Terpenoid chemistry. XIX. Dehydro- and Dehydroiso-myodesmone, toxic furanoid sesquiterpene ketones from Myoporum deserti

Abstract

A further essential-oil variety (the Theodore variety) of Myoporum deserti A. Cunn. yields an essential oil which contains c.50% of a mixture (1 : 1 to 2 : 1) of two previously undescribed furanoid sesquiterpene ketones which are (-)-1'S,5'S-1-[2'-(β-furyl)-5'-methylcyclopent-2'-enyl]-3-methylbut-2-en-l-one (4),b.p. 117º/1 mm, m.p. 26-27º, [x]D -254º, and (-)-5'S-1-[2'-(β-furyl)-5'-ethylcyclopent-l'-enyl]-3-methylbut-2-en-1-one (3), b.p. 118º/1 mm, [x]D -67º, and are dehydro derivatives of ketones known from the Jackson variety of M. desertz. The structures (3) and (4), deduced from spectral evidence, are confirmed by the base-catalysed equilibration of (3) and (4), the hydrogenation of (4) to dihydroisomyodesmone, and the oxidation of (3) to (+)-2-methylglutaric acid. The ketones are toxic to mice and have been recognized in M. deserti oils from plants growing in central Queensland in the vicinity of Theodore, Augathella, Tambo, and Jackson.