Vinyl sulfonamide synthesis for irreversible tethering via a novel α-selenoether protection strategy

Article abstract of DOI:10.1039/c8md00566d

Vinyl sulfonamides are valuable electrophiles for targeted protein modification and inhibition. We describe a novel approach to the synthesis of terminal vinyl sulfonamides which uses mild oxidative conditions to induce elimination of an α-selenoether masking group. The method complements traditional synthetic approaches and typically yields vinyl sulfonamides in high purity after aqueous work-up without requiring column chromatography of the final electrophilic product. The methodology is applied to the synthesis of covalent fragments for use in irreversible protein tethering and crucially enables the attachment of diverse fragments to the vinyl sulfonamide warhead via a chemical linker. Using thymidylate synthase as a model system, ethylene glycol is identified as an effective linker for irreversible protein tethering.

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RESEARCH ARTICLE
Vinyl sulfonamide synthesis for irreversible
tethering via a novel α-selenoether protection
strategy†
Cite this: DOI: 10.1039/
c8md00566d
Gregory B. Craven, a Dominic P. Affron,‡a Philip N. Raymond,a
a
David J. Mann b and Alan Armstrong
*
Vinyl sulfonamides are valuable electrophiles for targeted protein modification and inhibition. We describe
a novel approach to the synthesis of terminal vinyl sulfonamides which uses mild oxidative conditions to in-
duce elimination of an α-selenoether masking group. The method complements traditional synthetic ap-
proaches and typically yields vinyl sulfonamides in high purity after aqueous work-up without requiring col-
umn chromatography of the final electrophilic product. The methodology is applied to the synthesis of
covalent fragments for use in irreversible protein tethering and crucially enables the attachment of diverse
fragments to the vinyl sulfonamide warhead via a chemical linker. Using thymidylate synthase as a model
system, ethylene glycol is identified as an effective linker for irreversible protein tethering.
Received 16th November 2018,
Accepted 11th December 2018
DOI: 10.1039/c8md00566d
rsc.li/medchemcomm
target cysteine with high specificity. Terminal vinyl sulfon-
amides form stable protein adducts and are found in cova-
Introduction
Protein-reactive small molecules are being widely employed to
probe and modulate biological systems.1–3 These covalent
probes contain a reactive warhead that modifies the protein
and a specificity element, which selectively directs the war-
head to the target protein. To facilitate the design of such
probes, covalent fragments can be screened against recombi-
nant proteins using mass spectrometry and fluorescence-
based tethering methodologies as well as in biochemical as-
says to identify chemical starting points for ligand
optimisation.4–9 Alternatively, covalent fragments can be di-
rectly applied to cell-based disease models to identify new
protein targets through activity-based protein profiling
strategies.10–12 To maximise the efficiency of these ap-
proaches, libraries of covalent fragments are required which
contain chemical diversity of both the warhead and specificity
element. As such, methodologies that enable the synthesis of
new covalent fragments are of great importance.
lent inhibitors of multiple protein classes including
deubiquitylating enzymes (USP7 inhibitor),16 GTPases
(KRasIJG12C) inhibitor)17 and kinases (ERK2 and BTK inhibi-
tors)18,19 (Fig. 1). Relative to acrylamides, vinyl sulfonamides
are more electrophilic and therefore display a higher degree
of reactivity towards nucleophilic amino acids, making them
desirable warheads for targeting non-catalytic cysteine resi-
dues.20 Indeed, it has recently been shown that vinyl sulfon-
amides can undergo selective reaction with lysine residues
via an aza-Michael addition, offering the potential to target a
wide range of protein sites.21 Apart from their potential in co-
valent therapeutics, vinyl sulfonamides have also emerged as
The choice of reactive warhead is crucial to the success of
any covalent ligand approach and Michael acceptors, such as
vinyl sulfonamides,13 vinyl sulfones14 and acrylamides,15 can
a Department of Chemistry, Imperial College London, Molecular Sciences Research
Hub, White City Campus, Wood Lane, London W12 0BZ, UK.
E-mail: a.armstrong@imperial.ac.uk
b Department of Life Sciences, Imperial College London, South Kensington
Campus, London SW7 2AZ, UK
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c8md00566d
Fig. 1 Structures of terminal vinyl sulfonamide containing protein
‡ Equal contribution.
inhibitors.
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attractive reagents for chemical biology applications, being
used in the preparation of antibody–drug conjugates
(ADCs),22 in disulfide stapling,21 as chemical genetics
probes23 and for the specific introduction of fluorophores
and enrichment tags into proteins and peptides.24,25
Scheme
2
Proposed sulfonylation reagent
1
is inaccessible via
chlorination of sulfonate salt 2 due to rapid SO2 elimination.
We have previously reported methodology for synthesising
acrylamide fragment libraries26 but the synthesis of terminal
vinyl sulfonamides presents distinct challenges. The relatively
high electrophilicity of vinyl sulfonamides makes them in-
compatible with many reaction conditions and nucleophilic
functional groups and therefore late stage installation is gen-
erally required. However, vinyl sulfonamide formation is of-
ten characterised by poor substrate scope and low yields be-
cause the vinyl sulfonylation reagents (2-haloethane-1-sulfonyl
chloride or vinyl sulfonyl chloride) can undergo extensive
side reactions (Scheme 1).27 Unfortunately, the vinyl sulfon-
amide products themselves are often prone to polymerization
during silica gel chromatography which makes the removal
of such side-products challenging.28 We therefore investi-
gated an alternative route that would enable vinyl sulfon-
amide formation under mild conditions and in sufficient pu-
rity for use in biological assays without the need for column
chromatography. To achieve this, we looked to explore
whether vinyl sulfonamides could be masked as
α-selenoether ethyl sulfonamides and then be liberated un-
der mild oxidative conditions by in situ syn-elimination of the
resultant selenoxide, a strategy which has been successful in
acrylamide synthesis.29,30
phenomenon which has previously been documented for
similar thioether analogues.31
To circumvent this, a stepwise strategy was implemented
in which the amine substrate 4 is first sulfonylated with
1-bromoethane-1-sulfonyl chloride and then the bromide
displaced with phenyl selenide (Scheme 3a). The resulting
selenoether 6 is stable towards column chromatography or
further functionalisation and can be readily converted into
the corresponding vinyl sulfonamide 7 by treatment with the
mild oxidant sodium metaperiodate. As a proof of concept,
4-aminopiperidine 4a was taken through the reaction se-
quence (Scheme 3b): sulfonylation gave sulfonamide 5a in
high yield which successfully underwent selenide displace-
ment to give selenoether 6a. Pleasingly, oxidation with so-
dium metaperiodate gave vinyl sulfonamide 7a in excellent
purity (<95%) after a simple aqueous work up to remove the
water soluble by-products.
To investigate the synthetic utility of the method, attempts
were made to further functionalise intermediate 6a before
unmasking the vinyl moiety. The selenoether protecting
group was found to be compatible with t-butyl carbamate
Results and discussion
Synthesis of vinyl sulfonamides via α-selenoether oxidation
It was anticipated that the most direct route of preparing
α-selenoether ethyl sulfonamides precursors would be
through direct amine sulfonylation with the proposed sulfo-
nyl chloride reagent 1 (Scheme 2). Unfortunately, all efforts
to generate this key reagent from its parent sulfonate salt 2
were unsuccessful: desulfonylation to give alkyl chloride 3
was observed even under cryogenic chlorination conditions, a
Scheme
3 Synthesis of terminal vinyl sulfonamides. (a) General
Scheme
1
Strategies for the preparation of terminal vinyl
scheme and reaction conditions; (b) proof-of-concept study using 4-
sulfonamides.
aminopiperidine 4a and (c) substrate scope.
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deprotection and acetylation conditions, yielding N-acetyl sul-
fonamide 6b which was successfully converted into the corre-
sponding vinyl sulfonamide 7b, all in high yields.
Next, the scope of the main reaction sequence was evalu-
ated (Scheme 3c). Unfortunately, low yields were generally ob-
served for the selenide displacement step (ii), where an
unwanted proto-debrominated side product was typically ob-
served. However, both the sulfonylation (i) and oxidation (iii)
reactions proceeded well with aryl, alkyl and benzyl
substituted amines, yielding a diverse collection of terminal
vinyl sulfonamides with desirable fragment-like properties
(7c–g).
Fig. 2 Chemical linker approach for irreversible tethering.
It should be noted that for certain substrates, such as
indoline 5h, proto-debromination during the selenide dis-
placement step appeared to dominate the reaction and the
desired product (6h) could not be isolated (Scheme 4). This
unreliable transformation was expected to limit the synthetic
utility of the methodology with regards to library develop-
ment. However, we postulated that incorporation a chemical
linker between the fragment and vinyl sulfonamide function-
alities would allow the selenoether protecting group to be
installed prior to the fragment, enabling the synthesis of
each library member in two robust steps.
ylic acid functionalised scaffold was desired so that amine
fragments could be easily incorporated by amide bond
coupling.
To investigate the effect of linker length, two PEG-linked
scaffolds 13 (n = 1) and 14 (n = 2) were examined (Scheme 5).
N-Terminal functionalisation of the PEG linkers was achieved
by sequential sulfonylation and selenide displacement of
amines 9 and 10 to give alcohols 11 and 12 in reasonable
yields. Then the O-termini were capped with the versatile car-
boxylic acid functionality by alkylation of alcohols 11 and 12
with bromoacetic acid in excellent yields.
With the key intermediates 13 and 14 in hand, a variety of
amine fragments were converted into PEG-linked vinyl sul-
fonamides using a simple two step procedure. First, amide
bond formation was effected using either Lewis acid catalysis
with ZrCp2Cl2 (15a–c and 16a–b) or using stoichiometric acti-
vation with HATU (16d–f) (Scheme 6). Secondly, oxidation
with NaIO4 generated the vinyl sulfonamide, typically in suffi-
cient purity after aqueous work up that chromatography was
not required. Pleasingly, the methodology proved successful
for both PEG-linked scaffolds across a range of amine sub-
strates, including alkyl and aryl examples. Crucially, by pre-
installing the α-selenoether functionality into the linker, this
strategy generates each product in two reliable steps.
Synthesis of PEG-linked vinyl sulfonamide fragments
Irreversible tethering has emerged as an attractive method
for screening irreversible cysteine reactive-fragments against
recombinant proteins.32–34 Typically, libraries of electrophilic
fragments are incubated with the target protein and the de-
gree of protein modification is monitored by intact-protein
mass spectrometry (Fig. 2a). It was anticipated that incorpo-
ration of a flexible chemical linker between the vinyl sulfon-
amide warhead and the fragment could also enable effective
irreversible tethering if the linker allows the warhead to
adopt a cysteine-reactive conformation in the protein–ligand
complex (Fig. 2b). An appropriately designed chemical linker
would (1) make the library synthesis more efficient by incor-
porating the α-selenoether functionality prior to fragment in-
stallation, (2) facilitate efficient template-guided reactivity by
allowing access to a large number of reactive conformations
upon fragment coordination and (3) normalize the reactivity
of the vinyl sulfonamide warhead by insulating it from steric
and electronic influence of the fragment. PolyIJethylene)glycol
(PEG) was selected as a suitable linker because it is flexible,
resistant to nonspecific protein binding and confers en-
hanced aqueous solubility relative to alkyl linkers.35 A carbox-
Applying the chemical linker strategy to irreversible tethering
To investigate whether fragment binding can induce kinetic-
template guided tethering in the context of these PEG-linked
vinyl sulfonamide scaffolds, proof of concept experiments
were performed on thymidylate synthase (TS). Fragments de-
rived from N-tosyl D-proline are well characterised binders of
TS.36 In previous work, we have demonstrated that the cata-
lytic cysteine of TS reacts selectively with an acrylamide
Scheme
4 Attempted selenide displacement resulted in proto-
debrominated product.
Scheme 5 Preparation of carboxylic acid functionalised PEG linkers.
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cases, indicated by a low intensity peak for the native protein.
In the case of the longer linker (n = 2), the adduct corre-
sponding to labeling by negative control 16a (30 752 Da) had
equal intensity to the positive control 16b adduct (30 899 Da),
which indicates no kinetic template rate acceleration and this
modification probably corresponds to background reactivity.
Pleasingly, however, for the shorter linker (n = 1) tethering by
the positive control 15b occurred at a faster rate than the
negative control 15a, demonstrating that significant
template-guided rate enhancement was in operation.
For the positive controls 15a and 16a, the spacing between
the terminal vinyl carbon and the tosyl sulfonamide function-
alities are 13.4 Å and 16.0 Å respectively. Analysis of the previ-
ously published crystal structure of the N-tosyl D-proline frag-
ment in complex with TS (PDB: 1F4E) reveals that there is
only a 7.1 Å spacing between the reactive thiol of Cys146 and
the tosyl sulfonamide functionality of the bound fragment
and we attribute the observed selectivity for the shorter linker
to its closer match to this separation. We hypothesise that
the PEG(n = 2) linker is too long to enable an efficient reac-
tion once the fragment has bound into the active site of TS
which would account for the lack of positive/negative control
selectivity. However, we note that for proteins for which the
reactive cysteine residue lies further outside of the binding
pocket, such a long scaffold may be required for efficient
labelling.
Scheme 6 Two step synthesis of PEG-linked vinyl sulfonamides. *Am-
ide coupling by method A or B.
Since the PEG(n = 1) scaffold gave encouraging results in
the KTGT assay, a kinetic investigation was carried out to de-
termine whether the PEG(n = 1) linker is effective at normal-
izing the intrinsic reactivity of the vinyl sulfonamide war-
head. When investigating acrylamide reactivity for our
previously published study on KTGT, 1,3,4-thiadiazole-based
acrylamide 17 was identified as highly reactive and was there-
fore removed from the screening library.33 It was anticipated
that the PEG-linker would insulate the warhead from the
electronic properties of the fragment such that vinyl sulfon-
amides 15a, 15b and 15c would have similar intrinsic
reactivities.
functionalised N-tosyl D-proline fragment in the presence of
other acrylamides including benzyl acrylamide.33 Therefore
for this study, N-tosyl D-proline linked vinyl sulfonamides 15b
and 16b would serve as positive controls while benzyl linked
vinyl sulfonamides 15a and 16a as negatives.
Therefore thymidylate synthase was incubated separately
with binary mixtures of the positive and negative PEG-linked
vinyl sulfonamides and the reactions analyzed by mass
spectrometry (Fig. 3). After thirty minutes thorough modifica-
tion of thymidylate synthase had been achieved in both
In order to determine the intrinsic reactivity of electrophiles
towards conjugate thiol addition, an NMR-based rate study
was carried out, using a published procedure.32 Accordingly,
vinyl sulfonamides 15a, 15b and 15c were each reacted with ex-
cess N-acetyl cysteine methyl ester in a deuterated buffer sys-
tem and the concentration of the electrophile was monitored
1
over time by H NMR spectroscopy. As the electrophile is the
limiting reagent, the pseudo-first-order rate constant (kobs) was
extracted by plotting the natural logarithm of the electrophile
concentration over time (Scheme 7 and Fig. S1†).
The effectiveness of the linker is evident as only a 1.5
fold difference in reactivity was observed between least re-
active and most reactive fragments, with an average
pseudo-first-order rate constant of 3.77 × 10−3 s−1. Indeed,
1,3,4-thiadiazole 15c reacted most slowly of the three
electrophiles, which highlights that this linker will allow
screening of fragments that were previously thought of as
hyper reactive.
Fig. 3 Testing PEG-linked vinyl sulfonamides against TS. TS (10 μM)
was incubated with a mixture of positive control and negative control
ligands (each at 100 μM) and analyzed by intact protein mass spectro-
metry after 30 minutes. (a) Testing PEG(n = 1) ligands 15a and 15a (b)
testing PEG(n = 2) ligands 16a and 16b.
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spectra were deconvoluted with maximum entropy software
from Waters. Maximum entropy deconvolutions were
performed with a mass step of 1 over a minimum of 4 charge
states.
NMR rate study
To a 550 μL solution of N-acetyl cysteine methyl ester (94
mM) and internal standard dichloromethane (12 mM) in 4 : 1
deuterated PBS:DMSO-d6 was added 110 μL of electrophile
(60 mM) in DMSO-d6. The resulting solution was analyzed
1
immediately by H NMR, capturing spectra every 20 seconds
for 5 minutes. All spectra were phase and baseline corrected
using MestReNova before analysis. The integration of the vi-
nyl peaks relative to the dichloromethane peak was used to
monitor the electrophile concentration. The pseudo-first-
order rate constant was calculated from the linear gradient of
the natural logarithm of the electrophile concentration over
time. Deuterated PBS recipe: 20 mM Na3PO4, 50 mM NaCl in
D2O was adjusted to pD 8 with DCl solution.
Scheme 7 (a) NMR rate study. Vinyl sulfonamides (10 mM) were
reacted with N-acetyl cysteine methyl ester (78 mM) and the rate of
reaction monitored by 1H NMR spectroscopy. (b) Comparison of un-
linked and linker thiadiazole fragments for irreversible tethering.
Conflicts of interest
Conclusions
There are no conflicts to declare.
Incorporation of a linker into the KTGT construct is neces-
sary to provide a more robust screening assay and is expected
to advance this methodology by allowing fragments greater
flexibility for protein binding. Herein we have described a
novel methodology for the synthesis of terminal vinyl sulfon-
amide fragments and demonstrated its application to the
synthesis of unlinked and linked electrophilic fragments.
Ethylene glycol linked vinyl sulfonamides were found to have
homogeneous intrinsic reactivity and provide positive/nega-
tive selectivity in the KTGT assay. In addition, the linker was
able to modulate the reactivity of electrophiles that were pre-
viously considered unusable in libraries. The developed syn-
thetic route will allow the creation of large vinyl sulfonamide
linked fragment libraries, as incorporation of amine frag-
ments can be achieved in two robust steps.
Acknowledgements
This work was supported by grants from the Institute of
Chemical Biology (Imperial College London), the UK Engi-
neering and Physical Sciences Research Council (Studentship
award EP/F500416/1), Biotechnology and Biological Sciences
Research Council (Studentship award BB/J014575/1).
References
1 K. M. Backus, B. E. Correia, K. M. Lum, S. Forli, B. D.
Horning, G. E. González-Páez, S. Chatterjee, B. R. Lanning,
J. R. Teijaro, A. J. Olson, D. W. Wolan and B. F. Cravatt,
Nature, 2016, 534, 570–574.
2 D. S. Johnson, E. Weerapana and B. F. Cravatt, Future Med.
Chem., 2010, 2, 949–964.
Experimental
3 R. Schulz, A. Atef, D. Becker, F. Gottschalk, C. Tauber, S.
Wagner, C. Arkona, A. A. Abdel-Hafez, H. H. Farag, J.
Rademann and G. Wolber, J. Med. Chem., 2018, 61,
1218–1230.
Synthesis
All synthetic procedures and characterisation data are found
in the ESI.†
4 S. G. Kathman and A. V. Statsyuk, MedChemComm, 2016, 7,
576–585.
Protein labelling experiments
Thymidylate synthase (recombinantly expressed, 10 μM) in
ammonium bicarbonate (10 mM) and DTT (1 mM) solution
was treated with binary mixtures of ligands (15a + 15b) or
(16a + 16b) each at 100 μM and incubated at rt. The reactions
were analyzed by intact protein ESI mass spectrometry after
30 minutes: to a 25 μL aliquot of the reaction, 0.5% formic
acid (50 μL) and MeOH (50 μL) were added and the mixture
injected onto a Micromass LCT Premier mass spectrometer
at 30 μL min−1. Data was collected in the m/z range 500–2500
in positive ion mode using electrospray ionization and the
5 G. B. Craven, D. P. Affron, C. E. Allen, S. Matthies, J. G.
Greener, R. M. L. Morgan, E. W. Tate, A. Armstrong and D. J.
Mann, Angew. Chem., Int. Ed., 2018, 57, 5257–5261.
6 D. Becker, Z. Kaczmarska, C. Arkona, R. Schulz, C. Tauber,
G. Wolber, R. Hilgenfeld, M. Coll and J. Rademann, Nat.
Commun., 2016, 7, 12761.
7 R. M. Miller, V. O. Paavilainen, S. Krishnan, I. M. Serafimova
and J. Taunton, J. Am. Chem. Soc., 2013, 135, 5298–5301.
8 D. A. Erlanson, J. A. Wells and A. C. Braisted, Annu. Rev.
Biophys. Biomol. Struct., 2004, 33, 199–223.
This journal is © The Royal Society of Chemistry 2018
Med. Chem. Commun.

View Article Online
Research Article
MedChemComm
9 D. Becker, Z. Kaczmarska, C. Arkona, R. Schulz, C. Tauber,
G. Wolber, R. Hilgenfeld, M. Coll and J. Rademann, Nat.
Commun., 2016, 7, 12761.
10 L. A. Bateman, T. B. Nguyen, A. M. Roberts, D. K. Miyamoto,
W.-M. Ku, T. R. Huffman, Y. Petri, M. J. Heslin, C. M.
Contreras, C. F. Skibola, J. A. Olzmann and D. K. Nomura,
Chem. Commun., 2017, 53, 7234–7237.
20 M. E. Flanagan, J. A. Abramite, D. P. Anderson, A.
Aulabaugh, U. P. Dahal, A. M. Gilbert, C. Li, J. Montgomery,
S. R. Oppenheimer, T. Ryder, B. P. Schuff, D. P. Uccello,
G. S. Walker, Y. Wu, M. F. Brown, J. M. Chen, M. M.
Hayward, M. C. Noe, R. S. Obach, L. Philippe, V.
Shanmugasundaram, M. J. Shapiro, J. Starr, J. Stroh and Y.
Che, J. Med. Chem., 2014, 57, 10072–10079.
11 L. Bar-Peled, E. K. Kemper, R. M. Suciu, E. V. Vinogradova,
K. M. Backus, B. D. Horning, T. A. Paul, T.-A. Ichu, R. U.
Svensson, J. Olucha, M. W. Chang, B. P. Kok, Z. Zhu, N. T.
Ihle, M. M. Dix, P. Jiang, M. M. Hayward, E. Saez, R. J. Shaw
and B. F. Cravatt, Cell, 2017, 171, 696–709.
21 Z. Li, R. Huang, H. Xu, J. Chen, Y. Zhan, X. Zhou, H. Chen
and B. Jiang, Org. Lett., 2017, 19, 4972–4975.
22 R. Huang, Z. Li, Y. Sheng, J. Yu, Y. Wu, Y. Zhan, H. Chen
and B. Jiang, Org. Lett., 2018, 20, 6526–6529.
23 A. L. Garske, U. Peters, A. T. Cortesi, J. L. Perez and K. M.
Shokat, Proc. Natl. Acad. Sci. U. S. A., 2011, 108,
15046–15052.
12 J. L. Counihan, A. L. Wiggenhorn, K. E. Anderson and D. K.
Nomura, ACS Chem. Biol., 2018, 13, 1970–1977.
13 W. R. Roush, J. Cheng, B. Knapp-Reed, A. Alvarez-
Hernandez, J. H. McKerrow, E. Hansell and J. C. Engel,
Bioorg. Med. Chem. Lett., 2001, 11, 2759–2762.
24 R. Huang, Z. Li, P. Ren, W. Chen, Y. Kuang, J. Chen, Y.
Zhan, H. Chen and B. Jiang, Eur. J. Org. Chem., 2018, 2018,
829–836.
14 S. Y. Woo, J. H. Kim, M. K. Moon, S.-H. Han, S. K. Yeon,
J. W. Choi, B. K. Jang, H. J. Song, Y. G. Kang, J. W. Kim, J.
Lee, D. J. Kim, O. Hwang and K. D. Park, J. Med. Chem.,
2014, 57, 1473–1487.
15 P. A. Jackson, J. C. Widen, D. A. Harki and K. M.
Brummond, J. Med. Chem., 2017, 60, 839–885.
16 A. P. Turnbull, S. Ioannidis, W. W. Krajewski, A. Pinto-
Fernandez, C. Heride, A. C. L. Martin, L. M. Tonkin, E. C.
Townsend, S. M. Buker, D. R. Lancia, J. A. Caravella, A. V.
Toms, T. M. Charlton, J. Lahdenranta, E. Wilker, B. C.
Follows, N. J. Evans, L. Stead, C. Alli, V. V. Zarayskiy, A. C.
Talbot, A. J. Buckmelter, M. Wang, C. L. McKinnon, F. Saab,
J. F. McGouran, H. Century, M. Gersch, M. S. Pittman, C. G.
Marshall, T. M. Raynham, M. Simcox, L. M. D. Stewart, S. B.
McLoughlin, J. A. Escobedo, K. W. Bair, C. J. Dinsmore, T. R.
Hammonds, S. Kim, S. Urbé, M. J. Clague, B. M. Kessler and
D. Komander, Nature, 2017, 550, 481–486.
25 H. Chen, R. Huang, Z. Li, W. Zhu, J. Chen, Y. Zhan and B.
Jiang, Org. Biomol. Chem., 2017, 15, 7339–7345.
26 C. E. Allen, P. R. Curran, A. S. Brearley, V. Boissel, L.
Sviridenko, N. J. Press, J. P. Stonehouse and A. Armstrong,
Org. Lett., 2015, 17, 458–460.
27 C. S. Rondestvedt, J. Am. Chem. Soc., 1954, 76, 1926–1929.
28 J. Sinha, M. Podgórski, S. Huang and C. N. Bowman, Chem.
Commun., 2018, 54, 3034–3037.
29 K. B. Sharpless, R. F. Lauer and A. Y. Teranishi, J. Am. Chem.
Soc., 1973, 95, 6137–6139.
30 S.-R. Sheng, X.-C. Wang, X.-L. Liu and C.-S. Song, Synth.
Commun., 2003, 33, 2867–2872.
31 J. F. King and K. C. Khemani, Can. J. Chem., 1985, 63,
619–622.
32 S. G. Kathman, Z. Xu and A. V. Statsyuk, J. Med. Chem.,
2014, 57, 4969–4974.
33 R. H. Nonoo, A. Armstrong and D. J. Mann, ChemMedChem,
2012, 7, 2082–2086.
34 R. Cardoso, R. Love, C. L. Nilsson, S. Bergqvist, D. Nowlin, J.
Yan, K. K.-C. Liu, J. Zhu, P. Chen, Y.-L. Deng, H. J. Dyson,
M. J. Greig and A. Brooun, Protein Sci., 2012, 21, 1885–1896.
35 K. L. Prime and G. M. Whitesides, J. Am. Chem. Soc.,
1993, 115, 10714–10721.
36 D. A. Erlanson, A. C. Braisted, D. R. Raphael, M. Randal,
R. M. Stroud, E. M. Gordon and J. A. Wells, Proc. Natl. Acad.
Sci. U. S. A., 2000, 97, 9367–9372.
17 J. M. Ostrem, U. Peters, M. L. Sos, J. A. Wells and K. M.
Shokat, Nature, 2013, 503, 548–551.
18 R. A. Ward, N. Colclough, M. Challinor, J. E. Debreczeni, K.
Eckersley, G. Fairley, L. Feron, V. Flemington, M. A. Graham,
R. Greenwood, P. Hopcroft, T. D. Howard, M. James, C. D.
Jones, C. R. Jones, J. Renshaw, K. Roberts, L. Snow, M.
Tonge and K. Yeung, J. Med. Chem., 2015, 58, 4790–4801.
19 X. Li, Y. Zuo, G. Tang, Y. Wang, Y. Zhou, X. Wang, T. Guo, M.
Xia, N. Ding and Z. Pan, J. Med. Chem., 2014, 57, 5112–5128.
Med. Chem. Commun.
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