Heterobifunctional poly(ethylene glycol) and uses thereof

A compound of formula I′:

• wherein:
• n is 10-2500;
• R1 is —X(CH2CH2Y)m(CH2)n′R3, wherein:
• X is —O—, —S—, —C≡C—, or —CH2—;
• each Y is independently —O— or —S—;
• m is 0-10;
• n_′ is 0-10;
• and
• R3 is —N3, —CN, a mono-protected amine, a di-protected amine, a protected aldehyde, a protected hydroxyl, a protected carboxylic acid, a protected thiol, a 9-30 membered crown ether, or an optionally substituted group selected from aliphatic, a 5-8 membered saturated, partially unsaturated, or aryl ring having 0-4 heteroatoms independently selected from nitrogen, oxygen, or sulfur, an 8-10 membered saturated, partially unsaturated, or aryl bicyclic ring having 0-5 heteroatoms independently selected from nitrogen, oxygen, or sulfur, or a detectable moiety;
• R2 is halogen, N3, CN, a mono-protected amine, a di-protected amine, a protected hydroxyl, a protected aldehyde, a protected thiol, —NHR4, —N(R4)2, —SR4, —O(CH2CH2O)q(CH2)rR5, —OC(O)R4, or —OS(O)2R4;
• q and r are each independently 0-4;
• each R4 is independently an optionally substituted group selected from aliphatic, a 5-8 membered saturated, partially unsaturated, or aryl ring having 0-4 heteroatoms independently selected from nitrogen, oxygen, or sulfur, an 8-10-membered saturated, partially unsaturated, or aryl bicyclic ring having 0-5 heteroatoms independently selected from nitrogen, oxygen, or sulfur, or a detectable moiety, or:
• two R4 on the same nitrogen atom are taken together with said nitrogen atom to form an optionally substituted 4-7 membered saturated, partially unsaturated, or aryl ring having 1-4 heteroatoms independently selected from nitrogen, oxygen, or sulfur;
• and
• R5 is hydrogen, halogen, N3, CN, a mono-protected amine, a di-protected amine, a protected aldehyde, a protected hydroxyl, a protected carboxylic acid, a protected thiol, or an optionally substituted group selected from aliphatic, a 5-8 membered saturated, partially unsaturated, or aryl ring having 0-4 heteroatoms independently selected from nitrogen, oxygen, or sulfur, an 8-10 membered saturated, partially unsaturated, or aryl bicyclic ring having 0-5 heteroatoms independently selected from nitrogen, oxygen, or sulfur, or a detectable moiety,
• provided that:
• (a) when either of R1 or R2 is (EtO)2CH—, then the other of R1 or R2 is not —S—S-pyridin-2-yl, —OBn, —OC(O)C(CH3)═CH2, or —OC(O)CH═CH—CH═CH-Ph;
• (b) when either of R1 or R2 is —OBn, the other is not —OC(O)Cl;
• (c) R1 and R2 are not simultaneously —OC(O)CH═CH2;
• (d) when either of R1 or R2 is —CN, then the other is not -phthalimido;
• and
• (e) when either of R1 or R2 is acetyl, then the other is not —CN or -phthalimido.