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The importance for the right order of functional group introduction and manipulation (good timing) was demonstrated in the course of a total synthesis of phoslactomycin A. The synthetic strategy comprised a Cu(I)-thiophene carboxylate (CuTC, Liebeskind's reagent)-mediated coupling to introduce the Z,Z-diene at the final stage of the synthesis in the presence of a protected phosphate. Key features for the assembly of the C1-C13 fragment were an asymmetric dihydroxylation, an Evans-aldol reaction and an advanced protective group strategy. The C14-C21 fragment was accessible via an asymmetric 1,2-addition to cyclohexenone and a subsequent diastereoselective ketone reduction. One crucial task was the dihydroxylation of the C8-C9 alkene, the introduction of the C6-C7 double bond and the generation of the C25-nitrogen functionality. A second example consisted of the best sequence for the generation of the functional groups in the core part (first phosphorylation, second iodo-olefination, third azide/carbamate conversion). The synthetic solutions from this approach are compared with the already existing contributions in the phoslactomycin area.
A convergent total synthesis of the PP2A-inhibitor phoslactomycin A was achieved using a CuTC-mediated coupling of an alkenyl iodide C1−C13 fragment with an C14−C21 alkenyl stannane in the presence of a protected phosphate. Key features for the assembly of the C1−C13 fragment were an asymmetric dihydroxylation, an Evans−Aldol reaction, and a well-balanced protective group strategy. An asymmetric 1,4-addition to cyclohexenone was the key step in the preparation of the C14−C21 fragment.
The first total synthesis of phoslactomycin A is reported featuring Liebeskind’s copper(I) thiophene-2-carboxylate mediated coupling between alkenyl stannane F and iodoalkene E as a key fragment linkage reaction.
