Facile synthesis of 1-(acetic acid)-4,7,10-tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane: a reactive precursor chelating agent

1-(Acetic acid)-4,7,10-tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane (DOTA-Tris-^tBu ester or 1) is a precursor chelating agent for lanthanide ions and can be efficiently labeled with various functional moieties or macromolecules to improve the targeting specificity, intracellular delivery, bio-compatibility, and pharmacokinetics of resulting contrast media used in molecular imaging. This compound is commercially available but the extremely high cost seriously limits its wide utilization. Thus, we sought a convenient and inexpensive synthesis of DOTA-Tris-^tBu ester that is readily adapted for use in any laboratory. The synthetic approach described here is straightforward and has an overall yield of 92%. Significantly, the product can be purified conveniently without using of a time- and labor-intensive column chromatography. Other advantages of this method, such as operational convenience, starting material availability, and atom efficiency make it very attractive to prepare DOTA-Tris-^tBu ester in large quantity with a reduced cost.