Phosphomimetic sulfonamide and sulfonamidoxy analogues of (Lyso)phosphatidic acid

Article abstract of DOI:10.1016/j.tetlet.2006.08.066

Lysophosphatidic acid (LPA) and phosphatidic acid (PA) are potent bioactive lipid mediators of signal transduction and are inactivated by phosphatases. To obtain receptor-isoform selective ligands with neutral phosphomimetic head groups, we performed the stereoselective synthesis of LPA and PA analogues with trifluoromethanesulfonamide and trifluoromethanesulfonamidoxy moieties replacing the phosphomonoester.

Full text of DOI:10.1016/j.tetlet.2006.08.066

Tetrahedron Letters 47 (2006) 7607–7609
Phosphomimetic sulfonamide and sulfonamidoxy analogues
of (Lyso)phosphatidic acid
Joanna Gajewiak and Glenn D. Prestwich*
Department of Medicinal Chemistry, The University of Utah, 419 Wakara Way, Suite 205, Salt Lake City,
UT 84108-1257, United States
Received 19 July 2006; revised 17 August 2006; accepted 18 August 2006
Abstract—Lysophosphatidic acid (LPA) and phosphatidic acid (PA) are potent bioactive lipid mediators of signal transduction and
are inactivated by phosphatases. To obtain receptor-isoform selective ligands with neutral phosphomimetic head groups, we per-
formed the stereoselective synthesis of LPA and PA analogues with trifluoromethanesulfonamide and trifluoromethanesulfonami-
doxy moieties replacing the phosphomonoester.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
Phosphatidic acid (PA) regulates phosphoinositide
metabolism and plays key roles in cell growth and vesic-
ular trafficking of proteins.12 PA can be generated by the
action of phospholipase D on phosphatidylcholine (PC)
and other phospholipids, or by LPA-specific acyltrans-
ferases (LPAATs), which terminate LPA signaling. In
addition, the balance between LPA and PA contributes
to the regulation of membrane curvature of bilayer
vesicles.13,14
Lysophosphatidic acid (LPA, 1- or 2-acyl-sn-glycero-3-
phosphate) is an important signaling lipid that elicits a
variety of biological effects, including platelet aggrega-
tion, smooth muscle contraction, cell morphology, mod-
ulation and cell growth stimulation, and proliferation.1,2
LPA binds and activates five G-protein coupled recep-
tors (GPCRs) named LPA1, LPA2, LPA3, LPA4 and
LPA5. LPA1–3, which were formerly called endothelial
differentiation gene receptors (EDG)3 whereas LPA4
and LPA5 are members of the purinergic cluster in the
GPCR superfamily.4,5 LPA is a naturally occurring li-
gand for the intracellular hormone receptor PPARc.6,7
The therapeutic potential for isoform-selective, metabol-
ically-stabilized lysolipid analogues has been increas-
ingly recognized.8,9
Both LPA and PA are substrates for a family of lipid
phosphate phosphatases (LPPs), which regulate the
ratio between phosphate esters and their de-phosphoryl-
ated products.15–17 As integral membrane proteins,
LPPs act both inside and outside the cell14 to hydrolyze
LPA to monoacylglycerol (MAG) and PA to diacylgly-
cerol (DAG), the latter being an important activator of
protein kinase C. Our group has previously reported the
synthesis of a wide range of metabolically-stabilized
LPA and PA analogues,9 in which the 3-oxygen func-
tionality of the glyceryl backbone has been replaced
LPA is found in serum at micromolar concentrations
(1–20 lM), where it is mainly produced by stimulated
platelets. Elevated LPA concentrations are observed in
the plasma of patients with multiple myeloma and in
the ascites of patients with a variety of cancers, for
which it may be a marker for tumor progression.10,11
LPP hydrolysis
OH
OH
OH
OH
OH
OH
R
O
X
P
R
O
O
P
Keywords: Stereoselective phospholipid synthesis; Aminooxygroup;
Trifluoromethanesulfonamide; Trifluoromethanesulfonamidoxy; G-
protein coupled receptor.
O
O
O
O
2
1
*
Corresponding author. Tel.: +1 801 585 9051; fax: +1 801 585 9053;
e-mail addresses: joanna.gajewiak@pharm.utah.edu; gprestwich@
pharm.utah.edu
X= -CHF-, -CF2-, or -CHX
Figure 1.
0040-4039/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.08.066

7608
J. Gajewiak, G. D. Prestwich / Tetrahedron Letters 47 (2006) 7607–7609
O
RCOOH
RCOOH
OH
R
O
O
CF3SO2NH2, Na2CO3
90 oC, 56-85%
EDC, DMAP
EDC, DMAP
O
O
R
O
R
O
NHSO2CF3
HO
R
NHSO2CF3
CH2Cl2, rt
76-80%
CH2Cl2, rt
60-65%
O
O
O
4a-c
5a-c
6a-c
3
R a (8:0)
b (16:0)
c (18:1)
Scheme 1.
with methylene, fluoromethylene, and difluoromethyl-
ene (Fig. 1). We have also described cyclic18 and acyclic
phosphonates19 and phosphorothioates20 with potent
receptor-selective agonist or antagonist activities. We
now describe a synthetic route to two neutral phos-
phomimetics, in which the sn-3 phosphate monoester
is replaced by either a trifluoromethanesulfonamide
(TfN–) or trifluoromethanesulfonamidoxy (TfNO–)
moiety. A related phosphomimetic strategy had been
previously exploited to produce a sulfonamide analogue
of PC as an inhibitor of synovial PLA2,21 as well as a tri-
fluoromethylsulfonamide analogue of phosphotyrosine
as an inhibitor of the phosphatase.22 Based on electron-
ics, size, and H-bonding potential, among other factors,
it has been shown that sulfonamide-based ‘phosphate
isosteres’23 could act as cell-permeant effectors and
inhibitors.21
noate) or isoform-targeted analogues (palmitate and
oleate). Next, a trans stereo- and regio-selective epoxide
ring opening was accomplished in a single step to obtain
the TfN–LPA analogues.24 Thus, 4 was reacted neat
with trifluoromethylsulfonamide (TfNH2) and a cata-
lytic amount of anhydrous Na2CO3 at 90 °C, providing
the secondary alcohols 5a–c in up to 85%. Under these
conditions, the stereogenic carbon C-2 remains un-
changed.24 The purity of TfN–LPA compounds 5a–c
after flash chromatography was verified by 19F NMR
to be >99%. Next, esterification of the sn-2 hydroxyl
group afforded the desired TfN–PA analogues 6a–c in
up to 65% yield.
The TfNO–LPA and TfNO–PA analogues were synthe-
sized from enantiomerically pure (S)-solketal (7,
Scheme 2). First, condensation of alcohol 7 with N-
hydroxyphthalimide under Mitsunobu conditions.25,26
gave, after purification, intermediate 8 in 94% yield.
Phthalimide deprotection with hydrazine mono-
hydrate,26 followed by amidation with 0.5 M triflic
chloride (TfCl), DMAP and pyridine led to compound
10. Next, acidic cleavage of the isopropylidene group
with methanolic p-TsOH produced the expected diol
11 in 89% yield. Initial attempts to perform DCC—pro-
moted selective esterification of the primary hydroxyl
2. Results and discussion
The synthesis of TfN analogues (Scheme 1) commenced
with esterification of (R)-glycidol (3) with saturated
(octanoic and palmitic) and unsaturated (oleic) acid
using carbodiimide chemistry in good yields. These three
acyl chains were selected to provide water-soluble (octa-
O
0.5M CF3SO2Cl
DMAP, pyridine
Ph3P
PhtOH, DEAD
O
O
O
O
NH2NH2H2O
O
OH
O
O
N
O
O
ONH2
O
ONHSO2CF3
CH2Cl2, 0 oC - rt
77%
THF, 0 oC - rt
94%
CH2Cl2, -20 oC - rt
73%
9
7
8
10
RCOCl
2,4,6-collidine
p
-TsOH
OH
CH3OH
89%
R1
O
ONHSO2CF3
THF, -78 o
61-70%
C
O
R1: a (16:0)
12a,b
OH
b (18:1)
R2: (8:0)
HO
ONHSO2CF3
O
O
11
RCOCl
R2
O
2,4,6-collidine
R2
ONHSO2CF3
57%
O
13
Scheme 2.

J. Gajewiak, G. D. Prestwich / Tetrahedron Letters 47 (2006) 7607–7609
7609
group27,28 of diol 11, at 0–3 °C in CH2Cl2, gave disap-
pointing yields. However, selective acylation was readily
accomplished in up to 70% yield, using 0.95 equiv of the
acyl chloride in anhydrous THF at À78 °C and 2,4,6-
collidine as the base.29 A small amount of diester and
2-acyl isomer were obtained. Based on 19F NMR, the
purity of the final compounds was calculated to be
95% for 12a and 91% for 12b. By performing the acyla-
tion of diol 11 with 2 equiv of acyl chloride at room
temperature, the TfNO–PA analogues 13 were obtained
in 57% yield.
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The method described herein for the synthesis of LPA
and PA neutral analogues is facile and flexible with re-
spect to the backbone substituents as well as the choice
of acyl chain. Each of the LPA and PA analogues was
compared with LPA for potential agonist or antagonist
activity toward each of the LPA1–4 receptors,19,20 and
as potential inhibitors of LPP.30 Despite the utility of this
phosphate isostere in other lipid and protein phosphate
contexts, neither agonist, antagonist, nor inhibitory
activity was observed for any of the TfN–LPA, TfN–
PA, TfNO–LPA, or TfNO–PA analogues (A. Morris, J.
Aoki, personal communication). This appears to support
the requirement of an anionic head group for analogues
of LPA for proper activation of the LPA GPCRs.31
19. Xu, Y.; Aoki, J.; Shimizu, K.; Umezu-Goto, M.; Hama,
K.; Takanezawa, Y.; Yu, S.; Mills, G. B.; Arai, H.; Qian,
L.; Prestwich, G. D. J. Med. Chem. 2005, 48, 3319–
3327.
Acknowledgments
We thank the NIH (NS29632) and Echelon Biosciences,
an Aeterna Zentaris Company, for financial support of
this work.
20. Qian, L.; Xu, Y.; Simper, T. D.; Jiang, G.; Aoki, J.;
Umezo-Goto, M.; Arai, H.; Yu, S.; Mills, G. B.; Tsuka-
hara, R.; Makarova, N.; Fujiwara, Y.; Tigyi, G.; Prest-
wich, G. D. Chem. Med. Chem. 2006, 1, 376–383.
21. Pisabarro, M. T.; Ortiz, A. R.; Palomer, A.; Cabre, F.;
Garcia, L.; Wade, R. C.; Gago, F.; Mauleon, D.;
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thier, J.; Ghiro, E.; Gillard, J.; Gorys, V.; Poirier, M.;
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Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.tetlet.2006.08.066.
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