Review of Synthetic Routes and Final Forms of Integrase Inhibitors

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Review of Synthetic Routes and Final Forms of Integrase Inhibitors Dolutegravir, Cabotegravir, and Bictegravir David L Hughes Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/acs.oprd.9b00031 • Publication Date (Web): 13 Mar 2019 Downloaded from http://pubs.acs.org on March 14, 2019

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is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

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Organic Process Research & Development

Review of Synthetic Routes and Final Forms of Integrase Inhibitors Dolutegravir, Cabotegravir and Bictegravir David L. Hughes Cidara Therapeutics, Inc., 6310 Nancy Ridge Dr., Suite 101, San Diego, California 92121, United States [email protected]

1 ACS Paragon Plus Environment

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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GRAPHICAL ABSTRACT: H

H O N

O

H

N

O

Patent Literature

OH

F F

CH3

O

NH

O H

O

H3 C

O

O NH

F F

F

bictegravir

F

F

H N

N H

N

OH

N O

OH

O

Manufacturing Routes & Final Forms

dolutegravir

O

N

O

cabotegravir


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ABSTRACT: Bictegravir and dolutegravir are two recently approved integrase inhibitors for the treatment of HIV. A third inhibitor, cabotegravir, is in Phase 3 development. As a continuation of a series of articles on synthetic routes to newly approved drugs, the current article reviews the patent and journal literature regarding synthetic routes and final forms of these drugs.

KEYWORDS: Integrase inhibitors, synthetic routes, bictegravir, dolutegravir, cabotegravir, patents



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Anti-retroviral drugs to treat the human immunodeficiency virus (HIV) have transformed the acquired immunodeficiency syndrome (AIDS) over the past 30 years from a disease resulting in rapid death to a controllable chronic disease. The first drugs that were designed, developed, and commercialized in the 1980’s and 1990’s, targeted inhibition of the reverse transcriptase and protease enzymes of the virus. Resistance to the early drugs stimulated research into additional targets, and a third enzyme, integrase, emerged as an additional effective target. Integrase strand transfer inhibitors (INSTIs) impede HIV-1 replication by blocking the integrase enzyme, thereby thwarting insertion of the viral genome into the DNA of the host cell. These drugs are usually taken in combination with other HIV drugs to control the virus with orthogonal mechanisms of action, thereby maximizing viral suppression while minimizing development of resistance.1 As a continuation of a series of review articles on synthetic approaches and final forms of recently approved drugs,2 this article reviews the patent and journal literature on the design and development of routes to the integrase inhibitors dolutegravir, cabotegravir, and bictegravir. Since an extensive review of synthetic routes to dolutegravir was published in early 2016,3 the current focus will be on additional synthetic work published since 2015.

As outlined in Table 1, four integrase inhibitors have been approved globally since the first approval in 2007. A fifth INSTI, cabotegravir, is a long-acting INSTI currently in Phase 3 clinical trials.


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Table 1. Integrase Inhibitors Structure/generic name

Innovator company

O N N O

OH H N

N

H N

N

O

Fixed Dose Combinations

Merck

Year of first approval 2007

Gilead

2012

Stribild (elvitegravir + cobicistat + emtricitabine + tenofovir disoproxil fumarate)

F

Dutrebis (Lamivudine + raltegravir)

O raltegravir

O

O

F Cl

HO N

O

Genvoya (elvitegravir + cobicistat + emtricitabine + tenofovir alafenamide)

HO elvitegravir

CH3 O

O

N O

ViiV

OH F

2013

F

H N

N H

Juluca (dolutegravir + rilpivarine) Dolutegravir + emtricitabine + tenofovir alafenamide

O dolutegravir

O

H 3C

OH O

N O

TRIUMEG (dolutegravir + abacavir sulfate + lamivudine)

F

ViiV

Phase 3

Cabotegravir and rilpivarine (Phase 3)

Gilead

2018

Biktarvy (bictegravir + emtricitabine + tenofovir alafenamide)

F

H N

N H

O cabotegravir

H

O

OH O

N H

O

F

H N

N H

F

O

F

bictegravir



These integrase inhibitors include two common structural features that enable binding in the integrase active site, namely (1) a substituted benzyl group that binds within a hydrophobic pocket near the active site; and (2) a chelating oxygen atom triad (or dyad in the case of elvitegravir) that coordinates two Mg2+ ions (Figure 1).3,4

Amino acid triad O

O

O HO

H

O

... .

.....

.

O

N

O

F

F

H N

N H

O

Mg++

......

Mg

++

.. . ... ..

H

.

....

O.....

..

...... .... ..

O

......

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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O

F

Hydrophobic Pocket

Figure 1. Proposed binding of bictegravir

1. Dolutegravir and Cabotegravir Dolutegravir (brand name Tivicay) and cabotegravir are two closely related molecules designed and developed by GSK and Shionogi, now a part of ViiV Healthcare. Tivicay was approved in the U.S. in August, 2013 and in the EU in January, 2014. TRIUMEQ is a fixed dose combination that includes dolutegravir, abacavir sulfate, and lamivudine. Cabotegravir is a drug candidate being developed by ViiV Healthcare as a fixed-dose combination with rilpivirine as a oncemonthly or bi-monthly regimen. Top line Phase 3 data released in August, 2018 showed that coformulated cabotegravir/rilpivirine dosed once-monthly was non-inferior to standard of care, oral 3-drug therapy.


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As shown in Table 1, cabotegravir and dolutegravir are structurally very similar, with the only difference being the chiral 5-membered (cabotegravir) or the 6-membered cyclic (dolutegravir) hemiaminal. The inclusion of the chiral methyl group in the cyclic hemiaminal of both compounds was driven initially by considerations of synthetic practicality.5 With no chiral methyl group, the reaction of intermediate 1 with 1-aminopropanol (2) created the fused hemiaminal ring system 4 with a 1:1 mixture of enantiomers at the fused position (Scheme 1). The Medicinal Chemistry team concluded that separation of the two enantiomers, or a chiral synthesis of a single enantiomer, would not be practical for the long term.5 Therefore, a chiral center was introduced in three different positions in the 6-membered hemiaminal ring to study both the impact on drug attributes, such as potency and pharmacokinetics, as well as the ability to control the selectivity of the ring closure. Use of (3R)-aminobutan-1-ol (5) for the ring closure resulted in a 20:1 selectivity of at the fused position (compound 6), which was attributed to steric control in the transition state for the ring closure. Reaction with 4-amino-(2R)-methylbutanol (7) afforded a 9:1 selectivity of product 9, however, with the opposite stereochemistry relative to that of hemiaminal 6. With less steric hindrance in this case, the authors attributed the control of the ring closure of 9 to a transition state with both the methyl and methylene hemiaminal substituents in equatorial orientations. For the 5-membered ring system (cabotegravir), condensation with (2S)-amino-1-propanol (10) afforded the fused product 11 with 40:1 dr. Larger alkyl groups (Et, i-Pr, t-Bu) were also studied but afforded minimal, if any, synthetic advantage and had poorer potency and/or pharmacokinetic properties than the methyl derivatives. The 6-membered ring structure 6 (dolutegravir penultimate intermediate) and 5membered structure 11 (cabotegravir penultimate intermediate) were advanced into clinical development.



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Scheme 1. Diastereoselective Ring Closures

Ar

Ar O H N

NH O

NH

NH

H

O

O

N N

O

CO2Me

OBn O

OBn 3 HOAc

4

OH

Ar

Ar

O

H N N

O OBn O

H

O CO2Me

OBn 1

10 NH2

20:1 NH

N O

HO

NH2

CHO

O

O

2

Ar NH

NH

O

N N

O OH 5

NH2

O

OBn O 6

11

(Ar = 2,4 Difluoro)

(Ar = 2,4 Difluoro)

OH

7

NH2

Ar

Ar NH O

O

NH H O

N O

NH

CO2Me

O

NH H

N O

CO2Me OBn 8b

OBn 8a

Ar 9:1

NH O

H N

O

N

O OBn O

9 (Ar = 2,4 Difluoro)


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As discussed in the comprehensive article on synthetic routes to dolutegravir from Sandoz scientists, published in early 2016, ten routes to dolutegravir have been published either as journal articles or in the patent literature.3 Since then, several additional patents, patent applications, and journal articles have published and are discussed below. 1.1 Innovator Routes to Dolutegravir and Cabotegravir We start the discussion on routes to dolutegravir and cabotegravir with the joint publication from GlaxoSmithKline and MDR Chemical Science describing the development of a scalable, chromatography-free route to cabotegravir.6a,b Two variations are presented in this paper, with the difluorobenzyl group incorporated either early or late in the synthesis. In both approaches, pyridone 16 is a key intermediate that is prepared in a four-step, one-pot process (Scheme 2) starting from -ketoester 12, wherein the methyl ether serves as a hydroxyl protecting group until the final step of the synthesis. In the Medicinal Chemistry route (Scheme 1), a benzyl ether was used as a protecting group, but a methyl protecting group was selected for the further development. While no rationale was provided for the change in protecting group, it was perhaps driven by concerns with potential Pd-catalyzed defluorination and the need to remove Pd residues during final purification. -Ketoester 12 was treated with neat DMF-DMA to afford vinylogous dimethyl amide 13. After concentration to remove excess DMF-DMA, aminoacetaldehyde dimethyl acetal and MeOH were added to afford vinylogous amide 14. The mixture was concentrated, then dimethyl oxalate and LiOMe in MeOH were added to effect formation of pyridone 15. Selective hydrolysis with LiOH afforded pyridone-acid 16 in overall 61% yield as a white solid. The authors note that LiOH afforded the highest selectivity (10:1) for hydrolysis of the desired ester, with selectivity of only 3:1 for NaOH and KOH, but do not 9 ACS Paragon Plus Environment


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provide any information on purging of the undesired hydrolysis product nor whether the primary by-product is the undesired mono-acid or diacid or both. Scheme 2. One-Pot, Four-Step Route to Pyridone 16

O

O

O

OMe

MeO

OMe

MeO

O

O

DMF-DMA

NMe2

12

LiOMe MeOH

N H 14

OMe OMe

O

O MeO2C CO2Me

OMe OMe

13

OMe

MeO

MeOH H 2N

O

MeO2C N

OMe

LiOH -2 oC

CO2Me OMe

61% over 4 steps

OMe

HO2C

OMe N

CO2Me OMe OMe

16

15

Conversion of pyridone 16 to cabotegravir is outlined in Scheme 3. In the initial approach, aqueous hydrolysis of the acetal resulted in concomitant hydrolysis of the methyl ester and the resulting acid-acetal was unreactive in the subsequent step. Anhydrous conditions were therefore investigated, resulting in the development of a selective hydrolysis using MeSO3H and HOAc in CH3CN to furnish acid-aldehyde 17. Without work up, (S)-alaninol (10) was added to the mixture and warmed to 64 oC for 18.5 hours, resulting in ring closure to produce tricycle 18 with 34:1 dr. Crystallization from MeOH provided 18 in 74% yield with a dr of 41:1. Activation of the carboxylic acid with CDI in DME at 80 oC, followed by treatment with 2,4difluorobenzylamine (19), afforded amide 20 in 95% yield. Demethylation was a challenge due to the sensitive aminal moiety which was cleaved under standard conditions using silica or boron reagents. Guided by the mechanism of action of cabotegravir, where chelation to Mg is key for 10 ACS Paragon Plus Environment

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integrase inhibition, clean demethylation was accomplished with Mg salts, including MgI2, MgBr2, and MgCl2. While not discussed in the body of the publication, the authors note in the supplemental material that demethylation with LiBr was a more scalable procedure, affording cabotegravir in 93% isolated yield.6a Scheme 3. Route to Cabotegravir O

O

O

HO2C

OMe

HO2C

OMe

H 2N

MeSO3H N

CO2Me OMe

N

HOAc CH3CN

O

F

F

O

N

LiBr THF, water 93%

20

H

N O 18

O OH

N H F

F

O

O

N N

N

F

F 95%

34:1 dr H

O OMe

O

N

64 oC

O

N H

OMe

10

O 17

1) CDI, DME 80 oC NH2

HO2C

74%

OMe 16

2)

CO2Me

OH

cabotegravir

H

O

19

In the alternate approach, the benzyl group was incorporated early (Scheme 4). Reaction of acid 16 with CDI followed by 2,4-difluorobenzylamine (19) afforded benzyl amide 21. The acetal was hydrolyzed in neat formic acid to furnish aldehyde 22. Ring closure and demethylation were then carried out as a one-pot process. Use of Mg(OTf)2 afforded selectivity of 300:1 dr in the ring closure. Addition of NaBr, followed by crystallization from the reaction mixture, afforded cabotegravir in an unoptimized yield of 52%.6a



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Scheme 4. Alternate Route to Cabotegravir O HO2C N

O

1) CDI, THF reflux

OMe CO2Me OMe

NH2

2)

O OMe

N H F

F

N

F

OMe 16

60 oC, 3 h

OMe

21

19

CO2Me OMe

HCO2H

F O

OMe

N H F

N

F

OH 1) H2N Mg(OTf)2 , CH3CN 60 oC

O

CO2Me

22

2) NaBr, 60 oC

O

O OH

N H F

52% O

F

O

N N

cabotegravir

H

O

1.2 Alternate Routes to Dolutegravir and Cabotegravir The Medicines Patent Pool (MPP) is an organization focused on increasing access to life-saving medicines in low- and middle-income countries.7 The MPP negotiates with innovator companies to obtain patent licenses that allow generic drug companies to manufacture and distribute such medicines in developing countries prior to patent expiries. MPP has currently licensed 17 drugs, including 13 for HIV-AIDS. In 2014 the MPP negotiated a patent license for dolutegravir from ViiV Healthcare, opening the door for generic manufacture of this drug for distribution in 121 countries and allowing for development of fixed-dose combinations that include dolutegravir.8 As a part of the MPP program, a once-daily, fixed-dose combination of dolutegravir, emtricitabine, and tenofovir alafenamide, developed by Mylan NV, was tentatively approved by the FDA in Feb 2018 under the US President's Emergency Plan for AIDS Relief 12 ACS Paragon Plus Environment

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(PEPFAR).9 Mylan manufactures the product under licenses from the MPP (dolutegravir) and Gilead Sciences (tenofovir alafenamide). Based on the authorization to manufacture and distribute dolutegravir in the developing world, several generic companies have engaged in the development of new routes, discovery of novel crystalline polymorphs, and the manufacture of dolutegravir. This is evident from the number of patent applications for alternate routes and crystal forms of dolutegravir and cabotegravir that have been filed by generic companies, including Hetero, Laurus, Sun, Aurobindo, Mylan, Cipla, Micro, Lek, Assia, Teva, Ratiopharm, Sandoz, Hangzhou Pushai and Zentiva. Routes from Mylan, Laurus, and Hetero have been discussed in the Sandoz review3 and will not be covered here. The more recent routes from Mylan, Micro, Lek, and a flow route from MIT/Virginia Commonwealth are discussed below.

1.2.1 Micro Labs The route developed by Micro Labs (Scheme 5)10 is an adaptation of routes published by the Shionogi/GSK. The route starts with pyran 23 incorporating the benzyl-protected hydroxyl group, which was prepared in three steps and 62% yield from methyl 4-chloro-3-oxobutanoate, as described in a Shionogi patent.11 Scheme 5. Micro Labs Route to Dolutegravir



MeO2C

i-Pr2NEt MeO2C MeOH, 25 oC

OBn O

HOAc Toluene 90 oC

O

O

CO2Me

N

OMe

23

OBn

OMe

H 2N

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CO2Me OMe

O

OBn

N H F

NH2

24 OMe

O

F

CO2Me OMe

N

F

25

OMe

19 F 85% (two steps) O

1) MeSO3H, HOAc CH3CN, 65 oC 2) OH NH2 65 oC 78%

O

N H F

F

OBn

1) CF3CO2H CH2Cl2, 35 oC

O

2) toluene, 80 oC

N

dr 100-125:1 6

N H

O

3) NaOH, H2O MeOH, 65 oC 85%

O

O ONa

N H F

F

O

N N

Dolutegravir Sodium

H

O

Reaction of 23 with aminoacetaldehyde dimethyl acetal in MeOH under basic conditions afforded pyridone 24 in 85% yield. Impurities formed in this step included the hydrolysis product, carboxylic acid 26, and amide 27, although the levels of each were not provided. The reaction was worked up and the extract evaporated to dryness to provide the crude product that was used directly in the next step. In the innovator route, the diester 15 was selectively hydrolyzed to acid 16 with a reported selectivity of 10:1 (Scheme 2).6a To avoid the selective hydrolysis, Micro Labs carried out the amidation on diester 24.12 The best conditions were catalytic HOAc in toluene at 90 oC, providing amide 25 in 85% yield over the two steps after crystallization from 2-PrOH. The selectivity for reaction at the desired ester was not provided. The only by-product noted was 28 due to amine exchange in the pyridone ring.


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O OBn N

MeO

N 27

F

OBn N

OMe O

O

N H

CO2Me OMe

OMe

OMe O

OBn

HN

CO2Me OMe

26

F

O

O

HO2C

O OBn

N H

CO2Me

F

F

O

N N

28

F

29a: R = H 29b: R = TBS

F

RO

Figure 2. Impurities Formed in Micro Labs Route to Dolutegravir

Deprotection of the acetal using MeSO3H and HOAc in acetonitrile followed by addition of (3R)-aminobutan-1-ol for ring closure closely followed conditions previously disclosed (Scheme 3). The undesired diastereomer was present at the 0.8-1.0% level and could be efficiently removed in downstream processing. Impurity 29a, formed by opening of the aminal ring, proved difficult to remove via crystallization. Ultimately, the approach taken for its removal involved treatment of the reaction mixture with TBS-Cl to convert the primary alcohol to its TBS-ether 29b, which then could be removed via crystallization from MeOH, furnishing 6 with a 2-step yield of 78%. The deprotection of the benzyl group was accomplished using TFA in dichloromethane at 35 oC. Crystallization from toluene afforded dolutegravir in 90% yield. Treatment with NaOH in aq. MeOH generated the sodium salt that crystallized from the reaction mixture and was isolated in 95% yield.10



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Overall, the features that make this route attractive include the avoidance of the poorly selective hydrolysis, the understanding and control of impurities, and good yields across each step. 1.2.2 Flow Chemistry Route to Dolutegravir The above routes have been adapted to an efficient flow chemistry route to dolutegravir by Jamison, Roper, and co-workers.13 As outlined in Scheme 6, the first three steps were telescoped into a continuous process using four flow reactors in sequence, with isolation of pyridone 15 in 56% yield after flash chromatography. The first two steps were run neat while the final step was carried out in MeOH. Alternatively, when the three steps were split into two independent flow processes, higher yields were achievable. Combining the first two steps resulted in a chromatographed yield of 95% for enamine 14. Use of pure 14 in the next flow step then provided 15 in 91% yield after work up and concentration to dryness. No details were provided on by-product formation that resulted in the lower yield for the 3-step telescoped process.


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Scheme 6. Flow Chemistry for Preparation of Pyridone 15

O MeO

O

OMe

12 O

85 oC 10 min

OMe

H 2N

OMe

1

O

O OMe

MeO

70 oC 6.7 min

13

OMe

MeO

2

NMe2

O

N H 14

OMe OMe

OMe MeO

NMe2

25 oC 1.6 min 3

MeO2C CO2Me MeOH

85 oC 55 min 4

NaOMe MeOH

O MeO2C

OMe N

CO2Me OMe OMe

15 56% yield

The next three steps to the penultimate intermediate 23 were also telescoped into a flow chemistry process (Scheme 7). Instead of selective hydrolysis of the diester, direct amidation of diester 15 with 2,4-fluorobenzylamine 19 was carried out using a solvent system (HOAc, toluene) similar to that reported by Micro Labs10 and Shionogi12 (Scheme 5), with clean conversion to the mono-amide 21 at 200 oC and 124 min residence time. Deprotection of the acetal was carried out by adding p-TsOH-H2O in CH3CN to the outflow from reactor 1 (100 oC, 35 min residence time) followed by addition of (R)‐3‐aminobutan‐1‐ol in CH3CN (100 oC, 31 min residence time) to afford the penultimate intermediate 23 with a dr of 7:1. After chromatography to remove the undesired diastereomer, product 23 was isolated in 48% yield for the 3-step sequence. 17 ACS Paragon Plus Environment


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Scheme 7. Three-Step Flow Process to Penultimate Dolutegravir Intermediate

O MeO2C

OMe N 15

CO2Me OMe

p-TsOH H2O CH3CN

OMe AcOH

200 oC 124 min

O

O OMe

N H

1 Toluene

F

2

F

CO2Me OMe

N 21

NH2

100 oC 35 min

OMe

F 19 F OH O

F

O

CH3CN

O OMe

N H F

NH2

3 CO2Me

N 22 O

O OMe

N H F

100 oC 31 min

F

O

N N

23 7:1 H O 48% yield

Finally, the deprotection was carried out in flow using LiBr in THF at 100 oC with a residence time of 31 min to afford dolutegravir in 89% yield after purification (Scheme 8). Overall, dolutegravir was synthesized in three telescoped flow sequences with an overall yield 24 %. The authors noted they are developing a process with an end-to-end flow sequence in which all chromatographies are eliminated. 18 ACS Paragon Plus Environment

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Scheme 8. Flow Chemistry for Final Deprotection of Dolutegravir

O

LiBr THF

O

N H F

F

F

N H

O OH

N H

O

N 23

O

OMe

100 oC 31 min

O

F

O

N N

Dolutegravir

H

O

1.2.3 Mylan Routes to Dolutegravir Mylan patent application 2018/0244693 describes two routes that are variations on published routes.14 In the first route (Scheme 9), an allyl group is introduced early and used as a precursor to the aldehyde required for cyclization. As noted above in the GSK route (Scheme 2), LiOH affords 10:1 selectivity for the basic hydrolysis of diester 15. The lack of selectivity for basic hydrolysis of the diester 31 was addressed by Mylan by use of boric acid and acetic anhydride to generate boronate ester 32, which was then hydrolyzed to the carboxylic acid 33 with HCl/MeOH. Subsequently, amide 34 was prepared via its mixed anhydride and coupled with 2,4-difluorobenzylamine (19), then oxidation of the double bond to aldehyde 22 was carried out by several different protocols on scales ranging from 5-100 g, including (1) osmium tetroxide with sodium metaperiodate (64% yield), ruthenium chloride with potassium peroxymonosulfate (17% yield), ozone (72%), and ozonized oxygen (no yield). Compounds 31-33 are claimed in the patent.



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Scheme 9. Mylan Route to Dolutegravir Via An Allyl Precursor

O

O

O

1) DMF-DMA

OMe

MeO

OMe

MeO

O

2) H N 2

12

O MeO2C

OMe N

CO2Me

O

1) B(OH)3 Ac2O

B

O

HCl MeOH

OMe

O

90 oC

N

CO2Me 32

O

N

30

OAc

31

HO2C

NaOMe, MeOH

N H AcO

MeO2C CO2Me

OMe

1) i-BuOCOCl N-MeMorpholine CH2Cl2

CO2Me

2)

O

F

F

33

OMe

N H

F

NH2

O

N

CO2Me

34

19 F O

O OMe

N H

Oxidation F

F

CO2Me

N 22 O

In a second variation (Scheme 10),14 pyridone 16 was converted to the primary amide 35 using ammonium chloride, mediated by EDC and HOBt. Hydrolysis of the acetal and ring closure furnished amide 37. Reductive amidation was then carried out on the primary amide using


Page 21 of 48 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


triethylsilane and TFA, affording intermediate 23 in only 15% yield. Clearly this step would need significant optimization for this to be a viable route. Scheme 10. Route to Dolutegravir Via Late Stage Reductive Amidation O

O

HO2C

OMe N

CO2Me OMe OMe

EDC, HOBt NH4Cl

H2NOC

OMe MeSO3H N

i-Pr2NEt THF 74%

O

O H2NOC

OH N

CO2Me

NH2

O

N

o

70 C

N 37 H O

O

O

Et3SiH, TFA toluene CHO

OMe

H2NOC

OMe

F

HOAc CH3CN

OMe 35

16

36

CO2Me OMe

O OMe

N H F

F 23

F

O

N N H

O

15%

Both routes offer freedom to operate for Mylan once the compound patent on dolutegravir expires, but the oxidation of the allyl group to the aldehyde would require significant development to be viable on a commercial scale.

1.2.4 Lek Approach to Dolutegravir



Page 22 of 48

The approach disclosed by Lek starts with methyl acetoacetate (38) and differs from the other routes in that the –OMe group is absent in this starting material and is introduced late in the synthesis (Scheme 11).15 The tricyclic core was constructed in a fashion similar to the originator route via the 2-step sequence to prepare enamine 39 followed by ring closure with dimethyl oxalate. Rather than carrying out a selective hydrolysis of the diester, both esters were hydrolyzed with NaOH to produce intermediate 40. Hydrolysis of the acetal to the free aldehyde was accomplished with HOAc and MeSO3H in MeOH. The cyclocondensation of the diacid was successful with (R)-3-aminobutan-1-ol to afford the tricyclic intermediate 41 in 73% yield for the two steps. No information is provided for the diastereoselectivity for the ring closure. Similarly, cyclocondensation with (S)-2-aminopropanol (10) afforded the cabotegravir precursor in 75% yield (not shown).


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Scheme 11. Lek Approach to Dolutegravir Via Late Stage Hydroxyl Group Introduction O O

O

1) DMF-DMA

MeO

2) 38

1) HOAc MeSO3H CH3CN

HO2C N

CO2H OMe

OH

H

NH2

F 100% O

Cl

O

N

N

F

Cl O

N

F 43

N H

O

O ONa

N H

NaOH

Cl

F

N O Cl 61%

O

O

N H

O

O

F

NH2

O 41

O N

H

2)

F 19

DABCO CH3CN

N 42

O

N

O

N H

EtOH

HO2C

73%

F

1) EtOC(O)Cl Et3N CH2Cl2

O

N

40

O

2) NaOH

OMe

2) Et3N

OMe

F

OMe

N H 39

OMe

O

1) MeO2C CO2Me NaOMe

MeO

OMe

H 2N

O

O

N N

Dolutegravir H O Sodium

The cyclocondensation reaction with the free acid 41 presumably takes place via intermediate 44 in which the carboxylic acid is activated as a mixed anhydride with the aldehyde. The authors offer a mechanism similar to that proposed when the ester is present, with initial formation of the 23 ACS Paragon Plus Environment


Page 24 of 48

6-membered aminal ring to generate carboxylic acid 45 (Scheme 12). However, this route appears to be a dead end since amide formation with the unactivated acid 45 seems unlikely. An alternate pathway is formation of the amide bond first to generate aldehyde 46, then ring closure of the aminal cyclic system (Scheme 13). Scheme 12. Lek Proposed Formation of Tricycle 45 O

O

O

HO2C

HO2C

HO2C O

N

O

N

O

O

H 2N

OH

O

N N

OH H

NH

HO

44

?

45

O

46

Scheme 13. Alternate Pathway for Formation of Tricycle 46 O

O HO2C

HO2C O

N

O

N

O

HN

H 2N

OH

O

HO

47

44

OH

O

O HO2C

HO2C O

N

O

N N

N H

OH OH

H

O

46


Page 25 of 48 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


Interestingly, when the –OMe group is present, the cyclocondensation performs poorly with the diacid substrate, resulting in 99% ee

+ NH2

36) (a) Griffiths, G.; Previdoli, F. Process for the Production of 2-Azabicyclo[2.2.1]hept5-en-3-one, U.S. Patent 5,200,527, Apr 6, 1993. (b) Griffiths, G. G.; Previdoli, F. E., Diels-Alder Reaction of Methanesulfonyl Cyanide with Cyclopentadiene. Industrial Synthesis of 2-Azabicyclo[2.2.1]hept-5-en-3-one, J. Org. Chem., 1993, 58, 6129– 6131. (c) Rouhi, A. M., Simplifying Syntheses Is Always a Key Goal, Chem. Eng. News, July 14, 2003, Vol. 81, Number 28, p. 40. http://pubs.acs.org/cen/coverstory/8128/8128finechemicals1a.html (accessed Mar 4, 2019) 37) Gao, S.; Zhu, S.; Huang, R.; Li, H.; Wang, H.; Zheng, G., Engineering the Enantioselectivity and Thermostability of a (+ )--Lactamase from Microbacterium hydrocarbonoxydans for Kinetic Resolution of Vince Lactam (2Azabicyclo[2.2.1]hept-5-en-3-one), Appl. Environ. Microbiology, 2018, 84, e0178017. https://aem.asm.org/content/aem/84/1/e01780-17.full.pdf (accessed Mar 4, 2019).



Page 46 of 48

38) Review of Vince lactam preparation and uses: Singh, R.; Vince, R. 2Azabicyclo[2.2.1]hept-5-en-3-one: Chemical Profile of a Versatile Synthetic Building Block and its Impact on the Development of Therapeutics, Chem. Rev. 2012, 112, 4642–4686 39) Two synthetic routes to cis-3-acetoxy-5-hydroxycyclopent-1-ene (67) are outlined below. Route 1

MeCO3H

O

Pd(PPh3)4 HOAc THF 72-76% ref 41

ref 40

OAc

OH

OAc racemic OH

enzymatic

Ac2O imidazole ref 42

OAc

desymmetrization ref 42

OAc

Route 2 (Ref 43) OH AcCl

hv, O2 thiourea MeOH rose bengal

Et3N OH OH

OAc enzymatic desymmetrization OAc

OAc


Page 47 of 48 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


40) (a) Korach, M.; Nielson, D. R.; Rideout, W. H. Org. Synth., Coll. Vol. V, 1973, 414418. (b) Knapp, S.; Sabastian, M. J.; Ramanathan, H. J. Org. Chem. 1983, 24, 4786. 41) Deardorff, D. R.; Myles, D. C., Palladium(0)-Catalyzed syn-1,4-Addition of Carboxylic Acids to Cyclopentadiene Monoepoxide: cis-Acetoxy-5hydroxycyclopent-1-ene, Org. Synth., Coll. Vol 8, 1993, 13. 42) (a) Deardorff, D. R.; Windham, C. Q.; Craney, C. L., Enantioselective Hydrolysis of cis-3,5-Diacetoxycyclopentene: (1R,4S)-(+)-4-Hydroxy-2-cyclopentenyl Acetate, Org. Synth., Coll. Vol. 9, 1998, 487. (b) Tietze, L.; Stadler, C.; Böhnke, N. ; Brasche, G.; Grube, A., Synthesis of Enantiomerically Pure Cyclopentene Building Blocks, Synlett 2007, 485–487. 43) Shekhar, P.; Reddy, A. M.; Sheelu, G.; Reddy, B. V. S., Kumaraguru, T. Preparation of (1R,4S)-4-hydroxycyclopent-2-en-1-yl Acetate via Novozym-435 Catalyzed Desymmetrization of cis-3,5-Diacetoxy-1-cyclpentene, Tetrahedron 2018, 74, 66736679. 44) https://www.accessdata.fda.gov/drugsatfda_docs/nda/2018/210251Orig1s000ChemR. pdf (accessed Mar 4, 2019)

45) BIKTARVY European Public Assessment Report (EPAR): https://www.ema.europa.eu/documents/assessment-report/biktarvy-epar-publicassessment-report_en.pdf (accessed Mar 4, 2019)

46) (a) Carra, E. A.; Chen, I.; Zia, V. Sodium (2R, 5S, 13AR)-7,9-dioxo-10-((2,4,6trifluorobenzyl)carbamoyl)-2,3,4,5,7,9,13,13A-octahydro-2,547 ACS Paragon Plus Environment


Page 48 of 48

methanopyrido[1’,2’:4,5]pyrazino[2,1-B][1,3]oxazepine-8-Olate, U.S. Patent 9,708,342 B2, Jul 18, 2017. (b) Ibid, U.S. Patent Appl. 2018/0065986 A1, Mar 8, 2018. (c) Carra, E. A.; Chen, I.; Keaton, K. A.; Lazerwith, S. E.; Zia, V. Crystalline Forms of (2R, 5S, 13AR)-8-Hydroxy-7,9-dioxo-N-(2,4,6-trifluorobenzyl)2,3,4,5,7,9,13,13A-octahydro-2,5-methanopyrido[1’,2’:4,5]pyrazino[2,1B][1,3]oxazepine-10-carboxamide, U.S. Patent 10,098,886 B2, Oct 16, 2018.


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