Conospermum

The extraction of another local plant indigenous to Western Australia, namely smokebush [Conospermum sp. (Proteaceae)], yielded several novel compounds [9] but failed to locate the traces of conocurvone 4 present, a chemical later identified after a biological screening program by an American group [10]. Conocurvone has promising activity against HIV. 

Workers at the National Cancer Institute recently achieved a remarkable success in their search for active plant metabolites. During routine screening, extracts of a shrub indigenous to Australia were noted for their exceptionally high, and, more importantly, selective anti-HIV activity in a variety of cellular in vitro tests. The substance responsible for this effect was the naphthoquinone conocurvone la, which was isolated after an elaborate purification procedure in a yield of 22 mg per kg plant material Conospermum sp., Proteaceae). [1,2]... 

Conocurvone la is a deoxy-trimer of tereti-folion B (2a), a compound that has been known for longer and was first isolated from Conospermum teretifolium. The fast atom bombardment (FAB) mass spectrum of the tri-meric quinone revealed a molecular ion corresponding to the formula CeoHseOn, but the structure of la was in the end only fully elucidated by synthesis. The reason for this was that atropoisomeric equilibria were formed and led to more or less complex H-NMR spectra that varied with solvent and with temperature. The compound therefore appeared to be a complex mixture. However, the synthetic product was identical to the natural material, even in its chiroptical parameters, thus confirming the structure and also the low rotation barrier around the quinone-quinone axis, a property which has also been found for other quinonoid-quinonoid-coupled oligomers. 

Naphthoquinone trimer. Constit. of Conospermum incurvum. HIV inhibitor. [aJu -f 184 (c, 0.3 in MeOH). Related to Teretifolione B, T-00209. 

Constit. of the roots of Conospermum incurvum. Yellow powder. 

---