Patent ID: 7279150

Claim:
A compound of the formula: wherein Ch represents a chelating moiety comprising at least two nitrogens spaced by alkylene groups and to which carboxylic acid-bearing moieties are coupled; m is 0-3; each R 1 is independently a non-interfering substituent selected from the group consisting of halo, OR, NR 2 , SR, CN, NO 2 , SO 3 H, and R where R is alkyl or alkenyl optionally substituted by halo, or ═O, and optionally containing a heteroatom, such as O, S or N; l is 0-2; Z is S or O; R 2 is H or alkyl (1-4C); n is 1; and each R 3 is independently an optionally substituted saturated or unsaturated hydrocarbyl group containing at least 10C, and spacer is —CH 2 CH 2 — and/or includes a peptide, a pseudopeptide, or a polyalkylene glycol, optionally containing a cleavage site.