Certain samples of essential oils from Myoporum deserti, M. betcheanum, M. acuminatum, Eremophila maculata, and E. latrobei have been shown to contain myoporone and/or 10,ll-dehydromyoporone. The ambiguity regarding the stereochemistry of myoporone (previously known from M, bontioides) has been resolved,(-)-myoporone being shown to possess the S configuration by degradation to (S)-(+)-2-methylglutaric acid. (-)-Dehydromyoporone, m.p. 32.5-33.5, [x]D ? 15�, has the S configuration as shown by degradation to (S)-(-)-3-methyladipic acid and hydrogenation to (S)-(-)-myoporone, m.p. 17.5-19�, [x]D-5.3�. Both ketones activate the typical ngaione pathology on intraperitoneal injection into mice but myoporone is not toxic to sheep. Myoporone from Myoporum species shows wide variations in optical purity.

A common variety of Myopovum deserti A. Cunn. (Ellangowan Poison Bush) yields an essential oil consisting largely of the iridoid monoterpene, (1R)-1-methoxymyodesert-3-ene, C11Hls02, (1 R,4aS,7R,7aR)-1-methoxy-4,7-dimethyl-l,4a,5,6,7,7a-hexahydrocycopenta[c]pyran, b.p. 6772 mm, [@lo -165'. This cyclic acetal is hydrolysed to methanol and a mixture of two epimeric cyclopentanoid dialdehydes which are oxidized to the two epimeric trans,trans-nepetalinic acids and yield (+)-(R)actinidine with Brady's reagent. (1R)-1-Methoxymyodesert-3-ene is oxidized by ozone/hydrogen peroxide to (1R,2R,5R)-2-acetyl-5-methylcyclopentanecarboxylic acid.Hydrogenation yields mainly (1R)-methoxymyodesertan, hydrolysed by aqueous maleic acid at room temperature to methanol and a cyclic hemiacetal, (lR,4R,4aR,7R,7aR)-4,7-dimethyl-1,3,4,4a,5,6,7,7a-octahydrocyclopenta[c]pyran-1-01, Oxidation of this cis&-hemiacetal by bromine in acetate buffer yields a lactone further oxidized by chromic acid to (2R,1'S,2'R,3'R)-2-(2'-carboxy-3'-methylcyclopentyl)propionic acid.(1R)-1-Methoxymyodesertan, refluxed with aqueous phthalic acid, yields (+)-(4R,4aR,7R)-4,7-dimethyl-3,4,4a,5,6,7-hexahydrocyclopenta[c]pyran. Treatment of the hexahydropenta[c]pyran, the cis,cis-hemiacetal or (1R)-1-methoxymyodesertan with hydrochloric acid yields a tvans,transhemiacetal, (1 R,4R,4aR,7R,7aS)-4,7-dimethyl-1,3,4,4a,5,6,7,7a-octahydrocyclopenta[c]pyran-l-ol, which equilibrates in solution to a mixture of a-and j3-anomers. Spectral studies of these and other products establish the configuration of the natural product at C 1.(1R)-1-Methoxymyodesert-3-ene is not toxic to sheep as are the j3-substituted furans characteristic of most other chemovarieties of M. desevti.The shrub Myoporum deserti A. Cunn. (Ellangowan Poison Bush), which is found in the drier areas of Australia, is a well authenticated stock poison.' Previous parts2 of this series have described the isolation and chemistry of 11 toxic furanoid sesquiterpene ketones, such as (1) and (2), from various chemovarieties of the species but certain others contain iridoid monoterpenes accompanied by little or none of the toxic furanoid derivatives.

Two furanoid sesquiterpene ketones (designated myodesmone and isomyo- desmone) have been isolated from the essential oils of certain varieties of Myoporum deserti A. Cunn. and M. acuminatum R. Br. and have been shown to be toxic to mice, rats, and sheep. ��� (-)-Isomyodesmone, b.p. 107-109�/1 mm, m.p. 46.5-47�, [α]D -193�, is shown to be 1S,5S-2-(β-furyl)-5-methylcyclopent-2-enyl isobutyl ketone and is characterized as a dihydro derivative, m.p. 33-33.5�, and as a glycol, m.p. 173-173.5�. Brief treatment of isomyodesmone with base yields largely the epimeric epiisomyodesmone while prolonged treatment forms an equilibrium mixture of 1% (-)-isomyodesmone, 41% of (+)-epiisomyodesmone, and 58% of (-).myodesmone, oil, b.p. 107-109�/1 mm, [α]D -108�, which is 5S-2-(β-furyl)-5-methylcyclopentenyl isobutyl ketone. The proposed structures are supported by electronic, p.m.r., and mass spectral evidence and confirmed by the degradation of isomyodesmone to (+)-dihydrocitronellic acid and myodesmone to (+)-2- methylglutaric acid. ��� The toxicity to stock of the Jackson variety of M. deserti known from Jackson, Dulacca, Tchanning Creek, and Myall Park (and the Chinchilla variety of M. acuminatum) is attributed primarily to the presence of myodesmone and isomyodesmone which are present in closely equal amounts and together constitute 50-55% of the whole oil. Alternatively the plant may contain a toxic ketol precursor which is dehydrated to the myodesmones during steam distillation of the leaves.

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Synthetic specimens of 1,3,6,8-tetramethoxyanthraquinone and its 4-methoxy and 4-methoxycarbonyl derivatives have been prepared for comparison with products derived from the degradation of the pigments of the crinoids, Comatula pectinata and C. cratera.