Synthesis of the spiroketal moiety of didemnaketal A

Date

2014-12-12

Authors

Davy, Jason Alan

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Abstract

The ascidian isolation artifact didemnaketal A is a highly oxygenated polyisoprenoid capable of inhibiting HIV-1 protease through an unusual dissociative mechanism. However, recent synthetic efforts have cast doubt on stereochemical assignments in the originally published structure. In the interest of elucidating the true structure of didemnaketal A through total synthesis, we present a strategy for rapidly accessing the putative spiroketal fragment by exploiting its latent symmetry. In a single step, double Sharpless asymmetric dihydroxylation reactions (SAD) allowed us to simultaneously set all seven stereogenic centers and assemble this complex fragment from non-chiral material. The precursor was obtainable through a racemic synthesis in which the geometric isomers of a nine-membered cyclic enone converged in a ring-opening cross metathesis reaction (ROCM).

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Keywords

total synthesis, natural product, didemnaketal, spiroketal, radical cyclization

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