Patent ID: 7585852

Claim:
A cobalamin derivative of formula (1): wherein: (i) R b is a spacer-chelator group optionally carrying a metal atom; (ii) R c , R d , and R e are an antibiotic or antiproliferative therapeutic agent, or hydrogen; and R R is an antibiotic or antiproliferative therapeutic agent connected through a linker Z, or hydrogen, wherein the linker Z is selected from the group consisting of phosphates, phosphonates, carboxylic esters, alkylenes of 1 to 10 carbon atoms, and combinations thereof; (iii) with the proviso that at least one of the residues R c , R d , R e and R R are hydrogen; (iv) X is cyano, methyl, hydroxy, aquo or a 5′-deoxyadenosyl group; and (v) the central cobalt (Co) atom is optionally in the form of a radioactive isotope; and wherein the spacer-chelator group consists of an aliphatic chain of 2 to 4 carbon atoms carrying a chelator selected from the chelators of formulae (II) to (IX): wherein carboxyl groups in formulae (II) to (IX) may be present as esters; and said cobalamin derivative: (a) has no binding affinity or less than 20% binding affinity to transcobalamin II when compared to the binding affinity of non-modified cobalamin in a binding test, and (b) retains activity as a vitamin B12 substitute.