A chiral sensor for arginine and lysine

Article abstract of DOI:10.1021/ol991355u

(Graph presented) We provide access to a new class of C₁-or C₂-symmetrical host molecules 1 and 2 based on a spirobisindane skeleton. Whereas 1 is selective for short, rigid diamines, 2 prefers longer α,ω-dications. Of all the amino acid methyl esters, only those of lysine and arginine with the correct distance between their cationic groups form strong 1:1 complexes in DMSO with 2. NMR titrations reveal high association constants as well as discrimination between the enantiomers of lysine and arginine.

Full text of DOI:10.1021/ol991355u

ORGANIC
LETTERS
2000
Vol. 2, No. 5
605-608
A Chiral Sensor for Arginine and Lysine
,†
,‡
Mark Wehner,† Thomas Schrader,* Paolo Finocchiaro,* Salvatore Failla,‡ and
Giuseppe Consiglio‡
Institut fu¨r Organische Chemie und Makromolekulare Chemie,
Heinrich-Heine-UniVersita¨t Du¨sseldorf, UniVersita¨tsstrasse 1, D-40225 Du¨sseldorf,
Germany, and UniVersita´ di Catania, Facolta´ di Ingegneria, Istituto Chimico,
Citta´ UniVersitaria, Viale A. Doria, I-95125 Catania, Italy
thomas.schrader@uni-duesseldorf.de
Received December 15, 1999
ABSTRACT
We provide access to a new class of C - or C -symmetrical host molecules 1 and 2 based on a spirobisindane skeleton. Whereas 1 is selective
1
2
for short, rigid diamines, 2 prefers longer r,ω-dications. Of all the amino acid methyl esters, only those of lysine and arginine with the correct
distance between their cationic groups form strong 1:1 complexes in DMSO with 2. NMR titrations reveal high association constants as well
as discrimination between the enantiomers of lysine and arginine.
We recently introduced the xylylene bisphosphonate moiety
as a new general binding motif for amino alcohols1,2 and
used it for the construction of biomimetic adrenaline hosts3
as well as for the anomerselective recognition of amino
sugars.4 In this paper we present a new class of cleftlike
receptor molecules based on bisphosphonates and fully
equipped for multipoint binding of their dicationic substrate
(Figure 1).
tetraalkyl esters5 with LiBr: Refluxing a 40 mM solution of
the tetraalkyl ester with 1 equiv of dry lithium bromide in
2-hexanone or acetonitrile afforded after 5-100 h a precipi-
tate of the respective lithium salt, which was in many cases
analytically pure.6 The spirobisindane skeleton in 1 and 2
guarantees a high degree of rigidity, which should lead to a
pronounced preorganization of the different binding sites.
The mesitylene spacer in 2 was deliberately chosen, because
in former conformational analyses it was found that only
such sterically demanding moieties prevent rotation of the
bridge.5 A series of NMR binding experiments revealed a
remarkably different behavior of the two new host molecules
with respect to their chemoselectivity as well as their
enantioselectivity.
† Institut fu¨r Organische Chemie und Makromolekulare Chemie.
‡ Universita´ di Catania.
(1) Schrader, T. Angew. Chem., Int. Ed. Engl. 1996, 35, 2649-2651.
(2) Schrader, T. J. Org. Chem. 1998, 63, 264-272.
(3) Schrader, T.; Herm, M. Chem. Eur. J. 2000, 6, 1-9 (in press).
(4) Schrader, T. J. Am. Chem. Soc. 1998, 120, 11816-11817.
(5) (a) Consiglio, G. A.; Failla, S.; Finocchiaro, P. Phosphorus, Sulfur
Silicon 1998, 413, 134-139. (b) Consiglio, G. A.; Finocchiaro, P.; Failla,
S.; Hardcastle, K. I.; Ross, C.; Caccamese, S.; Giudice, G. Eur. J. Org.
Chem. 1999, 2799-2806.
Figure 1. Two new host molecules: the open-chain 1 has C2-
whereas macrocycle 2 has C1-symmetry.
The new host molecules were prepared by careful mono-
dealkylation of the respective cleftlike bisphosphonic acid
(6) Krawczyk, H. Synth. Commun. 1997, 27, 3151-3161.
10.1021/ol991355u CCC: $19.00 © 2000 American Chemical Society
Published on Web 02/19/2000

Job plots7 with 1, 2, and several R,ω-diammonium
compounds (Figure 2) proved that 1 forms 1:1 complexes
Figure 4. (a) The open host 1 allows short guest molecules to
penetrate deeply into the cleft. (b) The mesitylene bridge in 2,
however, provides a third hydrophobic binding site. This leads to
strong and chiral recognition of longer R,ω-diamines in DMSO.
Figure 2. Investigated chiral guest molecules: the distance between
the charged nitrogen atoms is successively increased by one carbon
or nitrogen atom.
The resulting binding curves were analyzed by nonlinear
regression methods and furnished the association constants
found in Table 1. It is obvious that the dependence of the
in all cases, whereas 2 binds two guest molecules as long as
they are shorter than lysine or arginine (Figure 3). This
Table 1. Association Constants Ka [M-1] from NMR Titrations
for Complexes of Hosts 1 and 2 with Dicationic Guests of
Varying N,N-Distance in DMSO at 20 °Ca
Ka(1:1) [M-1
]
Ka(1:1) [M-1
]
N+,N+-
open-chain
macrocycle
com- chiral
plex recogntn
guest distance
1b,c
2b,d
Cyc 2 atoms 8.4 × 103 ( 32%a 2.0 × 103 ( 20% 2:1
His 3 atoms 2.4 × 103 ( 11% 1.0 × 103 ( 32% 2:1
Orn 4 atoms 2.4 × 103 ( 28% 3.1 × 102 ( 38% n.d.
Lys 5 atoms 2.5 × 103 ( 14% 2.1 × 104 ( 26% 1:1
Arg 6 atoms 9.0 × 102 ( 43% 9.4 × 103 ( 42% 1:1
a Because of the strongly hygroscopic character of the bisphosphonate
salts, the DMSO solution contained ∼0.1% of water. b Errors are standard
deviations of the nonlinear regressions. c With 1 a 1:1 complex is formed
in all cases. d In all 2:1 complexes the phosphonates were calculated as
independent binding sites.
no
no
no
yes
yes
Figure 3. Job plots with 2 show 2:1 complexes for short guest
molecules, but 1:1 complexes for lysine and arginine. Left:
complexation of 2 with diaminocyclohexane (Cyc). Right: 2 with
arginine methyl ester (Arg).
divergent behavior could be explained with the different
sterical accessibility of the cleft in 1 and 2: In 1 there is
ample room for both cationic groups to approach the
phosphonate anions from within the cleft, with the effect
that small R,ω-diammonium compounds should lead to the
highest binding enthalpy, governed mainly by optimal
electrostatic interactions (Figure 4a). In 2, on the contrary,
the cleft is closed by the rigid mesitylene bridge, so that
only long R,ω-dicationic guests can reach from one phos-
phonate group to the other; at the same time their carbon
chain comes into close contact with the mesitylene bridge,
so that molecular recognition can be expected to become
more sensitive (Figure 4b).
order of total binding energies from the guest structure differs
enormously between host 1 and 2: the open chain host 1 is
selective for short rigid R,ω-diamines (Ka up to 8 × 103 M-1);
macrocycle 2, however, prefers longer dications (Ka up to
1.2 × 104 M-1). This is in perfect agreement with the above-
postulated binding mode.
No enantiodiscrimination is found for the open chain host
1, and even 2 can only distinguish between enantiomeric
guests with an N+‚‚‚N+ distance of more than five bonds.
Force field calculations9 suggest that only lysine and arginine
are long enough to span the bridged cleft of 2, so that two
salt bridges can be formed between their cationic groups and
the respective phosphonates. This indicates once more that
for an efficient chiral recognition the two binding sites within
the C2-symmetrical open chain host molecule 1 are not
sufficient. Only the additional third binding site offered in
C1-symmetrical macrocycle 2 by the chiral surface of the
We performed NMR titrations8 of various dicationic guests
with a successively increasing distance between their posi-
tively charged nitrogen atoms (Figure 2).
(7) (a) Job, P. Compt. Rend. 1925, 180, 928. (b) Blanda, M. T.; Horner,
J. H.; Newcomb, M. J. Org. Chem. 1989, 54, 4626.
(8) (a) Schneider, H. J.; Kramer, R.; Simova, S.; Schneider, U. J. Am.
Chem. Soc. 1988, 110, 6442. (b) Wilcox, C. S. In Frontiers in Supra-
molecular Chemistry; Schneider, H. J., Ed.; Verlag Chemie: Weinheim,
1991; p 123.
(9) Molecular Modeling Program: CERIUS2 from Molecular Simulations
Inc., Force field: Dreiding 2.21.
606
Org. Lett., Vol. 2, No. 5, 2000

mesitylene bridge leads to a detectable enantiomeric dis-
crimination. Although the ee’s are not very high (2:L-Arg,
17%; 2:L-Lys, 33%), well-resolved NMR signals are pro-
duced during the NMR titration, so that optically pure 2 may
be used as a shift reagent for the quantitative determination
of the enantiomeric purity of arginine and lysine derivatives
(Figure 5).
able to undergo this typical hydrogen bond pattern. Whereas
in arginine this must be the R-NH3+ group, lysine probably
prefers the flexible and sterically mobile ꢀ-amino group. Now
three binding sites evolve in the amino acid molecules, with
each exhibiting a different binding strength. This is the
prerequisite for chemoselective and also enantioselective
recognition, met only by arginine and lysine in our experi-
ments.
Few host molecules with enantioselective recognition of
arginine and lysine have been published to date: Jung et al.
developed monolayers of cyclohexapeptides immobilized on
gold whose interactions with aqueous amino acid solutions
were transduced by changes of the resonance frequency of
a quartz crystal microbalance.10 Enantiomeric arginine and
lysine recognition has also been achieved by podand and
crown-type amide derivatives of the naturally occurring
monensin ionophore.11 Polyclonal antibodies can be used in
an enantioselective enzyme-linked immunosorbent assay for
dinitrophenylamino acids.12 Finally, Famulok et al. used an
in vitro selection process to produce an L-citrullin binding
RNA aptamer, which was subjected to further evolution into
an L-arginine binder.13 All the above-mentioned methods,
Figure 5. Formation of the diastereomeric complexes can be
monitored as a typical signal splitting of distinct host NMR signals.
Different upfield shifts are observed for the two nonequivalent
aromatic receptor protons ortho to the phosphonate moiety in 2,
on complex formation with lysine methyl ester.
(10) Weiss, T.; Leipert, D.; Kaspar, M.; Jung, G.; Goepel, W. AdV. Mater.
1999, 11, 331-335.
(11) Maruyama, K.; Sohmiya, H.; Tsukube, H. Tetrahedron 1992, 48,
805-818.
(12) Hofstetter, H.; Hofstetter, O.; Wistuba, D. Anal. Chim. Acta 1996,
332, 285-290.
(13) Famulok, M. J. Am. Chem. Soc. 1994, 116, 1698-1706.
(14) Dilithium bis(5,5′ethylphosphonato)-6,6′-dihydroxy-3,3,3′,3′-tet-
ramethyl-1,1′-spiro-bisindane 1: To a solution of 1 (0.3 mmol) in dry
methylbutyl ketone (15 mL) was added lithium bromide (0.6 mmol), and
the mixture was heated to reflux for 1 h. The white precipitate was filtered,
suspended in diethyl ether, and sonicated for 0.5 h. The solid was filtered
again and dried under reduced pressure at 130 °C over phosphorus
pentoxide: yield 95%; 1H NMR (500 MHz, [D6]DMSO) δ ) 0.79 (t, 6H,
3JHH ) 14.5 Hz), 1.01 (s, 6H), 1.07 (s, 6H), 1.87 (d, 2H, 2JHH ) 13.2 Hz),
Additional structural information from a careful analysis
of the NMR data provides a more detailed picture of the
molecular recognition of long basic amino acids by 2: The
signal splitting of an aromatic host proton observed in the
complex between 2 and arginine occurs at the opposite end
of 2 compared to its complex with lysine. Since this effect
must originate from an interaction of that host proton with
the chiral environment of the R-C atom, the amino acids
obviously prefer an opposite orientation in the complex.
Only one of the nonequivalent O-CH2 methylene groups in
2 shows a strong downfield shift during the titration (used
for Ka calculation). This correlates well with an additional
N-Hδ+‚‚‚Oδ- hydrogen bond observed in the energy mini-
mization process (Figure 6). Only an ammonium group is
2
4
1.99 (d, 2H, JHH ) 13.2 Hz), 3.38 (m, 4H), 5.69 (d, 2Harom, JHP ) 4.4
3
Hz), 6.94 (d, 2Harom, JHP ) 12.6 Hz); 13C NMR (126 MHz, [D6]DMSO)
3
δ ) 14.13, 16.86 (d, JCP ) 7.3 Hz), 22.03, 25.70, 30.03, 30.84, 32.10,
42.69, 57.34, 59.13, 59.26 (d, 1JCP ) 42.5 Hz), 110.17 (d, 3JCP ) 10.9 Hz),
125.43 (d, 2JCP ) 6.07 Hz), 141.34 (d, 3JCP ) 12.1 Hz), 154.21, 160.15 (d,
2JCP ) 7.28 Hz); 31P{1H} NMR (202 MHz, [D6]DMSO) δ ) 13.85 ppm;
FAB-MS m/z ) 537 (100%, M+); IR (cm-1) 2956, 2903, 1508, 1474, 1418,
1363, 1184, 1125, 1041, 946, 780. To get an analytically pure sample the
lithium salt was protonated with HCl and filtered and the resulting
bisphosphonic acid dried under reduced pressure; calcd C 57.21, H 6.53;
found C 57.90, H 7.00. Dilithium bis(5,5′-ethylphosphonato)-6,6′-(2,4,5-
trimethyl-1,3-benzyloxy)-3,3,3′,3′-tetramethyl-1,1′-spiro-bisindane 2: To
a solution of 2 (0.3 mmol) in dry acetonitrile (15 mL) was added lithium
bromide (0.6 mmol), and the mixture was heated to reflux for 100 h. The
white precipitate was filtered, suspended in diethyl ether, and sonicated for
0.5 h. The solid was filtered again and dried under reduced pressure at 130
°C over phosphorus pentoxide: yield 90%; 1H NMR (500 MHz, [D4]-
methanol) δ ) 1.20 (s, 3H), 1.32 (t, 3H, 3JHH ) 14.5 Hz), 1.35 (t, 3H, 3JHH
2
) 14.5 Hz), 1.36 (s, 6H), 1.37 (s, 3H), 1.63 (s, 3H), 1.81 (d, 1H, JHH
)
12.6 Hz), 1.92 (d, 1H, 2JHH ) 12.7 Hz), 2.30 (d, 1H, 2JHH ) 12.6 Hz), 2.40
(d, 1H, 2JHH ) 12.0 Hz), 2.41 (s, 3H), 2.57 (s, 3H), 3.84 (m, 1H), 3.93 (m,
2
2
1H), 3.98 (m, 2H), 5.28 (dd, 2H, JHH ) 95.2 Hz), 5.29 (d, 2H, JHH
)
22.05 Hz), 5.53 (d, 1Harom
Hz), 6.83 (s, 1Harom); 7.54 (d, 1Harom
,
4JHP ) 5.1 Hz), 6.04 (d, 1Harom
,
4JHP ) 5.1
,
3JHP ) 13.9 Hz), 7.78 (d, 1Harom
,
3JHP ) 13.3 Hz); 13C NMR (126 MHz, [D4]methanol) δ ) 14.88, 17.11
(m), 19.84, 21.80, 31.02, 31.39, 31.70, 43.93, 44.00, 58.91, 59.12, 59.71,
61.08 (d, 2JCP ) 6.06 Hz), 61.26 (d, 2JCP ) 6.06 Hz), 65.35, 72.24, 109.46
(d, 3JCP ) 9.72 Hz), 121.64 (d, 3JCP ) 10.9 Hz), 123.63 (d, 1JCP ) 175.93
Hz), 129.38 (d, 2JCP ) 6.07 Hz), 129.61 (d, 2JCP ) 6.07 Hz), 130.31, 132.23,
132.32, 132.35, 138.01, 139.63, 141.07, 143.61 (d, 3JCP ) 13.3 Hz), 149.70
Figure 6. Energy-minimized structure of the proposed complex
geometry for Lys-2. Note the additional H-bond to the only
accessible ether oxygen on the left, which determines the relational
orientation of both partners.
3
4
2
(d, JCP ) 13.36 Hz), 153.77 (d, JCP ) 2.43 Hz), 154.49, 158.76 (d, JCP
) 2.42 Hz), 160.90 (d, JCP ) 2.42 Hz); 31P{1H} NMR (202 MHz, [D4]-
2
methanol) δ ) 12.90/14.09; FAB-MS m/z ) 681 (0.6%, M+); IR (cm-1
)
2956, 2870, 2900, 1508, 1474, 1396, 1362, 1200, 1185, 1125, 1046, 700,
781; (2 + H2O) calcd C 61.53, H 6.93; found C 61.94, H 6.73.
Org. Lett., Vol. 2, No. 5, 2000
607

however, either use complex synthetic structures or require
elaborated microbiological protocols.
Acknowledgment. We thank the Deutsche Forschungs-
gemeinschaft and the Fonds der Chemischen Industrie for
financial support.
In summary, we have presented a new class of rigid
receptor molecules for organic dicationic guests. Depending
on the accessibility of their cleft, these hosts are selective
for short or long R,ω-diammonium and -guanidinium
compounds. Because of their inherent chirality, we could
examine their potential for chiral discrimination and found
that only those host-guest combinations which allow a three-
point interaction were effective. Thus, the bridged macrocyle
2 represents a chiral shift reagent for arginine and lysine
derivatives. In the future we intend to develop new sensors
from 2 which selectively recognize N-terminal arginine and
lysine in peptides and proteins.
Supporting Information Available: Experimental pro-
cedures and full characterization for compounds 1 and 2,
NMR titration curves, Job plots, and force field calcula-
tions of complex geometries for selected complexes.
This material is available free of charge via the Internet at
http://pubs.acs.org.
OL991355U
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Org. Lett., Vol. 2, No. 5, 2000