Total Synthesis and Biological Evaluation of (-)-Apicularen A and Its Analogues

The total synthesis of (-)-apicularen A (1), a highly cytostatic 12-membered macrolide, and its analogues is described. The convergent and distinct approach not only provides 1, but also opens the opportunity to synthesize C10-C11 functional analogues of 1. The key steps of the total synthesis include assembling of iodoalkene 12 and aldehyde 13 by Nozaki-Hiyama-Kishi (NHK) coupling, stereospecific construction of 2,6-trans-disubstituted dihydropyran by Pd(II)-catalyzed 1,3-chirality transfer reaction, and Yamaguchi macrolactonization. The (17E,20Z,22Z)-heptadienoylenamine moiety in the side chain is installed by an efficient Cu(I)-mediated coupling to complete the synthesis. Analogues of C11-epi-, C11-deoxy-C10-alpha-hydroxy-, and C10-C11 dehydrated apicularen A 3-5 were also prepared. Cytostatic activities of (-)-apicularen A and the three analogues for three different cancer cell lines are described.