Development of a Scalable Synthesis of an Azaindolyl-Pyrimidine

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Development of a Scalable Synthesis of an AzaindolylPyrimidine Inhibitor of Influenza Virus Replication Jianglin Liang, John Cochran, Warren Dorsch, Ioana Davies, and Michael Clark Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/acs.oprd.6b00063 • Publication Date (Web): 08 Apr 2016 Downloaded from http://pubs.acs.org on April 9, 2016

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Organic Process Research & Development

Development of a Scalable Synthesis of an Azaindolyl-Pyrimidine Inhibitor of Influenza Virus Replication Jianglin (Colin) Liang,* John E. Cochran, Warren A. Dorsch, Ioana Davies and Michael P. Clark Vertex Pharmaceuticals Incorporated, 50 Northern Avenue, Boston, Massachusetts 02210, United States

ACS Paragon Plus Environment

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Table of Contents Graphic


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ABSTRACT: A scalable, asymmetric route for the synthesis of the influenza virus replication inhibitor 2 is presented. The key steps include an enzymatic desymmetrization of cis-1,3cyclohexanediester in 99% yield and 96% ee, SNAr displacement of a methanesulfinylpyrimidine and a Curtius rearrangement to form a morpholinyl urea. This high-yielding route allowed us to rapidly synthesize hundreds of grams of 2 in 99% purity to support in vivo studies.

Keywords: enzymatic desymmetrization; scale up; influenza virus inhibitor; Curtius rearrangement


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INTRODUCTION Each year in the United States, between 5 and 20% of the population becomes infected with influenza viruses. Influenza (flu) is a potentially fatal infectious disease responsible for more than 200,000 hospitalizations and from 3,000 to 49,000 deaths annually in the United States during nonpandemic seasons, as shown by recent reports.1 The current standard of care (SOC) for influenza in the United States is based on neuraminidase inhibitors (oseltamivir, zanamivir and peramivir), however, this class of antivirals is facing significant concern over viral resistance.2 Recently we reported the discovery of a novel class of orally bioavailable, azaindole-based inhibitors of human influenza virus replication, including VX-787 (1).3 Here we report the first scale-up synthesis of a related analog 2, a potent azaindole-based inhibitor. The structure of 2 is based on an azaindole-pyrimidine scaffold that contains a synthetically-challenging (1R,3S)-cisdiaminocyclohexane.

Initial Synthetic Route to Compound 2 The initial synthesis of 2 (Scheme 1 and Scheme 2) began with the cyclization of a commercially available cis/trans mixture of cyclohexane-1,3-dicarboxylic acid 3. Subjecting the mixture to DCC caused the cis-diacid to cyclize to the anhydride 4 which could be readily separated from


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unreacted trans-diacid. The anhydride 4 was re-opened with pTSA and triethylorthoformate in EtOH to give the pure cis-1,3-cyclohexane dicarboxylate ester 5 in 90% yield. Enzymatic desymmetrization4 using lipase AYS Amano5 selectively hydrolyzed the diester 5 in 90% yield and 96% ee to afford the cis-cyclohexane monoacid 6. Although Boaz reported that no emulsion was observed in this step,5a we encountered a significant emulsion using the same work up procedure. This may have been due to the scale on which we were performing the reaction (400 g), and the large loading (42wt%) of the lipase. Curtius rearrangement of enantiopure 6 with DPPA/TEA formed the corresponding intermediate isocyanate, that was trapped by BnOH to give Cbz-protected aminoester 7 in a one-pot sequence. N-protected amino ester 7 was hydrolyzed to acid 8 under basic conditions. However, a second Curtius rearrangement to convert 8 to 9 was unsuccessful and led to an unidentified by-product. Alternatively, 8 was converted to the corresponding primary amide and subsequent Hofmann rearrangement using CuBr2/LiOtBu worked efficiently to afford 88% yield of the desired Boc-protected amine 9, although the presence of copper salts made the work up challenging.6 Compound 9 was hydrogenated to give desired key intermediate 10 in almost quantitative yield (Scheme 1). With chiral mono-protected diaminocyclohexane 10 in hand, the remaining steps of synthesis are straight-forward. Compound 10 displaced the sulfoxide 113a to afford compound 12, and subsequent Boc deprotection, morpholine urea formation and de-tosylation formed the final compound 2 (Scheme 2).7


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Scheme 1 Initial Route to Key Intermediate Chiral cis-Diaminocyclohexane 10

This convergent route was developed by the medicinal chemistry team to explore SAR, particularly as compound 12 serves as an excellent intermediate for synthesizing a wide variety of analogs. However, the need to supply hundreds of grams of compound 2 for advanced studies required that we address the weaknesses of the synthetic route. Most notably the following specific challenges were identified as requiring change, improvement or elimination: (1) the high enzyme loading and difficult work up of lipase resolution; (2) the work-up and removal of copper salts following the Hofmann rearrangement; (3) the long overall sequence (12 total steps) and 8.7% overall yield; (4) the requirement for chromatographic purification after 6 of the 12 reactions.


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Scheme 2 Initial Synthesis of 2

Retrosynthetic Analysis To deliver hundreds of grams of compound 2, we set 4 goals for a new and improved synthesis: (1) simplified reaction work up; (2) minimal use of chromatography; (3) a shorter synthetic sequence; and (4) higher overall yield. With these goals in mind, we envisioned the retrosynthetic analysis shown in Scheme 3. We analyzed the initial route and identified 7 as a critical intermediate. Compound 2 could potentially be synthesized from acid 14 via Curtius rearrangement followed by reaction with morpholine. Acid 14 could be obtained by displacement of sulfoxide 11 with the amine 15 (from hydrogenation of 7), followed by an efficient global deprotection of both the ester and tosyl groups. The advantage of this route is that the morpholine-based urea is installed in a more direct manner and both the Hofmann rearrangement and Boc deprotection steps have been eliminated (Scheme 3).


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Scheme 3 Retrosynthetic Analysis of 2 F N

F H N

N

H N

F

O

N H

CO2H

N

F

N N

N

Curtius

H N

N

O

N H

F

14

2

N

O S

N

F N Enzymatic CbzHN Desymmetrization

HO2C

11

H2 N CO2Et

CO2H 3

N Ts

7

CO2Et 15

Scalable Synthesis of 2 The new synthesis was started with commercially available dicarboxylic acid 3 (mixture cis and trans-isomers). Reflux of 3 in AcCl overnight accomplished both the equilibration of the transisomer to cis-isomer, as well as the cyclization of the latter to the desired anhydride intermediate 4.8 The anhydride was refluxed in EtOH in the presence of H2SO4 to give the ring-opened mesodiester 5 in 94% yield over 2 steps after distillation in a two-step one-pot process. Since the enzymatic reaction conditions used in initial synthesis caused isolation problems, we lowered the lipase loading to 10wt% and found that reaction went to completion overnight and much less emulsion was observed during work up. Same 10wt% enzyme loading was used by Yoshida with a similar lipase in an enzymatic hydrolysis reaction on half-ton sacle.9 Acid 6 was isolated by aqueous extraction in 98% yield and 96% ee. All of the steps from the dicarboxylate acid 3


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through the monoester 6 were run on ca. 1 kg scale without any issue proving the robustness of the route (Scheme 4). Scheme 4 Scalable Synthesis of 2

1. AcCl, reflux CO2H 2. H2SO4, EtOH EtO2C

HO2C

CO2Et

94%

Lipase AYS buffer (pH 7.2)

HO2C

CO2Et

DPPA, TEA, BnOH, PhCH3

98% yield, 96% ee

3

85%

5

6 F

CbzHN

H2, Pd/C

CO2Et

H2N

CO2Et

11, DIPEA 73%

99% 7

N

N

85%

16

N Ts F

F N

CO2Et

N

F

15

LiOH, THF/H2O

H N

H N CO2H

N

1. DPPA, TEA, THF 2. Morpholine

N

H N N

H N

F

F N

N H

14

O

N

67% N

N H

2 O

Efforts were made to directly convert mono-acid 6 to amine 15 under Curtius conditions using HCl, however, the reaction was messy and low-yielding. So the intermediate isocyanate was trapped with benzyl alcohol, followed by hydrogenation to cleanly give amine 15 as an HCl salt. The SNAr displacement of sulfoxide 11 with amine 15 in the presence of Hunig’s base gave 16 in 73% yield by simple silica gel plug purification. Both ester hydrolysis and tosyl group removal were successfully carried out using LiOH, and compound 14 was precipitated out after acidification and collected by filtration. Compound 14 was treated with DPPA/TEA, followed by the addition of morpholine to form the desired urea. The final compound 2 was purified by chromatography, and fractions were collected, followed by trituration from MTBE to form


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MTBE solvate (1:1 ratio). This solvate was recrystallized from acetone/water to give pure compound 2 with >99% purity for in vivo studies.

CONCLUSION We have developed an enantioselective, scalable and efficient process for the synthesis of 2, a potent inhibitor of influenza virus replication. Compared with the initial synthesis, the sequence was shortened from 12 steps to 7 steps and overall yield was improved from 8.7% to 32%. The process from commercially available diacid 3 to enantiopure mono-acid 6 was significantly optimized with high yields and easy workups. All steps were run on 100+ gram scale and no chromatography was needed except at the final step. This scalable synthesis allowed us to synthesis and deliver hundreds of grams of high-purity material on time to support in vivo studies. EXPERIMENTAL SECTION General Information. All commercially available reagents and anhydrous solvents were used without further purification. Purity assessment for final compounds was based on analytical HPLC: 4.6 mm × 50 mm Waters YMC Pro-C18 column, 5 µm, 120A. Mobile phases are as follows: A, H2O with 0.2% formic acid; B, acetonitrile with 0.2% formic acid; gradient, 10−90% B in 3 min with 5 min run time. The flow rate is 1.5 mL/min. Unless specified otherwise, all compounds were ≥95% pure. Mass samples were analyzed on a Quattro LC, Quatro II or Thermo QExactive (for HRMS) mass spectrometer operated in a single MS mode with electrospray ionization. Samples were introduced into the mass spectrometer using


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chromatography. The mobile phase for all mass analysis consisted of acetonitrile−water mixtures with either 0.2% formic acid or ammonium formate. 1H NMR spectra were recorded using a Bruker Avance II-300 (300 MHz) or Bruker Avance II-400 (400 MHz) instrument. Column chromatography was performed using Teledyne ISCO RediSep normal phase (35−70 µm) or RediSep Gold normal phase (25−40 µm) silica flash columns using a Teledyne ISCO Companion XL purification system. The procedures outlined in this section are those employed for the reactions run at the largest scale. Analytical characterizations were obtained on materials that were representative or purified for that propose. Diethyl-cyclohexane-1,3-dicarboxylate (5). Commercially available diacid 3 (858 g, 4.98 mol, 3:1 trans/cis ratio) was mixed with acetyl chloride (1.5 L), and the mixture was heated to reflux overnight with mechanical stirring. A distillation setup was added to flask and the volatiles were removed by distillation in vacuo. The residual oil was dissolved in EtOH (3 L) and concentrated sulfuric acid (266 mL, 5 mol) was added slowly (exothermic). The mixture was heated to reflux overnight, and the volatiles were removed by rotary evaporation. The remaining oil was dissolved in DCM (5 L) and washed with 1 N NaOH (2 L). The organic layer was dried over MgSO4 and evaporated in vacuo to afford a dark brown oil. The oil was distilled under high vacuum to afford product 5 (1068.5 g, 94% yield) as a colorless oil (bp ~175oC). 1

H NMR (300 MHz, CDCl3) δ 4.13 (q, J = 7.1 Hz, 4H), 2.42 – 2.16 (m, 3H), 2.05 – 1.82 (m,

3H), 1.66 – 1.45 (m, 1H), 1.48 – 1.31 (m, 3H), 1.25 (t, J = 7.1 Hz, 6H). (1S,3R)-3-ethoxycarbonylcyclohexanecarboxylic acid (6). The diester 5 was mixed with pH 7.2 phosphate buffer (8 L, Aldrich). Amino lipase AYS (100 g) was added and the mixture was


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stirred overnight at RT. A drop in pH to 4.5 was observed. HPLC analysis was very clean showing only product. The reaction was acidified with concentrated HCl to pH 2 and filtered over celite. The celite cake was washed with EtOAc (2x800 mL), and filtrate was extracted with EtOAc (2x5 L). The combined organic layers were dried over MgSO4 and evaporated in vacuo to afford product 6 (922.5 g, 98% yield) as a yellow oil. Chiral HPLC showed 96% ee (Chiral Pak IA column, 4.6x250 mm, 5 µm, 90:10 heptane/isopropanol as mobile phase). Specific rotation: [α]20D= 3.92⁰ (c = 1.12 in DCM); 1H NMR (300 MHz, d6-DMSO) δ 12.10 (s, 1H), 4.05 (q, J = 7.1 Hz, 2H), 2.41 - 2.17 (m, 2H), 2.05 (d, J = 13.0 Hz, 1H), 1.93 - 1.70 (m, 3H), 1.41 - 1.10 (m, 7H). HRMS (ESI) [M+H]+ calculated for C10H17O4 201.1121, found 201.1119. Ethyl (1R,3S)-3-benzyloxycarbonylaminocyclohexanecarboxylate (7). To (1S,3R)-3ethoxycarbonylcyclohexanecarboxylic acid (6) (140 g, 700 mmol) in toluene (1.4 L) was added diphenylphosphoryazide (DPPA) (166 mL, 769 mmol) and triethylamine (107 mL, 769 mmol). The mixture was refluxed for 2 h under N2. Gas release was observed. The reaction mixture was cooled to 60oC and benzyl alcohol (87 mL, 839 mmol) was added in one portion. The mixture was heated to 80oC overnight. After cooling to RT, EtOAc (1 L) and water (1.5 L) were added, the mixture was stirred vigorously and the layers were separated. The organic layer was washed with brine, dried over Na2SO4, and evaporated in vacuo. The residual oil was dissolved in DCM (200 mL) and purified by filtration over a silica gel plug (1 kg). The plug was eluted with hexane/EtOAc (3:1), and the fractions were collected and evaporated in vacuo to afford 206 g of a sticky solid. 1H NMR showed it contained around 12wt% benzyl alcohol (calculated yield 85%). This solid was used directly in the next step. A sample of 7 for analytical characterization was prepared by ISCO silica gel chromatography.


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Specific rotation: [α]25D= -33.3o (c = 1 in DCM). 1 H NMR (300 MHz, CDCl3 ) δ 7.48 – 7.30 (m, 5H), 5.11 (s, 2H), 4.67 (s, 1H), 4.13 (q, J = 7.1 Hz, 2H), 3.55 (s, 1H), 2.42 (t, J = 11.8 Hz, 1H), 2.28 (d, J = 12.6 Hz, 1H), 2.10 – 1.79 (m, 3H), 1.50 – 1.19 (m, 6H), 1.19 – 1.00 (m, 1H). HRMS (ESI) [M+H]+ calculated for C17H24NO4 306.1700, found 306.1700. Ethyl (1R,3S)-3-aminocyclohexanecarboxylate (HCl salt) (15): Ethyl (1R,3S)-3benzyloxycarbonylaminocyclohexanecarboxylate (7) (270 g, 88% pure, 778 mmol) in MeOH (800 mL) was added to a Parr pressure reactor vessel. Palladium on carbon (18.8 g, 5% Pd by wt) was added. The reactor was pressurized under 50 psi of H2 and the reaction was maintained at this pressure for two days, until no further H2 consumption was observed. The mixture was filtered through celite to remove catalyst and to the filtrate was added 5N HCl in iPrOH (195 mL, 972 mmol). The resulting solution was stirred for 30 min and all solvents were removed in vacuo to afford a light yellow oil. MTBE (1 L) was added and the resulting suspension of white solid was stirred for 0.5 h. The suspension was filtered and the filter cake was washed with MTBE once, and then dried under vacuum in an oven to yield 15.(hydrochloride salt) as a white solid (160 g, 99% yield). Specific rotation: [α]20D= -6.4⁰ (c = 1 in MeOH); 1H NMR (300 MHz, d6-DMSO) δ 8.14 (s, 3H), 4.07 (q, J = 7.1 Hz, 2H), 3.13 – 2.92 (m, 1H), 2.48 – 2.32 (m, 1H), 2.15 (d, J = 12.2 Hz, 1H), 2.00 – 1.68 (m, 3H), 1.47 – 1.06 (m, 7H). HRMS (ESI) [M+H]+ calculated for C9H18NO2 172.1332, found 172.1333. Ethyl (1R,3S)-3-[[5-fluoro-2-[5-fluoro-1-(p-tolylsulfonyl)pyrrolo[2,3-b]pyridin-3yl]pyrimidin-4-yl]amino]cyclohexanecarboxylate (16): To the mixture of 5-fluoro-3-(5fluoro-4-methylsulfinyl-pyrimidin-2-yl)-1-(p-tolylsulfonyl)pyrrolo[2,3-b]pyridine (11)3a (181.4


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g, 404.4 mmol) , ethyl (1R,3S)-3-aminocyclohexanecarboxylate hydrochloride (15) (84 g, 404.4 mmol) in dry THF (4 L) was added DIPEA (155 mL, 890 mmol). The reaction mixture was heated to reflux under N2 for two days, and cooled down. EtOAc (4 L) was added and the solution was washed with brine (2x4 L). The organic layer was dried over Na2SO4 and concentrated down. The residual oil was purified by filtration over a silica gel plug (2 kg), followed by elution with 30% ethyl acetate in hexane. The fractions were collected and evaporated to dryness, yielding product 16 as a white solid (165 g, 73% yield). Specific rotation: [α]21D= -85.7⁰ (c = 1 in CHCl3). 1H NMR (400 MHz, CDCl3) δ 8.54 (s, 1H), 8.48 (dd, J = 9.0, 2.8 Hz, 1H), 8.35 - 8.29 (m, 1H), 8.14 - 8.06 (m, 3H), 7.33 - 7.28 (m, 2H), 5.11 (d, J = 6.5 Hz, 1H), 4.26 - 4.08 (m, 3H), 2.62 (tt, J = 11.7, 3.6 Hz, 1H), 2.49 (d, J = 12.6 Hz, 1H), 2.39 (s, 3H), 2.21 (d, J = 12.7 Hz, 1H), 2.09 (d, J = 11.7 Hz, 1H), 2.05 - 1.93 (m, 1H), 1.63 - 1.39 (m, 3H), 1.39 - 1.28 (m, 1H), 1.25 (t, J = 7.1 Hz, 3H). 19F NMR (282.4 MHz, CDCl3) -133.66, 158.31 ppm. HRMS (ESI) [M+H]+ calculated for C27H28F2N5O4S 556.1825, found 556.1829. (1R,3S)-3-[[5-fluoro-2-(5-fluoro-1H-pyrrolo[2,3-b]pyridin-3-yl)pyrimidin-4yl]amino]cyclohexanecarboxylic acid (14): To the mixture of ethyl (1R,3S)-3-[[5-fluoro-2-[5fluoro-1-(p-tolylsulfonyl)pyrrolo[2,3-b]pyridin-3-yl]pyrimidin-4yl]amino]cyclohexanecarboxylate (16) (164 g, 295 mmol) in THF (1 L) and water (1 L) was added LiOH (35.4 g, 1.48 mol). The reaction mixture was heated to reflux overnight. The reaction was cooled to 20oC, and 6 N HCl was added until the pH was adjusted to 6. THF was removed by evaporation in vacuo which precipitated a yellow solid. To the resulting suspension was added acetonitrile (500 mL) and the resulting suspension was stirred for 0.5 h. The suspension was filtered, and the cake was washed twice with water, acetonitrile and finally


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DCM. The resulting white solid was dried under vacuum at 50oC to afford 14 (93.6 g, 85% yield). Specific rotation: [α]21D= -109.4⁰ (c = 1 in DMSO). 1H NMR (300 MHz, d6-DMSO) δ 12.28 (s, 1H), 8.42 (dd, J = 9.8, 2.9 Hz, 1H), 8.35 – 8.18 (m, 2H), 8.14 (d, J = 4.0 Hz, 1H), 7.57 (s, 1H), 4.12 (d, J = 11.0 Hz, 1H), 2.51 – 2.34 (m, 1H), 2.36 – 2.13 (m, 1H), 2.13 – 1.74 (m, 3H), 1.66 – 1.15 (m, 4H). HRMS (ESI) [M+H]+ calculated for C18H18F2N5O2 374.1423, found 374.1427. N-[(1R,3S)-3-[[5-fluoro-2-(5-fluoro-1H-pyrrolo[2,3-b]pyridin-3-yl)pyrimidin-4yl]amino]cyclohexyl]morpholine-4-carboxamide (2): To the suspension of (1R,3S)-3-[[5fluoro-2-(5-fluoro-1H-pyrrolo[2,3-b]pyridin-3-yl)pyrimidin-4-yl]amino]cyclohexanecarboxylic acid (14) (65 g, 174 mmol) in dry THF (1.3 L) was added Et3N (34 mL, 244 mmol). The reaction was purged with nitrogen for 20 min. DPPA (45 mL, 209 mmol) was added and the mixture was heated to 50oC for 2 h. HPLC showed that all starting material was consumed. Morpholine (45.5 mL, 522 mmol) was added and the reaction was kept at reflux overnight. The reaction mixture was cooled to 20oC, and EtOAc (1 L) was added. The mixture was washed with saturated NaHCO3 (2x1 L), and evaporated under vacuum. The residual oil was purified on an ISCO Companion XL using 1.5 kg silica gel column and a gradient 0-20% of MeOH in DCM. The fractions were collected and evaporated, affording 68 g of crude white solid. MTBE (800 mL) was added and heated to reflux for 0.5 h, then cooled down. The suspension was filtered, and cake was dried under vacuum in oven at 50oC. 1H NMR showed it was 1:1 MTBE solvate. To the solid was added acetone/water (4:1, 120 mL) and the mixture was stirred for 0.5 h. The mixture was filtered, and cake was washed with DCM (2x50 mL), dried in oven under vacuum at 50oC to yield compound 2 as white solid with 99% chemical purity (54 g, 67%).


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Specific rotation: [α]21D= -165.7⁰ (c = 1 in MeOH). 1H NMR (300 MHz, d6-DMSO) δ 12.23 (s, 1H), 8.42 (dd, J = 9.8, 2.9 Hz, 1H), 8.34 - 8.18 (m, 2H), 8.14 (d, J = 4.0 Hz, 1H), 7.49 (d, J = 7.5 Hz, 1H), 6.33 (d, J = 7.6 Hz, 1H), 4.24 - 4.00 (m, 1H), 3.75 - 3.57 (m, 1H), 3.57 - 3.42 (m, 4H), 3.28 - 3.09 (m, 4H), 2.15 (d, J = 11.4 Hz, 1H), 2.01 (d, J = 11.2 Hz, 1H), 1.83 (d, J = 9.7 Hz, 2H), 1.60 - 1.07 (m, 4H). 19F NMR (282.4 MHz, d6-DMSO) -138.10, -158.25 ppm. HRMS (ESI) [M+H]+ calculated for C22H26F2N7O2 458.2111, found 458.2110.

ASSOCIATED CONTENT Supporting Information. 1

H NMR spectra for compounds 2, 5-7, 14-16.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Notes The authors declare no completing financial interest. ACKNOWLEDGMENT We thank Barry Davis for collecting high-resolution mass spectra, Marc Towle for chiral HPLC analysis, Jeremy Green for reviewing the manuscript and also thank the Flu chemistry team for support and preliminary work.


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ABBREVIATIONS SAR, structure-activity relationship; SOC, standard of care; DPPA, diphenylphosphoryl azid; DCC, N,N'-Dicyclohexylcarbodiimide; DCM, dichloromethane; THF, tetrahydrofuran; TEA, triethylamine; AcCl, acetyl chloride; BnOH, benzyl alcohol; MTBE, methyl tert-butyl ether. REFERENCES (1) (a) Morens D. M.; Taubenberger J. K.; Folkers, G. K.; Fauci A. S. Pandemic Influenza’s 500th Anniversary. Clinical Infectious Diseases: an Official Publication of the Infectious Diseases Society of America 2010, 51, 1442-1444. (b) Thompson, W. W.; Shay, D. K.; Weintraub, E.; Brammer, L.; Bridges, C. B.; Cox, N. J.; Fukuda, K. Influenza-associated hospitalizations in the United States. JAMA, J. Am. Med. Assoc. 2004, 292, 1333. (c) CDC. Seasonal Influenza: Key Facts about Influenza (Flu) and Flu Vaccine. http://cdc.gov/flu/keyfacts.htm (accessed October 19, 2015). (2) (a) Thorland, K.; Awad, T.; Boivin, G.; Thabane, L. Systematic review of influenza resistance to the neuraminidase inhibitors. BMC Infect. Dis. 2011, 11, 134. (b) Le, Q. M.; Kiso, M.; Someya, K.; Sakai, Y. T.; Nguyen, T. H.; Nguyen, K. H. L.; Pham, N. D.; Ngyn, H. H.; Yamada, S.; Muramoto, Y.; Horimoto, T.; Takada, A.; Goto, H.; Suzuki, Y.; Kawaoka, Y. Avian flu: isolation of drug-resistant H5N1 virus. Nature 2005, 437, 1108. (3) (a) Clark, M. P.; Ledeboer, M. W.; Davies, I.; Byrn, R. A.; Jones, S. M.; Perola, E.; Tsai, A.; Jacobs, M.; Nti-Addae, K.; Bandarage, U. K.; Boyd; M. J.; Bethiel, R. S.; Court, J. J.; Deng, H.; Duffy, J. P.; Dorsch, W. A.; Farmer, L. J.; Gao, H.; Gu, W.; Jackson, K.; Jacobs, D. H.; Kennedy, J. M.; Ledford, B.; Liang, J.; Maltais, F.; Murcko; M.; Wang, T.;


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Wannamaker, M. W.; Bennett, H. B.; Leeman, J. R.; McNeil, C.; Taylor, W. P.; Memmott, C.; Jiang, M.; Rijnbrand, R.; Bral, C.; Germann, U.; Nezami, A.; Zhang, Y.; Salituro, F. G.; Bennani, Y. L.; Charifson, P. S J. Med. Chem. 2014, 278, 6668. (b) Byrn, R. A.; Jones, S. M.; Bennett, H. B.; Bral, C.; Clark, M. P.; Jacobs, M. D.; Kwong, A. D.; Ledeboer, M. W.; Leeman, J. R.; McNeil, C. F.; Murcko, M. A.; Nezami, A.; Perola, E.; Rijnbrand, R.; Saxena, K.; Tsai, A. W.; Zhou, Y.; Charifson, P. S Antimicrob. Agents Chemother. 2015, 59. (c) Boyd, M. J.; Bandarage, U. K.; Bennett, H.; Byrn, R. R.; Davies, I.; Gu, W.; Jacobs, M.; Ledeboer, M. W.; Ledford, B.; Leeman, J. R.; Perola, E.; Wang, T.; Bennani, Y.; Clark, M. P.; Charifson, P. S. Bioorg. Med. Chem. Lett. 2015, 1990. (4) Garcia-Urdiales, E.; Alfonso, I.; Gotor, V. Chem. Rev. 2005, 105, 313. (5) (a) Boaz, N. W. Tetrahedron: Asymmetry 1999, 813. (b) Yamazaki, K.; Kaneko, Y.; Suwa, K.; Ebara, S.; Nakazawa, K.; Yasumo, K. Bioorganic. Med. Chem. 2005, 2509. (6) Yamaguchi, J.; Hoshi, K.; Takeda, T. Chem. Lett. 1993, 1273. (7) The experimental details of the initial synthesis were published in reference 3a, as well as in patent WO-2010148197. (8) (a) Hulme, A. T.; Johnston, A.; Florence, A. J.; Fernandes, P.; Shankland, K.; Bedford, C. T.; Welch, G. W. A.; Sadiq, G.; Haynes, D. A.; Motherwell, W. D. S.; Tocher, D. A.; Price, S. L. J. Am. Chem. Soc. 2007, 3649. (b) Goodwin, W.; Perkin, W. H. J. Chem.Soc. 1905, 87, 841.


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(9) Yoshida, S.; Obitsu, K.; Hayashi, Y.; Shibazaki, M.; Kimura, T.; Takahashi, T.; Asano, T.; Kubota, H.; Mukuta, T. Org. Process Res. Dev. 2012, 1527.


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Development of a Scalable Synthesis of an Azaindolyl-Pyrimidine

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