Terpenoid Chemistry. XXVIII. Furanosesquiterpene β-Ketols From Myoporum betcheanum, M. deserti, M. montanum and Other Myoporaceae

Abstract

All four of the myodesmoid β-ketols (la) formally derivable from (-)-(S)-myoporone (3a),three of the four myomontanoid β-ketols (2a) from ent-(3a) and two of the four 10,ll-dehydro myodesmoid β-ketols (lb) from (3b), have been found in Myoporaceous plants and characterized by g.1.c. retentions and by Kovats indices and mass spectra of their trimethylsilyl ethers. Five of these ketols have been obtained as crystalline solids whose stereochemistry has been determined in part. All are readily converted into myoporone or 10,11-dehydromyoporone by pyrolysis during distillation or gas chromatography, and by base or alumina. These facile ring-opening reactions have previously concealed the widespread occurrence of these furanosesquiterpene β-ketols in the Myoporaceae.

In the few specimens of Myoporum betcheanum, M. deserti and M. montanumwhich have been suitably examined, the β-ketols form a complex mixture of from four to eight ketols differing in carbon skeleton, unsaturation and/or stereochemistry. P-Ketols have been recognized in eight species of Myoporum and three of Eremophila. Both enantiomers of one myodesmoid ketol have been isolated. A mixture of ketols showed a toxicity similar to that of (-)-ngaione.

A quick and quantitative micro method for the preparation of g.l.c.-injectable carbon disulfide solutions of volatile leaf constituents is described.