Chemical linkers and conjugates thereof

1. A compound of the formula

wherein D is a drug moiety comprising a structure:

wherein the ring system A is a member selected from substituted and unsubstituted aryl, substituted and unsubstituted heteroaryl, and substituted and unsubstituted heterocycloalkyl groups;

E and G are members independently selected from H, substituted and unsubstituted alkyl, substituted and unsubstituted heteroalkyl, a heteroatom, a single bond, or E and G are joined to form a ring system selected from substituted and unsubstituted aryl, substituted and unsubstituted heteroaryl, and substituted and unsubstituted heterocycloalkyl;

X is a member selected from O, S and NR 23 ;

R 23 is a member selected from H, substituted and unsubstituted alkyl, substituted and unsubstituted heteroalkyl, and acyl;

R 3 is a member selected from the group consisting of (═O), SR 11 , NHR 11 and OR 11 ,

wherein R 11 is a member selected from the group consisting of H, substituted alkyl, unsubstituted alkyl, substituted heteroalkyl, unsubstituted heteroalkyl, diphosphates, triphosphates, acyl, C(O)R 12 R 13 , C(O)OR 12 , C(O)NR 12 R 13 , P(O)(OR 12 ) 2 , C(O)CHR 12 R 13 , SR 12 and SiR 12 R 12 R 14 ,

in which R 12 , R 13 , and R 14 are members independently selected from H, substituted and unsubstituted alkyl, substituted and unsubstituted heteroalkyl and substituted and unsubstituted aryl, wherein R 12 and R 13 together with the nitrogen or carbon 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;

R 4 , R 4′ , R 5 and R 5′ are members independently selected from the group consisting of H, substituted alkyl, unsubstituted alkyl, substituted aryl, unsubstituted aryl, substituted heteroaryl, unsubstituted heteroaryl, substituted heterocycloalkyl, unsubstituted heterocycloalkyl, halogen, NO 2 , NR 15 R 16 , NC(O)R 15 , OC(O)NR 15 R 16 , OC(O)OR 15 , C(O)R 15 , SR 15 , OR 15 , CR 15 ═NR 16 , and O(CH 2 ) n N(CH 3 ) 2

wherein n is an integer from 1 to 20;

R 15 and R 16 are independently selected from H, substituted and unsubstituted alkyl, substituted and unsubstituted heteroalkyl, substituted and unsubstituted aryl, substituted and unsubstituted heteroaryl, substituted and unsubstituted heterocycloalkyl, and substituted and unsubstituted peptidyl, wherein R 15 and R 16 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;

R 6 is a single bond which is either present or absent and when present R 6 and R 7 are joined to form a cyclopropyl ring; and

R 7 is CH 2 —X 1 or —CH 2 — joined in said cyclopropyl ring with R 6 , wherein

X 1 is a leaving group,

wherein at least one of R 11 , R 12 , R 13 , R 15 or R 16 , links said drug moiety D to L 1 , if present, or to —C(O)—;

each AA 1 is independently selected from the group consisting of natural amino acids and unnatural α-amino acids;

c is an integer from 1 to 20;

L 2 is a substituted alkyl, unsubstituted alkyl, substituted heteroalkyl, unsubstituted heteroalkyl, unsubstituted heterocycloalkyl, substituted heterocycloalkyl, substituted and unsubstituted aryl, and substituted and unsubstituted heteroaryl;

L 1 is a self-immolative linker;

m is an integer 0, 1, 2, 3, 4, 5, or 6;

o is 0 or 1;

L 4 is selected from substituted alkyl, unsubstituted alkyl, substituted aryl, unsubstituted aryl, substituted heteroalkyl, and unsubstituted heteroalkyl, any of which may be straight, branched, or cyclic; positively and negatively charged amino acid polymers; a polymer; and combinations thereof, wherein L 4 does not comprise a carboxylic acyl group directly attached to the N-terminus of (AA 1 ) c ;

p is 1; and

X 4 is a member selected from the group consisting of protected reactive functional groups, unprotected reactive functional groups, detectable labels, and targeting agents.

2. The compound of claim 1 , wherein o is 1 and -(AA 1 ) c -(L 2 )—C(O)— has the structure:

wherein R 24 is selected from the group consisting of H, substituted alkyl, unsubstituted alkyl, substituted heteroalkyl, and unsubstituted heteroalkyl;

each K is a member independently selected from the group consisting of substituted alkyl, unsubstituted alkyl, substituted heteroalkyl, unsubstituted heteroalkyl, substituted aryl, unsubstituted aryl, substituted heteroaryl, unsubstituted heteroaryl, substituted heterocycloalkyl, unsubstituted heterocycloalkyl, halogen, NO 2 , NR 21 R 22 , NR 21 COR 22 , OCONR 21 R 22 , OCOR 21 , and OR 21 ;

wherein R 21 and R 22 are independently selected from the group consisting of H, substituted alkyl, unsubstituted alkyl, substituted heteroalkyl, unsubstituted heteroalkyl, substituted aryl, unsubstituted aryl, substituted heteroaryl, unsubstituted heteroaryl, substituted heterocycloalkyl, unsubstituted heterocycloalkyl; and

a is an integer of 0, 1, 2, 3, or 4.

3. The compound of claim 2 , wherein m is not 0 and -(AA 1 ) c -(L 2 )—C(O)-(L 1 ) m - comprises the structure:

wherein each R 24 is a member independently selected from the group consisting of H, substituted alkyl, unsubstituted alkyl, substituted heteroalkyl, and unsubstituted heteroalkyl.

4. The compound of claim 2 , having the structure:

wherein Z is a member selected from O, S and NR 23 ,

wherein R 23 is a member selected from H, substituted and unsubstituted alkyl, substituted and unsubstituted heteroalkyl, and acyl; and

wherein X 1 is a halogen.

5. The compound of claim 1 , which is selected from the group consisting of:

wherein X 1 is Cl or Br, and Ab is an antibody, or fragment thereof.

6. The compound of claim 1 , wherein L 4 comprises a polyethylene glycol moiety.

7. The compound of claim 6 , wherein the polyethylene glycol moiety contains 2-6 repeat units.

8. The compound of claim 1 , wherein (AA 1 ) c is a peptide sequence cleavable by a protease expressed in tumor tissue.

9. The compound of claim 1 , wherein (AA 1 ), is a peptide sequence selected from the group consisting of Val-Cit, Val-Lys, Phe-Lys, Lys-Lys, Ala-Lys, Phe-Cit, Leu-Cit, Ile-Cit, Trp, Cit, Phe-Ala, Phe-N 9 -tosyl-Arg, Phe-N 9 -nitro-Arg, Phe-Phe-Lys, D-Phe-Phe-Lys, Gly-Phe-Lys, Leu-Ala-Leu, Ile-Ala-Leu, Val-Ala-Val, Ala-Leu-Ala-Leu (SEQ ID NO: 1), β-Ala-Leu-Ala-Leu (SEQ ID NO: 2) and Gly-Phe-Leu-Gly (SEQ ID NO: 3).

10. The compound of claim 1 , wherein (AA 1 ) c is Val-Cit or Val-Lys.

11. The compound of claim 1 , wherein D has the structure:

wherein Z is a member selected from O, S and NR 23

wherein R 23 is a member selected from H, substituted and unsubstituted alkyl, substituted and unsubstituted heteroalkyl, and acyl;

R 1 is H, substituted or unsubstituted lower alkyl, C(O)R 8 , or CO 2 R 8 , wherein R 8 is a member selected from group consisting of substituted alkyl, unsubstituted alkyl, NR 9 R 10 , NR 9 NHR 10 , and OR 9

in which R 9 and R 10 are members independently selected from H, substituted and unsubstituted alkyl, and substituted and unsubstituted heteroalkyl; and

R 2 is H, substituted alkyl or unsubstituted lower alkyl.

12. The compound of claim 1 , wherein D has the structure:

wherein Z is a member selected from O, S and NR 23

wherein R 23 is a member selected from H, substituted or unsubstituted alkyl, substituted or unsubstituted heteroalkyl, and acyl;

R 1 is H, substituted or unsubstituted lower alkyl, C(O)R 8 , or CO 2 R 8 , wherein R 8 is a member selected from NR 9 R 10 and OR 9 ,

in which R 9 and R 10 are members independently selected from H, substituted or unsubstituted alkyl and substituted or unsubstituted heteroalkyl;

R 1′ is H, substituted or unsubstituted lower alkyl, or C(O)R 8 , wherein R 8 is a member selected from NR 9 R 10 and OR 9 ,

in which R 9 and R 10 are members independently selected from H, substituted or unsubstituted alkyl and substituted or unsubstituted heteroalkyl;

R 2 is H, or substituted or unsubstituted lower alkyl or unsubstituted heteroalkyl or cyano or alkoxy; and

R 2′ is H, or substituted or unsubstituted lower alkyl or unsubstituted heteroalkyl.

13. A pharmaceutical formulation comprising a compound according to claim 1 and a pharmaceutically acceptable carrier.