Modulating Lectin Inhibition with N-Glycosyl-1,2,3-triazole Scaffolds The document describes a study that developed new molecular scaffolds using click chemistry to modulate inhibition of the lectin Ulex Europaeus lectin I (UEL-I). Six analogues were synthesized with varying flexibility. Computational modeling and NMR experiments showed the semi-rigid analogues were able to optimally interact with UEL-I. The study provides a library of molecules for further investigating UEL-I binding and modulation using simple synthetic methods, but future work is needed to test the molecules in vivo or in vitro and address potential toxicity issues from the click chemistry synthesis.

1. Modulating Lectin Inhibition with N-Glycosyl-1,2,3-
triazole Scaffolds
I. Azcune, E. Balentova, M. Sagartzazu-Aizpurua, J. I. Santos, J. I. Miranda, R. M. Fratila and J. M.
Aizpurua
Eur. J. Org. Chem. 2013, 2434 - 2444
Literature Highlights 16th
May 2013
S. Staderini
Supervisor: Prof. A. Marra

2. Introduction: Carbohydrates Roles
More than 50% of the proteins present in
humans are glycosylated
Involved in:
• Cell – cell recognition events
• Neuronal development
• Inflammatory processes
• Protein – folding and conformation
• Tertiary structure stabilization
• Proteolytic stability enhancement
D. P. Gamblin, E. M. Scanlan, B. G. Davis, Chem. Rev. 2008, 109, 131-163
L. Cipolla, F. Peri, Mini-Rev. Med. Chem. 2011, 11, 39-54

3. Introduction: Sialyl LewisX (sLeX)
N. Kaila, B. E. Thomas IV, Med. Res. Rev, 2002, 22, 566-601
P. Sears, C. – H. Wong, Angew. Chem. 1999, 111, 2446
Fisiology
1. sLeX adheres recognition domain
(CRD) of E and P selectins
2. Rolling, tethering and
extravasation of leukocytes in
the inflammatory cascade are
regulated
Pathology
1. Excessive and/or irregular
infiltration of leukocytes
2. Chronic inflammatory diseases:
RA, psoriasis
3. Acute diseases : stroke,
reperfusion injuries, myocardial
infarction
Main Goal: Inhibit sLeX – selectin
interaction
sLeX mimetics and selectins
antagonists are effective
therapeutics versus these disorders

4. Introduction: Sialyl LewisX (sLeX)
N. Kaila, B. E. Thomas IV, Med. Res. Rev, 2002, 22, 566-601
C. – H. Wong, F. Moris – Varas, S. - C. Hung, T. G. Marron, C. – C. Lin, K. W. Gong, G. Weitz –
Schimdt, J. Am. Chem. Soc. 1997, 119, 8152-8158
Starting Point
Two pharmacophores: fucose
moiety and COO- of sialyc acid.
Metabolically labile O-glycosidic
backbone.
Main issues to achieve:
• Reduce biodegradability
• Increase bioavailability
• Absence of chiral centers
• Easy availability from simple
synthetic routes Good activity, bad
pharmacology parameters

5. Target: Tuning sLeX Mimetics flexibility
Tuning the flexibility of the peptidomimetics scaffold can be considered a
design variable for modulating the mimetic – lectin interaction.
III
IV
V
VI

6. Synthesis: CuAAC cycloaddiction approach
Reagents and conditions:
a) EEDQ, CH2Cl2, -10 °C to RT, 16 h;
b) 20% piperidine in DMF, 30 min, RT;
c) Ac2O, K2CO3, RT;
d) CuSO4·5H2O, Na ascorbate,
tBuOH/H2O/THF, 1:1:1, 16 h, RT
IV
Previously reported: C. Palomo, J. M. Aizpurua, E.
Balentová, I. Azcune, J. I. Santos, J. Jiménez-Barbero, J.
Cancada, J. I. Miranda, Org. Lett. 2008, 10, 2227–2230.

7. Synthesis: CuAAC cycloaddiction approach
J. T. Lundquist, J. C. Pelletier, Org. Lett. 2002, 4, 3219–3221
Reaction conditions:
a) CuI, DIPEA, TBTA, MeCN,RT, 16 h;
b) CsF, MeCN,RT to 35 °C, 1–3 h;
c) CuSO4·5H2O, Na ascorbate, tBuOH/H2O, 1:1, 16 h, RT

8. Synthesis: CuAAC cycloaddiction approach
VI
Previously reported:J. M. Aizpurua, I. Azcune, R. M. Fratila,
E. Balentova, M. Sagartzazu-Aizpurua, J. I. Miranda, Org.
Lett. 2010, 12, 1584–1587.
The design of glycopeptidomimetics III–VI follows an increasing
conformational constraint criterion ranging from flexible to rigid.
Moreover, to minimize biodegradability and to avoid epimerization at α
carbon atoms, the natural O-glycosidic bond was replaced by 1,2,3
triazole linkages and the number of epimerizable centers was reduced.
H. C. Kolb, M. G. Finn, K. B. Sharpless, Angew. Chem. 2001, 113, 2056; Angew. Chem. Int. Ed.
2001, 40, 2004–2021.

9. Evaluation of Binding Affinity
• Final product obtained by deprotections (Pd/H2 and MeONa in MeOH)
• Experiments toward fucose-specific Ulex Europaeus lectin I (UEL-I)
• In silico evaluation of binding affinity using:
o a combination of NMR techniques (ROESY, STD-NMR)
o molecular dynamic modeling (NAMD, AMBER)
o docking simulations (AutoDock 3.0)

10. Molecular dynamics simulations

11. Docking calculations

12. STD-NMR experiments

13. STD-NMR experiments
• STD effects are observed for all six analogues
• Fucose exhibit the strongest signals
• Carboxylic group interaction can’t be detected (D2O)
• Central parts of the scaffolds do not take part in the interaction
• Rigid analogues have high value for fucose signals and very low intensities
for amino-acids ones
• 14b shows the triazole protons in contact with the surface, 14a shown
them far away from protein surface.

14. STD-NMR experiments
• STD effects are observed for all six analogues
• Fucose exhibit the strongest signals
• Carboxylic group interaction can’t be detected (D2O)
• Central parts of the scaffolds do not take part in the interaction
• Rigid analogues have high value for fucose signals and very low intensities
for amino-acids ones
• 14b shows the triazole protons in contact with the surface, 14a shown
them far away from protein surface.

15. Conclusions & Comments
• Two new families of “dipeptide-like” molecular scaffolds have been developed.
• A library of UEL-I binding molecules with different grades of flexibility is now
available for studies.
• Simple synthesis methodologies have been used (CuAAC) for and controlled
stereochemistry has been achieved.
• Lot of data have been collected regarding different conformers stability (Mol.
Dynamics), different complexes energies (Docking) and geometry of complexes
(STD-NMR).
• The semi-rigid conformations are able to modulate their conformation to the “best-
fitting” position.
• Mono- and bis-triazole can be useful as universal peptidomimetics.
• Lack of in vivo or in vitro studies: for a starting point it’s good to use calculations
and in silico data, but in a long-term perspective can be interesting to test these
molecules.
• CuAAC reaction: Cu toxicity drive to cell apoptosis, will they consider that problem?
Purification system must be extremely efficient to move to in vivo or in vitro.
• STD – NMR studies are focused on the fucose motif and forget completely to
consider the second pharmacophore, the acid.