Acid-labile trigger units

1. A compound of the following general formula (I):

wherein

Ar is a phenyl group having one or more hydrogens substituted with a substituent independently selected from the group consisting of an C 1-6 alkyl group, a C 1-6 thioalkyl group, a C 3-7 cycloalkyl group which may contain one or more heteroatoms, an C 1-6 alkoxy group, a C 1-6 dialkylamine group, an C 1-6 alkoxycarbonyl group, a C 1-6 trialkylammonium group, a nitro group, a hydroxy group, a C 1-6 perfluoroalkyl group, fluorine, chlorine and bromine,

n is 0 or 1,

R 1 , R 2 , R 5 and R 6 are independently selected from hydrogen, a linear or branched C 1-8 alkyl group, a phenyl group, a naphthyl group, a biphenyl group or a vinyl benzene group, or a group C,

R 3 , R 4 , R 7 and R 8 are independently selected from hydrogen or a group C, with the proviso that not more than one of R 1 to R 8 is a group C,

E is a moiety comprising at least one cytostatic agent as an effector unit which is selected from the group consisting of N-nitrosoureas, the anthracyclines doxorubicin, daunorubicin, epirubicin, idarubicin, 2-(4-diacetoxybutyl)doxorubicin; the anthraquinones mitoxantrone and ametantrone; the alkylating agents chlorambucil, bendamustine, melphalan, and oxazaphosphorines; the antimetabolites 5-fluorouracil, 2′-deoxy-5-fluorouridine, cytarabine, cladhbine, fludarabine, pentostatine, gemcitabine, 6-thioguanine and 6-mercaptopurine; the folic acid antagonists methotrexate, raltitrexed, pemetrexed and plevitrexed, the taxanes paclitaxel and docetaxel; the camptothecins topotecan, irinotecan (CPT-11), SN-38, 10-hydroxycamptothecin, GG211, lurtotecan, 9-aminocamptothecin and camptothecin; the lignans etoposide and podophyllotoxin; the Vinca alkaloids vinblastine, vincristine, vindesine and vinorelbine; calicheamicins; maytansinoids; auristatins; epothilones; tubulysins, rapamycin, salinosporamide, combretastatin, bleomycin; dactinomycin; plicamycin; mitomycin C and cis-configured platinum(II) complexes, and

C is a carrier group selected from the group consisting of serum proteins, antibodies or antibody fragments, synthetic polymers, dendrimers, peptides, growth factors, receptor-binding ligands, polysaccharids, microparticles, nanoparticles and protein-binding moieties capable of binding to a carrier molecule,

wherein the carrier group may be bound to the phenyl ring or to the benzylic carbon atom directly or via a linker.

2. The compound according to claim 1 , wherein Ar is selected from one of the following groups:

3. The compound according to claim 2 , wherein Ar is selected from one of the following groups:

4. The compound according to claim 1 , wherein the effector unit is bound via a —(O)O—, a —C(O)S—, a —C(O)NH—, a —CH 2 O—or a —C(O)NH—CH 2 N— group.

5. The compound according to claim 1 , wherein one of R 1 to R 8 is a carrier group C which is a protein-binding moiety selected from the group consisting of a maleimide group, a halogenacetamide group, a halogenacetate group, a pyridylthio group, a vinylcarbonyl group, an aziridin group, a disulfide group, a substituted or unsubstituted acetylene group, and a hydroxysuccinimide ester group.

6. The compound according to claim 1 , wherein one of R 1 to R 8 is a carrier group C which is a protein-binding moiety capable of in situ binding to cysteine-34 of serum albumin.

7. The compound according to claim 1 , which has the following general formula (II):

8. The compound according to claim 1 , wherein one of R 1 to R 8 is a carrier group C which is a synthetic polymer selected from the group consisting of poly(ethylene glycol) (PEG), monomethoxy PEG (mPEG), polyglycerol (PG), poly(ethylene amine) (PEI) and N-(2-hydroxy)propylmethacrylamide (HPMA) copolymers.

9. The compound according to claim 8 , wherein one of R 2 , R 3 , R 4 , R 6 R 7 and R 8 is the carrier group C, which is bound to the phenyl ring via a linker having one of the following structures, wherein m is an integer from 0 to 5:

10. The compound according to claim 9 , which has one of the following structures (III), (IV), (V), (VI), (VII) or (VIII), wherein PEG is poly(ethylene glycol) or monomethoxy poly(ethylene glycol):

11. The compound according to claim 1 , wherein the moiety E is a dendritic or linear system adapted to release one or more effector units upon cleavage of the imine bond in the compound of general formula (I).

12. A method for producing a compound of claim 1 , said method comprising attaching to moiety E a unit of the following structure

as a trigger group which can be cleaved pH-dependently, wherein E, n, Ar and R 1 to R 8 are as defined above.

13. A composition comprising the compound according to claim 1 , and optionally a pharmaceutically acceptable carrier and/or a pharmaceutically acceptable adjuvant and/or a diluent.