An Expedient Total Synthesis of Chivosazole†F: an Actin-Binding Antimitotic Macrolide from the Myxobacterium Sorangium Cellulosum.

A unified strategy for the chemical synthesis of the chivosazoles is described. This strategy is based on two closely related approaches involving the late-stage installation of the isomerization-prone (2Z,4E,6Z,8E)-tetraenoate motif, and an expedient fragment-assembly procedure. The result is a highly convergent total synthesis of chivosazole F through the orchestration of three mild Pd/Cu-mediated Stille cross-coupling reactions, including the use of a one-pot, site-selective, three-component process, in combination with controlled installation of the requisite alkene geometry.

Synthesis of the C15-C35 northern hemisphere subunit of the chivosazoles.

An advanced C15-C35 subunit of the chivosazole polyene macrolides was prepared in a convergent manner, exploiting boron-mediated aldol reactions for the stereocontrolled construction of the C15-C26 and C27-C35 segments, followed by their Pd/Cu-promoted Stille coupling to configure the signature (23E,25E,27Z)-triene motif. Correlation with a known C28-C35 degradation fragment of chivosazole A was also achieved.

Synthesis of the C1-C13 tetraenoate subunit of the chivosazoles.

Using a combination of asymmetric vinylogous Mukaiyama aldol and Stille cross-coupling reactions, an advanced polyene fragment of the chivosazoles was prepared in a highly stereocontrolled manner. This key C1-C13 pentaene subunit, featuring the conjugated (2E,4Z,6E,8Z)-tetraenoate motif and anti-configured C10 and C11 stereocenters of the chivosazoles, terminates in a (Z)-vinyl bromide for the planned cross-coupling to a northern hemisphere fragment.