Synthesis of octalactin lactone and side chain

Abstract Two key intermediates of (+)-octalactin A, a potent new cytotoxic natural product, have been synthesized in a direct, and efficient manner. Lactone 1 was made using a substrate controlled lactonization reaction using the carbodiimide EDCI and two crotylborane additions were used to access the precursor hydroxyacid. The importance of proper substitution in the hydroxyacid tether is noted for successful medium-ring lactonization. Synthesis of the side chain vinyl iodide 2 employed an asymmetric allenylboronate addition.