Terpenoid Chemistry. XXVII. Further Iridoid Constituents, (1R)- and (1S)-1-Acetoxymyodesert-3-ene, from Myoporum deserti (Myoporaceae).

Abstract

A further chemovariety of Myoporum deserti A. Cunn . yields an essential oil consisting predominantly of the iridoid hemiacetal esters, (+)-(1R)-and(-)-(1S)-1-acetoxymyodesert-3-ene. Hydrolysis of either ester yields (1S,2R,5R,1′ξ)-2-(1′-formylethyl)-5-methylcyclopentane-1-carbaldehyde and acetic acid or, in the presence of Brady's reagent, the bis-2,4-dinitrophenylhydrazone of the 1R-epimer. The stereochemistry at C1 of the esters follows from the close correlations in 1H and 13C n.m.r . spectra and o.r.d . curves of the (-)-ester and the ether (-)-(1R)-1-methoxymyodesert-3-ene. Hydrogenation of the esters in methanol yields mainly myodesertan , (4S)- myodesertan , (1R)-1- methoxymyodesertan and (1R, 4S)-1-methoxymyodesertan and usually no acetates. Acetolysis of (1R)-1-methoxymyodesertan even under mild conditions yields (1R, 7aS)- and (1S, 7aS)-1-acetoxymyodesertan with trans rather than cis ring junctions.