Hippospongic acid

Addition of sulfur nucleophiles such as phenylthiolate to diethyl l-(ethoxycarbonyl)vinylphos-phonate has been used in the synthesis of P-acetoxy- and p-hydroxy-a-methylene-y-butyrolac-tones Similarly, addition of isopropylthiolate to diethyl l-(ethoxycarbonyl)vinylphosphonate represents a key step in the synthesis of a-methylidenebutyrolactones such as confertin (Scheme arteannuin B, - - rhopaloic acid and hippospongic acid A Addition... 

More recently, Trost el al. also examined the ability to use aliphatic alcohols as competent nucleophiles in the palladium-catalyzed DYKAT of MBH adducts. High yield and enantioselectivity were obtained for both the kinetic transformation and dynamic kinetic transformation to alford substituted pyran products. The utility of this method was further demonstrated in the context of a concise total synthesis of the gastrulation inhibitor ( + )-hippospongic acid A (Scheme 3.138). ° ... 

Preparation of (/ )-26, which was converted to (+)-hippospongic acid (a marine triterpenoid). 

Asymmetric acetylation of tetrahydropyranyl alcohol ( )-26 with vinyl acetate and lipase AH gave (S)-27 and R)-26. The latter was converted to (+)-hippospongic acid A, a metabolite of a marine sponge (Figure 24.14) [17]. 

Ohta, S., Uno, M., Tokumasu, M., Hiraga, Y, and Ikegami, S. (1996a) Hippospongic acid A an imusual triterpenoic acid from a marine sponge, Hippospongia sp., which inhibits gastrulation of starfish embryos. Tetrahedron Lett., 37, 7765-7766. 

Hioki, H., Hamano, M., Mimura, Y, Kodama, M., Ohta, S., Yanai, M., and Ikegami, S. (1998) Revised stmcture, synthesis and absolute configuration of hippospongic acid A. Tetrahedron Lett., 39, 7745-7746. 

Takikawa, H., Koizumi, J., Kato, Y, and Mori, K. (1999) Triterpenoid total synthesis. Part 4. Synthesis of ( )-hippospongic acid A, a triterpene isolated from the marine sponge Hippospongia sp. J. Chem. Soc. Perkin Trans. I, 2n -2X] o. 

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