Exploration of amino alcohol derivatives as novel, potent, and highly selective sphingosine-1-phosphate receptor subtype-1 agonists

Article abstract of DOI:10.1016/j.bmcl.2010.02.098

In pursuit of a potent and highly selective sphingosine-1-phosphate receptor agonists with an improved in vivo conversion of the precursor to the active phospho-drug, we have utilized previously reported phenylamide and phenylimidazole scaffolds to identi

Full text of DOI:10.1016/j.bmcl.2010.02.098

Bioorganic & Medicinal Chemistry Letters 20 (2010) 2520–2524
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Exploration of amino alcohol derivatives as novel, potent, and highly
selective sphingosine-1-phosphate receptor subtype-1 agonists
b
b
a
a
Ghotas Evindar a, , Sylvie G. Bernier , Elisabeth Doyle , Malcolm J. Kavarana , Alexander L. Satz ,
Jeanine Lorusso b, Heather S. Blanchette b, Ashis K. Saha a, Gerhard Hannig b, Barry A. Morgan a,
William F. Westlin b
*
a Department of Medicinal Chemistry, Praecis Pharmaceuticals Incorporated, 830 Winter Street, Waltham, MA 02451, United States
b Department of Preclinical Research, Praecis Pharmaceuticals Incorporated, 830 Winter Street, Waltham, MA 02451, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
In pursuit of a potent and highly selective sphingosine-1-phosphate receptor agonists with an improved
in vivo conversion of the precursor to the active phospho-drug, we have utilized previously reported phe-
nylamide and phenylimidazole scaffolds to identify a selectivity enhancing moiety (SEM) and selectivity
enhancing orientation (SEO) within both pharmacophores. SEM and SEO have allowed for over 100 to
500-fold improvement in selectivity for S1P receptor subtype 1 over subtype 3. Utility of SEM and SEO
and further SAR study allowed for discovery of a potent and selective preclinical candidate PPI-4955
(21b) with an excellent in vivo potency and dose responsiveness and markedly improved overall
in vivo pharmacodynamic properties upon oral administration.
Received 23 November 2009
Revised 24 February 2010
Accepted 26 February 2010
Available online 3 March 2010
Keywords:
Sphingosine-1-phosphate (S1P) agonist
S1P1 agonists
Ó 2010 Elsevier Ltd. All rights reserved.
Phenylamide
Phenylimidazole
Immunosuppressants
Lymphopenia
Emergence of FTY-720 as a potent and orally bioavailable
immunomodulatory agent has unveiled novel therapeutic targets
within the sphingosine-1-phosphate (S1P) pathway. Upon in vivo
phosphorylation the pro-drug FTY-720 is converted to active
FTY-720-phosphate, a potent and non-selective S1P receptor ago-
nist (S1P1,3–5). The phospho-FTY-720 induces immunomodulatory
activity through direct alterations in lymphocyte trafficking1 via
triggering S1P receptor subtype 1 (S1P1) signaling cascade.2 This
has created a stimulating and highly competitive area of research
due to the fact that S1P receptors, a class of G-protein coupled
receptors (GPCRs), play major roles in several biological processes3
including cardiovascular and immune system function, and other
yet poorly defined effects on additional physiological systems.4
We recently reported two classes of S1P receptor agonists with
excellent potency at the S1P1 receptor and a relative low potency
on S1P3.5 In order to further improve the in vivo phosphorylation
of the pro-drug to active agonist in rodents, as well as reducing
the side effect profile of a non-selective S1P receptor agonist such
as bradycardia,6 while retaining the positive therapeutic proper-
ties, we explored medicinal chemistry optimization to further ex-
pand and improve our structure–activity relationship (SAR) while
monitoring both in vivo phosphorylation and the agonist selectiv-
ity for S1P receptor subtype 1 over subtype 3. In the design of po-
tent and selective sphingosine-1-phosphate receptor agonists in
our phenylamide and phenylimidazole analogs, we reported three
potent lead molecules, PPI-4621, PPI-4691 and PPI-4667 (Scheme
1) with moderate to good selectivity for S1P receptor subtype 1
over subtype 3 and in vivo activity in rodent.5
H2N
OH
OH
FTY-720
PPI-4621
H2N
O
Me
H
N
OH
O
NH2
Me
NH
N
OH
PPI-4691
PPI-4667
O
O
H2N
O
Me
H
N
OH
* Corresponding author. Tel.: +1 781 795 4423.
E-mail address: ghotas.x.evindar@gsk.com (G. Evindar).
Scheme 1.
0960-894X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2010.02.098

G. Evindar et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2520–2524
2521
in vivo phosphorylation in mouse than the 15% observed in the
previous lead molecule PPI-4667 (Fig. 1).
tail
linker
head-piece
H2N
We envisioned further SAR exploration of structural modifica-
tion and tolerability around the X section of the scaffold as a good
starting point as described in Schemes 2 and 3. One attempt was to
explore tolerability of a keto or an amide moiety replacing the
ether oxygen while maintaining the same number of atoms be-
tween the aniline and the biphenyl group. Synthesis of the desired
compounds is reported in Scheme 2. Reaction of Boc-protected 4-
aminobenzoic acid with oxalyl chloride gave acid chloride which
was then trapped with 4-ethynylbiphenyl through a cross-cou-
pling with copper iodide (I). Hydrogenation of the alkyne group fol-
lowed by removal of the Boc-protecting group afforded propanone
2. Acylation of the amino moiety of propanone 2 with orthogonally
protected amino acid 6,7 synthesized from the corresponding Boc-
amino acid 5, through an acid chloride intermediate followed by
the removal of the protecting groups with para-toluenesulfonic
acid afforded amino alcohol 7 (Y = CH2). The corresponding amide
was synthesized via coupling of 4-phenylbenzylamine 3 with 4-
aminobenzoic acid followed by sequential manipulations thereaf-
ter analogously to compound 2 to afford amino alcohol 7 (Y = NH).
The corresponding thio-ether based modifications were feasible
through Scheme 3. Reduction of the biphenyl acetic acid 8 with
BH3 and bromination of the alcohol product gave biphenyl ethyl
bromide 9. Biphenyl ethyl bromide 9 was then reacted with 4-
nitrobenzenethiol. Reduction of the nitro group with SnCl2 gave
the thio-aniline 10. One pot acid chloride formation of carboxylic
acid 6 and acylation of the thio-aniline 10 afforded thio-ether
amide 11. The thio-ether 11 then was selectively oxidized to the
corresponding sulfoxide and sulfone using meta-chloroperbenzoic
acid (mCPBA). Removal of the protecting groups gave the final
compound 12.
Me
H
N
OH
O
O
PPI-4667
H2N
O
Me
OH
H
N
X
R
n
Figure 1. Lead optimization from PPI-4667.
In pursuit of further improving agonist selectivity for S1P recep-
tor subtype 1 and to enhance in vivo phosphorylation of the pro-
drug alcohol, we performed extensive modifications in the phe-
nylamide scaffold (Fig. 1) through side-chain modifications and
4-aminophenol ring substitutions. Our earlier work on PPI-4621
indicated that substitutions on the linker 4-aminophenol provided
an agonist with low to moderate in vivo activity.5a Furthermore,
S1P1 selectivity was improved through incorporation of the biphe-
nyl system in the lipophilic tail of the scaffold.5b The SAR study
leading to PPI-4621 and PPI-4667 also revealed the tolerance of
the receptor for the ether lipophilic tail section of the molecule.
We predicted further lead optimization and structural modifica-
tion between the biphenyl tail moiety and the amide section of
the phenylamide linker of PPI-4667 with the goal of achieving a
more selective S1P receptor subtype-1 agonist with a better
The lymphopenia observed for a set of designed molecules is re-
ported in Table 1. The amino alcohol in vivo activity was deter-
mined by measuring redistribution of circulating lymphocytes in
mouse, 6 h after single oral administration of the pro-drug alcohol.
When the ether oxygen was replaced with a keto moiety, excellent
in vivo activity was observed analogous to the lead molecule PPI-
4667. However, the corresponding amide and the thio-ether
H
(a)
N
i,ii
Boc
NH2
NH2
HO
iii,iv
O
O
O
1
3
2
(b)
i,ii
iii,iv
H
N
v
O
NH2
Br
OH
4
8
9
(c)
Boc
N
Boc
H
O
Boc
NH
Me
N
NH2
vi,vii,viii
N
ix,x
HO
Me
OH
v
HO
O
O
S
S
O
Me
O
10
11
5
6
H2N
O
Me
H
N
H2N
O
H
N
Me
OH
OH
vi,vii
Y
X
O
7
12
Scheme 2. Reagents and conditions: (i) (COCl)2, DMF, THF, room temperature,
20 min; (ii) 4-ethynylbiphenyl, CuI, Et3N; (iii) H2, 10 Pd/C, MeOH; (iv) TFA, CH2Cl2;
(v) 4-aminobenzoic acid, HATU, DIPEA, DMF; (vi)TMS/CHN2, MeOH, 0 °C; (vii) 2,2-
dimethoxypropane, BF3ÁEt2O, acetone, room temperature, 4–12 h; (viii) LiOH, THF/
H2O/MeOH (2:1:1), reflux, 1–3 h; (ix) (COCl)2, DMF (catalytic), THF, room temper-
ature, 20 min then added two and stirred overnight; (x) para-toluenesulfonic acid,
MeOH, reflux, 3–12 h.
Scheme 3. Reagents and conditions: (i) BH3, THF, 0 °C, 2–3 h; (ii) CBr4, PPh3,
CH2Cl2; (iii) 4-nitrobenzenethiol, Et3N, THF; (iv) SnCl2, EtOH, reflux, 2–4 h; (v) (R)-
3-(tert-butoxycarbonyl)-2,2,4-trimethyloxazolidine-4-carboxylic acid, (COCl)2,
DMF (catalytic), THF, room temperature, 20 min then added 10 and stirred
overnight; (vi) used mCPBA to oxidize thio-ether, (1.0 equiv for sulfoxide and
2.00 equiv for sulfone), CH2Cl2, room temperature, 30 min; (vii) para-toluenesul-
fonic acid, MeOH, reflux, 3–12 h.

2522
G. Evindar et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2520–2524
Table 1
2-(biphenyl-4-yl)ethanol (13) on substituted 1-fluoro-4-nitroben-
zene in presence of base followed by hydrogenation of the nitro
group afforded substituted aniline 14. Coupling of the substituted
aniline 14 with (S)-2-(tert-butoxycarbonylamino)-3-hydroxy-2-
methylpropanoic acid using O-(7-azabenzotriazol-1-yl)-1,1,
3,3-tetramethyluronium hexafluorophosphate (HATU) and N,N-
diisopropylethylamine (DIPEA) followed by Boc removal afforded
amino alcohol 15. In cases where the R group was an ortho substi-
tution to the amine group in compound 14, coupling of the Boc-
amino acid with HATU generally afforded poor yield, therefore
the acid chloride approach was used analogous to Scheme 2 to gen-
erate the final alcohol 15. All the corresponding phosphates were
synthesized from amino alcohol 15 or the Boc-protected precursor
analogous to that reported by Evindar et al.5 The binding activity of
the designed agonists was measured using a [33P] binding assay
similarly to our earlier report5 (Table 3) and compared to S1P
and lead molecule PPI-4667-P. When R was CO2Me (16a), the ago-
nist showed relatively lower binding activity at receptor subtype 1
but with improved selectivity with respect to the lead molecule
PPI-4667-P. The hydrophilic carboxylic acid functional group
(16b) abolished the binding activity at both receptor subtypes
but the amide and the methyl amide (16c and 16d) analogs main-
tained a weak binding activity at S1P1. The corresponding nitrile
(16e) showed excellent binding activity on S1P1 with a threefold
improvement in selectivity over PPI-4667-P. When R was a halo-
gen (16f and 16g) the agonists maintained similar binding activity
to the lead molecule PPI-4667-P with a 2- to 4-fold improvement
in selectivity. The corresponding Me (16h) gave analogous result
as the halogen counterpart while the CF3 analog (16i) further im-
proved the agonist binding activity with respect to PPI-4667-P
from 1.05 to 0.24 nM. More significantly, the CF3 analog improved
the agonist selectivity for S1P receptor subtype 1 over 3 by
100-fold. However, the corresponding 2-CF3 (16j) showed no
improvement over the lead molecule PPI-4667-P. Therefore, this
Percent lymphopenia obtained upon 10 mg/kg oral (PO) administration of the alcohol
H2N
Me
H
N
OH
O
X
n
Agonist
n
X
%Lymphopenia
%In vivo phosphorylation
PPI-4667
7a
7b
12a
12b
12c
1
1
0
1
1
1
O
81
84
32
21
N
14
40
—
CO
NHCO
S
SO
SO2
—
—
—
N
aN = negligible.
showed low to negligible in vivo activity. Oxidation of the thio-
ether to either sulfoxide or sulfone ablated the modest in vivo
activity observed in the thio-ether 12a. The corresponding phos-
phate for amino alcohol 7a was synthesized from salt free amino
alcohol 7a in two steps utilizing diethyl chlorophosphate and
bromotrimethylsilane, as reported by Evindar et al.5, to determine
the agonist receptor binding activity and selectivity for S1P recep-
tor subtype 1 over subtype 3 (Table 2). The 7a-phosphate (7a-P)
showed analogous binding activity to PPI-4667 phosphate (PPI-
4667-P) with fivefold improvement in selectivity. More impor-
tantly, the in vivo phosphorylation analysis for amino alcohol 7a
showed 40% conversion to 7a-P, a threefold improvement over
PPI-4667. We speculated that the keto oxygen in amino alcohol
7a-P interacts with a specific region of the S1P receptor subtype
3 that lowers its affinity for the receptor subtype with minimal
changes in the agonist binding activity at receptor subtype 1,
therefore increasing the agonist selectivity for S1P receptor sub-
type 1 over 3. With the identification of this specific region within
the S1P receptor, we envisaged utilization of an ortho-substitution
adjacent to the oxygen ether in PPI-4667 to potentially induce an
analogous selectivity effect. Therefore, we initiated an exploration
with an extensive substitution and modification on the aminophe-
nol (the linker) region of the pharmacophore.
observation demonstrated
a selectivity enhancing orientation
(SEO) for the substitution position with respect to the agonist
side-chain (tail) component. The exploration also allowed for dis-
covery of several selectivity enhancing groups, especially CF3, as
a specific selectivity enhancing moiety (SEM).
In order to determine the pro-drug alcohol conversion to the ac-
tive phosphate drug and in vivo activity of the phosphate through
measuring redistribution of circulating lymphocytes in the mouse
6 h after oral administration of the compounds, the corresponding
alcohol to 16i was orally administered to the mouse at 10 mg/kg.
In pursuit of linker modification in the phenylamide pharmaco-
phore a number of targets were designed and synthesized as re-
ported in Scheme 4. Nucleophilic aromatic substitution of the
Table 2
[
33P] binding activity on S1P1 and S1P3–5 receptor subtypes
H2N
H
N
Me
O
O
P
HO OH
O
X
R
n
Agonist
n
X
R
hS1P1 IC50 (nM)
hS1P3 IC50 (nM)
hS1P4 IC50 (nM)
hS1P5 IC50 (nM)
S1P3/S1P1
S1P
—
1
1
1
1
1
1
1
1
1
1
1
1
—
CO
O
O
O
O
O
O
O
O
O
O
O
—
H
H
0.78
4.14
1.05
21
>10,000
150
500
3.4
0.8
1.3
6.0
0.24
6.4
0.92
3800
200
1.04
13.1
10.3
—
—
—
—
—
—
—
2.0
1360
43.6
—
—
—
—
—
—
—
—
7a-P
PPI-4667-P
16a
16b
16c
16d
16e
16f
16g
917
190
>476
—
—
—
588
356
769
542
18,750
109
3-CO2Me
3-CO2H
3-CONH2
3-CONHMe
3-CN
3-Cl
>10,000
>10,000
>1000
>1000
2000
285
1000
3250
4500
700
3-Br
16h
16i
16j
3-Me
3-CF3
2-CF3
—
3.4
—
—
87.2
—

G. Evindar et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2520–2524
2523
R
R
R
19
N
NH2
F
O
O
i,ii
OH
i
R'
R'
R
ii
O
Br
R
O
O
O
13
14
17
18
H2N
H
N
Me
iii,iv
v,vi
R
OH
O
O
O
Boc
N
R'
R'
O
iii, iv
v
NH2
Me
OH
R
NH
Me
15
OH
NH
NH
H2N
O
21
20
H
N
Me
O
O
P
Scheme 5. Reagents and conditions: (i) Alcohol, KOtBu, THF, 65 °C; (ii) Bu4NBr3,
CH2Cl2/MeOH (9:1 v/v), rt, 1–3 h; (iii) (R)-2-tert-butoxycarbonylamino-3-hydroxy-
2-methyl-propionic acid, Cs2CO3, DMF; (iv) AcONH4, toluene, 100 °C (v) TFA, CH2Cl2.
HO OH
O
R
16
zole analog while maintaining an excellent selectivity for the S1P1
subtype (Table 3). Further investigation of the corresponding pro-
drug 21a, upon oral administration in mouse at 10 mg/kg, demon-
strated a significant redistribution in circulating lymphocytes
resultinginmarkedinvivoactivity. Determinationoftheinvivocon-
version of the alcohol 21a to phosphate 21a-P was found to be 6.8%
at6 hafteroraladministrationinmice.Despitethelowconversionof
the alcohol to phosphate, a sufficient amount of active phosphate
was generated to induce a significant lymphopenia. In order to fur-
ther improve the in vivo conversion of the alcohol to phosphate in
the phenylimidazole pharmacophore, we decided to examine struc-
tural changes from amide 16i to phenylimidazole 21a-P. Our earlier
SAR revealed that the tail section of the S1P receptor is relatively for-
giving to structural and conformational changes,5 however the over-
all pharmacophore length is important in the agonist binding
activity. Changing the pharmacophore from phenylamide to phenyl-
imidazole adds about one bond length to the distance between the
phosphate group and the SEM. In order to account for this change,
we designed a reduction of a methylene unit in the tail region of
21a-P generating 21b-P (PPI-4955-P) (Table 3). Regardless of the
conformational changes from 21a-P to 21b-P, the tail modification
resulted in potent and highly selective 21b-P with significant
improvement over 21a-P in its binding activity. Oral administration
of the corresponding alcohol to 21b-P (21b or PPI-4955) in mouse at
10 mg/kg induced a marked drop in absolute lymphocyte counts at
6 h after administration. Furthermore, PPI-4995 in vivo conversion
to the phosphate 21b-P showed 10-fold improvement over the
phenylimidazole 21a. Removal of the SEM CF3 in 21b-P demon-
strated the importance of the group in improving the agonist selec-
tivity for the S1P receptor subtype 1 over 3 in phenylimidazole
Scheme 4. Reagents and conditions: (i) 2-(biphenyl-4-yl)ethanol, substituted 1-
fluoro-4-nitrobenzene , KOtBu, THF, 65 °C; (ii) H2, 10% Pd/C, MeOH/EtOAc (4:1 v/v);
(iii) (S)-2-(tert-butoxycarbonylamino)-3-hydroxy-2-methylpropanoic acid, HATU,
DIPEA, DMF; (iv) TFA, CH2Cl2; (v) excess diethyl phosphorochloridate, Et3N, CH2Cl2,
rt, 12–18 h; (vi) excess TMSBr, CH2Cl2, rt, 4–10 h.
Lymphocyte count analysis revealed less than a 20% decrease in
absolute lymphocyte counts. Further investigation revealed a mar-
ginal 2% in vivo conversion of the pro-drug alcohol to the corre-
sponding phosphate 16i leading to only modest reduction in
circulating lymphocytes. Since our earlier SAR and S1P agonist
receptor profile was transferable between phenylamide and phenyl-
imidazole scaffolds, we envisioned further investigation of the SEM
and in vivo phosphorylation of the pro-drug in the more rigid phen-
ylimidazole pharmacophore. The corresponding phenylimidazole to
phenylamide 16i and a number of designed analogs were prepared
as described in Scheme 5. A nucleophilic substitution reaction by
an alcohol on 4-fluoroacetophenone 17 afforded the ether-aceto-
phenone 18. The ether-acetophenone 14 was then converted to the
bromo-acetophenone 19 using Bu4NBr3 at ambient temperature.
The bromo-acetophenone 19 was then trapped with (R)-2-tert-but-
oxycarbonylamino-3-hydroxy-2-methyl-propionic acid affording
an intermediate ester which upon heating in presence of AcONH4
gave phenylimidazole 20. Removal of the Boc protecting group pro-
vided the amino alcohol 21. The corresponding phosphates to the
alcohols were synthesized from alcohol 20 analogous to those re-
ported by Evindar et al.5
A side by side comparison of the phenylamide 16i and the corre-
sponding phenylimidazole 21a-P revealed a relative lower binding
affinity to both S1P receptor subtypes 1 and 3 by the phenylimida-
Table 3
[
33P] binding activity on S1P1 and S1P3–5 receptor subtypes
R
O
NH2
n
N
Me
O
NH
O
P
HO
OH
Agonist
n
R
hS1P1 IC50 (nM)
hS1P3 IC50 (nM)
hS1P4 IC50 (nM)
hS1P5 IC50 (nM)
S1P3/S1P1
%La
%Cb
21a-P
21b-P
21c-P
2
1
1
CF3
CF3
H
9.4
0.23
1.03
>100,000
2000
6.5
4.4
4.87
184
9.6
9.6
>10,000
8695
19
64
85
—
6.8
70.1
—
20
a
Percent lymphopenia observed in mouse 6 h post dose upon 10 mg/kg oral (PO) administration of the corresponding alcohol.
Percent conversion of alcohol (pro-drug) to phosphate (drug) at 6 h dose administration upon 10 mg/kg oral (PO) administration of the alcohol.
b

2524
G. Evindar et al. / Bioorg. Med. Chem. Lett. 20 (2010) 2520–2524
Table 4
[c-
35S]GTP functional activity on S1P1 and S1P3 receptor subtypes
R
X
n
H2N
Me
O
O
Y
P
OH
HO
Agonist
n
X
R
Y
hS1P1 EC50 (nM)
hS1P3 EC50 (nM)
S1P3/S1P1
S1P
PPI-4667-P
7a-P
—
2
2
2
2
1
1
—
O
CO
O
O
O
—
H
H
CF3
CF3
CF3
H
—
Amide
Amide
Amide
Imidazole
Imidazole
Imidazole
5.6
0.52
18.3
1.44
22.4
1.62
2.2
2.4
120
—
231
>3000
>3000
>3000
>3000
54.8
>164
>2083
>134
>1852
25
16i
21a-P
21b-P
21c-P
O
In summary, in pursuit of improving the agonist selectivity for
12
10
8
S1P receptor subtype 1 over subtype 3, we have identified a selec-
tivity enhancing moiety (SEM) in both phenylamide and phenyl-
imidazole series. The ortho-CF3 substitution adjacent to the tail
section of the pharmacophore was found to be an excellent SEM
with a general improvement of 100- to 500-fold in agonist selectiv-
ity for S1P receptor 1 over 3. We demonstrated the importance of
the SEM orientation leading to discovery of the selectivity enhanc-
ing orientation (SEO) for the CF3 group. In pursuit of improving
in vivo conversion of the pro-drug alcohol to phosphate drug, we
have discovered a potent and selective lead molecule, PPI-4955
(21b) with significant improvement in both receptor profile and
in vivo phosphorylation. PPI-4955 was selected as a preclinical
candidate for further evaluation and was found to be potent with
excellent dose responsiveness and overall pharmacodynamic prop-
erties upon oral administration. Further SAR studies will be re-
ported in due course.
6
4
2
0
Vehicle
0.3 mg/kg 1.0 mg/kg 3.0 mg/kg 10.0 mg/kg
PPI-4955 (21b)
Figure 2. Dose–response lymphopenia for lead compound PPI-4955 (21b) relative
to the vehicle.
pharmacophore (21c-P). All the phenylimidazole analogs also
showed a significant potency at both S1P receptor subtypes 4 and 5.
In order to confirm the agonist potency and selectivity, a number
of designed phosphates were further investigated in [c-
35S]GTP
References and notes
functional assay8 as reported in Table 4. The keto-compound 7a-P,
analogous to binding data, once again showed a relatively lower
in vitro activity with improved selectivity for S1P subtype 1 over 3.
The agonist 16i activity and selectivity were confirmed in the assay
and demonstrated the importance of the SEM group in the phenyla-
mide scaffold. In the phenylimidazole analogs, 21a-P was relatively
less potent with respect to the corresponding phenylamide analog
16i, but showed an improved selectivity for S1P1 over S1P3. The
phenylimidazole analog with a short tail region (21a-P, PPI-4955-
P) demonstrated over 10-fold improvement in agonist potency
while maintaining the high degree of selectivity. The des-CF3 analog
abolished selectivity and again confirmed the importance of the SEM
in both phenylamide and phenyimidazole pharmacophore.
Due to high in vivo conversion of PPI-4955 (21b) to PPI-4955-P
(21b-P) and the phosphate receptor profile, the alcohol was chosen
as a preclinical lead molecule for further evaluation. PPI-4955 was
investigated in an in vivo dose–response when orally administered
in mice. The agonist showed significant lymphopenia at all doses be-
tween 0.3 mg/kg and 10 mg/kg at 6 h post-dose in mice (Fig. 2).
Overall, PPI-4955 demonstrated excellent dose responsiveness
when administered orally at doses between 0.3 and 10 mg/kg with
maximal activity observed at doses of 1 mg/kg and above.
1. (a) Sugiyama, A.; Yatomi, Y.; Ozaki, Y.; Hashimoto, K. Cardiovasc. Res. 2000, 46,
119; (b) Brinkmann, V.; Davis, M. D.; Heise, C. E.; Albert, R.; Cottens, S.; Hof, R.;
Bruns, C.; Prieschl, E.; Baumruker, T.; Hiestand, P.; Foster, C. A.; Zollinger, M.;
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was
methylpropanoic acid in three steps in overall 55–70% yield. For alternative
synthesis of (R)-3-(tert-butoxycarbonyl)-2,2,4-trimethyloxazolidine-4-
synthesized
from
(S)-2-(tert-butoxycarbonylamino)-3-hydroxy-2-
carboxylic acid (6) see: Clemens, J. J.; Davis, M. D.; Lynch, K. R.; Macdonald, T.
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