Targeted delivery of nicotinaminde adenine dinucleotide salvage pathway inhibitors

Abstract

Compounds and compositions are disclosed in which a NAMPT Drug Unit is linked to a targeting Ligand Unit through a Unit from which a NAMPT inhibitor compound or derivative thereof is released at the targeted site of action. Methods for treating diseases characterized by the targeted abnormal cells, such as cancer or an autoimmune disease, using the compounds and compositions of the invention are also disclosed.

1 . A Ligand Drug Conjugate (LDC) compound, wherein the compound is represented by the structure of: 
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, wherein 
         L is a Ligand Unit; 
         D is a NAMPT Drug Unit represented by the general structure of: 
       
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, wherein 
         the wavy line indicates the site of covalent attachment to L 0  or L R , depending on the presence or absence of L o ; 
         H N  is a NAMPT Head Unit, wherein the NAMPT Head Unit is a C 5 -C 24  heteroaryl or partially aromatic C 9 -C 24  heterocyclyl, optionally substituted, wherein the C 5 -C 24  heteroaryl or partially aromatic C 9 -C 24  heterocyclyl comprises an optionally substituted 5- or 6-membered nitrogen-containing heteroaromatic ring system corresponding to the heterocycle of nicotinamide, and is capable of interacting with enzymatically competent NAMPT homodimer at its nicotinamide mononucleotide binding site when the NAMPT Drug Unit is released from a Ligand Drug Conjugate compound as a NAMPT inhibitor (NAMPTi) compound or derivative thereof; 
         DA is a Donor-Acceptor Unit wherein the Donor-Acceptor Unit is or comprises a hydrogen bond donor or acceptor functional group and is bonded to a carbon skeletal atom at position 2 or 3 of the 5-membered nitrogen-containing heteroaromatic ring system or at position 3 or 4 of the 6-membered nitrogen-containing heteroaromatic ring system, with optional formal cyclization of DA back to an adjacent skeletal carbon atom of the 6-membered nitrogen-containing heteroaromatic ring system through an introduced optionally substituted non-aromatic carbon atom or an optionally substituted nitrogen, oxygen or sulfur atom resulting in a partially aromatic or fully aromatic fused 6,5- or 6,6-ring system, 
         wherein said bonding of DA is in relation to a skeletal nitrogen atom of the 5- or 6 membered nitrogen-containing heteroaromatic ring system and wherein said formal cyclization to the adjacent carbon atom of the 6-membered nitrogen-containing heteroaromatic ring system substantially retains the hydrogen bonding capability of the donor or acceptor functional group of DA in absence of said cyclization; 
         I N  is an Interconnecting Unit, wherein the Interconnecting Unit is or comprises —X 1 —[C(═O)] 0,1 —, —X 1 —S(═O) 1,2 —, —X 2 —C 6 -C 24  arylene-[C(═O)] 0,1 —, —X 2 —C 6 -C 24  arylene-[S(═O) 1,2 ] 0,1 , —X 2 —C 6 -C 24  arylene-O—, —X 2 —C 5 -C 24  heteroarylene-[C(═O) 0,1 ]—, —X 2 —C 5 -C 24  heteroarylene-[S(═O) 1,2 ] 0,1 , —X 2 —C 5 -C 24  heteroarylene-O— or —X 2 —C 3 -C 20  heterocyclo-[C(═O) 0,1 ]—, wherein the arylene, heteroarylene and heterocyclo are optionally substituted; 
         X 1  is optionally substituted C 5 -C 7  alkylene; 
         X 2  is absent or is an optionally substituted C 1 -C 4  alkylene; 
         T N  is a NAMPT Tail Unit, wherein the NAMPT Tail Unit is or comprises an optionally substituted amino-alcohol residue or a carboxylic acid-alcohol residue, the —O— or optionally substituted nitrogen of which is the site of covalent attachment to L 0 , or or L R , depending on the presence or absence of L 0 , or 
         T N  is or comprises an optionally substituted benzamide moiety, the amide nitrogen atom of which is bonded to I N  with optional cyclization of that atom back to I N  or to the remainder of T N , and the aromatic ring of which is at least substituted with a hydroxyl, thiol or amino residue, the —O—, —S— or optionally substituted nitrogen atom of which at position 3 or 4 relative to the site at which the amide carbonyl carbon atom is attached is the site of covalent attachment to L 0  or L R , depending on the presence or absence of L 0 , or 
         T N  is or comprises an optionally substituted aryl or biaryl moiety, an aromatic skeletal atom of which is bonded to I N , or to the remainder of T N , and wherein an aromatic ring of which is at least substituted with a hydroxyl, thiol or an amino residue, the —O—, —S— or optionally substituted nitrogen of which is the site of covalent attachment to L 0  or or L R , depending on the presence or absence of L 0 , respectively; and 
         wherein T N  or the remainder thereof is bonded to I N , wherein said remainder is an optionally substituted C 2 -C 7  heteroalkylene or an optionally substituted C 5 -C 6  heterocyclo, 
         L R  is a primary linker, which interconnects the Ligand Unit and Drug Unit optionally through L 0 , as indicated, which is an optional secondary linker; 
         subscripts a and b independently are 0 or 1, indicating the absence or presence, respectively, of A or B; 
         subscript n is 1, 2, 3 or 4; 
         A is a first optional Stretcher; and 
         B is a Branching Unit, when subscript b is 1 and subscript n is 2, 3 or 4, or B is absent, so that subscript b is 0, when subscript n is 1, 
         wherein each of A and B is an independently selected single unit or is optionally comprised or consists of at least two, three or four independently selected subunits; 
         Y is a Spacer Unit; and subscript y is 0, 1 or 2, indicating the absence or presence of one or two of Y, respectively, 
         provided that when subscript y is 1, Y is a Spacer Unit covalently attached to a heteroatom or moiety thereof of T N  selected from the group consisting of —O—, —S— and optionally substituted nitrogen, 
         provided that when subscript y is 2 so that Y y  is —Y—Y′, Y is a first Spacer Unit and Y′ is a second Spacer Unit or a functional group comprising the optionally substituted heteroatom from T N ; and 
         subscript w is 0 or 1, indicating the absence or presence, respectively, of W; wherein 
         when subscript w is 1, W is a Peptide Cleavable Unit, wherein enzymatic or non-enzymatic cleavage of either Unit initiates release of the NAMPT Drug Unit as a NAMPTi compound or derivative thereof from a drug linker moiety of a Ligand Drug Conjugate compound; and 
         when subscript w is 0, which indicates the absence of a Cleavable Unit, enzymatic or non-enzymatic cleavage of the bond between L R  and L 0 , when L 0  is present, or the bond between L R  and D, when L 0  is absent, initiates release of the NAMPT Drug Unit as a NAMPTi compound or derivative thereof; 
         wherein p′ is an integer ranging from 1 to 24. 
       
     
     
         2 . (canceled) 
     
     
         3 . The Ligand Drug Conjugate composition compound of  claim 1 , wherein the Donor Acceptor (DA) Unit is comprised of comprises an optionally substituted amide functional group or bioisostere thereof. 
     
     
         4 . (canceled) 
     
     
         5 . The Ligand Drug Conjugate compound of  claim 1 , wherein the 6-membered nitrogen-containing heteroaromatic ring system of H N  is that of pyridine with optional cyclization of DA back to the pyridine aromatic ring system through an introduced aromatic oxygen, sulfur or an optionally substituted nitrogen atom so that H N  contains a 6-5 fused aromatic ring system. 
     
     
         6 . The Ligand Drug Conjugate compound of  claim 1 , wherein each of the NAMPT homodimers of the enzymatically competent NAMPT homodimer has the amino acid sequence of SEQID 1. 
     
     
         7 . The Ligand Drug Conjugate compound of  claim 1 , wherein the NAMPT Head Unit has the structure of: 
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, 
         in particular, having the structure of: 
       
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, wherein 
         R 1  is hydrogen, —NH 2  or chloro; 
         R 2  is fluoro; 
         R 3  is hydrogen or —NH 2 ; 
         R 4  is hydrogen or optionally substituted C 1 -C 4  alkyl; and 
         the wavy line indicates the site of covalent attachment to DA and an adjacent aromatic carbon atom thereto is the site of said optional cyclization by DA to H N . 
       
     
     
         8 . The Ligand Drug Conjugate compound of  claim 3 , wherein the Donor-Acceptor Unit has the structure of: 
       
         
           
           
               
               
           
         
         in particular, having the structure of: 
       
       
         
           
           
               
               
           
         
         wherein R 4  is hydrogen or optionally substituted C 1 -C 4  alkyl; 
         DA is optionally cyclized to H N , wherein said cyclization is to the sp 2  carbon atom proximal to the carbonyl carbon (as indicated) through an introduced optionally substituted non-aromatic carbon atom or an optionally substituted aromatic heteroatom; 
         the wavy line indicates the site of covalent attachment to H N , and the aromatic carbon atom adjacent thereto is the site of said optional cyclization by DA to H N ; and 
         the pound sign (#) indicates the site of covalent attachment to I N , or 
         wherein the Donor-Acceptor Unit has the structure of: 
       
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, 
         in particular, having the structure of: 
       
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, wherein 
         X D  is O, S or NR S, wherein the nitrogen atom is optionally protonated and R D  is hydrogen or optionally substituted C 1 -C 4  alkyl; 
         each R 4  is independently selected from the group consisting of hydrogen and optionally substituted C 1 -C 4  alkyl, or both R 4  together with the nitrogen atoms to which they are attached and the intervening carbon atom(s) define an optionally substituted C 5 -C 6  heterocyclo; 
         the pound sign (#) indicates the site of covalent attachment to I N ; and the wavy line indicates the site of covalent attachment to H N , 
         wherein DA is optionally cyclized back to an adjacent aromatic carbon atom of H N , wherein said cyclization is from the indicated nitrogen atom so that R 4  bonded thereto is replaced by a covalent bond to said adjacent aromatic carbon atom, or is from X D  when X D  is —NR S, either directly or through an introduced —S(═O) 0-2  moiety, in which either instance R D  is replaced by a bond to said adjacent carbon atom or the sulfur atom of said introduced moiety. 
       
     
     
         9 . The Ligand Drug Conjugate compound of  claim 1 , wherein H N -DA- has the structure of: 
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, wherein 
         R 4  is hydrogen or optionally substituted C 1 -C 4  alkyl; and 
         the wavy line indicates the site of covalent attachment to I N , and 
         wherein the sp 2  carbon atom proximal to the carbonyl carbon atom is the site (as indicated) of optional cyclization to H N  through an introduced optionally substituted non-aromatic carbon atom or an optionally substituted aromatic heteroatom. 
       
     
     
         10 . The Ligand Drug Conjugate compound of  claim 1 , wherein the NAMPT Tail Unit is is or comprises an optionally substituted amino alcohol moiety,
 wherein the oxygen atom of the alcohol is the site of covalent attachment to L 0  or L R , depending on the presence or absence of L 0 , respectively,   in particular having the structure of:   
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, wherein 
         R 4  is hydrogen or optionally substituted C 1 -C 4  alkyl; 
         the wavy line indicates the site of covalent attachment to I N ; and 
         the pound sign (#) indicates the site of covalent to L 0  or L R , depending on the presence or absence of L 0 , respectively, or 
         wherein the Tail Unit is or comprises an optionally substituted benzamide moiety having a functional group providing a heteroatom that is the site of covalent attachment to L 0  or L R , depending on the presence or absence of L 0 , respectively, 
         in particular, having the structure of: 
       
       
         
           
           
               
               
           
         
         wherein X b  is —S— —O— or —NH—, optionally substituted; and 
         R 4  is hydrogen or optionally substituted C 1 -C 4  alkyl, wherein 
         the benzamide moiety is optionally cyclized to I N , wherein the amide nitrogen atom of the benzamide moiety is the site of said cyclization so that R 4  is replaced by a covalent bond to I N , 
         more particularly, having the structure of: 
       
       
         
           
           
               
               
           
         
         wherein the wavy line indicates the site of covalent attachment to I N ; 
         the pound sign (#) indicates the site of covalent attachment to L 0  or L R , depending on the presence or absence of L 0 , respectively. 
       
     
     
         11 . The Ligand Drug Conjugate compound of  claim 10 , wherein I N  is —CH 2 —(CH 2 ) 3-7 —CH 2 —, —CH 2 —(CH 2 ) 3-7 —CH 2 —O—, —CH 2 —(CH 2 ) 3-7 —C(═O)—, —CH 2 —(CH 2 ) 3-7 —S(═O) 2 — or —CH 2 —(CH 2 ) 3-7 —S(═O)—. 
     
     
         12 . The Ligand Drug Conjugate compound of claim DUI, wherein —I N -T N - has the structure of: 
       
         
           
           
               
               
           
         
         wherein X b  is —NH—, —O— or —S—; 
         the wavy line indicates the site of covalent attachment to DA; and 
         the pound sign (#) indicates the site of covalent attachment to L 0  or L R , depending on the presence or absence of L 0 , respectively. 
       
     
     
         13 . The Ligand Drug Conjugate compound of  claim 1 , wherein the NAMPT Drug Unit has the structure of: 
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, wherein 
         the pound sign (#) indicates the site of covalent attachment to L 0  or L R , depending on the presence or absence of L 0 , respectively. 
       
     
     
         14 . The Ligand Drug Conjugate compound of  claim 1  or 13, wherein L-L R - has the structure of: 
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, wherein 
         the indicated (#) nitrogen, carbon or sulfur atom is from the Ligand Unit; and wherein the wavy line indicates the site of covalent attachment to the remainder of the Conjugate structure. 
       
     
     
         15 . The Ligand Drug Conjugate compound of  claim 1 , wherein the compound is represented by the structure of Formula 1 or Formula 2: 
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, wherein 
         S is a sulfur atom of the Ligand Unit, which in Formula 2 is bonded to the carbon atom α or β to the carboxylic acid functional group of the indicated succinic acid amide (M 3 ) moiety; 
         R 6  is hydrogen or an optionally substituted C 1 -C 6  alkyl, which in Formula 2 is bonded to the saturated carbon atom adjacent to the carbon substituted by L-S—; 
         A o  is a second optional Stretcher Unit; 
         BU is a Basic Unit and R a3  is an optionally substituted C 1 -C 12  alkyl group; and 
         the dotted curved line indicates optional cyclization so that in the absence of said cyclization BU is an acyclic Basic Unit or in the presence of said cyclization BU is a cyclized Basic Unit in which Rat and BU together with the carbon atom to which both are attached, define an optionally substituted spiro C 3 -C 20  heterocycle containing a skeletal basic nitrogen atom of a secondary or tertiary amine functional group as the basic function group of the cyclic Basic Unit, 
         wherein the basic nitrogen atom of the acyclic Basic Unit or cyclic Basic Unit is optionally suitably protected by a nitrogen protecting group, dependent on the degree of substitution of the basic nitrogen atom, or is optionally protonated, 
         in particular, having the structure of: 
       
       
         
           
           
               
               
           
         
         wherein [HE] as A o  is an optional Hydrolysis Enhancing Unit; 
         subscript w is 1; 
         W is Peptide Cleavable Unit; and 
         wherein the remaining variable groups retain their previous meanings, 
         wherein protease action on the Peptide Cleavable Unit results in cleavage of the W-J′ bond within a drug linker moiety of a Ligand Drug Conjugate compound to initiate release of the NAMPT Drug Unit as NAMPTi compound or derivative thereof from that Ligand Drug Conjugate compound. 
       
     
     
         16 - 18 . (canceled) 
     
     
         19 . The Ligand-Drug Conjugate compound of claim wherein
 W is a Peptide Cleavable Unit for which the compound is represented by the structure of:   
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, wherein 
         R′ is hydrogen or —OC 1 -C 6  alkyl or other electron donating group; and 
         R a2  is hydrogen or C 1 -C 6  alkyl, optionally cyclized to BU, as indicated by the dotted curved line, 
         BU has the structure of —[C(R a1 )(R a1 )]—[c(R a1 )(R a1 )] 0-3 —N(R a3 )(R a3 ), 
         wherein in the absence of cyclization to R a2 , each R a1  independently is hydrogen or C 1 -C 4  alkyl, C 6 -C 10  aryl, C 5 -C 10  heteroaryl, (C 6 -C 10  aryl)-C 1 -C 4  alkyl-, or (C 5 -C 10  heteroaryl)-C 1 -C 4  alkyl-, optionally substituted, or two R a2  together with the carbon(s) to which they are attached and any intervening carbons define an optionally substituted C 3 -C 6  cycloalkyl; and 
         R a3  independently are hydrogen, optionally substituted C 1 -C 6  alkyl or R a3  together with the nitrogen atom to which both are attached define a C 3 -C 6  heterocyclyl in which the basic nitrogen atom is a skeletal atom, 
         or one of R a3  is —H and the other is optionally substituted C 1 -C 6  alkyl, optionally, substituted —C 1 -C 4  alkylene-(C 6 -C 10  aryl), or -R PEG1 —O—(CH 2 CH 2 O) 1-36 -R PEG2  wherein R PEG1  is C 1 -C 4  alkylene, and R PEG2  is —H or C 1 -C 4  alkyl; and 
         the basic nitrogen atom bonded to R a3  is optionally protonated; and 
         in the presence of cyclization one of R a1  or one of R a3  is replaced with a bond to a carbon atom of R a2  in which R a2  is C 1 -C 6  alkyl and the remaining R a1  and R a3  are as previously defined; and 
         wherein Y′ is —X a —, —O—C(═O)—X b — or —OC(═O)NH—CH 2 —X a —, 
         wherein X a  or X b  are from T N , wherein —X a — is O or S and X b  is —NH—; 
         V, Z 1 , and Z 2  are independently ═N— or ═C(R 24 )—, wherein each R 24  is independently selected from the group consisting of hydrogen and C 1 -C 12  alkyl, C 2 -C 12  alkenyl and C 2 -C 12  alkynyl, optionally substituted, and halogen; 
         wherein protease action on the Peptide Cleavable Unit cleaves the W—NH bond, wherein said cleavage within a drug linker moiety of a Ligand Drug Conjugate compound initiates release of the NAMPT Drug Unit as a NAMPTi compound or derivative thereof from that Ligand Drug Conjugate compound, 
         in particular by the structure of: 
       
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, 
         more particularly by the structure of: 
       
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, wherein the variable groups are as previously defined, or 
         the compound is represented particularly by the structure of: 
       
       
         
           
           
               
               
           
         
         or 
         or a pharmaceutically acceptable salt thereof; and wherein the variable groups are as previously defined. 
       
     
     
         20 . The Ligand-Drug Conjugate compound of  claim 15 , wherein comprises a dipeptide wherein the dipeptide provides for a recognition site for a regulatory or lysosomal protease for cleavage by said protease of the W-J′ bond or the W—NH bond when J′ is —NH within a Ligand Drug Conjugate compound so as to initiate release of the NAMPT Drug Unit as NAMPTi compound or derivative thereof from that Ligand Drug Conjugate compound. 
     
     
         21 . The Ligand-Drug Conjugate compound of claim wherein the W has the structure of: 
       
         
           
           
               
               
           
         
         wherein R 34  is benzyl, methyl, isopropyl, isobutyl, sec-butyl, —CH(OH)CH 3  or has the structure of 
       
       
         
           
           
               
               
           
         
       
       wherein the asterisk indicates the site of covalent attachment to the dipeptide backbone; and
 R 35  is methyl, —(CH 2 ) 4 —NH 2 , —(CH 2 ) 3 NH(C═O)NH 2 , —(CH 2 ) 3 NH(C═NH)NH 2 , or, —(CH 2 ) 2 CO 2 H; and 
 wherein the wavy lines indicate the points of covalent attachment of the dipeptide into the structure representing the Ligand-Drug Conjugate compound, 
 in particular W is selected from the group consisting of -Phe-Lys-, -Val-Ala-, -Val-Lys-, -Ala-Lys-, -Val-Cit-, -Phe-Cit-, -Leu-Cit-, -Ile-Cit-, -Phe-Arg-, and -Trp-Cit-, wherein Cit is citrulline. 
 
     
     
         22 . (canceled) 
     
     
         23 . The Ligand-Drug Conjugate compound of  claim 1 , wherein A or a subunit thereof has the structure of formula (3) or formula (4): 
       
         
           
           
               
               
           
         
         wherein the wavy lines indicated covalent attachment within the compound structure; 
         wherein K and L′ independently are C, N, O or S, provided that when K or L′ is O or S, R 41  and R 42  to K or R 43  and R 44  to L′ are absent, and when K or L′ are N, one of R 41 , R 42  to K or one of R 42 , R 43  to L′ are absent, and provided that no two adjacent L′ are independently selected as N, O, or S; 
         wherein subscripts e and f are independently selected integers that range from 0 to 12, and subscript g is an integer ranging from 1 to 12; 
         wherein G is hydrogen, optionally substituted C 1 -C 6  alkyl, —OH, —OR PR , —CO 2 H, CO 2 R PR , wherein R PR  is a suitable protecting, or 
         G is —N(R PR )(R PR ), wherein R PR  are independently a protecting group or R PR  together form a suitable protecting group, or 
         G is —N(R 45 )(R 46 ), wherein one of R 45 , R 46  is hydrogen or R PR , wherein R PR  is a suitable protecting group, and the other is hydrogen or optionally substituted C 1 -C 6  alkyl; 
         wherein R 38  is hydrogen or optionally substituted C 1 -C 6  alkyl; 
         R 39 -R 44  are independently selected from the group consisting of hydrogen, optionally substituted C 1 -C 6  alkyl, optionally substituted aryl, and optionally substituted heteroaryl, 
         or R 39 , R 40  together with the carbon atom to which both are attached, or R 41 , R 42  together with K to which both are attached when K is a carbon atom, define a C 3 -C 6  carbocyclo, and R 41 -R 44  are as defined herein, 
         or R 43 , R 44  together with L′ to which both are attached when L′ is a carbon atom define a C 3 -C 6  carbocyclo, and R 39 -R 42  are as defined herein, 
         or R 40  and R 41 , or R 40  and R 43 , or R 41  and R 43  to together with the carbon atom or heteroatom to which both are attached and the atoms intervening between those carbon atoms and/or heteroatoms define a C 5 -C 6  carbocyclo or a C 5 -C 6  heterocyclo, and R 39 , R 44  and the remainder of R 40 -R 43  are as defined herein, 
         provided that when K is O or S, R 41  and R 42  are absent, and when K is N, one of R 41 , R 42 , is absent, and when L′ is O or S, R 43  and R 44  are absent, and when L′ is N, one of R 43 , R 44  is absent, or 
         A or a subunit thereof is an alpha-amino, beta-amino or another amine-containing acid residue, 
         in particular, wherein formula (3) or formula (4) has the structure of formula (3a) or formula (4a): 
       
       
         
           
           
               
               
           
         
         wherein subscript e and f are independently 0 or 1. 
       
     
     
         24 . The Ligand-Drug Conjugate compound of  claim 1 , wherein the Ligand Unit is an antibody or an antigen-binding fragment thereof, thereby defining an antibody Ligand Unit of an antibody drug conjugate (ADC),
 wherein the antigen targeted by the antibody Ligand Unit is an accessible cell-surface antigen of abnormal cells that is capable of cellular internalization when bound to an ADC compound and is present in greater copy number on the abnormal cells in comparison to normal cells distant from the site of the abnormal cells, or the antigen is an accessible cell-surface antigen of a vascular epithelial cell in the vicinity of abnormal cells, wherein said antigen is capable of cellular internalization of bound ADC and is present in greater copy number on said cells in comparison to normal epithelial cells distant from the site of the abnormal cells.   
     
     
         25 . The Ligand Drug Conjugate compound  claim 24 , wherein subscript p′ is 2, 4, 8, or 10. 
     
     
         26 . The Ligand Drug Conjugate compound of  claim 19 , wherein the sulfur atom attached to the indicated succinimide (M 2 ) or succinic acid amide (M 3 ) moiety of a drug linker moiety of the Conjugate is that of an antibody or antigen-binding fragment thereof, thereby defining an antibody Ligand Unit, wherein the sulfur atom of the antibody Ligand Unit bonded to the succinic acid (M 2 ) moiety or succinic acid amide (M 3 ) moiety is that of a cysteine residue native to the antibody or antigen-binding fragment thereof or an introduced cysteine residue in the heavy chain or light chain of the antibody or antigen binding-fragment thereof. 
     
     
         27 . (canceled) 
     
     
         28 . A formulation comprising a Ligand Drug Conjugate compound of  claim 1  and at least one, two, three or more excipients,
 in particular, wherein the formulation is a pharmaceutically acceptable formulation or a precursor thereof, particularly wherein the pharmaceutically acceptable formulation precursor is a solid suitable for reconstitution as a solution for intravenous injection to a subject in need thereof, or the pharmaceutically acceptable formulation is a liquid suitable for intravenous injection to a subject in need thereof, more particularly in which the Ligand Drug Conjugate compound is present in an effective amount for treatment of a hyperproliferative disease or condition in said solid or liquid formulation. 
 
     
     
         29 . A method of treating a hyperproliferative disease or condition comprising the step of administering to a subject in need thereof having said disease or condition, in particular having a cancer, more particularly a leukemia or lymphoma, an effective amount of a Ligand Drug Conjugate compound of  claim 1 . 
     
     
         30 . A method of inhibiting the multiplication of a tumor cell or cancer cell, or causing apoptosis in a tumor or cancer cell by exposing said cell to an effective amount of a Ligand Drug Conjugate compound or a compound thereof of  claim 1 . 
     
     
         31 . A Drug Linker compound, wherein the compound is represented by the structure of: 
       
         
           
           
               
               
           
         
         or a salt thereof, wherein 
         L R  is a primary linker having a functional group capable interacting with a targeting agent to form a covalent bond to a Ligand Unit corresponding to or incorporating the targeting agent in a Ligand Drug Conjugate compound; 
         D is a NAMPT Drug Unit represented by the general structure of: 
       
       
         
           
           
               
               
           
         
         or a salt thereof, wherein 
         the wavy line indicates the site of covalent attachment to L 0 , as indicated, which is an optional secondary linker, or L R , depending on the presence or absence of L 0 , respectively; 
         H N  is a NAMPT Head Unit, wherein the NAMPT Head Unit is a C 5 -C 24  heteroaryl or partially aromatic C 9 -C 24  heterocyclyl, optionally substituted, wherein the C 5 -C 24  heteroaryl or partially aromatic C 9 -C 24  heterocyclyl comprises an optionally substituted or 6-membered nitrogen-containing heteroaromatic ring system corresponding to the heterocycle of nicotinamide, and is capable of interacting with enzymatically competent NAMPT homodimer at its nicotinamide mononucleotide binding site when the NAMPT Drug Unit is released from a Ligand Drug Conjugate compound as a NAMPT inhibitor (NAMPTi) compound or derivative thereof; 
         DA is a Donor-Acceptor Unit wherein the Donor-Acceptor Unit is or comprises a hydrogen bond donor or acceptor functional group and is bonded to a carbon skeletal atom at position 2 or 3 of the 5-membered nitrogen-containing heteroaromatic ring system or at position 3 or 4 of the 6-membered nitrogen-containing heteroaromatic ring system, with optional formal cyclization of DA back to an adjacent skeletal carbon atom of the 6-membered nitrogen-containing heteroaromatic ring system through an introduced optionally substituted non-aromatic carbon atom or an optionally substituted nitrogen, oxygen or sulfur atom resulting in a partially aromatic or fully aromatic fused 6,5- or 6,6-ring system, 
         wherein said bonding of DA is in relation to a skeletal nitrogen atom of the 5- or 6 membered nitrogen-containing heteroaromatic ring system and wherein said formal cyclization to the adjacent carbon atom of the 6-membered nitrogen-containing heteroaromatic ring system substantially retains the hydrogen bonding capability of the donor or acceptor functional group of DA in absence of said cyclization; 
         I N  is an Interconnecting Unit, wherein the Interconnecting Unit is or comprises —X 1 —[C(═O)] 0,1 —, —X 1 —S(═O) 1,2 —, —X 2 —C 6 -C 24  arylene-[C(═O)] 0,1 —, —X 2 —C 6 -C 24  arylene-[S(═O) 1,2 ] 0,1 , —X 2 —C 6 -C 24  arylene-O—, —X 2 —C 5 -C 24  heteroarylene-[C(═O) 0,1 ]—, —X 2 —C 5 -C 24  heteroarylene-[S(═O) 1,2 ] 0,1 , —X 2 —C 5 -C 24  heteroarylene-O— or —X 2 —C 3 -C 20  heterocyclo-[C(═O) 0,1 ]—, wherein the arylene, heteroarylene and heterocyclo are optionally substituted; 
         X 1  is optionally substituted C 5 -C 7  alkylene; 
         X 2  is absent or is an optionally substituted C 1 -C 4  alkylene; 
         T N  is a NAMPT Tail Unit, wherein the NAMPT Tail Unit is or comprises an optionally substituted amino-alcohol residue or a carboxylic acid-alcohol residue, the —O— or optionally substituted nitrogen of which is the site of covalent attachment to L 0 , or L R , depending on the presence or absence of L 0 , or 
         T N  is or comprises an optionally substituted benzamide moiety, the amide nitrogen atom of which is bonded to I N  with optional cyclization of that atom back to I N  or to the remainder of T N , and the aromatic ring of which is at least substituted with a hydroxyl, thiol or amino residue, the —O—, —S— or optionally substituted nitrogen atom of which at position 3 or 4 relative to the site at which the amide carbonyl carbon atom is attached is the site of covalent attachment to L 0  or L R , depending on the presence or absence of L 0 , or 
         T N  is or comprises an optionally substituted aryl or biaryl moiety, an aromatic skeletal atom of which is bonded to I N , or to the remainder of T N , and wherein an aromatic ring of which is at least substituted with a hydroxyl, thiol or an amino residue, the —O—, —S— or optionally substituted nitrogen of which is the site of covalent attachment to L 0  or L R , depending on the presence or absence of L 0 , respectively; and 
         wherein T N  or the remainder thereof is bonded to I N , wherein said remainder is an optionally substituted C 2 -C 7  heteroalkylene or an optionally substituted C 5 -C 6  heterocyclo,
 subscripts a and b independently are 0 or 1, indicating the absence or presence, respectively, of A or B; 
 subscript n is 1, 2, 3 or 4; 
 A is a first optional Stretcher; and 
 B is a Branching Unit, when subscript b is 1 and subscript n is 2, 3 or 4, or B is absent, so that subscript b is 0, when subscript n is 1, 
 wherein each of A and B is an independently selected single unit or is optionally comprised or consists of at least two, three or four independently selected subunits; 
 subscript y is 0, 1 or 2, indicating the absence or presence of one or two of Y, respectively; 
 Y is a Spacer Unit; and subscript y is 0, 1 or 2, indicating the absence or presence of one or two of Y, respectively, 
 provided that when subscript y is 1, Y is a Spacer Unit covalently attached to a heteroatom or moiety thereof of T N  selected from the group consisting of —O—, —S— and optionally substituted nitrogen, 
 provided that when subscript y is 2 so that Y y  is —Y—Y′, Y is a first Spacer Unit and Y′ is a second Spacer Unit or a functional group comprising the optionally substituted heteroatom from T N ; and 
 
         subscript w is 0 or 1, indicating the absence or presence, respectively, of W; wherein 
         when subscript w is 1, W is a Peptide Cleavable Unit enzymatic or non-enzymatic cleavage of that Unit in the Drug Linker Compound, or in a drug linker moiety of a Ligand Drug Conjugate compound or a N-acetyl-cysteine (NAC)conjugate prepared from the Drug Linker compound initiates release of the NAMPT Drug Unit as a NAMPTi compound or derivative therefrom, and 
         when subscript w is 0, which indicates the absence of a Cleavable Unit, enzymatic or non-enzymatic cleavage of the bond between the indicated L R  and L 0  moieties, when L 0  is present, or the bond between L R  and D, when L 0  is absent, initiates release of the NAMPT Drug Unit as a NAMPTi compound or derivative thereof from the Drug Linker compound or said drug linker moiety or NAC conjugate. 
       
     
     
         32 . (canceled) 
     
     
         33 . The Drug Linker compound of  claim 31 , wherein the Donor Acceptor (DA) Unit comprises an optionally substituted amide functional group or bioisostere thereof. 
     
     
         34 . (canceled) 
     
     
         35 . The Drug Linker compound of  claim 31 , wherein the 6-membered nitrogen-containing heteroaromatic ring system of H N  is that of pyridine with optional cyclization of DA back to the pyridine aromatic ring system through an introduced aromatic oxygen, sulfur or an optionally substituted nitrogen atom so that H N  contains a 6-5 fused aromatic ring system. 
     
     
         36 . The Drug Linker compound of  claim 31 , wherein each of the NAMPT homodimers of the enzymatically competent NAMPT homodimer has the amino acid sequence of SEQID 1. 
     
     
         37 . The Drug Linker compound of  claim 31 , wherein the NAMPT Head Unit has the structure of: 
       
         
           
           
               
               
           
         
         or a salt thereof, 
         in particular, having the structure of: 
       
       
         
           
           
               
               
           
         
         or a salt thereof, wherein 
         R 1  is hydrogen, —NH 2  or chloro; 
         R 2  is fluoro; 
         R 3  is hydrogen or —NH 2 ; 
         R 4  is hydrogen or optionally substituted C 1 -C 4  alkyl; and 
         the wavy line indicates the site of covalent attachment to DA and an adjacent aromatic carbon atom thereto is the site of said optional cyclization by DA to H N . 
       
     
     
         38 . The Drug Linker compound of  claim 31 , wherein the Donor-Acceptor Unit has the structure of: 
       
         
           
           
               
               
           
         
         in particular, having the structure of: 
       
       
         
           
           
               
               
           
         
         wherein R 4  is hydrogen or optionally substituted C 1 -C 4  alkyl; 
         DA is optionally cyclized to H N , wherein said cyclization is to the sp 2  carbon atom proximal to the carbonyl carbon (as indicated) through an introduced optionally substituted non-aromatic carbon atom or an optionally substituted aromatic heteroatom; 
         the wavy line indicates the site of covalent attachment to H N , and the carbon atom adjacent thereto is the site of said optional cyclization by DA; and 
         the pound sign (#) indicates the site of covalent attachment to I N , or 
         wherein the Donor-Acceptor Unit has the structure of: 
       
       
         
           
           
               
               
           
         
         or a salt thereof, 
         in particular, having the structure of: 
       
       
         
           
           
               
               
           
         
         or a salt thereof, wherein 
         X D  is O, S or NR S, wherein the nitrogen atom is optionally protonated and R D  is hydrogen or optionally substituted C 1 -C 4  alkyl; 
         each R 4  is independently selected from the group consisting of hydrogen and optionally substituted C 1 -C 4  alkyl, or both R 4  together with the nitrogen atoms to which they are attached and the intervening carbon atom(s) define an optionally substituted C 5 -C 6  heterocyclo; 
         the pound sign (#) indicates the site of covalent attachment to I N ; and the wavy line indicates the site of covalent attachment to H N , 
         wherein DA is optionally cyclized back to an adjacent aromatic carbon atom of H N , wherein said cyclization is from the indicated nitrogen atom so that R 4  bonded thereto is replaced by a covalent bond to said adjacent aromatic carbon atom, or is from X D  when X D  is —NR S, either directly or through an introduced —S(═O) 0-2  moiety, in which either instance R D  is replaced by a bond to said adjacent carbon atom or the sulfur atom of said introduced moiety. 
       
     
     
         39 . The Drug Linker compound of  claim 31 , wherein H N -DA- has the structure of: 
       
         
           
           
               
               
           
         
         or a salt thereof, wherein 
         R 4  is hydrogen or optionally substituted C 1 -C 4  alkyl; and 
         the wavy line indicates the site of covalent attachment to I N , and 
         wherein the sp 2  carbon atom proximal to the carbonyl carbon atom is the site (as indicated) of optional cyclization to H N  through an introduced optionally substituted non-aromatic carbon atom or an optionally substituted aromatic heteroatom. 
       
     
     
         40 . The Drug Linker compound of  claim 31 , wherein the NAMPT Tail Unit is or comprises an optionally substituted amino alcohol moiety,
 wherein the oxygen atom of the alcohol is the site of covalent attachment to L 0  or L R , depending on the presence or absence of L 0 , respectively,   in particular having the structure of.   
       
         
           
           
               
               
           
         
         or a pharmaceutically acceptable salt thereof, wherein 
         R 4  is hydrogen or optionally substituted C 1 -C 4  alkyl; 
         the wavy line indicates the site of covalent attachment to I N ; and 
         the pound sign (#) indicates the site of covalent to L 0  or L R , depending on the presence or absence of L 0 , respectively, or 
         wherein the Tail Unit is or comprises an optionally substituted benzamide moiety having a functional group providing a heteroatom that is the site of covalent attachment to L 0  or L R , depending on the presence or absence of L 0 , respectively, 
         in particular, having the structure of: 
       
       
         
           
           
               
               
           
         
         wherein X b  is —S— —O— or —NH—, optionally substituted; and 
         R 4  is hydrogen or optionally substituted C 1 -C 4  alkyl, wherein 
         the benzamide moiety is optionally cyclized to I N , wherein the amide nitrogen atom of the benzamide moiety is the site of said cyclization so that R 4  is replaced by a covalent bond to I N , 
         more particularly, having the structure of: 
       
       
         
           
           
               
               
           
         
         wherein the wavy line indicates the site of covalent attachment to I N ; 
         the pound sign (#) indicates the site of covalent attachment to L 0  or L R , depending on the presence or absence of L 0 , respectively. 
       
     
     
         41 . The Drug Linker compound of  claim 40 , wherein I N  is —CH 2 —(CH 2 ) 3-7 —CH 2 —, —CH 2 —(CH 2 ) 3-7 —CH 2 —O—, —CH 2 —(CH 2 ) 3-7 —C(═O)—, —CH 2 —(CH 2 ) 3-7 —S(═O) 2 — or —CH 2 —(CH 2 ) 3-7 — S(═O)—. 
     
     
         42 . The Drug Linker compound of  claim 31 , wherein —I N -T N - has the structure of: 
       
         
           
           
               
               
           
         
         wherein X b  is —NH—, —O— or —S—; 
         the wavy line indicates the site of covalent attachment to DA; and 
         the pound sign (#) indicates the site of covalent attachment to L 0  or L R , depending on the presence or absence of L 0 , respectively. 
       
     
     
         43 . The Drug Linker compound of  claim 31 , wherein the NAMPT Drug Unit has the structure of: 
       
         
           
           
               
               
           
         
         or a salt thereof, wherein 
         the pound sign (#) indicates the site of covalent attachment to L 0  or L R , depending on the presence or absence of L 0 , respectively. 
       
     
     
         44 . The Drug Linker compound of  claim 31 , wherein the Drug Linker compound is represented by the structure of: 
       
         
           
           
               
               
           
         
         or a salt thereof, wherein 
         R 6  is hydrogen or an optionally substituted C 1 -C 6  alkyl, which in Formula 2 is bonded to the saturated carbon atom adjacent to the carbon substituted by L-S—; 
         A o  is a second optional Stretcher Unit; 
         BU is a Basic Unit and R is an optionally substituted C 1 -C 12  alkyl group; and 
         the dotted curved line indicates optional cyclization so that in the absence of said cyclization BU is an acyclic Basic Unit or in the presence of said cyclization BU is a cyclized Basic Unit in which Rat and BU together with the carbon atom to which both are attached, define an optionally substituted spiro C 3 -C 20  heterocycle containing a skeletal basic nitrogen atom of a secondary or tertiary amine functional group as the basic function group of the cyclic Basic Unit, 
         wherein the basic nitrogen atom of the acyclic Basic Unit or cyclic Basic Unit is optionally suitably protected by a nitrogen protecting group, dependent on the degree of substitution of the basic nitrogen atom, or is optionally protonated, 
         in particular, having the structure of: 
       
       
         
           
           
               
               
           
         
         wherein [HE] as A o  is an optional Hydrolysis Enhancing Unit; 
         subscript w is 1; 
         W is Peptide Cleavable Unit; and 
         the remaining variable groups retain their previous meanings 
         wherein protease action on the Peptide Cleavable Unit resulting in cleavage of the W-J′ bond within the Drug Linker compound, or from the drug linker moiety of the Ligand Drug Conjugate compound or N-acetyl-cysteine (NAC) conjugate prepared from the Drug Linker compound initiates release of the NAMPT Drug Unit as NAMPTi compound or derivative thereof from that Ligand Drug Conjugate compound 
       
     
     
         45 .- 47 . (canceled) 
     
     
         48 . The Drug Linker compound of  claim 44 ,
 wherein W is a Peptide Cleavable Unit for which the Drug Linker compound is represented by the structure of:   
       
         
           
           
               
               
           
         
         or a salt thereof, wherein 
         R′ is hydrogen or —OC 1 -C 6  alkyl or other electron donating group; and 
         R a2  is hydrogen or C 1 -C 6  alkyl, optionally cyclized to BU, as indicated by the dotted curved line, 
         BU has the structure of —[C(R a1 )(R a1 )]—[c(R a1 )(R a1 )] 0-3 —N(R a3 )(R a3 ), 
         wherein in the absence of cyclization to R a2 , each R a1  independently is hydrogen or C 1 -C 4  alkyl, C 6 -C 10  aryl, C 5 -C 10  heteroaryl, (C 6 -C 10  aryl)-C 1 -C 4  alkyl-, or (C 5 -C 10  heteroaryl)-C 1 -C 4  alkyl-, optionally substituted, or two R a1  together with the carbon(s) to which they are attached and any intervening carbons define an optionally substituted C 3 -C 6  cycloalkyl; and 
         R a3  independently are hydrogen, optionally substituted C 1 -C 6  alkyl or R a3  together with the nitrogen atom to which both are attached define a C 3 -C 6  heterocyclyl in which the basic nitrogen atom is a skeletal atom, 
         or one of R a3  is —H and the other is optionally substituted C 1 -C 6  alkyl, optionally substituted —C 1 -C 4  alkylene-(C 6 -C 10  aryl), or -R PEG1 —O—(CH 2 CH 2 O) 1-36 -R PEG2 , wherein R PEG1  is C 1 -C 4  alkylene, and R PEG2  is —H or C 1 -C 4  alkyl; and 
         the basic nitrogen atom bonded to R a3  is optionally protonated; and 
         in the presence of cyclization one of R a1  or one of R a3  is replaced with a bond to a carbon atom of R a2  in which R a2  is C 1 -C 6  alkyl and the remaining R a1  and R a3  are as previously defined; and 
         wherein Y′ is —X a —, —O—C(═O)—X b — or —OC(═O)NH—CH 2 —X a —, 
         wherein X a  or X b  are from T N , wherein —X a — is O or S and X b  is —NH—; 
         V, Z 1 , and Z 2  are independently ═N— or ═C(R 24 )—, wherein each R 24  is independently selected from the group consisting of hydrogen and C 1 -C 12  alkyl, C 2 -C 12  alkenyl and C 2 -C 12  alkynyl, optionally substituted, and halogen; 
         wherein protease action on the Peptide Cleavable Unit cleaves the W—NH bond, wherein said cleavage within a drug linker moiety of a Ligand Drug Conjugate compound initiates release of the NAMPT Drug Unit as a NAMPTi compound or derivative thereof from that Ligand Drug Conjugate compound, 
         in particular by the structure of: 
       
       
         
           
           
               
               
           
         
         or a salt thereof, more particularly by the structure of: 
       
       
         
           
           
               
               
           
         
         or a salt thereof, or particular by the structure of: 
       
       
         
           
           
               
               
           
         
         or a salt thereof; and wherein and wherein the variable groups are as previously defined. 
       
     
     
         49 . The Drug Linker compound of  claim 44  wherein W comprises a dipeptide wherein the dipeptide provides for a recognition site for a regulatory or lysosomal protease for cleavage by said protease of the W-J′ bond or the W—NH bond when J′ is —NH within the Drug Linker compound or the drug linker moiety of the Ligand Drug Conjugate compound or N-acetyl-cysteine (NAC) conjugate prepared from the Drug Linker compound so as to initiate release of the NAMPT Drug Unit as NAMPTi compound or derivative from that Drug Linker compound, drug linker moiety or NAC conjugate. 
     
     
         50 . The Drug Linker compound of  claim 49 , wherein the W has the structure of: 
       
         
           
           
               
               
           
         
         wherein R 34  is benzyl, methyl, isopropyl, isobutyl, sec-butyl, —CH(OH)CH 3  or has the structure of 
       
       
         
           
           
               
               
           
         
       
       wherein the asterisk indicates the site of covalent attachment to the dipeptide backbone; and
 R 35  is methyl, —(CH 2 ) 4 —NH 2 , —(CH 2 ) 3 NH(C═O)NH 2 , —(CH 2 ) 3 NH(C═NH)NH 2 , or, —(CH 2 ) 2 CO 2 H; and 
 wherein the wavy lines indicate the points of covalent attachment of the dipeptide into the structure representing the Ligand-Drug Conjugate compound, 
 in particular W is selected from the group consisting of -Phe-Lys-, -Val-Ala-, -Val-Lys-, -Ala-Lys-, -Val-Cit-, -Phe-Cit-, -Leu-Cit-, -Ile-Cit-, -Phe-Arg-, and -Trp-Cit-, wherein Cit is citrulline. 
 
     
     
         51 . (canceled) 
     
     
         52 . The Drug Linker compound of  claim 31 , wherein A or a subunit thereof has the structure of formula (3) or formula (4): 
       
         
           
           
               
               
           
         
         wherein the wavy lines indicated covalent attachment within the compound structure; 
         wherein K and L′ independently are C, N, O or S, provided that when K or L′ is O or S, R 41  and R 42  to K or R 43  and R 44  to L′ are absent, and when K or L′ are N, one of R 41 , R 42  to K or one of R 42 , R 43  to L′ are absent, and provided that no two adjacent L′ are independently selected as N, O, or S; 
         wherein subscripts e and f are independently selected integers that range from 0 to 12, and subscript g is an integer ranging from 1 to 12; 
         wherein G is hydrogen, optionally substituted C 1 -C 6  alkyl, —OH, —OR PR , —CO 2 H, CO 2 R PR , wherein R PR  is a suitable protecting, or 
         G is —N(R PR )(R PR ), wherein R PR  are independently a protecting group or R PR  together form a suitable protecting group, or 
         G is —N(R 45 )(R 46 ), wherein one of R 45 , R 46  is hydrogen or R PR , wherein R PR  is a suitable protecting group, and the other is hydrogen or optionally substituted C 1 -C 6  alkyl; 
         wherein R 38  is hydrogen or optionally substituted C 1 -C 6  alkyl; 
         R 39 -R 44  are independently selected from the group consisting of hydrogen, optionally substituted C 1 -C 6  alkyl, optionally substituted aryl, and optionally substituted heteroaryl, 
         or R 39 , R 40  together with the carbon atom to which both are attached, or R 41 , R 42  together with K to which both are attached when K is a carbon atom, define a C 3 -C 6  carbocyclo, and R 41 -R 44  are as defined herein, 
         or R 43 , R 44  together with L′ to which both are attached when L′ is a carbon atom define a C 3 -C 6  carbocyclo, and R 39 -R 42  are as defined herein, 
         or R 40  and R 41 , or R 40  and R 43 , or R 41  and R 43  to together with the carbon atom or heteroatom to which both are attached and the atoms intervening between those carbon atoms and/or heteroatoms define a C 5 -C 6  carbocyclo or a C 5 -C 6  heterocyclo, and R 39 , R 44  and the remainder of R 40 -R 43  are as defined herein, 
         provided that when K is O or S, R 41  and R 42  are absent, and when K is N, one of R 41 , R 42 , is absent, and when L′ is O or S, R 43  and R 44  are absent, and when L′ is N, one of R 43 , R 44  is absent, or 
         A or a subunit thereof is an alpha-amino, beta-amino or another amine-containing acid residue, 
         in particular, wherein formula (3) or formula (4) has the structure of formula (3a) or formula (4a): 
       
       
         
           
           
               
               
           
         
         wherein subscript e and f are independently 0 or 1. 
       
     
     
         53 . (canceled) 
     
     
         54 . A method of preparing a Ligand Drug Conjugate compound or compound of  claim 1 , the method comprising the step of: contacting a Drug Linker compound of  claim 31  with a targeting agent having a reactive function group capable of interacting with the reactive functional group of the primary linker of the Drug Linker compound so as to form a covalent bond to between the Ligand Unit corresponding to the targeting agent and the primary linker of the Ligand Drug Conjugate corresponding in structure to the the primary linker of the Drug Linker compound. 
     
     
         55 . The method of  claim 54 , wherein the reactive functional group of the targeting agent is a cysteine thiol of an antibody, either native to the antibody through interchain disulfide bond reduction or introduced by genetic engineering into the antibody and the reactive functional group of the primary linker of the Ligand Drug Conjugate is a maleimide (M 1 ) moiety comprising the Stretcher Unit of that primary linker, whereby said contacting of said reactive functional groups provides the Ligand Drug Conjugate compound or compound of  claim 1  in which L is an antibody Ligand Unit.