Prodrug comprising a drug linker conjugate

The present invention relates to a prodrug or a pharmaceutically acceptable salt thereof comprising a drug linker conjugate D-L. The invention also relates to pharmaceutical compositions comprising said prodrugs and their use as medicaments.

To enhance physicochemical or pharmacokinetic properties of a drug in vivo such drug can be conjugated with a carrier.

Typically, carriers in drug delivery are either used in a non-covalent fashion, with the drug physicochemically formulated into a solvent-carrier mixture, or by covalent attachment of a carrier reagent to one of the drug's functional groups.

However the non-covalent approach requires a highly efficient drug encapsulation to prevent uncontrolled, burst-type release of the drug. Restraining the diffusion of an unbound, water soluble drug molecule requires strong van der Waals contacts, frequently mediated through hydrophobic moieties. Many conformationally sensitive drugs, such as proteins or peptides, are rendered dysfunctional during the encapsulation process and/or during subsequent storage of the encapsulated drug. In addition, such amino-containing drugs readily undergo side reactions with carrier degradation products (see, for example, D. H. Lee et al., J. Contr. Rel., 2003, 92, 291-299). Furthermore, dependence of the release mechanism of the drug upon biodegradation may cause interpatient variability.

Alternatively, the drugs may be conjugated to a carrier through covalent bonds. This approach is applied to various classes of molecules, from so-called small molecules, through natural products up to larger proteins. Covalent drug carrier conjugates can be divided into two groups. Firstly, conjugates, where the covalent bond between carrier and drug is mostly present during the action of the drug (“permanent covalent bond”), i.e. a derivative of the drug exhibits its pharmacological effects as it is known for the drug as such. Secondly, the covalent bond is mostly previously cleaved to release the drug as such, which can exhibit its known pharmacological effects. In the latter case the covalent drug carrier conjugate is called carrier linked prodrug or carrier prodrug.

In order to ensure cleavage of the covalent bond between carrier and drug easy removal of said bond in vivo is required to release the drug (prodrug activation).

Prodrug activation may occur by enzymatic or non-enzymatic cleavage of the bond between the carrier and the drug molecule, or a sequential combination of both, i.e. an enzymatic step followed by a non-enzymatic rearrangement.

Enzymatically induced prodrug activation is characterized in that the cleavage in enzyme-free in-vitro environment such as an aqueous buffer solution, of, e.g., an ester or amide may occur, but the corresponding rate of hydrolysis may be much too slow and not therapeutically useful. In an in-vivo environment, esterases or amidases are typically present and the esterases and amidases may cause significant catalytic acceleration of the kinetics of hydrolysis from twofold up to several orders of magnitude. Therefore, the cleavage is predominantly controlled by the enzymatic reaction.

A major drawback of predominantly enzymatic cleavage is interpatient variability. Enzyme levels may differ significantly between individuals resulting in biological variation of prodrug activation by the enzymatic cleavage. The enzyme levels may also vary depending on the site of administration. For instance it is known that in the case of subcutaneous injection, certain areas of the body yield more predictable therapeutic effects than others. To reduce this unpredictable effect, non-enzymatic cleavage or intramolecular catalysis is of particular interest.

Therefore, enzyme-independent autocatalytic cleavage of carrier and biologically active moiety is preferred. In most cases this is achieved by an appropriately designed linker moiety between the carrier and the biologically active moiety, which is directly attached to the functional group of a biologically active moiety via covalent bond.

Specific linker types are known in the art.

Y. Sohma et al., J. Med. Chem. 46 (2003), 4124-4135 describe ester based prodrugs, where the carrier is water-soluble and the biologically active moiety is derived from HIV-1 protease inhibitor KNI-727. The linker used is attached to the biologically active moiety via ester group. The mechanism of this prodrug system is cyclization-activation by cyclic imide formation for the cleavage of ester bonds.

However this is disadvantageous because of the instability of the ester functional group. Furthermore, ester groups may be less chemoselectively addressable for the conjugation of the carrier or linker and the drug.

A. J. Garman et al. (A. J. Garman, S. B. Kalindjan, FEBS Lett. 1987, 223 (2), 361-365 1987) use PEG5000-maleic anhydride for the reversible modification of amino groups in tissue-type plasminogen activator and urokinase. Regeneration of functional enzyme from PEG-uPA conjugate upon incubation at pH 7.4 buffer by cleavage of the maleamic acid linkage follows first order kinetics with a half-life of 6.1 h. A disadvantage of the maleamic acid linkage is the lack of stability of the conjugate at lower pH values. This limits the applicability of the maleamic acid linkage to biologically active agents which are stable at basic (high) pH values, as purification of the biologically active agent polymer conjugate has to be performed under basic (high pH) conditions to prevent premature prodrug cleavage.

In WO-A 2004/108070 prodrug system based on N,N-bis-(2-hydroxyethyl)glycine amide (bicine) linker is described. In this system two PEG carrier molecules are linked to a bicine molecule coupled to an amino group of the drug molecule. The first two steps in prodrug activation is the enzymatic cleavage of the first linkages connecting both PEG carrier molecules with the hydroxy groups of the bicine activating group. Different linkages between PEG and bicine are described resulting in different prodrug activation kinetics. The second step in prodrug activation is the cleavage of the second linkage connecting the bicine activating group to the amino group of the drug molecule. The main disadvantage of this system is the connection of the polymer to the bicine linker resulting in a slow hydrolysis rate of this second bicine amide linkage (t1/2>3 h in phosphate buffer). Consequently the release of a bicine-modified prodrug intermediate may show different pharmacokinetic, immunogenic, toxicological and pharmacodynamic properties as compared to the parent native drug molecule.

Another bicine-based system is described in WO-A 2006/136586.

Accordingly, there is a need for alternative carrier-linked prodrugs, where the linker allows an autocatalytic cleavage to release a drug in an unmodified form without remaining residues originating from the linker.

FIG. 1 shows an example of the cleavage resulting in a cyclic imide.

FIGS. 2A-2G , collectively referred to as FIG. 2 , depict further details concerning compound numerals, starting materials, synthesis method, molecular weight (MW), and MS data.

FIG. 3 shows in vivo and in vitro linker cleavage data of 13 b , wherein in vivo (triangles) and in vitro (diamonds) cleavage kinetics are shown by semilogarithmic representation.

Thus, an object of the present invention is to provide such drug linker conjugates, where the linker is covalently attached via a cleavable bond to a biologically active moiety (representing the drug after release), and where the linker is further covalently attached via a permanent bond to a carrier directly or via a spacer to form the carrier-linked prodrug.

This object is achieved by a prodrug or a pharmaceutically acceptable salt thereof comprising a drug linker conjugate D-L, wherein

-D is a nitrogen containing biologically active moiety; and -L is a non-biologically active linker moiety -L 1 represented by formula (I),

wherein the dashed line indicates the attachment to the nitrogen of the biologically active moiety by forming an amide bond;

X is C(R 4 R 4a ); N(R 4 ); O; C(R 4 R 4a )—C(R 5 R 5a ); C(R 5 R 5a )—C(R 4 R 4a ); C(R 4 R 4a )—N(R 6 ); N(R 6 )—C(R 4 R 4a ); C(R 4 R 4a )—O; or O—C(R 4 R 4a ); X 1 is C; or S(O); X 2 is C(R 7 , R 7a ); or C(R 7 , R 7a )—C(R 8 , R 8a ); X 3 is O; S; or N—CN; R 1 , R 1a , R 2 , R 2a , R 3 , R 3a , R 4 , R 4a , R 5 , R 5a , R 6 , R 7 , R 7a , R 8 , R 8a are independently selected from the group consisting of H; and C 1-4 alkyl; Optionally, one or more of the pairs R 1a /R 4a , R 1a /R 5a , R 4a /R 5a , R 7a /R 8a form a chemical bond; Optionally, one or more of the pairs R 1 /R 1a , R 2 /R 2a , R 4 /R 4a , RS/R 5a , R 7 /R 7a , R 8 /R 8a are joined together with the atom to which they are attached to form a C 3-7 cycloalkyl; or 4 to 7 membered heterocyclyl; Optionally, R 4 /R 6 are joined together with the atoms to which they are attached to form a saturated 4 to 7 membered heterocyclyl; Optionally, one or more of the pairs R 1 /R 4 , R 1 /R 5 , R 1 /R 6 , R 4 /R 5 , R 4 /R 6 , R 7 /R 8 , R 2 /R 3 are joined together with the atoms to which they are attached to form a ring A; Optionally, R 3 /R 3a are joined together with the nitrogen atom to which they are attached to form a 4 to 7 membered heterocycle; A is selected from the group consisting of phenyl; naphthyl; indenyl; indanyl; tetralinyl; C 3-10 cycloalkyl; 4 to 7 membered heterocyclyl; and 9 to 11 membered heterobicyclyl; and wherein L 1 is substituted with one to four groups L 2 -Z and optionally further substituted, provided that the hydrogen marked with the asterisk in formula (I) is not replaced by a substituent; wherein L 2 is a single chemical bond or a spacer; and Z is a carrier group.

It was surprisingly found, that the scope of cyclization-activation by cyclic imide formation can be extended from ester to even carrier-linked amide prodrugs, despite the much greater stability of the amide bond under aqueous conditions. It was observed that N,N′-biscarboxamides linked to a nucleophile carrying moiety through one amide bond and to the drug molecule through the second amide bond exhibit autohydrolysis in a range that is useful for prodrug applications. In addition, it was discovered that linkers can be designed that include a carrier permanently attached to the N,N′ biscarboxamide motif in such a fashion that cyclic imide formation can be employed as a self-activation principle in carrier-linked amide prodrug design.

Examples for such preferred cyclic cleavage products are substituted succinimide or glutarimide ring structures. Prerequisite for such cyclization activation is the presence of an amine-containing nucleophile in the linker structure and another amide bond which is not the amide prodrug bond but an amide bond substituted with a hydrogen atom.

In case of succinimide- or a glutarimide-activated prodrug cleavage, the amine-containing nucleophile serves as a neighbouring group to enhance the nucleophilicity of the nitrogen contained in the permanent amide bond which in turn attacks the prodrug amide carbonyl group and consequently induces intramolecular acylation of the permanent amide bond generating the cyclic imide ring.

Therefore preferred linker structures comprise a permanent linkage to a carrier, an amine-containing nucleophile, and a permanent amide bond with a hydrogen attached to the nitrogen of the amide bond. Corresponding carrier-linked prodrugs comprise a linker containing a permanent linkage to a carrier, an amine-containing nucleophile and said permanent amide bond, and a nitrogen containing biologically active moiety derived from the drug conjugated to the linker by means of a cleavable amide bond.

FIG. 1 shows an example of the cleavage resulting in a cyclic imide. The nitrogen of the biologically active moiety is shown as hydrogen containing amine, which results in a drug having a primary amine functional group. However also, e.g., a secondary amine may be part of the drug. For simplification reasons the one to four mandatory substituents L 2 -Z including the carrier are not shown.

Preferred properties of the prodrug are given by a half-life of hydrolysis in aqueous buffer at pH 7.4 and 37° C. between 1 h and 3 months; similar rates of hydrolysis under physiological conditions in buffer and plasma.

The prodrug according to the present invention may show excellent in vivo/in vitro correlation of linker cleavage, a high degree of enzyme independence and can be stored at lower pH (pH dependent cleavage).

Within the meaning of the present invention the terms are used as follows.

“Biologically active moiety D” means the part of the drug linker conjugate, which results after cleavage in a drug D-H of known biological activity.

“Non-active linker” means a linker which does not show the pharmacological effects of the drug derived from the biologically active agent.

“Alkyl” means a straight-chain or branched carbon chain. Each hydrogen of an alkyl carbon may be replaced by a substituent.

“C 1-4 alkyl” means an alkyl chain having 1-4 carbon atoms, e.g. if present at the end of a molecule: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl tert-butyl, or e.g. —CH 2 —, —CH 2 —CH 2 —, —CH(CH 3 )—, —CH 2 —CH 2 —CH 2 —, —CH(C 2 H 5 )—, —C(CH 3 ) 2 —, when two moieties of a molecule are linked by the alkyl group. Each hydrogen of a C 1-4 alkyl carbon may be replaced by a substituent.

“C 1-6 alkyl” means an alkyl chain having 1-6 carbon atoms, e.g. if present at the end of a molecule: C 1-4 alkyl, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl; tert-butyl, n-pentyl, n-hexyl, or e.g. —CH 2 —, —CH 2 —CH 2 —, —CH(CH 3 )—, —CH 2 —CH 2 —CH 2 —, —CH(C 2 H 5 )—, —C(CH 3 ) 2 —, when two moieties of a molecule are linked by the alkyl group. Each hydrogen of a C 1-6 alkyl carbon may be replaced by a substituent.

Accordingly, “C 1-18 alkyl” means an alkyl chain having 1 to 18 carbon atoms and “C 8-18 alkyl” means an alkyl chain having 8 to 18 carbon atoms. Accordingly, “C 1-50 alkyl” means an alkyl chain having 1 to 50 carbon atoms.

“C 2-50 alkenyl” means a branched or unbranched alkenyl chain having 2 to 50 carbon atoms, e.g. if present at the end of a molecule: —CH═CH 2 , —CH═CH—CH 3 , —CH 2 —CH═CH 2 , —CH═CH—CH 2 —CH 3 , —CH═CH—CH═CH 2 , or e.g. —CH═CH—, when two moieties of a molecule are linked by the alkenyl group. Each hydrogen of a C 2-50 alkenyl carbon may be replaced by a substituent as further specified. Accordingly, the term “alkenyl” relates to a carbon chain with at least one carbon carbon double bond. Optionally, one or more triple bonds may occur.

“C 2-50 alkynyl” means a branched or unbranched alkynyl chain having 2 to 50 carbon atoms, e.g. if present at the end of a molecule: —C≡CH, —CH 2 —C≡CH, CH 2 —CH 2 —C≡CH, CH 2 —C≡C—CH 3 , or e.g. —C≡C— when two moieties of a molecule are linked by the alkynyl group. Each hydrogen of a C 2-50 alkynyl carbon may be replaced by a substituent as further specified. Accordingly, the term “alkynyl” relates to a carbon chain with at lest one carbon carbon triple bond. Optionally, one or more double bonds may occur.

“C 3-7 cycloalkyl” or “C 3-7 cycloalkyl ring” means a cyclic alkyl chain having 3 to 7 carbon atoms, which may have carbon-carbon double bonds being at least partially saturated, e.g. cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclohexenyl, cycloheptyl. Each hydrogen of a cycloalkyl carbon may be replaced by a substituent. The term “C 3-7 cycloalkyl” or “C 3-7 cycloalkyl ring” also includes bridged bicycles like norbonane or norbonene. Accordingly, “C 3-5 cycloalkyl” means a cycloalkyl having 3 to 5 carbon atoms.

Accordingly, “C 3-10 cycloalkyl” means a cyclic alkyl having 3 to 10 carbon atoms, e.g. C 3-7 cycloalkyl; cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cyclohexenyl, cycloheptyl, cyclooctyl, cyclononyl, cyclodecyl. The term “C 3-10 cycloalkyl” also includes at least partially saturated carbomono- and -bicycles.

“Halogen” means fluoro, chloro, bromo or iodo. It is generally preferred that halogen is fluoro or chloro.

“4 to 7 membered heterocyclyl” or “4 to 7 membered heterocycle” means a ring with 4, 5, 6 or 7 ring atoms that may contain up to the maximum number of double bonds (aromatic or non-aromatic ring which is fully, partially or un-saturated) wherein at least one ring atom up to 4 ring atoms are replaced by a heteroatom selected from the group consisting of sulfur (including —S(O)—, —S(O) 2 —), oxygen and nitrogen (including ═N(O)—) and wherein the ring is linked to the rest of the molecule via a carbon or nitrogen atom. Examples for a 4 to 7 membered heterocycles are azetidine, oxetane, thietane, furan, thiophene, pyrrole, pyrroline, imidazole, imidazoline, pyrazole, pyrazoline, oxazole, oxazoline, isoxazole, isoxazoline, thiazole, thiazoline, isothiazole, isothiazoline, thiadiazole, thiadiazoline, tetrahydrofuran, tetrahydrothiophene, pyrrolidine, imidazolidine, pyrazolidine, oxazolidine, isoxazolidine, thiazolidine, isothiazolidine, thiadiazolidine, sulfolane, pyran, dihydropyran, tetrahydropyran, imidazolidine, pyridine, pyridazine, pyrazine, pyrimidine, piperazine, piperidine, morpholine, tetrazole, triazole, triazolidine, tetrazolidine, diazepane, azepine or homopiperazine.

“9 to 11 membered heterobicyclyl” or “9 to 11 membered heterobicycle” means a heterocyclic system of two rings with 9 to 11 ring atoms, where at least one ring atom is shared by both rings and that may contain up to the maximum number of double bonds (aromatic or non-aromatic ring which is fully, partially or un-saturated) wherein at least one ring atom up to 6 ring atoms are replaced by a heteroatom selected from the group consisting of sulfur (including —S(O)—, —S(O) 2 —), oxygen and nitrogen (including ═N(O)—) and wherein the ring is linked to the rest of the molecule via a carbon or nitrogen atom. Examples for a 9 to 11 membered heterobicycle are indole, indoline, benzofuran, benzothiophene, benzoxazole, benzisoxazole, benzothiazole, benzisothiazole, benzimidazole, benzimidazoline, quinoline, quinazoline, dihydroquinazoline, quinoline, dihydroquinoline, tetrahydroquinoline, decahydroquinoline, isoquinoline, decahydroisoquinoline, tetrahydroisoquinoline, dihydroisoquinoline, benzazepine, purine or pteridine. The term 9 to 11 membered heterobicycle also includes spiro structures of two rings like 1,4-dioxa-8-azaspiro[4.5]decane or bridged heterocycles like 8-aza-bicyclo[3.2.1]octane.

In case the compounds according to formula (I) contain one or more acidic or basic groups, the invention also comprises their corresponding pharmaceutically or toxicologically acceptable salts, in particular their pharmaceutically utilizable salts. Thus, the compounds of the formula (I) which contain acidic groups can be used according to the invention, for example, as alkali metal salts, alkaline earth metal salts or as ammonium salts. More precise examples of such salts include sodium salts, potassium salts, calcium salts, magnesium salts or salts with ammonia or organic amines such as, for example, ethylamine, ethanolamine, triethanolamine or amino acids. Compounds of the formula (I) which contain one or more basic groups, i.e. groups which can be protonated, can be present and can be used according to the invention in the form of their addition salts with inorganic or organic acids. Examples for suitable acids include hydrogen chloride, hydrogen bromide, phosphoric acid, sulfuric acid, nitric acid, methanesulfonic acid, p-toluenesulfonic acid, naphthalenedisulfonic acids, oxalic acid, acetic acid, tartaric acid, lactic acid, salicylic acid, benzoic acid, formic acid, propionic acid, pivalic acid, diethylacetic acid, malonic acid, succinic acid, pimelic acid, fumaric acid, maleic acid, malic acid, sulfaminic acid, phenylpropionic acid, gluconic acid, ascorbic acid, isonicotinic acid, citric acid, adipic acid, and other acids known to the person skilled in the art. If the compounds of the formula (I) simultaneously contain acidic and basic groups in the molecule, the invention also includes, in addition to the salt forms mentioned, inner salts or betaines (zwitterions). The respective salts according to the formula (I) can be obtained by customary methods which are known to the person skilled in the art like, for example by contacting these with an organic or inorganic acid or base in a solvent or dispersant, or by anion exchange or cation exchange with other salts. The present invention also includes all salts of the compounds of the formula (I) which, owing to low physiological compatibility, are not directly suitable for use in pharmaceuticals but which can be used, for example, as intermediates for chemical reactions or for the preparation of pharmaceutically acceptable salts.

The term “pharmaceutically acceptable” means approved by a regulatory agency such as the EMEA (Europe) and/or the FDA (US) and/or any other national regulatory agency for use in animals, preferably in humans.

“Pharmaceutical composition” means one or more active ingredients, and one or more inert ingredients, as well as any product which results, directly or indirectly, from combination, complexation or aggregation of any two or more of the ingredients, or from dissociation of one or more of the ingredients, or from other types of reactions or interactions of one or more of the ingredients. Accordingly, the pharmaceutical compositions of the present invention encompass any composition made by admixing a compound of the present invention and a pharmaceutically acceptable excipient (pharmaceutically acceptable carrier).

The term “excipient” refers to a diluent, adjuvant, or vehicle with which the therapeutic is administered. Such pharmaceutical excipient can be sterile liquids, such as water and oils, including those of petroleum, animal, vegetable or synthetic origin, including but not limited to peanut oil, soybean oil, mineral oil, sesame oil and the like. Water is a preferred excipient when the pharmaceutical composition is administered orally. Saline and aqueous dextrose are preferred excipients when the pharmaceutical composition is administered intravenously. Saline solutions and aqueous dextrose and glycerol solutions are preferably employed as liquid excipients for injectable solutions. Suitable pharmaceutical excipients include starch, glucose, lactose, sucrose, gelatin, malt, rice, flour, chalk, silica gel, sodium stearate, glycerol monostearate, talc, sodium chloride, dried skim milk, glycerol, propylene, glycol, water, ethanol and the like. The composition, if desired, can also contain minor amounts of wetting or emulsifying agents, or pH buffering agents. These compositions can take the form of solutions, suspensions, emulsions, tablets, pills, capsules, powders, sustained-release formulations and the like. The composition can be formulated as a suppository, with traditional binders and excipients such as triglycerides. Oral formulation can include standard excipients such as pharmaceutical grades of mannitol, lactose, starch, magnesium stearate, sodium saccharine, cellulose, magnesium carbonate, etc. Examples of suitable pharmaceutical excipients are described in “Remington's Pharmaceutical Sciences” by E. W. Martin. Such compositions will contain a therapeutically effective amount of the therapeutic, preferably in purified form, together with a suitable amount of excipient so as to provide the form for proper administration to the patient. The formulation should suit the mode of administration.

Preferably, X 3 is O.

Preferably, X is N(R 4 ), X 1 is C and X 3 is O.

Preferably, X 2 is C(R 7 R 7a ).

Preferably, L 1 is selected from the group consisting of

wherein R is H; or C 1-4 alkyl; Y is NH; O; or S; and R 1 , R 1a , R 2 , R 2a , R 3 , R 3a , R 4 , X, X 1 , X 2 have the meaning as indicated above.

Even more preferred, L 1 is selected from the group consisting of

wherein R has the meaning as indicated above.

At least one (up to four) hydrogen is replaced by a group L 2 -Z. In case more than one group L 2 -Z is present each L 2 and each Z can be selected independently. Preferably, only one group L 2 -Z is present resulting in the formula D-L 1 -L 2 -Z.

In general, L 2 can be attached to L 1 at any position apart from the replacement of the hydrogen marked with an asterisk in formula (I). Preferably, one to four of the hydrogen given by R, R 1 to R 8 directly or as hydrogen of the C 1-4 alkyl or further groups and rings given by the definition of R and R 1 to R 8 are replaced by L 2 -Z.

Furthermore, L 1 may be optionally further substituted. In general, any substituent may be used as far as the cleavage principle is not affected.

Preferably, one or more further optional substituents are independently selected from the group consisting of halogen; CN; COOR S ; OR 9 ; C(O)R 9 ; C(O)N(R 9 R 9a ); S(O) 2 N(R 9 R 9a ); S(O)N(R 9 R 9a ); S(O) 2 R 9 ; S(O)R 9 ; N(R 9 )S(O) 2 N(R 9a R 9b ); SR 9 ; N(R 9 R 9a ); NO 2 ; OC(O)R 9 ; N(R 9 )C(O)R 9a ; N(R 9 )S(O) 2 R 9a ; N(R 9 )S(O)R 9a ; N(R 9 )C(O)OR 9a ; N(R 9 )C(O)N(R 9a R 9b ); OC(O)N(R 9 R 9a ); T; C 1-50 alkyl; C 2-50 alkenyl; or C 2-50 alkynyl, wherein T; C 1-50 alkyl; C 2-50 alkenyl; and C 2-50 alkynyl are optionally substituted with one or more R 10 , which are the same or different and wherein C 1-50 alkyl; C 2-50 alkenyl; and C 2-50 alkynyl are optionally interrupted by one or more groups selected from the group consisting of T, —C(O)O—; —O—; —C(O)—; —C(O)N(R 11 )—; —S(O) 2 N(R 11 )—; —S(O)N(R 11 )—; —S(O) 2 —; —S(O)—; —N(R 11 )S(O) 2 N(R 11a )—; —S—; —N(R 11 )—; —OC(O)R 11 ; —N(R 11 )C(O)—; —N(R 11 )S(O) 2 —; —N(R 11 )S(O)—; —N(R 11 )C(O)O—; —N(R 11 )C(O)N(R 11a )—; and —OC(O)N(R 11 R 11a );

R 9 , R 9a , R 9b are independently selected from the group consisting of H; T; and C 1-50 alkyl; C 2-50 alkenyl; or C 2-50 alkynyl, wherein T; C 1-50 alkyl; C 2-50 alkenyl; and C 2-50 alkynyl are optionally substituted with one or more R 10 , which are the same or different and wherein C 1-50 alkyl; C 2-50 alkenyl; and C 2-50 alkynyl are optionally interrupted by one or more groups selected from the group consisting of T, —C(O)O—; —O—; —C(O)—; —C(O)N(R 11 )—; —S(O) 2 N(R 11 )—; —S(O)N(R 11 )—; —S(O) 2 —; —S(O)—; —N(R 11 )S(O) 2 N(R 11a )—; —S—; —N(R 11 )—; —OC(O)R 11 ; —N(R 11 )C(O)—; —N(R 11 )S(O) 2 —; —N(R 11 )S(O)—; —N(R 11 )C(O)O—; —N(R 11 )C(O)N(R 11a )—; and —OC(O)N(R 11 R 11a ); T is selected from the group consisting of phenyl; naphthyl; indenyl; indanyl; tetralinyl; C 3-10 cycloalkyl; 4 to 7 membered heterocyclyl; or 9 to 11 membered heterobicyclyl, wherein T is optionally substituted with one or more R 10 , which are the same or different; R 10 is halogen; CN; oxo (═O); COOR 12 ; OR 12 ; C(O)R 12 ; C(O)N(R 12 R 12a ); S(O) 2 N(R 12 R 12a ); S(O)N(R 12 R 12a ); S(O) 2 R 12 ; S(O)R 12 ; N(R 12 )S(O) 2 N(R 12a R 12 ); SR 12 ; N(R 12 R 12a ); NO 2 ; OC(O)R 12 ; N(R 12 )C(O)R 12a ; N(R 12 )S(O) 2 R 12a ; N(R 12 )S(O)R 12a ; N(R 12 )C(O)OR 12a ; N(R 12 )C(O)N(R 12a R 12 ); OC(O)N(R 12 R 12a ); or C 1-6 alkyl, wherein C 1-6 alkyl is optionally substituted with one or more halogen, which are the same or different; R 11 , R 11a , R 12 , R 12a , R 12b are independently selected from the group consisting of H; or C 1-6 alkyl, wherein C 1-6 alkyl is optionally substituted with one or more halogen, which are the same or different.

The term “interrupted” means that between two carbons a group is inserted or at the end of the carbon chain between the carbon and hydrogen.

L 2 is a single chemical bond or a spacer. In case L 2 is a spacer, it is preferably defined as the one or more optional substituents defined above, provided that L 2 is substituted with Z.

Accordingly, when L 2 is other than a single chemical bond, L 2 -Z is COOR S ; OR 9 ; C(O)R 9 ; C(O)N(R 9 R 9a ); S(O) 2 N(R 9 R 9a ); S(O)N(R 9 R 9a ); S(O) 2 R 9 ; S(O)R 9 ; N(R 9 )S(O) 2 N(R 9a R 9b ); SR 9 ; N(R 9 R 9a ); OC(O)R 9 ; N(R 9 )C(O)R 9a ; N(R 9 )S(O) 2 R 9a ; N(R 9 )S(O)R 9a ; N(R 9 )C(O)OR 9a ; N(R 9 )C(O)N(R 9a R 9b ); OC(O)N(R 9 R 9a ); T; C 1-50 alkyl; C 2-50 alkenyl; or C 2-50 alkynyl, wherein T; C 1-50 alkyl; C 2-50 alkenyl; and C 2-50 alkynyl are optionally substituted with one or more R 10 , which are the same or different and wherein C 1-50 alkyl; C 2-50 alkenyl; and C 2-50 alkynyl are optionally interrupted by one or more groups selected from the group consisting of -T-, —C(O)O—; —O—; —C(O)—; —C(O)N(R 11 )—; —S(O) 2 N(R 11 )—; —S(O)N(R 11 )—; —S(O) 2 —; —S(O)—; —N(R 11 )S(O) 2 N(R 11a )—; —S—; —N(R 11 )—; —OC(O)R 11 ; —N(R 11 )C(O)—; —N(R 11 )S(O) 2 —; —N(R 11 )S(O)—; —N(R 11 )C(O)O—; —N(R 11 )C(O)N(R 11a )—; and —OC(O)N(R 11 R 11a );

R 9 , R 9a , R 9b are independently selected from the group consisting of H; Z; T; and C 1-50 alkyl; C 2-50 alkenyl; or C 2-50 alkynyl, wherein T; C 1-50 alkyl; C 2-50 alkenyl; and C 2-50 alkynyl are optionally substituted with one or more R 10 , which are the same or different and wherein C 1-so alkyl; C 2-50 alkenyl; and C 2-50 alkynyl are optionally interrupted by one or more groups selected from the group consisting of T, —C(O)O—; —O—; —C(O)—; —C(O)N(R 11 )—; —S(O) 2 N(R 11 )—; —S(O)N(R 11 )—; —S(O) 2 —; —S(O)—; —N(R 11 )S(O) 2 N(R 11a )—; —S—; —N(R 11 )—; —OC(O)R 11 ; —N(R 11 )C(O)—; —N(R 11 )S(O) 2 —; —N(R 11 )S(O)—; —N(R 11 )C(O)O—; —N(R 11 )C(O)N(R 11a )—; and —OC(O)N(R 11 R 11a ); T is selected from the group consisting of phenyl; naphthyl; indenyl; indanyl; tetralinyl; C 3-10 cycloalkyl; 4 to 7 membered heterocyclyl; or 9 to 11 membered heterobicyclyl, wherein t is optionally substituted with one or more R 10 , which are the same or different; R 10 is Z; halogen; CN; oxo (═O); COOR 12 ; OR 12 ; C(O)R 12 ; C(O)N(R 12 R 12a ); S(O) 2 N(R 12 R 12a ); S(O)N(R 12 R 12a ); S(O) 2 R 12 ; S(O)R 12 ; N(R 12 )S(O) 2 N(R 12a R 12b ); SR 12 ; N(R 12 R 12a ); NO 2 ; OC(O)R 12 ; N(R 12 )C(O)R 12a ; N(R 12 )S(O) 2 R 12a ; N(R 12 )S(O)R 12a ; N(R 12 )C(O)OR 12a ; N(R 12 )C(O)N(R 12a R 12 ); OC(O)N(R 12 R 12a ); or C 1-6 alkyl, wherein C 1-6 alkyl is optionally substituted with one or more halogen, which are the same or different; R 11 , R 11a , R 12 , R 12a , R 11b are independently selected from the group consisting of H; Z; or C 1-6 alkyl, wherein C 1-6 alkyl is optionally substituted with one or more halogen, which are the same or different; provided that one of R 9 , R 9a , R 9b , R 10 , R 11 , R 11a , R 12 , R 12a , R 12b is Z.

More preferably, L 2 is a C 1-20 alkyl chain, which is optionally interrupted by one or more groups independently selected from —O—; and C(O)N(R 3aa ); optionally substituted with one or more groups independently selected from OH; and C(O)N(R 3aa R 3aaa ); and wherein R 3aa , R 3aaa are independently selected from the group consisting of H; and C 1-4 alkyl.

Preferably, L 2 has a molecular weight in the range of from 14 g/mol to 750 g/mol.

Preferably, L 2 is attached to Z via a terminal group selected from

In case L 2 has such terminal group it is furthermore preferred that L 2 has a molecular weight in the range of from 14 g/mol to 500 g/mol calculated without such terminal group.

Preferably, L is represented by formula (Ia)

wherein R 4 , L 2 , and Z have the meaning as indicated above, and wherein R 3aa , R 3aaa are independently selected from the group consisting of H; and C 1-4 alkyl; or are joined together with the nitrogen atom to which they are attached to form a 4 to 7 membered heterocycle. Preferably, R 4 is H; or methyl.

Preferably, L is represented by formula (Ib)

wherein R 1 , R 1a , R 4 , L 2 and Z have the meaning as indicated above, and wherein R 3aa is H; or C 1-4 alkyl. Preferably, R 4 is H; or methyl.

Preferably, R 1 in formula (I) is L 2 -Z.

Preferably, R 3 in formula (I) is L 2 -Z.

Preferably, R 3 , R 3a in formula (I) are joined together with the nitrogen atom to which they are attached to form a 4 to 7 membered heterocycle, wherein the heterocycle is substituted with L 2 -Z.

Preferably, D-H is a small molecule bioactive agent or a biopolymer.

Preferably, D-H is a biopolymer selected from the group of biopolymers consisting of proteins, polypeptides, oligonucleotides, and peptide nucleic acids.

“Oligonucleotides” means either DNA, RNA, single-stranded or double-stranded, siRNA, miRNA, aptamers, and any chemical modifications thereof with preferably 2 to 1000 nucleotides. Modifications include, but are not limited to, those which provide other chemical groups that incorporate additional charge, polarizability, hydrogen bonding, electrostatic interaction, and fluxionality to the nucleic acid ligand bases or to the nucleic acid ligand as a whole. Such modifications include, but are not limited to, 2′-position sugar modifications, 5-position pyrimidine modifications, 8-position purine modifications, modifications at exocyclic amines, substitution of 4-thiouridine, substitution of 5-bromo or 5-iodo-uracil; backbone modifications, methylations, unusual base-pairing combinations such as the isobases isocytidine and isoguanidine and the like. Modifications can also include 3′ and 5′ modifications such as capping and change of stereochemistry.

Preferably, D-H is a polypeptide selected from the group of polypeptides consisting of ACTH, adenosine deaminase, agalsidase, alfa-1 antitrypsin (AAT), alfa-1 proteinase inhibitor (API), alteplase, amylins (amylin, symlin), anistreplase, ancrod serine protease, antibodies (monoclonal or polyclonal, and fragments or fusions), antithrombin III, antitrypsins, aprotinin, asparaginases, atosiban, biphalin, bivalirudin, bone-morphogenic proteins, bovine pancreatic trypsin inhibitor (BPTI), cadherin fragments, calcitonin (salmon), collagenase, complement C1 esterase inhibitor, conotoxins, cytokine receptor fragments, DNase, dynorphine A, endorphins, enfuvirtide, enkephalins, erythropoietins, exendins, factor VII, factor VIIa, factor VIII, factor VIIIa, factor IX, fibrinolysin, fibroblast growth factor (FGF), growth hormone releasing peptide 2 (GHRP2), fusion proteins, follicle-stimulating hormones, gramicidin, ghrelin, desacyl-ghrelin, granulocyte colony stimulating factor (G-CSF), galactosidase, glucagon, glucagon-like peptides, glucocerebrosidase, granulocyte macrophage colony stimulating factor (GM-CSF), human heat shock proteins (HSP), phospho lipase-activating protein (PLAP), gonadotropin chorionic (hCG), hemoglobins, hepatitis B vaccines, hirudin, human serine protease inhibitor, hyaluronidases, idurnonidase, immune globulins, influenza vaccines, interleukins (1 alfa, 1 beta, 2, 3, 4, 6, 10, 11, 12, 13, 21), IL-1 receptor antagonist (rhIL-1ra), insulins, insulin like growth factors, insulin-like growth factor binding protein (rhIGFBP), interferons (alfa 2a, alfa 2b, alfa 2c, beta 1a, beta 1b, gamma 1a, gamma 1b), intracellular adhesion molecule, keratinocyte growth factor (KGF), P-selectin glycoprotein ligand (PSGL), transforming growth factors, lactase, leptin, leuprolide, levothyroxine, luteinizing hormone, lyme vaccine, natriuretic peptides (ANP, BNP, CNP and fragments), neuropeptide Y, pancrelipase, pancreatic polypeptide, papain, parathyroid hormone, PDGF, pepsin, peptide YY, platelet activating factor acetylhydrolase (PAF-AH), prolactin, protein C, thymalfasin, octreotide, secretin, sermorelin, soluble tumor necorsis factor receptor (TNFR), superoxide dismutase (SOD), somatropins (growth hormone), somatoprim, somatostatin, streptokinase, sucrase, terlipressin, tetanus toxin fragment, tilactase, thrombins, thymosin, thyroid stimulating hormone, thyrotropin, tumor necrosis factor (TNF), TNF receptor-IgG Fc, tissue plasminogen activator (tPA), TSH, urodilatin, urate oxidase, urokinase, vaccines, vascular endothelial growth factor (VEGF), vasoactive intestinal peptide, vasopressin, ziconotide, lectin and ricin.

Preferably, D-H is a protein prepared by recombinant DNA technologies.

Preferably, D-H is a protein selected from the group of proteins consisting of antibody fragments, single chain antigen binding proteins, catalytic antibodies and fusion proteins.

Preferably, D-H is a small molecule bioactive agent selected from the group of agents consisting of central nervous system-active agents, anti-infective, anti-allergic, immunomodulating, anti-obesity, anticoagulants, antidiabetic, anti-neoplastic, antibacterial, anti-fungal, analgesic, contraceptive, anti-inflammatory, steroidal, vasodilating, vasoconstricting, and cardiovascular agents with at least one primary or secondary amino group.

Preferably, D-H is a small molecule bioactive agent selected from the group of agents consisting of acarbose, alaproclate, alendronate, amantadine, amikacin, amineptine, aminoglutethimide, amisulpride, amlodipine, amotosalen, amoxapine, amoxicillin, amphetamine, amphotericin B, ampicillin, amprenavir, aminone, anileridine, apraclonidine, apramycin, articaine, atenolol, atomoxetine, avizafone, baclofen, benazepril, benserazide, benzocaine, betaxolol, bleomycin, bromfenac, brofaromine, carvedilol, cathine, cathinone, carbutamid, cefalexine, clinafloxacin, ciprofloxacin, deferoxamine, delavirdine, desipramine, daunorubicin, dexmethylphenidate, dexmethylphenidate, diaphenylsulfon, dizocilpine, dopamin, dobutamin, dorzolamide, doxorubicin, duloxetine, eflornithine, enalapril, epinephrine, epirubicin, ergoline, ertapenem, esmolol, enoxacin, ethambutol, fenfluramine, fenoldopam, fenoterol, fingolimod, flecamide, fluvoxamine, fosamprenavir, frovatriptan, furosemide, fluoexetine, gabapentin, gatifloxacin, gemiflocacin, gentamicin, grepafloxacin, hexylcaine, hydralazine, hydrochlorothiazide, icofungipen, idarubicin, imiquimod, inversine, isoproterenol, isradipine, kanamycin A, ketamin, labetalol, lamivudine, levobunolol, levodopa, levothyroxine, lisinopril, lomefloxacin, loracarbef, maprotiline, mefloquine, melphalan, memantine, meropenem, mesalazine, mescaline, methyldopa, methylenedioxymethamphetamine, metoprolol, milnacipran, mitoxantron, moxifloxacin, norepinephrine, norfloxacin, nortriptyline, neomycin B, nystatin, oseltamivir, pamidronic acid, paroxetine, pazufloxacin, pemetrexed, perindopril, phenmetrazine, phenelzine, pregabalin, procaine, pseudoephedrine, protriptyline, reboxetine, ritodrine, sabarubicin, salbutamol, serotonin, sertraline, sitagliptin, sotalol, spectinomycin, sulfadiazin, sulfamerazin, sertraline, sprectinomycin, sulfalen, sulfamethoxazol, tacrine, tamsulosin, terbutaline, timolol, tirofiban, tobramycin, tocamide, tosufloxacin, trandolapril, tranexamic acid, tranylcypromine, trimerexate, trovafloxacin, valaciclovir, valganciclovir, vancomycin, viomycin, viloxazine, and zalcitabine.

Preferably, Z is a polymer of at least 500 Da or a C 8-18 alkyl group.

Preferably, Z is selected from the group of optionally crosslinked polymers consisting of poly(propylene glycol), poly(ethylene glycol), dextran, chitosan, hyaluronic acid, alginate, xylan, mannan, carrageenan, agarose, cellulose, starch, hydroxyalkyl starch (HAS), poly(vinyl alcohols), poly(oxazolines), poly(anhydrides), poly(ortho esters), poly(carbonates), poly(urethanes), poly(acrylic acids), poly(acrylamides), poly(acrylates), poly(methacrylates), poly(organophosphazenes), polyoxazoline, poly(siloxanes), poly(amides), poly(vinylpyrrolidone), poly(cyanoacrylates), poly(esters), poly(iminocarbonates), poly(amino acids), collagen, gelatin, hydrogel or a blood plasma protein, and copolymers thereof.

Preferably, Z is a protein.

Preferably, Z is a protein selected from the group consisting of albumin, transferrin, immunoglobulin.

Preferably, Z is a linear or branched poly(ethylene glycol) with a molecular weight from 2,000 Da to 150,000 Da.

Even more preferred is a prodrug of the present invention, wherein D-H is a GLP-1 receptor agonist; L is L 1 represented by formula (I) as indicated above; and Z is a hydrogel. Even more preferably, in formula (I) X is N(R 4 ), X 1 is C and X 3 is O. Even more preferably, L is represented by formula (Ia) as indicated above.

GLP-1 is one of the intestinal peptide hormones that are released into the circulatory system after food intake. It augments the postprandial release of insulin, when nutritions (especially carbohydrates) are absorbed and their level postprandially elevated. GLP-1 associates with GLP-1 receptor sites located on pancreatic β-cells and elevates endogenous cAMP levels in a dose dependent manner. In isolated rat islets in the presence of above normoglycemic glucose levels, GLP-1 stimulates the release of insulin. A therapeutic potential for GLP-1 in type 2 diabetes patients was suggested before, owing to the profound efficacy of this insulinotropic peptide to stimulate secretion of insulin when glucose levels are elevated and to cease doing so upon return to normoglycemia. The antidiabetogenic effect of glucagon-like peptide-1 (7-36) amide in normal subjects and patients with diabetes mellitus is described e.g. in N. Engl. J. Med. 326(20):1316-1322. In vitro studies and animal experiments suggest that GLP-1 improves insulin sensitivity and has an anabolic effect on pancreatic β-cells. In humans, GLP-1 was also reported to suppress glucagon secretion, decelerate gastric emptying, and induce satiety, leading to weight loss if administered for weeks and months.

Exendin-4 is reported to associate with GLP-1 receptors located on pancreatic beta-cells with 2.5 times higher affinity than GLP-1. In isolated rat islets and beta-cells in presence of glucose, exendin enhances secretion of insulin in a dose-dependent fashion. Exendin-4 is a high potency agonist and truncated exendin-(9-39)-amide an antagonist at the glucagon-like peptide 1-(7-36)-amide receptor of insulin-secreting beta-cells (see J. Biol. Chem. 268(26):19650-19655). Studies in type 2 diabetic rodents revealed that exendin-4 is 5530-fold more potent than GLP-1 in lowering blood glucose levels. Also, the duration of glucose-lowering action after a single administration of exendin-4 is significantly longer compared to GLP-1 (see e.g. Diabetes 48(5):1026-1034). Plasma half-life of exendin-4 in humans was described to be only 26 minutes. Exendin-4 reduces fasting and postprandial glucose and decreases energy intake in healthy volunteers (see e.g. Am. J. Physiol. Endocrinol. Metab. 281(1):E155-61).

Accordingly in an even more preferred embodiment the GLP-1 receptor agonist is Exendin-4.

Hydrogels to be used are known in the art. Suitable hydrogels may be used which are described in WO-A 2006/003014. Accordingly, a hydrogel may be defined as a three-dimensional, hydrophilic or amphiphilic polymeric network capable of taking up large quantities of water. The networks are composed of homopolymers or copolymers, are insoluble due to the presence of covalent chemical or physical (ionic, hydrophobic interactions, entanglements) crosslinks. The crosslinks provide the network structure and physical integrity. Hydrogels exhibit a thermodynamic compatibility with water which allow them to swell in aqueous media. The chains of the network are connected in such a fashion that pores exist and that a substantial fraction of these pores are of dimensions between 1 nm and 1000 nm.

Another object of the present invention is a pharmaceutical composition comprising a prodrug of the present invention or a pharmaceutical salt thereof together with a pharmaceutically acceptable excipient.

Yet another object of the present invention is a prodrug of the present invention or a pharmaceutical composition of the present invention for use as a medicament.

Yet another object of the present invention is a method of treating, controlling, delaying or preventing in a mammalian patient in need of the treatment of one or more conditions comprising administering to said patient a therapeutically effective amount of a prodrug of the present invention or a pharmaceutical composition of the present invention or a pharmaceutically acceptable salt thereof.

Another object of the present invention is a prodrug precursor of formula Act-L, wherein L has the meaning as indicated above and Act is a leaving group.

Preferably, Act is chloride, bromide, fluoride, nitrophenoxy, imidazolyl, N-hydroxysuccinimidyl, N-hydroxybenzotriazolyl, N-hydroxyazobenzotriazolyl, pentafluorophenoxy, 2-thiooxo-thiazolidinyl, or N-hydroxysulfosuccinimidyl.

Materials and Methods

Materials: Side chain protected Exendin-4 (J. Eng et al., J. Biol. Chem. 1992, 267, 11, 7402-7405) on Rink amide resin, side chain protected BNP-32a (human, Cys10 and Cys26 exchanged for Ala) on chlorotrityl resin, side chain protected BNP-32b with ivDde side-chain protecting group on Lys 14 (human, Cys10 and Cys26 exchanged for Ala) on chlorotrityl resin, and side chain protected human growth hormone releasing factor fragment 1-29 amide (GRF(1-29)) on Rink amide (each synthesized by Fmoc-strategy) were obtained from Peptide Specialty Laboratories GmbH, Heidelberg, Germany. Standard side chain protecting groups were used except for Lys27 of Exendin-4 and Lys21 of GRF(1-29) where Mmt side-chain protecting groups were used.

40 kDa methoxy poly(ethylene glycol) maleimido-propionamide (PEG40 kDa-maleimide) was obtained from Chirotech Technology Ltd, Cambridge, UK.

2-Chlorotrityl chloride resin, Sieber amide resin and amino acids were from Merck Biosciences GmbH, Schwalbach/Ts, Germany, if not stated otherwise. Fmoc-D-Homocysteine(Trt)-OH and S-Trityl-3-mercaptopropionic acid (Trt-MPA) were obtained from Bachem AG, Bubendorf, Switzerland. O—(N-Fmoc-2-aminoethyl)-O′-(2-carboxyethyl)-undecaethyleneglycol (Fmoc-Pop-OH) was obtained from Polypure AS, Oslo, Norway. Fmoc-4-(2-aminoethyl)-1-carboxymethyl-piperazine (Fmoc-Acp-OH) was purchased from NeoMPS SA, Strasbourg, France. cis-Cyclohexane-1,2-dicarboxylic anhydride was obtained from Alfa Aesar GmbH & Co KG, Karlsruhe, Germany.

All other chemicals were from Sigma-ALDRICH Chemie GmbH, Taufkirchen, Germany.

Solid phase synthesis was performed on 2-Chlorotrityl chloride resin with a loading of 1.3 mmol/g or Sieber amide resin with a loading of 0.55 mmol/g. Syringes equipped with polypropylene frits were used as reaction vessels.

Loading of the first amino acid to resins was performed according to manufacturer's instructions.

Fmoc Deprotection:

For Fmoc protecting-group removal, the resin was agitated with Feb. 2, 1996 (v/v/v) piperidine/DBU/DMF (two times, 10 min each) and washed with DMF (ten times).

ivDde Deprotection:

For ivDde protecting-group removal, the resin was agitated with 98/2 (v/v) DMF/hydrazine hydrate (3 times, 10 min each) and washed with DMF (ten times).

Boc Protection:

The N-terminus of a peptide was boc-protected by agitating the resin with 30 eq (boc) 2 O and 60 eq pyridine in DCM. After 1 h the resin was washed with DCM (10 times).

Standard Coupling Condition for Acids:

Coupling of acids (aliphatic acids, Fmoc-amino acids) to free amino groups on resin was achieved by agitating resin with 3 eq of acid, 3 eq PyBOP and 6 eq DIEA in relation to free amino groups on resin (calculated based on theoretical loading of the resin) in DMF at room temperature. After 1 hour resin was washed with DMF (10 times).

3-Maleimido Propionic Acid Coupling:

Coupling of 3-maleimido propionic acid to free amino groups on resin was achieved by agitating resin with 2 eq of acid, 2 eq DIC and 2 eq HOBt in relation to free amino groups in DMF at room temperature. After 30 min, resin was washed with DMF (10 times).

Standard Protocol for Synthesis of Ureas on Resin:

Synthesis of ureas on resin was achieved by agitating resin with 2.5 eq of bis(pentafluorophenyl) carbonate, 5 eq DIEA, and 0.25 eq DMAP in relation to free amino groups in DCM/ACN 1/1 at room temperature. After 15 min resin was washed with DMF (10 times). 5 eq of amine was dissolved in DMF. Mixture was added to resin and agitated for 60 min at room temperature. Resin was washed with DMF (10 times).

Cleavage Protocol for Sieber Amide Resin:

Upon completed synthesis, the resin was washed with DCM (10 times), dried in vacuo and treated repeatedly (five times a 15 minutes) with 97/2/1 (v/v) DCM/TES/TFA. Eluates were combined, volatiles were removed under a nitrogen stream and product was purified by RP-HPLC. HPLC fractions containing product were combined and lyophilized.

Cleavage Protocol for 2-Chlorotrityl Chloride Resin:

Upon completed synthesis, the resin was washed with DCM, dried in vacuo and treated two times for 30 minutes with 6/4 (v/v) DCM/HFIP. Eluates were combined, volatiles were removed under a nitrogen stream and product was purified by RP-HPLC. HPLC fractions containing product were combined and lyophilized.

Cleavage Protocol for Rink Amide Resin:

Upon completed synthesis, the resin was washed with DCM, dried in vacuo and treated with 2 ml of TFA cleavage cocktail (TFA/TES/Water/DTT 95/2/2/1) per 100 mg resin for 60 min at room temperature. Volatiles were removed under a nitrogen stream. Unpolar side products and protecting groups were removed by precipitating peptide from diethyl ether. Precipitate was dried in vacuo and dissolved in ACN/water 1/1 and purified by RP-HPLC.

Amine containing products obtained as TFA salts were converted to the corresponding HCl salts using ion exchange resin (Discovery DSC-SAX, Supelco, USA). This step was performed in case the residual TFA was expected to interfere with e.g. a subsequent coupling reactions.

RP-HPLC Purification:

RP-HPLC was done on a 100×20 or a 100×40 mm C18 ReproSil-Pur 3000DS-3 5μ column (Dr. Maisch, Ammerbuch, Germany) connected to a Waters 600 HPLC System and Waters 2487 Absorbance detector. Linear gradients of solution A (0.1% TFA in H 2 O) and solution B (0.1% TFA in acetonitrile) were used. HPLC fractions containing product were lyophilized.

Analytics: Electrospray ionization mass spectrometry (ESI-MS) was performed on a Waters ZQ 4000 ESI instrument and spectra were, if necessary, interpreted by Waters software MaxEnt.

Size exclusion chromatography (SEC) was performed using an Amersham Bioscience AEKTAbasic system equipped with a Superdex200 10/300 column (Amersham Bioscience/GE Healthcare), if not stated otherwise. 10 mM sodium phosphate, 140 mM NaCl, pH 7.4, 3 mM EDTA was used as mobile phase

For Cation Exchange Chromatography, an Amersham Bioscience AEKTAbasic system was equipped with a Source 15S filled HR16/10 column (Amersham Bioscience/GE Healthcare).

Desalting was performed using an Amersham Bioscience AEKTAbasic system equipped with a HiPrep 26/10 Desalting column and 0.1% acetic acid in water as mobile phase.

In vitro linker hydrolysis and release of drug: Compounds were dissolved in buffer A (10 mM sodium phosphate, 140 mM NaCl, pH 7.4, 3 mM EDTA) or buffer B (0.1 M Acetat 3 mM EDTA, pH 4.0), and solution was filtered through a 0.2 μm filter and incubated at 37° C. Samples were taken at time intervals and analyzed by RP-HPLC at 215 nm and ESI-MS. UV-signals correlating to liberated drug molecule were integrated and plotted against incubation time. In case of identical retention times of prodrug and drug, ratio of mass signals was used to determine release kinetics.

For hydrogel conjugates, compounds were suspended in buffer A and incubated at 37° C. Samples were taken after centrifugation of the suspension and analyzed by RP-HPLC at 215 nm. UV-signals correlating to liberated drug molecule were integrated and plotted against incubation time.

Curve-fitting software was applied to estimate the corresponding halftime of release.

Acp 4-(2-aminoethyl)-1-carboxymethyl-piperazine

AcOH acetic acid

Boc t-butyloxycarbonyl

Dab 2,4-diaminobutyric acid

DBU 1,3-diazabicyclo[5.4.0]undecene

DCM dichloromethane

Dda dodecanoic acid

DIC diisopropylcarbodiimide

DIEA diisopropylethylamine

DMAP dimethylamino-pyridine

DMF N,N-dimethylformamide

DMSO dimethylsulfoxide

EDTA ethylenediaminetetraacetic acid

eq stoichiometric equivalent

Fmoc 9-fluorenylmethoxycarbonyl

HATU O-(7-Azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate

HFIP hexafluoroisopropanol

HEPES N-(2-hydroxyethyl)piperazine-N′-(2-ethanesulfonic acid)

HOBt N-hydroxybenzotriazole

ivDde 1-(4,4-Dimethyl-2,6-dioxo-cyclohexylidene)-3-methylbutyl

LCMS mass spectrometry-coupled liquid chromatography

Mal 3-maleimido propionyl

Mmt 4-methoxytrityl

MS mass spectrum

MW molecular mass

n.d. not determined

PfpOH pentafluorophenol

PyBOP benzotriazole-1-yl-oxy-tris-pyrrolidino-phosphonium hexafluorophosphate

RP-HPLC reversed-phase high performance liquid chromatography

RT room temperature

SEC size exclusion chromatography

Suc succinimidopropionyl

TCP 2-chlorotrityl chloride resin

TES triethylsilane

TMOB 2,4,6-trimethoxybenzyl

TFA trifluoroacetic acid

THF tetrahydrofurane

UV ultraviolet

VIS visual