Phosphoalkyl polymers comprising biologically active agents

A compound having the following structure (I):

• or a stereoisomer, pharmaceutically acceptable salt or tautomer thereof, wherein:
• M is, at each occurrence, independently a biologically active moiety (i) selected from an NSAID, a kinase inhibitor, an anthracycline, and an EGFR inhibitor, or (ii) having one of the following structures:
• L comprises a physiologically cleavable linker, wherein L is cleavable:
• at a pH ranging from 6 to 8, at a temperature ranging from 20° C. to 40° C. or by an enzyme;
• L1 is, at each occurrence, independently an alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene or heteroalkynylene linker;
• L2 and L3 are, at each occurrence, independently an optional alkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene or heteroatomic linker;
• R1 is, at each occurrence, independently H, alkyl or alkoxy;
• R2 and R3 are each independently —H, —OH, —SH, alkyl, alkoxy, alkylether, heteroalkyl, alkylaminyl, alkylcarbonyl, alkoxycarbonyl, Q or a protected form thereof, or L′, wherein the alkyl, alkoxy, alkylether, heteroalkyl, alkylaminyl, alkylcarbonyl and alkyloxycarbonyl are optionally substituted with hydroxyl, amino, sulfhydryl, phosphate, thiophosphate, phosphoalkyl, thiophosphoalkyl, phosphoalkylether or thiophosphoalkylether, or combinations thereof,
• R4 is, at each occurrence, independently OH, SH, O−, S−, ORd or SRd−;
• R5 is, at each occurrence, independently oxo, thioxo or absent;
• Rd is a cation;
• Q is, at each occurrence, independently a moiety comprising a reactive group, or protected form thereof, capable of forming a covalent bond with a complementary reactive group Q′ on a targeting moiety;
• L′ is, at each occurrence, independently a linker comprising a covalent bond to Q, a targeting moiety, a linker comprising a covalent bond to a targeting moiety, a solid support or solid support residue, a linker comprising a covalent bond to a solid support or solid support residue or a linker comprising a covalent bond to a further compound of structure (I);
• m is, at each occurrence, independently an integer of zero or greater, provided that at least one occurrence of m is an integer of three or greater;
• and
• n is an integer of one or greater.