Total Syntheses of the Proposed Biosynthetic Intermediates of Tetrodotoxin Tb-210B, Tb-226, Tb-242C, and Tb-258.

The collective synthesis of the four spiro -cyclic guanidines Tb-210B, Tb-226, Tb-242C, and Tb-258, all of which have been isolated from puffer fish and are considered possible biosynthetic intermediates of tetrodotoxin, has been achieved. Our synthesis is based on the stepwise deoxygenation or hydroxylation of a common intermediate, prepared from a known oxazoline.