"Click" saccharide/β-lactam hybrids for lectin inhibition

Article abstract of DOI:10.1021/ol8006259

(Figure Presented) Hybrid glycopeptide β-lactam mimetics designed to bind lectins or carbohydrate recognition domains in selectins have been prepared according to a "shape-modulating linker" design. This approach was implemented using the azide-alkyne "cl

Full text of DOI:10.1021/ol8006259

ORGANIC
LETTERS
2008
Vol. 10, No. 11
2227-2230
“Click” Saccharide/ꢀ-Lactam Hybrids for
Lectin Inhibition
Claudio Palomo,*,† Jesus M. Aizpurua,*,† Eva Balentova´, Itxaso Azcune,
J. Ignacio Santos, Jesu´s Jime´nez-Barbero,*,‡ Javier Can˜ada, and Jose´
Ignacio Miranda
Departamento de Qu´ımica Orga´nica-I, UniVersidad del Pa´ıs Vasco, Joxe Mari Korta
R&D Center, AVda, Tolosa-72, 20018 San Sebastia´n, Spain, and Centro de
InVestigaciones Biolo´gicas, CSIC, Ramiro de Maeztu-9, 28040 Madrid, Spain
jesusmaria.aizpurua@ehu.es
Received March 21, 2008
ABSTRACT
Hybrid glycopeptide ꢀ-lactam mimetics designed to bind lectins or carbohydrate recognition domains in selectins have been prepared according
to a “shape-modulating linker” design. This approach was implemented using the azide-alkyne “click” cycloaddition reaction, and as shown
by NMR/MD experiments, binding of the resulting mimetics to Ulex Europaeus Lectin-1 (UEL-1) occurred after a “bent-to-extended” conformational
change around a partially rotatable triazolylmethylene moiety.
Hybrid constructs1 of natural or unnatural molecular entities
are an important source of molecular diversity. This approach
often takes advantage of the inherent biological activity of
all or part of the components embodied in the conjugates.
For a successful design, however, it is not enough to decide
which fragments to incorporate into the hybrid but also to
know where to place them. Therefore, a precision crafting
is often necessary to generate hybrids permitting an efficient
molecular recognition of each and every bioactive fragment,
especially when the “rigid scaffold” design is used (Figure
1). We would like to outline here the advantages of an
alternative “shape-modulating linker” design which provides
partially flexible hybrids by connecting their rigid(ified)
components with rotatable covalent bonds. As an example
† Universidad del Pa´ıs Vasco.
‡ Centro de Investigaciones Biolo´gicas, CSIC.
(1) For reviews, see: (a) Mehta, G.; Singh, V. Chem. Soc. ReV. 2002,
31, 324–334. (b) Tietze, L.; Bell, H. P.; Chandrasekhar, S. Angew. Chem.,
Int. Ed. 2003, 42, 3996–4028. (c) Meunier, B. Chem. ReV. 2008, 104, 69–
77.
Figure 1. Semirigid hybrids: “shape-modulating linker” design.
10.1021/ol8006259 CCC: $40.75
Published on Web 05/09/2008
2008 American Chemical Society

of this design principle, we describe a novel family of
saccharide/ꢀ-lactam hybrids for lectin inhibition.
have shown increased activity and good selectivity against
several lectin receptors.6 Unfortunately, excessive flexibility
of the peptide backbone, biodegradability arising from
glycosidic or peptidic linkages, and epimerization of the
R-carbons are important drawbacks of this approach. Seeking
for peptidomimetics with more favorable pharmacodynamic
profiles, we have been focused over the past few years on
the design and synthesis of peptidomimetics based on
R-branched-R-amino-ꢀ-lactam scaffolds7 which are expected
to exhibit rigidified backbones and simultaneous enhanced
resistance to chemical and enzymatic hydrolysis by proteases
owing to the presence of the R,R-disubstitution pattern at
the azetidin-2-one ring. Now, we report the synthesis of
saccharide/ꢀ-lactam hybrids 3 incorporating the 1,2,3-tria-
zolylmethyl moiety8 as the shape-modulating linker.
Lectins2 are naturally occurring nonenzymatic saccharide-
binding proteins. They are involved in a variety of recogni-
tion events, including cell-cell interactions. For instance,
selectins3 gained attention a decade ago, when it was
demonstrated that the adhesion of the tetrasaccharide sia-
lylLewis-x (sLeX) 1 (Figure 2)4 to the carbohydrate-recogni-
Scheme 1. Retrosynthesis of Saccharide ꢀ-Lactam Hybrids 3
Retrosynthetically (Scheme 1), compounds 3 were discon-
nected at the 1,2,3-triazole ring and divided into the readily
available glycosyl azides 59 and R-(o-nosylamino)-R-prop-
argyl-ꢀ-lactam 4. The synthesis of the latter was planned
from the R-propargylserinate 6 and aminoester 7, according
to the procedure developed in our laboratory.7b
Figure 2. Design of Ser-Glu dipeptide-based mimetics 2 using the
interaction pattern of sLex 1 with E-Selectin (top). “Shape-
modulating linker”/ꢀ-lactam approach to semirigid saccharide/ꢀ-
lactam hybrids 3 (bottom).
(6) Tsukida, T.; Moriyama, H.; Kurokawa, K.; Achiha, T.; Inoue, Y.;
Kondo, H. H. J. Med. Chem. 1998, 41, 4279–4287.
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R. M.; Matute, C.; Domercq, M.; Gago, F.; Martin-Santamaria, S.; Linden,
A. J. Am. Chem. Soc. 2003, 125, 16243–16260. (b) Palomo, C.; Aizpurua,
J. M.; Balentova´, E.; Jime´nez, A.; Oyarbide, J.; Fratila, R.; Miranda, J. I.
Org. Lett. 2007, 9, 101–104.
tion domain (CRD) of E-selectin regulated the rolling,
tethering and transmigration of leukocytes on the vascular
endothelium. Irregular and excessive infiltration of leukocytes
is at the origin of acute and chronic inflammatory diseases
such as asthma, psoriasis, and rheumatoid arthritis.5
Low molecular weight carbohydrate-peptide mimetics
related to ꢀ-turned Ser-Glu dipeptide O-glycoside hybrids 2
(8) This heterocycle is readily accessible by the copper-catalyzed
azide-alkyne “click” cycloaddition reaction: (a) Kolb, H. C.; Finn, M. G.;
Sharpless, K. B. Angew. Chem., Int. Ed. 2001, 40, 2004–2021. For the use
of glycosyl azides in “click” reactions, see: (b) Dedola, S.; Nepogodiev,
S. A.; Field, R. A. Org. Biomol. Chem. 2007, 5, 1006–1017. (c) Kuijpers,
B. H. M.; Groothuys, S.; Keereweer, A. R.; Quaedflied, P. J. L. M.; Blaauw,
R. H.; Delft, F. L.; Rutjes, F. P. J. T. Org. Lett. 2004, 6, 3123–3126. (d)
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Supuran, C. T.; Poulsen, S.-A. J. Med. Chem. 2006, 49, 6539–6548. For
related multivalent saccharides rigidified using click reactions, see: (f)
Vrasidas, I.; Andre´, S.; Valentini, P.; Bo¨ck, C.; Lensch, M.; Kaltner, H.;
Liskamp, R. M. J.; Gabius, H.-J.; Pieters, R. J. Org. Biomol. Chem. 2003,
1, 803–810. (g) Salameh, B.; Leffler, H.; Nilsson, U. J. Bioorg. Med. Chem.
Lett. 2005, 15, 3344–3346. (h) Touaibia, M.; Wellens, A.; Shiao, T. C.;
Wang, Q.; Sirois, S.; Bouckaert, J.; Roy, R. Chem. Med. Chem. 2007, 2,
1190–1201.
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1998, 98, 833–862.
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103, 467–479. (b) Kranich, R.; Busemann, A. S.; Bock, D.; Schroeter-Maas,
S.; Beyer, D.; Heinemann, B.; Meyer, M.; Schierhorn, K.; Zahtten, R.; Wolf,
G.; Aydt, E. M. J. Med. Chem. 2007, 50, 1101–1115, (and references
therein)
(9) (a) Kunz, H.; Pfrengle, W.; Ruck, K.; Sager, W. Synthesis 1991,
103, 9–1042. (b) Gyorgydeak, Z.; Paulsen, H.; Szilagyi, L. J. Carb. Chem.
1993, 12, 139–163. (c) Bojarova, P.; Petraskova, L.; Ferrandi, E. E.; Monti,
D.; Pelantova, H.; Kuzma, M.; Simerska, P.; Kren, V. AdV. Synth. Catal.
2007, 349, 1514–1520.
(5) For reviews, see: (a) Carbohydrate-based Drug DiscoVery; Wong,
C.-H., Ed.; Wiley-VCH: Weinheim, 2003. (b) Romano, S. J. Treat. Respir.
Med. 2005, 4, 85–94.
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Org. Lett., Vol. 10, No. 11, 2008

Scheme 2
.
Preparation of ꢀ-Lactam Alkyne 4 from D-Serine
Table 1. “Click” Synthesis of R-(N-Glycosyltriazolyl)-ꢀ-lactams
10a-e from R-Propargyl-ꢀ-lactam 4 and Glycosyl Azides 5
R-Propargyl serinate 6 (Scheme 2) could be prepared from
D-serine in 69% yield using Seebach’s 1,3-oxazolidine
enolate alkylation method.10 However, attempts to transform
it into the key R-propargyl-ꢀ-lactam method7b proved
inefficient.11
Alternatively, we found that R-allyl serinate 8 cyclized
with 7 to the R-allyl-ꢀ-lactam 9 in excellent yield after two
synthetic operations. The allyl group of azetidin-2-one 9 was
oxidized to the corresponding R-acetaldehyde which, in turn,
was submitted “in situ” to the Ohira-Bestmann alkynyla-
tion12 with dimethyl acetyldiazomethylphosphonate reagent,
to afford the expected ꢀ-lactam alkyne 4 in 76% overall yield.
“Click” cycloaddition reaction of propargyl-ꢀ-lactam 4
with O-protected 2-azidosugars 5a-e derived from D-
mannose and L-fucose (Table 1) led to a clean and completely
anomer-specific reaction to form the ꢀ-lactam glycoconju-
gates13 10a-e in excellent yields. As shown in Table 1, this
chemically effective and operatively simple method was
applicable to the R- and ꢀ-anomers of both O-acetyl- and
O-benzyl-protected 1-azido-D-mannoses 5a-c (entries 1-3)
and 1-azido-L-fucoses 5d,e (entries 4 and 5).
a Yield of pure isolated products. b Measured in CH2Cl2 (c ) 1).
Scheme 3, the reaction of ꢀ-1-azido-L-fucose 19 with the
R-acetamido-R-propargyl-ꢀ-lactam resulting from the N-
denosylation of 4 provided the glycopeptidomimetic 20 in
excellent overall yield. Saponification of 20 with LiOH in
aqueous THF gave a product identical to 17.
The demonstration that these molecules could act as true
glycomimetics of modulable shape was evaluated by a
combined NMR/docking approach employing a model fu-
cose-binding lectin, Ulex Europaeus Lectin I (UEL-I), as
receptor. In fact, a clear interaction was found (Figure 3;
Conjugates 10a and 10e were submitted to N-denosyla-
tion14 and “in situ” N-acylation, followed by O-deprotection
to get the desired ligands (15-18) for lectin binding test
(Table 2).
Importantly, the “click” cycloaddition method could also
be extended to unprotected 1-azidosugars. As illustrated in
Table 2. Synthesis of R-(N-Glycosyltriazolyl)-ꢀ-lactam Hybrids
15-18
(10) Seebach, D.; Aebi, J. D.; Gander-Coquoz, M.; Naef, R. HelV. Chim.
Acta 1987, 70, 1194–1216.
(11) Reaction of 6 with o-Ns-Cl and KHCO3 in acetonitrile, followed
by “in situ” treatment of the resulting intermediate N-nosylaziridine (I) with
methyl R-aminoisobutirate 7 provided the N-peptidylazaserinate (II) in only
25% yield, along with several unidentified products.
yielda
product (%) product (%)
yield
entry ꢀ-lactam
R1
(12) (a) Ohira, S. Synth. Commun. 1989, 19, 561. (b) Mu¨ller, S.; Liepold,
B.; Roth, G. J.; Bestmann, H. J. Synlett 1996, 521.
1
2
3
4
10a
10a
10e
10e
Me
CH2CH2C8F17 12
Me 13
CH2CH2C8F17 14
11
99
55
93
72
15
16
17
18
>98
>98
>98
>98
(13) For other glycosidic ꢀ-lactam hybrids, see: (a) Kvaerno, L.; Werder,
M.; Hauser, H.; Carreira, E. M. J. Med. Chem. 2005, 48, 6035–6053. (b)
Dondoni, A.; Massi, A.; Sabbatini, S.; Bertolasi, V. AV. Synth. Catal. 2004,
346, 1355–1360. (c) Adinolfi, M.; Galletti, P.; Giacomini, D.; Iadonisi, A.;
Quintavalla, A.; Ravida, A. Eur. J. Org. Chem. 2006, 346, 69–73.
(14) Maligres, P. E.; See, M. M.; Askin, D.; Reider, P. J. Tetrahedron
Lett. 1997, 38, 5253–5256.
a Overall nonoptimized yields of pure isolated products. Three equiva-
lents of acid chloride or 5 equiv of anhydride was used in all examples.
Org. Lett., Vol. 10, No. 11, 2008
2229

Scheme 3. “Click” Reaction with Free Glycosyl Azides
(Figure 3C) STD-NMR15 experiments unequivocally showed
recognition of 17, with a distinctive signal resonance intensity
pattern. Indeed, all H atoms except those of methylene groups
H2 and H3 experienced STD effects, with the relative
intensities gathered in Figure 3C. Docking experiments with
Autodock 3.016 were performed to explain the experimental
results. Only the extended conformer (minor in solution) was
able to account for the observed STD effects. This fact was
also in agreement with the main cluster of minimum-energy
conformers calculated by AutoDock, which showed the
extended conformation of ligand 17 bind to UEL-1 by the
carboxylate group at residue Arg-222 and by the fucose 8-
and 9-OH groups to the Asp-87 and Glu-44 residues.
In conclusion, a short and practical procedure to obtain
lectin antagonist saccharide/ꢀ-lactam hybrid peptido-mimet-
ics has been developed by applying a “shape-modulating
linker” design. The “click” reaction required to form sac-
charide/ꢀ-lactam hybrids displays full anomer and config-
uration control and is compatible with either O-protected or
hydroxyl-free glycosyl azides. Owing to its simplicity, the
extension of this design to further families of ꢀ-lactam
hybrids is anticipated.
Figure 3. L-ꢀ-Fucose/ꢀ-lactam hybrid 17 is properly recognized
by Ulex Europaeus Lectin-I after conformation change. (A) Solution
conformation (bent) and ROESY magnification. (B) Complexed
conformation from docking (extended). (C) STD spectrum measured
at 298 K; signal enhancement normalized to H-10 in parentheses;
(D) 500 MHz H NMR spectrum measured in H2O-D2O 9:1 at
298 K.
Acknowledgment. We thank the Ministerio de Educacio´n
y Ciencia (MEC, Spain) (Projects: CTQ2006-13891/BQU
and CTQ10874-C02-01), UPV/EHU, and Gobierno Vasco
(ETORTEK-BiomaGUNE IE-05/143) for financial support
and SGIker UPV/EHU for NMR facilities. A grant from
Gobierno Vasco to I.A. is acknowledged.
1
Supporting Information Available: Preparation proce-
dures, physical and spectroscopic data for compounds 4-20,
and detailed MD, Docking, and NMR experiments for
compound 17. This material is available free of charge via
the Internet at http://pubs.acs.org.
see also the Supporting Information) between the L-ꢀ-fucose-
substituted mimetic 17 and UEL-I. The conformational
behavior of compound 17 in water was first checked by
Molecular Dynamics, revealing a highly populated and
homogeneous cluster of bent conformers, with a minor
contribution of extended conformers. This prediction was
confirmed experimentally by several long-range NOE cross-
peaks and, more particularly, by the close spatial arrangement
of the H5 triazole proton and the pro-R H2(R) proton of the
ꢀ-lactam ring (see Figure 3A). However, a conformational
selection process takes place upon binding to UEL-1. Indeed
OL8006259
(15) Mayer, M.; Meyer, B. Angew. Chem., Int. Ed. 1999, 38, 1784–
1788.
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(pdb code: 1JXN)
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