Total synthesis of the potent anticancer Aglaia metabolites (-)-silvestrol and (-)-episilvestrol and the active analogue (-)-4'-desmethoxyepisilvestrol.

Total synthesis of the anticancer 1,4-dioxane containing natural products silvestrol (1) and episilvestrol (2) is described by an approach based on the proposed biosynthesis of these novel compounds. The key steps included an oxidative rearrangement of the protected d-glucose derivative 11 to afford the 1,4-dioxane 12, which could be elaborated to the coupling partner 5 and a photochemical [3 + 2]-cycloadditon between the 3-hydroxyflavone 27 and methyl cinnamate followed by base-induced alpha-ketol rearrangement and reduction to give the cyclopentabenzofuran core 33. The core (-)-6 and 1,4-dioxane fragment 5 were united by a highly stereoselective Mitsunobu coupling with the modified azodicarboxylate DMEAD to afford the axial coupled product 36. Deprotection then gave episilvestrol (2). Silvestrol (1) was synthesized by a coupling between core (-)-6 and the dioxane 44 followed by deprotection. Compound 1 was also synthesized from episilvestrol (2) by a Mitsunobu inversion. In addition, the analogue 4'-desmethoxyepisilvestrol (46) was synthesized via the same route. It was found that 46 and episilvestrol 2 displayed an unexpected concentration-dependent chemical shift variation for the nonexchangeable dioxane protons. Synthetic compounds 1, 2, 38, 46, and 54 were tested against cancer cells lines, and it was found that the stereochemistry of the core was critical for activity. Synthetic analogue 4'-desmethoxyepisilvestrol (46) was also active against lung and colon cancer cell lines.

Total synthesis of (-)-reveromycin a.

The asymmetric total synthesis of (-)-reveromycin A is described. The key steps involved a Lewis acid catalyzed inverse electron demand hetero-Diels-Alder reaction followed by hydroboration/oxidation to afford the spiroketal core 4 in a highly stereoselective manner and introduction of the C18 hemisuccinate by high-pressure acylation.