Bifunctional linker

A method for activating a first amine-containing compound having a primary or secondary amine function thereon towards reaction with a second amine-containing compound having a primary or secondary amine function thereon, comprising the step of contacting said first amine-containing compound with at least a stoichiometric equivalent of a selective bifunctional sequential linker having the formula

• Y.dbd.C.dbd.N--Q--A--C(O)--Z
• wherein Q is a homoaromatic or heteroaromatic ring system;
• A is a single bond or an unsubstituted or substituted divalent C.sub.1-30 bridging group;
• Y is O or S;
• and Z is Cl, Br, I, N.sub.3, N-succinimidyloxy, imidazolyl, 1-benzotriazolyloxy, OAr where Ar is an electron-deficient activating aryl group, or OC(O)R where R is --A--Q--N.dbd.C.dbd.Y or C.sub.4-20 tertiary-alkyl;
• thereby forming an amide bond to the acyl group of said linker and producing a resultant isocyanate or isothiocyanate derivative of said first amine-containing compound substantially without reaction with the N.dbd.C.dbd.Y group of said linker.

A derivative of a primary or secondary amine-containing ligand, joined at the amine nitrogen, and having the formula

• Y.dbd.C.dbd.N--Q--A--C(O)-amine
• wherein Q is a homoaromatic or heteroaromatic ring system;
• A is a single bond or an unsubstituted or substituted divalent C.sub.1-30 bridging group;
• and Y is O or S.

A conjugate of a first primary or secondary amine-containing ligand and a second primary or secondary amine-containing ligand, each joined at the amine nitrogen, and having the formula

• amine-C(Y)NH--Q--A--C(O)-amine'
• wherein Q is a homoaromatic or heteroaromatic ring system;
• A is a single bond or an unsubstituted or substituted divalent C.sub.1-30 bridging group;
• and Y is O or S.