- Email: [email protected]
Facile Pd-catalyzed amination of imidazolin-1-yl chloroazines under microwave irradiation: toward a new kinase-inhibitory chemotype
Tetrahedron Letters 56 (2015) 2827–2831
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Facile Pd-catalyzed amination of imidazolin-1-yl chloroazines under microwave irradiation: toward a new kinase-inhibitory chemotype Prashant Mujumdar a, Pakornwit Sarnpitak a, Anton Shetnev b, Mikhail Dorogov b, Mikhail Krasavin c,⇑ a
Eskitis Institute for Drug Discovery, Griffith University, Nathan, Queensland 4111, Australia The Ushinsky Yaroslavl State Pedagogical University, 108 Respublikanskaya St., Yaroslavl 150000, Russian Federation c Institute of Chemistry, St. Petersburg State University, 26 Universitetskyi Prospekt, Peterhof, 198504, Russian Federation b
a r t i c l e
i n f o
Article history: Received 10 February 2015 Revised 13 April 2015 Accepted 16 April 2015 Available online 20 April 2015 Keywords: 2-Imidazoline Chemical instability Microwave irradiation Buchwald–Hartwig amination Kinase inhibitors Hinge region binders
a b s t r a c t The imidazolin-1-yl azine moiety, constructed using a recently developed Buchwald–Hartwig-type arylation methodology, displays excellent chemical stability under subsequent microwave-assisted Pd-catalyzed amination with a range of N-nucleophiles. This finding extends the usage of imidazolin-1-yl azines for bioactive compound library design. The latter is exemplified herein by the discovery of micromolar kinase inhibitors. Ó 2015 Elsevier Ltd. All rights reserved.
Recently, we developed a Pd-catalyzed protocol to efficiently arylate 2-imidazolines with various haloazines and electrondeficient haloaromatics.1 Since then, we have developed a new series of orally available, efficacious anti-inflammatory inhibitors of cyclooxygenase-2 utilizing said protocol.2 At the same time, several examples of the chemical instability of the poorly studied imidazolin-1-yl azine moiety have surfaced. Under Bechamp reduction conditions (Fe, NH4Cl, EtOH/H2O, 70 °C, 16 h), N-(pyrid2-yl)imidazolines 1 underwent an unexpected hydrolytic ringopening, which found utility as an unusual entry into imidazo[4,5-b]pyridines 2.3 Furthermore, attempts to perform direct nucleophilic aromatic substitution of N-(haloazine)imidazolines like 3 with morpholine either led, under thermal conditions, to the formation of the ring-opened product 4 or triggered, in the presence of NaH, aromatization to give imidazole 5 (Scheme 1).4 In our initial report on imidazoline N-arylation,1 we provided three pilot examples indicating that compounds such as 3 could be substrates for further Pd-catalyzed coupling reactions with either another 2-imidazoline or a secondary amine. No damage to the imidazoline core was observed which was significant, in light of the known tendency of 2-imidazolines5 as well amidines in general6,7 to undergo transamination with various amines. Considering the importance of such a modification for the ⇑ Corresponding author. Tel.: +7 931 3617872; fax: +7 812 428 6939. E-mail address: [email protected] (M. Krasavin). http://dx.doi.org/10.1016/j.tetlet.2015.04.059 0040-4039/Ó 2015 Elsevier Ltd. All rights reserved.
generation of a library based on the imidazolin-1-yl azine core, we sought to ascertain a broader scope for the Pd-catalyzed amination of imidazolin-1-yl azines, employing various azine linkers and a range of N-nucleophiles. Unfortunately, the prolonged time required for these reactions to go to completion under conventional heating,1 hinders performing them in an array format. Therefore, we also aimed to evaluate the amination of 2-imidazoline-containing chloroazines under microwave irradiation8 to achieve shorter reaction times. This strategy was expected to have some risk, considering reports that microwave irradiation can significantly facilitate the transamination of amidines.9 Herein, we report the results of these studies and solid evidence of the scaffolds being chemically compatible with microwave-assisted Buchwald–Hartwig-type amination. In addition, we have investigated this chemotype in the context of designing novel, therapeutically relevant kinase inhibitors. Using the robust protocol of Fujioka et al.,10 we prepared ten 2-imidazolines 6a–j and N-arylated them, on 300–500 mg scale, with various dichloroazines, using the earlier published protocol employing conventional heating.1 While the yields of 2-imidazolines from their respective aldehydes have already been noted as being good to excellent,1,3 we were also pleased to find the yields of the arylation step to be quite satisfying and chromatographic purification of the respective imidazolin-1-yl azine products 7a–w to be rather straightforward (Scheme 2, Table 1). With the twenty-three substrates 7a–w at hand, we proceeded to undertake
2828
P. Mujumdar et al. / Tetrahedron Letters 56 (2015) 2827–2831
Br
NH2
Br Fe, NH4 Cl
N N
O
EtOH/H2O, 70 C 16-24 h
N NO2
Br
N
N
o
N
NH 2
N
N
NO2
1
2 NH2
Cl
N
morpholine N 120 o C
N
O
O
N
N
N 4
N
N N N
morpholine
3
NaH/THF r.t.
N O
N
N
N
N 5
N
Scheme 1. Illustrative cases of the chemical instability of imidazolin-1-yl azines.
O
1) ethylene diamine (1.05 equiv.), DCM, 0 o C, 20 min
R
R 2) NBS (1.05 equiv.), DCM, 0 oC → r.t., 16 h
N
O
N
R=
N
N 6a, 68%
6b, 63%
6c, 96%
6d, 94%
6e, 76%
N
HN 6a-j
Pd(OAc) 2 (2 mol%) BINAP (4 mol%) Cs 2CO3 (1-3 equiv.) toluene, 100 o C, 16-20 h
Cl azine Cl
F O
N N F
6f, 77%
R 6g, 91%
6h, 78%
6i, 63%
6j, 81%
azine
Cl 7a-w (yields are provided in Table 1) Scheme 2. Preparation of the starting materials 7a–w for the subsequent Buchwald–Hartwig coupling study.
a broader survey of Buchwald–Hartwig-type couplings with various N-nucleophiles, in order to establish the chemical compatibility of the imidazolin-1-yl azine cores with this reaction (Scheme 3). Gratifyingly, the reactions proceeded to completion on 3–5 mmol scale in much shorter times (40–60 min) compared to conventional heating, with no appreciable degradation of the 2-imidazoline core. This allowed us to obtain novel, diversely substituted compounds 8a–w in good yields after simple chromatographic purification (Table 1).11 From their spectroscopic data, it was evident the imidazolin-1-yl azine core remained intact in all products 8a–w. Interestingly, attempted preparation of the symmetrically substituted bis-imidazolinyl azines (8d, 8f, 8k) in one step, via the use of 2 equiv of the respective 2-imidazolines (6c, 6d, 6h) resulted in complex product mixtures, under conventional heating or microwave irradiation alike. Therefore, stepwise introduction of imidazoline moieties into the dihaloazine core appears to be essential. Mostly associated with the modulation of adrenergic and imidazoline receptors,12,13 2-imidazoline-containing compounds cover a large biological space and are a privileged14,15 class of
compounds.16 However, kinase inhibition has not been documented for compounds based on the 2-imidazoline scaffold. We were puzzled by the lack of such reports in the literature, attributing this to the novelty of the imidazolin-1-yl azine chemotype. Indeed, with the highly polar, nitrogen-rich molecular framework, compounds 8a–w were likely to be good candidates for forming hydrogen-bonding interactions with the hinge region of protein kinases.17 In order to verify this hypothesis without undertaking a massive library synthesis and a laborious screening exercise, we diluted our pilot library 8a–w into a larger virtual library of 1235 diverse compounds of the same general structure and undertook an in silico docking prioritization of these compounds against a panel of human kinases, followed by Tanimoto similarity clustering of the virtual hits (this work will be subject to a separate disclosure).18 As the result of this effort, compounds 8i, 8j, 8m, 8q, and 8r emerged as representatives of the highest-scoring clusters.19 These compounds were screened against a panel of 48 human kinases provided by Cerep (France).20 The 240 data points collected for the five compounds revealed that three of the five compounds tested exhibited >30% inhibition of only a few
2829
P. Mujumdar et al. / Tetrahedron Letters 56 (2015) 2827–2831 Table 1 Compounds 7a–w and 8a–w prepared in this work
Cl Compound
azine
R
NuH
Isolated yield of 7 (%)
Isolated yield of 8 (%)
69
44
6i
67
56
6e
78
64
6c
88
65
6f
72
47
6d
72
45
69
38
91
72
6g
88
58
6g
67
61
6h
68
66
6d
83
53
6j
58
61
73
81
77
72
82
64
82
78
Cl N
Cl
N
Cl
N N
Cl
N N
Cl
7(8)a
7(8)b
7(8)c
N
Cl Cl
N Cl
7(8)d
NH2
N
Cl
N 1
7(8)e
Cl
N
2
Cl
N N
F3 C
O
N
Cl
Cl
7(8)f
N 1
O Cl
7(8)g
2
Cl
N N
F3 C
N
7(8)h
Cl
Cl N
O
HN
OH
N
Cl
Cl
7(8)i
N
N
1
O
2
Cl
7(8)j
N
H2 N
Cl
N N
Cl
Cl
N
7(8)k
N 1
Cl
7(8)l
2
Cl
N N
F3 C 1
Cl
7(8)m
2
Cl
N N
F
Cl 7(8)n
Cl N 1
7(8)o
Cl
O
H2 N
N
F 1
2
N
Cl
7(8)p
O
2
N
Cl
HN
N
Cl
O
H2 N
N
F
Cl
Cl N
7(8)q
N
HN
O
F (continued on next page)
2830
P. Mujumdar et al. / Tetrahedron Letters 56 (2015) 2827–2831
Table 1 (continued)
Cl Compound
azine
R
NuH
Isolated yield of 7 (%)
Isolated yield of 8 (%)
68
77
6a
79
56
6b
78
63
78
71
65
82
75
60
Cl F
N
Cl
7(8)r
Cl
HN
OH
N F Cl
N
Cl
7(8)s
Cl 7(8)t
Cl N
N
7(8)u
N
7(8)v
Cl
N
Cl
N N
Cl
F
N
N N
Cl
NH2 HN
O
Cl Cl
NH2
7(8)w
F
N N R
azine Cl 7a-w
NuH
N
Pd(OAc) 2 (2 mol%) BINAP (4 mol%) Cs2 CO3 (1 equiv.) toluene, MW, 130 o C, 40-60 min
R
Acknowledgements N azine Nu 8a-w
Scheme 3. The ‘second’ Buchwald coupling of substrates 7a–w under microwave irradiation.
This research was supported by the Russian Scientific Fund (project grant 14-50-00069). The authors are grateful to Dr. Andreas Hofmann (Griffith University), Dr. Paul Taylor (University of Edinburgh) and Dr. Alain-Dominique Gorse (Queensland Facility for Advanced Bioinformatics, Australia) for their help in selecting the compounds for the kinase panel testing. Supplementary data
therapeutically relevant kinases: IRK21 (8i), TRKA22 (8m), Src23 (8m), CDK1/224 (8r), and TAOK225 (8r). Concentration–response retesting of the same compound–kinase pairs at five different concentrations (0.3 lM, 3 lM, 10 lM, 30 lM, 0.1 mM) confirmed compound 8m as a 10 lM inhibitor of TRKA and Src as well as compound 8r as a 10 lM inhibitor of CDK1/2 and TAOK2. However, compound 8i produced only partial inhibition of IRK in the concentration range (see ESI). While the inhibitory potencies of 8m and 8r are low compared to clinically used kinase inhibitors (e.g., imatinib which is a nanomolar inhibitor of bcr-Abl26), the two compounds represent valuable starting points for further development, in a similar fashion to the new 4–470 lM kinase inhibitory cores that have recently been harvested from the commercial domain by Urich et al.17 using an innovative computational approach. In summary, we have demonstrated that Buchwald–Hartwigtype coupling of N-(chloroazinyl)-2-imidazolines 7a–w with a range of N-nucleophiles (2-imidazolines, primary and secondary amines) is chemically compatible with the imidazolin-1-yl azine scaffold when performed under microwave irradiation. We also have shown that the newly established chemotype can exert kinase inhibitory activity and therefore, the Buchwald–Hartwig coupling chemistry described herein can serve as a valuable tool for further library generation and optimization of the biological activity.
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tetlet.2015.04. 059. References and notes 1. Krasavin, M. Tetrahedron Lett. 2012, 53, 2876–2880. 2. Sarnpitak, P.; Mujumdar, P.; Morisseau, C.; Hwang, S. H.; Hammock, B.; Iurchenko, V.; Zozulya, S.; Gavalas, A.; Geronikaki, A.; Ivanenkov, Y.; Krasavin, M. Eur. J. Med. Chem. 2014, 84, 160–172. 3. Mujumdar, P.; Grkovic, T.; Krasavin, M. Tetrahedron Lett. 2013, 54, 3336–3340. 4. Parchinsky, V. Z.; Krasavin, M. Unpublished results. 5. Butler, R. N.; Fitzgeraldm, K. J. J. Chem. Soc., Perkin Trans. 1 1989, 155–157. 6. Vincent, S.; Mons, S.; Lebeau, L.; Mioskowski, C. Tetrahedron Lett. 1997, 38, 7527–7530. 7. Furth, P. S.; Reitman, M. S.; Cook, A. F. Tetrahedron Lett. 1997, 38, 5403–5406. 8. Aguado, L.; Canela, M.-D.; Thibaut, H. J.; Priego, E.-M.; Camarasa, M.-J.; Leyssen, P.; Neyts, J.; Perez-Perez, M. J. Eur. J. Med. Chem. 2012, 49, 279–288. 9. Pereira, M.-F.; Thiery, V.; Besson, T. Tetrahedron Lett. 2007, 48, 7657–7659. 10. Fujioka, H.; Murai, K.; Ohba, Y.; Hiramatsu, A.; Kita, Y. Tetrahedron Lett. 2005, 46, 2197–2199. 11. Typical experimental protocol for microwave-assisted Buchwald–Hartwigtype coupling of 7a–w with various N-nucleophiles. A 5-mL sealable microwave vial equipped with a stirring bar was charged with 7 (3–5 mmol), an N-nucleophile (1.1 equiv), anhydrous Cs2CO3 and toluene (1.5 mL). The mixture was set on rapid stirring at rt while a catalyst solution was prepared by mixing Pd(OAc)2 (0.02 equiv) and BINAP (0.04 equiv) in toluene (0.5 mL) at 100 °C, until a colored clear solution was formed. The latter was added to the microwave vial by a pipette. The vial was sealed and irradiated in Biotage Initiator™ microwave reactor (operating at 100 W) at 130 °C for 40 min (for 2imidazoline coupling partners) or 60 min (for primary and secondary amines).
P. Mujumdar et al. / Tetrahedron Letters 56 (2015) 2827–2831
12. 13. 14.
15. 16. 17. 18. 19.
The contents of the vial were poured over a plug of Celite. The latter was washed with an ample quantity of ethyl acetate and the filtrate evaporated. The crude product was purified by flash column chromatography using an appropriate gradient of MeOH in dichloromethane as eluent to give an analytically pure coupling product 8. Piletz, J. E.; Halaris, A.; Ernsberger, P. R. Crit. Rev. Neurobiol. 1994, 9, 29–66. Parini, A.; Moudanos, C. G.; Pizzinat, N.; Lanier, S. M. Trends Pharmacol. Sci. 1996, 17, 13–16. Evans, B. E.; Rittle, K. E.; Bock, M. G.; DiPardo, R. M.; Freidinger, R. M.; Whitter, W. L.; Lundell, G. F.; Veber, D. F.; Anderson, P. S. J. Med. Chem. 1988, 31, 2235– 2246. Welsch, M. E.; Snyder, S. A.; Stockwell, B. R. Curr. Opin. Chem. Biol. 2010, 14, 347–361. Krasavin, M. Eur. J. Med. Chem. 2015. http://dx.doi.org/10.1016/ j.ejmech.2014.11.028. Urich, R.; Wishart, G.; Kiczun, M.; Richters, A.; Tidten-Luksch, N.; Rauh, D.; Sherborne, B.; Wyatt, P. G.; Brenk, R. ACS Chem. Biol. 2013, 8, 1044–1052. Sarnpitak, P.; Mujumdar, P.; Taylor, P.; Cross, M.; Coster, M.; Gorse, A.-D.; Krasavin, M.; Hofmann, A. submitted for publication. Characterization data for the five in silico hits: 8i—beige solid, mp = 220 °C (decomp.); 1H NMR (500 MHz, CDCl3) d 8.40 (s, 1H), 7.44 (d, J = 1.7 Hz, 1H), 7.43 (d, J = 15.7 Hz, 1H), 7.34 (d, J = 15.8 Hz, 1H), 7.08–7.00 (m, 2H), 6.90 (tt, J = 8.7, 2.4 Hz, 1H), 6.48 (d, J = 3.3 Hz, 1H), 6.43 (dd, J = 3.4, 1.8 Hz, 1H), 5.54 (s, 1H), 4.21 (t, J = 9.2 Hz, 2H), 4.06 (t, J = 9.3 Hz, 2H), 3.91 (t, J = 9.1 Hz, 2H), 3.56 (t, J = 9.1 Hz, 2H); 13C NMR (125 MHz, CDCl3) d 162.7 (d, JC–F = 250.6 Hz), 162.6 (d, JC–F = 250.4 Hz), 159.0, 157.9, 157.7, 157.4, 152.0, 143.7, 135.0 (t, JC– F = 10.0 Hz), 112.0, 111.7, 111.6, 111.5, 111.4, 105.7 (t, JC–F = 25.2 Hz), 92.8, 53.4, 51.9, 50.4, 48.3; LC–MS (ESI+): m/z found 421 (calculated 421); Anal. calcd for C22H18F2N6O: C, 62.85; H, 4.32; N, 19.99; found: C, 63.02; H, 4.42; N, 20.07; 8j—light yellow solid, mp = 215–217 °C; 1H NMR (500 MHz, CDCl3) d 8.16 (d, J = 5.7 Hz, 1H), 7.73 (d, J = 16.0 Hz, 1H), 7.49 (d, J = 1.7 Hz, 1H), 7.23 (d, J = 15.8 Hz, 1H), 7.06–7.01 (m, 2H), 6.86–6.80 (m, 1H), 6.67 (d, J = 3.5 Hz, 1H), 6.51 (dd, J = 3.5, 1.8 Hz, 1H), 6.33 (d, J = 5.6 Hz, 1H), 4.30 (t, J = 9.2 Hz, 2H), 4.06 (t, J = 9.2 Hz, 2H), 3.96 (t, J = 9.4 Hz, 2H), 3.76 (t, J = 9.4 Hz, 2H); 13C NMR (125 MHz, CDCl3) d 162.3 (dd, JC–F = 250.0, 12.5 Hz), 159.0, 157.7, 157.6, 157.5, 151.8, 143.7, 136.6 (t, JC–F = 12.5 Hz), 125.5, 115.5, 113.2, 113.1, 112.3, 111.6
20. 21. 22. 23. 24. 25. 26.
2831
(dd, JC–F = 25.0, 12.5 Hz), 104.6 (t, JC–F = 25.0 Hz), 100.4, 53.3, 51.8, 50.2, 48.2; LC–MS (ESI+): 421 (calculated 421); Anal. calcd for C22H18F2N6O: C, 62.85; H, 4.32; N, 19.99; found: C, 62.68; H, 4.45; N, 19.87; 8m—yellow oil; 1H NMR (500 MHz, CDCl3) d 8.06 (d, J = 5.0 Hz, 1H), 7.27–7.28 (m, 2H), 7.26 (s, 2H), 7.22–7.24 (m, 2H), 7.18–7.20 (m, 2H), 7.13 (d, J = 10.0 Hz, 2H), 4.42 (s, 2H), 4.22 (s, 2H), 3.96–3.99 (m, 4H), 3.92–3.94 (m, 2H), 3.86–3.89 (m, 2H); 13C NMR (125 MHz, CDCl3) d 163.2, 158.6 (unresolved d), 158.5, 150.4 (d, JC–F = 29.4 Hz), 147.5, (d, JC–F = 28.0 Hz), 143.2 (d, JC–F = 254.0 Hz), 138.1, 135.1, 131.1, 129.9, 128.9, 128.8, 126.7, 126.6, 56.7, 56.1, 49.6, 44.6, 37.1, 36.0; LC–MS (ESI+): 415 (calculated 415); Anal. calcd for C24H23FN6: C, 69.55; H, 5.59; N, 20.28; found: C, 69.27; H, 5.68; N, 20.43; 8q—white solid, mp = 159–161 °C, 1H NMR (500 MHz, CDCl3): d 7.06–7.05 (m, 2H), 6.87 (tt, J = 8.8, 2.25 Hz, 1H), 5.23 (s, 1H), 4.16 (t, J = 8.8 Hz, 2H), 4.03 (t, J = 9.2 Hz, 2H), 3.68 (t, J = 4.75 Hz, 4H), 3.36 (t, J = 4.9 Hz, 4H), 2.27 (s, 3H); 13C NMR (125 MHz, CDCl3): d 167.0, 163.1, 162.7 (dd, JC–F = 247.5, 12.5 Hz), 159.3, 158.9 (t, JC–F = 2.5 Hz), 135.8 (t, JC–F = 8.75 Hz), 111.8 (dd, JC–F = 18.75, 6.25 Hz), 105.2 (t, JC–F = 2.5 Hz), 86.2, 66.5 (2 carbons), 53.5, 50.5, 44.4 (2 carbons), 26.0; LC–MS (ESI+): 360 (calculated 360); Anal. calcd for C18H19F2N5O: C, 60.16; H, 5.33; N, 19.49; found: C, 60.04; H, 5.47; N, 19.63; 8r—light brown solid, mp = 176–178 °C. 1H NMR (500 MHz, CD3OD): d 7.76 (s, 1H), 7.37 (s, 1H), 7.14–7.10 (m, 3H), 4.24–4.20 (m, 2H), 4.14–4.11 (m, 2H), 3.83–3.78 (m, 1H), 3.62–3.58 (m, 2H), 2.91–2.86 (m, 2H), 1.78–1.75 (m, 2H), 1.38–1.31 (m, 2H), –OH proton in exchange; 13C NMR (125 MHz, CD3OD): d 164.2 (dd, JC–F = 247.5, 12.5 Hz), 161.7, 153.5, 149.1, 138.1 (t, JC–F = 11.25 Hz), 124.1, 120.6, 112.3 (dd, JC–F = 20.0, 7.5 Hz), 105.7 (t, JC–F = 26.25 Hz), 68.2, 54.1, 51.1, 42.7 (2 carbons), 34.6 (2 carbons); LC–MS (ESI+): 360 (calculated 360); Anal. calcd for C18H19F2N5O: C, 60.16; H, 5.33; N, 19.49; found: C, 60.38; H, 5.18; N, 19.81. http://www.cerep.fr/cerep/users/pages/catalog/profiles/catalog.asp. Schmid, E.; Hotz-Wagen, A.; Hack, V.; Droege, W. FASEB J. 1999, 13, 1491–1500. Benito-Gutiérrez, E.; Garcia-Fernàndez, J.; Comella, J. X. Mol. Cell. Neurosci. 2006, 31, 179–192. Luo, W.; Slebos, R. J.; Hill, S.; Li, M.; Brábek, J.; Amanchy, R.; Chaerkady, R.; Pandey, A.; Ham, A. L.; Hanks, S. K. J. Proteome Res. 2008, 7, 3447–3460. Cross, F. R.; Yuste-Rojas, M.; Gray, S.; Jacobson, M. D. Mol. Cell. 1999, 4, 11–19. Chen, Z.; Hutchison, M.; Cobb, M. H. J. Biol. Chem. 1999, 274, 28803–28807. Savage, D. G.; Antman, K. H. N. Eng. J. Med. 2002, 346, 683–693.
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Facile Pd-catalyzed amination of imidazolin-1-yl chloroazines under microwave irradiation: toward a new kinase-inhibitory chemotype Prashant Mujumdar a, Pakornwit Sarnpitak a, Anton Shetnev b, Mikhail Dorogov b, Mikhail Krasavin c,⇑ a
Eskitis Institute for Drug Discovery, Griffith University, Nathan, Queensland 4111, Australia The Ushinsky Yaroslavl State Pedagogical University, 108 Respublikanskaya St., Yaroslavl 150000, Russian Federation c Institute of Chemistry, St. Petersburg State University, 26 Universitetskyi Prospekt, Peterhof, 198504, Russian Federation b
a r t i c l e
i n f o
Article history: Received 10 February 2015 Revised 13 April 2015 Accepted 16 April 2015 Available online 20 April 2015 Keywords: 2-Imidazoline Chemical instability Microwave irradiation Buchwald–Hartwig amination Kinase inhibitors Hinge region binders
a b s t r a c t The imidazolin-1-yl azine moiety, constructed using a recently developed Buchwald–Hartwig-type arylation methodology, displays excellent chemical stability under subsequent microwave-assisted Pd-catalyzed amination with a range of N-nucleophiles. This finding extends the usage of imidazolin-1-yl azines for bioactive compound library design. The latter is exemplified herein by the discovery of micromolar kinase inhibitors. Ó 2015 Elsevier Ltd. All rights reserved.
Recently, we developed a Pd-catalyzed protocol to efficiently arylate 2-imidazolines with various haloazines and electrondeficient haloaromatics.1 Since then, we have developed a new series of orally available, efficacious anti-inflammatory inhibitors of cyclooxygenase-2 utilizing said protocol.2 At the same time, several examples of the chemical instability of the poorly studied imidazolin-1-yl azine moiety have surfaced. Under Bechamp reduction conditions (Fe, NH4Cl, EtOH/H2O, 70 °C, 16 h), N-(pyrid2-yl)imidazolines 1 underwent an unexpected hydrolytic ringopening, which found utility as an unusual entry into imidazo[4,5-b]pyridines 2.3 Furthermore, attempts to perform direct nucleophilic aromatic substitution of N-(haloazine)imidazolines like 3 with morpholine either led, under thermal conditions, to the formation of the ring-opened product 4 or triggered, in the presence of NaH, aromatization to give imidazole 5 (Scheme 1).4 In our initial report on imidazoline N-arylation,1 we provided three pilot examples indicating that compounds such as 3 could be substrates for further Pd-catalyzed coupling reactions with either another 2-imidazoline or a secondary amine. No damage to the imidazoline core was observed which was significant, in light of the known tendency of 2-imidazolines5 as well amidines in general6,7 to undergo transamination with various amines. Considering the importance of such a modification for the ⇑ Corresponding author. Tel.: +7 931 3617872; fax: +7 812 428 6939. E-mail address: [email protected] (M. Krasavin). http://dx.doi.org/10.1016/j.tetlet.2015.04.059 0040-4039/Ó 2015 Elsevier Ltd. All rights reserved.
generation of a library based on the imidazolin-1-yl azine core, we sought to ascertain a broader scope for the Pd-catalyzed amination of imidazolin-1-yl azines, employing various azine linkers and a range of N-nucleophiles. Unfortunately, the prolonged time required for these reactions to go to completion under conventional heating,1 hinders performing them in an array format. Therefore, we also aimed to evaluate the amination of 2-imidazoline-containing chloroazines under microwave irradiation8 to achieve shorter reaction times. This strategy was expected to have some risk, considering reports that microwave irradiation can significantly facilitate the transamination of amidines.9 Herein, we report the results of these studies and solid evidence of the scaffolds being chemically compatible with microwave-assisted Buchwald–Hartwig-type amination. In addition, we have investigated this chemotype in the context of designing novel, therapeutically relevant kinase inhibitors. Using the robust protocol of Fujioka et al.,10 we prepared ten 2-imidazolines 6a–j and N-arylated them, on 300–500 mg scale, with various dichloroazines, using the earlier published protocol employing conventional heating.1 While the yields of 2-imidazolines from their respective aldehydes have already been noted as being good to excellent,1,3 we were also pleased to find the yields of the arylation step to be quite satisfying and chromatographic purification of the respective imidazolin-1-yl azine products 7a–w to be rather straightforward (Scheme 2, Table 1). With the twenty-three substrates 7a–w at hand, we proceeded to undertake
2828
P. Mujumdar et al. / Tetrahedron Letters 56 (2015) 2827–2831
Br
NH2
Br Fe, NH4 Cl
N N
O
EtOH/H2O, 70 C 16-24 h
N NO2
Br
N
N
o
N
NH 2
N
N
NO2
1
2 NH2
Cl
N
morpholine N 120 o C
N
O
O
N
N
N 4
N
N N N
morpholine
3
NaH/THF r.t.
N O
N
N
N
N 5
N
Scheme 1. Illustrative cases of the chemical instability of imidazolin-1-yl azines.
O
1) ethylene diamine (1.05 equiv.), DCM, 0 o C, 20 min
R
R 2) NBS (1.05 equiv.), DCM, 0 oC → r.t., 16 h
N
O
N
R=
N
N 6a, 68%
6b, 63%
6c, 96%
6d, 94%
6e, 76%
N
HN 6a-j
Pd(OAc) 2 (2 mol%) BINAP (4 mol%) Cs 2CO3 (1-3 equiv.) toluene, 100 o C, 16-20 h
Cl azine Cl
F O
N N F
6f, 77%
R 6g, 91%
6h, 78%
6i, 63%
6j, 81%
azine
Cl 7a-w (yields are provided in Table 1) Scheme 2. Preparation of the starting materials 7a–w for the subsequent Buchwald–Hartwig coupling study.
a broader survey of Buchwald–Hartwig-type couplings with various N-nucleophiles, in order to establish the chemical compatibility of the imidazolin-1-yl azine cores with this reaction (Scheme 3). Gratifyingly, the reactions proceeded to completion on 3–5 mmol scale in much shorter times (40–60 min) compared to conventional heating, with no appreciable degradation of the 2-imidazoline core. This allowed us to obtain novel, diversely substituted compounds 8a–w in good yields after simple chromatographic purification (Table 1).11 From their spectroscopic data, it was evident the imidazolin-1-yl azine core remained intact in all products 8a–w. Interestingly, attempted preparation of the symmetrically substituted bis-imidazolinyl azines (8d, 8f, 8k) in one step, via the use of 2 equiv of the respective 2-imidazolines (6c, 6d, 6h) resulted in complex product mixtures, under conventional heating or microwave irradiation alike. Therefore, stepwise introduction of imidazoline moieties into the dihaloazine core appears to be essential. Mostly associated with the modulation of adrenergic and imidazoline receptors,12,13 2-imidazoline-containing compounds cover a large biological space and are a privileged14,15 class of
compounds.16 However, kinase inhibition has not been documented for compounds based on the 2-imidazoline scaffold. We were puzzled by the lack of such reports in the literature, attributing this to the novelty of the imidazolin-1-yl azine chemotype. Indeed, with the highly polar, nitrogen-rich molecular framework, compounds 8a–w were likely to be good candidates for forming hydrogen-bonding interactions with the hinge region of protein kinases.17 In order to verify this hypothesis without undertaking a massive library synthesis and a laborious screening exercise, we diluted our pilot library 8a–w into a larger virtual library of 1235 diverse compounds of the same general structure and undertook an in silico docking prioritization of these compounds against a panel of human kinases, followed by Tanimoto similarity clustering of the virtual hits (this work will be subject to a separate disclosure).18 As the result of this effort, compounds 8i, 8j, 8m, 8q, and 8r emerged as representatives of the highest-scoring clusters.19 These compounds were screened against a panel of 48 human kinases provided by Cerep (France).20 The 240 data points collected for the five compounds revealed that three of the five compounds tested exhibited >30% inhibition of only a few
2829
P. Mujumdar et al. / Tetrahedron Letters 56 (2015) 2827–2831 Table 1 Compounds 7a–w and 8a–w prepared in this work
Cl Compound
azine
R
NuH
Isolated yield of 7 (%)
Isolated yield of 8 (%)
69
44
6i
67
56
6e
78
64
6c
88
65
6f
72
47
6d
72
45
69
38
91
72
6g
88
58
6g
67
61
6h
68
66
6d
83
53
6j
58
61
73
81
77
72
82
64
82
78
Cl N
Cl
N
Cl
N N
Cl
N N
Cl
7(8)a
7(8)b
7(8)c
N
Cl Cl
N Cl
7(8)d
NH2
N
Cl
N 1
7(8)e
Cl
N
2
Cl
N N
F3 C
O
N
Cl
Cl
7(8)f
N 1
O Cl
7(8)g
2
Cl
N N
F3 C
N
7(8)h
Cl
Cl N
O
HN
OH
N
Cl
Cl
7(8)i
N
N
1
O
2
Cl
7(8)j
N
H2 N
Cl
N N
Cl
Cl
N
7(8)k
N 1
Cl
7(8)l
2
Cl
N N
F3 C 1
Cl
7(8)m
2
Cl
N N
F
Cl 7(8)n
Cl N 1
7(8)o
Cl
O
H2 N
N
F 1
2
N
Cl
7(8)p
O
2
N
Cl
HN
N
Cl
O
H2 N
N
F
Cl
Cl N
7(8)q
N
HN
O
F (continued on next page)
2830
P. Mujumdar et al. / Tetrahedron Letters 56 (2015) 2827–2831
Table 1 (continued)
Cl Compound
azine
R
NuH
Isolated yield of 7 (%)
Isolated yield of 8 (%)
68
77
6a
79
56
6b
78
63
78
71
65
82
75
60
Cl F
N
Cl
7(8)r
Cl
HN
OH
N F Cl
N
Cl
7(8)s
Cl 7(8)t
Cl N
N
7(8)u
N
7(8)v
Cl
N
Cl
N N
Cl
F
N
N N
Cl
NH2 HN
O
Cl Cl
NH2
7(8)w
F
N N R
azine Cl 7a-w
NuH
N
Pd(OAc) 2 (2 mol%) BINAP (4 mol%) Cs2 CO3 (1 equiv.) toluene, MW, 130 o C, 40-60 min
R
Acknowledgements N azine Nu 8a-w
Scheme 3. The ‘second’ Buchwald coupling of substrates 7a–w under microwave irradiation.
This research was supported by the Russian Scientific Fund (project grant 14-50-00069). The authors are grateful to Dr. Andreas Hofmann (Griffith University), Dr. Paul Taylor (University of Edinburgh) and Dr. Alain-Dominique Gorse (Queensland Facility for Advanced Bioinformatics, Australia) for their help in selecting the compounds for the kinase panel testing. Supplementary data
therapeutically relevant kinases: IRK21 (8i), TRKA22 (8m), Src23 (8m), CDK1/224 (8r), and TAOK225 (8r). Concentration–response retesting of the same compound–kinase pairs at five different concentrations (0.3 lM, 3 lM, 10 lM, 30 lM, 0.1 mM) confirmed compound 8m as a 10 lM inhibitor of TRKA and Src as well as compound 8r as a 10 lM inhibitor of CDK1/2 and TAOK2. However, compound 8i produced only partial inhibition of IRK in the concentration range (see ESI). While the inhibitory potencies of 8m and 8r are low compared to clinically used kinase inhibitors (e.g., imatinib which is a nanomolar inhibitor of bcr-Abl26), the two compounds represent valuable starting points for further development, in a similar fashion to the new 4–470 lM kinase inhibitory cores that have recently been harvested from the commercial domain by Urich et al.17 using an innovative computational approach. In summary, we have demonstrated that Buchwald–Hartwigtype coupling of N-(chloroazinyl)-2-imidazolines 7a–w with a range of N-nucleophiles (2-imidazolines, primary and secondary amines) is chemically compatible with the imidazolin-1-yl azine scaffold when performed under microwave irradiation. We also have shown that the newly established chemotype can exert kinase inhibitory activity and therefore, the Buchwald–Hartwig coupling chemistry described herein can serve as a valuable tool for further library generation and optimization of the biological activity.
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.tetlet.2015.04. 059. References and notes 1. Krasavin, M. Tetrahedron Lett. 2012, 53, 2876–2880. 2. Sarnpitak, P.; Mujumdar, P.; Morisseau, C.; Hwang, S. H.; Hammock, B.; Iurchenko, V.; Zozulya, S.; Gavalas, A.; Geronikaki, A.; Ivanenkov, Y.; Krasavin, M. Eur. J. Med. Chem. 2014, 84, 160–172. 3. Mujumdar, P.; Grkovic, T.; Krasavin, M. Tetrahedron Lett. 2013, 54, 3336–3340. 4. Parchinsky, V. Z.; Krasavin, M. Unpublished results. 5. Butler, R. N.; Fitzgeraldm, K. J. J. Chem. Soc., Perkin Trans. 1 1989, 155–157. 6. Vincent, S.; Mons, S.; Lebeau, L.; Mioskowski, C. Tetrahedron Lett. 1997, 38, 7527–7530. 7. Furth, P. S.; Reitman, M. S.; Cook, A. F. Tetrahedron Lett. 1997, 38, 5403–5406. 8. Aguado, L.; Canela, M.-D.; Thibaut, H. J.; Priego, E.-M.; Camarasa, M.-J.; Leyssen, P.; Neyts, J.; Perez-Perez, M. J. Eur. J. Med. Chem. 2012, 49, 279–288. 9. Pereira, M.-F.; Thiery, V.; Besson, T. Tetrahedron Lett. 2007, 48, 7657–7659. 10. Fujioka, H.; Murai, K.; Ohba, Y.; Hiramatsu, A.; Kita, Y. Tetrahedron Lett. 2005, 46, 2197–2199. 11. Typical experimental protocol for microwave-assisted Buchwald–Hartwigtype coupling of 7a–w with various N-nucleophiles. A 5-mL sealable microwave vial equipped with a stirring bar was charged with 7 (3–5 mmol), an N-nucleophile (1.1 equiv), anhydrous Cs2CO3 and toluene (1.5 mL). The mixture was set on rapid stirring at rt while a catalyst solution was prepared by mixing Pd(OAc)2 (0.02 equiv) and BINAP (0.04 equiv) in toluene (0.5 mL) at 100 °C, until a colored clear solution was formed. The latter was added to the microwave vial by a pipette. The vial was sealed and irradiated in Biotage Initiator™ microwave reactor (operating at 100 W) at 130 °C for 40 min (for 2imidazoline coupling partners) or 60 min (for primary and secondary amines).
P. Mujumdar et al. / Tetrahedron Letters 56 (2015) 2827–2831
12. 13. 14.
15. 16. 17. 18. 19.
The contents of the vial were poured over a plug of Celite. The latter was washed with an ample quantity of ethyl acetate and the filtrate evaporated. The crude product was purified by flash column chromatography using an appropriate gradient of MeOH in dichloromethane as eluent to give an analytically pure coupling product 8. Piletz, J. E.; Halaris, A.; Ernsberger, P. R. Crit. Rev. Neurobiol. 1994, 9, 29–66. Parini, A.; Moudanos, C. G.; Pizzinat, N.; Lanier, S. M. Trends Pharmacol. Sci. 1996, 17, 13–16. Evans, B. E.; Rittle, K. E.; Bock, M. G.; DiPardo, R. M.; Freidinger, R. M.; Whitter, W. L.; Lundell, G. F.; Veber, D. F.; Anderson, P. S. J. Med. Chem. 1988, 31, 2235– 2246. Welsch, M. E.; Snyder, S. A.; Stockwell, B. R. Curr. Opin. Chem. Biol. 2010, 14, 347–361. Krasavin, M. Eur. J. Med. Chem. 2015. http://dx.doi.org/10.1016/ j.ejmech.2014.11.028. Urich, R.; Wishart, G.; Kiczun, M.; Richters, A.; Tidten-Luksch, N.; Rauh, D.; Sherborne, B.; Wyatt, P. G.; Brenk, R. ACS Chem. Biol. 2013, 8, 1044–1052. Sarnpitak, P.; Mujumdar, P.; Taylor, P.; Cross, M.; Coster, M.; Gorse, A.-D.; Krasavin, M.; Hofmann, A. submitted for publication. Characterization data for the five in silico hits: 8i—beige solid, mp = 220 °C (decomp.); 1H NMR (500 MHz, CDCl3) d 8.40 (s, 1H), 7.44 (d, J = 1.7 Hz, 1H), 7.43 (d, J = 15.7 Hz, 1H), 7.34 (d, J = 15.8 Hz, 1H), 7.08–7.00 (m, 2H), 6.90 (tt, J = 8.7, 2.4 Hz, 1H), 6.48 (d, J = 3.3 Hz, 1H), 6.43 (dd, J = 3.4, 1.8 Hz, 1H), 5.54 (s, 1H), 4.21 (t, J = 9.2 Hz, 2H), 4.06 (t, J = 9.3 Hz, 2H), 3.91 (t, J = 9.1 Hz, 2H), 3.56 (t, J = 9.1 Hz, 2H); 13C NMR (125 MHz, CDCl3) d 162.7 (d, JC–F = 250.6 Hz), 162.6 (d, JC–F = 250.4 Hz), 159.0, 157.9, 157.7, 157.4, 152.0, 143.7, 135.0 (t, JC– F = 10.0 Hz), 112.0, 111.7, 111.6, 111.5, 111.4, 105.7 (t, JC–F = 25.2 Hz), 92.8, 53.4, 51.9, 50.4, 48.3; LC–MS (ESI+): m/z found 421 (calculated 421); Anal. calcd for C22H18F2N6O: C, 62.85; H, 4.32; N, 19.99; found: C, 63.02; H, 4.42; N, 20.07; 8j—light yellow solid, mp = 215–217 °C; 1H NMR (500 MHz, CDCl3) d 8.16 (d, J = 5.7 Hz, 1H), 7.73 (d, J = 16.0 Hz, 1H), 7.49 (d, J = 1.7 Hz, 1H), 7.23 (d, J = 15.8 Hz, 1H), 7.06–7.01 (m, 2H), 6.86–6.80 (m, 1H), 6.67 (d, J = 3.5 Hz, 1H), 6.51 (dd, J = 3.5, 1.8 Hz, 1H), 6.33 (d, J = 5.6 Hz, 1H), 4.30 (t, J = 9.2 Hz, 2H), 4.06 (t, J = 9.2 Hz, 2H), 3.96 (t, J = 9.4 Hz, 2H), 3.76 (t, J = 9.4 Hz, 2H); 13C NMR (125 MHz, CDCl3) d 162.3 (dd, JC–F = 250.0, 12.5 Hz), 159.0, 157.7, 157.6, 157.5, 151.8, 143.7, 136.6 (t, JC–F = 12.5 Hz), 125.5, 115.5, 113.2, 113.1, 112.3, 111.6
20. 21. 22. 23. 24. 25. 26.
2831
(dd, JC–F = 25.0, 12.5 Hz), 104.6 (t, JC–F = 25.0 Hz), 100.4, 53.3, 51.8, 50.2, 48.2; LC–MS (ESI+): 421 (calculated 421); Anal. calcd for C22H18F2N6O: C, 62.85; H, 4.32; N, 19.99; found: C, 62.68; H, 4.45; N, 19.87; 8m—yellow oil; 1H NMR (500 MHz, CDCl3) d 8.06 (d, J = 5.0 Hz, 1H), 7.27–7.28 (m, 2H), 7.26 (s, 2H), 7.22–7.24 (m, 2H), 7.18–7.20 (m, 2H), 7.13 (d, J = 10.0 Hz, 2H), 4.42 (s, 2H), 4.22 (s, 2H), 3.96–3.99 (m, 4H), 3.92–3.94 (m, 2H), 3.86–3.89 (m, 2H); 13C NMR (125 MHz, CDCl3) d 163.2, 158.6 (unresolved d), 158.5, 150.4 (d, JC–F = 29.4 Hz), 147.5, (d, JC–F = 28.0 Hz), 143.2 (d, JC–F = 254.0 Hz), 138.1, 135.1, 131.1, 129.9, 128.9, 128.8, 126.7, 126.6, 56.7, 56.1, 49.6, 44.6, 37.1, 36.0; LC–MS (ESI+): 415 (calculated 415); Anal. calcd for C24H23FN6: C, 69.55; H, 5.59; N, 20.28; found: C, 69.27; H, 5.68; N, 20.43; 8q—white solid, mp = 159–161 °C, 1H NMR (500 MHz, CDCl3): d 7.06–7.05 (m, 2H), 6.87 (tt, J = 8.8, 2.25 Hz, 1H), 5.23 (s, 1H), 4.16 (t, J = 8.8 Hz, 2H), 4.03 (t, J = 9.2 Hz, 2H), 3.68 (t, J = 4.75 Hz, 4H), 3.36 (t, J = 4.9 Hz, 4H), 2.27 (s, 3H); 13C NMR (125 MHz, CDCl3): d 167.0, 163.1, 162.7 (dd, JC–F = 247.5, 12.5 Hz), 159.3, 158.9 (t, JC–F = 2.5 Hz), 135.8 (t, JC–F = 8.75 Hz), 111.8 (dd, JC–F = 18.75, 6.25 Hz), 105.2 (t, JC–F = 2.5 Hz), 86.2, 66.5 (2 carbons), 53.5, 50.5, 44.4 (2 carbons), 26.0; LC–MS (ESI+): 360 (calculated 360); Anal. calcd for C18H19F2N5O: C, 60.16; H, 5.33; N, 19.49; found: C, 60.04; H, 5.47; N, 19.63; 8r—light brown solid, mp = 176–178 °C. 1H NMR (500 MHz, CD3OD): d 7.76 (s, 1H), 7.37 (s, 1H), 7.14–7.10 (m, 3H), 4.24–4.20 (m, 2H), 4.14–4.11 (m, 2H), 3.83–3.78 (m, 1H), 3.62–3.58 (m, 2H), 2.91–2.86 (m, 2H), 1.78–1.75 (m, 2H), 1.38–1.31 (m, 2H), –OH proton in exchange; 13C NMR (125 MHz, CD3OD): d 164.2 (dd, JC–F = 247.5, 12.5 Hz), 161.7, 153.5, 149.1, 138.1 (t, JC–F = 11.25 Hz), 124.1, 120.6, 112.3 (dd, JC–F = 20.0, 7.5 Hz), 105.7 (t, JC–F = 26.25 Hz), 68.2, 54.1, 51.1, 42.7 (2 carbons), 34.6 (2 carbons); LC–MS (ESI+): 360 (calculated 360); Anal. calcd for C18H19F2N5O: C, 60.16; H, 5.33; N, 19.49; found: C, 60.38; H, 5.18; N, 19.81. http://www.cerep.fr/cerep/users/pages/catalog/profiles/catalog.asp. Schmid, E.; Hotz-Wagen, A.; Hack, V.; Droege, W. FASEB J. 1999, 13, 1491–1500. Benito-Gutiérrez, E.; Garcia-Fernàndez, J.; Comella, J. X. Mol. Cell. Neurosci. 2006, 31, 179–192. Luo, W.; Slebos, R. J.; Hill, S.; Li, M.; Brábek, J.; Amanchy, R.; Chaerkady, R.; Pandey, A.; Ham, A. L.; Hanks, S. K. J. Proteome Res. 2008, 7, 3447–3460. Cross, F. R.; Yuste-Rojas, M.; Gray, S.; Jacobson, M. D. Mol. Cell. 1999, 4, 11–19. Chen, Z.; Hutchison, M.; Cobb, M. H. J. Biol. Chem. 1999, 274, 28803–28807. Savage, D. G.; Antman, K. H. N. Eng. J. Med. 2002, 346, 683–693.