An assessment of calixarene amides as potential magnetic resonance imaging enhancement agents for gadolinium(III)

The compound 5, 11, 17, 23-tert-butyl-25,26,27,28-carbamoyloxymethoxycalix[4]arene (1) has been evaluated as a ligand for potential use as a magnetic resonance imaging agent with gadolinium(III). The assessment procedures include high field relaxivity H-1 NMR measurements as well as UV-Vis stability constant measurement for the Gd(III) complex. Although the selected ligand proved to be unsuitable for in vivo applications because of the low stability constant for the complex it forms, the relaxivity value of R = 3.40(6) mM(-1) s(-1) is quite reasonable. These initial results however point to some future ligand modifications that are necessary in order to successfully design calixarene-based MRI enhancement agents for Gd(III).