Synthesis and Evaluation of Non-Hydrolyzable Phospho-Lysine Peptide Mimics

Article abstract of DOI:10.1002/chem.202003947

The intrinsic lability of the phosphoramidate P?N bond in phosphorylated histidine (pHis), arginine (pHis) and lysine (pLys) residues is a significant challenge for the investigation of these post-translational modifications (PTMs), which gained attention rather recently. While stable mimics of pHis and pArg have contributed to study protein substrate interactions or to generate antibodies for enrichment as well as detection, no such analogue has been reported yet for pLys. This work reports the synthesis and evaluation of two pLys mimics, a phosphonate and a phosphate derivative, which can easily be incorporated into peptides using standard fluorenyl-methyloxycarbonyl- (Fmoc-)based solid-phase peptide synthesis (SPPS). In order to compare the biophysical properties of natural pLys with our synthetic mimics, the pK_a values of pLys and analogues were determined in titration experiments applying nuclear magnetic resonance (NMR) spectroscopy in small model peptides. These results were used to compute electrostatic potential (ESP) surfaces obtained after molecular geometry optimization. These findings indicate the potential of the designed non-hydrolyzable, phosphonate-based mimic for pLys in various proteomic approaches.

Full text of DOI:10.1002/chem.202003947

Accepted Article
Accepted Article
Title: Synthesis and evaluation of non-hydrolyzable phospho-lysine
peptide mimics
Authors: Anett Hauser, Eleftheria Poulou, Fabian Müller, Peter
Schmieder, and Christian Hackenberger
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
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content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.202003947
Link to VoR: https://doi.org/10.1002/chem.202003947
01/2020

10.1002/chem.202003947
Chemistry - A European Journal
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Synthesis and evaluation of non-hydrolyzable phospho-lysine
peptide mimics
Anett Hauser[a],[b], Eleftheria Poulou[a], Fabian Müller[b], Peter Schmieder[a], Christian P.R.
Hackenberger[a],[b],*
[a]
[b]
Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Robert-Rössle-Strasse 10, 13125 Berlin, Germany
Department of Chemistry, Humboldt-Universität zu Berlin, Brook-Taylor-Strasse 2, 12489 Berlin, Germany
* Corresponding author: Prof. Christian Hackenberger, hackenbe@fmp-berlin.de
Supporting information for this article is given via a link at the end of the document.
Abstract: The intrinsic lability of the phosphoramidate P–N bond
in phosphorylated histidine (pHis), arginine (pHis) and lysine
(pLys) residues is a significant challenge for the investigation of
these post-translational modifications (PTMs), which gained
attention rather recently. While stable mimics of pHis and pArg
have contributed to study protein substrate interactions or to
generate antibodies for enrichment as well as detection, no such
analogue has been reported yet for pLys. We herein report the
synthesis and evaluation of two pLys mimics, a phosphonate and
a phosphate derivative, which can easily be incorporated into
peptides using standard fluorenyl-methyloxycarbonyl- (Fmoc-)-
based solid-phase peptide synthesis (SPPS). In order to compare
the biophysical properties of natural pLys with our synthetic
mimics, we determined the pKa values of pLys and of the
analogues in titration experiments applying nuclear magnetic
resonance (NMR) spectroscopy in small model peptides. These
results were used to compute electrostatic potential (ESP)
surfaces obtained after molecular geometry optimization. Our
findings indicate the potential of our designed non-hydrolyzable,
phosphonate-based mimic for pLys in various proteomic
approaches.
intrinsic lability is particularly challenging. These specific
experimental requirements have to be met by adjustment of
existing cell extraction, enrichment protocols and MS techniques.
Recent reports on His and Arg phosphorylation demonstrate the
successful improvements of phospho-binding strategies including
TiO2,[3] immobilized metal affinity chromatography (IMAC),[4]
hydroxyapatite[5] or strong anion exchange (SAX),[6] despite the
fact that virtually no discrimination between various phospho-
species can be achieved with these methods. Besides that,
phospho-amino acid-specific protocols could be developed for
pHis and pArg employing stable analogues of the endogenous
phosphorylation. Such molecules were designed for the
generation of antibodies (Abs)[7] or to study interacting proteins.[8]
Among phosphoramidates, pLys is less studied and its role in the
cellular context remains to be examined. Detected in vivo already
in 1977, pLys has been reported as an acid-labile PTM of histone
H1[9] and only preliminary details on interacting proteins have
been published.[10] Despite recent documentations on incidental
pLys identification with phospho-specific enrichment techniques[5-
6]
and an indirect proof for the phosphorylation event via
derivatization,[11] no pLys-mimicking analogues suitable for Ab
generation or binding partner examination were obtained so far.
To enable the study of lysine phosphorylation, our group has
recently developed two different synthetic methods for the site-
selective synthesis of pLys peptides. Such peptides can be
obtained via the chemoselective Staudinger-phosphite reaction[12]
delivering either a photo-caged pLys in unprotected peptides[13] or
free phosphoramidates when combining a base-cleavable solid
support and base-labile phosphoramidate protecting groups[14]
(Figure 1A). With those model peptides in hand, the stability of
pLys under various pH and temperature conditions as well as
suitable tandem-MS techniques were investigated.[13, 15]
Introduction
Post-translational phosphorylation of proteins occurs on almost all
nucleophilic amino acid side chains.[1] Vast efforts, especially in
the area of phosphoproteomics, are undertaken to identify new
phosphorylation sites and advance the understanding of
underlying mechanisms of this most important post-translational
modification. For the highly abundant, acid-stable phosphate
esters of serine, threonine and tyrosine, (pSer, pThr, pTyr),
phospho-specific enrichment and
mass spectrometric-
To augment the box of chemical tools to study lysine
phosphorylation, we now propose two different Fmoc-protected
amino acid building blocks as stable pLys mimics, namely
phosphonate 1 and phosphate 2 (Figure 1B).
(MS-)based phosphoproteomic methods yielded thousands of
phosphorylation sites.[2] In contrast, acid-labile phosphorylations
are less explored and the chemical and temperature-related
1
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In order to evaluate the ability of our proposed mimics to serve as
pLys mimics, pKa values of peptides containing either 1, 2 or pLys
were determined in NMR titration experiments and the electron
densities visualized as electrostatic potential (ESP) maps. Our
findings demonstrate that both building blocks show sufficient
stability and can be incorporated into peptides by standard SPPS
in contrast to a phosphoramidate building block, which would
deliver the native pLys peptide.
with an improved pH and temperature stability profile. As both
building blocks were envisioned to be incorporated into peptides
by Fmoc-based SPPS and give free phosphonate or phosphate
directly upon cleavage from the solid support, we determined
acid-labile benzyl (Bn) groups as suitable for side chain protection.
Synthesis Phospho-Lysine Mimic Building Blocks for SPPS
The bis-Bn- and Fmoc-protected phosphonate building block 1
(Fmoc-hCys(OBn)2)-OH) was obtained as a thioether of Fmoc-
protected hCys (Scheme 1). First, vinylphosphonic acid was
converted into the benzyl ester in two steps to give vinyl-
phosphonate 4. Therefore, commercially available Fmoc-
hCys(Trt)-OH was deprotected under acidic conditions using 50%
trifluoroacetic acid (TFA), 2% triisopropylsilane (TIS) and 0.1%
ethanedithiol (EDT) in CH2Cl2. It became evident that short
reaction times, cooling of the reaction mixture and immediate
purification of the free thiol 5 were required to minimize cyclization
and thiolactone formation. For example, running the deprotection
for 30 minutes and purifying the reaction mixture after overnight
EDT evaporation yielded approximately 50% conversion to the
thiolactone. Under optimized conditions, 5 was isolated in 80%
yield with 6% thiolactone as side product. Conjugate addition of 4
to 5 at slightly basic pH 8.5 and elevated temperatures delivered
compound 1 in 68% yield.
Furthermore, the observed pKa value of phosphonate 1 points
towards the great potential of this analogue to be used as pLys
surrogate mimic in future applications, such as Ab generation and
substrate-protein interaction studies.
A. Previous Work
O
O
chemoselective synthesis
site-specifc installation
detection via MS/MS
✓
✓
✓
P
H2
N
N3
Chemoselective
Staudinger-phosphite
reaction
O
e
i
e
e
i
e
p
p
p
p
t
d
t
intrinsically acid labile
d
B. This Work
O
O
P
BnO
BnO
Two different
stable analogues
P
O
HO
BnO
S
Fmoc
OH
Fmoc
N
OH
stable mimics
N
✓
✓
H
H
O
O
suitable for SPPS
O
O
2
1
P
Y
O
Fmoc
SPPS
Fmoc
SPPS
X
e
i
e
p
p
X : S or CH2
Y : CH2 or O
t
d
Figure 1: A. pLys peptides can be obtained in directly from solid support or after
cleavage from resin in a two-step protocol. B. pLys analogues 1 and 2 can be
installed during SPPS to obtain acid-stable phosphonates (X: S, Y: CH2) or
phosphates (X: CH2, Y: O).
Results and Discussion
Design of Phospho-Lysine Analogues
Phosphoramidates contain a high energy P–N bond (ΔG° = –10.3
- –14 kcal/mol),[16] which translates in a decreased stability at
lower pH and higher temperatures. Presumably, pLys is prone to
hydrolysis due to the protonation of the ε-nitrogen (pKa of N-(n-
butyl) phosphoramidate is 9.9),[17] even though this value has
never been determined for pLys itself. Besides the unique charge
distribution illustrated in Figure 1A, the length of the alkyl side
chain is the most characteristic property of pLys. Therefore, we
envisioned two types of phosphorous derivatives to identify a
suitable pLys mimic (Figure 1B), which are both easily accessible:
The first derivative 1 exhibits a non-hydrolyzable phosphonate,
which would be obtained via a conjugate addition of alkene-
phosphonates with homocysteine (hCys).[18] The other analogue
2 is a phosphate monoester derived from 6-hydroxynorleucine
Scheme 1: Synthesis of phosphonate mimic 1. (i) (COCl)2, CH2Cl2, cat. DMF,
0 °C to rt., 19 h; (ii) BnOH, Et3N, THF, 0 °C to rt., 17 h; (iii) TFA/TIS/EDT/CH2Cl2
(50/2/0.1/47.9), 0 °C, 5 min; (iv) 50 mM NaHCO3/DMF (2/1), pH 8.5, 50 °C, 4 h;
(Bn
= benzyl, Ph = phenyl, Fmoc = fluorenylmethyloxycarbonyl, DMF=
dimethylformamide, THF = tetrahydrofuran, TFA = trifluoroacetic acid, TIS =
triisopropylsilane, EDT = 1,2-ethanedithiol).
Bn- and Fmoc-protected phosphate 2 could be obtained in a
convenient one-pot synthesis following a previously described
protocol for Bn-protected pSer, pThr and pTyr derivatives[19]
(Scheme 2). Starting from phosphorous trichloride, the first
chloride atom was exchanged with benzyl alcohol. Subsequent
reaction with commercially available Fmoc-Nle(6-OH)-OH
furnished the proposed, intermediate cyclic phosphite 6, which
2
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10.1002/chem.202003947
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was directly hydrolyzed and oxidized to yield the desired
to test whether a corresponding pLys building block would be
suitable for Fmoc-based SPPS. We hypothesized that the
electron-withdrawing Tc-protecting group would increase the
stability of the P–N bond against TFA treatment required for
peptide deprotection and cleavage. As shown in Scheme 4, the
Tc-protected pLys building block 3 was obtained starting from
benzyloxycarbonyl- (Cbz-)protected Lys, in which the acid was
first converted into the benzyl ester 9 before the protected
phosphoramidate 10 was formed via nucleophilic substitution with
compound 2 in 77% yield.
bis(2,2,2-trichloroethyl)
phosphorochloridate.
Change
of
Scheme 2: Synthesis of Fmoc-Nle(OPO(OH)(OBn))-OH 2. (i) BnOH, THF, 0 °C,
5 min; (ii) 2,6-lutidine, 0 °C to rt., 90 min; (iii) H2O, 0 °C, 5 min; (iv) NaBr,
NaBrO3, 0 °C to rt., 72 h; (Bn = benzyl, Fmoc = fluorenylmethyloxycarbonyl,
THF = tetrahydrofuran)
protecting groups to building block
3
was induced by
hydrogenation, in which acidic conditions were required to not
affect the Tc-protecting group, followed by reaction with Fmoc-
succinimide (Fmoc-OSu). Monomer
3 was obtained after
Peptide Synthesis with Phospho-Lysine Analogues
purification on silica column in 59% overall yield. Next, the
building block 3 was tested toward its performance in SPPS
analogous for building blocks 1 and 2 using HATU-coupling
conditions. While we were able to isolate the desired product 12,
we also observed substantial formation of side products (Fig. S1).
Furthermore, the deprotection of 12 to give the free
phosphoramidate was only possible to a certain extent under the
Next, we used both Fmoc-protected building blocks 1 and 2 in the
synthesis of tripeptides 8a and 8b (Scheme 3). To measure pKa
values for the phosphorous moiety in a peptidic system, we
synthesized 8 with a C-terminal amide, an N-terminal acetyl group,
a glycine and a UV-active Tyr residue. 1 and 2 (2 eq.) were
coupled using HATU ((1-[Bis(dimethylamino)methylene]-1H-
1,2,3-triazolo[4,5-b]pyridinium3-oxide-hexafluoro-phosphate) to
deliver peptides 7a and 7b on the solid support followed by
standard Fmoc-SPPS protocols. For the thioether-containing
peptide 8a, EDT and trimethylsilylbromide were added to the
cleavage cocktail to avoid oxidation to the sulfoxide.[20] Both
peptides 8a and 8b were obtained in good isolated yields, which
demonstrates the acid stability of these mimics as well as the
general applicability of building blocks 1 and 2 in standard Fmoc-
based SPPS.
previously
reported
hydrogenation
conditions
despite
considerable optimization efforts (Scheme 4).
Cl3C
Cl3C
Cl3C
O
O
O
O
NH2
P
P
NH
NH
O
O
Cl3C
iii
i, ii
Cbz
OH
N
OH
O
Cbz
OBn
H
H2N
N
O
H
O
9
+ Cl-PO(OCH2CCl3)2
11
74%
10
Cl3C
iv
Cl3C
O
O
P
O
O
NH
O
P
NH
Fmoc
SPPS
Cl3C
O
O
Cl3C
O
H
H
O
N
N
N
H
OH
Fmoc
OH
N
O
H
O
OH
3
12
59%
14%
v
R
HN
O
P
O
P
O
O
H
8d
R
O
O
O
O
H
H
N
8c
8e
O
N
N
OH
Ratio
(UPLC,
220 nm)
H
O
Scheme 3: Fmoc-based SPPS of peptides employing mimics 1 and 2.
1
1
3
OH
Furthermore, to compare the pKa values of 1- or 2-containing
peptides with pLys peptides, we also aimed to synthesize the
corresponding pLys peptide 8c (AcTyrpLysGlyCONH2). In light of the
successful Fmoc-based SPPS of pArg peptides using a bis(2,2,2-
trichloroethyl)- (Tc-)protected pArg building block,[21] we wanted
Scheme 4: Synthesis of Fmoc-Lys(NPO(OTc)2)-OH 3 and Fmoc-based SPPS
employing monomer 3. (i) SOCl2, BnOH neat, 0 °C to rt., 2 h; (ii) bis(2,2,2-
trichloroethyl) phosphorochloridate, Et3N, ACN, rt., 5 h; (iii) H2, Pd/C,
AcOH/TFA/MeOH (5/5/90), rt., 1 h; (iv) Fmoc-OSu, Et3N, H2O/ACN (1/1), rt.,
4 h; v) H2, 10% Pd/C, (NH4)2CO3 pH 8.0, EtOH, r.t, 2h, (Bn = benzyl, Cbz =
3
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benzyloxycarbonyl, Fmoc = fluorenylmethyloxycarbonyl, TFA = trifluoroacetic
Sampson reported the potentiometrically detected pKa values of
9.9 and 2.9 for N-(n-butyl)phosphoramidate for the protonation on
nitrogen and one phosphoryl oxygen, respectively,[17, 22] which
gave us an estimate for the pKa values of pLys. An elegant
technique for the pKa determination is NMR titration since this
acid, Su= succinimide)
While the desired peptide 8c was formed with maximum 20%
conversion and significant P–N bond cleavage to the lysine
peptide 8d was observed, the major fraction of detected product
was the mono-ethyl-protected intermediate 8e.
non-invasive
analytical
technique
enables
accurate
Because of these observations, we decided to synthesize peptide
8c following our chemoselective in solution protocol,[13] which
delivered peptide 8c in 45% yield, significantly higher than the
yield obtained with the Tc-protected pLys approach (see SI,
section 3.5). With the three peptides 8a-c in hand, we tested their
enzymatic stability against the promiscuous alkaline phosphatase
(ALP). The substrates 8a-c were tested for stability towards ALP
under optimized conditions. Briefly, 1 mM substrate was dissolved
in 50 mM Tris, 1 mM MgCl2, 1 mM ZnCl2, pH 8.2, at 30 °C and
was incubated with 0.05 U ALP for 2 h. and the amount of
released inorganic phosphate (Pi) was determined via
photometric read-out. ALP hydrolyzed the phosphoramidate bond
in 8c as expected, thereby demonstrating enzyme activity.
Furthermore, treatment of 8b with ALP yielded in a Pi release,
which indicated susceptibility of the phosphate analogue towards
phosphatases. To our delight, the phosphonate analogue 8a
remained intact when incubated with ALP, further verifying the
stability of this derivative against hydrolysis (Fig. S2).
measurements at desired temperatures at a given pH. Our
experimental set up was inspired by the NMR titration conducted
by Gamcsik et al. on phosphoramidic acid and other
phosphoramides.[23] Samples were prepared at
a
1 mM
concentration in 40 mM KCl (water + 10% deuterium oxide) and
kept at low temperature to minimize P–N bond hydrolysis for 8c.
The pH of each sample was adjusted before measurement and
checked again afterwards. Proton (1H), phosphorous (31P) 1D as
well as 1H-31P-heteronuclear multiple bond coupling (HMBC)
NMR spectra were recorded from pH 2 to pH 11 on a 600 MHz
(1H frequency) spectrometer at 278 K and subsequently used for
calculations of pKa values (Figure 2A, exemplified for 8a, see Fig.
S3 for 8b). In order to do so, the chemical shift of 31P was plotted
against the pH values and resulting curves fitted with sigmoidal
functions wherein pKa values were obtained from the inflection
points (Figure 2B). We further evaluated the data by plotting and
1
fitting of the H chemical shifts – ζ-protons for phosphonate 8a
and ε-protons for phosphate 8b and phosphoramidate 8c (Fig.
S4).
Charge Distribution of Phospho-Lysine and its Mimics
Next, we aimed to evaluate the charge distribution of peptides
8a-c at physiological pH. In a previous study, Benkovic and
A
B
O
HO
P
HO
Buffer at
different pHs
S
O
O
H
N
H
pH2
pH3
N
N
H
NH2
pH4
pH5
pH6
pH7
pH8
pH9
pH10
O
O
OH
pH11
ppm
8a
21
20
19
18
17
16
15
pH11
pH2
pH3
pH4
pH5
pH6
pH7
pH8
pH9
pH10
8c
ppm
15
16
17
18
19
20
21
22
Figure 2: A. NMR titration experiments of peptide 8a. Conditions: NMR spectra of a solution containing 1 mM peptide in 40 mM KCl (H2O + 10% D2O) were recorded
at distinct pH values on a 600 MHz (1H frequency) spectrometer at 278 K. Shown are the overlay of 1D-31P spectra at different pH values and extracted correlation
signals between e-protons and phosphorous from 1H,31P-HMBC experiments. B. Graphical visualization of 31P NMR measurements for phosphonate 8a (red),
phosphate 8b (blue) and phosphoramidate 8c (black).
4
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Our findings indicated that for each of the three variants the first
pKa could not be determined, because they were below pH 2. In
case of the phosphonate 8a, the pKa between the mono-
protonated phosphoryl oxygen and the di-anionic compound was
7.08±0.03 (R2 = 0.9999), thus both species were in a rather
balanced equilibrium at physiological conditions (Figure 3). The
second pKa of phosphate 8b at 6.54±0.13 (R2 = 0.9991) pointed
towards a more pronounced charge state of –2 at pH 7. For pLys
peptide 8c it was possible to determine two pKa values, one at
2.88±0.30 and the second at 9.64±0.07 (R2 = 0.9995). This result
correlates with the complete deprotonation of the phosphoryl
oxygens (pKa2) and the deprotonation of the amine (pKa3).
Comparing the change in ppm (Δppm) at the pKa values with
those reporedt by Gamcsik et al. supported our assignments of
charge states, whereby a smaller value indicated a protonation
change on oxygen, while a larger value correlated with the
protonation of nitrogen.[23] Along these lines, we observed Δppm
of 5.09 ppm and 8.82 pm for pKa2 and pKa3 for 8c. This can also
be seen in Figure 2B as the Δppm for 8a and 8b representing
protonation of oxygen are below 3.5 ppm each. Interestingly,
increasing pH values resulted in an upfield move of 31P chemical
shift for phosphonate 8a but
a
downfield move for
phosphoramidate 8c and phosphate 8b (Figure 2B). This
behavior has been described already for adenosine nucleotide
analogues in the early 1980s, in which phosphonate derivatives
of triphosphates exhibited the same pattern as observed now.[24]
The net charges of the side chains of interest of 8a, 8b and 8c at
pH 7 are illustrated in Figure 3A. To visualize the charge
distribution, electrostatic potential (ESP) maps were calculated for
optimized structures as shown in Figure 3B (see SI, section 2.10
for details). Even though the relaxed structures had great
geometrical similarity, the charge distributions showed clear
differences. While the charge density was well spread over the
whole molecule with only a slightly negative partial charge at the
phosphoryl oxygens in pLys peptide 8c as well as the mono-anion
of 8a, the di-anionic species of 8a and 8b exhibited distinct charge
fluctuations diversity across the structures. This comparison
indicates that phosphonate 8a is the more suitable mimic for pLys
at physiological pH.
Figure 3: A. Various states of charge and calculated pKa values for 8a, 8b and 8c. Highlighted in red is the protonation of each species at physiological conditions.
nd. = not determined. B. Calculated ESP maps relying on DFT-optimized molecular structures of 8a, 8b and 8c at pH 7.0, visualized with Molden 5.9.
protected pLys building block failed to efficiently deliver pLys
Conclusion
peptides when applied in SPPS. Subsequent stability studies and
In conclusion, we designed both, a phosphonate and a phosphate
NMR measurements showed that phosphonate 8a is a very
analogue of pLys, and evaluated their potency to act as pLys
promising non-hydrolyzable mimic of pLys with a comparable
mimics by comparing their pKa values. Both analogues were
charge distribution, thus opening the opportunity of acting as an
obtained as suitably protected building blocks, which were used
inhibitor for pLys interacting enzymes. Instead, phosphate 8b
in the straightforward Fmoc-based SPPS to obtain model
exhibited a charge distribution at physiological pH, which strongly
peptides for the pKa measurements. In contrast, a novel Tc-
5
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differs from pLys 8c, thereby indicating a lower probability to be
recognized by pLys-selective proteins. Although these
experiments have been conducted with model substrates, we
believe that these findings point toward very promising pLys
analogues with high stability for the generation of pLys-specific
Abs or the screen for binding partners.
[6] G. Hardman, S. Perkins, P. J. Brownridge, C. J. Clarke, D. P.
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Experimental Section
Detailed experimental procedures, compound characterization
and supplementary figures can be found in the supporting
information.
Acknowledgements
This research was supported by the DFG (SFB 765) and the
Evonik Stiftung (Doctoral fellowship to A.H.). We thank Prof.
Dorothea Fiedler for providing ALP aliquots.
[8] a) M. F. Eerland and C. Hedberg, J Org Chem 2012, 77, 2047-
2052; b) J. Fuhrmann, V. Subramanian, D. J. Kojetin and P. R.
Thompson, Cell Chem Biol 2016, 23, 967-977.
Keywords: post-translational modification • phosphorylation •
labile phosphorylation • phospho-lysine • solid-phase peptide
synthesis analogues
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Entry for the Table of Contents
O
O
O
O
O
BnO
P
P
P
NH2
SPPS
HO
O
BnO
S
S
Fmoc
OH
N
H
peptide
Phospho-lysine analogue
peptide
O
Comparable charge distribution
with phospho-lysine
A stable mimic: We introduce a phosphonate amino acid as a stable non-hydrolyzable mimic of phospho-lysine (pLys), which can
be readily incorporated into peptides by Fmoc-based solid-phase peptide synthesis.
Institute and/or researcher Twitter usernames: The Hackenberger Group (@PhosphorusFive), FMP Berlin (@LeibnizFMP)
8
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