A synthetic receptor for nicotine from a dynamic combinatorial library

Article abstract of DOI:10.1021/ol302260n

Designing synthetic receptors that bind biologically relevant guests in an aqueous solution remains a considerable challenge. We now report a new synthetic receptor for nicotine, selected from a dynamic combinatorial library, that binds this guest in water at neutral pH through a combination of hydrophobic and π-π interactions.

Full text of DOI:10.1021/ol302260n

ORGANIC
LETTERS
2012
Vol. 14, No. 21
5404–5407
A Synthetic Receptor for Nicotine from a
Dynamic Combinatorial Library
Saleh Hamieh,† R. Frederick Ludlow,‡,§ Olivier Perraud,‡, Kevin R. West,‡,^
Elio Mattia,† and Sijbren Otto*,†
Centre for Systems Chemistry, Stratingh Institute, University of Groningen,
Nijenborgh 4, 9747 AG Groningen, The Netherlands, and Department of Chemistry,
University of Cambridge, Lensfield Road, Cambridge CB2 1EW, U.K.
s.otto@rug.nl
Received September 7, 2012
ABSTRACT
Designing synthetic receptors that bind biologically relevant guests in an aqueous solution remains a considerable challenge. We now report a
new synthetic receptor for nicotine, selected from a dynamic combinatorial library, that binds this guest in water at neutral pH through a
combination of hydrophobic and πꢀπ interactions.
(S)-Nicotine (Scheme 1) is a toxic alkaloid produced by
the tobacco plant.1 Nicotine has been used as a natural
insecticide,2 and its potential as a therapeutic agent for
treatment of Alzheimer’s,3,4 Parkinson’s,5 and psychiatric
diseases6 and as a pain controller7 has been investigated.
Nicotine acts principally as a potent agonist on the
nicotinic acetylcholine receptors such as R4β28 and induces
the release of several neurotransmitters.9 Intake of nicotine
often gives rise to addiction.10 At present, smoke cessation
treatments include nicotine replacement therapy11 where
nicotine is usually administered in a small quantity as a
nicotine β-cyclodextrin complex.12 Despite the important
biological roles of nicotine, relatively few synthetic recep-
tors for nicotine have been published to date.13ꢀ15 Indeed,
molecular recognition of nicotine in water is challenging
given the relatively hydrophilic nature of this alkaloid (log
D = 0.41 at pH 7.4).16
† University of Groningen.
‡ University of Cambridge.
§ Present address: Astex Pharmaceuticals, 436 Cambridge Science Park,
Cambridge, CB4 0QA, U.K.
ꢀ
Present address: Laboratoire de Chimie, Ecole Normale Superieure de
Lyon, CNRS 46, Allee d Italie, 69364 Lyon, France.
0
Here we report the use of dynamic combinatorial
chemistry17 as a simple and powerful tool for the discovery
ꢀ
^ Present address: BP Oil UK Ltd., Whitchurch Hill, Pangbourne, Read-
ing, Berkshire, RG8 7QR, U.K.
(1) Molecules of Death, 2nd ed.; Waring, R. H., Steventon, G. B.,
Mitchell, S. C., Eds.; Imperial College Press: London, U.K., 2007; Chapter
13, p 233.
(9) Kauer, J. A.; Malenka, R. C. Nat. Rev. Neurosci. 2007, 8, 844.
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C. Y. PLoS one 2011, 4, e18619.
(2) Wink, M. Theor. Appl. Genet. 1988, 75, 225.
(3) Oxidative Stress and Age-Related Neurodegeneration; Luo, Y.,
Packer, L., Eds.; CRC Press: Florida, United States, 2005; Chapter 16, p 265.
(4) Ono, K.; Hasegawa, K.; Yamada, M.; Naiki, H. Biol. Psychiatry
2002, 52, 880.
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Br. J. Pharmacol. 2009, 156, 1178.
(12) Davaran, S.; Rashidi, M. R.; Khandaghi, R.; Hashemi, M.
Pharmacol. Res. 2005, 51, 233.
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(6) Neural Mechanisms of Action of Drugs of Abuse and Natural
(13) Kearney, P. C.; Mizoue, L. S.; Kumpf, R. A.; Forman, J. E.;
McCurdy, A.; Dougherty, D. A. J. Am. Chem. Soc. 1993, 115, 9907.
(14) Zhou, Y.; Yu, H.; Zhang, L.; Xu, H.; Wu, L.; Sun, J.; Wang, L.
Microchim. Acta 2009, 164, 63.
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Reinforcers; Ubach, M. M., Mondragon-Ceballos, R., Eds.; Research Sign-
post: India, 2008; Chapter 2, p 121.
(7) Gaigeot, M. P.; Cimas, A.; Seydou, M.; Kim, J. Y.; Lee, S.;
Schermann, J. P. J. Am. Chem. Soc. 2010, 132, 18067.
(8) Xiu, X.; Puskar, N. L.; Shanata, J. A. P.; lester, H. A.; Dougherty,
D. A. Nature 2009, 458, 534.
(15) Berglund, J.; Cedergren, L.; Andersson, S. B. Int. J. Pharm.
1997, 156, 195.
(16) Log D quantifies the octanolꢀbuffer partioning. See: Zhu, C.;
Jian, L.; Chen, T.-M.; Hwang, K.-K. Eur. J. Med. Chem. 2002, 37, 399.
r
10.1021/ol302260n
Published on Web 10/12/2012
2012 American Chemical Society

Scheme 1. Structure of Nicotine and the Main Constituents of the Dynamic Combinatorial Library Designed to Recognize Nicotine
Made from Building Blocks 1 and 2
of a new synthetic receptor that can bind nicotine in water
at neutral pH.
library (DCL), receptor fragments (building blocks) react
reversibly with one another to form a mixture of inter-
converting library members that is under thermodynamic
control. The libraries are adaptive, i.e. introducing a guest
into a DCL of potential hosts will shift the equilibrium in
favor of (ideally) the best receptor(s) for the guest. Thus,
the guest drives the construction of the receptor from
smaller fragments.
Despite having only a few degrees of freedom, nicotine
lacks a well-defined conformation in solution.18 Therefore
designing a receptor for it using classical organic synthe-
sis is challenging. Dynamic combinatorial chemistry is a
powerful alternative approach for providing potential
receptors.19 In this approach it is sufficient to know the
functional groups of the target, while it is not necessary to
know their relative orientations. In a dynamic combinatorial
We selected building blocks 1 and 2 capable of reversible
covalent associations, using thiolꢀdisulfide exchange in
water, and displaying motifs potentially suitable for nico-
tine recognition. Nicotine contains both hydrophobic and
hydrophilic functionalities, and it is monoprotonated at
physiological pH. Building block 1 features a hydrophobic
surface area and exhibits the conformational flexibility
required to produce a diverse product distribution.
For both building blocks 1 and 2, aromatic moieties may
provide πꢀπ and cationꢀπ interactions with the guest and
the sulfonamide moieties of 1 may be able to interact with
the protonated pyrrolidine moiety of nicotine through
hydrogen bonding. Carboxylate groups in both building
blocks serve as water solubilizing groups and may interact
electrostatically with the protonated nicotine. The synth-
esis of building block 1 is outlined in Scheme 2. We first
prepared amine 11 which carries protected thiol and
carboxylic acid groups. This compound is a useful inter-
mediate for preparing building blocks for reversible di-
sulfide chemistry, as it may in principle be coupled to any
carboxylic acidorsulfonylchlorideand can be preparedon
a large scale (15 g). Coupling amine 11 to bis-sulfonyl
chloride 13, followed by deprotection, afforded dithiol 1 in
moderate yield. Synthesis of building block 2 has been
reported elsewhere.20
(17) For recent reviews, see: (a) Otto, S. Acc. Chem. Res.
201210.1021/ar200246j. (b) Moulin, E.; Cormos, G.; Giuseppone, N. Chem.
Soc. Rev. 2012, 41, 1031. (c) Cougnon, F. B. L.; Sanders, J. K. M. Acc.
Chem. Res. 201110.1021/ar200240m. (d) Hunt, R. A. R.; Otto, S. Chem.
Commun. 2011, 47, 847. (e) Dynamic Combinatorial Chemistry; Reek,
J. N. H., Otto, S., Eds.; Wiley-VCH: Weinheim, 2010. (f) Dynamic
Combinatorial Chemistry: In Drug Discovery, Bioorganic Chemistry,
And Materials Science; Miller, B. L., Ed.; John Wiley & Sons, Inc.:
Hoboken, New Jersy, 2010. (g) Corbett, P. T.; Leclaire, J.; Vial, L.; West,
K. R.; Wietor, J. L.; Sanders, J. K. M.; Otto, S. Chem. Rev. 2006, 106, 3652.
(18) Takeshima, T.; Fukumoto, R.; Egawa, T.; Konoka, S. J. Phys.
Chem. A 2002, 106, 8734.
(19) (a) Belowich, M. E.; Stoddart, J. F. Chem. Soc. Rev. 2012, 41,
2003. (b) Klein, J. M.; Saggiomo, V.; Reck, L.; Luning, U.; Sanders,
J. K. M. Org. Biomol. Chem. 2012, 10, 60. (c) Cougnon, F. B. L.; Jenkins,
N. A.; Pantos, G. D.; Sanders, J. K. M. Angew. Chem., Int. Ed. 2012, 51,
1443. (d) Stefankiewicz, A. R.; Sambrook, M. R.; Sanders, J. K. M.
Chem. Sci. 2012, 3, 2326. (e) Beeren, S. R.; Sanders, J. K. M.; Sanders,
J. K. M. J. Am. Chem. Soc. 2011, 133, 3804. (f) Chung, M.-K.; Severin,
K.; Lee, S. J.; Waters, M. L.; Gagne, M. R. Chem. Sci. 2011, 2, 744.
(g) Rodriguez-Docampo, Z.; Eugenieva-Ilieva, E.; Reyheller, C.;
Belenguer, A. M.; Kubik, S.; Otto, S. Chem. Commun. 2011, 47, 9798.
(h) Beeren, S. R. Chem. Sci. 2011, 2, 1560. (i) Bru, M.; Alfonso, I.; Botle,
M.; Burguete, M. I.; Luis, S. V. Chem. Commun. 2011, 47, 283. (j) Klein,
J. M.; Saggiomo, V.; Reck, L.; Mcpartlin, M.; Pantos, G. D.; Luning,
U.; Sanders, J. K. M. Chem. Commun. 2011, 47, 3371. (k) Schleef, F.;
Luning, U. Eur. J. Org. Chem. 2011, 2062. (l) Ladame, S. Org. Biomol.
Chem 2008, 6, 219. (m) Ludlow, R. F.; Otto, S. J. Am. Chem. Soc. 2008,
130, 12218. (n) Vial, L.; Ludlow, R. F.; Leclaire, J.; Perez-Fernandez, R.;
Otto, S. J. Am. Chem. Soc. 2006, 128, 10253.
Org. Lett., Vol. 14, No. 21, 2012
5405

Scheme 2. Synthesis of Building Block 1
Two libraries were prepared by mixing equimolar
amounts of building blocks 1 and 2 (5 mM in total), with
and without nicotine, and allowing these to oxidize and
equilibrate in aqueous solution (50 mM borate buffer,
pH 8.4) in the presence of air following standard protocols.21
The compositions of the resulting DCLs were analyzed
by HPLC and mass spectrometry (Figure 1). Cyclic mono-
mer 3, homodimer 4, heterodimer 5, homotetramer 6, and
catenane 7 were the major products in the absence of
nicotine. The asymmetric structure of 2 gives rise to four
different isomers of 6 and many different isomers of
catenane 7.20 When nicotine was introduced into the
DCL, the area of the peak corresponding to heterodimer
5 increased by an amplification factor22 of 3 relatively to
the untemplated DCL, at the expense of most of the other
library members.23 Introduction of nicotine drives the
conversion of 40% of dithiols 1 and 2 into the formation
of this receptor. Receptor 5 was isolated using preparative
Figure 1. HPLC analysis of the libraries made from equimolar
amount of dithiols 1 and 2 (5 mM in total), (a) in the absence
(top) and in the presence (bottom) of nicotine (2.5 mM).
(b) Amplification factors for the main library members.
located in the shielding cones of the aromatic rings of
receptor 5. Incontrast, the protons close tothe pyrrolidinyl
nitrogen, including the N-methyl protons, show a down-
field shift. These observations suggest that the pyridine
moiety, and not the pyrrolidine group of nicotine, is
located within the cavity of receptor 5; i.e. the formation
1
HPLC and characterized using H NMR, mass spectro-
metry, and elemental analysis.
The binding between 5 and nicotine was investigated
using 1H NMR spectroscopy. The signals of the pyridine
protons f, g, h, and i of complexed nicotine are notably
shielded relative to the corresponding signals for these
protons in unbound nicotine (Figure 2). The observed
shielding (Δδ g 0.29 ppm) suggests that the pyridine is
(20) West, K. R.; Ludlow, R. F.; Corbett, P. T.; Besenius, P. P.;
Mansfeld, F. M.; Cormack, P. A. G.; Sherrington, D. C.; Goodman,
J. M.; Stuart, M. C. A.; Otto, S. J. Am. Chem. Soc. 2008, 130, 10834.
(21) Otto, S.; Furlan, R. L. E; Sanders, J. K. M. J. Am. Chem. Soc.
2000, 122, 12063.
(22) The amplification factor of a library member corresponds to the
ratio of the HPLC-UV peak areas in the presence and in the absence of
the template.
(23) The fact that the homotetramer 6 was amplified in a library made
from building blocks 1 and 2 suggests that it may also have affinity for
nicotine. However 6 aggregates extensively, preventing its use as a
synthetic receptor (cf. ref 20).
Figure 2. 1H NMR analyses of nicotine (top), receptor 5
(18.2 mM) in the presence of 1 equiv of nicotine (middle), and
receptor 5 (18.2 mM) (bottom). Spectra were recorded at 300 K
in 200 mM borate buffer (pD 8.4).
5406
Org. Lett., Vol. 14, No. 21, 2012

of πꢀπ interactions appears to be favored over cationꢀπ
interactions.
to be driven predominantly by πꢀπ and hydrophobic
interactions. Our results show that it is possible, after the
design of only building block receptor fragments, to use
dynamic combinatorial chemistry to obtain a receptor that
is able to bind nicotine in water at neutral pH. Disulfide-
based receptorsof thistypemay find application ascarriers
for nicotine that are able to release the alkaloid upon
reduction of the disulfide linkages triggered by intracellu-
lar glutathione.25
The equilibrium constant for the binding of nicotine to
receptor 5 in 50 mM borate buffer (pH 8.4) was found tobe
1.81 ꢁ 103 Mꢀ1 as determined by isothermal titration
calorimetry (ITC). This affinity is comparable to that for
binding of nicotine to a cyclophane reported by Dougherty
et al.13 and significantly higher than the affinities of
β-cyclodextrin and cucurbit[7]uril for (S)-nicotine (Ka =
20ꢀ250 and 360 Mꢀ1 respectively).14,15
Performing ITC titrationson the binding of receptor5 to
nicotine at pH 6.9 and 9.3 led to comparable binding
constants: 3.43 ꢁ 103 and 3.52 ꢁ 103 Mꢀ1, respectively.
This indicates that binding affinity is only weakly de-
pendent on the protonation state of nicotine (pKA = 7.8)24
supporting the notion that cationꢀπ interactions do not
play a major role in the binding. Instead, binding appears
Acknowledgment. This work was supported by the
DCC Marie-Curie research training network, the EPSRC,
the University of Groningen, NWO, and COST CM0703
and CM1005.
Supporting Information Available. Experimental de-
tails. This material is available free of charge via the
Internet at http://pubs.acs.org.
(24) Petersson, E. J.; Choi, A.; Dahan, D. S.; Lester, H. A.; Dougherty,
D. A. J. Am. Chem. Soc. 2002, 124, 12662.
(25) West, K. R.; Otto, S. Curr. Drug Discovery Technol. 2005, 2, 123.
The authors declare no competing financial interest.
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