Amine Synthesis Using the Amine Donor N-Phenyl Putrescine and the Johnson Matthey Transaminase Biocatalyst Library
Amine Synthesis Using the Amine Donor N-Phenyl Putrescine and the Johnson Matthey Transaminase Biocatalyst Library
Smart amine donors facilitate production of amines at high percentage yields
Chiral amines are important building blocks in the pharmaceutical, agrochemical and chemical industries. There is a drive to augment traditional transition metal catalysts with ‘green’ alternatives such as biocatalysts. Transaminase (TA) biocatalysts can be used in combination with ‘smart’ sacrificial amine donors to synthesise a variety of aliphatic and aromatic amines from the corresponding aldehydes and ketones. Despite their enormous potential, the unfavourable reaction equilibrium often limits the widespread application of TAs for industrial synthesis. Recently we disclosed a new biomimetic amine donor N-phenyl putrescine (NPP), which was inspired by the biosynthesis of the dipyrroloquinoline alkaloids. NPP was demonstrated to have good activity with a library of commercial and wild-type TAs (total 25 TAs). This work focused on exploring the use of NPP with the Johnson Matthey TA kit (17 biocatalysts; eight S-selective and nine R-selective) and three different amine acceptors (vanillin, benzaldehyde and acetophenone). NPP worked well with all 17 TAs and gave the corresponding amine products vanillylamine, benzylamine and methylbenzylamine (MBA) in up to 85% high-performance liquid chromatography (HPLC) yield. From the screen, STA-14 was identified as a good biocatalyst for further analysis and used in a comparative screen of NPP versus the commonly used donor iPrNH2. It was found that NPP was the best amine donor and used to prepare S-methylbenzylamine in >99.5% enantiomeric excess (e.e.). This work, combined with our previous study, highlights the potential of NPP in the biocatalytic synthesis of amines.
The use of biocatalysis for the asymmetric production of chiral amines is an attractive alternative to traditional chemical methods (1–4). Amongst the enzymes capable of this transformation, TA biocatalysts are the most attractive due to no requirements for expensive cofactors or recycling. TAs catalyse the transfer of an amine group from a sacrificial amine donor to both aldehyde and prochiral ketone acceptors using the cofactor pyridoxal 5′-phosphate (PLP, also known as vitamin B6) to generate the desired primary amine or a chiral amine in an enantioselective fashion (5–7). The synthetic utility of these TA biocatalysts is demonstrated in the pharmaceutical industry by the manufacture of sitagliptin (brand name Januvia® by Merck & Co Inc, USA), an antidiabetic drug (8). The biocatalysts have also been applied to the large-scale synthesis of orexin, AZD1480 (JAK2 kinase inhibitor) and an intermediate in the synthesis of antibiotic Besifloxacin (9–11). Although the notorious unfavourable equilibrium of TA reactions (12, 13) requires the amine donor iPrNH2 in high excess (1 M), accompanied with in situ removal of the byproduct acetone (14).
An alternative strategy to overcome the unfavourable equilibrium is the use of amino acids and enzymatic cascades or smart amine donors such as o-2-(4-nitrophenyl)ethan-1-amine (N-PEA), o-xylyenediamine (OXDA) and cadaverine (15–21). However, so far these have not been suitable on an industrial scale due to the difficulty in removing products or incompatibility at wider pH ranges. Recently we disclosed a new biomimetic amine donor N-phenyl putrescine (NPP), which was inspired by the biosynthesis of the dipyrroloquinoline alkaloid natural products such as incargranine B (Figure 1) (22, 23).
It was proposed that after transfer of the NPP amine group, the resultant enamine and iminium ion dimerise through an irreversible Povarov reaction. This gives rise to an insoluble dimeric NPP product, which is easily removed, thus driving amine formation. Previously, NPP was demonstrated to have good activity with a library of commercial (Codexis®, USA, 24 TAs) and wild-type TAs (Chromobacterium violaceum (CVTA) and Halomonas elongata omega transaminase (HEWT)) (24, 25), for various aldehyde and ketone acceptors across a range of temperatures and pH.
In this article, we explore the use of NPP with the 17 TAs from the Johnson Matthey ‘chiral amine’ collection, which contains eight S- and nine R-selective biocatalysts. NPP performed well with all the TAs in the collection using vanillin, benzaldehyde and acetophenone as substrates. Good HPLC yields (up to 85%) of the corresponding amine products were obtained.
All reagents and solvents were purchased from Sigma-Aldrich, USA, and Thermo Fisher Scientific, USA, and used without further purification. The amine donor NPP was prepared as previously published (22).
The TAs from the Johnson Matthey chiral amine kit were used in both the screening and the scale-up reaction. The annotations are as follows: STA refers to a TA biocatalyst that generates the S-enantiomer of the amine product (eight were used: STA-1, STA-2, STA-13, STA-14, STA-113, STA-118, STA-120 and STA-121). RTA refers to a TA biocatalyst that generates the R-enantiomer of the amine product (nine were used: RTA-25, RTA-40, RTA-45, RTA-57, RTA-58, RTA-102, RTA-103, RTA-104 and RTA-105). The TAs in the kit are provided as lyophilised, purified His-tag recombinant versions purified by immobilised affinity chromatography (IMAC).
Stock solutions of TAs and NPP were made up using reaction buffer, stock solutions of acceptor substrates were made using 100% dimethylsulfoxide (DMSO).
2.1.1 High-Performance Liquid Chromatography Analysis
HPLC methods were carried out using a SIL-20A HT instrument fitted with autosampler (Shimadzu, Japan), LC-20AD pump, SPD-20A ultraviolet-visible detector, CBM-20Alite system controller and a CTO-20A column oven. Analysis of the TA screens were carried out on a LunaTM 5 μm C18 column (Phenomenex, USA; 250 mm × 4.6 mm, 100 Å) at 210 nm. Product elution for reactions with benzaldehyde and acetophenone proceeded with a gradient of 15–72% CH3CN in water over 12 min (1.0 ml min–1 at 30°C). Product elution for reactions with vanillylamine proceeded with a gradient of 10–80% CH3CN in water over 12 min (1.0 ml min–1) at 30°C. Chiral HPLC analysis of MBA was carried out on a CHIRALPAKTM IBN-5 column (Daicel Chiral Technologies, USA; hexane (0.5% triethylamine)): isocratic elution iPrOH 90:10 (v:v), flow rate 1.0 ml min–1, 254 nm, 30°C.
2.2 Enzyme Screening Methods
Substrates (vanillin or benzaldehyde or MBA) (50 μl, 100 mM), NPP (100 μl, 100 mM) and TA (100 μl, 10 mg ml–1) were added to a GilsonTM Research® Plus mechanical pipette and made up to 500 μl with (4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid) (HEPES) buffer (350 μl, pH 7.5, 100 mM, 0.1 mM PLP). For each TA the reaction was set up in triplicate and left to shake at 240 rpm at 30°C. An aliquot (200 μl) was removed, quenched with trifluoroacetic acid (TFA, 10 μl, 10% in water). The supernatant (50 μl) was collected by centrifugation (10 min maximum speed, benchtop centrifuge) and diluted into water (350 μl). Internal standard ((S)-MBA for benzaldehyde reactions or benzylamine for acetophenone reaction) (4 μl, 100 mM) was added. The supernatant (100 μl) was collected by centrifugation (10 min maximum speed (13 g), benchtop centrifuge) for analysis by reverse phase HPLC (see Section 2.1.1).
2.3 Scale-up Biocatalytic Reaction
Acetophenone (60 mg, 0.5 mmol) was dissolved in DMSO (5 ml) and added to a HEPES pH 7.5 buffer solution (45 ml, HEPES (100 mM) containing PLP (0.1 mM), NPP (248.9 mg, 1 mmol)) and STA-14 (100 mg). The reaction was incubated at 30°C with shaking at 240 rpm for 48 h. The reaction mixture was quenched by addition of concentrated aqueous hydrochloric acid to pH 2 and filtered through a pad of Celite®. The filtrate was collected and adjusted to pH 12 using 5 M aqueous sodium hydroxide. The organics were extracted into dichloromethane (3 ml × 50 ml), dried over sodium sulfite and concentrated under reduced pressure. The crude residue was dissolved in a minimal volume of dichloromethane and purified by flash chromatography (dichloromethane:7 M ammonia in methanol 100:0 to 90:10, RF 0.40 at 90:10) to give MBA 32 mg, 52.8% (67.5% HPLC yield).
3.1 Quantitative Screen of Vanillin and N-Phenyl Putrescine with Johnson Matthey Transaminase Library
We began our screening of the synthetic utility of the NPP amine donor with the Johnson Matthey library (17 TAs) using vanillin aldehyde as the amine acceptor (Figure 2(a)). Reaction conditions: vanillin (10 mM), NPP (20 mM), TA (2 mg ml–1), HEPES (pH 7.5, 100 mM), PLP (0.1 mM), DMSO (10%), 30°C, 48 h. Reactions were performed in triplicate and errors determined by standard deviation. The resulting TA product, vanillylamine, is a useful intermediate in the synthesis of various molecules used in the agrochemical, flavour and pharmaceutical industries (26).
The reaction was monitored by reverse phase HPLC and the production of the vanillylamine (elution at 5.8 min) was quantified (Figure 2(b) and 2(c)). All 17 of the TA biocatalysts in the library gave the desired product with seven members of the TA library (STA-1, STA-13, STA-14, STA-113, STA-118, STA-121 and RTA-45) giving HPLC yields >80%.
3.2 Quantitative Screen of N-Phenyl Putrescine with Johnson Matthey Transaminase Library
We next screened the Johnson Matthey library with NPP as the amine donor and benzaldehyde as the amine acceptor (Figure 3, R = H). Reaction conditions: amine acceptor (10 mM), NPP (20 mM), TA (2 mg ml–1), HEPES (pH 7.5, 100 mM), PLP (0.1 mM), DMSO (10%), 30°C, 48 h. Reactions were performed in triplicate and errors determined by standard deviation. Quantitative analysis by reverse phase HPLC showed that all 17 of the TAs accepted NPP as an amine donor, with nine TAs (STA-13, STA-14, STA-113, STA-118, STA-120, STA-121, RTA-45, RTA-58 and RTA-105) giving yields of the benzylamine product between 60–85%. The utility of NPP was also demonstrated in the more difficult reaction of acetophenone to MBA (Figure 3: MBA, R = CH3). The MBA product was obtained with 16 out of 17 TAs in the collection, with STA-14 giving the highest yield of amine (40% HPLC yield).
3.3 Comparison of N-Phenyl Putrescine and iPrNH2 as Amine Donors
In our previous work we compared NPP with iPrNH2 (the current industrial standard amine donor) using three TAs from the Codexis® kit (ATA-234, ATA-238 and ATA-251) and one wild-type TA (HEWT). In each case, NPP outperformed iPrNH2 under identical reaction conditions in terms of percentage HPLC yield of the desired amine products. Having identified STA-14 from the Johnson Matthey TA kit as the best biocatalyst from the new screen, we compared NPP to iPrNH2 as amine donors in reactions with vanillin, benzaldehyde and acetophenone (Figure 4(a)). Reaction conditions: Amine acceptor (10 mM), NPP (20 mM) or iPrNH2 (20 mM), TA (2 mg ml–1), HEPES (pH 7.5, 100 mM), PLP (0.1 mM), DMSO (10%), 30°C, 48 h. Reactions were performed in triplicate and errors determined by standard deviation. The formation of the corresponding amine products were monitored and quantified using the same reverse phase HPLC analysis. In each case NPP once again outperformed the industrial amine donor iPrNH2 under identical reaction conditions (Figure 4(b)). When using iPrNH2 the percentage yields of the amine product never exceeded 25%, compared to NPP which gave percentage yields ranging from 40–98%. We also investigated how many equivalents of iPrNH2 would be required to obtain the same percentage yield as NPP (Figure S8 in the Supplementary Information). In the case of acetophenone, the highest yield of 22% was obtained when using 50 equivalents (500 mM) of iPrNH2. Only when applying 100 equivalents (1 M) of the iPrNH2 amine donor for the synthesis of benzylamine, did the HPLC percentage yields compare to those achieved with NPP.
3.4 Preparative Scale Reaction of Methylbenzylamine
Since our screen identified STA-14 as the best biocatalyst for the production of MBA using NPP and acetophenone (Figure 3), this combination was chosen for a preparative scale reaction. The characteristic precipitate due to the formation of the NPP dimer that accompanies amine formation was observed and easily removed by filtration and chiral product MBA (32 mg, 52.8%) was isolated via flash chromatography. The percentage e.e. of the isolated product was determined by chiral HPLC and shown to be >99.5% (S)-MBA, the high enantioselectivity anticipated from using the STA-14 biocatalyst (Figure 5).
Smart amine donors have the potential to facilitate the production of amines at high percentage yields. We recently prepared the novel amine donor NPP and showed that it can be used with wild type TA biocatalysts, as well as a commercial TA library (Codexis®). NPP performed well across a range of temperatures (20–45°C), amine donor equivalents (from one to four) and pH (6.0–11.0). It could also be used to prepare the corresponding amine products from ‘difficult’ substrates such as indanone and pre-sitagliptin ketone. Furthermore, NPP outperformed the most commonly used industrial amine donor iPrNH2.
Here, we used a similar strategy to screen NPP with the 17 members of the Johnson Matthey TA biocatalyst library. We used three amine acceptors (vanillin, benzaldehyde and acetophenone) with NPP and demonstrated its acceptance by all of the TAs in the kit. We identified nine TAs as suitable candidates (with a bar of >60% yield) for the production of primary amines with STA-14 being the best biocatalyst across the three substrates. Using STA-14 in a comparative study, it was shown that NPP outperformed iPrNH2 under identical reaction conditions when used for the synthesis of the three amine products. Finally, after a screen of the full library with acetophenone, the best performing TA (STA-14) was used to prepare enantiopure S-MBA.
The results of this work, combined with the analysis in our previous study, confirms NPP as an easy to prepare smart amine donor that should find synthetic utility in the preparation of various target amines. As well as the single TA biocatalyst studies reported here, we also envisage NPP being incorporated into a range of biocatalytic cascades that are being developed for the synthesis of a wide variety of pharmaceutical targets (27, 28).
Our future work will focus on a structural and mechanistic understanding that aims to rationalise why NPP is a good amine donor with most PLP-dependent TA biocatalysts. We are also adapting the core NPP structure to incorporate functionality that will further improve the properties of this versatile reagent.
U. T. Bornscheuer, G. W. Huisman, R. J. Kazlauskas, S. Lutz, J. C. Moore, K. Robins, Nature, 2012, 485, (7397), 185 LINK https://doi.org/10.1038/nature11117
K. Chen, F. H. Arnold, Nat. Catal., 2020, 3, (3), 203 LINK https://doi.org/10.1038/s41929-019-0385-5
P. N. Devine, R. M. Howard, R. Kumar, M. P. Thompson, M. D. Truppo, N. J. Turner, Nat. Rev. Chem., 2018, 2, (12), 409 LINK https://doi.org/10.1038/s41570-018-0055-1
J. B. Pyser, S. Chakrabarty, E. O. Romero, A. R. H. Narayan, ACS Cent. Sci., 2021, 7, (7), 1105 LINK https://doi.org/10.1021/acscentsci.1c00273
S. A. Kelly, S. Mix, T. S. Moody, B. F. Gilmore, Appl. Microbiol. Biotechnol., 2020, 104, (11), 4781 LINK https://doi.org/10.1007/s00253-020-10585-0
F. Guo, P. Berglund, Green Chem., 2017, 19, (2), 333 LINK https://doi.org/10.1039/c6gc02328b
I. Slabu, J. L. Galman, R. C. Lloyd, N. J. Turner, ACS Catal., 2017, 7, (12), 8263 LINK https://doi.org/10.1021/acscatal.7b02686
C. K. Savile, J. M. Janey, E. C. Mundorff, J. C. Moore, S. Tam, W. R. Jarvis, J. C. Colbeck, A. Krebber, F. J. Fleitz, J. Brands, P. N. Devine, G. W. Huisman, G. J. Hughes, Science, 2010, 329, (5989), 305 LINK https://doi.org/10.1126/science.1188934
Y. Feng, Z. Luo, G. Sun, M. Chen, J. Lai, W. Lin, S. Goldmann, L. Zhang, Z. Wang, Org. Process Res. Dev., 2017, 21, (4), 648 LINK https://doi.org/10.1021/acs.oprd.7b00074
Z. Peng, J. W. Wong, E. C. Hansen, A. L. A. Puchlopek-Dermenci, H. J. Clarke, Org. Lett., 2014, 16, (3), 860 LINK https://doi.org/10.1021/ol403630g
L. Frodsham, M. Golden, S. Hard, M. N. Kenworthy, D. J. Klauber, K. Leslie, C. Macleod, R. E. Meadows, K. R. Mulholland, J. Reilly, C. Squire, S. Tomasi, D. Watt, A. S. Wells, Org. Process Res. Dev., 2013, 17, (9), 1123 LINK https://doi.org/10.1021/op400133d
M. Fuchs, J. E. Farnberger, W. Kroutil, Eur. J. Org. Chem., 2015, (32), 6965 LINK https://doi.org/10.1002/ejoc.201500852
S. A. Kelly, S. Pohle, S. Wharry, S. Mix, C. C. R. Allen, T. S. Moody, B. F. Gilmore, Chem. Rev., 2017, 118, (1), 349 LINK https://doi.org/10.1021/acs.chemrev.7b00437
L. Leipold, D. Dobrijevic, J. W. E. Jeffries, M. Bawn, T. S. Moody, J. M. Ward, H. C. Hailes, Green Chem., 2019, 21, (1), 75 LINK https://doi.org/10.1039/c8gc02986e
E. Busto, R. C. Simon, B. Grischek, V. Gotor-Fernández, W. Kroutil, Adv. Synth. Catal., 2014, 356, (9), 1937 LINK https://doi.org/10.1002/adsc.201300993
A. P. Green, N. J. Turner, E. O’Reilly, Angew. Chem. Int. Ed., 2014, 53, (40), 10714 LINK https://doi.org/10.1002/anie.201406571
D. Baud, N. Ladkau, T. S. Moody, J. M. Ward, H. C. Hailes, Chem. Commun., 2015, 51, (97), 17225 LINK https://doi.org/10.1039/c5cc06817g
A. Gomm, W. Lewis, A. P. Green, E. O’Reilly, Chem. Eur. J., 2016, 22, (36), 12692 LINK https://doi.org/10.1002/chem.201603188
A. Gomm, S. Grigoriou, C. Peel, J. Ryan, N. Mujtaba, T. Clarke, E. Kulcinskaja, E. O’Reilly, Eur. J. Org. Chem., 2018, (38), 5282 LINK https://doi.org/10.1002/ejoc.201800799
I. Slabu, J. L. Galman, C. Iglesias, N. J. Weise, R. C. Lloyd, N. J. Turner, Catal. Today, 2018, 306, 96 LINK https://doi.org/10.1016/j.cattod.2017.01.025
R. Cairns, A. Gomm, C. Peel, M. Sharkey, E. O’Reilly, ChemCatChem, 2019, 11, (19), 4738 LINK https://doi.org/10.1002/cctc.201901430
C. A. McKenna, M. Štiblariková, I. De Silvestro, D. J. Campopiano, A. L. Lawrence, Green Chem., 2022, 24, (5), 2010 LINK https://doi.org/10.1039/d1gc02387j
P. D. Brown, A. C. Willis, M. S. Sherburn, A. L. Lawrence, Angew. Chem. Int. Ed., 2013, 52, (50), 13273 LINK https://doi.org/10.1002/anie.201307875
U. Kaulmann, K. Smithies, M. E. B. Smith, H. C. Hailes, J. M. Ward, Enzyme Microb. Technol., 2007, 41, (5), 628 LINK https://doi.org/10.1016/j.enzmictec.2007.05.011
L. Cerioli, M. Planchestainer, J. Cassidy, D. Tessaro, F. Paradisi, J. Mol. Catal. B: Enzym., 2015, 120, 141 LINK https://doi.org/10.1016/j.molcatb.2015.07.009
R. Roddan, E. M. Carter, B. Thair, H. C. Hailes, Nat. Prod. Rep., 2022, 39, (7), 1375 LINK https://doi.org/10.1039/d2np00008c
A. Fryszkowska, P. N. Devine, Curr. Opin. Chem. Biol., 2020, 55, 151 LINK https://doi.org/10.1016/j.cbpa.2020.01.012
M. A. Huffman, A. Fryszkowska, O. Alvizo, M. Borra-Garske, K. R. Campos, K. A. Canada, P. N. Devine, D. Duan, J. H. Forstater, S. T. Grosser, H. M. Halsey, G. J. Hughes, J. Jo, L. A. Joyce, J. N. Kolev, J. Liang, K. M. Maloney, B. F. Mann, N. M. Marshall, M. McLaughlin, J. C. Moore, G. S. Murphy, C. C. Nawrat, J. Nazor, S. Novick, N. R. Patel, A. Rodriguez-Granillo, S. A. Robaire, E. C. Sherer, M. D. Truppo, A. M. Whittaker, D. Verma, L. Xiao, Y. Xu, H. Yang, Science, 2019, 366, (6470), 1255 LINK https://doi.org/10.1126/science.aay8484
Catherine McKenna thanks the Engineering & Physical Sciences Research Council (EPSRC Centre for Doctoral Training in Critical Resource Catalysis (CRITICAT), EP/L016419/1); the authors thank The School of Chemistry, University of Edinburgh, UK; and Kimberley Dodds thanks Johnson Matthey, UK, for funding.
Kimberley Dodds graduated from the University of Edinburgh, UK, in 2021 with an MChem (Hons) in Medicinal and Biological Chemistry. Since 2021 Kimberley has been studying for her PhD in the biocatalysis field within the Campopiano and Lawrence groups working on amine donors for transaminase (TA) biocatalysis. This work is funded by Johnson Matthey, UK.
Catherine McKenna graduated from the University of Edinburgh in 2017 with an MChem (Hons) in Medicinal and Biological Chemistry, whilst carrying out her industrial placement at GSK, UK. From 2017–2021 Catherine carried out her PhD in the Campopiano and Lawrence groups on amine donors for TA biocatalysis. Catherine joined Almac group biocatalysis in 2021.
Beatriz Domínguez gained her PhD in Synthetic Organic Chemistry from the University of Vigo, Spain, and then moved to the UK where she worked with Professor Tom Brown at the University of Southampton, UK, and with Professor Guy Lloyd-Jones at the University of Bristol, UK. In 2002 she joined Synetix, soon to become part of Johnson Matthey and has worked at Johnson Matthey’s facilities in Cambridge since. Beatriz has gained broad experience in the application of metal catalysis and biocatalysis, working closely with fine chemicals companies to deliver optimal catalysts for chemical processes.
Andrew Lawrence completed his undergraduate studies at the University of Oxford, St John’s College, UK (2006) and subsequently obtained a DPhil degree in 2010 under the supervision of Professor Sir Jack Baldwin FRS and Professor Rob Adlington. Andy then moved to Australia to spend two years as a postdoctoral research fellow with Professor Mick Sherburn at the Australian National University (ANU) in Canberra. In 2012, Andy began an Australian Research Council Discovery Early Career Researcher Award (DECRA) Fellowship at the ANU before moving back to the UK in 2013 for an academic position at the University of Edinburgh. He is now full Professor (Chair of Organic Synthesis) at the University of Edinburgh.
Dominic Campopiano completed his undergraduate studies at the University of Glasgow, UK, before moving to the University of Edinburgh for his PhD. This was followed by a three-year postdoctoral position at the University of Leicester, UK, and another three years back at the University of Edinburgh before being promoted to Lecturer in 1998. In 2006 Dominic became a Royal Society of Edinburgh/Scottish Executive Research Fellow and was subsequently promoted to Reader in 2013 and most recently to Professor of Industrial Biocatalysis in 2015. He is also a Fellow of the Royal Society of Chemistry.