Synthesis of a transmembrane ionophore based on a C2-symmetric polyhydroxysteroid derivative

The synthesis of the C2-symmetric bis-(20S)-5α-23,24-bisnorchol-16-en-3β,6α,7β-triol-22-terephthaloate (), active as Na+-transporting transmembrane channel, has been achieved in 16 steps (10% overall yield) starting from the commercially available androst-5-en-3β-ol-17-one (). The straightforward stereospecific functionalization of the side-chain, via the ‘ene’ reaction, and the successful regioselective terephthaloylation of the C-22 hydroxy group, illustrate the efficiency of the synthetic strategy.