New water-soluble sulfonylphosphoramidic acid derivatives of the COX-2 selective inhibitor cimicoxib. A novel approach to sulfonamide prodrugs

Article abstract of DOI:10.1021/jm040844j

The synthesis and pharmacological evaluation of new water-soluble phosphoramidate derivatives of the COX-2 selective inhibitor cimicoxib (4) are described. The sulfonylphosphoramidic acid derivative 10 was converted to 4 in human plasma and showed excelle

Full text of DOI:10.1021/jm040844j

J . Med. Chem. 2004, 47, 5579-5582
5579
New Wa ter -Solu ble Su lfon ylp h osp h or a m id ic Acid Der iva tives of th e COX-2
Selective In h ibitor Cim icoxib. A Novel Ap p r oa ch to Su lfon a m id e P r od r u gs
Carmen Almansa,* J avier Bartrol´ı, J ordi Belloc, Fernando L. Cavalcanti, Rosa Ferrando, Luis A. Go´mez,
Isabel Ramis, Elena Carceller, Manuel Merlos, and J ulia´n Garc´ıa-Rafanell
Research Center, Grupo Uriach. Av. Cam´ı Reial, 51-57, E-08184, Palau-Solita` i Plegamans, Spain
Received May 10, 2004
The synthesis and pharmacological evaluation of new water-soluble phosphoramidate deriva-
tives of the COX-2 selective inhibitor cimicoxib (4) are described. The sulfonylphosphoramidic
acid derivative 10 was converted to 4 in human plasma and showed excellent in vivo activity
in the rat carrageenan-edema test. Pharmacokinetic evaluation in dogs indicated that 10
behaved as a prodrug, immediately converting to 4 and giving an identical profile to that of
the parent compound. These results represent the first description of phosphoramidic acids as
prodrugs for the sulfonamido group. Compound 10 also exhibited an important and sustained
analgesic effect in the hyperalgesia test in rats and a high aqueous solubility at pH higher
than 7. This profile led to the selection of 10 (UR-14048) for further development in the
parenteral treatment of acute pain.
In the management of severe or moderately severe
pain, parenteral treatments are preferred because of the
rapid onset of action. Such situations often arise in
hospitals, after surgery or after injury.1 Recent surveys
have shown that postoperative pain is considered poorly
managed, due to side-effect limitations of available
injectable medications, such as opioids and nonsteroidal
antiinflammatory drugs (NSAID). In this regard, the
most used nonnarcotic analgesic for these indications,
ketorolac (1), has been associated with the appearance
of significant side effects.2
Inhibition of cyclooxygenase (COX), one of the key
enzymes involved in the degradation of arachidonic acid
to prostaglandins, is the main target for NSAID. A
decade ago, two isoforms of COX were identified:3 one
(COX-2) is inducible and expressed mainly in inflam-
matory cells and the other (COX-1) is cytoprotective and
constitutively expressed in many tissues such as stom-
ach, kidney, and platelets. This discovery led to the
F igu r e 1.
development of COX-2 selective inhibitors,4 which showed
a similar efficacy to nonselective NSAID but reduced
gastrointestinal toxicity. Rofecoxib5 and celecoxib6 were
the first COX-2 selective inhibitors to reach the market,
followed by valdecoxib (2)7 and etoricoxib.8 However,
none of these agents was suitable for parenteral for-
mulation due to low water solubility. The strategy of
developing water-soluble prodrugs was foreseen, and
parecoxib9 (3), the sodium salt of the propanoyl prodrug
of valdecoxib, was recently marketed for the hospital
treatment of postoperative pain. The elegant work of
Talley and co-workers showed that among different acyl
derivatives only the propionyl group provided the
desired in vivo conversion in several species to the
parent compound.
(4),10 a new COX-2 inhibitor, which is currently under-
going phase II clinical trials for the oral treatment of
acute pain and osteoarthritis. Taking into account the
medical need for postsurgical pain treatments, the
development of a parenteral formulation was under-
taken. However, it was soon realized that the low water
solubility of 4 precluded this approach.
A search for possible sulfonamide prodrugs indicated
that the only reports described in the literature were
those of valdecoxib derivatives9 and a previous report11
based also on acyl sulfonamides. Other approaches
including sulfonylamidines, sulfonylureas,11 and sulfo-
nyl imidates12 were unsuitable for our purposes, since
these functions did not carry ionizable groups. The
preparation of phosphoramidate derivatives of general
formula I (Figure 1) was envisaged as an interesting
approximation, since high water solubility seemed to be
achievable through the formation of alkaline salts, due
to the predicted pKa value of 5 for the NH group. We
As a result of our efforts toward the development of
safer antiinflammatory agents, we identified cimicoxib
* To whom correspondence should be addressed: Research Center,
Grupo Uriach. Av. Cam´ı Reial, 51-57, E-08184 Palau-Solita` i Plega-
mans, Spain. Tel:
902471511. Fax:
938649692. E-mail:
chem-almansa@uriach.com.
10.1021/jm040844j CCC: $27.50 © 2004 American Chemical Society
Published on Web 09/24/2004

5580 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 22
Almansa et al.
Sch em e 1a
Ta ble 1. PK Parameters of 4 after Iv Administration of 2
Mg/kg 4 or 1 Mg/kg 10 to Dogs
parameter 2 mg/kg of 4
t1/2 (h)
1 mg/kg of 10
5.0 ( 0.3
4.9 ( 0.7
AUC/dose (ng h/ mL)
Cl (mL/h/kg)
3253.4 ( 781.8
292.2 ( 46.1
2116.8 ( 387.0
3641.1 ( 1384.8
273.2 ( 125.8
1856.9 ( 529.1
Vd (mL/kg)
Resu lts a n d Discu ssion
The possible prodrug behavior of derivatives 5-10
was initially evaluated by studying their conversion in
human plasma to the parent compound 4. While the
esters 5-9 remained unchanged for the 24 h evaluation
period, compound 10 was converted to 4, with a conver-
sion of 40% after 24 h incubation.
Compound 10 was then evaluated in the rat carra-
geenan-induced paw edema assay. It was intravenously
administered at 3 mg/kg to rats, 10 min before edema
induction by injection of λ-carrageenan. Paw volume was
then measured at different times after injection and the
percentage of inhibition calculated by comparison of the
areas under the curve of treated and control groups.
Compound 10 showed good potency, with 34.8 ( 2.9%
inhibition, identical to that of the parent compound 4
and similar to that of parecoxib 3 (32.6 ( 2.8%),
administered at the same dose.
a
(i) 2 N NaOH, ClPO(OR)2, THF, 20 °C, 6 h; (ii) NaI, acetone,
50 °C, 18 h; (iii) (1) ISiMe3, CH2Cl2, 0 °C, 1 h, (2) H2O/acetone, 20
°C, 18 h.
report here our results on the investigation of the use
of phosphoramidate salts as a new approach to water-
soluble sulfonamide prodrugs.
Ch em istr y
A preliminary pharmacokinetic study of compound 10
in dogs was then undertaken in order to evaluate its in
vivo conversion to 4 in a different species. The plasma
half-life of 10 was not determined in this experiment,
but high levels of 4 were detected within minutes of the
intravenous administration of 10. The pharmacokinetic
parameters obtained for 4 given as an intravenous
suspension of 4 or as an intravenous solution of 10 were
roughly the same (see Table 1), indicating an immediate
and complete in vivo conversion. Moreover, in vitro
metabolic studies in human microsomes indicated a 74%
conversion of 10 to 4 after incubation for 2 h. This result
suggests that 10 could have a short half-life in humans,
rapidly converting to the active drug 4.
To determine the in vivo activity in an experimental
model of acute inflammatory pain, 10 was evaluated in
comparison to ketorolac (1) and parecoxib (3) in the
carrageenan-induced thermal hyperalgesia test20 in rat
after intravenous administration at 3, 10, and 30 mg/
kg. Morphine (4 mg/kg) was used as a positive control.
As indicated in Figure 2, compound 10 at 3 mg/kg
showed a significant increase in the withdrawal latency
to thermal stimulation of the inflamed paw, as com-
pared to vehicle controls. The activity profile of 10 was
similar to that of ketorolac (1) and parecoxib (3), but
10 exhibited a faster onset of action. Morphine exerted
a more potent effect initially, but it rapidly disappeared
and was negligible at 4 h.
The synthesis of I from 4 proved to be more difficult
than expected. Initially, we envisioned the reaction with
the corresponding dialkyl chlorophosphate to give di-
alkyl phosphoramidates, followed by stepwise hydrolysis
of the ester groups. However, attempts to adapt alter-
native procedures reported in the literature13-15 gave
unsatisfactory results. Only when using an adaptation
of a method16 that involves reaction of the previously
formed sulfonamide sodium salt with diethyl chloro-
phosphate was the diethyl derivative 5 isolated in 30%
yield. To increase yields and avoid the formation of the
intermediate salt, the in situ addition of NaOH to 4 was
investigated. It was found that maintaining the reaction
mixture in solution, by adding 2 N NaOH simulta-
neously to the dropwise addition of 7 equiv of diethyl
chlorophosphate, resulted in high yields (74-86%) of 5.
The same procedure was applied for the preparation of
the dimethyl (6) and diphenyl (7) esters.
The monoethyl and monomethyl esters 8 and 9 were
isolated as sodium salts by treatment of the correspond-
ing diesters 5 and 6 with sodium iodide.17
There are only four described procedures for the
preparation of phosphoramidic acid derivatives of sul-
fonamides,18 which in the best case18a involves a four-
step synthesis. After trying without success the direct
conversion of 4 into 10 by treatment with POCl3 in
pyridine, we turned our attention to the hydrolysis of
dialkyl esters with trimethylsilyl iodide, which had been
reported for obtaining phosphonic acid derivatives of
guanidines.19 When 5 was treated with 5 equiv of
iodotrimethylsilane, followed by aqueous hydrolysis, the
phosphoramidic acid 10 was obtained in 80% yield. This
two-step procedure has been used to prepare 200 g of
compound 10. (Scheme 1).
As indicated above, an adequate aqueous solubility
was of critical importance in order to develop an
intravenous dosage form. The highly acidic character
of 10 (experimental21 pKa1, 1.70; pKa2, 5.46; pKa3, 9.83)
provided a pH of 2.6 and a solubility of only 1.3 mg/
mL, when dissolving a sample of 5 mg in 1 mL of water.
However, an equilibrium solubility22 greater than 100
mg/mL was observed in phosphate-buffered aqueous
media at pH ) 7 or higher. The trisodium, dipotassium,
and tripotassium salts of 10 were prepared, giving also
The sodium and potassium salts of 10 were prepared
by treatment with NaOH or KOH, respectively, in
ethanol, followed by recrystallization.

Sulfonylphosphoramidates of Cimicoxib
J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 22 5581
was dried over Na2SO4 and the solvent was eliminated to
afford 5 as a white solid (2.0 g, 74%): mp 188 °C; 1H NMR
(300 MHz, CDCl3 δ TMS) 1.29 (t, J ) 7.1 Hz, 6 H), 2.0 (b b,
H2O + NH), 3.90 (s, 3 H), 4.12 (m, 4 H), 6.93 (m, 3 H), 7.23 (d,
J ) 8.7 Hz, 2 H), 7.63 (s, 1 H), 8.02 (d, J ) 8.7 Hz, 2 H). Anal.
(C20H22ClN3O6PS) C, H, N.
Following a similar procedure compound 6 [Anal. (C18H18
-
ClFN3O6PS‚0.5H2O) C, H, N] and 7 [Anal. (C28H22ClFN3O6-
PS‚H2O) C, H; N: calcd, 6.65; found, 5.92] were obtained.
Eth yl N-[4-[4-Ch lor o-5-(3-flu or o-4-m eth oxyp h en yl)im i-
dazol-1-yl]ph en ylsu lfon yl]ph osph or am idate Sodiu m Salt
(8). To a suspension of 5 (1 g, 1.9 mmol) in acetone (14 mL)
was added NaI (284 mg, 1.9 mmol), and the resulting mixture
was stirred at reflux overnight under an argon atmosphere.
It was concentrated to dryness and the crude product obtained
was purified by chromatography on silica gel using EtOAc/
MeOH/AcOH mixtures of increasing polarity as eluent. The
i
product obtained was next recrystallized from PrOH to afford
F igu r e 2. Time course evaluation in the rat thermal hyper-
algesia model after intravenous administration of ketorolac
(1, 3 mg/kg), parecoxib (3, 3 mg/kg), 10 (3 mg/kg), and
morphine (4 mg/kg). ***p< 0.001; **p< 0.01; *p < 0.05 versus
vehicle.
554 mg of 8 as a white solid (57%): 1H NMR (300 MHz, CDCl3
+ CD3OD δ TMS) 1.20 (m, 3 H), 3.74 (m, 2 H), 3.90 (s, 3 H),
4.30 (s, H2O + NH), 6.95 (m, 3 H), 7.29 (d, J ) 7.7 Hz, 2 H),
7.74 (s, 1 H), 8.06 (d, J ) 7.7 Hz, 2 H). Anal. (C18H17ClFN3-
NaO6PS‚0.5H2O) C, H, N.
Following a similar procedure, compound 9 was obtained.
Anal. (C17H15ClFN3NaO6PS‚0.4iPrOH) C, H, N.
high solubilities in water. Finally, the in situ prepara-
tion of the trisodium salt of 10 (by adding 3 equiv of
NaOH) gave a solubility greater than 50 mg/mL in 0.9%
NaCl. These results indicated the feasibility of 10 for
the development of an intravenous formulation.
N-[4-[4-Ch lor o-5-(3-flu or o-4-m eth oxyph en yl)im idazole-
1-yl]p h en ylsu lfon yl]p h osp h or a m id ic Acid (10). To a sus-
pension of 5 (1.0 g, 1.9 mmol) in CH2Cl2 (22 mL) was added
iodotrimethylsilane (1.3 mL, 9.6 mmol) dropwise, under a
nitrogen atmosphere and at 0 °C. The mixture was stirred for
1 h at 0 °C and the solvent was eliminated. The residue was
cooled to 0 °C and treated with a mixture of acetone (22 mL)
and H2O (0.76 mL). After stirring at 0 °C for 1 h the mixture
was stirred at room temperature overnight. The suspension
thus obtained was filtered and the solid was washed with
acetone and dried. Compound 10 was obtained as a yellowish
solid (0.7 g, 80%): mp 190-193 °C; 1H NMR (300 MHz, CDCl3
δ TMS) 3.91 (s, 3 H), 4.46 (s, H2O + 3 H), 6.95 (m, 3 H), 7.31
(d, J ) 8.7 Hz, 2 H), 7.78 (s, 1 H), 8.04 (d, J ) 8.7 Hz, 2 H).
Anal. (C16H14ClFN3O6PS) C, H, N.
In summary, we have described the synthesis and
pharmacological evaluation of new phosphoramidate
derivatives of the COX-2 selective inhibitor cimicoxib,
4. The sulfonylphosphoramidic acid derivative 10 was
converted to 4 in human plasma and showed excellent
in vivo activity in the rat carrageenan test. Pharmaco-
kinetic evaluation in dogs indicated that 10 behaved as
a prodrug, immediately converting to 4 and giving an
identical profile to the parent compound. These results
represent the first description of phosphoramidic acids
as prodrugs for the sulfonamido group. Compound 10
exhibited also an important and sustained analgesic
effect in the hyperalgesia test in rats and a high aqueous
solubility at pH higher than 7. For this reason, com-
pound 10 (UR-14048) has been selected for further
development in the parenteral treatment of acute pain.
Tr isod iu m N-[4-[4-Ch lor o-5-(3-flu or o-4-m eth oxyp h en -
y l)im id a zo l-1-y l]p h e n y ls u lfo n y l]p h o s p h o r a m id a t e
(10.3Na ). To a solution of 10 (0.15 g, 0.3 mmol) in EtOH (2
mL),was added NaOH powder (39 mg, 0.96 mmol) in EtOH (4
mL), and the resulting mixture was stirred under argon
atmosphere at room temperature for 1 h. The mixture was
concentrated to dryness and the resulting solid was recrystal-
i
lized from PrOH (20 mL), to afford the trisodium salt of 10 as
a white solid (0.16 g; 95%). Anal. (C16H11ClFN3Na3O6PS‚2H2O)
C, H, N.
Exp er im en ta l Section
Ca r r a geen a n -In d u ced R a t P a w E d em a Assa y. Male,
Sprague-Dawley rats (150-175 g) were used. Edema was
produced by injecting 0.1 mL of a solution of 1% λ-carrageenan
in the hindpaw. Paw volume was measured by water displace-
ment with a plethysmometer (UGO BASILE) before and 1, 2,
3 and 4 h after treatment. The compounds were administered
by intravenous route as a solution in PBS (1 mL/kg) 10 min
before carrageenan injection and after being hydrated with
H2O (5 mL). The percentages of inhibition were calculated by
comparing the areas under the curve of treated and control
animals.
Melting points were determined with a Mettler FP 80
central processor melting point apparatus and are uncorrected.
1H NMR(300 MHz) spectra were recorded on a Bruker Avance
DPX-300 spectrometer. They are reported in ppm on the δ
scale, from the reference indicated. Combustion analyses were
performed with a Carlo Erba 1108 analyzer. Liquid chroma-
tography was performed with a forced flow (flash chromatog-
raphy) of the indicated solvent system on SDS silica gel
Chromagel 60 ACC (230-400 mesh). Analytical thin-layer
chromatography (TLC) was performed with Macherey-Nagel
0.25 mm silica gel SIL G-25 plates.
In cu ba tion in Hu m a n P la sm a . Human plasma was
obtained by centrifugation (15 min, 2800g, 4 °C) of human
blood. DMSO solutions of test compounds (equivalent to 1 µM
of 7) were added to individual tubes (1%) and these were
maintained at 37 °C for 24 h. The concentration of 7 was
determined using LC-MS.
Th er m a l Hyp er a lgesia Test. Male, Wistar rats were
treated with an intraplantar injection of carrageenan (0.75 mg/
paw). Two hours later, rats were submitted consecutively to
thermal stimulation of both the noninflamed and the inflamed
hindpaws by means of a mobile infrared radiant source. Test
compounds were administered iv at the doses of 3, 10, and 30
mg/kg, 105 min after carrageenan, and compared with a
Dieth yl N-[4-[4-Ch lor o-5-(3-flu or o-4-m eth oxyp h en yl)-
im id a zole-1-yl]p h en ylsu lfon yl]p h osp h or a m id a te (5). To
a mixture of 4-[4-chloro-5-(3-fluoro-4-methoxyphenyl)imidazol-
1-yl]benzenesulfonamide (4, 2.0 g, 5.2 mmol) in 1 N NaOH (7.2
mL) (pH 13.4) under a nitrogen atomosphere was added a
solution of diethyl chlorophosphate (5.2 mL, 36.4 mmol) in
THF (28 mL) during 5 h. To keep the reaction mixture in
solution a 2 N NaOH aqueous solution was added simulta-
neously. Once the addition was finished, the mixture was
stirred for 1 h at room temperature. Ethyl acetate was added
and the phases were separated. The organic phase was washed
with 0.01 N NaOH and the combined aqueous phases were
brought to pH 4 and extracted with EtOAc. The organic phase

5582 J ournal of Medicinal Chemistry, 2004, Vol. 47, No. 22
Almansa et al.
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Ack n ow led gm en t . We thank M. Carmen Torres,
Concepcio´n Gonza´lez, Consol Ferreri, Guadalupe Mar-
t´ınez, Nuria Recasens, Teresa Gamero, J ose´ Antonio
Garc´ıa, Ana Ester Sanahuja, J ordi Vilar, and Assumpta
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(21) Ionization constants were measured by potentiometric titration
in 0.15 M KCl at 25 °C using a PCA200 instrument (Sirius
Analytical Instruments).
(22) Equilibrium solubilities were obtained by adding solid com-
pounds directly to an aqueous medium, followed by stirring at
room temperature for 16 h. Suspensions were then filtered and
the remaining concentration in the solution was measured by
HPLC.
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