Synthesis of Naturally Occurring Decanolides



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Decanolides, 10-membered ring lactones, are examples of natural compounds having biological interest. these molecules have been found to play diverse biological roles in the different organisms from which they are isolated. Decanolides, along with other medium membered rings (ranging from eight to twelve atoms), are difficult to synthesize due to entropic factors (probability of chain ends meeting) and enthalpic factors (transannular strain development in the transition state). It is therefore important to develop and optimize different approaches for the syntheses of these compounds.

Phoracantholide I, an odiferous defensive secretion from the metasternal gland of the eucalypt longicorn beetle, Phoracantha synonym, consists of a 10-membered ring lactone. Our synthesis uses Schreiber's ozonolysis methodology to generate a key unsymmetrical aldehyde-ester-alkene intermediate. Ozonolytic cleavage of cyclohexene followed by in situ nucleophilic attach by 4-penten-2-ol generates an a-alkoxy hydroperoxide which can be dehydrated to provide an unsymmetrical aldehyde-ester-alkene intermediate in 42% yield. Finally use of Grubbs RCM catalyst followed by hydrogenation of the crude reaction mixture generates ( _+) -Phoracantholide I in 4 steps and 12% yield overall.

Jasmine ketolactone was the first decanolide to be extracted from a plant. It was isolated in 1964 by Demole and Stolle from the oil of Jasmine grandiflorum L. Approaches towards the total synthesis of jasmine ketolactone, a more complex target than phoracantholide I, are also reported suing the same ozonolysis methodology.

Herbarumin I is a decanolide which was recently isolated from the fungus Phoma herbarum. It belongs to a family of lactones which have been shown to exhibit significant phytotoxic effects affecting the germination and growth of Amaranthus hypochodriacus seedlings. Our purpose for synthesizing herbarumin I is to test its affects on Arabidopsis thaliana and determine the functional groups responsible for its phytotoxic activity. Experimental procedures for the synthesis of herbarumin I were adapted from Furstner et al.


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