In a previous report3 from these laboratories, the total synthesis of the antibiotic ionophore lasalocid A was presented. The basic design of this synthesis was predicated on a desire to define a synthetic strategy that could be applied to the construction of other polyether antibiotics, both natural and nonnatural. An example of the use of this strategy for the construction of a synthetic lasalocid analogue, ent-X537A, is reported here. Lasalocid A is ...