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Bisalkylation of suitably protected L-glutamic acid and L-lysine derivatives with tert-butyl N-(2-bromoethyl)iminodiacetate 2, followed by deprotection of the omega functional group affords N, N-bis[2-[bis[2-(1, 1-dimethylethoxy)-2-oxoethyl]amino]ethyl]-L-glutamic acid 1-(1, 1-dimethylethyl) ester 4 and N2,N2-bis[2-[bis[2-(1, 1-dimethylethoxy)-2-oxoethyl]amino]ethyl]-L-lysine 1,1-dimethylethyl ester 7. Such compounds feature a carboxylic or an amino group, respectively, which are available for conjugation with a suitable partner via formation of an amide bond. The conjugates, which can be prepared in this way, contain a chelating subunit in which all five acetic residues of DTPA are available for the complexation of metal ions. Direct bisalkylation of glycine with 2 promptly gives N, N-bis[2-[bis[2-(1,1-dimethylethoxy)-2-oxoethyl]amino]ethyl]glycine 11. The latter allows to achieve conjugates in which the central acetic group of DTPA is selectively converted into an acetamide.

A straightforward and efficient synthesis of Gd-DTPA-cholesterol is reported. This new lipophilic gadolinium complex can be easily incorporated into mixed micelles in order to achieve MRI contrast agents with increased relaxivity. These supramolecular systems can find potential application in magnetic resonance angiography (MRA).

A series of structurally different Gd(III) conjugates incorporating a bile acid moiety have been prepared. Polyaminopolycarboxylic ligands such as diethylenetriaminepentaacetic acid (DTPA) and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetracetic acid (DOTA) have been selected as chelating subunit for the Gd(III) ion. Cholic acid, cholylglycine, and cholyltaurine have been incorporated as the bile acid moieties. In first generation conjugates the Gd(III) complex is linked to the carboxyl group of cholic acid. Second generation conjugates feature the attachment of the Gd(III) complex to the 3 position of the steroidic backbone of the bile acid. Finally, in third generation conjugates the Gd(III) complex is attached to the epsilon nitrogen atom of cholyllysine. The conjugates are eliminated through the biliary route to a various extent (7.5 to 77% in rats) according to their structural features. Among the most promising terms, a second generation conjugate in which the Gd(III) complex is linked to cholic acid through the 3alpha hydroxy group seems to enter hepatocytes using the Na(+)/taurocholate transporter. Noticeably, some of the second generation conjugates are characterized by very high tolerabilities (LD(50) up to 9.5 mmol/kg) after intravenous administration in mice.