Disulfide prodrugs and linkers and stabilizers useful therefor

A compound having the structure:

• or a pharmaceutically acceptable salt thereof;
• wherein
• X and Z are members independently selected from O, S and NR23
• wherein
• R23 is a member selected from H, substituted or unsubstituted alkyl, substituted or unsubstituted heteroalkyl, and acyl;
• R1 is H, substituted or unsubstituted lower alkyl or C(O)R8, wherein R8 is a member selected from NR9R10 and OR9,
• in which
• R9, and R10 are members independently selected from H, substituted or unsubstituted alkyl and substituted or unsubstituted heteroalkyl;
• R2 is H or substituted or unsubstituted lower alkyl;
• R11 is C(O)NR12R13, in which
• R12 and R13 are members independently selected from H, substituted or unsubstituted alkyl, substituted or unsubstituted heteroalkyl and substituted or unsubstituted aryl, and at least one of R12 and R13 comprises an enzymatically cleaveable disulfide group
• R4 and R5 are members independently selected from H, substituted or unsubstituted alkyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted heterocycloalkyl, halogen, NO2, NR15 R16, NC(O)R15, OC(O)NR15R16, OC(O)OR15, C(O)R15, OR15
• wherein
• R15 and R16 are independently selected from H, substituted or unsubstituted alkyl, substituted or unsubstituted heteroalkyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted heterocycloalkyl and substituted or unsubstituted peptidyl, wherein R15 and R16 together with the nitrogen atom to which they are attached are optionally joined to form a substituted or unsubstituted heterocycloalkyl ring system having from 4 to 6 members, optionally containing two or more heteroatoms;
• and
• X1 is a leaving group.