Total synthesis of altohyrtin A (spongistatin 1): an alternative synthesis of the CD-spiroacetal subunit

The CD-spiroacetal containing C16–C28 subunit 2, as used in the total synthesis of the potent cytotoxic macrolide, altohyrtin A (spongistatin 1), was prepared by an alternative route using substrate-based stereocontrol in the two aldol bond constructions generating the acyclic precursor 4.