Three-component synthesis of neoglycopeptides using a Cu(II)-triggered aminolysis of peptide hydrazide resin and an azide-alkyne cycloaddition sequence

Article abstract of DOI:10.1021/ol201659x

Copper(II)-induced oxidative aminolysis of hydrazides generates Cu(I), the catalyst of the azide-alkyne cycloaddition. This feature was exploited to design a novel solid phase detaching three-component reaction permitting the conversion of supported pepti

Full text of DOI:10.1021/ol201659x

ORGANIC
LETTERS
2011
Vol. 13, No. 16
4336–4339
Three-Component Synthesis of
Neoglycopeptides Using a Cu(II)-Triggered
Aminolysis of Peptide Hydrazide Resin and
an AzideÀAlkyne Cycloaddition Sequence
Jean-Philippe Ebran, Nabil Dendane, and Oleg Melnyk*
CNRS UMR 8161, Univ Lille Nord de France, Institut Pasteur de Lille, IFR 142
Molecular and Cellular Medicine, 1 rue du Pr Calmette 59021 Lille Cedex, France
oleg.melnyk@ibl.fr
Received June 22, 2011
ABSTRACT
Copper(II)-induced oxidative aminolysis of hydrazides generates Cu(I), the catalyst of the azideÀalkyne cycloaddition. This feature was exploited
to design a novel solid phase detaching three-component reaction permitting the conversion of supported peptide hydrazides into 1,2,3-triazole
linked C-terminal neoglycopeptides.
Multicomponent reactions (MCRs) represent a chemi-
cal process involving at least three reactants for the in-
herent formation of several covalent bonds in one opera-
tion.1 By definition, MCRs are chemo- and regioselective,
convergent step-efficient procedures and take place with
high atom economy.2 Another important feature implies
the diminution of waste production due to the decrease of
synthetic or isolation steps along with saving time.3
organic azides and terminal alkynes (CuAAC) has been
playing an outstanding role in various fields of chemistry
and biochemistry7 research. The resulting 1,4-disubsti-
tuted 1,2,3-triazoles are obtained in high yields with ex-
clusive regioselectivity under mild reaction conditions.
However, only few reports describe the implementation
of CuAAC in MCRs.8,9 Most of these MCRs were de-
signed to circumvent the handling of azides, whose synth-
esis and isolation can be problematic due to their potential
explosive or unstable nature. For example, three-component
Since its discovery reported by Meldal4 and Sharpless,5 the
copper(I)-catalyzed Huisgen6 1,3-dipolar cycloaddition of
ꢀ
(1) Multicomponent Reactions; Zhu, J., H. Bienayme, Eds.; Wiley-
VCH: Weinheim, 2005.
(7) For recent reviews, see: (a) Meldal, M.; Tornøe, C. W. Chem. Rev.
2008, 108, 2952–3015. (b) Debola, S.; Nepogodiev, S. A.; Field, R. A.
Org. Biomol. Chem. 2007, 5, 1006–1017. (c) Amblard, F.; Cho, J. H.;
Schinazi, R. F. Chem. Rev. 2009, 109, 4207–4220. (d) Pedersen, D. S.;
Abell, A. Eur. J. Org. Chem. 2011, 13, 2399–2411.
(8) (a) Appukkuttan, P.; Dehaen, W.; Fokin, V. V.; Van der Eycken,
E. Org. Lett. 2004, 6, 4223–4225. (b) Bogdan, A. R.; Sach, N. W. Adv.
Synth. Catal. 2009, 351, 849–854. (c) Alonso, F.; Moglie, Y.; Radivoy,
G.; Yus, M. Adv. Synth. Catal. 2010, 352, 3208–3214. (d) Odlo, K.;
Høydahl, E. A.; Hansen, T. V. Tetrahedron Lett. 2007, 48, 2097–2099. (e)
Crowley, J. D.; Bandeen, P. H. Dalton Trans. 2010, 39, 612–623.
(9) (a) Feldman, A. K.; Colasson, B.; Fokin, V. V. Org. Lett. 2004, 6,
3897–3899. (b) Ackerman, L.; Potukuchi, H. K.; Landsberg, D.;
Vicente, R. Org. Lett. 2008, 10, 3081–3084.
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(2) (a) Bienayme, H.; Hulme, C.; Oddon, G.; Schmitt, P. Chem.;
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Eur. J. 2000, 6, 3321–3329. (b) Bienayme, H.; Bouzid, K. Angew. Chem.,
Int. Ed. 1998, 37, 2234–2237. (c) Trost, B. M. Angew. Chem., Int. Ed.
1995, 34, 259–281.
(3) Lalli, C.; Bouma, J. M.; Bonne, D.; Masson, G.; Zhu, J. Chem.;
Eur. J. 2011, 17, 880–889.
(4) Tornøe, C. W.; Christensen, C.; Meldal, M. J. Org. Chem. 2002,
67, 3057–3064.
(5) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B.
Angew. Chem., Int. Ed. 2002, 41, 2596–259.
(6) (a) Huisgen, R.; Szeimies, G.; Moebius, L. Chem. Ber. 1965, 98,
4014–4021. (b) Huisgen, R. Pure Appl. Chem. 1989, 61, 613–628.
r
10.1021/ol201659x
Published on Web 07/18/2011
2011 American Chemical Society

copper catalyzed reactions in which azides are generated in
situ from corresponding alkyl8 or aryl9 halides and sodium
azide in the presence of terminal alkynes give access to
diversely substituted 1,2,3-triazoles.
We describe hereinafter a novel three-component reac-
tion based on a Cu(II)-triggered aminolysis of peptide
hydrazide resin and an azideÀalkyne cycloaddition se-
quence. This process is delimited by the dashed square in
Scheme 1.
protecting groups furnishes target peptide 8. Overall, this
MCR encompasses four chemical transformations: the
oxidation of hydrazide 2 into diazene 3, the reduction of
Cu(II) into Cu(I), the diazene aminolysis which results in
the detachment of the peptide chain from the resin, and
finally the CuAAC.
This proof of concept study is illustrated with the
synthesis of neoglycopeptides, for which the R group is a
carbohydrate or carbohydrate mimic in the general for-
mula 8 (Scheme 1). Several reports describe the application
of CuAAC for the synthesis of these biologically signifi-
cant conjugates10 using either alkynyl11 or azido12 oligo-
saccharides. Recently, Brimble et al.13 has combined Native
Chemical Ligation and CuAAC in a one-pot process
leading to neoglycopeptides from unprotected propargyl-
peptides and azido glycans.14 However, the strategy de-
picted in Scheme 1 constitutes the first MCR approach to
neoglycopeptides.
Scheme 1. Principle of Three-Component Reaction
Neoglycoconjugates 8 (R = carbohydrate/carbohydrate
mimic) feature a sugar moiety directly linked to the
C-terminus of the peptide chain. The preparation of such
neoglycoconjugates has not been reported before. Conse-
quently, as a step toward the study of the MCR, we
undertook their synthesis by a stepwise approach as shown
in Scheme 2. Model sequence Ac-ILKEPVYX (X = Gly,
Ala, Ser, Val, or His) was assembled on resin 1, which
allows Fmoc-SPPS and racemization-free synthesis of
peptide amides by mild Cu(II)-oxidative aminolysis of
the hydrazinocarbonyl bond.15 3-Azidopropylamine hy-
drochloride 4 required for the oxidative aminolysis reac-
tion was obtained in two steps starting from commercially
available N-(3-bromopropyl)phtalimide (see Supporting
Information). The use of this ammonium salt avoids the
handling of 3-azidopropylamine, which is volatile.16 For-
mation of acyldiazene intermediate 3 (Scheme 1) from
protected peptide hydrazide resin 2 requires 2 equiv of
Cu(II). We used for this step 0.5 equiv of Cu(OAc)2 with
air bubbling to allow the recycling of the formed Cu(I)
into Cu(II) by molecular oxygen (Scheme 2). Oxidative
aminolysis of model peptidyl resins 2aÀe followed by
ꢀ
(10) (a) Perez-Balderas, F.; Ortega-Munoz, M.; Morales-Sanfrutos,
J.; Hernandez-Mateo, F.; Calvo-Flores, F. G.; Calvo-Asın, Isac-Garcıa,
~
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V.; Seeberger, S. Angew. Chem., Int. Ed. 2004, 43, 900–903. (c) Tejler, J.;
Tullberg, E.; Frejd, T.; Leffer, H.; Nilsson, U. J. Carbohydr. Res. 2006,
341, 1353–1362.
(11) (a) Groothuys, S.; Kuijers, B. H. M.; Quaedflieg, P. J. L. M.;
Roelen, H. C. P. F.; Wiertz, R. W.; Blaauw, R. H.; van Delft, F. L.;
Rutjes, F. P. J. Synthesis 2006, 18, 3146–3152. (b) Miller, N.; Williams,
G. M.; Brimble, M. A. Org. Lett. 2009, 11, 2409–2412.
(12) (a) Lin, H.; Walsh, C. J. Am. Chem. Soc. 2004, 126, 13998–
14003. (b) Kuijers, B. H. M.; Groothuys, S.; Keereweer, A. B. R.;
Quaedflieg, P. J. L. M.; Blaauw, R. H.; van Delft, F. L.; Rutjes,
F. P. J. Org. Lett. 2004, 6, 3123–3126. (c) Wan, Q.; Chen, J.; Chen, G.;
Danishefsky, S. J. J. Org. Chem. 2006, 71, 8244–8249. (d) Macmillan, D.;
Blanc, J. Org. Biomol. Chem. 2006, 4, 2847–2850.
(13) Lee, D. J.; Mandal, K.; Harris, P. W. R.; Brimble, M. A.; Kent,
S. B. H. Org. Lett. 2009, 11, 5270–5273.
(14) Dawson, P. E.; Muir, T. W.; Clark-Lewis, I.; Kent, S. B. H.
Science 1994, 266, 776–779.
One of the components of this MCR is the protected
peptidyl resin2, which isobtainedfrom arylhydrazineresin
1 using standard solid phase peptide synthesis (SPPS).
Copper(I), the catalyst of CuAAC, is generated in situ
during oxidation of arylhydrazine resin 2 by copper(II).
Aminolysis of the resulting supported peptidyl diazene
resin 3 by azido amine 4 releases the protected azido
peptide 5 in solution. Cu(I) formed in the first step of the
MCR catalyzes the CuAAC between azido peptide 5 and
alkyne 6 to give triazole 7. Finally, removal of peptide
(15) (a) Millington, C. R.; Quarrell, R.; Lowe, G. Tetrahedron Lett.
1998, 39, 7201–7204. (b) Ludolph, B.; Eisele, F.; Waldmann, H. J. Am.
Chem. Soc. 2002, 124, 5954–5955. (c) Brunsveld, L.; Watzke, A.; Durek,
T.; Alexandrov, K.; Goody, R. S.; Waldmann, H. Chem.;Eur. J. 2005,
11, 2756–2772.
Org. Lett., Vol. 13, No. 16, 2011
4337

Table 1. Yields for 1,2,3-Triazole Peptides 10À15
Scheme 2. Stepwise Synthesis of 1,2,3-Triazole Peptides 10À15
deprotection in TFA and reversed-phase (RP) HPLC
purification successfully furnished C-terminal azido pep-
tides 9aÀdwith 12À29% overall yields starting from resin 1.
Synthesis of peptide 9e with the C-terminal His residue
was problematic whose yield was only 4%. This is prob-
ably due to the capacity of the imidazole group to chelate
with copper.
The Cu(I)-catalyzed 1,3-azideÀalkyne cycloaddition
was optimized using azido peptide 9b (X = Ala) and
4-phenyl-1-butyne 6a (R = CH2Ph) as a model alkyne
(Scheme 2). Several solvents and catalysts were screened at
room temperature. The CuI/DIEA system in DMF4 was
unsatisfactory. Likewise, no product formation was ob-
a Isolated yields. Products were purified by RP-HPLC.
served with CuSO4 5H2O/sodium ascorbate (NaAsc) 10/
3-azidopropyl amine hydrochloride 4, and alkyne 6. As pre-
viously indicated, the oxidative aminolysis of the hydrazide
bond requires 2 equiv of Cu(II). The use of substoichio-
metric amounts of Cu(II) for this step must be compen-
sated by the introduction of an oxidant in the process, such
as molecular oxygen, which oxidizes Cu(I) back to Cu(II).
However, azideÀalkyne cycloaddition requires mainte-
nance of a high concentration of Cu(I) in solution. This
is usually achieved by using Cu(II) and a reductant such as
sodium ascorbate. At first glance, these two chemical
reactions appear incompatible. But this apparent problem
can be resolved by using stoichiometric amounts of Cu(II)
for the hydrazide oxidation stepand by working rigorously
under aninert atmosphere (O2 < 1 ppm), thereby avoiding
the oxidation of Cu(I) to Cu(II).
3
100 mol % catalyst in aqueous acetonitrile. Alternately,
this catalyst successfully yielded 1,3-triazole 8a in 4 h using
tBuOH/H2O as solvent (99% convertion, 89% isolated,
entry 1, Table 1). Decreasing CuSO4 5H2O/ascorbate
3
loading to 5/50 mol % led to a conversion of 93%, but
the reaction time needed to be extended to 20 h. Con-
sequently, optimized reaction conditions corresponded
to CuSO4 5H2O/NaAsc 10/100 mol % in tBuOH/H2O
3
1/1 by vol.
The utility of this procedure was confirmed by examin-
ing a series of alkyne monosaccharides 6b,c and mannose
mimics17 6d,e along with C-terminal azido peptides 9aÀd
(72À82% isolated yields, entries 2À5, Table 1). Cycloaddi-
tion of His peptide 9e with lactose derivative 6f permitted
the isolation of neoglypeptide 15 albeit with a lower yield
(entry 5, Table 1).
Optimization of experimental conditions was performed
using protected peptide hydrazide resin 2b (X = Ala), 2
These preliminary experiments set the stage for studying
the MCR between protected peptide hydrazide resin 2,
(16) Stability of 4 at rt was confirmed by thermogravimetric analysis
(see Supporting Information). Synthesis of 3-azidopropyl amine as a free
base is reported in several papers: (a) Carboni, B.; Benalil, A.; Vaultier,
Scheme 3. Study of the MCRÀDeprotection Sequence
€
M. J. Org. Chem. 1993, 58, 3736–3741. (b) Knor, S.; Modlinger, A.;
Poethko, T.; Schottelius, M.; Wester, H.-J.; Kessler, H. Chem.;Eur. J.
2007, 13, 6082–6090. (c) Tamanini, E.; Rigby, S. E. J.; Motevalli, M.;
Todd, M. H.; Watkinson, M. Chem.;Eur. J. 2009, 15, 3720–3728. For a
review on azides, see: Scriven, E. F. V.; Turnbull, K. Chem. Rev. 1988,
88, 297–368.
(17) (a) Grandjean, C.; Rommens, C.; Gras-Masse, H.; Melnyk, O. J.
Chem. Soc., Perkin Trans. 1 1999, 2967–2975. (b) Grandjean, C.; Gras-
Masse, H.; Melnyk, O. Chem.;Eur. J. 2001, 7, 230–239. (c) Chenevier,
P.; Grandjean, C.; Loing, E.; Malingue, F.; Angyalosi, G.; Gras-Masse,
H.; Roux, D.; Melnyk, O.; Bourel-Bonnet, L. Chem. Commun. 2002,
2446–7. (d) Angyalosi, G.; Grandjean, C.; Lamirand, M.; Auriault, C.;
Gras-Masse, H.; Melnyk, O. Bioorg. Med. Chem. Lett. 2002, 12, 2723–
2727. (e) Grandjean, C.; Gras-Masse, H.; Melnyk, O. Chemistry 2001, 7,
230–9.
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Org. Lett., Vol. 13, No. 16, 2011

Table 2. Results for the MCRÀDeprotection Sequence
a 2 equiv of amine 4. b 1.5 equiv of amine 4.
equiv of ammonium salt 4, 2 equiv of 4-phenyl-1-butyne
6a, and 2.5 equiv of copper(II) acetate in the presence of N,
N-diisopropylethylamine (DIPEA) (Scheme 3, Table 2).
We first examined the influence of the solvents on the
MCR efficiency. Dichloromethane (entry 3, Table 2)
proved superior to THF (entry 1) and DMF (entry 2); this
may be due to the better swelling of the polystyrene resin in
the former solvent. In each case, C-terminal azido peptide
9b was identified as a major side product (∼30% by RP-
HPLC). Using a mixture of pyridine and dichloromethane
for the MCR improved the isolation of target peptide 10
(entry 4) and decreased the proportion of 9b 2-fold. In a
control experiment, we replaced Cu(II) by Cu(I) using
pyridine/dichloromethane as solvent. Formation of pep-
tide 10 was not observed, but the 1,2,3-triazole product 16
formed from the cycloaddition of azidopropylamine 4 and
4-phenyl-1-butyne 6a could be isolated with a 84% yield
(entry 5). This experiment shows the importance of Cu(II)
for triggering the MCR. Note that 1,2,3-triazole product
16 can be formed during the MCR once Cu(I) has been
generated during the hydrazide oxidation step. 16 can
participate also in the aminolysis of diazene resin 3
(Scheme 1). Peptide 7 is thus potentially the end product
of two different chemical pathways.
The application of the MCR to peptidyl resin 2b (X =
Ala) and shikimic derivative 6d successfully furnished
neoglycopeptide 17. We used only 1.5 equiv of amine 4
for this reaction to further minimize the formation of azido
peptide 9b, which was indeed barely detected in the crude
product. The RP-HPLC chromatogram shown in Figure 1
highlights the good purity of the crude neoglycopeptide 17
releasedduring the MCR. A similar resultwasobtained for
the MCR involving resin 2a (X = Gly) and quinic
derivative 6e (entry 7, Table 2).
Figure 1. RP-HPLC chromatogram of the crude MCR with
peptidyl resin 2b (X = Ala) and shikimic derivative 6d.
alkyne, resulting in the formation of peptides modified at
the C-terminus through an amino 1,2,3-triazole linker.
Cu(I), the catalyst of the 1,3-cycloaddition reaction, is
formed during the oxidative aminolysis step, which also
allows the cleavage of the peptide from the solid sup-
port. The MCR was applied to the synthesis of a novel
family of neoglycopeptides. This reaction can poten-
tially be used for the synthesis of a large variety of
peptide derivatives starting from Fmoc-SPPS as-
sembled peptidyl resins.
Acknowledgment. We acknowledge financial support
from the French Ministry of Research (Medicen, DOSCA),
ꢀ
^
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Canceropole Nord-Ouest, Region Nord Pas de Calais, and
the European Community. We thank Emmanuelle Boll
(CNRS) for NMR experiments.
In conclusion, we have described a novel Cu(II)-
triggered MCR based on an oxidative aminolysis 1,3-
cycloaddition sequence. The MCR process requires a
peptide hydrazide resin, an amino azide linker, and an
Supporting Information Available. Experimental pro-
cedures and characterization data for all peptides. This
material is available free of charge via the Internet at
http://pubs.acs.org.
Org. Lett., Vol. 13, No. 16, 2011
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