Improved synthesis of 10-(2-alkylamino-2-oxoethyl)-1,4,7,10- tetraazacyclododecane-1,4,7-triacetic acid derivatives bearing acid-sensitive linkers

Alkylation of the hydrobromide salts of 1,4,7-tris(methoxycarbonylmethyl)- 1,4,7,10-tetraazacyclododecane and 1,4,7-tris(ethoxycarbonylmethyl)-1,4,7,10- tetraazacyclododecane with appropriate α-bromoacetamides, followed by hydrolysis, provides convenient access to 10-(2-alkylamino-2-oxoethyl)-1,4,7,10- tetraazacyclododecane-1,4,7-triacetic acid derivatives that contain acid-sensitive functional groups. The utility of the method is demonstrated by improved syntheses of two known 1,4,7,10-tetraazacyclododecane-1,4,7,10- tetraacetic acid monoamides bearing acid-sensitive ω-tritylthio alkyl chains in much greater yields based on cyclen as the starting material. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]