Peptides modified by the phosphine group for marking with 99M TC and 186-188 RE or paramagnetic agents

Chelating compounds having the following general structural formula:

• ##STR16## in which R.sub.1 and R.sub.2 are selected independently from the group consisting of:
• H, linear or branched C.sub.1 -C.sub.5 alkyl, linear or branched substituted C.sub.1 -C.sub.5 alkyl, OH, C.sub.1 -C.sub.5 alkoxy, phenoxy, and substituted phenyl groups,
• and in which A is alkylene carbonyl or alkylene amino in which the alkylene has from 1 to 4 carbon atoms and may be linear or branched,
• and in which, when A is alkylene carbonyl, B is:
• ##STR17## in which R.sub.3 is a group selected from the radicals constituting the lateral chain of a natural amino-acid;
• R.sub.4 is selected from the group consisting of:
• H, linear or branched C.sub.1 -C.sub.4 alkyl groups, --CH.sub.2 --C.sub.6 H.sub.5, --(CH.sub.2).sub.r NH.sub.2 where r is an integer from 1 to 4, --(CH.sub.2).sub.p -- CONH.sub.2 where p is an integer from 1 to 3, --(CH.sub.2).sub.n XR.sub.5 where n is 1 or 2 and X is selected from --O.sup.-, --S.sup.-, and --COO.sup.-, and R.sub.5 is H or a protector group;
• Z is OH, OMe, NH.sub.2 or is the same as R.sub.4, or Z is a peptide with biological properties useful for diagnosis, radiotherapy or magnetic resonance, bonded to the preceding carbon atom by means of its N-terminal group;
• and in which, when A is alkylene amino, B is selected from the group consisting of:
• ##STR18## where R.sub.1, R.sub.2, R.sub.3, R.sub.4, n and Z have the meanings given above and R.sub.6 has the same meaning as R.sub.3 given above, or has the meaning of Z given above, and Y is H or ##STR19## where R.sub.1, R.sub.2 and n have the meanings given above.