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UBC Theses and Dissertations

Studies towards the total synthesis of ionomycin Daynard, Timothy S.

Abstract

An optically pure precursor to ionomycin (1) consisting of the thirty two carbon backbone and protected functional groups of the target molecule was synthesized by the coupling of two subunits between C₁₅ and C₁₆ via the Suzuki reaction. An enantioselective route to the C₁₁-C₁₅ fragment 57 was developed. This unit was coupled to the C₁-C₁₀ fragment 53 to provide the left half 162a (C₁-C₁₅) of the target molecule. Hydroboration of this 2-methyl terminal alkene with 9-BBN generated an asymmetric center at C₁₄ and provided the alkylborane moiety necessary for the Suzuki coupling reaction. The resulting alkylborane was reacted with the alkenyl iodide fragment 200 (C1₆-C₃₂) in the presence of the palladium catalyst PdCI₂(dppf) and sodium hydroxide to afford the coupled products 203a,b in 79% yield with the stereochemistry about the double-bond exclusively E and as a 57:43 mixture of epimers about C₁₄.

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