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On‐bead combinatorial synthesis and imaging of europium(III)‐based paraCEST agents aids in identification of chemical features that enhance CEST sensitivity
Author(s) -
Singh Jaspal,
Rustagi Vineeta,
Zhang Shanrong,
Sherry A. Dean,
Udugamasooriya D. Gomika
Publication year - 2017
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.4588
Subject(s) - chemistry , europium , dota , paramagnetism , steric effects , ligand (biochemistry) , metal ions in aqueous solution , metal , combinatorial chemistry , ion , chelation , inorganic chemistry , stereochemistry , organic chemistry , biochemistry , physics , receptor , quantum mechanics
The rate of water exchange between the inner sphere of a paramagnetic ion and bulk water is an important parameter in determining the magnitude of the chemical exchange saturation transfer signal from paramagnetic CEST agents (paraCEST). This is governed by various geometric, steric and ligand field factors created by macrocyclic ligands surrounding the paramagnetic metal ion. Our previous on‐bead combinatorial studies of di‐peptoid–europium(III)–1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetic acid (DOTA)–tetraamide complexes revealed that negatively charged groups in the immediate vicinity of the metal center strongly enhances the CEST signal. Here, we report a solid phase synthesis and on‐bead imaging of 76 new DOTA derivatives that are developed by coupling with a single residue onto each of the three arms of a DOTA–tetraamide scaffold attached to resin beads. This single residue predominantly carries negatively charged groups blended with various physico‐chemical characteristics. We found that non‐bulky negatively charged groups are best suited at the immediate vicinity of the metal ion, while positive, bulky and halogen containing moieties suppress the CEST signal. Copyright © 2017 John Wiley & Sons, Ltd.