A new and efficient preparation of 2-aminothiazole-5-carbamides: applications to the synthesis of the anti-cancer drug dasatinib Bang-Chi Chen,*a Rulin Zhao,a Bei Wang,a Roberto Droghini,b Jean Lajeunesse,b Pierre Sirard,b Masaki Endo,b Balu Balasubramanian,a and Joel C. Barrisha
aDiscovery Chemistry, Bristol-Myers Squibb Research and Development, Princeton, NJ 08543, USA bProcess Research and Development, Bristol-Myers Squibb Pharmaceutical Research Institute, Candiac, Quebec J5R1J1, Canada E-mail:
[email protected]
Dedicated to Professor Franklin A Davis on his 70th birthday Abstract A new and efficient method has been developed for the synthesis of 2-amino-N-(-(2-chloro-6methylphenyl)-thiazole-5-carboxamide. The new method involves a chemoselective abromination of ß-ethoxyacrylamide followed by a one-pot treatment with thiourea to give the desired 2-aminothiazole-5-carboxylamide in excellent yield. Application of this new method to the efficient synthesis of the anti-cancer drug dasatinib was demonstrated. Keywords: Synthesis, 2-aminothiazole-5-carbamide, anti-cancer drug, dasatinib, SPRYCEL®
Introduction N-(2-Chloro-6-methylphenyl)-2-[[6-[4-(2-hydroxyethyl)-1-piperazinyl)]-2-methyl-4pyrimidinyl]-amino)]-1,3-thiazole-5-carboxamide (BMS-354825, dasatinib, SPRYCEL®) is a novel multi-targeted kinase inhibitor recently approved in several countries for the treatment of chronic myelogenous leukemia (CML) as well as Philadelphia chromosome-positive acute lymphocytic leukemia (ALL). Dasatinib exhibits greater potency than imatinib mesylate (Gleevec®) and inhibits the majority of kinase mutations in imatinib-resistant CML.1-4 Unlike imatinib, which binds to the inactive conformation of Bcr-Abl, dasatinib binds to the active form of the enzyme.1,5 The ability to inhibit SRC-family kinases such as Hck and Lyn, in addition to binding to the active conformation of BCR-ABL, may both contribute to the effectiveness of dasatinib against imatinib-resistant tumors.6
Me 1
BMS-354825, Dasatinib, SPRYCEL® N-(2-Chloro-6-methylphenyl)-2-[[6-[4-(2-hydroxyethyl)-1-piperazinyl)]-2-methyl-4pyrimidinyl]amino)]-1,3-thiazole-5-carboxamide 1 was previously prepared from 2chlorothiazole 2 via a sulfur directed ortho-lithiation and subsequent nucleophilic coupling with 2-chloro-6-methylphenyl isocyanate 3 to give the core intermediate, 2-chloro-N-(2-chloro-6methylphenyl)-thiazole-5-carboxamide 4.7 Amide nitrogen protection of 4 with NaH and 4methoxybenzyl chloride followed by another NaH mediated coupling of 4-amino-6-chloro-2methyl pyrimidine 6 gave an advanced intermediate 7. Deprotection of the PMB group of 7 afforded the penultimate intermediate, 2-(6-chloro-2-methylpyri-midin-4-ylamino)-N-(2-chloro6-methylphenyl)thiazole-5-carboxamide 8, which was condensed with 1-(2hydroxyethyl)piperazine to give final product 1.7 Me N
R Me N
Cl N N C SCl O S OCl Cl
23 4, R=H 5, R=PMB HN
R MeCl
NH2 N N S N N Cl N O N ClMe
Me 6 7, R=PMB8, R=H
Results and Discussion In a separate project, we required a facile method for the preparation of 2-aminothiazole-5carboxamides to facilitate SAR studies which would also be amenable to large scale synthesis. Our initial focus was to use ethyl 2-aminothiazole-5-carboxylate 10 as core intermediate which could be readily prepared in large scale using a process that was previously developed by us via electrophilic a-bromination of ethyl ß-ethoxyacrylate 9 followed by thiazole ring formation with thiourea.8 N-Boc protection of ethyl 2-aminothiazole-5-carboxylate 10, ester hydrolysis and carboxylic acid group activation followed by coupling with anilines gave the desired 2-N-Bocaminothiazole-5-carboxamides 13 in fair to good overall yields with simple anilines, which were successfully used in our SAR studies.7 However, coupling with 2-chloro-6-methylaniline 12 was unsatisfactory and not amenable for large scale synthesis of 1, presumably due to the steric hindrance of the aniline. Thus, we decided to initially prepare ß-ethoxyacrylamide 15 instead by coupling of the readily available ß-ethoxy acryloyl chloride 14 with aniline 12, followed by formation of the 2-aminothiazole-5-carboxamide 13 using an analogous protocol to the one developed for ethyl ß-ethoxyacrylate 9. The primary advantages of this new approach would be elimination of the protection and deprotection steps needed in the previous synthesis, in addition to elimination of the need for use and handling of n-BuLi and NaH on scale. The main concerns, however, were the potential competitive electrophilic bromination on the amide-nitrogen9 and the phenyl ring10 vs. the desired a-bromination. Herein, we report our findings on the abromination of ß-ethoxyacrylamide 15, subsequent thiazole ring formation and overall synthesis of dasatinib 1. 1. NBS
1. (Boc)2O, DMAP NN
Dioxane-H2OEtO THF BocHN 2. thiourea H2N
OHOEt S SOEt 2. NaOH, MeOH 91% OO 11 O 67% 109 N Me1. (COCl)2, cat. DMF, CH2Cl2 H2N H N
S Me O
ClH2N
13 2. /CH2Cl2, DIPEA
1. NBS, dioxane, H2O Cl 12 3. TFA 2. thiourea rt to 80oC EtO EtO
Me 12, pyr, THF H Cl
N 0oC to rt, overnight OO
Cl
74% 14 15 Thus, treatment of ß-ethoxy acryloyl chloride 14 2-chloro-6-methylaniline 12 in THF using pyridine as base afforded N-(2-chloro-6-methylphenyl) ß-ethoxy acrylamide 15 in 74% yields.11 Next, we subjected ß-ethoxy acrylamide 15 to the NBS mediated thiazole formation in a mixture of dioxane and water followed by addition of thiourea and heating to effect the ring closure. To our satisfaction, the desired 2-aminothiazole-5-carboxamide 13 was obtained in 95% yield. No N-bromination or phenyl ring bromination by-products were observed under these reaction conditions. With an efficient method available for the large scale synthesis of 2-amino-N-(-(2-chloro-6methylphenyl)-thiazole-5-carboxamide 13, we next turned our attention to the direct coupling of 13 with 4,6-dichloro-2-methylpyrimidine 16.12 Using NaO-tBu as base, the coupling reaction took place smoothly in THF from 10°C to room temperature. The reaction was complete in 1.5h affording the desired product, 2-(6-chloro-2-methylpyrimidin-4-ylamino)-N-(2-chloro-6-methylphenyl)thiazole-5-carboxamide 8 in 86% isolated yield.7 Coupling of 8 with 1-(2hydroxyethyl)piperazine in dioxane and subsequent HCl salt formation following the previously reported conditions gave the final product, N-(2-Chloro-6-methylphenyl)-2-[[6-[4-(2hydroxyethyl)-1-piperazin-yl)]-2-methyl-4-pyrimidinyl]amino)]-1,3-thiazole-5-carboxamide (1, dasatinib, SPRYCEL®), in 91% yield.7
13 10oC to rt, 1.5h 8 (86%) HO 1. N NH N H N N H Me
S DIPEA, dioxane, reflux 12h HClNN N O HO NCl2. 2N HCl Me 1 (91%)
Conclusions In summary, a new and efficient method has been developed for the synthesis of 2aminothiazole-5-carboxamide 13. The new method involved a chemoselective a-bromination of ß-ethoxyacrylamides followed by a one-pot treatment with thiourea to give the desired 2aminothiazole-5-carboxylamide excellent yields. Compared to previous methods for the preparation of 2-aminothiazole-5-carboxylamides, this new approach not only avoids the generation and handling of air and moisture sensitive organometallic intermediates, the need for additional protection and deprotection steps, but also affords higher overall yields. Consequently, the new method is simpler in terms of experimental manipulation and operation and is shorter in overall synthetic sequence. Furthermore, the new method was successfully used in the scale synthesis of our newly developed anti-cancer drug dasatinib 1. The application of this new method for the synthesis of other aminothiazole based biologically active compounds will be reported in due course.
Experimental Section General. Proton NMR spectra were recorded with a Bruker DRX-400 spectrometer using CDCl3 or DMSO-d6 as solvent and TMS as an internal standard. Chemical shifts (d) are given from TMS (0 ppm) as internal standard for proton NMR. All other reagents and solvents were commercial products and were used as received unless otherwise noted. All reactions were monitored by HPLC using a Shimadzu LC-10AS system and YMS ODS-A S5 4.6x50mm column with linear gradient system of H2O-MeOH-H3PO4 90:10:0.2 to 10:90:0.2 over 4 min. and at a flow rate of 4 mL/min. All compounds were of >99% purity by analytical HPLC analyses. Melting points are uncorrected. (E)-N-(2-Chloro-6-methylphenyl)-3-ethoxyacrylamide 15. To a cold stirring solution of 2chloro-6-methylaniline (59.5 g 0.42 mol) and pyridine (68 ml, 0.63 mol) in tetrahydrofuran (600 mL) was added 3-ethoxyacryloyl chloride (84.7 g, 0.63 mol) slowly keeping the temp at 0-5°C. The mixture was then warmed and stirred 2 h. at 20°C. Hydrochloric acid (1N, 115 mL) was added at 0-10°C. The mixture was diluted with water (310 mL) and the resulting solution was concentrated under vacuum to a thick slurry. The slurry was diluted with toluene (275 mL) and stirred 15 min. at 20-22°C then 1 h at 0°C. The solid was collected by vacuum filtration, washed with water (2 x 75 mL) and dried to give 74.1 g (73.6 % yield) of (E)-N-(2-chloro-6methylphenyl)-3-ethoxyacrylamide 15. 1H NMR (400 Hz, DMSO-d6) d 1.26 (t, 3H, J= 7 Hz), 2.15 (s, 3H), 3.94 (q, 2H, J= 7 Hz), 5.58 (d, 1H, J=12.4 Hz), 7.10-7.27 (m, 2H, J=7.5 Hz), 7.27 7.37 (d, 1H, J=7.5 Hz), 7.45(d, 1H, J=12.4 Hz), 9.28 (s, 1H). 2-Amino-N-(2-chloro-6-methylphenyl)thiazole-5-carboxamide 13. To a mixture of (E)-N-(2chloro-6-methylphenyl)-3-ethoxyacrylamide 15 (5.00 g 20.86 mmol) in 1,4-dioxane (27 mL) and water (27 mL) was added N-bromosuccinimide (4.08 g, 22.9 mmol) at -10 to 0°C. The slurry was warmed and stirred at 20-22°C for 3h. Thiourea (1.60g, 21 mmol) was added and the mixture heated to 80°C. After 2h, the resulting solution was cooled to 20-22° and conc. ammonium hydroxide (4.2 mL) was added dropwise. The resulting slurry was concentrated under vacuum to about half volume and cooled to 0-5°C. The solid was collected by vacuum filtration, washed with cold water (10 mL) and dried to give 5.3 g (94.9 % yield) of 2-amino-N(2-chloro-6-methylphenyl)thiazole-5-carboxamide 13. 1H NMR (400 MHz, DMSO-d6) d 2.19 (s, 3H), 7.09-7.29 (m, 2H, J=7.5), 7.29-7.43 (d, 1H, J=7.5), 7.61 (s, 2H), 7.85 (s, 1H), 9.63 (s, 1H). 13H NMR (400 MHz, DMSO-d6) d 172.47, 159.88, 144.08, 143.48, 139.19, 134.05, 132.81, 129.31, 127.31, 121.00, 18.66. Anal. Calcd for C11H10ClN3OS: C, 49.34; H, 3.76; N, 15.69; S, 11.97; Cl, 13.24. Found: C, 49.17; H, 3.37; N, 15.33; S, 11.96; Cl, 13.33. 2-(6-Chloro-2-methylpyrimidin-4-ylamino)-N-(2-chloro-6-methylphenyl)thiazole-5carboxamide 8. To a stirring solution of 2-amino-N-(2-chloro-6-methylphenyl)thiazole-5carboxamide 13 (5.00 g, 18.67 mmole) and 4,6-dichloro-2-methylpyrimidine (3.65 g 22.4/mmol) in tetrahydrofuran (65 mL) was added a 30% wt. solution of sodium t-butoxide in tetrahydrofuran (21.1 g, 65.36 mmol) slowly with cooling to keep the temperature at 10-20°C. The mixture was stirred at room temperature for 1.5 h and cooled to 0-5°C. Hydrochloric acid, 2N (21.5 mL) was added slowly and the mixture stirred 1.75 h at 0-5°C. The solid was collected by vacuum filtration, washed with water (15 mL) and dried to give 6.63 g (86.4 % yield) of 2-(6chloro-2-methylpyrimidin-4-ylamino)-N-(2-chloro-6-methylphenyl)thiazole-5-carboxamide 8. 1H NMR (400 MHz, DMSO-d6) d 2.24 (s, 3H), 2.59 (s, 3H), 6.95 (s, 1H), 7.26 (d, J = 7.7 Hz, 1H), 7.30 (dd, J = 6.1, 6.7 Hz, 1H), 7.41 (d, J = 7.7 Hz, 1H), 8.32 (s, 1H), 10.02, (s, 1H), 12.24 (br s, 1H), identical by comparisons with literature data.7
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