Isomeric DTPA-amide macrocycles of p-xylenediamine and their complexation with Gd3+. (28th May 2015)

• Record Type: Journal Article
• Authors: Navarro, Rosa Elena; Soberanes, Yedith; D-Yañez, Sheyla; Jatomea, Olivia; Ramírez, José Zeferino; Inoue, Motomichi
• Is Part Of: Polyhedron. Volume 92(2015)
• Page Start: 105
• Page End: 110
• Publication Date: 2015-05-28
• Subjects: Cyclophanes -- Diethylenetriaminepentaacetic acid (DTPA) -- Gadolinium(III) complexes -- Macrocycles -- Conformational isomers; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2015.03.011
• Languages: English
• ISSNs: 0277-5387

Abstract

Graphical abstract: Three macrocycles have been isolated from reactions between DTPA dianhydride and p -xylenediamine: a 2 + 2-cyclization macrocycle in a high yield, and two 1 + 1-macrocyclic isomers which differ in coordination capability toward Gd 3+ . Abstract: Three DTPA-amide cyclophanes – including conformational isomers – have been isolated by optimizing the conditions of a reaction between diethylenetriaminepentaacetic (DTPA) dianhydride and p -xylenediamine: a 2 + 2-cyclization product, abbreviated as (cy2)H6, that integrates two phenylene groups in the macrocyclic frame and bears six pendant –CH2 CO2 H arms, and two isomeric 1 + 1-macrocyles, (cy1)H3, carrying three arms. A crucial factor for controlling the ring size is the concentration in the reaction. For (cy2)H6, whose binuclear Gd 3+ complex is a potential paramagnetic protein sensor, the synthetic method has been established in 70% yield. The isomerism of (cy1)H3 is due to the conformation of the rigid macrocyclic frame; the 1 H NMR and geometry optimization show that the conformation is of quasi-C2 symmetry in one (cy1)H3 isomer, and of quasi-mirror symmetry in the other. Their distinct conformations define the chemical properties and coordination capability toward Gd 3+ : in the C2 -symmetric isomer, the amino nitrogen is less basic and the N–H bond is more covalent than in the mirror-symmetric isomer; the former forms a mononuclear Gd 3+ complex whereas the latter does not show sign of complexation with Gd 3+ .