were consistent with equivalent data previously reported in the literature ( de Freitas Araujo et al., 2009). In addition, this extract also contained a chromatographically inseparable mixture of n -alkanes (0.30% w/w). 1 H NMR and GC-MS analysis of this mixture was consistent with nonacosane (C 29 H 60) as the major component and heptacosane (C 27 H 56) as the minor component (see: Supporting Information) ( Lytovchenko et al., 2009). Neither of these long-chain alkanes has previously been reported from any Lomatia species. This suggests that these hydrocarbons represent major components of the epicuticular wax coating of the characteristically robust Proteaceae leaves. The PHWE extract provided glucose as a mixture of α- and β- anomers (see: Supporting Information).

Juglone (1), as well as other naphthoquinone pigments, have previously been isolated from numerous Lomatia species, including the Tasmanian endemic L. tinctoria ( Moir and Thompson, 1973) . A range of related naphthoquinones have been isolated from other Lomatia species, including: lomatiol (2) ( Fig. 1 ), which has been identified in the seeds of both endemic Tasmanian L. tinctoria and L. polymorpha ( Hooker, 1936) , and naphtharazin (3) from various species ( Moir and Thompson, 1973). Perhaps the presence of a single naphthoquinone in L. tasmanica reflects the primitive and ancient position of L. tasmanica within the lineage, as an evolved trend of increased pigment composition complexity is observed within later descendants within the genus ( Moir and Thompson, 1973). While it is possible that juglone 1 can be produced during extraction from its glycoside 1,4,8-trihydroxynaphthalene-1-Oβ- D- glucose 6 ( Duroux et al., 1998), extraction of fresh leaves from a representative specimen of L. tasmanica with diethyl ether for 5 min in an oxygen-free atmosphere did not detect the presence of glycoside 6. This indicates that naphthoquinone 1 is not an artefact of extraction/ isolation and is a true natural product.

Juglone (1), like many naphthoquinones, exhibits antifungal ( Meazza et al., 2003; Wianowska et al., 2016), antimycobacterial activity ( Tran et al., 2004), and is a reported antifeedant towards insects ( Akhtar et al., 2012). In addition, juglone is reported to affect plant development, including the promotion of cell division, cell elongation and root formation ( Compton and Preece, 1988). Naphthoquinone 1 also has reported allelopathic activity and toxicity towards plants, with its bioactivity as a phytotoxin first reported in 1928 ( Davis, 1928). It has been reported that plants may release juglone to stunt the growth of competing plants found in close proximity; and may serve to provide a chemical ecological advantage (eg. Topal et al., 2006). The reported bioactivity of juglone may provide some insight into the chemical ecological defenses that L. tasmanica may have developed (perhaps against fungus), as well as interactions and environmental pressures that L. tasmanica may have been exposed to over time.

Figures

Fig. 1. Juglone (1), lomatiol (2), and naphtharazin (3).