Benzofuran derivatives as potent, orally active S1P1 receptor agonists: A preclinical lead molecule for MS

Article abstract of DOI:10.1021/ml100227q

We have discovered novel benzofuran-based S1P₁ agonists with excellent in vitro potency and selectivity. 1-((4-(5-Benzylbenzofuran-2-yl)-3- fluorophenyl)methyl) azetidine-3-carboxylic acid (18) is a potent S1P ₁ agonist with >1000× s

Full text of DOI:10.1021/ml100227q

pubs.acs.org/acsmedchemlett
Benzofuran Derivatives as Potent, Orally Active S1P1
Receptor Agonists: A Preclinical Lead Molecule for MS
Ashis K. Saha,*,†,∧ Xiang Yu,† Jian Lin,† Mercedes Lobera,† Anurag Sharadendu,† Srinivas Chereku,†
Nili Schutz,† Dalia Segal,† Yael Marantz,† Dilara McCauley,† Scot Middleton,§ Jerry Siu,§
‡
^
^
#
#
€
Roland W. Burli, Janet Buys, Michelle Horner, Kevin Salyers, Michael Schrag,
Hugo M. Vargas,^ Yang Xu,# Michele McElvain, and Han Xu
†EPIX Pharmaceuticals Inc., 167 Worcester Street, Suite 201, Wellesley Hills, Massachusetts 02481, United States,
Departments of ‡Medicinal Chemistry, §Inflammation Research, Molecular Pharmacology, ^Comparative Biology
and Safety Sciences, and #Pharmacokinetics and Drug Metabolism, Amgen Inc., One Amgen Center Drive, Thousand Oaks,
California 91320, United States
ABSTRACT We have discovered novel benzofuran-based S1P1 agonists with
excellent in vitro potency and selectivity. 1-((4-(5-Benzylbenzofuran-2-yl)-3-
fluorophenyl)methyl) azetidine-3-carboxylic acid (18) is a potent S1P1 agonist
with >1000ꢀ selectivity over S1P3. It demonstrated a good in vitro ADME
profile and excellent oral bioavailability across species. Dosed orally at 0.3 mg/kg, 18
significantly reduced blood lymphocyte counts 24 h postdose and demonstrated
efficacy in a mouse EAE model of relapsing MS.
KEYWORDS Sphingosine-1 phosphate receptor, S1P1, S1P3, benzofuran, relapsing
MS, immunomodulators, lymphopenia
urrent therapeutic options for multiple sclerosis (MS)
are all injectable, and a need for an effective oral agent
C
exists. Myelin reactive T cells (lymphocytes) in the
peripheral immune system play a key role in MS.1-6 Regula-
tion of sphingosine-1 phosphate receptor subtype-1 (S1P1), a
G-protein-coupled receptor (GPCR) expressed on T lympho-
cytes, could produce a new class of immunomodulators with
a novel mechanism of action. Lymphocyte egress from
lymphoid tissues requires the lipid mediator S1P1 and is
required for the emigration of lymphocytes from the thymus
and the trafficking of lymphocytes in secondary lymphoid
organs.7-9
The pro-drug FTY-720 upon phosphorylation activates the
S1P1 receptor.10 It was successful in advanced clinical trials
for relapsing-remitting MS and was recently recommended
for approval by an FDA advisory committee for relapsing
MS.11,12 It is, however, a nonselective S1P receptor agonist
with potent affinity for four of five S1P receptor subtypes.
Agonism of S1P3 is believed to cause chronotropic side
effects.13-16 We aimed to develop a novel, selective S1P1
agonist from knowledge-based lead design and computa-
tional chemistry approaches.
Figure 1. FTY-720-P, early S1P1 agonists, and Predix scaffold.
aDisplacement of [33P]-labeled sphingosine-1-phosphate (S1P)
from human S1P receptors expressed on CHO cell membranes.
Findings from Merck17,18 revealed that unlike FTY-720-P
and related compounds requiring intracellular phosphoryla-
tion, hydrophobic S1P screening hits such as oxadiazole
SEW-2871 when decorated with a polar headgroup not only
demonstrate strong binding to S1P1 receptors but are far
more selective against S1P3. The structure-activity relation-
ship (SAR) that emerged indicated that minor variation of
the core scaffold could influence receptor binding potency as
well as selectivity (Figure 1). For example, compounds A, B,
and C differ very little (see oxadiazole ring) yet demonstrate
>10-fold difference in S1P1 potency between each of them.
Received Date: September 29, 2010
Accepted Date: November 2, 2010
Published on Web Date: November 09, 2010
r
2010 American Chemical Society
97
DOI: 10.1021/ml100227q ACS Med. Chem. Lett. 2011, 2, 97–101
|

pubs.acs.org/acsmedchemlett
Table 1. SAR of 5-Substituted Benzofuran Corea
Table 2. Lead Optimization of Benzofuran Corea
GTPγSb hS1P1
EC50 (μM)
hS1P3 Ca2þ
EC50 (μM)
hS1P1
RI EC50 (μM)
no.
R
1
2
3
4
5
6
7
8
9
n-Bu
0.35
0.52
0.44
0.6
>25
>7.2
>4.3
>25
1.9
2.48
NA
O-n-Bu
CH2Ph
2.07
0.46
0.15
0.354
5.03
NA
cHex
CH2CH(CH3)2
CH2CH2Ph
3-Pyr
0.38
0.58
>1
>25
>25
>25
1.44
O-Ph
0.51
1.5
N(CH2)5
0.62
a Data represents an average of at least two determinations. b Com-
pound induced binding of [35S]-GTPγS to human S1P-1 receptors
expressed on CHO cell membranes (EC50). NA, not available.
Selectivity against S1P3 receptor of course improves signifi-
cantly as a consequence.
Our in silico group developed models of the S1P1 receptor
using PREDICT methodology.19 Docking of the Merck inhibitors
provided insight and supported the medicinal chemistry ob-
servation that small changes to the core five-member ring
structures could lead to potent, selective, and novel new S1P1
agonists. Utilizing this SAR insight, we designed several novel
scaffolds each consisting of the azetidine carboxylate, a mod-
erately polar core that lacks an H-bond donor and hydrophobic
tail group. The scaffolds were designed with the additional
consideration that the initial hit exploration library must be
synthesizable using cluster synthesis approach. Mol wt, CLog P,
and calculated ADME properties were evaluated prior to
synthesis decisions. Among conceived designs, scaffold D
(Figure 1), with its fused 5,6-heterocycle core with several
combinations of the X and Yatoms, was favored due to overall
superior match with our pharmacophore hypothesis. In this
paper, we describe the successful discovery of benzofuran
(X = O; Y = C)-based potent, selective S1P1 agonists.
Benzofuran 1 with the tail 5-n-butyl group, one of the first
members of initial benzofuran lead-seeking compounds, de-
monstrated submicromolar potency in the GTPγS assay for the
S1P1 receptor (Tabl e 1 ). It had no activity at hS1P3 as deter-
mined by Ca2þ mobilization in hS1P3- in Gq/i5- transfected
CHO-K1 cells. In an assay measuring receptor internalization
(RI) of an hS1P1-GFP fusion protein in U2Os cells, compound 1
demonstrated micromolar potency. The RI data were deemed
to be functionally more relevant and were run in parallel
whenever feasible. The two assays generally correlated with
each other. For SAR purposes, however, the GTPγS assay for the
S1P1 receptor remained a primary screen. An effort was
undertaken to investigate the benzofuran motif over other
exploratory scaffolds in view of its novelty, initial potency,
and generally good early ADME properties. Initial changes
focused on the tail region. Analogue 2 with a 5-n-butyloxy
a Data represents an average ofat least two determinations. b Compound
induced binding of [35S]-GTPγS to human S1P-1 receptors expressed on
CHO cell membranes. c Percent efficacy is reported relative to 1.0 μM
1-(4-(6-benzylbenzofuran-2-yl)-3-fluorobenzyl)azetidine-3-carboxylic acid
18 (for hS1P1 RI); NA, not available.
group retained submicromolar S1P1 potency. Compounds 3
with 5-benzyl group, 4 with 5-cyclohexyl, and 5 with 5-isobutyl
all demonstrated submicromolar activities in the GTPγS assay.
Compounds 3and 4were full agonists in the RI screen (data not
shown). Substitution with a 5-phenethyl group (6) or a phenoxy
(8) was tolerated. Introduction of more polar groups such as a
r
2010 American Chemical Society
98
DOI: 10.1021/ml100227q ACS Med. Chem. Lett. 2011, 2, 97–101
|

pubs.acs.org/acsmedchemlett
Figure 2. Compound 18 dosed orally reduces blood lymphocyte
counts in female Lewis rats 24 h postdose (N = 5/group; bars
represent average blood lymphocyte counts þ SE; circles represent
average plasma concentration ( SE; *P < 0.05 vs vehicle by ANOVA/
Dunnett's multiple comparison test; vehicle = 20% captisol, pH 2).
Figure 3. Compound 18 data in experimental autoimmune en-
cephalitis (EAE) SJL mice model of MS.
pyridyl (7) led to substantial loss of S1P1 potency. Interestingly,
the piperidine derivative 9 retained micromolar S1P1 potency;
it, however, was poorly selective (∼2ꢀ) over S1P3 receptor.
This initial data demonstrated that hydrophobic groups were
preferred in the tail region of the benzofuran core.
Table 3. Mean Compound 18 PK Parameters in Pie Clinical
Species
species
CL (L/h/kg)
Vss (L/kg)
T1/2,Z (h)
MRT (h)
F %
rata
NHPb
caninec
0.138
0.309
0.266
1.7
1
12.1
4.7
12.7
3.4
9
80
88
51
Data from the lead optimization phase of benzofuran S1P
modulators are shown in Table 2. Moving the tail substituent
from the 5-position to the benzofuran-6-position led to loss in
S1P1 receptor potency (10). Replacement of the core phenyl
ring with 5-atom heteroaromatic moieties such as thiazole
(11) also led to loss of potency. The thiophene (12) retained
potency. We next studied substituents in the core phenyl
ring. Small groups such as fluoro (13), chloro (15), and
methoxy (14) at the 3-position were tolerated. Interestingly,
a 3-pyridyl replacement (16) of phenyl demonstrated reten-
tion of in vitro potency and selectivity. Combining the
5-benzyl tail substituent with the core 3-fluoro-phenyl ring
produced compound 18 with less than 200 nM potency in
the GTPγS screen. Furthermore, it demonstrated less than
100 nM potency in the hS1P1 RI assay. The 2-fluorophenyl
analogue 17 showed a 4-5-fold reduced hS1P1 potency
relative to 3-fluorophenyl analogue 18. The 3-fluorophenyl
group when combined with 5-cyclo-hexyl tail moiety de-
monstrated potency similar to analogue 18. Retaining the
optimal 3-fluorophenyl ring but combining with somewhat
more polar tail groups (20 and 21) led to loss in potency.
One of our key preclinical lead criteria was >1000-fold
S1P1 selectivity over S1P3. Benzofuran analogue 18
achieved highest selectivity with demonstrated EC50 values
of 16 nM for hS1P1 in the GTPγS binding assay and 27 μM for
hS1P3 in the Ca2þ-flux assay, respectively. The ADME profile
was favorable with a half-life in human liver microsomes of
over 90 min. Clearance in the rat appeared to be primarily
metabolic. Permeability across Caco-2 monolayers was
moderate to good with low efflux characteristics.
2.2
21.1
a Male Sprague-Dawley (iv: 1 mg/kg, DMSO, N = 3; po: 3 mg/kg,
20% captisol, pH 4.0, N = 3). b NHP = nonhuman primate, male cyno-
molgus (iv: 1 mg/kg, 5% hydroxypropyl-β-cyclodextrin, N = 3; po: 5 mg/
kg, 5% hydroxypropyl-β-cyclodextrin, N = 3.). c Male beagle (iv: 2 mg/kg,
20% captisol, pH 4.0, N = 3; po: 3 mg/kg, 20% captisol, pH 4.0, N = 3).
Compound 18 demonstrated efficacy comparable to FTY-
720 at (10 mg/kg po) nearly completely reversing the course
of disease in Experimental Autoimmune Encephalitis (EAE)
SJL mice model of multiple sclerosis (Figure 3). Preclin-
ical pharmacokinetic (PK) in rat, nonhuman primate, and
canine indicated that compound 18 had low clearance
(corresponding to 4-15% of liver blood flow), a moderate
steady state volume of distribution (1.0-2.2 L/kg), a mod-
erate to long half-life (5-21 h), and good oral bioavailability
(51-88%; Table 3). In vitro studies established that com-
pound 18 neither inhibited nor induced human cytochrome
P450 enzymes. Compound 18 was nonmutagenic (Ames
and micronucleus negative) and did not significantly inhibit
the hERG channel (patch clamp: IC50, 17 μM). In humans, it
was predicted to have low clearance and a 5-10 h half-life,
which would make it suitable for once a day dosing.
In a 4 day repeated dose toxicity study in rats, exposure was
dose proportional up to 60 mg/kg. The brain/serum ratio was
consistent across doses (10-16-fold), while the volume of
distribution was 10-fold lower than FTY720. The NOAEL was
20 mg/kg. To examine if lack of S1P3 potency corresponded to
an absence of chronotropic effect, compound 18 was dosed in
telemetered female SD rats as an oral bolus in a volume of 5
mg/mL in 20% captisol. The mean arterial pressure (MAP) was
moderately elevated at 20 and 40 mg/kg from 4 to 6 h after
dosing, with peak effects corresponding to Cmax. There was no
effect on heart rate at all doses, confirming a no-effect level for
HR changes at 40 mg/kg po, indicating a wide margin for S1P3-
mediated cardiovascular toxicity. The mechanism underlying
the elevated MAP is uncertain.
Compound 18 produced comparable lymphopenia activ-
ity to FTY720 in Lewis rats with dose-dependent reduction in
circulating blood lymphocytes 24 h postdose. Near maximal
lymphopenia (75% reduction in lymphocytes vs vehicle)
was achieved at doses of 1 and 3 mg/kg (Figure 2). Onset of
lymphopenia was rapid across species in mice, rat, and
nonhuman primates, with short recovery times in lympho-
cytes counts (less than 48 h).
r
2010 American Chemical Society
99
DOI: 10.1021/ml100227q ACS Med. Chem. Lett. 2011, 2, 97–101
|

pubs.acs.org/acsmedchemlett
Scheme 1. Synthesis of 18a
Present Addresses: ∧Chembiotek, ATCG Life Sciences Company,
Block BN, Plot 7, Saltlake Electronics Complex, Sector V, Kolkata
700091, India.
ACKNOWLEDGMENT We thank Sheila Dewitt, Epix, and Sharon
Pick and Victor Cee, Amgen, for assistance in coordinating
completion of this manuscript. We also thank Pini Orbach, Sharon
Shacham, and Oren Becker for their contributions to the S1P
program at Epix.
REFERENCES
(1)
Chun, J; Hartung, H. Mechanism of Action of Oral Fingolimod
(FTY720) in Multiple Sclerosis. Clin. Neuropharmacol. 2010,
33 (2), 91–101.
(2)
Kappos, L.; Radue, E.-W.; O'Connor, P.; Polman, C.; Hohlfeld,
R.; Calabresi, P; Selmaj, K.; Agoropoulou, C.; Leyk, M.; Zhang-
Auberson, L.; Burtin, P. A. Placebo-Controlled Trial of Oral
Fingolimod in Relapsing Multiple Sclerosis. N. Engl. J. Med.
2010, 362, 387–401.
a (a) KOH, DMSO, 20 h, 84%. (b) PPA, benzene, 89%. (c) n-BuLi, THF,
-78 ꢀC. (d) B(iPrO)3. (e) 2 N HCl or NH4Cl (66% yield after steps c-e).
(f) PdCl2(Ph3P)2 (5 mol %) Et3N, EtOH, 100 ꢀC, microwave, 65%.
(g) AcOH, NaCNBH3, DCM/MeOH, 56%.
(3)
Cohen, J. A.; Barkhof, F.; Comi, G.; Hartung, H.-P.; Khatri, B. O.;
Montalban, X.; Pelletier, J.; Capra, R.; Gallo, P.; Izquierdo, G.;
Tiel-Wilck, K.; de Vera, A.; Jin, J.; Stites, T.; Wu, S.; Aradhye, S.;
Kappos, L. Oral Fingolimod or Intramuscular Interferon for
Relapsing Multiple Sclerosis. N. Engl. J. Med. 2010, 362, 402–415.
Brinkmann, V. FTY720 (fingolimod) in multiple sclerosis:
therapeutic effects in the immune and the central nervous
system. Br. J. Pharmacol. 2009, 158 (5), 1173–1182.
Foster, C. A.; Howard, L. M.; Schweitzer, A.; Persohn, E.;
Hiestand, P. C.; Balatoni, B.; Reuschel, R.; Beerli, C.; Schwartz,
M.; Billich, A. Brain Penetration of the Oral Immunomodula-
tory Drug FTY720 and its Phosphorylation in the Central
Nervous System During Experimental Autoimmune Ence-
phalomyelitis: Consequences for Mode of Action in Multiple
Sclerosis. J. Pharmacol. Exp. Ther. 2007, 323 (2), 469–476.
Kataoka, H.; Sugahara, K.; Shimano, K.; Teshima, K.; Koyama,
M.; Fukunari, A.; Chiba, K. FTY720, Sphingosine 1-Phosphate
Receptor Modulator, Ameliorates Experimental Autoimmune
Encephalomyelitis by Inhibition of T Cell Infiltration. Cell. Mol.
Immunol. 2005, 2, 439–448.
The synthesis of compound 18 is described in Scheme 1.
The 5-benzyl benzofuran 25 was prepared via a two-step
reaction, starting from the alkylation of phenol 22 with
2-bromo-1,1- diethoxyethane 23, followed by cyclization
with polyphosphoric acid (PPA) in benzene at reflux tem-
perature. The boronic acid functionality was selectively
incorporated at the 2-position of the benzofuran ring of 26
under our modified conditions using n-BuLi and B(iPrO)3 at
low temperature. Suzuki C-C coupling of boronic acid 26
and aryl halide 27 was carried out in a microwave apparatus
using 5 mol % palladium(II) catalyst, triethyl amine, and
ethanol as the solvent at 100 ꢀC, cleanly yielding 4-(5-
benzylbenzofuran-2-yl)-3-fluorobenzaldehyde 28. Reduc-
tive amination of the aldehyde with azetidine-3-carboxylic
acid 29 provided the desired compound 18 as its zwitterion.
In summary, knowledge-based scaffold hopping com-
bined with computation chemistry tools led to identification
of the benzofuranyl core as a novel new S1P1 lead series.
Rapid optimization efforts designed to enhance potency,
while balancing lipophilicity led to 3-fluorophenyl benzofur-
an 18, which was found to have potent S1P1 activity and
excellent S1P3 selectivity. Oral dosing of 18 in rats (1 mg/kg)
resulted in a statistically significant reduction in circulating
lymphocytes 24 h postdose, as well as efficacy in the mice
EAE model of MS. The overall profile of compound 18 led to
nomination for preclinical development including follow-on
GLP toxicology studies. Such studies revealed pro-convulsive
activity at doses of 40 mg/kg and higher. Optimization efforts
toward scaffolds that avoid such toxic properties will be the
subject of upcoming manuscripts.
(4)
(5)
(6)
(7)
(8)
(9)
Baumruker, T; Billich, A; Brinkmann, V. FTY720, an Immu-
nomodulatory Sphingolipid Mimetic: Translation of a Novel
Mechanism into Clinical Benefit in Multiple Sclerosis. Expert
Opin. Invest. Drugs 2007, 16 (3), 283–289.
Chiba, K.; Matsuyuki, H.; Maeda, Y.; Sugahara, K. Role of
Sphingosine 1-Phosphate Receptor type 1 in Lymphocyte
Egress from Secondary Lymphoid Tissues and Thymus. Cell.
Mol. Immunol. 2006, 3 (1), 11–19.
Brinkmann, V. FTY720: Mechanism of Action and Potential
Benefit in Organ Transplantation. Yonsei Med. J. 2004, 45 (6),
991–997.
(10) Verzijl, D.; Peters, S. L. M.; Alewijnse, A. E. Sphingosine-1-
Phosphate Receptors: Zooming in on Ligand-Induced Intra-
cellular Trafficking and Its Functional Implications. Mol. Cells
2010, 29 (2), 99–104.
(11) Swedin, H. FDA Advisory Committee Unanimously Recom-
mends Approval of Novartis Investigational Treatment
FTY720 to Treat Relapsing Remitting MS. Novartis Press
Release, PR Newswire, June 10, 2010.
SUPPORTING INFORMATION AVAILABLE Experimental
procedures and characterization data for 1-21 and details of in
vitro and in vivo assays. This material is available free of charge via
the Internet at http://pubs.acs.org.
(12) Cohen, J. A.; et al. Oral fingolimod or intramuscular inter-
feron for relapsing multiple sclerosis. N. Engl. J. Med. 2010,
362 (5), 402–415.
AUTHOR INFORMATION
Corresponding Author: *Tel: þ91 33 4000 7004 (India); (978)
(13) Kovarik, J. M.; Lu, M.; Riviere, G.; Barbet, I.; Maton, S.;
Goldwater, D. R.; Schmouder, R. L. The Effect on Heart Rate
212-5462 (USA). E-mail: ashis.saha@tcgls.com.
r
2010 American Chemical Society
100
DOI: 10.1021/ml100227q ACS Med. Chem. Lett. 2011, 2, 97–101
|

pubs.acs.org/acsmedchemlett
of Combining Single-dose Fingolimod with Steady-state Ate-
nolol or Diltiazem in Healthy Subjects. Eur. J. Clin. Pharmacol.
2008, 64 (5), 457–463.
(14) Schmouder, R.; Serra, D.; Wang, Y.; Kovarik, J. M.; DiMarco, J.;
Hunt, T. L.; Bastien, M.-C. FTY720: Placebo-Controlled Study
of the Effect on Cardiac Rate and Rhythm in Healthy Subjects.
J. Clin. Pharmacol. 2006, 46, 895–904.
(15) Forrest, M.; Sun, S.-Y.; Hajdu, R.; Bergstrom, J.; Card, D.;
Doherty, G.; Hale, J.; Keohane, C.; Meyers, C.; Milligan, J.;
Mills, S.; Nomura, N.; Rosen, H.; Rosenbach, M.; Shei, G.-J.;
Singer, I. I.; Tian, M.; West, S.; White, V.; Xie, J.; Proia, R. L.;
Mandala, S. Immune Cell Regulation and Cardiovascular
Effects of Sphingosine-1-phosphate Receptor Agonists in
Rodents are Mediated via Distinct Receptor Subtypes.
J. Pharmacol. Exp. Ther. 2004, 309, 758–768.
(16) Sanna, M. G.; Liao, J.; Jo, E.; Alfonso, C.; Ahn, M.-Y.; Peterson,
M. S.; Webb, B.; Lefebvre, S.; Chun, J.; Gray, N.; Rosen, H.
Sphingosine 1-Phosphate (S1P) Receptor Subtypes S1P1 and
S1P3, Respectively, Regulate Lymphocyte Recirculation and
Heart Rate. J. Biol. Chem. 2004, 279, 13839–13848.
(17) Hale, J. J.; Lynch, C. L.; Neway, W.; Mills, S. G.; Hajdu, R.;
Keohane, C.; Ann; Rosenbach, M. J.; Milligan, J. A.; Shei, G.-J.;
Parent, S. A.; Chrebet, G.; Bergstrom, J.; Card, D.; Ferrer, M.;
Hodder, P.; Strulovici, B.; Rosen, H.; Mandala, S. A Rational
Utilization of High-Throughput Screening Affords Selective,
Orally Bioavailable 1-Benzyl-3-carboxyazetidine Sphingosine-
1-phosphate-1 Receptor Agonists. J. Med. Chem. 2004, 47
(27), 6662–6665.
(18) Li, Z.; Chen, W.; Hale, J. J.; Lynch, C. L.; Mills, S. G.; Hajdu, R.;
Keohane, C. A.; Rosenbach, M. J.; Milligan, J. A.; Shei, G.-J.;
Chrebet, G.; Parent, S. A.; Bergstrom, J.; Card, D.; Forrest, M.;
Quackenbush, E. J.; Wickham, L.; Alexandra, V.; Hugo, E.; Rose,
M.; Rosen, H.; Mandala, S. Discovery of Potent 3,5-Diphenyl-
1,2,4-oxadiazole Sphingosine-1-phosphate-1 (S1P1) Receptor
Agonists with Exceptional Selectivity against S1P2 and S1P3.
J. Med. Chem. 2005, 48 (20), 6169–6173.
(19) Shacham, S.; Marantz, Y.; Bar-Haim, S.; Kalid, O.; Warshaviak,
D.; Avisar, N.; Inbal, B.; Heifetz, A.; Fichman, M.; Topf, M.;
Naor, Z.; Noiman, S.; Becker, O. M. PREDICT Modeling and
In-Silico Screening for G-Protein Coupled Receptors. Proteins
2004, 57, 51–86.
r
2010 American Chemical Society
101
DOI: 10.1021/ml100227q ACS Med. Chem. Lett. 2011, 2, 97–101
|