The present invention relates to platinum complexes with diazabicyclohydrocarbon compounds, processes for preparing said complexes and the use thereof as pharmaceutically active compounds, in particular as cytostatic compounds.

The discovery of the antitumor activity of cisplatin, cis-(NH ₃ ) ₂ PtCl2, prompted an intense screening of related Pt complexes in a search of possibly more effective and at the same time less toxic analogues. In chemotherapy, the prototypical cisplatin is particularly active in the treatment of testicular and ovarian cancers and also in the treatment of bladder, head, and neck cancers, as well as small cell and non-small cell lung cancer. Substantial side-effects are dose-limiting nephrotoxicity, gastrointestinal toxicity, ototoxicity, neurotoxicity, and myelosuppression. Patients experience inter alia nausea, vomiting, and anorexia, which are only partly alleviated by antiemetics, and also numbness, tinnitus, and reduced hearing. A major problem is an inherent and the development of an acquired platinum resistance of refractory tumors. Various X-ray structure determinations have been performed on cisplatin and its solvent adducts (no water adduct).

Cisplatin Carboplain Qxaliplatin

Structures of Cisplatin, Carboplatin and Oxaliplatin.

Already from early screenings, carboplatin emerged as a further platinum based and clinically applied second generation anti-cancer agent. In carboplatin the rather labile chloride anions of cisplatin are replaced with 1 ,1 -cyclobutane- dicarboxylate (CBDCA), representing a dianionic substituted malonate ligand. Carboplatin exhibits lower reactivity and slower DNA binding kinetics, but otherwise appears to act with cell DNA in quite a similar way as cisplatin. Carboplatin has a very similar activity profile against cancers as for cisplatin. While there are generally less adverse effects, the main drawbacks of carboplatin are that it does not sort out the problem of platinum resistance and its myelosuppressive effect. This causes the blood cell and platelet output of bone marrow to decrease quite dramatically, sometimes to as low as 10% of its usual production levels. Carboplatin is generally less active than cisplatin. This is clinically usually overcome by increasing the dosage to a 4:1 ratio compared to cisplatin. Due to its relative inertness, most of the carboplatin remains unaltered in the blood stream and becomes egested by urine. The structure of carboplatin is known; in addition numerous further Pt-CBDCA complexes and various other Pt- malonate complexes have been structurally investigated.

Oxaliplatin, ,2-diamino-cyclohexane platinum(ll)oxalate, is considered as a third generation Pt-based anti-cancer drug. Instead of NH ₃ , oxaliplatin contains the chiral trans-1 ,2-diaminocyclohexane (DACH) ligand as a neutral "carrier ligand". While the also potent Pt-dichloride (DACH)PtCI ₂ is scarcely soluble in water, the oxalate (DACH)Pt(C2O ₄ ) dissolves well. Oxaliplatin has gained almost worldwide approval in the treatment of colon cancers starting from 1998. Dose-limiting toxicity is neurotoxicity. Interestingly, the enantiomer is more potent than the trans-(S,S) enantiomer and both of these are more efficient than the cis-(f?,S) isomer. These facts are attributed both to the relative flat structures of the trans isomers, allowing for an easier approach of the trans isomeric complexes to cell DNA, and to the specific hydrogen bonding between the primary amine N-H functions and DNA purine bases. As a consequence, recognition and repair of DNA damage by platinum are impeded, resulting in reduced platinum resistance as compared to the first and second generation drugs. While cisplatin is administered intravenously due to its high hydrophilicity, an increased lipophilicity of a derivative drug would be required for oral administration and intestinal uptake. Cisplatin and its homologues obey the general formula cis-Pt(ll)A ₂ Y2, in which A represents a neutral amine ligand bearing 1 -3 protons, and Y (Y ₂ , respectively) represents an anionic leaving group such as halide, oxalate, and malonate. The amine is viewed as a "carrier ligand" which assists penetration of the neutral drug through the cell membrane. Y undergoes hydrolysis under physiological conditions, fast for chloride and slower for oxalate and malonate.

In the prior art, Black et al. (Tetrahedron Vol. 51 , No. 7, pp. 2055-2076, 1995) reported about synthesis and metal complexes of symmetrically 1 ,5-diphenyl (at positions W ¹ and W ² in formula (I)) and some N-substituted bispidinones, however, pharmaceutical studies revealed that such complex structures as disclosed by Black do not have any significant pharmaceutical activity.

It emerged from structure-activity relationship studies that certain requirements must be fulfilled by a Pt complex to expose anti-tumor activity. These are, inter alia, two amino functions in cis position at a Pt(ll) or Pt(IV) center, with the amino groups possessing H atoms to allow for hydrogen bonding, presumably to the purine bases of the cell DNA. The anionic ligands must be able to slowly hydrolyze under physiologic conditions. Relatively few Pt(ll) complexes with secondary amine ligands have been investigated; in that respect, monodentate amine and chelating acyclic or cyclic diamine ligands can be differentiated.

Basic studies concerning simple cisplatin, carboplatin and oxaliplatin analogs were presented by the one of the inventors of the present invention at the 243rd ACS

National Meeting & Exposition in San Diego in March 2012. Ongoing research work of the inventors, leading to the present invention, revealed that specific Pt- bispidine analogs of said cisplatin, carboplatin and oxaliplatin show some cytotoxicity. The Pt-bispidine complexes of the present invention belong

apparently to the first complexes containing a bicyclic diamine ligand and having a remarkable cytotoxicity It was further found that cytotoxicity, hydro- and lipophilicity and thereby membrane permeability can be adjusted by modification of the bispidine part of the compounds.

In a first aspect, the present invention is directed to a diazabicyclohydrocarbon-Pt complex of the general formula (I):

Wherein:

R ¹ , R ² , R ³ and R ⁴ may be the same or different and may each be C1-C3- alkylene, optionally being substituted by one or more substituents selected from the group consisting of -OH, -X, methyl, ethyl, methoxy and ethoxy;

R ⁵ may be -O-, -CO-, -C(OR ⁶ )(OR ⁷ )-, -N(R ⁶ )-, or C C ₃ -alkylene, said C C ₃ - alkylene optionally being substituted by one or more substituents selected from the group consisting of -OH, -OR ⁶ , -NR ⁶ R ⁷ , -X, Ci to C ₆ alkyl, C ₂ to C ₆ alkenyl, C2 to C6 alkynyl, C2 to C ₅ heteroaryl, each optionally further substituted by Ci to C ₆ alkyl, -X, Ci to C ₆ halogen substituted alkyl, -OR ⁶ , - NR ⁶ R ⁷ , and -(C=O)R ⁶ , wherein each of said R ⁶ and R ⁷ may be the same or different and may be independently selected from the group consisting of hydrogen and Ci to C6 alkyl optionally substituted by -OH, -OCH3, -OC2H ₅ , - X, -CH ₃ , -CH ₂ X, -CHX ₂ , and -CX ₃ , or in the case of -C(OR ⁶ )(OR ⁷ )- may together form a C2 to C6 aliphatic hydrocarbon ring; W ¹ and W ² may be the same or different and may each be hydrogen, -OH, -X, methyl, methoxy, -CO ₂ R ⁶ - wherein R ⁶ may have the meaning as given before, and

R ⁸ and R ⁹ each represent a monodentate ligand or R ⁸ and R ⁹ may together form a bidentate ligand, and

X is halogen,

with the proviso, that at least one of W ¹ and W ² is not hydrogen if R ¹ , R ² , R ³ , R ⁴ and R ⁵ each are methylene. In the formulae of the inventive compounds, X stands for halogen, in particular F or CI . In the case of -C(OR ⁶ )(OR ⁷ )-, R ⁶ and R ⁷ may together form a C ₂ to C ₆ aliphatic hydrocarbon ketal ring which may be prepared by reacting the respective ketone with an α,ω-diol. In some particular embodiments of the complexes of the invention, at least one of R ¹ to R ⁵ is not methylene. According to the invention, alkylene is to be understood as -(CH ₂ )- chain with the indicated number of C- atoms. In some embodiments, R ⁵ may represent a Ci -C3-alkylene group wherein said Ci to C ₆ alkyl, C ₂ to C ₆ alkenyl, or C ₂ to C ₆ alkynyl substituents may form a hydrocarbon ring with said Ci -C3-alkylene group, said hydrocarbon ring optionally substituted by -OH, -OCH ₃ , -OC ₂ H ₅ , -X, -CH ₃ , -CH ₂ X, -CHX ₂ , and -CX ₃ .

In some embodiments, R ¹ , R ² , R ³ and R ⁴ may be the same or different and may also each be Ci -C3-alkylene being substituted by one or more substituents selected from the group consisting of -OH, -X, Ci to C ₄ alkyl and Ci to C ₄ alkoxy. Preferred embodiments of the present invention encompasse said diazabicyclo-Pt complex of the general formula (I) substituted at the 9-position and/or 1 ,5 positions with substituents R ⁵ , W ¹ and W ² having the definitions as given above and wherein R ¹ , R ² , R ³ and R ⁴ are methylene or ethylene, R ⁸ , R ⁹ and X are each as defined before.

Particularly preferred is a diazabicyclo-Pt complex of the general formula (I) wherein R ⁵ is -O-, -CO-, -C(OR ⁶ )(OR ⁷ )-, -N(R ⁶ )- or C or C ₂ -alkylene optionally being substituted by one or more substituents selected from the group consisting of -OH, -OR ⁶ , -NR ⁶ R ⁷ and -X, wherein each of said R ⁶ and R ⁷ may be the same or different and may be independently selected from the group consisting of hydrogen and Ci to Ce alkyl optionally substituted by -OH, -OCH ₃ , -OC ₂ H5,

W ¹ and W ² are the same or different and may each be hydrogen, -OH, -X, methyl or methoxy,

R ¹ , R ² , R ³ and R ⁴ are methylene,

R ⁶ and R ⁷ may be the same or different and may be independently selected from the group consisting of hydrogen and Ci to Ce alkyl optionally substituted by -OH, - OCH3, -OC2H5, -X, -CH ₃ , -CH ₂ X, -CHX ₂ , and -CX ₃ ,

X is halogen such as CI or F, and

R ⁸ and R ⁹ each represent a monodentate ligand or R ⁸ and R ⁹ may together form a bidentate ligand,

with the proviso, that at least one of W ¹ and W ² is not hydrogen if R ¹ , R ² , R ³ , R ⁴ and R ⁵ each are methylene.

In some embodiments, the Ci-C ₃ -alkylene group for R ⁵ is substituted by one or more substituents selected from the group consisting of -OH, -OR ⁶ , -NR ⁶ R ⁷ , -X, Ci to C6 alkyl, C ₂ to C6 alkenyl, C ₂ to C6 alkynyl, C ₂ to C ₅ heteroaryl, each optionally further substituted by Ci to C ₆ alkyl, -X, Ci to C ₆ halogen substituted alkyl, -OR ⁶ , - NR ⁶ R ⁷ , and -(C=O)R ⁶ , wherein each of said R ⁶ and R ⁷ may be the same or different and may be selected from the group consisting of hydrogen or Ci to C6 alkyl optionally substituted by -OH, -OCH3, -OC ₂ H ₅ , -X, -CH ₃ , -CH ₂ X, -CHX ₂ , and - CX ₃ , or in the case of -C(OR ⁶ )(OR ⁷ )- may together form a C ₂ to C ₆ aliphatic hydrocarbon ring; and the other substituents are as defined before.

In another embodiment of the present invention of the diazabicyclo-Pt complex of the general formula (I), R ⁵ may be -O-, -CO-, -C(OR ⁶ )(OR ⁷ )-, -N(R ⁶ )-, wherein R ⁶ , R ⁷ and the other substituents are as defined before.

Smaller substituents of R ¹ to R ⁴ that allow for low steric hindrance between the Pt- complex and DNA purine bases are preferred. However, R ⁵ can also be substituted by sterically more demanding substituents, as being located on the opposite side of the Pt central atom.

In another embodiment, a diazabicyclo-Pt complex, wherein R ¹ , R ² , R ³ and R ⁴ each represent a methylene or ethylene bridge, each optionally being substituted by one or more substituents selected from the group consisting of hydrogen, -OH, -X (halogen), methyl, ethyl, methoxy and ethoxy, and R ⁵ represents -CO-, -C(OR ⁶ )(OR ⁷ )-, -N(R ⁶ )-, wherein R ⁶ , R ⁷ and the other substituents are as defined before, is encompassed.

In case of monodentate ligands, R ⁸ and R ⁹ can be anionic or neutral and are preferably selected from the group consisting of -X, OH ₂ , -OCO ₂ H, -OSO ₃ H, - OPO3H2, acetate and other monoanionic carboxylates, -OR ^a , -NR ^a R ^a , and R ^a R ^a NC(O)H, wherein R ^a may be the same or different and may be independently selected from the group consisting of -H, -CH ₃ , and -C2H ₅ . Preferred examples for the monodentate ligands are -X, -OCO ₂ H, -OSO3H, -OPO ₃ H ₂ , acetate, water, and -OH. In case that R ⁸ and R ⁹ are neutral, a corresponding complex anion may be selected from -X, -OCO ₂ H, -OSO3H, -OPO ₃ H ₂ , acetate. In case of a bidentate ligand, this ligand may be a bidentate ligand of the formula - (O,S,NH)-R-(NH,S,O)-, wherein R is a bridging Ci to C ₆ hydrocarbon group being optionally substituted by one or more substituents selected from the group consisting of hydrogen, -OH, -OCH3, -OC ₂ H ₅ , -X, -CH ₃ , -CH ₂ X, -CHX ₂ , and -CX ₃ , straight chain, branched or cyclic Ci to C6 alkyl, C ₂ to C6 alkenyl, C ₂ to C6 alkynyl, C ₂ to C ₅ heteroaryl, halogen, -OR ⁶ , -NR ⁶ R ⁷ , and -(C=O)R ⁶ , wherein each of said R ⁶ and R ⁷ may be the same or different and may be selected from the group consisting of hydrogen or Ci to C6 alkyl optionally substituted by -OH, -OCH3, - OC ₂ H ₅ , -X, -CH ₃ , -CH ₂ X, -CHX ₂ , and -CX ₃ , In such case, R of the bidentate ligand of the formula -(O,S,NH)-R-(NH,S,O)- can particularly be a bridging Ci-C ₄ -alkylene group, being optionally substituted by one or more substituents selected from the group consisting of -OH, -OCH3, -OC ₂ H ₅ , - X, -CH ₃ , -CH ₂ X, -CHX ₂ , and -CX ₃ , straight chain, branched or cyclic Ci to C ₆ alkyl, C ₂ to C ₆ alkenyl, C ₂ to C ₆ alkynyl, C ₂ to C ₅ heteroaryl, halogen, -OR ⁶ , -NR ⁶ R ⁷ , and -(C=O)R ⁶ , wherein each of said R ⁶ and R ⁷ may be the same or different and may be selected from the group consisting of hydrogen or Ci to Ce alkyl optionally substituted by -OH, -OCH ₃ , -OC ₂ H ₅ , -X, -CH ₃ , -CH ₂ X, -CHX ₂ , and -CX ₃ .

In a further embodiment, the bidentate ligand is a bidentate ligand of the formula (O,S,NH)-R-(NH,S,O)- wherein R is a bridging malonate-type ligand such as 1 ,1 - cyclobutanedicarboxylato or a 2,4-pentanedionate ligand, or a -(C=O)-(C=O)- (oxalate) ligand, or an inorganic dianionic ligand such as -OSO ₃ - and -OPO(OH)O-.

A bidentate ligand is particularly a 1 ,1 -cyclobutanedicarboxylato ligand or a -O-(C=O)-(C=O)-O- ligand.

A method for producing the Pt-complexes with the bispidine or bispidine derivatives as defined by general formula (I) is shown in the Reaction Schemes as shown in the Figures 1 to 4. In more detail, Figures 1 to 4 show:

Fig. 1 : General Reaction Scheme for preparing diazabicyclohydrocarbon-Pt complexes of the general formula (I);

Fig. 2: Synthesis of spiro[bispidin-9,2'-[1 ,3]dioxolane] ((C ₂ H ₄ O ₂ )C ₇ H ₁₀ (NH) ₂ );

Fig. 3: Synthesis of Pt(ll)-Bispidin complexes, and

Fig. 4: Synthesis of Pt(ll)-Bispidin-9,9-diole complexes.

It was found that Pt being coordinated by bispidine or bispidine derivatives as defined by general formula (I) can be produced by reacting the respective diazabicycio compound with a Pt complex being coordinated by 1 ,5-hexadiene or derivatives thereof as exemplified in the Reaction Scheme 1 shown in Fig. 1 .

Such diazabicyclo-Pt complexes produced by this or any appropriate method can be used as a cytotoxic agent. The inventors of the present invention have carried out pharmaceutical tests for evaluating the pharmaceutical efficacy of the inventive compounds. The results can be taken form the tests below following the preparation of the inventive compounds. The invention is further illustrated by the following preparation examples.

Example 1 :

For synthesis of the Pt-bispidine analog of cisplatin, (1 ,5-hexadiene)PtCl2 was reacted with the parent bispidine (C ₇ Hi ₄ N ₂ ) in DMF at 70 °C for 3 h. By displacement of the 1 ,5-hexadiene ligand an intense yellow reaction solution is formed. Slow recooling of the solution to ambient temperature afforded large pale yellow crystals of the DMF adduct (C ₇ Hi ₄ N ₂ )PtCI ₂ DMF (1 b) in 87% yield (Figure 3). No byproducts have been detected in the mother liquor (NMR). An X-ray structure determination revealed a dinuclear structure of 1 b in which the DMF ligands are bound by N-H- CHNMe ₂ hydrogen bridge bonds. These appear to be weak, as DMF (b.p. 153 °C) can be fully removed in a vacuum at 50 °C within 24 hours to give solvent free (C ₇ Hi N ₂ )PtCI ₂ (1 a). The latter recrystallizes from the less basic /V-methyl formamide (NMF) without inclusion of solvent. Considering that cisplatin does form an adduct with NMF, the NH hydrogen atoms of the bispidine ligand in 1 a are apparently less protic than those of the ammonia ligands in cisplatin. No direct synthesis of 1 a in NMF was possible due to substantial decomposition of the reaction mixture under these conditions.

While complexes 1 a,b appear insoluble in most solvents at ambient temperature, including CH ₂ CI ₂ and THF, they dissolve increasingly well in water, DMF, and DMSO, in particular when warmed (50 °C). From warm water (C ₇ Hi N ₂ )PtCI ₂ -3H ₂ O (1 c) crystallizes at ambient temperature, with only little hydrolysis of the Pt-CI bonds (NMR). Example 2

Synthesis of the Pt-bispidine analog (C ₇ Hi ₄ N ₂ )Pt{(O ₂ C) ₂ C ₄ H ₆ } (2a) of carboplatin was done by stirring a suspension of complex 1 and the equimolar amount of Ag ₂ (cbdca) in water in the dark at ambient temperature for 2 days (Figure 3). We found no need to first convert 1 into the iodide, which was suggested by others. The malonate product complex is more soluble in water than the dichloride 1 and remains in solution when AgCI precipitates and is removed by filtration. Rapid evaporation of the water under vacuum by heating the vessel up to 50 °C leaves quantitatively solute-free and pure 2a. Recrystallization of the compound from a smaller amount of water affords the pentahydrate (C ₇ H ₁₄ N ₂ )Pt{(O ₂ C) ₂ C H ₆ }-5xH ₂ O (2b). 2b was characterized by an X-ray structure determination revealing an embedding of the complex molecules in an intricate network of water molecules. Solubility of 2 in DMF is poor.

Example 3.

Similarly, for the synthesis of the Pt-bispidine analog of oxaliplatin, complex 1 was reacted with 2 equiv of AgNO3 in aqueous solution to give, besides precipitated AgCI, the soluble diaqua complex [(C ₇ H ₁₄ N ₂ )Pt(OH ₂ )2](NO3)2- Treatment of the latter with disodium oxalate gave poorly soluble (C ₇ Hi ₄ N ₂ )Pt(C ₂ O ₄ ) (3) as a colorless precipitate (Figure 3). Recrystallization of 3 from hot water afforded thin colorless needles of 3 in moderate yield (44%). Thus, 3 does not form a water solute compound, unlike 1 c and 2b. It furthermore cannot be recrystallized from DMF in which it is hardly soluble up to 100 °C.

Example 4 - (Spiro[bispidin-9,2'-[1 ,31dioxolane1)platinum(ll)dichloride (4)

A solution of (C ₆ Hi ₀ )PtCI ₂ (3.48 g, 10.0 mmol) and spiro[bispidin-9,2'-

[1 ,3]dioxolane] ((C ₂ H ₄ O ₂ )C ₇ Hio(NH) ₂ , FW184.2) (1 .84 g, 10.0 mmol) in 150 ml_ of DMF was heated to 100 °C for two hours. A light yellow precipitate was formed, which after cooling to ambient temperature was isolated by filtration, washed with diethyl ether, and dried under vacuum: yield 4.36 g (97%) (Figure 4). Anal. Calcd for C ₉ Hi6Cl ₂ N ₂ O ₂ Pt (450.2): C, 24.01 ; H, 3.58; CI, 15.75; N, 6.22; O, 7.1 1 ; Pt, 43.33. Found: CI, 15.45; N, 6.02; Pt, 42.24. IR (neat): v = 3173 (NH) cm ^"1 . El MS (350 °C): m/e (%) = 449 ([M] ⁺ , 3), 413 ([M - HCI] ⁺ , 3), 377 ([M - 2HCI] ⁺ , 2), 99 (100). It decomposes above 300 °C without melting. The compound is insoluble in all solvents, including DMSO. No NMR characterization was performed. Example 5 - (Bispidin-9,9-diol)platinum(ll)dichloride (5)

A suspension of light yellow 4 (450 mg, 1 .00 mmol) in 40 mL of 6 N HCI was heated to 100 °C for 2 hours to give a yellow solution. All volatiles were removed in a vacuum to leave a bright yellow residue. This was repeatedly washed with small volumes of cold H ₂ O and cold ethanol to remove any acid and glycol, and the solid was dried again under vacuum (Figure 4). Recrystallization from boiling water and slow cooling afforded yellow needles: yield 360 mg (85%); mp 320 °C dec. IR (neat): v = 3394 (OH), 3310 (OH), 3223 (NH), 3180 (NH) cm ^"1 . ESIpos MS (DMF): m/e (%) = 871 ([2M + Na] ⁺ , 10), 446 ([M + Na] ⁺ , 100). Anal. Calcd for C ₇ H ₁₄ Cl ₂ N ₂ O ₂ Pt (424.2): C, 19.82; H, 3.33; N, 6.60; CI, 16.72; Pt, 45.99. Found: C, 20.02; H, 3.24; N, 6.71 ; CI, 16.78; Pt, 46.28.

Example 6 - (Bispidin-9,9-diol)platinum(ll)(1 ,1 -cvclobutanedicarboxylate) (6)

A warm (50 °C) solution of 5 (424 mg, 1 .00 mmol) in water (40 mL) was added to Ag ₂ (cbdca) (358 mg, 1 .00 mmol) suspended in water (10 mL). The reaction mixture was stirred in the dark for 24 hours and the precipitated AgCI was removed by filtration to leave a colorless solution. Concentration of the solution to 20 mL and standing overnight at room temperature gave a first crop of colorless needles. Further concentration of the mother liquor to half of the volume and cooling to 4 °C overnight gave a second crop of the product. According to X-ray diffraction the needles represent the dihydrate 6a. Drying the compound under vacuum at 50 °C overnight afforded the anhydrous 6: yield 370 mg (75%) (Figure 4). The anhydrous 6 decomposes at 260 °C to give black solid. IR (neat): v - 3394 (br, OH), 3161 (br, NH) cm ^-1 . Anal. Calcd for Ci ₃ H ₂ oN ₂ O ₆ Pt (495.4): C, 31 .52; H, 4.07; N, 5.62; Pt, 39.23. Found: C, 31 .38; H, 4.07; N, 5.62; Pt, 39.23. ESIpos MS: m/e (%) = 518 ([M + Na] ⁺ , 100), 540 ([M + 2 Na - H] ⁺ , 45). The complex dissolves well in water, DMF, and DMSO. Example 7 - (Bispidin-9,9-diol)platinum(ll)(oxalate) (7)

Combining a solution of 5 (424 mg, 1 .00 mmol) in warm water (40 mL; 50 °C) with a solution of AgNO3 (325 mg, 1 .91 mmol) in water (10 mL) immediately gave a colorless precipitate of AgCI. The mixture was stirred for five hours in the dark. The precipitate was filtered off and to the filtrate was added Na ₂ C ₂ O (128 mg, 0.95 mmol). The reaction mixture was stirred overnight and the product was obtained as a colorless precipitate, which was collected by filtration (Figure 4). Recrystallization from hot water afforded thin colorless needles: yield 400 mg (91 %); mp 310 °C dec. IR (neat): v = -3300 (vbr, OH), 321 1 (NH), 3104 (NH) cm ^-1 . Anal. Calcd for C ₉ H ₁₄ N ₂ O ₆ Pt (441 .3): C, 24.49; H, 3.20; N, 6.35; Pt, 44.21 . Found: C, 24.42; H, 3.25; N, 6.27; Pt, 44.04. ESIpos MS (DMF): m/e (%) = 905 ([2M + Na] ⁺ , 20), 464 ([M + Na] ⁺ , 100). The compound dissolves only poorly in water and even less so in DMF.

The compounds prepared in Examples 1 to 3 have been further tested for their pharmaceutical efficacy. The biological data have been obtained according to the following MTT cell viability assays.

MTT cell viability assays.

The rate of cell-survival under the action of test compounds was evaluated by an improved MTT assay as previously described for 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide (MTT, Applichem, Germany) (Mueller, H., Kassack, M. U., Wiese, M. J. Biomol. Screen. 2004, 9, 506-515).

The assay is based on the ability of viable cells to metabolize yellow MTT to violet formazane crystals that can be detected spectrophotometrically. In brief, A2780 (ECACC, Salisbury, UK) and A2780 CisR cells (established by exposure of A2780 cells to weekly cycles of 2 μηηοΙ/L cisplatin over a period of 24 weeks) were seeded at a density of 8,000 cells/well in 96well plates (Corning, Germany) in 90 μΙ_ drug-free complete medium. After an incubation period of 24 h at 37 °C under humidified air supplemented with 5% CO ₂ , cells were exposed to dilutions of the test compounds in 100 L/well. Stock solutions were prepared in a concentration of 10 ^"2 M in water, and serial dilutions were prepared by using sodium chloride 0.9%. Incubation was ended after 72 h and cell survival was determined by addition of 25 L/well MTT solution (5 mg/mL in phosphate buffered saline). After an incubation period of 10 min at 37 °C, the medium was carefully removed. The intracellular formazan product was solubilized by adding 75 μΙ DMSO/well. Absorbance was measured at 544 nm and 690 nm with a FLUOstar microplate-reader (BMG LabTech, Offenburg, Germany). The absorbance of untreated control cells was taken as 100% viability. All tests were performed in triplicate.

Data Analysis.

Indicated are mean values ± standard error of the mean. Concentration/inhibition curves were fitted to the data by nonlinear regression analysis using the four parameter logistic equation (GraphPad Prism).

Resistance factor of bispidine analogs 1 a, 2a, 3 and cisplatin, carboplatin, and oxaliplatin in the cisplatin resistance model A2780 / A2780 CisR.

ICso [μΜ]

Cpd. A2780 A2780 CisR resistance

factor

cisplatin 1 .38 16.2 1 1 .7

1a 4.20 10.6 2.52

carboplatin 4.23 40.2 9.50

2a 8.84 57.1 6.46

oxaliplatin 0.21 0.95 4.52

3 7.24 35.3 4.88

Values are means ± SEM derived from a representative experiment

performed in triplicate. The resistance factor was calculated as the

ratio of the IC ₅ o value of the A2780 CisR cells and the IC ₅ o value of

the corresponding sensitive parental A2780 cell line.