A method of attaching a moiety capable of binding to a biological entity to an amino substituted metal chelating ligand or a metal complex thereof the method comprising: (a) reacting an amino substituted metal chelating ligand or a metal complex thereof with a molecule of the formula: wherein L is a bond or a linking moiety and R is H or a moiety capable of binding to a biological entity or a protected form thereof or a synthon thereof; (b) isolating the compound or a metal complex thereof thus produced. wherein the amino substituted metal chelating ligand has the formula: Lig-NH 2 wherein Lig is a nitrogen containing macrocyclic metal ligand of the formula: V is selected from the group consisting of N and CR 1; each R x and R y are independently selected from the group consisting of H, CH 3, CO 2 H, NO 2, CH 2 OH, H 2 PO 4, HSO 3, CN, CONH 2 and CHO; each p is independently an integer selected from the group consisting of 2, 3, and 4; R 1 is selected from the group consisting of H, OH, halogen, NO 2, NH 2, optionally substituted C 1 -C 12 alkyl, optionally substituted C 6 -C 18 aryl, cyano, CO 2 R 2, NHR 3, N(R 3) 2; R 2 is selected from the group consisting of H, halogen, an oxygen protecting group, optionally substituted C 1 -C 12 alkyl, optionally substituted C 2 -C 12 alkenyl, optionally substituted C 2 -C 12 alkynyl and optionally substituted C 2 -C 12 heteroalkyl; each R 3 is independently selected from the group consisting of H, a nitrogen protecting group, optionally substituted C 1 -C 12 alkyl, -(C=O)-substituted C 1 -C 12 alkyl, optionally substituted C 2 -C 12 alkenyl, optionally substituted C 2 -C 12 alkynyl and optionally substituted C 2 -C 12 heteroalkyl. (a) reacting an amino substituted metal chelating ligand or a metal complex thereof with a molecule of the formula: wherein L is a bond or a linking moiety and R is H or a moiety capable of binding to a biological entity or a protected form thereof or a synthon thereof; (b) isolating the compound or a metal complex thereof thus produced. wherein the amino substituted metal chelating ligand has the formula: Lig-NH 2 wherein Lig is a nitrogen containing macrocyclic metal ligand of the formula: V is selected from the group consisting of N and CR 1; each R x and R y are independently selected from the group consisting of H, CH 3, CO 2 H, NO 2, CH 2 OH, H 2 PO 4, HSO 3, CN, CONH 2 and CHO; each p is independently an integer selected from the group consisting of 2, 3, and 4; R 1 is selected from the group consisting of H, OH, halogen, NO 2, NH 2, optionally substituted C 1 -C 12 alkyl, optionally substituted C 6 -C 18 aryl, cyano, CO 2 R 2, NHR 3, N(R 3) 2; R 2 is selected from the group consisting of H, halogen, an oxygen protecting group, optionally substituted C 1 -C 12 alkyl, optionally substituted C 2 -C 12 alkenyl, optionally substituted C 2 -C 12 alkynyl and optionally substituted C 2 -C 12 heteroalkyl; each R 3 is independently selected from the group consisting of H, a nitrogen protecting group, optionally substituted C 1 -C 12 alkyl, -(C=O)-substituted C 1 -C 12 alkyl, optionally substituted C 2 -C 12 alkenyl, optionally substituted C 2 -C 12 alkynyl and optionally substituted C 2 -C 12 heteroalkyl. wherein Lig is a nitrogen containing macrocyclic metal ligand of the formula: V is selected from the group consisting of N and CR 1; each R x and R y are independently selected from the group consisting of H, CH 3, CO 2 H, NO 2, CH 2 OH, H 2 PO 4, HSO 3, CN, CONH 2 and CHO; each p is independently an integer selected from the group consisting of 2, 3, and 4; R 1 is selected from the group consisting of H, OH, halogen, NO 2, NH 2, optionally substituted C 1 -C 12 alkyl, optionally substituted C 6 -C 18 aryl, cyano, CO 2 R 2, NHR 3, N(R 3) 2; R 2 is selected from the group consisting of H, halogen, an oxygen protecting group, optionally substituted C 1 -C 12 alkyl, optionally substituted C 2 -C 12 alkenyl, optionally substituted C 2 -C 12 alkynyl and optionally substituted C 2 -C 12 heteroalkyl; each R 3 is independently selected from the group consisting of H, a nitrogen protecting group, optionally substituted C 1 -C 12 alkyl, -(C=O)-substituted C 1 -C 12 alkyl, optionally substituted C 2 -C 12 alkenyl, optionally substituted C 2 -C 12 alkynyl and optionally substituted C 2 -C 12 heteroalkyl.