Practical synthesis of roscovitine and CR8

Article abstract of DOI:10.1021/op800284k

Roscovitine and CR8 are potent inhibitors of cyclin-dependent kinases. A scalable synthesis of both inhibitors is described. In the case of CR8, the biarylmethylamine moiety was obtained as a stable and high-purity salt.

Full text of DOI:10.1021/op800284k

Organic Process Research & Development 2009, 13, 641–644
Practical Synthesis of Roscovitine and CR8
Nassima Oumata,† Yoan Ferandin,‡ Laurent Meijer,‡ and Herve´ Galons*,†
Laboratoire de Chimie Organique 2, INSERM U 648, UniVersite´ Paris-Descartes, 4 aVenue de l’ObserVatoire,
75270 Paris cedex 06, France, and C.N.R.S., Protein Phosphorylation and Human Disease Group, Station Biologique, B.P. 74,
29682 Roscoff cedex, Bretagne, France
Abstract:
lower concentrations. In this study,5 CR8, 10b, was identified
as a highly efficacious agent, 25-50 times more potent than
(R)-roscovitine at inducing apoptotic cell death and its ac-
companying biochemical events and therefore suitable for
preclinical development.6 We herein describe a protocol for a
scalable synthesis of roscovitine and CR8 (Scheme 1).
Roscovitine and CR8 are potent inhibitors of cyclin-dependent
kinases. A scalable synthesis of both inhibitors is described. In the
case of CR8, the biarylmethylamine moiety was obtained as a
stable and high-purity salt.
2. Results and Discussion
1. Introduction
We first focussed our work on the production of roscovitine.
Roscovitine can be prepared in a simple three-step procedure
(Scheme 1). In the last step, a chromatographic purification of
roscovitine is required.7 The three-step procedure has been
optimized with the goal of avoiding any chromatographic
isolation of either the intermediates or the target compound. In
the first step, 2,6-dichloropurine 7, was converted into 6-ben-
zylaminopurine 8a, upon heating with benzylamine in n-butanol.
Alkylation of 8a was regioselectively accomplished in the
usual way upon treatment with isopropylbromide in the
presence of K2CO3.5 Amination with (R)-2-aminobutanol
was then performed. However, in this last step, the
isolation of the material was plagued by the formation of
side compounds (which had lower Rf than 10a in thin-
layer chromatography (TLC)). The key feature affecting
the reaction’s outcome based on an in-depth study
appeared to be the quantity of (R)-2-aminobutanol. The
best compromise between reaction rate and isolated yield
was obtained with 8 mol equiv. In the optimized condi-
tions, 10a was purified by crystallization without the need
of chromatographic purification. Indeed, the reaction
proceeded faster to completion with 10 mol equiv.
However, the isolated yield was diminished (65% instead
of 89%).
Abnormalities in protein phosphorylation have been observed
in numerous major human diseases,1 strongly encouraging the
search for pharmacological inhibitors of protein kinases.2 The
2,6,9-trisubstituted purines were among the first low-molecular
weight inhibitors of cyclin-dependent kinases (CDKs).3 One of
these, (R)-roscovitine, 10a (CYC202, Seliciclib), has now
reached clinical phase 2 trials against nonsmall cell lung cancer
and nasopharyngeal cancer.4 In this context we have pursued
an intensive search for improved analogues of roscovitine,
taking into account their ability to interact with CDKs (guided
by the CDK2/ and CDK5/roscovitine crystal structures), to
maintain high kinase selectivity, and to induce cell death at
* E-mail: herve.galons@univ-paris5.fr. Telephone: +33.(0)1.53.73.96.84.
† INSERM U 648, Universite´ Paris-Descartes.
‡ C.N.R.S., Protein Phosphorylation and Human Disease Group.
(1) (a) Knockaert, M.; Greengard, P.; Meijer, L. Pharmacological inhibitors
of cyclin-dependent kinases. Trends Pharmacol. Sci. 2002, 23, 417–
425. (b) Malumbres, M.; Barbacid, M. Cell cycle kinases in cancer.
Curr. Opin. Genet. DeV. 2007, 17, 60–5.
(2) (a) Malumbres, M.; Pevarello, P.; Barbacid, M.; Bischoff, J. R. CDK
inhibitors in cancer therapy: what is next. Trends Pharmacol. Sci. 2008,
29, 16–21. (b) Sharma, P. S.; Sharma, R.; Tyagi, R. Inhibitors of cyclin
dependent kinases: Useful targets for cancer treatment. Curr. Cancer
Drug Targets 2008, 8, 53–75.
(3) (a) Vesely, J.; Havlicek, L.; Strnad, M.; Blow, J. J.; Donella-Deana,
A.; Pinna, L.; Letham, D. S.; Kato, J. Y.; De´tivaud, L.; Leclerc, S.;
Meijer, L. Inhibition of cyclin-dependent kinases by purine derivatives.
Eur. J. Biochem. 1994, 224, 771–786. (b) De Azevedo, W. F.; Leclerc,
S.; Meijer, L.; Havlicek, L.; Strnad, M.; Kim, S. H. Inhibition of cyclin-
dependent kinases by purine analogues: crystal structure of human
cdk2 complexed with roscovitine. Eur. J. Biochem. 1997, 243, 518–
526. (c) Meijer, L.; Borgne, A.; Mulner, O.; Chong, J. P. J.; Blow,
J. J.; Inagaki, N.; Inagaki, M.; Delcros, J. G.; Moulinoux, J. P.
Biochemical and cellular effects of roscovitine, a potent and selective
inhibitor of the cyclin-dependent kinases cdc2, cdk2 and cdk5. Eur.
J. Biochem. 1997, 243, 527–536. (d) Chang, Y. T.; Gray, N. G.;
Rosania, G. R.; Sutherlin, D. P.; Kwon, S.; Norman, T. C.; Sarohia,
R.; Leost, M.; Meijer, L.; Schultz, P. G. Synthesis and application of
functionally diverse 2,6,9-trisubstituted purine libraries as CDK
inhibitors. Chem. Biol. 1999, 6, 361–375.
In the case of CR8, 10b, a practical route to the key building
block 6 had to be secured. Commercially available 4-pyridyl-
benzaldehyde, 1, was converted into the oxime 2 using
hydroxylamine hydrochloride and AcONa in EtOH at rt.
Reduction of 2 was first performed using LiAlH4 in THF. TLC
of the crude reaction mixture showed four to five spots less
polar than that for the targeted amine 3. When this crude amine
(5) Oumata, N.; Bettayeb, K.; Ferandin, Y.; Demange, L.; Lopez-Giral,
A.; Goddard, M.-L.; Myrianthopoulos, V.; Mikros, E.; Flajolet, M.;
Greengard, P.; Meijer, L.; Galons, H. Roscovitine-derived, dual-
specificity inhibitors of cyclin-dependent kinases (CDKs) and casein
kinase 1 (CK1). J. Med. Chem. 2008, 51, 5229–5242.
(4) (a) Meijer, L.; Raymond, E. Roscovitine and other purines as kinase
inhibitors. From starfish oocytes to clinical trials. Acc. Chem. Res.
2003, 36, 417–425. (b) Meijer, L.; Bettayeb, K.; Galons, H. Rosco-
vitine (CYC202, Seliciclib). In Monographs on enzyme inhibitors.
CDK inhibitors and their potential as anti-tumor agents; Smith, P. J.,
Yue, E., Eds.; CRC Press, Taylor & Francis: Boca Raton, FL, 2006;
Vol. 2, Chapter 9, pp 187-226.
(6) Bettayeb, K.; Oumata, N.; Echalier, A.; Ferandin, Y.; Endicott, J.;
Galons, H.; Meijer, L. CR8: A potent and selective, roscovitine-derived
inhibitor of cyclin-dependent kinases. Oncogene 2008, 27, 5797–807.
(7) Meijer, L.; Bisagni, E.; Legrave´rend, M. Novel purine derivatives
having, in particular, antiproliferative properties, and biological uses
thereof. PCT WO 97/20842, 1997.
10.1021/op800284k CCC: $40.75  2009 American Chemical Society
Published on Web 02/26/2009
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Scheme 1a
a Reagents and conditions: a) NH2OH ·HCl, NaOAc; b) H2 Pd/C, or LiAlH4,THF; c) Boc2O, NEt3; d) CH2Cl2, TFA; e) benzylamines, BuOH, 110°C; f) 2-bromopropane,
K2CO3, DMSO, 18-20 °C; g) (R)-2-aminobutan-1-ol, heat, 160°C.
was reacted in the next step, compound 7b was isolated in
moderate yield. Several attempts to purify 3 as salts were
unsuccessful. Hydrogenation of 2 was then investigated.
Although the TLC of the mixture looked clean, the NMR
spectrum of the crude amine showed a 6:1 mixture of the desired
amine 3 and an impurity. In order to identify this side product,
the crude reaction mixture was submitted to protection with
di-tertbutyldicarbonate. Interestingly, the Boc protected deriva-
tive 4, crystallized easily from Et2O, and acylated impurity 5
was well rejected in the mother liquors. The bis-trifluoroacetate
was not hygroscopic and could be kept at rt for at least six
months. Compound 5 was identified as a piperidine derivative.
The hydrogenation conditions were investigated in detail
(reaction time, temperature, pressure, solvent). In particular, the
influence of pressure on yield and selectivity was measured in
the range of 1-10 atm. The reaction rate was low below 3
atm. Noticeable amounts of the piperidine derivative (12-15%)
were formed at 10 atm. Under optimized conditions (5 atm,
18-24 h reaction time) some over-reduction could not be
completely avoided, leading to 3-5% 5 in the crude reaction
mixture after acylation. The acylated derivative, 4, was con-
verted into the bis-trifluoroacetate salt 6 which was isolated in
good overall yield (80-85% from the aldehyde) and purity
(>98%). The bis-trifluoroacetate 6 was not hygroscopic and
could be stored at rt for at least 6 months. Condensation of 6
with 2,6-dichloropurine was performed in the presence of 4
molar equiv of NEt3. The last two synthetic steps were achieved
using the same conditions for the synthesis of roscovitine to
afford CR8 in 72-76% overall yield.
Interestingly, the piperidine 5 had been previously incorpo-
rated in other series of active compounds.8 Therefore, a selective
route to this compound was investigated. The monoprotected
piperidine 5 was easily obtained upon adding 1 molar equiv of
AcOH in the hydrogenation medium.
In summary, the synthesis of both CDK inhibitors could be
performed at a 30-50 g scale without relying on time-
consuming and costly chromatography purification steps. In the
particular case of CR8, the presented procedure circumvents
the low solubility of biaryls.9 Biarylamines, being privileged
pharmacophore structures, are part of numerous biologically
active products;10 therefore, the herein reported simple procedure
could find other applications.
Experimental Section
Melting points were determined on a Kofler hot-stage
(Reichert) and are uncorrected. NMR spectra were recorded
on Bruker Avance 400 MHz (100 MHz for 13C NMR).
Chemical shifts are given in ppm downfield of tetramethylsilane
(TMS) used as an internal standard. Reactions were monitored
(8) Kuduk, S. D.; Chang, R. K.; Ng, C.; Murphy, K. L.; Ransom, R. W.;
Tang, C.; Prueksaritamont, T.; Friedinger, R. M.; Pettibone, D. J.;
Bock, M. G. Bradykinin B1 antagonists: SAR studies in the 2,3-
diaminopyridine series. Bioorg. Med. Chem. Lett. 2005, 15, 3925–
3929.
(9) Brown, A.; Brown, L.; Brown, T. B.; Calabrese, A.; Ellis, D.; Puhalo,
N.; Smith, C. R.; Wallace, O.; Watson, L. Triazole oxytocin
antagonists: Identification of aryl ether replacements for a biaryl
substituent. Bioorg. Med. Chem. Lett. 2008, 18, 5242–5444.
(10) Horton, D. A.; Bourne, G. T.; Mark, L.; Smythe, M. L. The
combinatorial synthesis of bicyclic privileged structures or privileged
substructures. Chem. ReV 2003, 103, 893–930.
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by TLC using Merk silica gel 60F-254 thin layer plates. Column
chromatography was carried out on SDS Chromagel 60 ACC,
40-63 µm. The HPLC analyses were carried out on a system
consisting of a Waters 600 system controller, a Jones chroma-
tography heater-chiller oven and a Waters 994 photodiode
array detector.
first triturated with 20 mL of cyclohexane. The cyclohexane
was decanted, and 20 mL of Et2O was added. The salt
crystallized and was washed with 10 mL of Et2O. Yield 87%,
mp 165-168 °C. 1H NMR (CDCl3): δ 4.11(s, 2H, CH2), 4.99
(br, 3H, NH), 7.23 (t, 1H, Hpyridyl), 7.38 (m, 2H, Hphenyl), 7.73
(dt, 2H, Hpyridyl), 7.94 (d, J ) 7.83 Hz, 2H Hphenyl), 8.61 (d, J )
4.08 Hz,1H, Hpyridyl), 8.7 (br s, 3H H3N). 13C NMR (DMSO-
d6): δ 41.28, 115.42 (q, JC-F ) 293 Hz), 120.16, 122.41, 126.49,
128.59, 134.41, 137.40, 137.43, 148.29, 154.29, 157.77 (q,
JC-C-F ) 35 Hz). Anal. (C16H14N2O4F6) Calc: C, 46.61; H,
3.42; N, 6.79; found: 46.84; H, 3.53; N, 6.43.
Synthesis of 6-Arylmethylamino-2-chloropurines. To a
solution of 1 (23 g, 0.1 mol) in 200 mL of n-BuOH were added
the primary amine (0.12 mol) and NEt3 (synthesis of 8a: 22.5
mL, 0.16 mol; synthesis of 8b: 70 mL, 0.50 mol). After 3 h
heating at 110 °C, the mixture was cooled to 20 °C, and the
solid was filtrated, washed with 5 mL of cold n-BuOH, and
dried in vacuo.
4-(2-Pyridyl)benzaldehyde Oxime (2). To a solution of 1
(36.6 g, 0.2 mol) in 50 mL of EtOH and 20 mL of H2O were
added hydroxylamine hydrochloride (15.27, 0.21 mol) and
AcONa, 3H2O (29.90 g, 0.21 mol). The resulting slurry was
stirred for 12 h at rt. The mixture was concentrated to dryness,
and the resulting solid was washed with H2O (2 × 5 mL) and
1
EtOH, (1 × 5 mL). Yield 97%, mp 138-139 °C: H NMR
(CDCl3): δ 7.16 (m, 1H, Hpyridyl), 7.60 (d, J ) 8.08 Hz 2H,
Hphenyl), 7.67 (m, 2H, Hpyridyl), 7.91 (d, J ) 8.08 Hz, 2H, Hphenyl),
8.08 (s, 1H, H-C)N), 8.61 (d, J ) 3.28 Hz, 1H, Hpyridyl), 10.70
(bs, 1H, OH). 13C NMR (CDCl3): δ 119.45, 121.49, 125.60,
125.95, 128.98, 132.60, 136.02, 138.74, 147.08, 148.54.
tert-Butyloxycarbonyl-4-(2-pyridyl)phenylmethylamine (4).
To a solution of 2 (19.8 g, 0.1 mol) in 200 mL of EtOH was
added 1 g of 10% Pd/C, and the suspension was submitted to
hydrogenation at 5 atm for 18 h at rt. The catalyst was filtered
on celite and washed with EtOH (2 × 20 mL). The solution
was concentrated in vacuo, and the resulting viscous oil, 3, was
used in the next step without any purification. The crude amine,
3, was dissolved in 150 mL of THF. The solution was cooled
to 0 °C; NEt3 (17 mL, 0.11 mol) and ditert-butyldicarbonate,
(Boc)2O (24 g, 0.11 mol) were added. The resulting solution
was stirred at rt for 4 h. The mixture was concentrated in vacuo
and triturated with 30 mL of Et2O. The resulting solid was
washed with Et2O (2 × 10 mL). Yield: 89%, mp 87-89 °C.
1H NMR (CDCl3): δ 1.47(s, 9H, C(CH3)3), 4.37(d, 2H J ) 5.3
Hz, CH2), 4.93 (br, 1H, NH), 7.22 (m, 1H, Hpyridyl), 7.38 (d, J
) 8.08 Hz, 2H, Hphenyl), 7.73 (m, 2H, Hpyridyl), 7.95 (d, 2H,
Hphenyl), 8.68 (d, J ) 4.08 Hz, 1H, Hpyridyl). 13C NMR (CDCl3):
δ 28.25, 44.15, 78.86, 120.05, 121.95, 126.87, 127.38, 136.59,
138.29, 139.65, 149.53, 155.49, 156.69. Anal. (C17H20N2O2)
Calc: C, 71.81; H, 7.09; N, 9.85; found: C, 71.45; H, 6.98; N,
9.66.
2-Chloro-6-phenylmethylaminopurine (8a): yield 95%;
1
mp > 250 °C. H NMR (DMSO-d6): δ 4.80 (s, 2H, CH2),
7.45-7.70(m, 5H, Hphenyl), 7.91(s, 1H, H-8). (Solubility in
DMSOd6 or in CD3OD was to low for recording a 13C NMR
spectrum). Anal. (C12H10N5Cl) Calc: C, 55.50; H, 3.88; N,
26.97; found: C, 55.81; H, 3.73; N, 26.41.
2-Chloro-6-[4-(2-pyridyl)phenylmethylamino]purine (8b):
yield 93%; mp > 250 °C. 1H NMR (DMSO-d6): δ 4.80 (s, 2H,
CH2), 7.20 (m, 1Η, Ηpyridyl), 7.45 (d, 2H, J ) 8 Hz, Hphenyl),
7.72 (m, 2H, Hpyridyl), 7.95 (m, 3H, Hphenyl and H-8), 8.54 (d,
1H, J ) 4.8 Hz, Hpyridyl). Anal. (C17H13N6Cl) Calc: C, 60.63;
H, 3.89; N, 24.95; found: C, 60.80; H, 3.98; N, 24.61.
Alkylation of Chloropurines 9. To a solution of 8 (0.08
mol) in DMSO (100 mL) at 18-20 °C were added K2CO3
(35.52 g, 0.24 mol) and 2-bromopropane (19 mL, 0.2 mol).
After 5 h stirring at 18-20 °C, 2-bromopropane (4.7 mL, 0.05
mL) was added, and the stirring continued at the same
temperature for 5 h. After addition of 200 mL of cold (5 °C)
H2O, the mixture was extracted with EtOAc (3 × 100 mL, and
the combined organic layers were washed with brine (3 × 50
mL), dried, and dried over Na2SO4. Derivatives 9, which
crystallized upon concentration, were triturated once with 5 mL
of 2-propanol and were collected by filtration.
tert-Butyloxycarbonyl-4-(2-piperidyl)benzylamine (5). In
the reduction step 1 molar equiv of CH3COOH was added.
Otherwise, the procedure was accomplished according to the
method described in the preceding section. Compound 4 did
not crystallize and was purified by column chromatography
using CH2Cl2/MeOH/NEt3 (98:2:0.1) as eluent. Yield 65%, oil.
1H NMR (CDCl3): δ 1.44 (s, 9H, tert-Bu), 1.43-1.93 (m, 6H,
Hpiperidyl), 2.78 (td, 1H, J ) 11.6, 3.1 Hz, Hpiperidyl), 3.19 (d, 1H,
J ) 11.6 Hz, Hpiperidyl), 3.58 (dd, 1H, J ) 10.4, 2.4 Hz, Hpiperidyl),
4.24 (d, 2H, J ) 5.8 Hz, CH2), 4.81 (br, 1H, NH), 7.19 (d, J )
7.5 Hz, 2H, Hphenyl), 7.38 (d, 2H, Hphenyl); 13C NMR (CDCl3):
δ 5.2, 25.7, 28.33, 30.22, 34.8, 44.3, 47.65, 61.92, 126.85,
127.41, 137.58, 144.49, 155.83. Anal. (C17H26N2O2) Calc: C,
70.31; H, 9.02; N, 9.65; found: C, 70.39; H, 9.24; N, 9.48.
4-(2-Pyridyl)benzylamine Ditrifluoroacetate (6). To a
cooled (0 °C) solution of 3 (18 g, 0.063 mol) in 85 mL of
CH2Cl2 was added 85 mL of anhydrous CF3COOH. The cooling
bath was removed, and the mixture was stirred at rt for 2 h.
The mixture was evaporated to dryness, and the residue was
2-Chloro-6-phenylmethylamino-9-iso-propylpurine (9a):
1
yield 85%, mp 180-182 °C. H NMR (DMSO): δ 1.58 (d,
6H, J ) 6.8 Hz, CH(CH3)2), 4.90 (hept, 1H, CH(CH3)2),
6-7.25-7.50 (m, 5H, Hphenyl), 8.16 (s, 1H, H-8). 13C NMR
(DMSO): δ 21.81, 43.19, 46.04, 117.98, 126.44, 126.85, 127.67,
137.03, 137.97, 148.93, 153.03, 154.45. Anal. (C15H16N5Cl)
Calc: C, 59.70; H, 5.34; N, 23.21; found: C, 59.60; H, 5.22; N,
23.36.
2-Chloro-6-[4-(2-pyridyl)phenylmethylamino]-9-iso-pro-
pylpurine (9b): yield 86%, mp 187-189 °C. 1H NMR
(CDCl3): δ 1.58 (d, 6H, J ) 6.8 Hz, CH(CH3)2), 4.79 (hept,
1H, CH(CH3)2), 4.85 (bs, 2H, NHCH2), 6.59 (bs, 1H, NHCH2),
7.20-7.23 (m, 1H, Hpyridyl), 7.49 (d, 2H, J ) 8 Hz, Hphenyl),
7.73-7.71 (m, 2H, Hpyridyl), 7.79 (s, 1H, H-8), 7.98 (d, 2H,
Hphenyl), 8.71 (d, 1H, J ) 4.8 Hz, Hpyridyl). 22.52, 44.07, 46.78,
118.72, 120.25, 122.08, 127.01, 128.04, 136.66, 137.67, 138.54,
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139.02, 149.57, 154.15, 155.15, 156.67. Anal. (C20H19N6Cl)
Calc: C, 63.41; H, 5.05; N, 22.18; found: C, 63.27; H, 5.20; N,
22.35.
3.79-3.85 (m, 1H, CHNH), 4.54 (hept, 1H, CH(CH3)2), 4.76
(m, 2H, NHCH2), 4.90 (bs, 1H, CHNH), 6.10 (bs, 1H, NHCH2),
7.16 (td, 1H, J ) 5.4 and J′ ) 1.6 Hz, Hpyridyl), 7.41 (d, 2H, J
) 8.4 Hz, Hphenyl), 7.45 (s, 1H, 8-H), 7.63-7.70 (m, 2H, Hpyridyl),
7.89 (d, 2H, J ) 8.4 Hz, Hphenyl), 8.62 (d, 1H, J ) 4.8 Hz,
Hpyridyl). 13C NMR (CDCl3): δ 10.5, 22.3, 22.4, 24.1, 38.0, 45.9,
55.0, 66.8, 113.6, 120.0, 120.9, 125.5, 126.8 (×2), 127.7, 130.0,
134.1, 135.9, 137.7, 140.0, 149.1, 154.1, 156.8, 159.1. Anal.
(C24H29N7O) Calc: C, 66.80; H, 6.77; N, 22.72; found: C, 66.43;
H, 6.65; N, 22.51.
Amination by Nucleophilic Substitution of the 2-Chlorine
(10). A mixture of chloropurines, 9 (0.138 mol), and (R)-2-
aminobutan-1-ol (104.10 mL, 1.11 mol) was heated under N2
at 160 °C for 8 h. After cooling, H2O (100 mL) was added,
and the mixture was extracted with EtOAc (4 × 100 mL). The
organic layer was washed with warm (50 °C) H2O (2 × 50
mL), dried, and evaporated until dryness. Crystallization oc-
curred after addition of 10 mL of EtOAc. The crystals of
trisubstituted purines 10 were collected by filtration.
(R)-2-(1-Hydroxybut-2-ylamino)-6-(benzylaminopurine)-
9-isopropylpurine. Roscovitine (10a): yield 89%, mp 108-110
°C. 1H NMR (CDCl3): δ 0.96 (m, 3H), 1.44 (d, 6H, CH(CH3)2).
1.53 (m, 2H, CH2CH3), 3.57(m, CHNH), 3.75(m, 1H, HOCH),
3.84 (m,1H, HOCH), 4.52 (hept, J ) 6.5 Hz, 1H, CH(CH3)2),
4.71 (bs, 2H, CH2), 4.91 (bs, 1H), 7.28-7.30 (m, 6H).13C NMR
(CDCl3): δ 10.84, 22.44, 22.50, 24.90, 44.24, 56.13, 68.06,
114.55, 127.16, 127.58, 128.45, 134.43, 138.90, 154.84, 159.97.
Anal. (C20H20N6O) Calc: C, 61.52; H, 6.45; N, 26.90; found:
C, 61.64; H, 6.25; N, 26.64.
Acknowledgment
This research was supported by grants from the EEC (FP6-
2002-Life Sciences & Health, PRO-KINASE Research Project)
(L.M.), the “Cance´ropole Grand-Ouest” grant (L.M.), the
“Institut National du Cancer” (INCa “Cancer De´tection
d’innovations 2006”) (L.M.), the “Association France-Alzhe-
imer Finiste`re” (L.M.), and the “Ligue Nationale contre le
Cancer (Comite´ du Finiste`re)” (L.M.).
Supporting Information Available
NMR spectra of 4-(2-pyridyl)benzylamine ditrifluoroacetate
(6), roscovitine (10a), and CR8 (10b). This material is available
free of charge via the Internet at http://pubs.acs.org.
(R)-2-(1-Hydroxybut-2-ylamino)-6-[4-(2-pyridyl)phenyl-
methylamino]-9-iso-propylpurine. CR8 (10b): yield 92%, mp
1
89-93 °C. H NMR (CDCl3): δ 0.95 (t, 3H, J ) 7.2 Hz,
CH3CH2), 1.47 (d, 6H, J ) 6.8 Hz, CH(CH3)2), 1.50-1.60 (m,
2H, CH3CH2), 3.56 (dd, 1H, J ) 10.8 and J′ ) 2.8 Hz,
CH2OH), 3.75 (dd, 1H, J ) 10.8 Hz, and J′ ) 2.4, CH2OH),
Received for review November 9, 2008.
OP800284K
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