Advertisement

Total synthesis of antiviral drug, nirmatrelvir (PF-07321332)

  • Chandra Shekhar
    Affiliations
    Department of Organic Synthesis and Process Chemistry, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500007, India

    Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
    Search for articles by this author
  • Rajesh Nasam
    Affiliations
    Department of Organic Synthesis and Process Chemistry, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500007, India

    Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
    Search for articles by this author
  • Siva Ramakrishna Paipuri
    Affiliations
    Department of Organic Synthesis and Process Chemistry, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500007, India

    Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
    Search for articles by this author
  • Prakash Kumar
    Affiliations
    Department of Organic Synthesis and Process Chemistry, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500007, India

    Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
    Search for articles by this author
  • Kiranmai Nayani
    Affiliations
    Department of Organic Synthesis and Process Chemistry, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500007, India

    Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
    Search for articles by this author
  • Srihari Pabbaraja
    Affiliations
    Department of Organic Synthesis and Process Chemistry, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500007, India

    Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
    Search for articles by this author
  • Prathama S. Mainkar
    Affiliations
    Department of Organic Synthesis and Process Chemistry, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500007, India

    Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
    Search for articles by this author
  • Srivari Chandrasekhar
    Correspondence
    Corresponding author. Department of Organic Synthesis and Process Chemistry, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500007, India.
    Affiliations
    Department of Organic Synthesis and Process Chemistry, CSIR-Indian Institute of Chemical Technology, Hyderabad, 500007, India

    Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
    Search for articles by this author
Open AccessPublished:October 18, 2022DOI:https://doi.org/10.1016/j.tchem.2022.100033

      Abstract

      The emergence and rapid spread of coronavirus disease 2019 (COVID-19), a potentially fatal disease, caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), has swiftly led to public health crisis worldwide. Hence vaccines and antiviral therapeutics are an important part of the healthcare response to combat the ongoing threat by COVID-19. Here, we report an efficient synthesis of nirmatrelvir (PF-07321332), an orally active SARS-CoV-2 main protease inhibitor.

      Graphical abstract

      Keywords

      Abbreviations:

      SARS-CoV (severe acute respiratory syndrome coronavirus), SAR (structure activity relationship), FDA (Food and Drug Administration), MsCl (methanesulfonyl chloride), Boc (tert-butyloxycarbonyl), HATU (1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxide hexafluorophosphate), NMM (N-methylmorpholine), DMAP (4-dimethylaminopyridine), TMSCl (trimethylsilyl chloride), LiHMDS (lithium bis(trimethylsilyl)amide), DMP (Dess–Martin periodinane)

      1. Introduction

      The present pandemic has challenged scientists to quickly identify molecules/scaffolds that have shown antiviral activity and can help in mitigation of the disease caused by SARS-CoV-2. Researchers from academic institutions and industries explored molecules which had earlier progressed in the drug discovery pipeline and verified their activity against COVID-19. In addition to early molecules such as remdesivir, favipiravir, umifenovir, etc. PF-00835231 [
      • de Vries M.
      • Mohamed A.S.
      • Prescott R.A.
      • Valero-Jimenez A.M.
      • Desvignes L.
      • O'Connor R.
      • Steppan C.
      • Devlin J.C.
      • Ivanova E.
      • Herrera A.
      • Schinlever A.
      • Loose P.
      • Ruggles K.
      • Koralov S.B.
      • Anderson A.S.
      • Binder J.
      • Dittmann M.
      A comparative analysis of SARS-CoV-2 antivirals characterizes 3CLpro inhibitor PF-00835231 as a potential new treatment for COVID-19.
      ], which had shown potential activity against SARS-CoV-1 was also considered. To build structure activity relationship (SAR) around PF-00835231, analogues were synthesized by modifying the constituent amino acids and six important analogues were considered for further development. The most promising analogue, PF-07321332 (nirmatrelvir), has been approved by FDA in December 2021 as an antiviral combination pill that can be taken at home to prevent people infected with COVID-19 from becoming severely ill. Nirmatrelvir (1) is a SARS-Cov-2 main protease (Mpro) inhibitor and sold in combination with ritonavir, a CYP3A inhibitor, as Paxlovid™ (brand name) [
      • Lamb Y.N.
      Nirmatrelvir Plus Ritonavir: First Approval.
      ].
      Nirmatrelvir (1) is a tripeptide protein mimetic and was identified by carrying out SAR studies on some of the clinical candidates/approved molecules. Lufotrelvir (2) and dipeptide of boceprevir (3) formed the basis of constitution of nirmatrelvir. The pyrrolidine amino acid fragment of lufotrelvir [
      • Hoffman R.L.
      • Kania R.S.
      • Brothers M.A.
      • Davies J.F.
      • Ferre R.A.
      • Gajiwala K.S.
      • He M.
      • Hogan R.J.
      • Kozminski K.
      • Li L.Y.
      • Lockner J.W.
      • Lou J.
      • Marra M.T.
      • Mitchell Jr., L.J.
      • Murray B.W.
      • Nieman J.A.
      • Noell S.
      • Planken S.P.
      • Rowe T.
      • Ryan K.
      • Smith III, G.J.
      • Solowiej J.E.
      • Steppan C.M.
      • Taggart B.
      Discovery of ketone-based covalent inhibitors of coronavirus 3CL proteases for the potential therapeutic treatment of COVID-19.
      ] and the dipeptide fragment of boceprevir [
      • Howe A.Y.M.
      • Venkatraman S.
      The discovery and development of boceprevir: a novel, first-generation inhibitor of the hepatitis C virus NS3/4A serine protease.
      ] gave rise to the basic skeleton of nirmatrelvir. The phosphate prodrug functionality of 2 was replaced with a –CN group in 1. During the studies carried out for identification of boceprevir, the potency of the molecule increased due to the incorporation of the gem-dimethyl cyclopropyl proline moiety. Using this clue, the same was introduced in analogues for identification of potent molecules for treating SARS-CoV-2. Thus, the bicyclic amino acid in boceprevir 3 and nirmatrelvir 1 has helped in increasing the potency of the molecules (Fig. 1).
      Fig. 1
      Fig. 1Structure of antivirals.

      2. Results and discussion

      Our research group has focused on the synthesis of peptides and peptidomimetics [
      • Donikela S.
      • Nayani K.
      • Mainkar P.S.
      • Chandrasekhar S.
      Gram scale solution-phase synthesis of heptapeptide side chain of teixobactin.
      • Kallepu S.
      • Kavitha M.
      • Yeeravalli R.
      • Manupati K.
      • Jadav S.S.
      • Das A.
      • Mainkar P.S.
      • Chandrasekhar S.
      Total synthesis of desmethyl jahanyne and its lipo-tetrapeptide conjugates derived from parent skeleton as BCL-2-mediated apoptosis-inducing agents.
      • Chandrasekhar S.
      • Kiranmai N.
      • Kiran M.U.
      • Devi A.S.
      • Reddy G.P.K.
      • Idris M.
      • Jagadeesh B.
      Novel helical foldamers: organized heterogeneous backbone folding in 1:1 α/Nucleoside-Derived–β-Amino acid sequences, chem.
      • Jagannadh B.
      • Reddy M.S.
      • Rao C.L.
      • Prabhakar A.
      • Jagadeesh B.
      • Chandrasekhar S.
      Self-assembly of cyclic homo- and hetero-β-peptides with cis-furanoid sugar amino acid and β-hGly as building blocks.
      • Chandrasekhar S.
      • Reddy M.S.
      • Babu B.N.
      • Jagadeesh B.
      • Prabhakar A.
      • Jagannadh B.
      Expanding the conformational pool of cis-β-Sugar amino acid: accommodation of β-hGly motif in robust 14-helix.
      ]. The consideration of nirmatrelvir, for clinical trials, as an oral antiviral drug, enthused us to take up the synthesis of 1. The molecule is comprised of three amino acids (L-tert-leucine, bicyclic proline and cyano lactam residue), all unnatural and thus, developing scalable and stereoselective synthetic strategies to achieve the target molecule are imperative. Based on the literature, it was noticed that the bicyclic gem-dimethyl cyclopropyl proline amino acid is the key fragment, which increased the potency of the analogue. We thus set out to first synthesize bicyclic amino acid (4) and then followed by the synthesis of nirmatrelvir (1). The retrosynthetic strategy is based on the conversion of trans-4-hydroxy proline to alkene via elimination of hydroxy group which would undergo cyclopropanation to yield 4 and further its conversion to dimer acid 5. On the other hand, L-glutamic acid could be converted to alcohol 6 which can be oxidized to aldehyde followed by its conversion to nitrile 7. The coupling of fragments 5 and 7 will lead to nirmatrelvir 1 (Scheme 1).
      Scheme 1
      Scheme 1Retrosynthesis of bicyclic amino acid (4) and nirmatrelvir (1).
      In literature, the synthesis of bicyclic amino acid [
      • Venkatraman S.
      • Bogen S.L.
      • Arasappan A.
      • Bennett F.
      • Chen K.
      • Jao E.
      • Liu Y.-T.
      • Lovey R.
      • Hendrata S.
      • Huang Y.
      • Pan W.
      • Parekh T.
      • Pinto P.
      • Popov V.
      • Pike R.
      • Ruan S.
      • Santhanam B.
      • Vibulbhan B.
      • Wu W.
      • Yang W.
      • Kong J.
      • Liang X.
      • Wong J.
      • Liu R.
      • Butkiewicz N.
      • Chase R.
      • Hart A.
      • Agrawal S.
      • Ingravallo P.
      • Pichardo J.
      • Kong R.
      • Baroudy B.
      • Malcolm B.
      • Guo Z.
      • Prongay A.
      • Madison V.
      • Broske L.
      • Cui X.
      • Cheng K.-C.
      • Hsieh Y.
      • Brisson J.-M.
      • Prelusky D.
      • Korfmacher W.
      • White R.
      • Bogdanowich-Knipp S.
      • Pavlovsky A.
      • Bradley P.
      • Saksena A.K.
      • Ganguly A.
      • Piwinski J.
      • Girijavallabhan V.
      • Njoroge F.G.
      Discovery of (1R,5S)-N-[3-Amino-1-(Cyclobutylmethyl)-2,3-Dioxopropyl]- 3-[2(S)-[[[(1,1-Dimethylethyl)Amino]Carbonyl]Amino]-3,3-Dimethyl-1-Oxobutyl]- 6,6-dimethyl-3-azabicyclo[3.1.0]Hexan-2(S)-Carboxamide (SCH 503034), a selective, potent, orally bioavailable hepatitis C virus NS3 protease inhibitor: a potential therapeutic agent for the treatment of hepatitis C infection.
      ,
      • Nair L.G.
      • Saksena A.
      • Lovey R.
      • Sannigrahi M.
      • Wong J.
      • Kong J.
      • Fu X.
      • Girijavallabhan V.
      A facile and efficient synthesis of 3,3-dimethyl isopropylidene proline from (+)-3-Carene.
      ,
      • Li T.
      • Liang J.
      • Ambrogelly A.
      • Brennan T.
      • Gloor G.
      • Huisman G.
      • Lalonde J.
      • Lekhal A.
      • Mijts B.
      • Muley S.
      • Newman L.
      • Tobin M.
      • Wong G.
      • Zaks A.
      • Zhang X.
      Efficient, chemoenzymatic process for manufacture of the boceprevir bicyclic [3.1.0]Proline intermediate based on amine oxidase-catalyzed desymmetrization.
      ] is reported from pyroglutamic acid [
      • Venkatraman S.
      • Bogen S.L.
      • Arasappan A.
      • Bennett F.
      • Chen K.
      • Jao E.
      • Liu Y.-T.
      • Lovey R.
      • Hendrata S.
      • Huang Y.
      • Pan W.
      • Parekh T.
      • Pinto P.
      • Popov V.
      • Pike R.
      • Ruan S.
      • Santhanam B.
      • Vibulbhan B.
      • Wu W.
      • Yang W.
      • Kong J.
      • Liang X.
      • Wong J.
      • Liu R.
      • Butkiewicz N.
      • Chase R.
      • Hart A.
      • Agrawal S.
      • Ingravallo P.
      • Pichardo J.
      • Kong R.
      • Baroudy B.
      • Malcolm B.
      • Guo Z.
      • Prongay A.
      • Madison V.
      • Broske L.
      • Cui X.
      • Cheng K.-C.
      • Hsieh Y.
      • Brisson J.-M.
      • Prelusky D.
      • Korfmacher W.
      • White R.
      • Bogdanowich-Knipp S.
      • Pavlovsky A.
      • Bradley P.
      • Saksena A.K.
      • Ganguly A.
      • Piwinski J.
      • Girijavallabhan V.
      • Njoroge F.G.
      Discovery of (1R,5S)-N-[3-Amino-1-(Cyclobutylmethyl)-2,3-Dioxopropyl]- 3-[2(S)-[[[(1,1-Dimethylethyl)Amino]Carbonyl]Amino]-3,3-Dimethyl-1-Oxobutyl]- 6,6-dimethyl-3-azabicyclo[3.1.0]Hexan-2(S)-Carboxamide (SCH 503034), a selective, potent, orally bioavailable hepatitis C virus NS3 protease inhibitor: a potential therapeutic agent for the treatment of hepatitis C infection.
      ] (involving nine steps) or (+)-3-carene7 (involving eleven steps). The proposed synthesis of key bicyclic fragment 4 commenced from Boc-trans-4-hydroxy L-proline benzyl ester 8 which was obtained from commercially available trans 4-hydroxy L-proline, using literature protocol [
      • Qiu X.
      • Qing F.
      Practical synthesis of boc-protected cis-4-trifluoromethyl and cis-4-Difluoromethyl-L-prolines.
      ]. The hydroxy group was mesylated using methanesulfonyl chloride, triethylamine and DMAP to get 9 in quantitative yield. Compound 9 was treated with diphenyldiselenide [
      • Qiu X.-L.
      • Qing F.-L.
      Synthesis of 3’-deoxy-3’-difluoromethyl azanucleosides from trans-4-hydroxy-L-proline.
      • Priem C.
      • Geyer A.
      Synthetic marine sponge collagen by late-stage dihydroxylation.
      • Flashman E.
      Evidence for a stereoelectronic effect in human oxygen sensing.
      ] and sodium borohydride to afford phenylselenyl derivative 10 in 78% yield. The oxidation of intermediate selenide 10, with hydrogen peroxide and subsequent elimination with pyridine smoothly gave the alkene 11 in 75% yield. This compound upon cobalt(II)-catalyzed dimethylcyclopropanation [
      • Werth J.
      • Uyeda C.
      Cobalt-catalyzed reductive dimethylcyclopropanation of 1,3-dienes.
      ,

      D.R. Owen, M.Y. Pettersson, M.R. Reese, M.F. Sammons, J.B. Tuttle, P.R. Verhoest, L. Wei, Q. Yang, X. Yang, Nitrile-containing Antiviral Compounds, Pfizer Inc. WO 2021/250648 A1.

      ] using 2,2-dichloropropane, zinc metal, zinc bromide and Co(II)-complex gave target bicyclic dimethylcyclopropyl amino acid fragment 4 in 68% yield. Thus, the synthesis of bicyclic amino acid 4 was achieved from Boc trans-4-hydroxy L-proline benzylester 8 in four steps in 40% overall yield. To facilitate peptide coupling on either side, the amino acid residue 4 was treated with either 4 ​N hydrochloric acid to give free amine benzyl ester as HCl salt 12 or Pd/C–H2 to give Boc-protected free acid 13 (Scheme 2).
      Scheme 2
      Scheme 2Synthesis of cyclopropyl fragment 4 and its coupling partners (12, 13).
      The amine hydrochloride of bicyclic fragment 12 was coupled with N-trifluoroacetyl L-tert-leucine 14 (obtained from N-trifluoro acetylation on L-tert-leucine) [
      • Rosso V.W.
      • Pazdan J.L.
      • Venit J.J.
      Rapid optimization of the hydrolysis of N′-Trifluoroacetyl-S-tert-leucine-N-methylamide using high-throughput.
      • Li L.
      • Yang T.
      • Zhang T.
      • Zhu B.
      • Chang J.
      Organocatalytic asymmetric tandem cyclization/michael addition via oxazol-5(2H)-One formation: access to perfluoroalkyl-containing N,O-acetal derivatives.
      ] using HATU, in presence of NMM, DMAP to give dipeptide 15 in 71% yield (Scheme 3).
      Scheme 3
      Scheme 3Synthesis of dipeptide 15.
      The synthesis of cyano amine 7 was achieved from protected L-glutamic acid 16 (Scheme 4). L-Glutamic acid was silylated with TMSCl, esterified using methanol [
      • Hanessian S.
      • Margarita R.
      • Tian Q.
      • Nayyar N.K.
      • Babu S.
      • Chen L.
      • Tao J.
      • Lee S.
      • Tibbetts A.
      • Moran T.
      • Liou J.
      • Guo M.
      • Kennedy T.P.
      An efficient synthesis of a key intermediate for the preparation of the rhinovirus protease inhibitor AG7088 via asymmetric dianionic cyanomethylation of N-Boc-L-(+)-glutamic acid dimethyl ester.
      • Yang S.
      • Chen S.-J.
      • Hsu M.-F.
      • Wu J.-D.
      • Tseng C.-T.K.
      • Liu Y.-F.
      • Chen H.-C.
      • Kuo C.-W.
      • Wu C.-S.
      • Chang L.-W.
      • Chen W.-C.
      • Liao S.-Y.
      • Chang T.-Y.
      • Hung H.-H.
      • Shr H.-L.
      • Liu C.-Y.
      • Huang Y.-A.
      • Chang L.-Y.
      • Hsu J.-C.
      • Peters C.J.
      • Wang A.H.-J.
      • Hsu M.-C.
      Synthesis, crystal structure, structure-activity relationships, and antiviral activity of a potent SARS coronavirus 3CL protease inhibitor.
      ] and the amine group was protected with FmocCl in presence of sodium carbonate as a base to yield protected glutamic acid 16. The diester 16 was subjected to mono-alkylation with bromoacetonitrile using LiHMDS in THF to give cyano compound 17. The cyano diester 17 was cyclized to lactam 18 using CoCl2.6H2O and sodium borohydride [
      • Reddy P.A.
      • Hsiang B.C.H.
      • Latifi T.N.
      • Hill M.W.
      • Woodward K.E.
      • Rothman S.M.
      • Ferrendelli J.A.
      • Covey D.F.
      3,3-Dialkyl- and 3-alkyl-3-benzyl-substituted 2-pyrrolidinones: a new class of anticonvulsant agents.
      • Tian Q.
      • Nayyar N.K.
      • Babu S.
      • Chen L.
      • Tao J.
      • Lee S.
      • Tibbetts A.
      • Moran T.
      • Liou J.
      • Guo M.
      • Kennedy T.P.
      An efficient synthesis of a key intermediate for the preparation of the rhinovirus protease inhibitor AG7088 via asymmetric dianionic cyanomethylation of N-Boc-L-(+)-Glutamic acid dimethyl ester.
      • Zhai Y.
      • Zhao X.
      • Cui Z.
      • Wang M.
      • Wang Y.
      • Li L.
      • Sun Q.
      • Yang X.
      • Zeng D.
      • Liu Y.
      • Sun Y.
      • Lou Z.
      • Shang L.
      • Yin Z.
      ]. The ester functionality in lactam 18 was reduced to alcohol 6 using sodium borohydride in THF:MeOH (2:1). Alcohol 6, upon oxidation with Dess-Martin periodinane (DMP), afforded aldehyde 19. A one-pot conversion of aldehyde 19 to nitrile 20 was achieved by the treatment of aldehyde with iodine and ammonia solution [
      • Talukdar S.
      • Hsu J.-L.
      • Chou T.-C.
      • Fang J.-M.
      Direct transformation of aldehydes to nitriles using iodine in ammonia water.
      • Gálvez J.A.
      • Clavería-Gimeno R.
      • Galano-Frutos J.J.
      • Sancho J.
      • Velazquez-Campoy A.
      • Abian O.
      • Díaz-de-Villegas M.D.
      Stereoselective synthesis and biological evaluation as inhibitors of hepatitis C virus RNA polymerase of GSK3082 analogues with structural diversity at the 5-position.
      ]. Finally, the Fmoc-deprotection of compound 20 using diethylamine resulted in the formation of cyano amine fragment 7.
      Scheme 4
      Scheme 4Synthesis of cyano amine fragment 7.
      Dipeptide 15 on debenzylation using Pd/C, H2 in methanol gave dimer acid 5 in 93% yield. The dimer acid (5) is ready to be coupled with amine 7 to give Nirmatrelvir [
      • Zhao Y.
      • Fang C.
      • Zhang Q.
      • Zhang R.
      • Zhao X.
      • Duan Y.
      • Wang H.
      • Zhu Y.
      • Feng L.
      • Zhao J.
      • Shao M.
      • Yang X.
      • Zhang L.
      • Peng C.
      • Yang K.
      • Ma D.
      • Rao Z.
      • Yang H.
      Crystal structure of SARS-CoV-2 main protease in complex with protease inhibitor PF-07321332.
      ]. The amine 7 was coupled with dimer acid 5, using HATU in presence of NMM and DMAP, to afford the target molecule nirmatrelvir 1 (Scheme 5). The spectral data of compound 1 was found to be in agreement with the reported literature values [
      • Owen D.R.
      • Allerton C.M.N.
      • Anderson A.S.
      • Aschenbrenner L.
      • Avery M.
      • Berritt S.
      • Boras B.
      • Cardin R.D.
      • Carlo A.
      • Coffman K.J.
      • Dantonio A.
      • Di L.
      • Eng H.
      • Ferre R.A.
      • Gajiwala K.S.
      • Gibson S.A.
      • Greasley S.E.
      • Hurst B.L.
      • Kadar E.P.
      • Kalgutkar A.S.
      • Lee J.C.
      • Lee J.
      • Liu W.
      • Mason S.W.
      • Noell S.
      • Novak J.J.
      • Obach R.S.
      • Ogilvie K.
      • Patel N.C.
      • Pettersson M.
      • Rai D.K.
      • Reese M.R.
      • Sammons M.F.
      • Sathish J.G.
      • Singh R.S.P.
      • Steppan C.M.
      • Stewart A.E.
      • Tuttle J.B.
      • Updyke L.
      • Verhoest P.R.
      • Wei L.
      • Yang Q.
      • Zhu Y.
      An oral SARS-CoV-2 mpro inhibitor clinical candidate for the treatment of COVID-19.
      ].
      Scheme 5
      Scheme 5Synthesis of Nirmatrelvir 1.
      The present work provides nirmatrelvir 1 in three steps from amine hydrochloride 12, whereas the earlier report [
      • Owen D.R.
      • Allerton C.M.N.
      • Anderson A.S.
      • Aschenbrenner L.
      • Avery M.
      • Berritt S.
      • Boras B.
      • Cardin R.D.
      • Carlo A.
      • Coffman K.J.
      • Dantonio A.
      • Di L.
      • Eng H.
      • Ferre R.A.
      • Gajiwala K.S.
      • Gibson S.A.
      • Greasley S.E.
      • Hurst B.L.
      • Kadar E.P.
      • Kalgutkar A.S.
      • Lee J.C.
      • Lee J.
      • Liu W.
      • Mason S.W.
      • Noell S.
      • Novak J.J.
      • Obach R.S.
      • Ogilvie K.
      • Patel N.C.
      • Pettersson M.
      • Rai D.K.
      • Reese M.R.
      • Sammons M.F.
      • Sathish J.G.
      • Singh R.S.P.
      • Steppan C.M.
      • Stewart A.E.
      • Tuttle J.B.
      • Updyke L.
      • Verhoest P.R.
      • Wei L.
      • Yang Q.
      • Zhu Y.
      An oral SARS-CoV-2 mpro inhibitor clinical candidate for the treatment of COVID-19.
      ] utilises six steps. The use of Burgess reagent is avoided in our protocol, thereby reducing the cost of synthesizing the product. The protocol uses appropriately substituted amino acids to give better yields with lesser number of steps.

      3. Conclusions

      In conclusion, synthesis of nirmatrelvir (PF-07321332) has been achieved in fewer steps than the reported protocols, using chemicals which are easily accessible. The key steps of the synthesis involve an asymmetric Co(II)-catalyzed dimethyl cyclopropanation to provide bicyclic amino acid and one-pot conversion of aldehyde group to nitrile for other amino acid. The manuscript provides an alternate route for the synthesis of the approved molecule which has the potential to be scaled up.

      Data availability

      Data will be made available on request.

      Declaration of competing interest

      The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

      Acknowledgements

      The authors thank the Council of Scientific and Industrial Research ( CSIR ), Ministry of Science and Technology, Government of India for research facilities and supporting research in antivirals through HCP-0041. CS, SRP and PK thanks the University Grants Commission ( UGC ), Government of India for the research fellowship. S. C. thanks the Science and Engineering Research Board ( SERB ), Government of India for J C Bose fellowship ( SB/S2/JCB-002/2015 ). IICT communication no. IICT/Pubs./2022/123. This work has been submitted for patent through CSIR (Ref. No. 0044NF2022).

      Appendix A. Supplementary data

      The following are the Supplementary data to this article:

      References

        • de Vries M.
        • Mohamed A.S.
        • Prescott R.A.
        • Valero-Jimenez A.M.
        • Desvignes L.
        • O'Connor R.
        • Steppan C.
        • Devlin J.C.
        • Ivanova E.
        • Herrera A.
        • Schinlever A.
        • Loose P.
        • Ruggles K.
        • Koralov S.B.
        • Anderson A.S.
        • Binder J.
        • Dittmann M.
        A comparative analysis of SARS-CoV-2 antivirals characterizes 3CLpro inhibitor PF-00835231 as a potential new treatment for COVID-19.
        J. Virol. 2021; 95 (e01819–20)
        • Lamb Y.N.
        Nirmatrelvir Plus Ritonavir: First Approval.
        2022: 1-7 (Drugs)
        • Hoffman R.L.
        • Kania R.S.
        • Brothers M.A.
        • Davies J.F.
        • Ferre R.A.
        • Gajiwala K.S.
        • He M.
        • Hogan R.J.
        • Kozminski K.
        • Li L.Y.
        • Lockner J.W.
        • Lou J.
        • Marra M.T.
        • Mitchell Jr., L.J.
        • Murray B.W.
        • Nieman J.A.
        • Noell S.
        • Planken S.P.
        • Rowe T.
        • Ryan K.
        • Smith III, G.J.
        • Solowiej J.E.
        • Steppan C.M.
        • Taggart B.
        Discovery of ketone-based covalent inhibitors of coronavirus 3CL proteases for the potential therapeutic treatment of COVID-19.
        J. Med. Chem. 2020; 63: 12725-12747
        • Howe A.Y.M.
        • Venkatraman S.
        The discovery and development of boceprevir: a novel, first-generation inhibitor of the hepatitis C virus NS3/4A serine protease.
        J. Clin. Transl. Hepatol. 2013; 1: 22-32
      1. (a)
        • Donikela S.
        • Nayani K.
        • Mainkar P.S.
        • Chandrasekhar S.
        Gram scale solution-phase synthesis of heptapeptide side chain of teixobactin.
        Synlett. 2019; 30: 2268-2272
      2. (b)
        • Kallepu S.
        • Kavitha M.
        • Yeeravalli R.
        • Manupati K.
        • Jadav S.S.
        • Das A.
        • Mainkar P.S.
        • Chandrasekhar S.
        Total synthesis of desmethyl jahanyne and its lipo-tetrapeptide conjugates derived from parent skeleton as BCL-2-mediated apoptosis-inducing agents.
        ACS Omega. 2018; 3: 63-75
      3. (c)
        • Chandrasekhar S.
        • Kiranmai N.
        • Kiran M.U.
        • Devi A.S.
        • Reddy G.P.K.
        • Idris M.
        • Jagadeesh B.
        Novel helical foldamers: organized heterogeneous backbone folding in 1:1 α/Nucleoside-Derived–β-Amino acid sequences, chem.
        Commun. Now. 2010; 46: 6962-6964
      4. (d)
        • Jagannadh B.
        • Reddy M.S.
        • Rao C.L.
        • Prabhakar A.
        • Jagadeesh B.
        • Chandrasekhar S.
        Self-assembly of cyclic homo- and hetero-β-peptides with cis-furanoid sugar amino acid and β-hGly as building blocks.
        Chem. Commun. 2006; : 4847-4849
      5. (e)
        • Chandrasekhar S.
        • Reddy M.S.
        • Babu B.N.
        • Jagadeesh B.
        • Prabhakar A.
        • Jagannadh B.
        Expanding the conformational pool of cis-β-Sugar amino acid: accommodation of β-hGly motif in robust 14-helix.
        J. Am. Chem. Soc. 2005; 127 (and the references cited therein): 9664-9665
        • Venkatraman S.
        • Bogen S.L.
        • Arasappan A.
        • Bennett F.
        • Chen K.
        • Jao E.
        • Liu Y.-T.
        • Lovey R.
        • Hendrata S.
        • Huang Y.
        • Pan W.
        • Parekh T.
        • Pinto P.
        • Popov V.
        • Pike R.
        • Ruan S.
        • Santhanam B.
        • Vibulbhan B.
        • Wu W.
        • Yang W.
        • Kong J.
        • Liang X.
        • Wong J.
        • Liu R.
        • Butkiewicz N.
        • Chase R.
        • Hart A.
        • Agrawal S.
        • Ingravallo P.
        • Pichardo J.
        • Kong R.
        • Baroudy B.
        • Malcolm B.
        • Guo Z.
        • Prongay A.
        • Madison V.
        • Broske L.
        • Cui X.
        • Cheng K.-C.
        • Hsieh Y.
        • Brisson J.-M.
        • Prelusky D.
        • Korfmacher W.
        • White R.
        • Bogdanowich-Knipp S.
        • Pavlovsky A.
        • Bradley P.
        • Saksena A.K.
        • Ganguly A.
        • Piwinski J.
        • Girijavallabhan V.
        • Njoroge F.G.
        Discovery of (1R,5S)-N-[3-Amino-1-(Cyclobutylmethyl)-2,3-Dioxopropyl]- 3-[2(S)-[[[(1,1-Dimethylethyl)Amino]Carbonyl]Amino]-3,3-Dimethyl-1-Oxobutyl]- 6,6-dimethyl-3-azabicyclo[3.1.0]Hexan-2(S)-Carboxamide (SCH 503034), a selective, potent, orally bioavailable hepatitis C virus NS3 protease inhibitor: a potential therapeutic agent for the treatment of hepatitis C infection.
        J. Med. Chem. 2006; 49: 6074-6086
        • Nair L.G.
        • Saksena A.
        • Lovey R.
        • Sannigrahi M.
        • Wong J.
        • Kong J.
        • Fu X.
        • Girijavallabhan V.
        A facile and efficient synthesis of 3,3-dimethyl isopropylidene proline from (+)-3-Carene.
        J. Org. Chem. 2010; 75: 1285-1288
        • Li T.
        • Liang J.
        • Ambrogelly A.
        • Brennan T.
        • Gloor G.
        • Huisman G.
        • Lalonde J.
        • Lekhal A.
        • Mijts B.
        • Muley S.
        • Newman L.
        • Tobin M.
        • Wong G.
        • Zaks A.
        • Zhang X.
        Efficient, chemoenzymatic process for manufacture of the boceprevir bicyclic [3.1.0]Proline intermediate based on amine oxidase-catalyzed desymmetrization.
        J. Am. Chem. Soc. 2012; 134: 6467-6472
        • Qiu X.
        • Qing F.
        Practical synthesis of boc-protected cis-4-trifluoromethyl and cis-4-Difluoromethyl-L-prolines.
        J. Org. Chem. 2002; 67: 7162-7164
      6. (a)
        • Qiu X.-L.
        • Qing F.-L.
        Synthesis of 3’-deoxy-3’-difluoromethyl azanucleosides from trans-4-hydroxy-L-proline.
        J. Org. Chem. 2005; 70: 3826-3837
      7. (b)
        • Priem C.
        • Geyer A.
        Synthetic marine sponge collagen by late-stage dihydroxylation.
        Org. Lett. 2018; 20: 162-165
      8. (c)
        • Flashman E.
        Evidence for a stereoelectronic effect in human oxygen sensing.
        Angew. Chem. Int. Ed. 2009; 48: 1784-1787
        • Werth J.
        • Uyeda C.
        Cobalt-catalyzed reductive dimethylcyclopropanation of 1,3-dienes.
        Angew. Chem. Int. Ed. 2018; 57: 13902-13906
      9. D.R. Owen, M.Y. Pettersson, M.R. Reese, M.F. Sammons, J.B. Tuttle, P.R. Verhoest, L. Wei, Q. Yang, X. Yang, Nitrile-containing Antiviral Compounds, Pfizer Inc. WO 2021/250648 A1.

      10. (a)
        • Rosso V.W.
        • Pazdan J.L.
        • Venit J.J.
        Rapid optimization of the hydrolysis of N′-Trifluoroacetyl-S-tert-leucine-N-methylamide using high-throughput.
        Chem. Dev. Techniq, Org. Process Res. Dev. 2001; 5: 294-298
      11. (b)
        • Li L.
        • Yang T.
        • Zhang T.
        • Zhu B.
        • Chang J.
        Organocatalytic asymmetric tandem cyclization/michael addition via oxazol-5(2H)-One formation: access to perfluoroalkyl-containing N,O-acetal derivatives.
        J. Org. Chem. 2020; 85: 12294-12303
      12. (a)
        • Hanessian S.
        • Margarita R.
        Tetrahedron Lett. 1998; 39: 5887-5890
      13. (b)
        • Tian Q.
        • Nayyar N.K.
        • Babu S.
        • Chen L.
        • Tao J.
        • Lee S.
        • Tibbetts A.
        • Moran T.
        • Liou J.
        • Guo M.
        • Kennedy T.P.
        An efficient synthesis of a key intermediate for the preparation of the rhinovirus protease inhibitor AG7088 via asymmetric dianionic cyanomethylation of N-Boc-L-(+)-glutamic acid dimethyl ester.
        Tetrahedron Lett. 2001; 42: 6807-6809
      14. (c)
        • Yang S.
        • Chen S.-J.
        • Hsu M.-F.
        • Wu J.-D.
        • Tseng C.-T.K.
        • Liu Y.-F.
        • Chen H.-C.
        • Kuo C.-W.
        • Wu C.-S.
        • Chang L.-W.
        • Chen W.-C.
        • Liao S.-Y.
        • Chang T.-Y.
        • Hung H.-H.
        • Shr H.-L.
        • Liu C.-Y.
        • Huang Y.-A.
        • Chang L.-Y.
        • Hsu J.-C.
        • Peters C.J.
        • Wang A.H.-J.
        • Hsu M.-C.
        Synthesis, crystal structure, structure-activity relationships, and antiviral activity of a potent SARS coronavirus 3CL protease inhibitor.
        J. Med. Chem. 2006; 49: 4971-4980
      15. (a)
        • Reddy P.A.
        • Hsiang B.C.H.
        • Latifi T.N.
        • Hill M.W.
        • Woodward K.E.
        • Rothman S.M.
        • Ferrendelli J.A.
        • Covey D.F.
        3,3-Dialkyl- and 3-alkyl-3-benzyl-substituted 2-pyrrolidinones: a new class of anticonvulsant agents.
        J. Med. Chem. 1996; 39: 1898-1906
      16. (b)
        • Tian Q.
        • Nayyar N.K.
        • Babu S.
        • Chen L.
        • Tao J.
        • Lee S.
        • Tibbetts A.
        • Moran T.
        • Liou J.
        • Guo M.
        • Kennedy T.P.
        An efficient synthesis of a key intermediate for the preparation of the rhinovirus protease inhibitor AG7088 via asymmetric dianionic cyanomethylation of N-Boc-L-(+)-Glutamic acid dimethyl ester.
        Tetrahedron Lett. 2001; 42: 6807-6809
      17. (c)
        • Zhai Y.
        • Zhao X.
        • Cui Z.
        • Wang M.
        • Wang Y.
        • Li L.
        • Sun Q.
        • Yang X.
        • Zeng D.
        • Liu Y.
        • Sun Y.
        • Lou Z.
        • Shang L.
        • Yin Z.
        J. Med. Chem. 2015; 58: 9414-9420
      18. (a)
        • Talukdar S.
        • Hsu J.-L.
        • Chou T.-C.
        • Fang J.-M.
        Direct transformation of aldehydes to nitriles using iodine in ammonia water.
        Tetrahedron Lett. 2001; 42: 1103-1105
      19. (b)
        • Gálvez J.A.
        • Clavería-Gimeno R.
        • Galano-Frutos J.J.
        • Sancho J.
        • Velazquez-Campoy A.
        • Abian O.
        • Díaz-de-Villegas M.D.
        Stereoselective synthesis and biological evaluation as inhibitors of hepatitis C virus RNA polymerase of GSK3082 analogues with structural diversity at the 5-position.
        Eur. J. Med. Chem. 2019; 171: 401-419
        • Zhao Y.
        • Fang C.
        • Zhang Q.
        • Zhang R.
        • Zhao X.
        • Duan Y.
        • Wang H.
        • Zhu Y.
        • Feng L.
        • Zhao J.
        • Shao M.
        • Yang X.
        • Zhang L.
        • Peng C.
        • Yang K.
        • Ma D.
        • Rao Z.
        • Yang H.
        Crystal structure of SARS-CoV-2 main protease in complex with protease inhibitor PF-07321332.
        Protein Cell. 2021; : 1-5
        • Owen D.R.
        • Allerton C.M.N.
        • Anderson A.S.
        • Aschenbrenner L.
        • Avery M.
        • Berritt S.
        • Boras B.
        • Cardin R.D.
        • Carlo A.
        • Coffman K.J.
        • Dantonio A.
        • Di L.
        • Eng H.
        • Ferre R.A.
        • Gajiwala K.S.
        • Gibson S.A.
        • Greasley S.E.
        • Hurst B.L.
        • Kadar E.P.
        • Kalgutkar A.S.
        • Lee J.C.
        • Lee J.
        • Liu W.
        • Mason S.W.
        • Noell S.
        • Novak J.J.
        • Obach R.S.
        • Ogilvie K.
        • Patel N.C.
        • Pettersson M.
        • Rai D.K.
        • Reese M.R.
        • Sammons M.F.
        • Sathish J.G.
        • Singh R.S.P.
        • Steppan C.M.
        • Stewart A.E.
        • Tuttle J.B.
        • Updyke L.
        • Verhoest P.R.
        • Wei L.
        • Yang Q.
        • Zhu Y.
        An oral SARS-CoV-2 mpro inhibitor clinical candidate for the treatment of COVID-19.
        Science. 2021; 374: 1586-1593