JIB-09649; No of Pages 11 Journal of Inorganic Biochemistry xxx (2015) xxx–xxx

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Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands Stefan Mollin a, Radostan Riedel a, Klaus Harms a, Eric Meggers a,b,⁎ a b

Fachbereich Chemie, Philipps-Universität Marburg, Hans-Meerwein-Straße, 35043 Marburg, Germany College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, People's Republic of China

a r t i c l e

i n f o

Available online xxxx Keywords: Rh complexes Stereochemistry Synthesis Enzyme inhibition Protein kinases

a b s t r a c t Octahedral metal complexes are attractive structural templates for the design of enzyme inhibitors as has been demonstrated, for example, with the development of metallo-pyridocarbazoles as protein kinase inhibitors. The octahedral coordination sphere provides untapped structural opportunities but at the same time poses the drawback of dealing with a large number of stereoisomers. In order to address this challenge of controlling the relative metal-centered configuration, the synthesis of rhodium(III) pyridocarbazole complexes with facially coordinating acyclic tridentate ligands was investigated. A strategy for the rapid synthesis of such complexes is reported, the diastereoselectivities of these reactions were investigated, the structure of several complexes were determined by X-ray crystallography, the high kinetic stability of such complexes in thiol-containing solutions was demonstrated in 1H-NMR experiments, and the protein kinase inhibition ability of this class of complexes was confirmed. It can be concluded that the use of multidentate ligands is currently maybe the most practical strategy to avoid a large number of possible stereoisomers in the course of exploiting octahedral coordination spheres as structural templates for the design of bioactive molecules. © 2015 Elsevier Inc. All rights reserved.

1. Introduction Metal complexes are an attractive class of compounds for drug development, as imaging reagents, and as tool compounds for chemical biology (for metal complexes in the life sciences, see [1–21]). Our laboratory contributed to this area of research by employing inert metal complexes as sophisticated structural scaffolds for the design of enzyme inhibitors, in particular inhibitors for protein kinases based on a meanwhile well established ATP-competitive metallo-pyridocarbazole scaffold (Fig. 1A) [22]. Metals such as Ru(II), Os(II), Rh(III), and Ir(III) are capable of forming highly stable complexes and provide new opportunities for building small molecular geometries which might be able to populate unique regions of chemical space going along with potential novel biological properties [23–32]. Strikingly, an octahedral geometry permits high structural complexity as can be illustrated by its rich stereochemistry: whereas a tetrahedral center is capable of building a maximum of two enantiomers, an octahedral center can form up to 30 stereoisomers [33]. Organic chemistry has developed a large number of sophisticated synthetic methods to control the relative and absolute stereochemistry at tetrahedral carbons and this has tremendously advanced the ability to synthesize structurally complicated optically active molecules in an

economical fashion. Unfortunately, this is not the case for octahedral metal complexes [34]. The enormous potential opportunities of octahedral metal complexes to serve as sophisticated structural scaffolds is therefore currently offset by the difficulties to control the metal configuration in the course of the coordination chemistry, which typically results in the formation of undesired or inseparable mixtures of stereoisomers. A progress in the area of biomedical research with metalcontaining compounds as structural scaffolds therefore requires progress for the development of suitable strategies to control the metalcentered stereochemistry. Here we report our progress in controlling the relative stereochemistry of octahedral rhodium(III) complexes [35, 36] with acyclic tridentate ligands, thereby reducing the number of possible diastereomers (Fig. 1B). We report a strategy for the rapid synthesis of octahedral rhodium(III) complexes bearing the pyridocarbazole heterocycle, investigate the structure of several complexes by X-ray crystallography, demonstrate the high kinetic stability of such complexes in thiol-containing solutions, and we demonstrate the inhibition of protein kinases by such rhodium(III) complexes. 2. Experimental section 2.1. Materials and methods

⁎ Corresponding author at: Fachbereich Chemie, Philipps-Universität Marburg, HansMeerwein-Straße, 35043 Marburg, Germany. Tel.: +49 6421 2821534; fax: +49 6421 2822189. E-mail address: [email protected] (E. Meggers).

Reactions were carried out using oven-dried glassware and conducted under a positive pressure of nitrogen unless otherwise specified. The synthesis of pyridocarbazole ligands 1a and 1b [37,38],

http://dx.doi.org/10.1016/j.jinorgbio.2015.01.005 0162-0134/© 2015 Elsevier Inc. All rights reserved.

Please cite this article as: S. Mollin, et al., Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands, J. Inorg. Biochem. (2015), http://dx.doi.org/10.1016/j.jinorgbio.2015.01.005

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S. Mollin et al. / Journal of Inorganic Biochemistry xxx (2015) xxx–xxx

A)

A B

D C B)

H N

O

O

H N

Improved O Stereocontrol

A

A N

N

N

N M

M D

O

B C

≤ 24 stereoisomers

D

B C

≤ 4 stereoisomers for fac-coordination

Fig. 1. Metal complexes as protein kinase inhibitors. A) Binding of the octahedral pyridocarbazole metal complex scaffold to the ATP-binding site of a protein kinase. The metal center in combination with the coordinating ligands A–D controls the shape and functional group presentation of the molecular scaffold und thus determines in large parts its biological properties. B) Multidentate ligands used as a tool to reduce the number of possible stereoisomers.

2-(methyl(pyridin-2-ylmethyl)amino)acetic acid [39], bis(pyridin-2ylmethyl)sulfide [40], and 2-(pyridin-2-ylmethylamino)acetic acid [41] has been reported. The literature known 2-(pyridin-2ylmethylthio)acetic acid [42] and N-methyl-N-bis(pyridin-2ylmethyl)amine [43] were prepared via modified procedures. Rhodium(III) chloride hydrate, bis(pyridin-2-ylmethyl)amine and other chemicals as well as all solvents were used as received from standard suppliers. Silica gel chromatography was performed with silica gel 60 from Merck KGaA (particle size of 4.0–6.3 μM). NMR spectra were recorded on an Avance 300 (300 MHz), DRX 400 (400 MHz), or Avance 500 (500 MHz) spectrometer. Infrared spectra were recorded on a Bruker Alpha FTIR. High resolution mass spectra were obtained with a Finnigan LTQ-FT instrument using either APCI or ESI. 2.2. Synthesis 2.2.1. Complex 2a A mixture of the N-benzylpyridocarbazole 1a (15.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 16 h. The solvent was removed and the crude material was purified by silica gel chromatography with CH2Cl2/MeOH 50:1. The combined product eluents were dried in vacuo to provide complex 2a as red solid (20.0 mg, 31.6 μmol, 79%). Rf = 0.36 (CH2Cl2/MeOH 20:1). 1H-NMR (300 MHz, DMSO-d6): δ (ppm) 9.27 (dt, J = 5.4, 0.9 Hz, 1H), 9.22 (dd, J = 8.4, 1.0 Hz, 1H), 8.68 (d, J = 7.6 Hz, 1H), 7.98 (dd, J = 8.4, 5.4 Hz, 1H), 7.84 (d, J = 8.4 Hz, 1H), 7.63 (td, J = 7.1, 1.3 Hz, 1H), 7.44–7.27 (m, 6H), 4.92 (s, 2H), 3.11 (s, 3H), 2.95 (s, 3H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 168.7, 168.6, 152.7, 151.2, 148.9, 142.0, 137.1, 135.2, 130.2, 128.6, 127.3, 127.2, 127.0, 125.9, 124.2, 124.1, 122.6, 120.9, 120.0, 114.7, 114.5, 113.1, 40.8, 3.9, 3.5. IR (film) ν (cm−1): 3065, 2929, 2261, 1753, 1698, 1495, 1418, 1389, 1341, 1229, 1140, 1015, 822, 751, 700. HRMS calcd for C28H21Cl2N5O2Rh (M + H)+ 632.0122, found 632.0099.

2.2.2. Complex 2b A mixture of N-TBS-pyridocarbazole 1b (16.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 2 h. The solvent was removed and the crude material was purified by silica gel chromatography with CH2Cl2/MeOH 50:1. The combined product eluents were dried in vacuo to provide complex 2b as red solid (15.2 mg, 28.0 μmol, 70%). Rf = 0.31 (CH2Cl2/ MeOH 20:1). 1H-NMR (300 MHz, DMSO-d6): δ (ppm) 11.25 (bs, 1H), 9.25 (d, J = 5.4 Hz, 1H), 9.22 (d, J = 8.4 Hz, 1H), 8.67 (d, J = 7.9 Hz, 1H), 7.95 (dd, J = 8.4, 5.4 Hz, 1H), 7.82 (d, J = 8.3 Hz, 1H), 7.63–7.58 (m, 1H), 7.42–7.37 (m, 1H), 3.11 (s, 3H), 2.95 (s, 3H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 170.4, 170.1, 152.5, 151.1, 148.8, 142.2, 135.2, 131.2, 126.7, 124.3, 124.1, 123.8, 122.7, 120.8, 119.7, 114.6, 114.4, 114.3, 3.8, 3.5. IR (film) ν (cm− 1): 3436, 3061, 2727, 2255, 1752, 1709, 1418, 1345, 1230, 1140, 1051, 1026, 824, 759, 638. HRMS calcd for C21H14Cl2N5O2RhNa (M + Na)+ 563.9472, found 563.9473. 2.2.3. Ligand 4a A mixture of 2-(chloromethyl)pyridine (5.10 g, 40.0 mmol), ethyl 2-mercaptoacetate (7.21 g, 60.0 mmol) and potassium carbonate (11.1 g, 80.0 mmol) in THF (100 mL) was refluxed overnight. The reaction mixture was concentrated, water (100 mL) was added, and the mixture was extracted with ethyl acetate (3x 100 mL). The combined organic layers were dried over sodium sulfate, filtered and concentrated. After purification by silica gel chromatography with n-hexane/ ethyl acetate 1:1 the ethyl ester was obtained as light yellow oil (6.70 g, 31.8 mmol, 79%). Rf = 0.27 (n-hexane/EtOAc 1:1). 1H-NMR (300 MHz, CDCl3): δ (ppm) 8.57 (d, J = 4.6 Hz, 1H), 7.66 (td, J = 7.7, 1.8 Hz, 1H), 7.36 (d, J = 7.8 Hz, 1H), 7.18 (ddd, J = 7.5, 4.9, 0.9 Hz, 1H), 4.17 (q, J = 7.1 Hz, 2H), 3.96 (s, 2H), 3.20 (s, 2H), 7.18 (t, J = 7.1 Hz, 3H). 13C-NMR (75 MHz, CDCl3): δ (ppm) 170.4, 157.8, 149.8, 136.8, 123.4, 122.2, 61.5, 38.4, 33.1, 14.3. IR (film) ν (cm− 1): 3053, 2982, 2933, 1726, 1589, 1471, 1435, 1270, 1149, 1124, 1027, 789, 749, 693, 582 cm− 1. HRMS calcd for C10H14NO2S (M + H)+ 212.0739, found 212.0740. The ethyl ester (408 mg, 1.93 mmol) was diluted in sodium hydroxide solution (1 M, 2.32 mL, 2.32 mmol) and the resulting suspension was stirred at room temperature for 3 h. The homogenous mixture was then neutralized with hydrochloric acid (1 M, 2.32 mL, 2.32 mmol) and stirred for further 30 min. The solvent was removed and the residue was dissolved in ethanol, treating in an ultrasonic bath, and filtered to remove the sodium chloride. The filtrate was concentrated and dried to obtain the product as white solid (380 mg, 1.85 mmol, 96%). 1 H-NMR (300 MHz, CD3OD): δ (ppm) 8.47 (d, J = 5.2 Hz, 1H), 7.95 (td, J = 7.8, 1.4 Hz, 1H), 7.58 (d, J = 7.9 Hz, 1H), 7.43 (d, J = 5.4 Hz, 1H), 3.95 (s, 2H), 3.14 (s, 2H) ppm. 13C-NMR (75 MHz, CDCl3): δ (ppm) 173.5, 158.0, 147.8, 141.8, 126.4, 124.8, 37.2, 34.1. IR (film) ν (cm-1): 3366, 3059, 2922, 1702, 1588, 1475, 1431, 1385, 1296, 1203, 1153, 1086, 1000, 787, 751, 696, 584 cm−1. HRMS calcd for C8H8NO2S (M–Na)– 182.0281, found 182.0282. 2.2.4. Complexes 5a and 5a′ A mixture of N-benzylpyridocarbazole 1a (15.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 16 h. To the resulting red solution, 2-(pyridin-2ylmethylthio)acetic acid (4a) (8.2 mg, 44.8 μmol) was added and the reaction mixture was refluxed at 90 °C for further 6 h. Then the solvent was removed and the crude material was purified by silica gel chromatography with CH2Cl2/MeOH (gradient 50:1 to 20:1). The combined product eluents of each stereoisomer were dried in vacuo to provide complex 5a as red solid (7.6 mg, 11.0 μmol, 28%) and complex 5a′ as red solid (6.8 mg, 9.80 μmol, 25%). 2.2.4.1. 5a. Rf = 0.29 (CH2Cl2/MeOH 20:1). 1H-NMR (300 MHz, DMSOd6): δ (ppm) 9.98 (d, J = 5.7 Hz, 1H), 9.28 (dd, J = 8.5, 1.0 Hz, 1H),

Please cite this article as: S. Mollin, et al., Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands, J. Inorg. Biochem. (2015), http://dx.doi.org/10.1016/j.jinorgbio.2015.01.005

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8.72 (d, J = 5.2 Hz, 1H), 8.65 (dd, J = 6.9, 1.9 Hz, 1H), 8.43 (td, J = 7.7, 1.4 Hz, 1H), 8.10–8.07 (m, 2H), 7.98 (t, J = 6.7 Hz, 1H), 7.42 (d, J = 7.4 Hz, 2H), 7.35 (t, J = 7.5 Hz, 2H), 7.29–7.20 (m, 3H), 5.76 (d, J = 7.2 Hz, 1H), 4.91 (s, 2H), 4.84 (d, J = 17.7 Hz, 1H), 4.45 (d, J = 17.7 Hz, 1H), 4.10 (d, J = 17.4 Hz, 1H), 3.69 (d, J = 17.5 Hz, 1H). 13 C-NMR (100 MHz, DMSO-d6): δ (ppm) 178.3, 168.8, 168.6, 162.4, 153.7, 152.9, 149.7, 148.8, 142.1, 140.8, 137.1, 135.0, 130.0, 128.6, 127.3, 127.3, 126.9, 125.9, 125.6, 124.5, 124.4, 123.3, 120.9, 119.8, 115.0, 113.3, 112.0, 44.4, 40.8, 37.4. IR (film) ν (cm−1): 3035, 2921, 1750, 1693, 1651, 1496, 1420, 1388, 1301, 1229, 1147, 1027, 744, 699, 630. HRMS calcd for C32H22ClN4O4RhS (M)+ 661.0411, found 661.0418. 2.2.4.2. 5a′. Rf = 0.22 (CH2Cl2/MeOH 20:1). 1H-NMR (300 MHz, DMSOd6): δ (ppm) 9.86 (d, J = 5.4 Hz, 1H), 9.16 (dd, J = 8.4, 1.0 Hz, 1H), 8.71 (d, J = 7.8 Hz, 1H), 8.32 (td, J = 7.7, 1.5 Hz, 1H), 8.00–7.88 (m, 3H), 7.74 (dd, J = 8.4, 5.3 Hz, 1H), 7.62 (d, J = 8.2 Hz, 1H), 7.55 (td, J = 8.3, 1.2 Hz, 1H), 7.44–7.25 (m, 6H), 4.93 (d, J = 17.5 Hz, 1H), 4.92 (s, 2H), 4.78 (d, J = 17.8 Hz, 1H), 3.94 (d, J = 17.6 Hz, 1H), 3.81 (d, J = 17.7 Hz, 1H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 178.6, 168.8, 168.7, 162.1, 152.6, 152.6, 150.8, 149.7, 149.7, 142.2, 140.2, 137.1, 134.7, 130.1, 128.6, 127.31, 127.27, 126.8, 125.7, 125.6, 124.5, 124.2, 121.1, 119.9, 114.9, 114.5, 112.7, 43.8, 40.8, 37.5. IR (film) ν (cm−1): 3065, 2924, 1749, 1694, 1650, 1499, 1421, 1388, 1304, 1231, 1057, 1027, 801, 752, 701, 630. HRMS calcd for C32H22ClN4O4RhS (M)+ 661.0411, found 661.0426. 2.2.5. Complexes 5b and 5b′ A mixture of N-benzylpyridocarbazole 1a (15.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 16 h. To the resulting red solution, 2-(pyridin-2ylmethylamino)acetic acid (4b) (7.5 mg, 44.8 μmol) was added and the reaction mixture was refluxed at 90 °C for further 6 h. Then the solvent was removed and the crude material was purified by silica gel chromatography with CH2Cl2/MeOH (gradient 50:1 to 20:1). The combined product eluents of each stereoisomer were dried in vacuo to provide complex 5b as red solid (5.6 mg, 8.07 μmol, 21%) and complex 5b′ as red solid (4.7 mg, 6.77 μmol, 17%). 2.2.5.1. 5b. Rf = 0.20 (CH2Cl2/MeOH 20:1). 1H-NMR (300 MHz, DMSOd6): δ (ppm) 9.71 (d, J = 5.7 Hz, 1H), 9.28 (dd, J = 8.4, 1.1 Hz, 1H), 8.81 (d, J = 5.1 Hz, 1H), 8.66 (d, J = 7.2 Hz, 1H), 8.43 (td, J = 7.8, 1.5 Hz, 1H), 8.09 (dd, J = 8.4, 5.2 Hz, 1H), 8.02–7.98 (m, 1H), 7.94 (d, J = 7.7 Hz, 1H), 7.74 (m, 1H), 7.41–7.17 (m, 7H), 5.72 (d, J = 7.3 Hz, 1H), 4.94 (s, 2H), 4.33 (d, J = 16.7 Hz, 1H), 4.16 (dd, J = 16.5, 4.5 Hz, 1H), 3.85–3.76 (m, 1H), 3.37 (m, J = 17.5 Hz, 1H). 13C-NMR (100 MHz, DMSO-d6): δ (ppm) 180.5, 169.0, 168.8, 162.7, 153.8, 152.1, 149.0, 143.0, 140.7, 137.2, 134.6, 129.9, 128.6, 127.3, 127.1, 126.7, 125.8, 124.4, 124.2, 123.7, 123.2, 121.0, 119.6, 114.7, 112.6, 112.0, 61.7, 55.9, 40.8. IR (film) ν (cm- 1): 3067, 2889, 1696, 1657, 1633, 1495, 1422, 1387, 1338, 1300, 1231, 1029, 742, 699. HRMS calcd for C32H24ClN5O4Rh (M + H)+ 680.0566, found 680.0572. 2.2.5.2. 5b′. Rf = 0.16 (CH2Cl2/MeOH 20:1). 1H-NMR (300 MHz, DMSOd6): δ (ppm) 9.59 (d, J = 5.7 Hz, 1H), 9.16 (dd, J = 8.4 Hz, J = 1.0 Hz, 1H), 8.74 (d, J = 7.8 Hz, 1H), 8.32 (td, J = 7.8, 1.5 Hz, 1H), 7.96–7.85 (m, 3H), 7.75–7.70 (m, 3H), 7.57–7.52 (m, 1H), 7.41–7.28 (m, 6H), 4.94 (s, 2H), 4.53 (dd, J = 16.8, 5.1 Hz, 1H), 4.30 (d, J = 17.4 Hz, 1H), 3.61 (dd, J = 17.3, 7.6 Hz, 1H), 3.43 (d, J = 17.2 Hz, 1H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 180.6, 169.0, 168.8, 162.5, 153.6, 151.0, 150.3, 150.0, 143.0, 140.2, 137.2, 134.4, 130.0, 128.6, 127.3, 127.1, 126.7, 125.5, 124.2, 124.1, 123.8, 123.2, 121.0, 119.8, 114.8, 114.4, 112.0, 60.9, 57.4, 40.7. IR (film) ν (cm-1): 3075, 2924, 1747, 1692, 1643, 1498, 1424, 1387, 1337, 1298, 1232, 1127, 1025, 822, 755. HRMS calcd for C32H23ClN5O4RhNa (M + Na)+ 702.0386, found 702.0390.

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2.2.6. Complexes 5c and 5c′ 2.2.6.1. Method A. A mixture of N-benzylpyridocarbazole 1a (15.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 16 h. To the resulting red solution, 2(methyl(pyridin-2-ylmethyl)amino)acetic acid (4c) (8.1 mg, 44.8 μmol) was added and the reaction mixture was refluxed at 90 °C for further 6 h. Then the solvent was removed and the crude material was purified by silica gel chromatography with CH2Cl2/MeOH (gradient 50:1 to 20:1). The combined product eluents of each stereoisomer were dried in vacuo to provide complex 5c as red solid (5.8 mg, 8.36 μmol, 21%) and complex 5c′ as red solid (11.8 mg, 17.0 μmol, 43%). 2.2.6.2. Method B. A mixture of complex 6 (15.8 mg, 40.0 μmol) and N-benzylpyridocarabzole 1a (15.1 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 16 h. The solvent was removed and the crude material was purified by silica gel chromatography with CH2Cl2/MeOH (gradient 50:1 to 20:1). The combined product eluents of each stereoisomer were dried in vacuo to provide complex 5c as red solid (14.0 mg, 20.4 μmol, 51%) and complex 5c′ as red solid (4.7 mg, 6.80 μmol, 17%). 2.2.6.3. 5c. Rf = 0.22 (CH2Cl2/MeOH 20:1). 1H-NMR (300 MHz, DMSOd6): δ (ppm) 9.66 (d, J = 5.5 Hz, 1H), 9.30 (d, J = 8.4 Hz, 1H), 8.92 (d, J = 5.1 Hz, 1H), 8.67 (d, J = 6.9 Hz, 1H), 8.47 (td, J = 7.8, 1.1 Hz, 1H), 8.14 (dd, J = 8.4, 5.2 Hz, 1H), 8.05–7.99 (m, 2H), 7.44–7.20 (m, 7H), 5.77 (d, J = 7.4 Hz, 1H), 4.92 (s, 2H), 4.56 (d, J = 16.0 Hz, 1H), 4.26 (d, J = 15.9 Hz, 1H), 3.95 (d, J = 17.6 Hz, 1H), 3.66 (d, J = 17.6 Hz, 1H), 1.87 (s, 3H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 179.2, 168.9, 168.7, 160.9, 152.9, 152.5, 149.2, 148.9, 141.9, 141.2, 137.2, 135.0, 130.1, 128.6, 127.4, 126.8, 126.3, 124.6, 124.5, 123.7, 123.3, 121.1, 119.7, 115.2, 113.3, 112.0, 71.5, 65.8, 50.7, 40.8 ppm. IR (film) ν (cm−1): 2924, 2877, 1750, 1694, 1657, 1492, 1422, 1387, 1343, 1231, 737, 698. HRMS calcd for C33H25ClN5O4RhNa (M + Na)+ 716.0542, found 716.0533. 2.2.6.4. 5c′. Rf = 0.17 (CH2Cl2/MeOH 20:1). 1H-NMR (300 MHz, DMSOd6): δ (ppm) 9.54 (d, J = 5.7 Hz, 1H), 9.18 (dd, J = 8.4, 0.9 Hz, 1H), 8.74 (d, J = 7.8 Hz, 1H), 8.36 (td, J = 7.8, 1.4 Hz, 1H), 8.06 (d, J = 5.2 Hz, 1H), 7.96–7.90 (m, 2H), 7.80–7.74 (m, 2H), 7.58 (td, J = 7.7, 1.4 Hz, 1H), 7.45–7.27 (m, 6H), 4.92 (s, 2H), 4.67 (d, J = 16.7 Hz, 1H), 4.57 (d, J = 16.7 Hz, 1H), 3.76 (s, 2H), 1.79 (s, 3H). 13C-NMR (125 MHz, DMSOd6): δ (ppm) 179.1, 168.9, 168.8, 160.7, 152.6, 151.4, 150.8, 149.3, 142.1, 140.7, 137.2, 134.8, 130.2, 128.6, 127.4, 127.3, 126.9, 126.0, 124.4, 124.2, 123.7, 123.2, 121.2, 119.9, 115.1, 114.6, 112.8, 70.6, 67.3, 51.1, 40.8. IR (film) ν (cm− 1): 3065, 2929, 2855, 1751, 1695, 1653, 1584, 1499, 1422, 1390, 1351, 1308, 1233, 755, 700. HRMS calcd for C33H25ClN5O4RhNa (M + Na)+ 716.0542, found 716.0535. 2.2.7. Complexes 5d and 5d′ A mixture of N-TBS-pyridocarbazole 1b (16.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 2 h. To the resulting red solution, 2-(pyridin-2ylmethylthio)acetic acid (4a) (8.2 mg, 44.8 μmol) was added and the reaction mixture was refluxed at 90 °C for further 3 h. Then the solvent was removed and the crude material was purified by silica gel chromatography with CH2Cl2/MeOH (gradient 50:1 to 20:1). The combined product eluents of each stereoisomer were dried in vacuo to provide complex 5d as red orange solid (5.3 mg, 8.73 μmol, 22%) and complex 5d′ as red solid (9.2 mg, 15.2 μmol, 38%). 2.2.7.1. 5d. Rf = 0.27 (CH2Cl2/MeOH 15:1). 1H-NMR (300 MHz, DMSOd6): δ (ppm) 11.26 (bs, 1H), 9.97 (d, J = 5.9 Hz, 1H), 9.27 (d, J = 8.4 Hz, 1H), 8.71 (d, J = 5.1 Hz, 1H), 8.65 (d, J = 7.2 Hz, 1H), 8.42 (t, J = 7.7 Hz, 1H), 8.09–8.04 (m, 2H), 7.23 (t, J = 6.6 Hz, 1H), 7.27–7.18 (m, 2H), 5.75 (d, J = 7.8 Hz, 1H), 4.82 (d, J = 17.6 Hz, 1H),

Please cite this article as: S. Mollin, et al., Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands, J. Inorg. Biochem. (2015), http://dx.doi.org/10.1016/j.jinorgbio.2015.01.005

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S. Mollin et al. / Journal of Inorganic Biochemistry xxx (2015) xxx–xxx

4.44 (d, J = 17.7 Hz, 1H), 4.09 (d, J = 17.4 Hz, 1H), 3.69 (d, J = 17.6 Hz, 1H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 178.3, 170.6, 170.2, 162.4, 153.7, 152.7, 149.6, 148.7, 142.3, 140.8, 135.1, 131.1, 126.7, 125.9, 125.6, 124.6, 124.2, 123.3, 120.9, 119.6, 114.7, 114.5, 111.9, 44.4, 37.4. IR (film) ν (cm−1): 3220, 3059, 2960, 2922, 2854, 2360, 1751, 1709, 1653, 1415, 1345, 1305, 1260, 1230, 1089, 1020, 799, 747. HRMS calcd for C25H16ClN4O4RhSNa (M + Na)+ 628.9528, found 628.9532. 2.2.7.2. 5d′. Rf = 0.22 (CH2Cl2/MeOH 15:1). 1H-NMR (300 MHz, DMSOd6): δ (ppm) 11.25 (bs, 1H), 9.86 (d, J = 5.6 Hz, 1H), 9.15 (d, J = 8.3 Hz, 1H), 8.71 (d, J = 8.0 Hz, 1H), 8.31 (t, J = 7.8 Hz, 1H), 7.99 (d, J = 7.9 Hz, 1H), 7.94–7.88 (m, 2H), 7.71 (dd, J = 8.3, 5.2 Hz, 1H), 7.62 (d, J = 8.2 Hz, 1H), 7.53 (t, J = 7.6 Hz, 1H), 7.38 (t, J = 7.4 Hz, 1H), 4.91 (d, J = 17.4 Hz, 1H), 4.77 (d, J = 17.5 Hz, 1H), 3.92 (d, J = 17.7 Hz, 1H), 3.81 (d, J = 17.7 Hz, 1H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 178.7, 170.6, 170.2, 162.1, 152.6, 152.4, 150.7, 149.6, 142.4, 140.2, 134.8, 131.2, 126.6, 125.7, 125.6, 124.3, 123.4, 121.1, 119.7, 114.7, 114.4, 114.1, 43.8, 37.6. IR (film) ν (cm− 1): 3178, 3057, 2923, 2855, 1749, 1707, 1626, 1501, 1421, 1344, 1270, 1233, 1021, 754, 643. HRMS calcd for C25H16ClN4O4RhSNa (M + Na)+ 628.9528, found 628.9532. 2.2.8. Complexes 5e and 5e′ A mixture of N-TBS-pyridocarbazole 1b (16.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 2 h. To the resulting red solution, 2-(pyridin-2ylmethylamino)acetic acid (4b) (7.5 mg, 44.8 μmol) was added and the reaction mixture was refluxed at 90 °C for further 3 h. Then the solvent was removed and the crude material was purified by silica gel chromatography with CH2Cl2/MeOH (gradient 50:1 to 15:1). The combined product eluents of each stereoisomer were dried in vacuo to provide complex 5e as red orange solid (5.3 mg, 8.99 μmol, 23%) and complex 5e′ as red solid (4.7 mg, 7.97 μmol, 20%). 2.2.8.1. 5e. Rf = 0.23 (CH2Cl2/MeOH 15:1). 1H-NMR (400 MHz, DMSOd6): δ (ppm) 11.22 (s, 1H), 9.72 (d, J = 5.6 Hz, 1H), 9.26 (dd, J = 8.3, 0.8 Hz, 1H), 8.80 (d, J = 5.1 Hz, 1H), 8.65 (d, J = 7.5 Hz, 1H), 8.42 (td, J = 7.8, 1.2 Hz, 1H), 8.06 (dd, J = 8.4, 5.2 Hz, 1H), 8.00 (t, J = 6.8 Hz, 1H), 7.94 (d, J = 7.9 Hz, 1H), 7.70 (m, 1H), 7.24 (t, J = 7.0 Hz, 1H), 7.18 (td, J = 7.6, 1.2 Hz, 1H), 5.71 (d, J = 8.1 Hz, 1H), 4.32 (d, J = 16.7 Hz, 1H), 4.16 (dd, J = 16.5, 4.9 Hz, 1H), 4.09 (dd, J = 17.5, 8.3 Hz, 1H), 3.38 (m, 1H). 13C-NMR (100 MHz, DMSO-d6): δ (ppm) 180.5, 170.7, 170.3, 162.7, 153.5, 152.1, 148.9, 143.2, 140.7, 134.7, 130.9, 126.4, 125.8, 124.5, 124.0, 123.7, 123.3, 121.0, 119.4, 114.5, 113.9, 111.9, 61.6, 55.9. IR (film) ν (cm− 1): 3428, 3178, 2923, 2854, 1750, 1704, 1647, 1499, 1423, 1345, 1230, 1023, 748, 642, 497. HRMS calcd for C25H17ClN5O4RhSNa (M + Na)+ 611.9916, found 611.9918. 2.2.8.2. 5e′. Rf = 0.18 (CH2Cl2/MeOH 15:1). 1H-NMR (300 MHz, DMSOd6): δ (ppm) 11.23 (s, 1H), 9.58 (d, J = 5.5 Hz, 1H), 9.15 (d, J = 8.2 Hz, 1H), 8.73 (d, J = 7.8 Hz, 1H), 8.32 (td, J = 7.7, 1.2 Hz, 1H), 7.95–7.85 (m, 3H), 7.73–7.68 (m, 3H), 7.53 (t, J = 7.4 Hz, 1H), 7.38 (t, J = 7.4 Hz, 1H), 4.52 (dd, J = 17.0, 5.9 Hz, 1H), 4.29 (d, J = 17.7 Hz, 1H), 3.60 (dd, J = 17.1, 7.2 Hz, 1H), 3.45 (m, 1H). IR (film) ν (cm−1): 3380, 3172, 2922, 2854, 1749, 1702, 1648, 1423, 1347, 1297, 1232, 1151, 1025, 822, 756, 642, 493. HRMS calcd for C25H17ClN5O4RhNa (M + Na)+ 611.9916, found 611.9912. 2.2.9. Complexes 5f and 5f′ A mixture of N-TBS-pyridocarbazole 1b (16.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 2 h. To the resulting red solution, 2(methyl(pyridin-2-ylmethyl)amino)acetic acid (4c) (8.1 mg, 44.8 μmol) was added and the reaction mixture was refluxed at 90 °C for further 3 h. Then the solvent was removed and the crude material was purified by silica gel chromatography with CH2Cl2/MeOH (gradient 50:1 to 15:1). The combined product eluents of each stereoisomer were dried

in vacuo to provide complex 5f as red orange solid (3.0 mg, 5.13 μmol, 13%) and complex 5f′ as red solid (7.3 mg, 12.1 μmol, 30%). 2.2.9.1. 5f. Rf = 0.23 (CH2Cl2/MeOH 15:1). 1H-NMR (300 MHz, DMSOd6): δ (ppm) 11.27 (bs, 1H), 9.66 (d, J = 5.4 Hz, 1H), 9.30 (d, J = 8.0 Hz, 1H), 8.91 (d, J = 5.2 Hz, 1H), 8.68 (d, J = 7.9 Hz, 1H), 8.47 (t, J = 7.9 Hz, 1H), 8.12 (dd, J = 8.4, 5.2 Hz, 1H), 8.05–7.99 (m, 2H), 7.29–7.18 (m, 2H), 5.75 (d, J = 7.8 Hz, 1H), 4.56 (d, J = 15.9 Hz, 1H), 4.26 (d, J = 15.9 Hz, 1H), 3.95 (d, J = 17.3 Hz, 1H), 3.67 (d, J = 17.3 Hz, 1H), 1.86 (s, 3H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 179.2, 170.6, 170.3, 160.9, 152.7, 152.5, 149.0, 148.8, 142.1, 141.2, 135.1, 131.1, 126.6, 126.3, 124.7, 124.2, 123.7, 123.4, 121.1, 119.6, 115.0, 114.6, 111.9, 71.5, 65.8, 50.7. IR (film) ν (cm− 1): 3225, 2952, 2924, 1714, 1668, 1414, 1346, 1260, 1088, 1018, 872, 798, 746. HRMS calcd for C26H19ClN5O4RhNa (M + Na)+ 626.0073, found 626.0083. 2.2.9.2. 5f′. Rf = 0.17 (CH2Cl2/MeOH 15:1). 1H-NMR (300 MHz, DMSOd6): δ (ppm) 11.24 (s, 1H), 9.54 (d, J = 5.5 Hz, 1H), 9.18 (d, J = 7.8 Hz, 1H), 8.73 (d, J = 7.9 Hz, 1H), 8.36 (td, J = 7.7, 1.3 Hz, 1H), 8.04 (d, J = 5.2 Hz, 1H), 7.96–7.90 (m, 2H), 7.79–7.72 (m, 2H), 7.56 (td, J = 7.7, 1.0 Hz, 1H), 7.40 (t, J = 7.3 Hz, 1H), 4.66 (d, J = 16.6 Hz, 1H), 4.55 (d, J = 16.7 Hz, 1H), 3.75 (s, 2H), 1.78 (s, 3H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 179.1, 170.6, 170.3, 160.7, 152.4, 151.4, 150.7, 149.2, 142.3, 140.7, 134.8, 131.2, 126.6, 125.9, 124.3, 124.2, 123.6, 121.1, 119.7, 114.8, 114.5, 114.1, 70.6, 67.3, 51.1. IR (film) ν (cm−1): 3445, 3221, 3065, 2926, 1709, 1654, 1418, 1346, 1264, 1231, 1088, 1016, 798, 765, 640. HRMS calcd for C26H19ClN5O4RhNa (M + Na)+ 626.0073, found 626.0082. 2.2.10. Complex 6 A mixture 2-(methyl(pyridin-2-ylmethyl)amino)acetic acid (4c) (16.2 mg, 89.6 μmol) and RhCl3 · 3H2O (21.0 mg, 80.0 μmol) in MeCN/ H2O 1:1 (8.0 mL) was refluxed at 90 °C for 16 h. The solvent was removed and the crude material was purified by silica gel chromatography with CH2Cl2/MeOH (gradient 50:1 to 20:1). The combined product eluents were dried in vacuo to provide complex 6 as light yellow solid (21.4 mg, 54.3 μmol, 68%). Rf = 0.27 (CH2Cl2/MeOH 20:1). 1H-NMR (300 MHz, CD3CN): δ (ppm) 8.83 (d, J = 5.5 Hz, 1H), 8.05 (td, J = 7.8, 1.4 Hz, 1H), 7.63–7.57 (m, 2H), 4.89 (d, J = 16.0 Hz, 1H), 4.29 (d, J = 16.1 Hz, 1H), 3.98 (dd, J = 16.9, 0.9 Hz, 1H), 3.53 (d, J = 16.9 Hz, 1H), 3.18 (s, 3H), 2.65 (s, 3H). 13C-NMR (125 MHz, CD3CN): δ (ppm) 179.2, 160.7, 152.0, 141.1, 126.7, 124.5, 123.8, 73.9, 69.5, 53.9, 4.7. IR (film) ν (cm−1): 3526, 2970, 2926, 2324, 2257, 1648, 1442, 1351, 1310, 1262, 927, 893, 770, 470. HRMS calcd for C11H14Cl2N3O2RhNa (M + Na)+ 415.9410, found 415.9410. 2.2.11. N-Methyl-N-bis(pyridin-2-ylmethyl)amine (7c) An aqueous formaldehyde solution (37%, 17 mL, 200 mmol) was added to a solution of bis(pyridin-2-ylmethyl)amine (1.99 g, 10.0 mmol) in MeOH at 0 °C. Then NaBH3CN (1.26 g, 20.0 mmol) was added at 0 °C and the reaction was stirred for 1 h at room temperature. The reaction mixture was carefully poured into stirring icecold H2O (50 mL) and extracted with Et2O (3x 50 mL). The combined organic layers were washed with sat. NaCl solution, dried over MgSO4, filtered and concentrated. The crude material was purified by silica gel chromatography with n-hexane/EtOAc 10:1 to obtain the product as light yellow oil (1.96 g, 9.19 mmol, 92%). Rf = 0.35 (n-hexane/EtOAc 10:1).1H-NMR (300 MHz, CDCl3): δ (ppm) 8.54 (d, J = 4.9 Hz, 2H), 7.65 (td, J = 7.7, 1.8 Hz, 2H), 7.50 (d, J = 7.7 Hz, 2H), 7.17–7.12 (m, 2H), 3.76 (s, 4H), 2.30 (s, 3H). 13C-NMR (75 MHz, CDCl3): δ (ppm) 159.5, 149.2, 136.5, 123.2, 122.1, 63.8, 42.9. IR (film) ν (cm−1): 3386, 3061, 2840, 2798, 1664, 1591, 1473, 1435, 1368, 1039, 997, 762, 620 cm−1. HRMS calcd for C13H16N3 (M + H)+ 214.1339, found 214.1338.

Please cite this article as: S. Mollin, et al., Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands, J. Inorg. Biochem. (2015), http://dx.doi.org/10.1016/j.jinorgbio.2015.01.005

S. Mollin et al. / Journal of Inorganic Biochemistry xxx (2015) xxx–xxx

2.2.12. Complex 8a A mixture of N-benzylpyridocarbazole 1a (15.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 16 h. To the resulting red solution, bis(pyridin-2ylmethyl)sulfide (7a) (8.7 mg, 40.0 μmol) was added and the reaction mixture was refluxed at 90 °C for further 3 h. Then the solvent was removed and the crude material was purified by silica gel chromatography with MeCN/H2O/sat. KNO3 solution (200:3:3). The combined product eluents were concentrated, washed with H2O (3 × 5 mL), and dried in vacuo to provide complex 8a as red solid (14.9 mg, 18.8 μmol, 47%). Rf = 0.46 (MeCN/H2O/sat. KNO3 solution, 200:3:3). 1H-NMR (300 MHz, DMSO-d6): δ (ppm) 9.79 (d, J = 5.9 Hz, 1H), 9.72 (d, J = 5.8 Hz, 1H), 9.28 (dd, J = 7.5, 2.0 Hz, 1H), 8.72 (d, J = 7.5 Hz, 1H), 8.38 (td, J = 7.7, 1.4 Hz, 1H), 8.26 (td, J = 7.7, 1.4 Hz, 1H), 8.06 (d, J = 7.8 Hz, 1H), 7.95–7.83 (m, 5H), 7.44–7.20 (m, 7H), 5.58 (d, J = 8.1 Hz, 1H), 5.18 (d, J = 18.3 Hz, 1H), 5.05 (d, J = 18.3 Hz, 1H), 4.95–4.85 (m, 4H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 168.8, 168.5, 163.4, 163.3, 152.7, 152.5, 151.3, 150.8, 148.5, 148.5, 141.8, 141.3, 140.7, 137.1, 135.6, 130.1, 128.6, 127.34, 127.30, 127.1, 126.3, 125.8, 125.6, 124.9, 124.7, 123.6, 121.2, 120.1, 115.4, 113.8, 112.0, 44.7, 44.2, 40.8. IR (film) ν (cm− 1): 3420, 3037, 2958, 2910, 1749, 1692, 1605, 1494, 1383, 1333, 1269, 1228, 1145, 1028, 737, 697, 628. HRMS calcd for C36H26ClN5O2RhS (M)+ 730.0545, found 730.0544. 2.2.13. Complex 8b A mixture of N-benzylpyridocarbazole 1a (15.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 16 h. To the resulting red solution, bis(pyridin-2ylmethyl)amine (7b) (8.0 mg, 40.0 μmol) was added and the reaction mixture was refluxed at 90 °C for further 3 h. Then the solvent was removed and the crude material was purified by silica gel chromatography with MeCN/H2O/sat. KNO3 solution (200:3:3). The combined product eluents were concentrated, washed with H2O (3 × 5 mL), and dried in vacuo to provide complex 8b as red solid (13.0 mg, 16.8 μmol, 42%). Rf = 0.40 (MeCN/H2O/sat. KNO3 solution, 200:3:3). 1H-NMR (300 MHz, DMSO-d6): δ (ppm) 9.53 (d, J = 5.9 Hz, 1H), 9.46 (d, J = 5.8 Hz, 1H), 9.28 (dd, J = 8.4, 1.0 Hz, 1H), 8.72 (d, J = 7.4 Hz, 1H), 8.69–8.64 (m, 1H), 8.35 (td, J = 7.8, 1.3 Hz, 1H), 8.24 (td, J = 7.8, 1.4 Hz, 1H), 8.02 (d, J = 5.2 Hz, 1H), 7.90–7.77 (m, 5H), 7.42–7.20 (m, 7H), 5.66 (d, J = 8.1 Hz, 1H), 4.94 (s, 2H), 4.92–4.86 (m, 1H), 4.68–4.51 (m, 3H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 168.9, 168.7, 163.4, 153.4, 150.8, 150.3, 149.6, 149.0, 142.7, 141.2, 140.7, 137.1, 135.3, 130.1, 128.6, 127.6, 127.4, 127.2, 127.0, 126.2, 126.1, 124.7, 124.6, 123.8, 123.5, 123.4, 121.2, 119.9, 115.0, 113.1, 111.9, 62.1, 61.0, 40.8. IR (film) ν (cm− 1): 3450, 3070, 2926, 1749, 1695, 1610, 1583, 1496, 1395, 1354, 1232, 1147, 1109, 1034, 760, 699. HRMS calcd for C36H27ClN6O2Rh (M)+ 713.0932, found 713.0934. 2.2.14. Complex 8c A mixture of N-benzylpyridocarbazole 1a (15.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 16 h. To the resulting red solution, N-methyl-Nbis(pyridin-2-ylmethyl)amine (7c) (8.5 mg, 40.0 μmol) was added and the reaction mixture was refluxed at 90 °C for further 3 h. Then the solvent was removed and the crude material was purified by silica gel chromatography with MeCN/H2O/sat. KNO3 solution (200:3:3). The combined product eluents were concentrated, washed with H2O (3 × 5 mL), and dried in vacuo to provide complex 8c as red solid (14.9 mg, 18.9 μmol, 47%). Rf = 0.41 (MeCN/H2O/sat. KNO3 solution, 200:3:3). 1H-NMR (300 MHz, DMSO-d6): δ (ppm) 9.47 (d, J = 5.7 Hz, 1H), 9.40 (d, J = 5.7 Hz, 1H), 9.31 (dd, J = 8.4, 0.9 Hz, 1H), 8.74 (d, J = 7.6 Hz, 1H), 8.40 (td, J = 7.8 Hz, J = 1.3 Hz, 1H), 8.28 (td, J = 7.8, 1.3 Hz, 1H), 8.02 (d, J = 5.2 Hz, 2H), 7.95–7.84 (m, 4H), 7.80 (d, J = 7.9 Hz, 1H), 7.44–7.23 (m, 7H), 5.67 (d, J = 8.1 Hz, 1H), 5.00 (d, J = 17.9 Hz, 1H), 4.94 (m, 4H), 4.72 (d, J = 17.1 Hz, 1H), 2.10 (s, 3H). 13CNMR (125 MHz, DMSO-d6): δ (ppm) 168.8, 168.6, 162.1, 161.8, 152.4,

5

151.3, 150.3, 150.0, 148.5, 148.5, 141.7, 137.1, 135.7, 130.2, 128.6, 127.39, 127.36, 127.1, 126.5, 124.9, 124.8, 123.8, 123.42, 123.36, 121.4, 120.1, 115.6, 113.9, 112.0, 71.6, 70.4, 51.6, 40.8. IR (film) ν (cm− 1): 3425, 3056, 2932, 1750, 1694, 1610, 1493, 1384, 1332, 1228, 1145, 1026, 740, 698, 628, 498. HRMS calcd for C37H29ClN6O2Rh (M)+ 727.1090, found 727.1087. 2.2.15. Complex 8d A mixture of N-TBS-pyridocarbazole 1b (16.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 2 h. To the resulting red solution, bis(pyridin-2ylmethyl)sulfide (7a) (8.7 mg, 40.0 μmol) was added and the reaction mixture was refluxed at 90 °C for further 2 h. Then the solvent was removed and the crude material was purified by silica gel chromatography with MeCN/H2O/sat. KNO3 solution (200:3:3). The combined product eluents were concentrated, washed with H2O (3 × 5 mL), and dried in vacuo to provide complex 8d as red solid (9.9 mg, 14.1 μmol, 35%). Rf = 0.39 (MeCN/H2O/sat. KNO3 solution, 200:3:3). 1H-NMR (300 MHz, DMSO-d6): δ (ppm) 11.34 (s, 1H), 9.79 (d, J = 5.9 Hz, 1H), 9.72 (d, J = 5.8 Hz, 1H), 9.27 (dd, J = 7.8, 1.7 Hz, 1H), 8.72 (d, J = 7.6 Hz, 1H), 8.37 (td, J = 7.8, 1.4 Hz, 1H), 8.25 (td, J = 7.7, 1.4 Hz, 1H), 8.05 (d, J = 7.6 Hz, 1H), 7.94–7.83 (m, 5H), 7.30 (t, J = 7.5 Hz, 1H), 7.22 (t, J = 7.7 Hz, 1H), 5.57 (d, J = 8.2 Hz, 1H), 5.16 (d, J = 18.3 Hz, 1H), 5.03 (d, J = 18.3 Hz, 1H), 4.90 (d, J = 18.3 Hz, 1H), 4.87 (d, J = 18.2 Hz, 1H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 170.5, 170.0, 163.4, 163.3, 152.7, 152.2, 151.3, 150.7, 148.4, 142.0, 141.3, 140.7, 135.7, 131.1, 126.9, 126.3, 125.8, 125.6, 124.8, 124.7, 123.6, 121.1, 119.9, 115.0, 111.8, 44.7, 44.2. IR (film) ν (cm−1): 3058, 1752, 1706, 1604, 1491, 1412, 1343, 1270, 1230, 1019, 750, 642. HRMS calcd for C29H20ClN5O2Rh (M)+ 640.0076, found 640.0065. 2.2.16. Complex 8e A mixture of N-TBS-pyridocarbazole 1b (16.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 2 h. To the resulting red solution, bis(pyridin-2ylmethyl)amine (7b) (8.0 mg, 40.0 μmol) was added and the reaction mixture was refluxed at 90 °C for further 2 h. Then the solvent was removed and the crude material was purified by silica gel chromatography with MeCN/H2O/sat. KNO3 solution (200:3:3). The combined product eluents were concentrated, washed with H2O (3 × 5 mL), and dried in vacuo to provide complex 8e as red solid (11.5 mg, 16.8 μmol, 42%). Rf = 0.33 (MeCN/H2O/sat. KNO3 solution, 200:3:3). 1H-NMR (300 MHz, DMSO-d6): δ (ppm) 11.30 (bs, 1H), 9.54 (d, J = 5.8 Hz, 1H), 9.47 (d, J = 5.7 Hz, 1H), 9.28 (d, J = 8.3 Hz, 1H), 8.72 (d, J = 7.8 Hz, 1H), 8.59 (m, 1H), 8.35 (t, J = 7.8 Hz, 1H), 8.24 (td, J = 7.7, 1.3 Hz, 1H), 8.00 (d, J = 5.2 Hz, 1H), 7.89–7.81 (m, 4H), 7.77 (d, J = 8.0 Hz, 1H) 7.29 (t, J = 7.3 Hz, 1H), 7.21 (t, J = 7.7 Hz, 1H), 5.65 (d, J = 8.3 Hz, 1H), 4.88 (m, 1H), 4.65–4.53 (m, 3H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 170.6, 170.2, 163.4, 163.3, 153.1, 150.8, 150.1, 149.7, 148.8, 142.8, 141.2, 140.7, 135.4, 131.1, 126.7, 126.2, 126.1, 124.7, 124.4, 123.7, 123.4, 121.1, 119.7, 114.8, 114.4, 111.8, 62.1, 61.0. IR (film) ν (cm− 1): 3455, 3118, 2920, 1749, 1701, 1493, 1413, 1345, 1230, 1021, 826, 764, 643. HRMS calcd for C29H21ClN6O2Rh (M)+ 623.0464, found 623.0455. 2.2.17. Complex 8f A mixture of N-TBS-pyridocarbazole 1b (16.1 mg, 40.0 μmol) and RhCl3 · 3H2O (10.5 mg, 40.0 μmol) in MeCN/H2O 1:1 (4.0 mL) was refluxed at 90 °C for 2 h. To the resulting red solution, N-methyl-Nbis(pyridin-2-ylmethyl)amine (7c) (8.5 mg, 40.0 μmol) was added and the reaction mixture was refluxed at 90 °C for further 2 h. Then the solvent was removed and the crude material was purified by silica gel chromatography with MeCN/H2O/sat. KNO3 solution (200:3:3). The combined product eluents were concentrated, washed with H2O (3 × 5 mL), and dried in vacuo to provide complex 8f as red solid (10.9 mg, 15.6 μmol, 39%). Rf = 0.31 (MeCN/H2O/sat. KNO3 solution,

Please cite this article as: S. Mollin, et al., Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands, J. Inorg. Biochem. (2015), http://dx.doi.org/10.1016/j.jinorgbio.2015.01.005

6

S. Mollin et al. / Journal of Inorganic Biochemistry xxx (2015) xxx–xxx

Scheme 1. Synthesis of reactive Rh(III)-pyridocarbazole precursor complexes. TBS = tertbutyltrimethylsilyl.

200:3:3). 1H-NMR (300 MHz, DMSO-d6): δ (ppm) 11.33 (s, 1H), 9.46 (d, J = 5.8 Hz, 1H), 9.40 (d, J = 5.8 Hz, 1H), 9.30 (dd, J = 8.4, 1.0 Hz, 1H), 8.74 (d, J = 7.2 Hz, 1H), 8.40 (td, J = 7.8, 1.4 Hz, 1H), 8.28 (td, J = 7.8, 1.4 Hz, 1H), 8.00 (d, J = 5.2 Hz, 1H), 7.95–7.84 (m, 4H), 7.80 (d, J = 7.8 Hz, 1H) 7.31 (td, J = 7.5, 1.0 Hz, 1H), 7.24 (td, J = 7.7, 1.4 Hz, 1H), 5.66 (d, J = 8.1 Hz, 1H), 5.02–4.84 (m, 3H), 4.72 (d, J = 17.1 Hz, 1H), 2.10 (s, 3H). 13C-NMR (125 MHz, DMSO-d6): δ (ppm) 170.5, 170.1, 162.1, 161.7, 152.2, 151.4, 150.1, 150.0, 148.4, 148.4, 141.8, 141.6, 141.1, 135.8, 131.2, 126.9, 126.5, 124.9, 124.7, 123.7, 123.44, 123.40, 121.3, 119.9, 115.4, 115.1, 111.9, 71.6, 70.4, 51.6. IR (film) ν (cm−1): 3431, 3053, 2959, 2024, 1909, 1753, 1753, 1705, 1610, 1493, 1416, 1340, 1230, 1022, 749, 641. HRMS calcd for C30H23ClN6O2Rh (M)+ 637.0621, found 637.0612. 2.3. Stability test To a 10 mM argon purged solution of compound 5f′ in DMSOd6 (0.5 mL) was added a 25 mM argon purged solution of βmercaptoethanol in D2O (0.1 mL). The resulting mixture was monitored immediately and periodically by 1H-NMR. 2.4. Protein kinase assays Kinases and substrates were purchased from Millipore or MoBiTec. IC50 values were obtained by a conventional radioactive assay in which kinase activity was measured by the degree of phosphorylation

of a substrate with [γ-33P]ATP (Perkin-Elmer). For the determination of protein kinase activities at defined inhibitor concentration (finally 100 nM), the rhodium complexes, which were added to the assay solution as concentrated DMSO stock solutions, were preincubated at room temperature in MOPS (20 mM), Mg(OAc)2 (30 mM) and DMSO (5%, resulting from inhibitor stock solution) at pH 7.0 in the presence of substrate S6 (50 μM), and kinase Pim1 (1.6 nM). For the determination of IC50 values, various concentrations of the rhodium complexes were incubated in equal mixtures. After 30 min, the reaction was initiated by adding ATP to a final concentration of 100 μM including [γ-33P]ATP in a final volume of 25 μL. After incubation for 30 min, the reaction was terminated by spotting 15 μL onto circularP81 phosphocellulose paper (diameter 2.1 cm, Whatman), followed by washing three times with 0.75% phosphoric acid and once with acetone. The dried P81 papers were transferred to scintillation vials and 5 mL of scintillation cocktail were added. The counts per minute (CPM) were measured with a BeckmannCounter LS6500 Multi Purpose Scintillation Coulter. Enzyme activities were defined as CPM quotient of the sample with 100 nM inhibitor and the control sample, each corrected by the background CPM. IC50 values were determined in duplicate from sigmoidal curve fits.

2.5. Single-crystal X-ray diffraction studies Single crystals of complex 2a were obtained upon standing in a mixture of DMF and MeCN at room temperature for approximately two weeks. Single crystals of complex 3 were obtained from 2a upon standing in a mixture of DMSO and DMF at room temperature for several days weeks. Single crystals of complex 5c were obtained from a solution in DMSO which was covered with acetone upon slow evaporation at room temperature over one week. Single crystals of complex 5c′ were obtained in a mixture of CH2Cl2 and Et2O upon slow evaporation for approximately two weeks at room temperature. Single crystals of complex 5e were obtained in a 10:1 mixture of H2O and DMSO upon standing for approximately three weeks at room temperature. The intensity data sets for all compounds were collected at 100 K using a STOE IPDS-2 T or STOE IPDS2 system. With the exception of 5c the data were corrected for absorption effects using multi scanned reflections [44]. The structures were solved using direct methods {SIR-92 [45] (2a), SIR2008 [46] (5c, 5d′)} or Patterson methods (DIRDIF08 [47], 4) and refined using the full matrix least squares procedure implemented in SHELX-97 [48]. Hydrogen atoms were included at calculated positions. In 3 disordered DMF is present, in 5d′ disordered CH2Cl2 and MeOH with occupation factors 0.88 and 0.90.

Fig. 2. Crystal structure of precursor complex 2a. ORTEP drawing with 50% probability thermal ellipsoids. Selected bond distances (Å) and angles (°): N1-Rh1 = 2.051(3), N4-Rh1 = 2.048(2), N28-Rh1 = 2.012(3), N31-Rh1 = 2.053(2), Cl1-Rh1 = 2.3073(8), Cl2-Rh1 = 2.3332(8), N28-Rh1-N31 = 90.49(10), Cl1-Rh1-Cl2 = 91.72(3).

Please cite this article as: S. Mollin, et al., Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands, J. Inorg. Biochem. (2015), http://dx.doi.org/10.1016/j.jinorgbio.2015.01.005

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Fig. 3. Crystal structure of complex 3 which was obtained from 2a upon standing in a mixture of DMSO and DMF. Solvent molecules are omitted. ORTEP drawing with 50% probability thermal ellipsoids. Selected bond distances (Å) and angles (°): N1-Rh1 = 2.075(2), N4-Rh1 = 2.049(2), Cl1-Rh1 = 2.3219(7), Cl2-Rh1 = 2.3349(7), O28-Rh1 = 2.0918(19), Rh1S1 = 2.2184(7), N4-Rh1-O28 = 86.96(8), N4-Rh1-S1 = 88.56(7), O28-Rh1-S1 = 175.50(5).

3. Results and discussion 3.1. Pyridocarbazole metal complexes as kinase inhibitors A common feature of all here discussed metal complexes is a bidentate pyrido[2,3-a]pyrrolo[3,4-c]carbazole-5,7(6H)-dione ligand in its monoanionic, indole-deprotonated form (Scheme 1). This heterocyclic pyridocarbazole ligand was initially inspired by the natural protein kinase inhibitor staurosporine and enables the corresponding pyridocarbazole metal complexes to interact with the ATP-binding site of protein kinases [22,49]. Whereas the benzyl group of the pyridocarbazole 1a mainly serves as a crystallization handle, the tert-butyldimethylsilyl (TBS)-protected pyridocarbazole 1b was instead employed for the synthesis of bioactive rhodium complexes containing

unprotected maleimide moieties that are capable of hydrogen bonding with the hinge region of the ATP binding site of kinases (Fig. 1A) [49]. 3.2. Rhodium(III) precursor complexes Previous initial results from our laboratory on rhodium(III) complexes encouraged us to further pursue the development of bioactive inert rhodium(III) complexes [35,36]. Work on pyridocarbazole complexes with ruthenium(II) [50], platinum(II) [51], and rhodium(III) [35] demonstrated the usefulness of developing metallo-pyridocarbazole complexes which bear (semi)labile coordinating ligands and thereby serve as reactive precursors for the rapid synthesis of the desired metal complexes through ligand substitution chemistry. Scheme 1 shows

Scheme 2. Synthesis of Rh(III)-pyridocarbazoles 5a–f and 5a′–f′ from in situ synthesized precursor complexes 2a and 2b. Reaction conditions: 5a–c/5a′–c′: MeCN/H2O 1:1, 90 °C, 16 h; 5d– f/5d′–f′: MeCN/H2O 1:1, 90 °C, 3 h. The diastereomers were separated by standard flash silica gel chromatography. Shown are the isolated yields of the individual diastereomers.

Please cite this article as: S. Mollin, et al., Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands, J. Inorg. Biochem. (2015), http://dx.doi.org/10.1016/j.jinorgbio.2015.01.005

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Fig. 4. Crystal structure of complex 5c. Solvent molecules are omitted. ORTEP drawing with 50% probability thermal ellipsoids. Selected bond distances (Å) and angles (°): N1-Rh1 = 2.043(8), N4-Rh1 = 2.028(7), N30-Rh1 = 2.022(8), N37-Rh1 = 2.053(8), O35-Rh1 = 2.020(6), Cl1-Rh1 = 2.353(3), O35-Rh1-N4 = 172.8(3), N30-Rh1-N1 = 176.8(3), N1-Rh1N37 = 96.7(3), N30-Rh1-Cl1 = 88.0(2), N37-Rh1-Cl1 = 174.4(2), N1-Rh1-Cl1 = 88.0(2).

that we accomplished the synthesis of such Rh(III)-pyridocarbazole precursor complexes by reacting the heterocycles 1a and 1b with RhCl3 trihydrate in MeCN/H2O 1:1 at 90 °C to afford the complexes 2a and 2b in yields of 79% and 70%, respectively. The benzyl group at the maleimide moiety of complex 2a enabled us to obtain a crystal structure of 2b which

is displayed in Fig. 2. The structure demonstrates that rhodium is coordinated in a bidentate fashion to the deprotonated pyridocarbazole ligand 1a, in addition to two acetonitrile and two chloride ligands, each arranged in a cis fashion. This complex is quite reactive, as can be demonstrated by the crystal structure of complex 3 which was obtained upon

Fig. 5. Crystal structure of complex 5c′. Solvent molecules are omitted. ORTEP drawing with 50% probability thermal ellipsoids. Selected bond distances (Å) and angles (°): N1-Rh1 = 2.077(3), N4-Rh1 = 2.016(4), N30-Rh1 = 2.042(4), N37-Rh1 = 2.077(4), O35A-Rh1 = 2.010(3), Cl1-Rh1 = 2.3391(12), O35A-Rh1-N4 = 95.16(14), N30-Rh1-N1 = 97.78(14), N1Rh1-N37 = 95.48(13), N30-Rh1-Cl1 = 95.59(11), N37-Rh1-Cl1 = 175.49(11), N1-Rh1-Cl1 = 88.96(10).

Fig. 6. Crystal structure of complex 5d′. Solvent molecules are omitted. ORTEP drawing with 50% probability thermal ellipsoids. Selected bond distances (Å) and angles (°): N1-Rh1 = 2.033(10), N4-Rh1 = 2.038(8), N21-Rh1 = 2.061(9), O18-Rh1 = 2.020(8), S1-Rh1 = 2.280(3), Cl1-Rh1 = 2.362(3), N1-Rh1-N21 = 93.6(4), N1-Rh1-S1 = 92.8(3), O18-Rh1-Cl1 = 89.9(2), S1-Rh1-Cl1 = 176.94(13).

Please cite this article as: S. Mollin, et al., Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands, J. Inorg. Biochem. (2015), http://dx.doi.org/10.1016/j.jinorgbio.2015.01.005

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3.3. Rhodium(III) complexes with acyclic tridentate ligands

Scheme 3. Alternative synthesis of complexes 5c and 5c′, resulting in a switched diastereoselectivity.

Scheme 4. Synthesis of Rh(III)-pyridocarbazoles 8a–f from in situ synthesized precursor complexes 2a and 2b. Reaction conditions: 8a–c: MeCN/H2O 1:1, 90 °C, 3 h; 8d–f: MeCN/H2O 1:1, 90 °C, 2 h. The nitrate counterions result from silica gel chromatography with MeCN/H2O/sat. KNO3 (200:3:3) solutions.

leaving 2a standing in a mixture of DMSO and DMF for several days. In this complex, the two acetonitrile ligands are replaced by one DMSO and the very weak ligand DMF (Fig. 3).

The reactive acetonitrile precursor complexes 2a and 2b were typically synthesized in situ followed by direct substitution reactions with other ligands. For instance, the in situ generated precursor complexes 2a or 2b were reacted with the tridentate ligands 4a, 4b, or 4c in MeCN/H2O 1:1 at 90 °C for several hours to provide the complexes 5 as shown in Scheme 2 (for metal complexes with these ligands, see [52–56]). In all cases, only two out of four possible diastereomers were observed and could be resolved by silica gel chromatography. In the observed product complexes, the tridentate ligands 4a–c coordinate in a facial fashion with the carboxylate ligand being oriented either cis (diastereomers 5a–f) or trans (diastereomers 5a′–f′) to the indole moiety of the pyridocarbazole heterocycle as exemplified by the X-ray structures of 5c, 5c′, 5d′ (Figs. 4–6), and 5e (see Supplementary data). It is interesting to note that the diastereoselectivity can be strongly influenced by a modified reaction path as shown in Scheme 3. Accordingly, the reaction of ligand 4c first with RhCl3 trihydrate in MeCN/H2O 1:1 at 90 °C afforded the complex 6 (68%), which was reacted with the pyridocarbazole ligand 1a to afford the diastereomers 5c and 5c′ in a yield of 68% with a diastereomeric ratio of 3.0:1.0 as opposed to 1.0:2.0 following the route starting with the precursor complex 2a as shown in Scheme 2. Thus, the here investigated pyridylcarboxylate ligands 4a–c only coordinate in a facial fashion to rhodium(III) which reduces the number of possible diastereomers to two. Importantly for practical reasons, the diastereoselectivity can be modulated by the choice of the reaction route (Scheme 2 versus Scheme 3) and the two diastereomers can be separated by standard flash silica gel chromatography. Analogous to the synthesis of complexes 5, the in situ generated precursor complexes 2a or 2b were reacted with bis(pyridin-2ylmethyl)sulfide (7a), bis(pyridin-2-ylmethyl)amine (7b), or Nmethyl-N-bis(pyridin-2-ylmethyl)amine (7c) to afford the complexes 8a–f as single diastereomers in yields of 35–47% (Scheme 4) (for rhodium complexes with these ligands, see [57–62]). Due to their symmetry and preference for facial coordination, only one diastereomer was generated. Although we were not able to verify the stereochemistry by single crystal X-ray diffraction studies, the relative configurations of complexes 8a–f were assigned unequivocally by 1H-NMR with the most important indicator being an upfield shifted indole proton

Fig. 7. COSY spectrum of Rh(III) complex 8d. Shown is the aromatic region with assignments of the signals.

Please cite this article as: S. Mollin, et al., Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands, J. Inorg. Biochem. (2015), http://dx.doi.org/10.1016/j.jinorgbio.2015.01.005

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3.6. Comparison between Rh(III) and Ru(II) Since the majority of our previous work on the design of metalbased enzyme inhibitors was based on ruthenium in the diamagnetic oxidation state II it is interesting to compare the advantages and disadvantages of Rh(III) over Ru(II). Two clear current drawbacks of rhodium are the high price for RhCl3 as well as the overall sluggish chemistry which is indicated by the typical low to moderate yields in the ligand exchange reactions. However, it is likely that chemistry can be improved by fine tuning the reaction conditions or even by exploiting oxidative addition reactions Rh(I) → Rh(III). On the other hand, the synthesized Rh(III) complexes displayed an intriguing kinetic stability that appears to be superior to related Ru(II) complexes. Furthermore, Rh(III) is suitable for coordination to hard ligands such as carboxylates and amine whereas Ru(II) becomes prone to oxidation under such circumstances. Fig. 8. Stability evaluation of compound 5f′ (8.3 mM) in DMSO-d6/D2O 5:1 in the presence of β-mercaptoethanol (4.2 mM). Shown are the aromatic regions of the 1H-NMR spectra right after the addition of β-mercaptoethanol (0 h) and after 24 h.

(labeled as A4 in Fig. 7) which can be explained by the aromatic ring current of one closeby pyridine moieties (Fig. 7).

3.4. Stability studies A crucial requirement for such rhodium complexes to serve as solely structural templates in biomedical research are their chemical stabilities under biological conditions. Typically, aliphatic thiols such as glutathione or cysteine which are present in the cytoplasm in millimolar concentrations constitute due to their softness and nucleophilicity the biggest challenge for substitutionally labile transition metal complexes. To assess the inertness of the here synthesized rhodium(III) pyridocarbazole complexes, we incubated the complex 5f′ in deuterated DMSO/D2O 5:1 and in the presence of 4.2 mM β-mercaptoethanol and monitored its stability by 1H-NMR. As displayed in Fig. 8, no changes were detected after 24 h, thus confirming the inertness of rhodium(III) complex 5f′. It is quite surprising that the chloride ligand cannot be replaced by millimolar concentrations of an aliphatic thiol. However, this inertness is supported by our experimental observation that the chloride ligand can be substituted by other monodentate ligands only under harsh reaction conditions. For example, the replacement of chloride by DMSO takes place only in the presence of AgOTf at 150 °C (88%) (see Supporting Information).

4. Conclusions We here introduced rhodium(III) pyridocarbazole complexes coordinated to acyclic tridentate ligands, deviced a convenient synthesis of such complexes, investigated their relative stereochemistries by X-ray crystallography, verified the high kinetic inertness of such complexes under biological relevant conditions, and determined in preliminary studies the protein kinase inhibition properties of this class of complexes. From the obtained results we conclude that rhodium(III) is a very attractive metal for the design of inert octahedral metal-based enzyme inhibitors and nicely complements ruthenium(II) in its ligand preference. Furthermore, acyclic tridentate ligands provide a practical strategy to avoid large numbers of possible stereoisomers in the course of exploiting octahedral coordination spheres as structural templates for the design of bioactive molecules. Future work will address the in vitro and in vivo properties of such rhodium(III) complexes (for rhodium complexes with biological activities, see [66–78]). Acknowledgments This work was supported by the German Research Foundation (ME1805/2-1) and the LOEWE research cluster SynChemBio of the Federal State of Hessen (Germany). The authors would like to acknowledge the contribution of the COST action CM1105. Appendix A. Supplementary data Supplementary data to this article include crystallographic data, 1HNMR and 13C-NMR spectra of synthesized complexes, and protein kinase inhibition data, and can be found online at http://dx.doi.org/10. 1016/j.jinorgbio.2015.01.005.

3.5. Protein kinase inhibition References Next, we wanted to gain insight into the ability of this class of octahedral rhodium complexes to serve as protein kinase inhibitors and we selected the protein kinase Pim1 as our representative target since Pim1 has been demonstrated by us to display a general affinity for pyridocarbazole metal complexes [35,38,49,50,63–65]. Accordingly, complexes 5d–f, 5d′–f′, and 8d–f (all complexes with non-modified maleimide moiety) were tested for their inhibition of Pim1 at the concentration of 100 nM. Revealingly, out of the assayed nine complexes, two compounds displayed a very strong Pim1 inhibition: the bis(pyridin-2ylmethyl)sulfide complex 8d and the N-methylbis(pyridin-2ylmethyl)amine complex 8f reduced the Pim1 activity to below 1% (see Supplementary data for more details). Concentration dependent inhibition experiments resulted in IC50 (concentration of compound at which the enzyme activity is reduced to 50%) values of 3.4 nM for 8f and 1.8 nM for 8d. Thus, these results demonstrate that rhodium(III) pyridocarbazole complexes containing acyclic tridentate ligands are promising scaffolds for the design of protein kinase inhibitors.

[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19]

R. Alberto, J. Organomet. Chem. 692 (2007) 1179–1186. B.M. Zeglis, V.C. Pierre, J.K. Barton, Chem. Commun. (2007) 4565–4579. T.W. Hambley, Science 318 (2007) 1392–1393. A. Levina, A. Mitra, P.A. Lay, Metallomics 1 (2009) 458–470. R.W.-Y. Sun, C.-M. Che, Coord. Chem. Rev. 253 (2009) 1682–1691. F.R. Keene, J.A. Smith, J.G. Collins, Coord. Chem. Rev. 253 (2009) 2021–2035. K.L. Haas, K.J. Franz, Chem. Rev. 109 (2009) 4921–4960. U. Schatzschneider, Eur. J. Inorg. Chem. (2010) 1451–1467. G. Gasser, I. Ott, N. Metzler-Nolte, J. Med. Chem. 54 (2011) 3–25. E.A. Hillard, G. Jaouen, Organometallics 30 (2011) 20–27. U. Schatzschneider, Inorg. Chim. Acta 374 (2011) 19–23. A. Bergamo, G. Sava, Dalton Trans. 40 (2011) 7817–7823. C.-M. Che, R.W.-Y. Sun, Chem. Commun. 47 (2011) 9554–9560. M. Patra, G. Gasser, ChemBioChem 13 (2012) 1232–1252. C.G. Hartinger, N. Metzler-Nolte, P.J. Dyson, Organometallics 31 (2012) 5677–5685. K.K.-W. Lo, A.W.-T. Choi, W.H.-T. Law, Dalton Trans. 41 (2012) 6021–6047. P.K. Sasmal, C.N. Streu, E. Meggers, Chem. Commun. 49 (2013) 1581–1587. Z. Liu, P.J. Sadler, Acc. Chem. Res. 47 (2014) 1174–1185. D.-L. Ma, H.-Z. He, K.-H. Leung, D.S.-H. Chan, C.-H. Leung, Angew. Chem. Int. Ed. 52 (2013) 7666–7682. [20] L. Oehninger, R. Rubbiani, I. Ott, Dalton Trans. 42 (2013) 3269–3284.

Please cite this article as: S. Mollin, et al., Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands, J. Inorg. Biochem. (2015), http://dx.doi.org/10.1016/j.jinorgbio.2015.01.005

S. Mollin et al. / Journal of Inorganic Biochemistry xxx (2015) xxx–xxx [21] K.D. Mjos, C. Orvig, Chem. Rev. 114 (2014) 4540–4563. [22] E. Meggers, G.E. Atilla-Gokcumen, H. Bregman, J. Maksimoska, S.P. Mulcahy, N. Pagano, D.S. Williams, Synlett 8 (2007) 1177–1189. [23] E. Meggers, Chem. Commun. (2009) 1001–1010. [24] C.L. Davies, E.L. Dux, A.-K. Duhme-Klair, Dalton Trans. (2009) 10141–10154. [25] C.-M. Che, F.-M. Siu, Curr. Opin. Chem. Biol. 14 (2010) 255–261. [26] E. Meggers, Angew. Chem. Int. Ed. 50 (2011) 2442–2448. [27] N.L. Kilah, E. Meggers, Aust. J. Chem. 65 (2012) 1325–1332. [28] K.J. Kilpin, P.J. Dyson, Chem. Sci. 4 (2013) 1410–1419. [29] C.-H. Leung, H.-Z. He, L.-J. Liu, M. Wang, D.S.-H. Chan, D.-L. Ma, Coord. Chem. Rev. 257 (2013) 3139–3151. [30] A. de Almeida, B.L. Oliveira, J.D.G. Correira, G. Soveral, A. Casini, Coord. Chem. Rev. 257 (2013) 2689–2704. [31] N.P.E. Barry, P.J. Sadler, Chem. Commun. 49 (2013) 5106–5131. [32] M. Dörr, E. Meggers, Curr. Opin. Chem. Biol. 19 (2014) 76–81. [33] J.C. Bailor, J. Chem. Educ. 34 (1957) 334–338. [34] E. Meggers, Eur. J. Inorg. Chem. (2011) 2911–2926. [35] S. Dieckmann, R. Riedel, K. Harms, E. Meggers, Eur. J. Inorg. Chem. (2012) 813–821. [36] S. Mollin, S. Blanck, K. Harms, E. Meggers, Inorg. Chim. Acta 393 (2012) 261–268. [37] H. Bregman, D.S. Williams, E. Meggers, Synthesis (2005) 1521–1527. [38] N. Pagano, J. Maksimoska, H. Bregman, D.S. Williams, R.D. Webster, F. Xue, E. Meggers, Org. Biomol. Chem. 5 (2007) 1218–1227. [39] C. Incarvito, A.L. Rheingold, A.L. Gavrilova, C.J. Qin, B. Bosnich, Inorg. Chem. 40 (2001) 4101–4108. [40] S.M. Berry, D.C. Bebout, Inorg. Chem. 44 (2005) 27–39. [41] R.G. Lacoste, G.V. Christoffers, A.E. Martell, J. Am. Chem. Soc. 87 (1965) 2385–2388. [42] H. Franz, G. Buchmann, Pharmazie 23 (1968) 648–651. [43] J. Astner, M. Weitzer, S.P. Foxon, S. Schindler, F.W. Heinemann, J. Mukherjee, R. Gupta, V. Mahadevan, R. Mukherjee, Inorg. Chim. Acta 361 (2008) 279–292. [44] A.L. Spek, A. Platon, Multipurpose Crystallographic Tool, Utrecht University, Utrecht, The Netherlands, 1998. [45] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, J. Appl. Crystallogr. 26 (1993) 343–350. [46] M.C. Burla, R. Caliandro, M. Camalli, B. Carrozzini, G.L. Cascarano, L. De Caro, C. Giacovazzo, G. Polidori, D. Siliqi, R. Spagna, J. Appl. Crystallogr. 40 (2007) 609–613. [47] P.T. Beurskens, G. Beurskens, R. de Gelder, J.M.M. Smits, S. Garcia-Granda, R.O. Gould, The DIRDIF08 program system, Technical Report of the Crystallography Laboratory, University of Nijmegen, The Netherlands, 2008. [48] G.M. Sheldrick, Acta Crystallogr. 64A (2008) 112. [49] L. Feng, Y. Geisselbrecht, S. Blanck, A. Wilbuer, G.E. Atilla-Gokcumen, P. Filippakopoulos, K. Kräling, M.A. Celik, K. Harms, J. Maksimoska, R. Marmorstein, G. Frenking, S. Knapp, L.-O. Essen, E. Meggers, J. Am. Chem. Soc. 133 (2011) 5976–5986. [50] H. Bregman, P.J. Carroll, E. Meggers, J. Am. Chem. Soc. 128 (2006) 877–884. [51] D.S. Williams, P.J. Carroll, E. Meggers, Inorg. Chem. 46 (2007) 2944–2946. [52] H. He, J.E. Morley, B. Twamley, R.H. Groeneman, D.-K. Bučar, L.R. MacGillivray, P.D. Benny, Inorg. Chem. 48 (2009) 10625–10634. [53] X. Wang, J.J. Vittal, Inorg. Chem. 42 (2003) 5135–5142. [54] S. Mundwiler, L. Candreia, P. Häfliger, K. Ortner, R. Alberto, Bioconjug. Chem. 15 (2004) 195–202.

[55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65]

[66] [67]

[68] [69] [70] [71] [72] [73] [74] [75] [76]

[77] [78]

11

T. Ama, T. Yonemura, M. Yamaguchi, Bull. Chem. Soc. Jpn. 79 (2006) 1063–1065. X. Wang, J.D. Ranford, J.J. Vittal, J. Mol. Struct. 796 (2006) 28–35. T. Yoshimura, K. Umakoshi, Y. Sasaki, Inorg. Chem. 42 (2003) 7106–7115. D.G.H. Hetterscheid, J.M.M. Smits, B. de Bruin, Organometallics 23 (2004) 4236–4246. D.G.H. Hetterscheid, M. Klop, R.J.N.A.M. Kicken, J.M.M. Smits, E.J. Reijerse, B. de Bruin, Chem. Eur. J. 13 (2007) 3386–3405. W.I. Dzik, C. Creusen, R. de Gelder, T.P.J. Peters, J.M.M. Smits, B. de Bruin, Organometallics 29 (2010) 1629–1641. W.I. Dzik, L.F. Arruga, M.A. Siegler, A.L. Spek, J.N.H. Reek, B. de Bruin, Organometallics 30 (2011) 1902–1913. B. de Bruin, J.A.W. Verhagen, C.H.J. Schouten, A.W. Gal, D. Feichtinger, D.A. Plattner, Chem. Eur. J. 7 (2001) 416–422. J.É. Debreczeni, A.N. Bullock, G.E. Atilla, D.S. Williams, H. Bregman, S. Knapp, E. Meggers, Angew. Chem. Int. Ed. 45 (2006) 1580–1585. H. Bregman, E. Meggers, Org. Lett. 8 (2006) 5465–5468. J. Maksimoska, D.S. Williams, G.E. Atilla-Gokcumen, K.S.M. Smalley, P.J. Carroll, R.D. Webster, P. Filippakopoulos, S. Knapp, M. Herlyn, E. Meggers, Chem. Eur. J. 14 (2008) 4816–4822. B. Weber, A. Serafin, J. Michie, C. van Rensburg, J.C. Swarts, L. Böhm, Anticancer Res. 24 (2004) 763–770. A. Dorcier, W.H. Ang, S. Bolano, L. Gonsalvi, L. Juillerat-Jeannerat, G. Laurenczy, M. Peruzzini, A.D. Phillips, F. Zanobini, P.J. Dyson, Organometallics 25 (2006) 4090–4096. A.M. Angeles-Boza, H.T. Chifotides, J.D. Aguirre, A. Chouai, P.K.-L. Fu, K.R. Dunbar, C. Turro, J. Med. Chem. 49 (2006) 6841–6847. A. Dorcier, C.G. Hartinger, R. Scopelliti, R.H. Fish, B.K. Keppler, P.J. Dyson, J. Inorg. Biochem. 102 (2008) 1066–1076. M.A. Scharwitz, I. Ott, Y. Geldmacher, R. Gust, W.S. Sheldrick, J. Organomet. Chem. 693 (2008) 2299–2309. J.D. Aguirre, A.M. Angeles-Boza, A. Chouai, C. Turro, J.-P. Pellois, K.R. Dunbar, Dalton Trans. (2009) 10806–10812. R. Bieda, M. Dobroschke, A. Triller, I. Ott, M. Spehr, R. Gust, A. Prokop, W.S. Sheldrick, ChemMedChem 5 (2010) 1123–1133. Y. Geldmacher, R. Rubbiani, P. Wefelmeier, A. Prokop, I. Ott, W.S. Sheldrick, J. Organomet. Chem. 696 (2011) 1023–1031. B.Y.-W. Man, H.-M. Chan, C.-H. Leung, D.S.-H. Chan, L.-P. Bai, Z.-H. Jiang, H.-W. Li, D.-L. Ma, Chem. Sci. 2 (2011) 917–921. H.-J. Zhong, H. Yang, D.S.-H. Chan, C.-H. Leung, H.-M. Wang, D.-L. Ma, R. Seifert, PLoS One 7 (2012) e49574. Y. Geldmacher, K. Splith, I. Kitanovic, H. Alborzinia, S. Can, R. Rubbiani, M.A. Nazif, P. Wefelmeyer, A. Prokop, I. Ott, S. Wölfl, I. Neundorf, W.S. Sheldrick, J. Biol. Inorg. Chem. 17 (2012) 631–636. H.-J. Zhong, K.-H. Leung, L.-J. Liu, L. Lu, D.S.-H. Chan, C.-H. Leung, D.-L. Ma, ChemPhysChem 79 (2014) 508–511. C.-H. Leung, H.-J. Zhong, D.S.-H. Chan, D.-L. Ma, Coord. Chem. Rev. 257 (2013) 1764–1776.

Please cite this article as: S. Mollin, et al., Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands, J. Inorg. Biochem. (2015), http://dx.doi.org/10.1016/j.jinorgbio.2015.01.005

Octahedral rhodium(III) complexes as kinase inhibitors: Control of the relative stereochemistry with acyclic tridentate ligands.

Octahedral metal complexes are attractive structural templates for the design of enzyme inhibitors as has been demonstrated, for example, with the dev...
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