Low molecular weight polyethylene glycol drug conjugates having improved drug biological activity

A polyethylene glycol-(drug)4 conjugate of general formula (III), the conjugate being formed by linking low molecular weight polyethylene glycol with four drug molecules,

• wherein:
• a′, b′, c′ and d′ may be identical or different and be an integer of 0-20;
• X is a linking group, selected from a group consisting of
• i is an integer of 0-10;
• and, TA, TA′, TA″ and TA′″ are target compounds that may be identical or different, selected from a group consisting of sumatriptan, dorzolamide, irinotecan, camptothecin, dasatinib, paclitaxel, docetaxel, Dccyclovirobuxinum D, diethylstilbestrol, estradiol, prazosin, terazosin, metoclopramide, ursodesoxycholic acid, rapamycin, scopolamine, and procaine.