Single-step, quantitative derivatization of amino, carboxyl, and hydroxyl groups in iodothyronine amino acids with ethanolic pivalic anhydride containing 4-dimethylaminopyridine.

Reaction of thyroxine with ethanol and pivalic anhydride in the presence of 4-dimethylaminopyridine quantitatively forms N,O-dipivalyl thyroxine ethyl ester. Other iodothyronines react similarly and the procedure is moisture insensitive. Apparently this reaction is successful, in contrast to similar procedures reported for the derivatization of alpha-amino acids, because it overcomes the problem in other procedures of irreversible side reactions arising from an oxazolone intermediate.