pubs.acs.org/joc
reaction should be chemoselective toward the designed
Selective Immobilization of Peptides Exclusively via
N-Terminus Cysteines by Water-Driven Reactions on
Surfaces
functional group in a peptide to control the orientation of
the immobilized ligands for optimal binding between the
ligands and the targeted receptors.2,9-14 Many aqueous-
compatible chemoselective reactions are potentially suitable
for immobilization, including native chemical ligation,15
aldehyde-based coupling,16 Staudinger ligation,17 Diels-
Alder reaction,18 “Click” chemistry,19,20 maleimide-thiol
coupling,21 and multicomponent reactions.22,23 Among
these reactions, maleimide chemistry is commonly used for
peptide immobilization.24 Because maleimide-thiol cou-
pling does not distinguish the subtle difference in reactivity
between cysteines at different positions in a peptide, this
method is limited to immobilizing peptides not containing
internal cysteines, and requires adding a terminus cysteine
into the peptide for immobilization purposes. In a recent
study, we discovered a class of chemoselective reactions
between cysteine and amino squarate derivatives that is
driven optimally by the hydrogen bonds from the sol-
vent-water.25 Structural study suggests that this reaction
may also be facilitated by the more nucleophilic cysteine
residues at neutral pH.25 Here, we describe the use of this
reaction to facilitate the immobilization of unprotected
peptides exclusively via N-terminus cysteines while tolerat-
ing the presence of cysteines at other positions (Figure 1).
We used self-assembled monolayers (SAMs) of alka-
nethiols on gold films to elucidate this immobilization chem-
istry. This class of monolayers allows the control of both
surface chemistry and the polycrystalline structure of the
supporting gold films.26 The monolayer consists of mixed
alkanethiols, one terminated with an amino phenoxy squarate
Preeti Sejwal, Sri Kamesh Narasimhan, Deepali Prashar,
Debjyoti Bandyopadhyay, and Yan-Yeung Luk*
Department of Chemistry, Syracuse Biomaterials Institute,
Syracuse University, Syracuse, New York 13244
Received February 11, 2009
Immobilizing peptides or proteins on bioinert surfaces
enables the elucidation of ligand-receptor interaction in
complex biological systems. Here, we report a highly
chemoselective surface reaction that immobilizes peptides
exclusively via N-terminus cysteine residue in a peptide. At
pH 5.5, only N-terminus cysteines of peptides couple
covalently with phenoxy amino squarate moieties presented
on self-assembled monolayers (SAMs) of alkanethiols on
gold films. The selectivity of this surface reaction can
tolerate the presence of internal cysteines in close proximity
to basic residues such as histidines. We demonstrated this
selective surface reaction by mammalian cell adhesion and
by SAMDI mass spectroscopy of the SAMs.
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ꢀ
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such as identifying new ligand-receptor binding1-5 and for
studying adhesion biology.6-8 The ideal immobilization
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DOI: 10.1021/jo901085u
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Published on Web 07/28/2009
J. Org. Chem. 2009, 74, 6843–6846 6843
2009 American Chemical Society