Potent CXCR4 antagonists containing amidine type peptide bond isosteres

Article abstract of DOI:10.1021/ml200047e

A series of FC131 [cyclo(-d-Tyr-Arg-Arg-Nal-Gly-)] analogues containing amidine type peptide bond isosteres were synthesized as selective CXC chemokine receptor type 4 (CXCR4) antagonists. An isosteric amidine substructure was constructed by a macrocyclization process using nitrile oxide-mediated C-N bond formation. All of the amidine-containing FC131 analogues exhibited potent SDF-1 binding inhibition to CXCR4. The Nal-Gly-substituted analogue was characterized as one of the most potent cyclic pentapeptide-based CXCR4 antagonists reported to date. The improved activity against human immunodeficiency virus (HIV) type-1 X4 strains suggested that addition of another basic amidine group to the peptide backbone effectively increases the selective binding of the peptides to CXCR4 receptor.

Full text of DOI:10.1021/ml200047e

LETTER
pubs.acs.org/acsmedchemlett
Potent CXCR4 Antagonists Containing Amidine Type Peptide Bond
Isosteres
Eriko Inokuchi,† Shinya Oishi,*,† Tatsuhiko Kubo,† Hiroaki Ohno,† Kazuya Shimura,‡ Masao Matsuoka,‡ and
Nobutaka Fujii*,†
†Graduate School of Pharmaceutical Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan
‡Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan
S Supporting Information
b
ABSTRACT: A series of FC131 [cyclo(-D-Tyr-Arg-Arg-Nal-Gly-)] analogues
containing amidine type peptide bond isosteres were synthesized as selective
CXC chemokine receptor type 4 (CXCR4) antagonists. An isosteric amidine
substructure was constructed by a macrocyclization process using nitrile oxide-
mediated CꢀN bond formation. All of the amidine-containing FC131 analo-
gues exhibited potent SDF-1 binding inhibition to CXCR4. The Nal-Gly-
substituted analogue was characterized as one of the most potent cyclic
pentapeptide-based CXCR4 antagonists reported to date. The improved activity against human immunodeficiency virus (HIV)
type-1 X4 strains suggested that addition of another basic amidine group to the peptide backbone effectively increases the selective
binding of the peptides to CXCR4 receptor.
KEYWORDS: Amidine, chemokine, CXCR4 antagonist, FC131, nitrile oxide, peptidomimetics
XC chemokine receptor type 4 (CXCR4) is a G protein-
coupled receptor1 for stromal cell-derived factor 1 (SDF-1)2
bioactivity.17ꢀ19 For example, replacement of several peptide
bonds with reduced amide bonds 5 or alkene dipeptide isosteres
6 resulted in greatly reduced bioactivity (Figure 2), which suggests
that these isosteric substructures are not appropriate for mod-
ifications of FC131. On the basis of these previous studies of
FC131 derivatives and the common structural features of highly
potent CXCR4 antagonists, we envisioned that addition of basic
functional group(s) onto FC131 could improve its potency.
Recently, we established a novel synthetic approach for
amidine type peptide bond isosteres 7 using nitrile oxide-
mediated CꢀN bond formation.20 Amidine type peptide bond
isosteres were designed based on substitution of the peptide bond
carbonyl (CdO) group with an imino (CdNH) group.21,22
Under physiological conditions, the positive charge of the
protonated amidines 70 is delocalized over two nitrogens. Sub-
structure 70 contributes both the double bond character of
peptide bond 4 and the basic character of reduced amide bond
isostere 50. Therefore, the addition of this acyclic amidine group
to the framework was expected to enhance the bioactivity with-
out inducing large conformational change in the backbone
structure. Accordingly, amidine-containing FC131 analogues
15a,b and 15dꢀf were designed, in which each peptide bond
was replaced with the amidine substructure (Table 1). Com-
pounds 15c and 15g were also designed as epimers of 15b (at the
Nal position) and 15f (at the Tyr position), respectively. In this
study, we investigated the contribution of amidine units to the
bioactivity of amidine-containing FC131 analogues 15aꢀg.
C
that plays a critical role in the metastasis of mammary carcinoma3
and in human immunodeficiency virus (HIV) type-1 infection.4
CXCR4 is an important therapeutic target for these diseases.5 To
date, several types of CXCR4 antagonists with a variety of
scaffolds have been reported (Figure 1).6ꢀ11 Although the
scaffolds of these antagonists have little in common, the antago-
nists all contain a number of basic groups. For example, the
polyphemusin II-derived anti-HIV peptide, T140 1,6 has seven
basic Arg and Lys residues. Another example is the small
molecule antagonist AMD3100, which contains eight secondary
or tertiary amino nuclei.7 Crystal structure analysis and mutation
experiments of the receptor indicated that the ion-pairing inter-
action between the basic functional groups of the antagonists
and the acidic residues in CXCR4 contributes to the potent
bioactivity.12ꢀ14
FC131 [cyclo(-D-Tyr-Arg-Arg-Nal-Gly-), Nal = 3-(2-naphthyl)-
alanine] 2 is a highly potent CXCR4 antagonist (Figure 1).15
Using the peptide library approach, the potent anti-HIV activity
of T140 1 was reproduced with the appropriate arrangement of
basic and aromatic residues on the cyclic pentapeptide frame-
work of FC131. Further systematic structureꢀactivity studies,
such as alanine-scanning or amino acid optimizations, have been
conducted to identify the structural and electrostatic require-
ments for the bioactivity of FC131.16 Substitution of an Arg
residue in 2 with the epimeric N-methyl-D-arginine led to
identification of cyclic pentapeptide-based CXCR4 antagonist,
FC122 3, which is the most potent CXCR4 antagonist among the
FC131 derivatives reported to date.16 However, backbone mod-
ification of 2 using peptide bond isosteres did not improve the
Received: February 15, 2011
Accepted: March 27, 2011
Published: March 28, 2011
r
2011 American Chemical Society
477
dx.doi.org/10.1021/ml200047e ACS Med. Chem. Lett. 2011, 2, 477–480
|

ACS Medicinal Chemistry Letters
LETTER
Figure 1. Structures of reported CXCR4 antagonists. Bold residues are basic residues. Nal = 3-(2-naphthyl)alanine.
resins 10d and 10e, di-Boc-protected arginine [Arg(Boc)2]-
derived aldehyde was utilized for the preparation of Arg-Arg-
and Arg-Nal-substituted analogues 15d and 15e. Peptide elonga-
tion was performed by the standard Fmoc-based solid-phase
synthesis using N,N0-diisopropylcarbodiimide (DIC)/N-hydro-
xybenzotriazole (HOBt) in DMF. The cleavage of peptide
aldoxime resin 11b provided the linear peptide aldoxime 12b,
which was treated with N-chlorosuccinimide and triethylamine
to afford cyclic amidoxime (N-hydroxyamidine) 13b.20 After
Raney Ni-mediated reduction to the amidine 14b, deprotection
with a cocktail of 1M TMSBr, thioanisole/TFA, m-cresol, and
1,2-ethanedithiol gave the desired amidine-containing FC131
analogue 15b. The analogues 15a and 15cꢀg were synthesized
by the same procedure. During this nitrile oxide-mediated
cyclization, significant epimerizations of the activated C termini
of the peptides were not observed.23
Figure 2. Structures of the peptide bond and the mimetics.
The potency of the resulting FC131 analogues 15aꢀg to
inhibit [125I]-SDF-1 binding to CXCR4 was evaluated (Table 1).
Peptides 15aꢀe were more potent than the control peptides 2
and 3. This indicates that the basic amidine units had the
expected effect of increasing the affinity with the receptor. By
contrast, substitution of the Tyr-Arg dipeptide decreased the
CXCR4 antagonistic activity (15f and 15g). These observations
were consistent with our previous study, in that the D-Tyr-Arg
peptide bond is an indispensable functional group that is required
to maintain the peptide conformation and the interaction with
the receptor. Potent bioactivity of D-MeArg-substituted peptide
(3) indicated that the amide hydrogen of Arg is not critical to the
bioactivity,16 while the local backbone conformation, particularly
with respect to the orientation of D-Tyr carbonyl oxygen, may
contribute to the receptor binding. Less potent bioactivity of 15f
and 15g supports the significant contribution of D-Tyr carbonyl
group in peptides 2 and 3.
Nal-Gly-modified analogues 15b and 15c were the most
potent inhibitors of the compounds synthesized in this study.
At this Nal-Gly dipeptide position, the amidine substructure was
more appropriate than the reduced amide motif (ꢀCH2ꢀNHꢀ),
which exhibited slightly lower bioactivity than FC131 in our
previous study.17 It is interesting that modification at the Arg-Nal
dipeptide (15d) gave potent bioactivity, whereas replacement of
this dipeptide with the reduced amide bond in our earlier study
reduced receptor binding.17 This indicates that the high bioactivity
of 15d could be caused by conformational advantage rather than
Table 1. Inhibitory Activity of FC131 and the Derivatives
15aꢀg against [125I]-SDF-1 Binding to CXCR4
peptide
sequencea
IC50 (nM)b
FC131 (2)
FC122 (3)
15a
cyclo(-D-Tyr-Arg-Arg-Nal-Gly-)
cyclo(-D-Tyr-D-MeArg-Arg-Nal-Gly-)
cyclo(-D-Tyr-Arg-Arg-Nal-Gly-Ψ-)
cyclo(-D-Tyr-Arg-Arg-Nal-Ψ-Gly-)
cyclo(-D-Tyr-Arg-Arg-D-Nal-Ψ-Gly-)
cyclo(-D-Tyr-Arg-Arg-Ψ-Nal-Gly-)
cyclo(-D-Tyr-Arg-Ψ-Arg-Nal-Gly-)
cyclo(-D-Tyr-Ψ-Arg-Arg-Nal-Gly-)
cyclo(-Tyr-Ψ-Arg-Arg-Nal-Gly-)
126 ( 68
37 ( 20
9.4 ( 3.0
4.2 ( 0.31
4.9 ( 1.1
11 ( 2.9
16 ( 7.2
679 ( 132
334 ( 6.2
15b
15c
15d
15e
15f
15g
a Ψ indicates the ψ[ꢀC(dNH)ꢀNHꢀ] substructure. Nal, 3-(2-
naphthyl)alanine. b IC50 values are the concentrations for 50% inhibition
of the [125I]-SDF-1R binding to CXCR4 transfectant of HEK293 cells.
Synthesis of the L-Nal-Gly-substituted analogue 15b is shown
in Scheme 1 as a representative preparation of peptides 15aꢀg.
The first Nal residue was loaded onto aminooxy-2-chlorotrityl
resin 820 by treatment with Fmoc-3-(2-naphthyl)alaninal 9b
under acid-free conditions to give aldoxime resin 10b. To
prevent possible intramolecular cyclization between side chain
guanidino and aldehyde groups in the preparation of aldoxime
478
dx.doi.org/10.1021/ml200047e |ACS Med. Chem. Lett. 2011, 2, 477–480

ACS Medicinal Chemistry Letters
LETTER
Scheme 1. Synthesis of Amidine-Containing FC131 Analogue 15b
Table 2. Anti-HIV Activity of FC131 and the Derivatives
(data not shown), which is reported to be an alternative receptor
of SDF-1.
15aꢀg
Anti-HIV activity based on inhibition of human immunode-
ficiency virus type 1 (HIV-1) entry into target cells was examined
by the MAGI assay using NL4-3, IIIB, and Ba-L strains (Table 2).
NL4-3 and IIIB strains use CXCR4 for entry into cells, and the
FC131 analogues 15aꢀe showed very potent anti-HIV activity
against these strains. The two Tyr-Arg-substituted peptides 15f
and 15g only moderately inhibited infection with these two
strains, which was similar to their inhibitory effects against SDF-
1-CXCR4 binding. The Ba-L strain uses CCR5 for entry to cells,
and none of the peptides showed inhibitory activity against this
strain even with the peptides at 10 μM. This result indicates that
peptides 15aꢀg show similar target specificity to FC131 as
selective CXCR4 antagonists.26 The cytotoxicity of analogues
15aꢀg was not observed even at 10 μM in the MAGI assay.
In conclusion, we developed novel potent cyclic pentapeptide-
based CXCR4 antagonists containing amidine type peptide bond
isosteres. Substitutions of four peptide bonds in FC131, except
for the D-Tyr-Arg position, with an amidine motif, improved the
inhibitory activity against SDF-1 binding and HIV-1 infection by
X4 strains. It was also demonstrated that the analogues were
selective antagonists for CXCR4 and not for CXCR7 and CCR5,
which are the targets shared by SDF-1 (CXCR7) and HIV-1
(CCR5). Further studies to understand the binding mode of
these peptidomimetics and to develop derivatives with multiple
amidine motifs in a single molecule are in progress.
EC50 (nM)a
peptide
NL4-3
IIIB
Ba-L
b
FC131 (2)
FC122 (3)
15a
21 ( 4.3
7.6 ( 0.34
1.3 ( 0.43
1.4 ( 0.44
2.2 ( 0.04
4.4 ( 1.0
1.9 ( 0.47
300 ( 57
248 ( 55
21 ( 5.9
7.6 ( 1.1
ꢀ
b
ꢀ
b
0.61 ( 0.10
1.0 ( 0.23
2.0 ( 0.59
6.3 ( 0.47
1.2 ( 0.29
258 ( 47
238 ( 37
ꢀ
b
15b
ꢀ
b
15c
ꢀ
b
15d
ꢀ
b
15e
ꢀ
b
15f
ꢀ
b
15g
ꢀ
a EC50 is the concentration that blocks HIV-1 infection by 50%. b No
inhibitory activity was observed at 10 μM.
the basicity. The partial double bond character of the amidine
motif in 15d might favorably constrain the cyclic configuration
and place the side chains in the appropriate spatial orientations of
the pharmacophore.
Recent reports of the docking model of FC131-CXCR4
interactions indicated that the amino group of the Gly-D-Tyr
peptide bond forms a hydrogen bond to the carbonyl group of
Ala95.24,25 It was also suggested that the Arg-Arg dipeptide is
surrounded by acidic residues in CXCR4 (Glu288 and
Asp262).24,25 The potent bioactivities of Gly-D-Tyr- and Arg-
Arg-substituted analogues 15a and 15e may support the presence
of these favorable interactions, which were enhanced by the
introduction of positively charged amidine motifs. In particular,
the amidine in the Arg-Arg dipeptide could form salt bridge(s)
with the negatively charged residues.
Interestingly, both stereoisomers of Nal-Gly- and Tyr-Arg-
modified analogues (15b,c and 15f,g) showed similar antagonis-
tic activities [15b (IC50 = 4.2 nM) and 15c (IC50 = 4.9 nM); 15f
(IC50 = 679 nM) and 15g (IC50 = 334 nM)]. This is in contrast
to the suggestion that the bioactivity of FC131 derivatives is
sensitive to the configurations of the component residues.16,17
These results may suggest that the local conformation around
the amidine motif is more flexible in cyclic pentapeptides than
in the original peptide bond. Of note, none of the peptides
15aꢀg showed inhibition against SDF-1-CXCR7 interaction
’ ASSOCIATED CONTENT
S
Supporting Information. Experimental procedures and
b
characterization data for all new compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*Tel: þ81-75-753-4551. Fax: þ81-75-753-4570. E-mail: soishi@
pharm.kyoto-u.ac.jp (S.O.) and nfujii@pharm.kyoto-u.ac.jp
(N.F.).
Funding Sources
This work was supported by Grants-in-Aid for Scientific Research
and Targeted Protein Research Program from MEXT and Health
andLaborScienceResearchGrants(ResearchonHIV/AIDS,Japan).
479
dx.doi.org/10.1021/ml200047e |ACS Med. Chem. Lett. 2011, 2, 477–480

ACS Medicinal Chemistry Letters
LETTER
E.I. was supported by a JSPS Research Fellowship for Young
Scientists.
CXCR4 reveals that T140 is an inverse agonist and that AMD3100 and
ALX40-4C are weak partial agonists. J. Biol. Chem. 2002, 277, 24515–
24521.
(14) Wu, B.; Chien, E. Y. T.; Mol, C. D.; Fenalti, G.; Liu, W.;
Katritch, V.; Abagyan, R.; Brooun, A.; Wells, P.; Bi, F. C.; Hamel, D. J.;
Kuhn, P.; Handel, T. M.; Cherezov, V.; Stevens, R. C. Structures of the
CXCR4 chemokine GPCR with small-molecule and cyclic peptide
antagonists. Science 2010, 330, 1066–1071.
(15) Fujii, N.; Oishi, S.; Hiramatsu, K.; Araki, T.; Ueda, S.; Tama-
mura, H.; Otaka, A.; Kusano, S.; Terakubo, S.; Nakashima, H.; Broach,
J. A.; Trent, J. O.; Wang, Z.; Peiper, S. C. Molecular-size reduction of a
potent CXCR4-chemokine antagonist using orthogonal combination of
conformation- and sequence-based libraries. Angew. Chem., Int. Ed.
2003, 42, 3251–3253.
(16) Ueda, S.; Oishi, S.; Wang, Z.; Araki, T.; Tamamura, H.;
Cluzeau, J.; Ohno, H.; Kusano, S.; Nakashima, H.; Trent, J. O.; Peiper,
S. C.; Fujii, N. Structureꢀactivity relationships of cyclic peptide-based
chemokine receptor CXCR4 antagonists: disclosing the importance of
side-chain and backbone functionalities. J. Med. Chem. 2007,
50, 192–198.
(17) Tamamura, H.; Araki, T.; Ueda, S.; Wang, Z.; Oishi, S.; Esaka,
A.; Trent, J. O.; Nakashima, H.; Yamamoto, N.; Peiper, S. C.; Otaka, A.;
Fujii, N. Identification of novel low molecular weight CXCR4 antago-
nists by structural tuning of cyclic tetrapeptide scaffolds. J. Med. Chem.
2005, 48, 3280–3289.
(18) Tamamura, H.; Hiramatsu, K.; Ueda, S.; Wang, Z.; Kusano, S.;
Terakubo, S.; Trent, J. O.; Peiper, S. C.; Yamamoto, N.; Nakashima, H.;
Otaka, A.; Fujii, N. Stereoselective synthesis of [L-Arg-L/D-3-(2-
naphthyl)alanine]-type (E)-alkene dipeptide isosteres and its applica-
tion to the synthesis and biological evaluation of pseudopeptide
analogues of the CXCR4 antagonist FC131. J. Med. Chem. 2005,
48, 380–391.
(19) Narumi, T.; Hayashi, R.; Tomita, K.; Kobayashi, K.; Tanahara,
N.; Ohno, H.; Naito, T.; Kodama, E.; Matsuoka, M.; Oishi, S.; Fujii, N.
Synthesis and biological evaluation of selective CXCR4 antagonists
containing alkene dipeptide isosteres. Org. Biomol. Chem. 2010,
8, 616–621.
(20) Inokuchi, E.; Yamada, A.; Hozumi, K.; Tomita, K.; Oishi, S.;
Ohno, H.; Nomizu, M.; Fujii, N. Org. Biomol. Chem. 2011, DOI:
10.1039/c0ob01193b.
(21) Moser, H.; Fliri, A.; Steiger, A.; Costello, G.; Schreiber, J.;
Eschenmoser, A. Poly(dipeptamidinium) salts: Definition and methods
of preparation. Helv. Chim. Acta 1986, 69, 1224–1262.
’ ABBREVIATIONS
CXCR4, CXC chemokine receptor type 4; HIV-1, human im-
munodeficiency virus type 1; Nal, 3-(2-naphthyl)alanine; DIC,
N,N0-diisopropylcarbodiimide; HOBt, N-hydroxybenzotriazole;
SDF-1, stromal cell-derived factor 1
’ REFERENCES
(1) Loetscher, M.; Geiser, T.; O'Reilly, T.; Zwahlen, R.; Baggiolini,
M.; Moser, B. Cloning of a human seven-transmenbrane domain
receptor, LESTR, that is highly expressed in leukocytes. J. Biol. Chem.
1994, 269, 232–237.
(2) Nagasawa, T.; Kikutani, H.; Kishimoto, T. Molecular cloning and
structure of a pre-B-cell growth-stimulating factor. Proc. Natl. Acad. Sci.
U.S.A. 1994, 91, 2305–2309.
(3) M€uller, A.; Homey, B.; Soto, H.; Ge, N.; Catron, D.; Buchanan,
M. E.; McClanahan, T.; Murphy, E.; Yuan, W.; Wagner, S. N.; Barrera,
J. L.; Mohar, A.; Verꢀastegui, E.; Zlotnik, A. Involvement of chemokine
receptors in breast cancer metastasis. Nature 2001, 410, 50–56.
(4) Feng, Y.; Broder, C. C.; Kennedy, P. E.; Berger, E. A. HIV-1 entry
cofactor: functional cDNA cloning of a seven-transmembrane, G
protein-coupled receptor. Science 1996, 272, 872–877.
(5) O'Hayre, M.; Salanga, C. L.; Handel, T. M.; Hamel, D. Emerging
concepts and approaches for chemokine-receptor drug discovery. Expert
Opin. Drug Discovery 2010, 5, 1109–1122.
(6) Tamamura, H.; Xu, Y.; Hattori, T.; Zhang, X.; Arakaki, R.;
Kanbara, K.; Omagari, A.; Otaka, A.; Ibuka, T.; Yamamoto, N.;
Nakashima, H.; Fujii, N. A low-molecular-weight inhibitor against the
chemokine receptor CXCR4: A strong anti-HIV peptide T140. Biochem.
Biophys. Res. Commun. 1998, 253, 877–882.
(7) Bridger, G. J.; Skerlj, R. T.; Thornton, D.; Padmanabhan, S.;
Martellucci, S. A.; Henson, G. W.; Abrams, M. J.; Yamamoto, N.; De
Vreese, K.; Pauwels, R.; De Clercq, E. Synthesis and structureꢀactivity
relationships of phenylenebis(methylene)-linked bis-tetraazamacro-
cycles that inhibit HIV replication. Effects of macrocyclic ring size and
substituents on the aromatic linker. J. Med. Chem. 1995, 38, 366–378.
(8) Doranz, B. J.; Grovit-Ferbas, K.; Sharron, M. P.; Mao, S.-H.;
Bidwell Goetz, M.; Daar, E. S.; Doms, R. W.; O'Brien, W. A. A small-
molecule inhibitor directed against the chemokine receptor CXCR4
prevents its use as an HIV-1 coreceptor. J. Exp. Med. 1997,
186, 1395–1400.
(9) Bridger, G. J.; Skerlj, R. T.; Hernandez-Abad, P. E.; Bogucki,
D. E.; Wang, Z.; Zhou, Y.; Nan, S.; Boehringer, E. M.; Wilson, T.;
Crawford, J.; Metz, M.; Hatse, S.; Princen, K.; De Clercq, E.; Schols, D.
Synthesis and structureꢀactivity relationships of azamacrocyclic C-X-C
chemokine receptor 4 antagonists: Analogues containing a single
azamacrocyclic ring are potent inhibitors of T-cell tropic (X4) HIV-1
replication. J. Med. Chem. 2010, 53, 1250–1260.
(10) Skerlj, R. T.; Bridger, G. J.; Kaller, A.; McEachern, E. J.;
Crawford, J. B.; Zhou, Y.; Atsma, B.; Langille, J.; Nan, S.; Veale, D.;
Wilson, T.; Harwig, C.; Hatse, S.; Princen, K.; De Clercq, E.; Schols, D.
Discovery of novel small molecule orally bioavailable C-X-C chemokine
receptor 4 antagonists that are potent inhibitors of T-tropic (X4) HIV-1
replication. J. Med. Chem. 2010, 53, 3376–3388.
(22) Jones, R. C. F.; Ward, G. J. Amide bond isosteres: imidazolines
in pseudopeptide chemistry. Tetrahedron Lett. 1988, 29, 3853–3856.
(23) Epimerizations in the preparation of protected cyclic peptides
13b and 13f were verified by the comparative HPLC analysis of the
amidine isomers 14b/14c and the amidoxime isomers 13f/13g, respec-
tively (14b, 90% de; 13f, 95% de; see the Supporting Information for
details).
ꢁ
(24) Vabenø, J.; Nikiforovich, G. V.; Marshall, G. R. A minimalistic
3D pharmacophore model for cyclopentapeptide CXCR4 antagonists.
Biopolymers 2006, 84, 459–471.
ꢁ
(25) Vabenø, J.; Nikiforovich, G. V.; Marshall, G. R. Insight into the
binding mode for cyclopentapeptide antagonists of the CXCR4 recep-
tor. Chem. Biol. Drug Des. 2006, 67, 346–354.
(26) Oishi, S.; Masuda, R.; Evans, B.; Ueda, S.; Goto, Y.; Ohno, H.;
Hirasawa, A.; Tsujimoto, G.; Wang, Z.; Peiper, S. C.; Naito, T.; Kodama,
E.; Matsuoka, M.; Fujii, N. Synthesis and application of fluorescein- and
biotin-labeled molecular probes for the chemokine receptor CXCR4.
ChemBioChem 2008, 9, 1154–1158.
(11) Zhan, W.; Liang, Z.; Zhu, A.; Kurtkaya, S.; Shim, H.; Snyder,
J. P.; Liotta, D. C. Discovery of small molecule CXCR4 antagonists.
J. Med. Chem. 2007, 50, 5655–5664.
(12) Rosenkilde, M. M.; Gerlach, L.-O.; Jakobsen, J. S.; Skerlj, R. T.;
Bridger, G. J.; Schwartz, T. W. Molecular mechanism of AMD3100
antagonism in the CXCR4 receptor. J. Biol. Chem. 2004, 279, 3033–
3041.
(13) Zhang, W.; Navenot, J.-M.; Haribabu, B.; Tamamura, H.;
Hiramatsu, K.; Omagari, A.; Pei, G.; Manfredi, J. P.; Fujii, N.; Broach,
J. R.; Peiper, S. C. A point mutation that confers constitutive activity to
480
dx.doi.org/10.1021/ml200047e |ACS Med. Chem. Lett. 2011, 2, 477–480