SYNTHESIS, CHARACTERIZATION, AND CRYSTAL-STRUCTURE OF THE GADOLINIUM(III) CHELATE OF (1R,4R,7R)-ALPHA,ALPHA',ALPHA''-TRIMETHYL-1,4,7,10-TETRAAZACYCLODODECANE-1,4,7-TRIACETIC ACID (DO3MA)

The tetraazatricarboxylicmacrocycle, (1R,4R,7R)-alpha,alpha,alpha''-trimethyl-1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3MA) (4) was synthesized by the simultaneous hydrogenolysis and deformylation of 10-formyl-1,4,7-tris(benzyloxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane(N-CHO-DO3MA-THE)(11). Chelation of DO3MA with gadolinium acetate resulted in a diastereomerically pure Gd(III) chelate, Gd(DO3MA) (4a). X-ray structure analysis of Gd(DO3MA) crystals revealed that the three asymmetric carbons bearing alpha-methyl groups all have the (R)-configuration and that the chelate crystallizes as a dimer, [(DO3MA)Gd][(DO3MA)Gd(H20)2], in which both the Gd atoms are enneacoordinate. Crystal data are as follows: [2(GdC17H29N4O6).2H2O1-4H2O, a = 17.471-(6) angstrom, b = 25.495(6) angstrom, c = 10.146(3) angstrom, V = 4520(4) angstrom3, P2(1)2(1)2(1), Z = 4, R = 0.035, R(w) = 0.044. The relativity of Gd(DO3MA) was found to be 4.4 +/- 0.1 mM-1 s-I at 20 MHz and 40-degrees-C. The measured stability constant of Gd(DO3MA) was log K(eq) = 25.3, which makes Gd(DO3MA) the most stable heptadentate chelate known for Gd(III).