Total synthesis of (R)- and (S)-turmerone and (7S,9R)-bisacumol by an efficient chemoenzymatic approach

An enantioselective synthesis of (R)-, (S)-turmerone and (7S,9R)-bisacumol is described. The enantiomerically pure key intermediates, a substituted butanoate ester and acid are utilized in the synthesis of both enantiomers of turmerone. The lipase catalyzed resolution studies of the acetate of bisacumol have been exploited towards the total synthesis of the naturally occurring cytotoxic sesquiterpene, (7S,9R)-bisacumol with high diastereoselectivity (94% de).

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(3R)-Ethyl-3-(4-methylphenyl)butanoateC13H18O2[α]D25=-26.2 (c 3.5, CHCl3)Source of chirality: enzymatic resolutionAbsolute configuration: (3R)

(3S)-3-(4-Methylphenyl)butanoic acidC11H14O2[α]D25=+34.2 (c 1.0, CHCl3)Source of chirality: enzymatic resolutionAbsolute configuration: (3S)

(3S)-3-(4-Methylphenyl)-1-butanolC11H16O[α]D25=+30.1 (c 1.0, CHCl3)Source of chirality: enzymatic resolutionAbsolute configuration: (3S)

(3S)-3-(4-Methylphenyl)butanalC11H14O[α]D25=+41.9 (c 1.0, CHCl3)Source of chirality: enzymatic resolutionAbsolute configuration: (3S)

(6S)-2-Methyl-6-(4-methylphenyl)-2-hepten-4-oneC15H20O[α]D25=+80.2 (c 1.2, CHCl3)Source of chirality: enzymatic resolutionAbsolute configuration: (6S)

(4R,6S)-2-Methyl-6-(4-methylphenyl)-2-hepten-4-olC15H22O[α]D25=+14.8 (c 1.0, CHCl3)Source of chirality: enzymatic resolutionAbsolute configuration: (4R,6S)