Mispyric acid

In 1999, Hecht and coworkers isolated mispyric acid (59, Figure 2.50), a monocyclic triperpene dicar-boxylic acid, from the stem bark of an Australian plant Mischocarpus pyriformis as an inhibitor of DNA... 

Figure 2.50 shows our synthetic plan of mispyric acid (59). l,5-Dimethoxy-l,4-cyclohexadiene was chosen as the starting material, and its stepwise alkylation with two different alkylating agents, R X and R2X, was thought to provide 59. Of course, optical resolution of an intermediate was necessary to synthesize both the enantiomers of 59. 

To continue the synthesis (Figure 2.52), (-)-ketone E was treated with methylene triphenylphosphorane to give F. Deprotection followed by oxidation of F afforded the naturally occurring (+)-mispyric acid (59), whose absolute configuration was determined as 25,45. Similarly, the other diastereomer G obtained by optical resolution afforded unnatural (2R,4R)-(—)-59. ... 

Figure 2.53 Determination of the absolute configuration of (+)-mispyric acid by CD measurements...

Imamura Y, Takikawa H, Sasaki M, Mori K. Triterpenoid total synthesis. Synthesis and absolute configuration of mispyric acid. Org. Biomol. Chem. 2004 2 2236-2244. 

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