Synthesis of the acyltetronic acid ionophore tetronasin (ICI M139603)

A synthetic strategy for the preparation of tetronasin 1, an acyltetronic acid ionophore demonstrating antibiotic, antiparasitic and growth promotion in ruminants is described. The key step involves a metal mediated cyclization reaction which creates two rings and four new stereocentres in a highly efficient manner. The configurations of three of these stereocentres are as required for the synthesis of tetronasin. The remaining stereocentre is readily epimerised to the natural configuration at a later stage of the synthesis.