Y-type discrete polyethylene glycol derivative and preparation method thereof

A Y-type discrete polyethylene glycol derivative having the structure of formula (I):

• wherein:
• A1, A2, and A3 are the same or different Y—X—(CH2)n structures, wherein n is an integer from 0 to 12;
• X is a linking group selected from the group consisting of —(CH2)i—, —(CH2)iNH—, —(CH2)iOCOO—, —(CH2)iOCONH—, —(CH2)iNHCONH—, —OC(CH2)iCOO—, —(CH2)iCOO— and —(CH2)iCONH—, i is an integer from 0 to 10;
• Y is a reactive end group selected from the group consisting of hydrogen, C1-C6 alkyl, C1-C6 alkoxy, hydroxy, amino, aminomethyl, maleimido, carboxyl, sulfhydryl, succinimide carbonate, succinimide acetate, succinimide propionate, succinimide succinate, succinimide, dithiopyridinyl, propionic acid group, aldehyde group, thioester group, acryloxy, azido, glutaric acid group, hydrazide, alkynyl, p-nitrophenyl carbonate, isocyanato, o-dithiopyridinyl, silane, carboxymethyl, vinyl sulfone group and vitamin H;
• E1 is a discrete polyethylene glycol group with a structure of (CH2CH2O)j, j is an integer from 0 to 100;
• E2 is a discrete polyethylene glycol group with a structure of (CH2CH2O)k, k is an integer from 0 to 100;
• E3 is a discrete polyethylene glycol group with a structure of (CH2CH2O)l, l is an integer from 0 to 100;
• and
• r, s and t are independently selected from the group consisting of 0, 1, 2 or 3.