Chemical coupling linker and use thereof

A compound or a pharmaceutically acceptable salt, ester, stereoisomer, tautomer or isotope-labeled compound thereof, wherein the compound has a structure represented by Formula II:

• wherein:
• LG is a leaving group or a reactive group;
• X is selected from the group consisting of —O—, —NR2— and —CHR3—;
• R2 and R3 are each independently selected from the group consisting of hydrogen and C1-6 alkyl;
• the C1-6 alkyl is optionally substituted with one or more groups independently selected from the group consisting of amino, alkylamino, nitrogen-containing heterocyclyl, sulfonic acid group, carboxylic acid group, quaternary ammonium salt, hydroxyl and alkoxy;
• each L3 is independently selected from the group consisting of single bond, C1-6 alkylene, —O—, —(CH2CH2O)y—, oxime group, an amino acid residue, a fragment of a polypeptide formed with 2 to 10 amino acids, 4- to 16-membered heterocyclylene, 5- to 16-membered heteroarylene, amino, acyl, —CO—NH— and —NH—CO—;
• the C1-6 alkylene, oxime group, amino, 4- to 16-membered heterocyclylene, 5- to 16-membered heteroarylene, —CO—NH— and —NH—CO— are optionally substituted with one or more groups independently selected from the group consisting of sulfonic acid group, phosphoric acid group, carboxylic acid group, amide group, quaternary ammonium salt, hydroxyl, alkyl, alkoxy, alkoxyalkyl, alkynyl and azido;
• each L4 is independently selected from the group consisting of an amino acid residue, a fragment of a polypeptide formed with 2 to 10 amino acids, glycosyl, phenylene, benzyl, benzyloxy, benzyloxycarbonyl, aminobenzyloxycarbonyl, acylbenzyloxycarbonyl, 5- to 16-membered heteroarylene, C1-6 alkylene, —(CH2CH2O)y—, acyl and amino;
• the C1-6 alkylene and amino are optionally substituted with one or more groups independently selected from the group consisting of sulfonic acid group, phosphoric acid group, carboxylic acid group, amide group, sulfone group, sulfoxide group, quaternary ammonium salt, hydroxyl, alkyl, alkoxy, alkoxyalkyl, alkylaminoalkyl, alkynyl and azido, and the phenylene, benzyl, benzyloxy, benzyloxycarbonyl, aminobenzyloxycarbonyl, acylbenzyloxycarbonyl are optionally substituted with pyranosyl or furanosyl;
• each D is independently selected from the group consisting of a fragment of an effector molecule, and the effector molecule is, for example, a cytotoxin, an immunostimulant, a pro-apoptotic agent, a protein degrading agent or a hormone receptor modulator;
• preferably, the effector molecule is connected to L4 via an amino or hydroxyl thereon;
• m is an integer of 1 to 20;
• n is an integer of 1 to 20;
• x is an integer of 1 to 10;
• y is an integer of 1 to 20.