Manufacture of the PI3K Î²-Sparing Inhibitor Taselisib. Part 2

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Manufacture of the PI3K #-Sparing Inhibitor Taselisib. Part 2: Development of a Highly Efficient and Regioselective Late-Stage Process Frédéric St-Jean, Travis Remarchuk, Remy Angelaud, Diane E. Carrera, Danial Beaudry, Sushant Malhotra, Andrew McClory, Archana Kumar, Gerd Ohlenbusch, Andreas Schuster, and Francis Gosselin Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/acs.oprd.9b00050 • Publication Date (Web): 06 Mar 2019 Downloaded from http://pubs.acs.org on March 7, 2019

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Organic Process Research & Development

Manufacture of the PI3K -Sparing Inhibitor Taselisib. Part 2: Development of a Highly Efficient and Regioselective Late-Stage Process Frédéric St-Jean,*,† Travis Remarchuk,† Rémy Angelaud,*,† Diane E. Carrera,† Danial Beaudry,† Sushant Malhotra,† Andrew McClory,† Archana Kumar,† Gerd Ohlenbusch,+ Andreas M. Schuster,+ and Francis Gosselin† †

Department of Small Molecule Process Chemistry, Genentech Inc., 1 DNA Way, South San Francisco, CA 94080, USA +

Small Molecules Technical Development PTDC-C, F. Hoffmann-La Roche Ltd., Grenzacherstrasse 124, 4070 Basel, Switzerland

ACS Paragon Plus Environment

1

Organic Process Research & Development 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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TOC


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ABSTRACT A highly efficient and regioselective manufacturing route for the PI3K -sparing inhibitor taselisib was developed. Highlights of the synthesis include: 1) magnesium-mediated formation of

a

challenging

cyclic

amidine;

2)

regioselective

imidazole

construction

via

alkylation/condensation with bromopyruvic acid; and 3) triazole formation with N’-isopropyl acetamidrazone (IPAA) to generate the key bromobenzoxazepine core intermediate. Subsequent highly

efficient

one-pot

palladium-catalyzed

Miyaura

borylation/Suzuki

cross-

coupling/saponification, followed by a CDI-mediated coupling with ammonia, led to the pentacyclic taselisib. This new synthetic approach provides a more efficient route to taselisib with a significant decrease in PMI compared to the previous early-development routes to the benzoxazepine core. Finally, implementation of a controlled crystallization provided the active pharmaceutical ingredient (API) with the desired polymorphic form.

Keywords:

Suzuki-Miyaura cross-coupling, Miyaura borylation, benzoxazepine, late-stage

development, 1,2,4-triazole, amidine.


3


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INTRODUCTION Taselisib (GDC-0032)1 is an orally bioavailable, potent and selective small molecule inhibitor of class I phosphoinositide 3-kinase (PI3K). It is active against all isoforms of the kinase (α, β, δ, and γ), but exhibits 30 fold less potent inhibition against the β form; which is postulated to play a role in insulin signaling and glucose homeostasis.2 Recently, it has been demonstrated that taselisib has increased activity against PIK3CA-mutant breast cancer.3 As part of a phase I to phase III accelerated drug development program, multi-kilogram amounts of taselisib active pharmaceutical ingredient (API) were required to support human clinical studies. The late-stage synthetic strategy involved a key carbon-carbon bond formation between bromobenzoxazepine 1 and the boronic ester derived from bromopyrazole 2 (Figure 1). Much of the development effort was spent on preparing the highly functionalized tetracyclic compound 1, for which three different manufacturing approaches were explored. The Negishi route 1 had many critical synthetic drawbacks, which led to the development of chloroketone [3+2] route 2 (Figure 1), as discussed in our preceding Part 1 paper.4 This second route was viable for early-development API manufacturing, but still suffered from some synthetic issues that needed to be addressed, including: formation of a regioisomer at the imidazole nitrogen alkylation step; formation of a difficult-to-purge N-vinyl impurity during the construction of the benzoxazepine ring; and use of an unstable -chloroketone intermediate under

cryogenic

conditions

for

the

imidazole

ring

synthesis.


4

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Figure 1. Early vs. late-stage development retrosynthetic approaches to taselisib

These limiting aspects were mitigated in the development of the cyclic amidine route 3 (Figure 2), which starts from the same commodity material (4-bromo-2-fluorobenzonitrile) as route 2. The key difference is that the benzoxazepine ring is now formed first, to access intermediate 3, which then undergoes alkylation/condensation with bromopyruvic acid to provide the imidazole ring of intermediate 4. This can then undergo an amide coupling/condensation with isopropyl acetamidrazone (IPAA) 5 to access the desired benzoxazepine 1, the key intermediate en route to taselisib. In this approach, all heterocycle formations are now highly regioselective and no regioisomers have been detected, which considerably increased the overall purification efficiency and yield (vide infra). As a result, route 3 greatly improved environmental metrics, such as process mass intensity (PMI)5, compared to early development routes 1 and 2. Herein,


5


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the development of this sustainable manufacturing process for taselisib is discussed.

Figure 2. Revised retrosynthetic analysis of 1 (Route 3)

RESULTS AND DISCUSSION Development towards the manufacture of 1 To demonstrate the strategy illustrated in Figure 2, SNAr displacement of the aryl fluoride on 4-bromo-2-fluorobenzonitrile was first established with N-Boc-protected ethanolamine, using t-BuOK (1.2 equiv) at 0 °C and gave rise to the desired product 6 in 68% yield (Scheme 1). Subsequent deprotection with HCl in EtOH provided the corresponding amine hydrochloride salt 7•HCl. Furthermore, under the same conditions, the reaction was successfully run with unprotected ethanolamine to afford 7 directly in 91% yield. It is worth noting that under these conditions, the undesired N-addition product was not observed. Scheme 1. SNAr reaction to access 7•HCl

After successful proof-of-concept for this first SNAr step had been demonstrated, there were several issues that needed to be addressed prior to scaling up this transformation. The reaction was found to be very exothermic and required long addition times of t-BuOK (up to 30 minutes


6

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for a 5 g scale reaction). This exotherm resulted from deprotonation of the ethanolamine and could be successfully controlled by preforming the aminoalkoxide. and adding that mixture to a solution of 4-bromo-2-fluorobenzonitrile. Thus, for scale-up THF was replaced with the greener alternative 2-MeTHF, and a solution of 4-bromo-2-fluorobenzonitrile in 2.5 volumes (V) of 2MeTHF was instead added to a solution of the preformed aminoalkoxide in 7.6 V of 2-MeTHF at 0 °C. Using this order of addition, the exotherm was completely dose-controlled. Subsequent work on the amidine cyclization step showed that the HCl salt of 7 was much more reactive than the free base form (see Table 1), thus an efficient process for generating and isolating 7•HCl was implemented. It was found that the salt could be formed by adding 101 mol% of HCl directly to the reaction mixture after warming the solution to room temperature. Both aqueous and organic solutions of HCl (IPA, EtOH, dioxane) led to the formation of 7•HCl which can be isolated by filtration. However, analysis of the material formed by direct addition of HCl without aqueous work-up revealed that it had lower than expected assay with a residue on ignition (ROI) of up to 15.5%.6 Furthermore, it was also observed that the glassware was being etched by the formation of HF during acidification to form the HCl salt. For these reasons, aqueous washes with water and 13wt% NaCl solution prior to acidification were implemented to remove the residual KF salt. Finally, acidification was performed with HCl in 1-propanol instead of ethanol to avoid the formation of the potential mutagenic impurity EtCl.7 Next, we turned our attention to the development of the key intramolecular cyclization to form the benzoxazepine ring system. We attempted to initiate this cyclization from 7•HCl with catalytic protic acids and bases, however no product was observed until we switched to a Lewis acidic system (Table 1). In the presence of 20 mol% Zn(ClO4) in dioxane at 80 °C, 24%


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conversion to 3 was obtained alongside formation of dimer 8 after 24 h (Table 1, entry 1). Prolonged heating resulted in an increase in dimer 8 formation. Interestingly, the use of CuCl (100 mol%) resulted in complete suppression of dimer formation. However, when these conditions were performed on gram scale, the heterogeneous reaction stalled and only 13 A% HPLC of amidine was obtained (Table 1, entry 2). Switching to a solution of 130 mol% of trimethylaluminum8 in toluene resulted in a homogeneous reaction mixture that was reproducible on gram scale, giving 83 A% HPLC of 3 and only 1 A% HPLC of the dimer (Table 1, entry 3). Table 1. Evaluation of Lewis acid mediated cyclization

Time (h)

7•HCl

80

24

34

23

23

CuCl /100

80

24

87

13

0

toluene

AlMe3/180

100

14

3

95

ND

3.0 g

tolueneb

AlMe3/180

100

14

9

83

ND

260 g

toluene

AlMe3/170

100

5

5

86

ND

Lewis Temp Acid/mol% (°C)

Entry

Scale

Solvent

1

0.1 g

dioxane

Zn(ClO4)2/20

2

1.0 g

EtOH

3

2.0 g

4 5

(A%)a

3

8

(A%) a (A%)a

a

Determined by HPLC (254 nm) analysis of the crude reaction mixture. b7 employed as the corresponding free base.


8

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Further investigation of the intramolecular cyclization showed that the reaction stalled when starting from 7 (free base) with ~9 A% of the starting material remaining, even when the stoichiometry of AlMe3 was increased to 180 mol% (Table 1, entry 4). While this cyclization procedure using 170 mol% AlMe3 in toluene at 100 °C was successfully demonstrated on 260 g to provide 3 in 70% yield with >99 A% purity by HPLC after isolation, the hazardous pyrophoric properties of AlMe3 led us to try and find an alternative reagent. After screening a number of Lewis acids, such as ZnCl2, Al(Oi-Pr)3, MgBr2, i-PrMgCl, t-BuMgCl, PhMgBr, ZnOTf, TiCl4 and Mg(OMe)2, only the latter proved to mediate the cyclization in high yield.9 While the initial hit was promising, work-up of this reaction proved laborious as the addition of water resulted in the formation of gels (presumably Mg(OH)2) rendering the extraction of amidine 3 very difficult. This was reflected in the low isolated yield (56%), from a reaction conversion of 88 A% HPLC (Table 2, entry 1). Using MeTHF as a co-solvent solved the gelling issues and amidine 3 could then be isolated in >97% yield (Table 2, entry 2). However, obtaining the desired MeTHF/MeOH composition while using Mg(OMe)2 proved to be operationally difficult as the reagent came as a 1M solution in MeOH and had to undergo a distillation. Thus the Mg(OMe)2 solution was substituted with solid Mg(OEt)2, which afforded similar high conversions to the desired product 3. Upon scale-up, it was found that dissolving Mg(OEt)2 and 7•HCl in MeOH (4V) before adding the 2-MeTHF (8V) was required to obtain near complete conversion (Table 2, entry 2). No dimer 8 was observed using these conditions. Table 2. Optimization of cyclization with Mg(OR)2


9


Scale

Entrya

Mg(OR)2

1

Mg(OMe)2b

2

b

Solvent

(g) (base/reaction) 0.5

Page 10 of 36

7•HCl b

3 b

Yieldc

(A%)

(A%)

6

88

56

2

98

97.5

2

98

97

MeOH (15V) MeOH (5V) MeOH (4V)

Mg(OMe)2

5.0

2-MeTHF (8V) MeOH (4V)

3

a

Mg(OEt)2

50.0

2-MeTHF (15V)

General conditions: 7•HCl (1.8 mmol, 100 mol%) and Mg(OMe)2 (1M in MeOH, 3.6 mmol,

200 mol%) or Mg(OEt)2 (3.6 mmol, 200 mol%) were dissolved in MeOH or MeOH/THF and the mixture was stirred at 70 °C for 24h. bDetermined by HPLC analysis (254 nm) of the crude reaction mixture. cIsolated yield after workup. The optimization of the work up conditions for the Mg-promoted amidine formation focused primarily on fully solubilizing the resulting magnesium salts to prevent emulsions after quench. A reverse quench of the reaction with 10 volumes of a 13% aqueous NH4Cl solution gave a clean phase separation with pH 10, which allowed extraction of up to 40% of the product10 from the aqueous phase. In order to increase the efficiency of the extraction, it was necessary to adjust the


10

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pH to 11 by addition of 2N aqueous NaOH.11 Although this process was successfully demonstrated on 50 g of 7•HCl and provided cyclic amidine free base 3 in 97% yield and 98 A% purity by HPLC (table 2, entry 3), the workup/isolation was lengthy and an alternative procedure was investigated using acidic conditions instead. By simply adding 5N HCl in 1-propanol to the crude reaction mixture, the corresponding amidine hydrochloride salt 3•HCl could be isolated as a solid directly. However, to increase recovery and reduce Mg salt content in the product, MeOH had to be removed first by distillation with continuous 2-MeTHF addition. With this new efficient isolation, 3•HCl could be obtained as a white solid in 89% yield and 99.3 A% HPLC purity (vide infra). Next, the imidazole ring formation to 4 was investigated. Earlier development work had shown that the imidazole ring could be successfully installed on a related acyclic amidine through a tandem alkylation/condensation sequence with bromopyruvic acid (BPA, 130 mol%) and 1,1,3,3-tetramethylguanidine (TMG, 400 mol%) in NMP.12 Complete conversion to the desired imidazole 4 was achieved by applying these same conditions to 3•HCl in NMP (5V) at 50 °C (Scheme 2). Scheme 2. Imidazole 4 formation with bromopyruvic acid from amidine 3•HCl

Slow acidification and addition of water resulted in direct crystallization of the product from the reaction mixture as a single regioisomer.13 However, while the yield using this technique was high (91% yield), the material obtained was a dark purple colored solid. Adding BPA as a


11


Page 12 of 36

solution in 2-MeTHF (2V) and implementing a carbon treatment prior to isolation with aqueous HCl resulted a lighter colored solid. For scale up, the amount of TMG was increased to 475 mol% from 400 mol% to ensure robustness of the reaction. Imidazole 4 was isolated by slow addition of 3N aqueous HCl over 2 h followed by filtration and was obtained in 91% yield with high purity (99.8 A% HPLC) and an acceptable color profile. Next, the synthesis of 1,2,4-triazole 1 was inspired by the reported work from Castanedo and coworkers,14 who used a three-component approach with a carboxylic acid, a primary amidine and a monosubstituted hydrazine via intermediates I and II (Figure 3 (A)). To improve efficiency, an alternative strategy, where intermediate II could be directly intercepted, was implemented with the direct coupling of acid 4 with an acetamidrazone (Figure 3 (B)). This method, which had not previously been reported, used intermediate IPAA 5, which had already been synthesized on kg scale to build the triazole ring in both route 1 and 2 (Figure 1) to taselisib.1

Figure 3. Three vs two-component approaches to 1,2,4-triazoles In the published three-component methodology, HATU was used as coupling reagent. For the two-component approach (Figure 3 (B)) safer and greener 1,1’-carbonyldiimidazole (CDI) was


12

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instead used for optimization. Two separate screens were performed to first assess the acyl imidazole 10 formation with CDI and second, to identify the optimal base to convert 10 with IPAA•HCl (5) to the corresponding imidazole 1 (Scheme 3). Conversion of starting material acid 4 (100 mol%) to acyl imidazole intermediate 10 was monitored using 140 mol% of CDI in 10 volumes of solvent (THF, 2-MeTHF, DMF, DMA, NMP, NEP, t-amyl alcohol and isoamyl alcohol) for 30 min at rt. Polar aprotic solvents were found to give the highest conversions with NMP providing not only the highest conversion (>98 A%), but also the cleanest HPLC profile and was thus selected for further optimization. Scheme 3. One-pot triazole formation to 1

The second screen was performed to identify the optimal base for the amide coupling between activated intermediate 10 and 5 (Table 3). Potassium carbonate (entry 10, Table 3) was found to give the highest conversion by HPLC to the desired triazole 1, which was simply isolated by crystallization after water addition, in >85% yield and >99 A% purity.15

Table 3. Base screen for conversion of acyl imidazole intermediate 10 to triazole 1

Entry a

Base

1

DIPEA

Triazole 1 (A%)b 85


13


a

2

DBU

85

3

TMG

60

4

DMAP

25

5

NMM

85

6

pyridine

70

7

proton sponge

50

8

collidine

75

9

DABCO

90

10

K2CO3

95

Page 14 of 36

General procedure: acid 4 (16 mmol, 100 mol%) was dissolved in NMP (10 vol), then CDI

(22 mmol, 140 mol%) was added and stirred at rt for 30 min. Base (32 mmol, 200 mol%) was then charged, followed by addition of 5 (32 mmol, 200 mol%), and the mixture was heated to 75 C for 16 h. bDetermined by HPLC analysis (254 nm) of the crude reaction mixture after 16 h.

To ensure consistent performance during this new one-pot triazole formation, a robust synthesis of IPAA•HCl (5) was needed.16 It was discovered that, by simply adding isopropyl hydrazine•HCl to CH3CN at 70 C in the presence of 150 mol% of HCl gas, 5 could be directly isolated by filtration of the reaction mixture (Scheme 4) in 65% yield and 100 A% HPLC purity.17,18 It is worth noting that this efficient bond-forming reaction has a very high atom economy.19 Furthermore, because IPAA•HCl was obtained in high quality in this new process, its loading could be lowered down to 140 mol% from 200 mol% in the triazole ring formation step with no impact on the isolated yield of 1 (Scheme 5).


14

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Scheme 4. Synthesis of IPAA•HCl (5)

The

4-step

reaction

sequence

starting

from

commercially

available

4-bromo-2-

fluorobenzonitrile to 1 was successfully demonstrated on pilot plant scale (Scheme 5). This process generated >200 kg of 1 in 56% yield over 4 steps and >99.9 wt% purity.

Scheme 5. Manufacture of 1 on pilot plant scale.

Development towards the endgame manufacturing of taselisib


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The final steps to generate taselisib from 1 consisted of three reactions. First, a one-pot three-step Miyaura borylation/Suzuki/saponification reaction sequence between bromobenzoxazepine 1 and bromopyrazole 2 to access carboxylic acid 13 (Scheme 6). Second, an amidation step to convert 13 to crude API, and finally, a recrystallization to provide taselisib with the required polymorphic form (Scheme 7). Scheme 6. One-pot Miyaura borylation, Suzuki coupling and saponification to acid 13

Various Pd catalysts were screened for the optimization of the Miyaura borylation20 reaction in the one-pot sequence (Table 4). Using conditions similar to those reported in the literature,21 only the Pd(XPhos) system using Buchwald Pd(XPhos) G1 and G2 pre-catalysts22 (entry 8 and 9) led to complete conversion to the desired boronic ester 11. After further optimization, the reaction was run with with 125 mol% of bis(pinacolato)diboron (B2Pin2)23 and 125 mol% of AcOK in 10 volumes of EtOH at 75 C with only 0.3 mol% of pre-catalyst Pd(XPhos) G2 and 0.6 mol% of extra XPhos ligand and afforded 100% conversion of 2 to the corresponding borylated ester 11.

Table 4. Catalyst screen for the Miyaura borylation of 2 to boronic ester 11

Entry a

Catalyst

Bromopyrazole 2 Conversion (A%)b

Borylated Pyrazole 11 (A%)b

1

Pd(t-Bu3P)2

95

45


16

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a

2

Pd(Cy3P)2Cl2

25

15

3

Pd(dtbpf)2Cl2c

85

65

4

Pd(di-(t-butyl)(4-fluoromethylphenyl)phosphine)2Cl2

75

75

5

Pd(dppf)Cl2d

65

35

6

Pd(Amphos)2Cl2e

95

80

7

PdCl2(P(t-Bu)2Ph)2

95

80

8

Buchwald G1 XPhosf

100

100

9

Buchwald G2 XPhosf

100

100

General conditions: Bromopyrazole 2 (3.8 mmol, 100 mol%), 1 mol% catalyst, B2Pin2 (4.8

mmol, 125 mol%), KOAc (4.8 mmol, 125 mol%) in EtOH (20 V), 75 C, 16 h. bDetermined by HPLC analysis (254 nm) of the reaction mixture after 16h. cdppf = 1,1′-Ferrocenediylbis(diphenylphosphine); ddtbpf = 1,1′-Bis(di-tert-butylphosphino)ferrocene; eAmphos = (4-(N,NDimethylamino)phenyl)di-tert-butyl phosphine; fXPhos = 2-Dicyclohexylphosphino-2′,4′,6′triisopropylbiphenyl. The solution containing 11 was then directly subjected to the Suzuki-Miyaura conditions by adding 1 (90 mol %) and aqueous LiOH (1M, 200 mol%). The cross-coupling reaction was then carried at the same temperature, without the need for an additional catalyst charge. Full conversion to ester intermediate 12, and upon addition of more LiOH (3.5M, 300 mol%), complete conversion to acid 13 (>99 A%) was reached after 16 h. Subsequent workup and acidification with aqueous HCl (12N, 500 mol%), provided acid 13 as a solid after filtration in 88% yield and with high purity (>98 A% HPLC). The isolation of acid 13 initially was complicated by foaming of the material upon crystallization by acid addition (most likely due to hydrophobicity of 13). The acid to precipitate the product was changed from HCl to H2SO4 due


17


Page 18 of 36

to corrosivity issues. The foaming issue was solved by addition of 1-propanol to the aqueous solution of 13-lithium salt before reacidification. Another added benefit from using 1-propanol was a greater purging power of the residual Pd present in 13 (99 A%). Crude taselisib was then isolated via concentration and water addition (7V) to afford a white solid in 91% yield and 99.7 A% HPLC purity on 12.5 kg scale. Optimal crystallization conditions to obtain the desired polymorphic Form B were investigated. First, a screen was performed to identify a single solvent or solvent combination that would provide the API in high yield and purity with the desired crystal Form B (Table 5). In this study, a lower purity lot of taselisib (97.2 A% purity) was slurried in the selected solvent mixture, heated until a homogeneous solution was obtained, and was then cooled to rt to allow for the crystallization of solids that were submitted to X-ray powder diffraction analysis (XRPD). Most solvent systems


18

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afforded the API in very high purity (>99.6 A% HPLC) with the desired Form B,24 except for MeOH which provided the wrong methanoate Form A (entry 1 and 2, Table 5) and benzyl alcohol that gave low recovery (entry 5, Table 5). Isoamyl alcohol (entry 3, Table 5) was selected for development since it provided the API with the desired crystal Form B in 96% yield and 99.6 A% HPLC purity. Table 5. Solvent screen for the crystallization of taselisib

a

Purity

Entry a

Solvent (V)

Anti-Solvent (V)

XRPD

Yield

1

MeOH (30)b

iPrOAc (5)

Form A & B

78%

99.6

2

MeOH (26)d

none

Form A

80%

99.9

3

Isoamyl alcohol (15)c

none

Form B

96%

99.6

4

Ethyl lactate (8)c

none

Form B

60%

99.9

5

Benzyl alcohol (6)c

iPrOAc (10)

Form B

36%

97.5

6

NMP (5)b

iPrOAc (10)

Form B

42%

99.9

7

AcOH (5)b

iPrOAc (10)

Form B

25%

99.9

(A%)e

All experiments were performed on 5 g scale with 97.2 A% purity taselisib. bTwo-solvent

crystallizations (entries 5-7) were heated until a homogeneous solution was obtained then, 10V of iPrOAc (5V for entry 1) were added and the solution was then, seeded, cooled to rt and the solids were filtered and dried at 80 C for 16 h. cSingle solvent crystallizations (entries 2-4) used the same procedure as the two-solvent crystallizations, but were not seeded. dDrying a sample of the methanoate solvate (Form A) between 100–120 °C under vacuum for >16 h resulted in a form change to Form B without impact on the purity of taselisib as determined by HPLC. e

Determined by HPLC analysis of the isolated solid.


19


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Further investigation into crystallization parameters was done to ensure a robust procedure could be developed. In those experiments, crude taselisib (5g, 97.2 A% purity) was suspended in isoamyl alcohol (22 V), the mixture was heated to 100 C until a homogeneous solution is obtained, cooled down using different cooling ramps (0.05 C/min, 0.1 C/min and 1.0 C/min), and the solids were filtered and dried. In those experiments, a few important trends were observed: 1) the optimal seeding point to promote secondary nucleation was found to be between 75–90 °C; 2) no large crystals25 were generated using a fast cooling ramp (1.0 ºC/min), but using a slower cooling ramp (0.05 to 0.3 ºC/min), desired crystal growth was promoted and bigger crystals26 were observed; 3) the isoamyl alcohol solvate of taselisib was formed when it was isolated at low temperatures (99.9 A% purity by HPLC.

Scheme 9. PMI comparison between the early-stage (Negishi and [3+2]) and the late-stage (cyclic amidine) manufacture routes to taselisib


21


Page 22 of 36

EXPERIMENTAL SECTION General Information. Unless otherwise noted, all reactions were run under a nitrogen atmosphere, and solvents and reagents were used without further purification. Nuclear magnetic resonance (NMR) measurements were carried out on a Bruker Avance 600 spectrometer at 25C. The 600 MHz machine is equipped with a 5 mm CryoProbe. Data for 1H NMR chemical shifts () are reported in parts per million (ppm) downfield from tetramethylsilane [(CH3)4Si] (TMS; δ  0 ppm). Since TMS is not present in the solution, chemical shifts are experimentally referenced to the center line of the residual proton signal in deuterated NMR solvent. Signals are reported as follows: chemical shift (ppm), multiplicity (s, singlet; bs, broad singlet; d, doublet; t, triplet; q, quartet; h, heptet; dd, doublet of doublet; m, multiplet), integration, coupling constant (Hz). Data for

13

C NMR are reported in terms of chemical shift (ppm) with

13

C signal of the

deuterated solvent as reference. Melting points were measured by differential scanning calorimetry

(Mettler-Toledo

4bromo2fluorobenzonitrile

differential (CAS#105942-08-3),

scanning

calorimeter

isopropylhydrazine

DSC2).

hydrochloride

(CAS#16726-41-3), bromopyruvic acid (CAS#1113-59-3) and compound 2 (CAS#1040377-17-


22

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0) were commercially available and used as is. A% indicates area % purity by HPLC unless otherwise noted throughout the experimental section and supporting information. See supporting information for analytical methods, spectral and chromatographic data. Synthesis of 2-(5-bromo-2-cyanophenoxy)ethan-1-aminium chloride (7•HCl): Ethanolamine (41.6 kg, 681 mol, 1.1 equiv) was dissolved in 2-MeTHF (100 L) followed by addition of tBuOK (84.5 kg, 753 mol, 1.2 equiv) at 5 °C. The mixture was stirred for 40 minutes, and a solution of 4bromo2fluorobenzonitrile (130.0 kg, 650 mol, 1.0 equiv) in 2-MeTHF (320 L) was added. The mixture was stirred for 3 h until an IPC sample showed complete conversion (target 4bromo2fluorobenzonitrile < 0.1 A%). Water (400 L) was added at 25 °C to quench the reaction. The layers were separated and the lower aqueous phase was discarded. A solution of 3N HCl in n-PrOH (272 kg) was added to the organic phase and the suspension was heated to 70 °C and stirred for 3 h at this temperature. The suspension was cooled to 20 °C and the product was isolated by filtration and washed with 2-MeTHF (3 x 65 L). The product was dried at 45 °C under reduced pressure until constant weight was attained. 7•HCl was isolated in 91% yield (164 kg) as a white powder (99.4 wt%, 99.4 A%). mp (DSC): 246.1 °C. HRMS (EI) m/z Calcd for C9H9BrN2O: 239.9898; found: 239.9903. 1H NMR (600 MHz, DMSO-d6) δ ppm 8.29 (br s, 3H), 7.73 (d, J = 8.3 Hz, 1H), 7.60 (d, J = 1.7 Hz, 1H), 7.37 (dd, J = 8.3, 1.7 Hz, 1H), 4.43 (t, J = 5.2 Hz, 2H), 3.25–3.21 (m, 2H);

13

C NMR (151 MHz, DMSO-d6) δ = 159.8, 135.2, 128.6, 124.8,

116.7, 115.7, 100.4, 66.1, 37.8. Synthesis of 8-bromo-2,3-dihydrobenzo[f][1,4]oxazepin-5-aminium chloride (3•HCl): 7•HCl (74.5 kg, 268 mol, 1.0 equiv) was charged into a reactor and suspended in MeOH (300 L). The solution was cooled to 0 °C and Mg(OEt)2 (65.3 kg, 571 mol, 2.1 equiv) was added


23


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within 60-90 minutes while keeping the temperature < 10°C (exothermic reaction: +15 °C temperature rise observed in laboratory!). The thin brownish slurry was stirred for 1 h at 15 °C and 2-MeTHF (600 L) was added. Then, the mixture was heated to 65 °C for about 45 h until inprocess control showed complete consumption of starting material (target 7 < 2.0 A%). The slurry was concentrated to 360 L by distillation under reduced pressure with continuous addition of 2-MeTHF. An in-process control sample from the reaction mixture confirmed the removal of MeOH (target MeOH < 4.0 wt%). 2-MeTHF (525 L) was added, the mixture was cooled to 15 °C and a 5-6 N HCl in n-PrOH (310 kg) was added. The slurry was stirred for 4 h at 15 °C, filtered and the cake washed with 2-MeTHF (670 L). The product was dried at 55 °C under reduced pressure until constant weight is attained. 3•HCl was isolated in 87% yield (64.4 kg) as a white powder (99.4 wt%; 99.4 A%). mp (DSC): 255.7 °C. HRMS (EI) m/z Calcd for C9H9BrN2O: 239.9898; found: 239.9905. 1H NMR (600 MHz, DMSO-d6)  ppm 10.36 (br s, 1H), 9.50 (br s, 1H), 9.43 (br s, 1H), 7.67–7.58 (m, 2H), 7.51 (d, J = 1.0 Hz, 1H), 4.46 (t, J = 5.3 Hz, 2H), 3.52 (q, J = 5.2 Hz, 2H).

13

C NMR (151 MHz, DMSO-d6) δ = 165.3, 156.4, 132.4,

128.9, 128.0, 126.5, 120.8, 77.5, 41.1. Synthesis of 9-bromo-5,6-dihydrobenzo[f]imidazo[1,2-d][1,4]oxazepine-2-carboxylic acid (4): 3•HCl (61.9 kg, 223 mol, 1.0 equiv) was added to NMP (315 L), the mixture was heated to 50 C, and N,N,N',N'-tetramethylguanidine (122 kg, 1059 mol, 4.8 equiv) was added. Bromopyruvic acid (48.4 k g, 290 mol, 1.3 equiv) was then added as a solution in 2-MeTHF (74 L). The reaction mixture was stirred until conversion was confirmed (target < 5 A% intermediate (a) 13 ). The reaction slurry was transferred into a second vessel containing preheated water (945 L) at 50 C. The first vessel was rinsed with NMP (315 L) and transferred to the second vessel. The combined solution was filtered through a charcoal pad (Norit A Supra, 6 kg) at 50 C to


24

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remove colored impurities. The second vessel and charcoal pad were rinsed with NMP (130 L) and combined with the main solution. Then, 3 N HCl (170 kg) was added at 50 C within 2 h (target pH ~2.5) to initiate product crystallization, and the mixture was cooled to 10 °C. Crude 4 was isolated by filtration and washed with water (750 L). The cake was dried at 85 C under reduced pressure to provide crude 4 in about 94% yield (65.4 kg) as a light pink powder (96.8 wt%; 97.3 A%). Crude 4 (63.5 kg, 205 mol, 1.0 equiv) was slurried in a mixture of NMP (64 L) and toluene (660 L), heated to 110 °C and toluene (65 L) was distilled off to remove water. Then, more toluene (1015 L) was added and the resulting slurry was cooled to 10 C and filtered. The cake was washed with toluene (580 L) and dried at 85 C under reduced pressure to provide 4 in 90% yield (57.2 g) as a light pink white powder (>99.9 wt%, >99.9 A%). mp (DSC): 263.3 °C. HRMS (EI) m/z Calcd for C12H9BrN2O3: 307.9797; found: 307.9805. 1H NMR (600 MHz, DMSO-d6) δ ppm 13.08–11.46 (m, 1H), 8.31 (d, J = 8.7 Hz, 1H), 7.98 (s, 1H), 7.32 (dd, J = 8.7, 2.1 Hz, 1H), 7.27 (d, J = 1.9 Hz, 1H), 4.54–4.44 (m, 4H). 13C NMR (151 MHz, DMSO-d6) δ = 163.5, 155.9, 143.7, 132.6, 131.4, 128.9, 125.3, 123.1, 122.3, 117.2, 68.7, 49.5. Synthesis of (Z)-N'-isopropylacetohydrazonamide hydrochloride (5): Isopropylhydrazine hydrochloride (35.0 kg, 317 mol, 1.0 equiv) was suspended in MeCN (420 L) in an autoclave. Gaseous HCl (17.5 kg, 480 mol, 1.5 equiv) was introduced at 40 °C. The reaction was heated to 70 °C for 36 h. After reaction conversion (monitored as the N-iPr-hydrazone derivative with benzaldehyde < 8.0 A%), the reaction mixture was diluted with MeCN (210 L) and 210 L were distilled off under atmospheric pressure. The operation was repeated once more to remove excess HCl. MeOH (43 L) and MeCN (210 L) were added and the mixture was cooled to 25 °C. The


25


Page 26 of 36

solid by-products were removed by filtration and rinsed with MeCN (35 L). The filtrate was further concentrated by distillation at 65 °C under reduced pressure to a final volume of 380 L (target MeOH < 1.0-1.5 wt% by GC). The suspension was cooled to 20 °C within 1 h and product 5 was isolated by filtration, washed with MeCN (70 L) and then dried at 65 °C under reduced pressure until constant weight was attained. 5 was isolated in 65% yield (29.0 kg) as a white powder (98.7 wt%, >99.9 A%). mp (TGA): 162.8 °C. HRMS (EI) m/z Calcd for C5H13N3: 115.1109; found: 115.1112. 1H NMR (600 MHz, D2O) δ ppm 3.11 (dtd, J = 12.6, 6.3, 6.3, 0.7 Hz, 1H), 2.18 (d, J = 0.8 Hz, 3H), 1.07–0.98 (m, 6H).

13

C NMR (151 MHz, D2O) δ = 165.8,

50.2, 19.3, 19.3, 15.2. Synthesis

of

9-bromo-2-(1-isopropyl-3-methyl-1H-1,2,4-triazol-5-yl)-5,6-

dihydrobenzo[f]imidazo[1,2-d][1,4]oxazepine (1): 4 (21.9 kg, 71 mol, 1.0 equiv) was dissolved in NMP (240 L) and the solution was heated to 40 C. 1,1-Carbonyldiimidazole (CDI, 16.4 kg, 1.4 equiv) was added and the mixture was stirred until activation of the starting material was verified by an HPLC IPC sample (target 4 < 3 A%). Compound 5 (15.3 kg, 108 mol, 1.5 equiv) and K2CO3 (12.5 kg, 90 mol, 1.3 equiv) were added and the reaction mixture was heated to 85 C. The suspension was stirred at this temperature until complete consumption of the activated starting material by an HPLC IPC sample was observed (target 10 < 0.50 A%). Then, the mixture was cooled to 55 C, water (295 L) was added within 4.5 h and the suspension was cooled to 10 C. The slurry was filtered, washed with water (200 L) and dried at 90 C under reduced pressure to give 1 in 83% yield (22.8 kg) as a white powder (99.9 A%) as Form B crystal. mp (DSC): 257  258 C. HRMS (ESI-CID) m/z Calcd for [M+H]+ C24H29N8O2: 461.2408; found: 461.2409.

1

H NMR

(600 MHz, DMSO-d6)  ppm 8.41 (s, 1H), 8.37 (d, J = 8.4, 1H), 8.02 (s, 1H), 7.88 (m, 1H), 7.45 (dd, J = 8.4, 1.7 Hz, 1H), 7.36 (d, J = 1.7 Hz, 1H), 7.20 (br s, 1H), 6.84 (br s, 1 H), 5.83 (sept, J = 6.6 Hz, 1H), 4.53–4.51 (m, 2H), 4.52 (m, 2H), 2.26 (s, 3H), 1.75 (s, 6H), 1.47 (d, J = 6.7 Hz, 6H). 13C NMR (DMSO-d6, 151 MHz) δ = 173.8, 158.3, 155.9, 147.3, 144.0, 136.6, 134.6, 130.3, 129.9, 126.4, 123.6, 120.4, 119.3, 116.2, 115.3, 68.3, 64.5, 49.9, 49.7, 25.5, 25.5, 22.3, 22.3, 13.8.


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ASSOCIATED CONTENT The Supporting Information is available free of charge. 1

H and

13

C characterization of compounds and impurities, HPLC, infrared, mass spectroscopy,

XRPD and UV data can be found in the Supporting Information. AUTHOR INFORMATION Corresponding Authors * E-mail: [email protected] * E-mail: [email protected] ORCID Frédéric St-Jean: 0000-0001-8818-0218 Rémy Angelaud: 0000-0002-3324-6184 Francis Gosselin: 0000-0001-9812-4180 Author Contributions The manuscript was written through contributions of all authors. Notes The authors declare no competing financial interest.


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Page 32 of 36

ACKNOWLEDGMENT The authors thank Dr. Jeff Stults for solid-state characterization, Dr. Christian Lautz and Martin Betschart for the development of the PAT (NIR) method and Dr. Antonio DiPasquale for the XRay crystal structures.

References

1

The discovery synthesis of taselisib has been reported: Ndubaku, C. O.; Heffron, T. P.; Staben,

S. T.; Baumgardner, M.; Blaquiere, N.; Bradley, E.; Bull, R.; Do, S.; Dotson, J.; Dudley, D.; Edgar, K. A.; Friedman, L. S.; Goldsmith, R.; Heald, R. A.; Kolesnikov, A.; Lee, L.; Lewis, C.; Nannini, M.; Nonomiya, J.; Pang, J.; Price, S.; Prior, W. W.; Salphati, L.; Sideris, S.; Wallin, J. J.; Wang, L.; Wei, B.; Sampath, D.; Olivero, A. G. Discovery of 2-{3-[2-(1-Isopropyl-3-methyl1H-1,2–4-triazol-5-yl)-5,6-dihydrobenzo[f]imidazo[1,2-d][1,4]oxazepin-9-yl]-1H-pyrazol-1-yl}2-methylpropanamide (GDC-0032): A β-Sparing Phosphoinositide 3-Kinase Inhibitor with High Unbound Exposure and Robust in Vivo Antitumor Activity. J. Med. Chem. 2013, 56, 4597– 4610. 2

Staben, S. T.; Ndubaku, C.; Blaquiere, N.; Belvin, M.; Bull, R. J.; Dudley, D.; Edgar, K.; Gray,

D.; Heald, R.; Heffron, T. P.; Jones, G. E.; Jones, M.; Kolesnikov, A.; Lee, L.; Lesnick, J.; Lewis, C.; Murray, J.; McLean, N. J.; Nonomiya, J.; Olivero, A. G.; Ord, R., Pang, J.; Price, S.; Prior, W. W.; Rouge, L.; Salphati, L.; Sampath, D.; Wallin, J.; Wang, L.; Wei, B.; Weismann, C.; Wu, P. Discovery of thiazolobenzoxepin PI3-kinase inhibitors that spare the PI3-kinase β isoform. Bioorg. Med. Chem. Lett. 2013, 23, 2606-2613.


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3

Juric, D.; Krop, I.; Ramanathan, R. K.; Wilson, T. R.; Ware, J. A.; Sanabria Bohorquez, S. M.;

Savage, H. M.; Sampath, D.; Salphati, L.; Lin, R. S.; Jin, H.; Parmar, H.; Hsu, J. Y., Von Hoff, D. D.; Baselga, J. Phase I Dose Escalation Study of Taselisib (GDC-0032), an Oral PI3K Inhibitor, in Patients with Advanced Solid Tumors. Cancer Discovery 2017, 7, 704-715. 4

Remarchuk, T.; Angelaud, R.; Askin, D.; Kumar, A.; Thompson, A. S.; Cheng, H.; Reichwein,

J. F.; Chen, Y.; St-Jean, F. Manufacture of the PI3K -Sparing Inhibitor Taselisib. Part 1: EarlyStage Development Routes to the Bromobenzoxazepine Core. Org. Process Res. Dev. 2019, XX, X-X. 5

Jimenez-Gonzalez, C.; Ponder, C. S.; Broxterman, Q. B.; Manley, J. B. Using the Right Green

Yardstick: Why Process Mass Intensity Is Used in the Pharmaceutical Industry To Drive More Sustainable Processes. Org. Process Res. Dev. 2011, 15, 912-917. 6

It was hypothesized that high ROI results are attributed to the presence of potassium salts in the

form of KF and/or KCl 7

Holder, J. W. Analysis of Chloroethane Toxicity and Carcinogenicity Including a Comparison

with Bromoethane. Toxicology and Industrial Health 2008, 24, 655-675. 8

For the use of AlMe3 to facilitate an intramolecular cyclization to form an amidine see:

Garigipati, R.S. An Efficient Conversion of Nitriles to Amidines. Tetrahedron Lett. 1970, 31, 1969-1972.


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Dalziel, M. E.; Deichert, J. A.; Carrera, D. E.; Beaudry, D.; Han, C.; Zhang, H.; Angelaud, R.

Magnesium Ethoxide Promoted Conversion of Nitriles to Amidines and Its Application in 5,6Dihydroimidazobenzoxazepine Synthesis. Org. Lett. 2018, 20, 2624–2627 10

Determined by assay yield using HPLC analysis.

11

If the pH went above 11, precipitation of solid magnesium hydroxide in the aqueous phase was

observed rendering the phase cut difficult. 12

Angelaud, R.; Beaudry, D. R.; Carrera, D. E.; Malhotra, S.; Remarchuk, T.; St-Jean, F. Process

for Making Benzoxazepin Compounds. US Patent 9,303,043, September 18, 2014. 13

Although two alkylation pathways (a) and (b) leading to two different imidazole regioisomers

4 and 9 respectively are possible, regioisomer 9 was not detected (10 and 10-100 m chord length particles were observed by Focus

Beam Reflectance Measurement (FBRM). 26

A high concentration of 10-100 and 100-1000 m chord length particles were observed by

FBRM. 27

Taselisib was classified as health hazard category (HHC) band 3B substance requiring strict

containment measures to ensure low API concentration in air (1 µg to 50 ng/m3).


36

Manufacture of the PI3K Î²-Sparing Inhibitor Taselisib. Part 2

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