Discovery of a potent and selective COX-2 inhibitor in the alkoxy lactone series with optimized metabolic profile.

Article abstract of DOI:10.1016/S0960-894X(02)00739-4

The COX-2 inhibitor DFP [5,5-dimethyl-3-(2-propoxy)-4-methanesulfonylphenyl)-2(5H)-furanone] was found to have a long half-life in humans. Analogues have been characterized in order to optimize pharmacokinetics. This has lead to the discovery of 5(S)-(5-ethyl-5-methyl-3-(2-propoxy)-4-methanesulfonylphenyl)-2(5H)-furanone analogue 11 a potent and selective COX-2 inhibitor which is metabolized to a greater extent than DFP upon incubation with rat and human hepatocytes, suggesting a shorter half-life in humans.

Full text of DOI:10.1016/S0960-894X(02)00739-4

Bioorganic & Medicinal Chemistry Letters 12 (2002) 3317–3320
Discovery of a Potent and Selective COX-2 Inhibitor in the
Alkoxy Lactone Series with Optimized Metabolic Profile
Yves Leblanc,a,* Patrick Roy,a Zhaoyin Wang,a Chun Sing Li,a Nathalie Chauret,a
Deborah A. Nicoll-Griffith,a Jose M. Silva,a Yves Aubin,a James A. Yergey,a
Chi Chung Chan,a Denis Riendeau,a Christine Brideau,a Robert Gordon,a
Lijing Xu,a Janine Webb,b Denise M. Viscoc and Petpiboon Prasita
aDepartment of Medicinal Chemistry, Merck Frosst Centre for Therapeutic Research, PO Box 1005,
Pointe Claire-Dorval, Quebec, Canada H9R 4P8
bMerck Research Laboratories, Harlow, Essex, UK
cMerck Research Laboratories, Rahway, NJ, USA
Received 23 July 2002; accepted 13 August 2002
Abstract—The COX-2 inhibitor DFP [5,5-dimethyl-3-(2-propoxy)-4-methanesulfonylphenyl)-2(5H)-furanone] was found to have a
long half-life in humans. Analogues have been characterized in order to optimize pharmacokinetics. This has lead to the discovery
of 5(S)-(5-ethyl-5-methyl-3-(2-propoxy)-4-methanesulfonylphenyl)-2(5H)-furanone analogue 11 a potent and selective COX-2
inhibitor which is metabolized to a greater extent than DFP upon incubation with rat and human hepatocytes, suggesting a shorter
half-life in humans.
# 2002 Elsevier Science Ltd. All rights reserved.
Since the discovery that the cyclooxygenase exists in two
isoforms1 it has been demonstrated that selective cyclo-
oxygenase-2 (COX-2) inhibitors have the desirable
therapeutic effects of nonsteroidal antiinflammatory
drugs (NSAIDS) with less gastrointestinal side effects
associated with dual COX-1/2 inhibitors.2À4
COX-2 inhibitor was shown to be potent and selective
in human ex vivo assays.14 However, the human half-
life of DFP was found to be long, with a value of 64 h.14
It has been well documented that metabolic processes
play an important role in the excretion of COX-2
inhibitors.15À17 In vivo and in vitro studies with DFP in
Heretofore, several groups have reported COX-2 selec-
tive inhibitors such as rofecoxib,5 celecoxib,6 etoricoxib,7
valdecoxib,8 and others.9,10
Following the discovery of rofecoxib (VIOXX), several
efforts were made to identify other selective COX-2
inhibitors in the lactone series. This work lead to the
discovery of DFU(1)11 DFP(2).12 DFP was found to be
a potent and highly selective COX-2 inhibitor with
excellent pharmacokinetic properties in a variety of
species. In addition, pre-clinical data showed that DFP
possesses anti-inflammatory activity in animals.13 This
*Corresponding author. Tel.: +1-514-428-3096; fax: +1-514-428-
4900; e-mail: yves_leblanc@merck.com
0960-894X/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S0960-894X(02)00739-4

3318
Y. Leblanc et al. / Bioorg. Med. Chem. Lett. 12 (2002) 3317–3320
animal models showed that metabolism, at the alkoxy
side chain, is the key determinant in its clearance.18
DFP has a very low turn over in human in vitro meta-
bolism experiments19 thus correlating with the long
human half-life. Therefore, modifications made to the
structure of DFP, introducing sites for increased meta-
bolism would be expected to provide COX-2 inhibitors
with reduced half-life in humans.
With the goal of increasing the metabolism of DFP,
modifications at the 3-and 5-positions on the molecule
were considered. As already reported in our previous
paper,12 several 3-alkoxy analogues were prepared.
Longer alkoxy groups at the 3-position gave analogues
with more metabolism, that correlated with increased
clearance in pre-clinical species (data not shown). How-
ever, the isopropoxy substituent at the 3-position was
found to be the ultimate group for COX-2 inhibitory
potency, selectivity and pharmacokinetics in different
species. The second approach was to keep the iso-
propoxy group and modify the substitution at the C-5
position of the lactone ring. It is known from study of
several analogues in this series, that the gem-dimethyl
groups at the C-5 position are metabolically inert.18,20
Thus, trifluoroethyl and ethyl analogues were prepared
to provide potential sites for metabolic oxidation. The
biological and metabolic profiles of these analogues are
described herein.
Scheme 1.
The analogue 11 was prepared as described in Scheme 1.
The a-bromoketone 321 was heated in DMF in the pre-
sence of LiCl at 100 ꢀC for 7 h to provide the vinyl
ketone compound 4 in 84% yield. Treatment of ketone
4 with (S)-CBS and borane afforded the alcohol 5 in
86% yield with an enantiomeric excess of 88%. The
absolute stereochemistry of the alcohol 5 was proven by
X-ray crytallographic analysis. The allylic alcohol 5 was
then epoxidized using Sharpless conditions to give the
epoxy alcohol 6 in 77% yield. After protection of the
alcohol as its 1-ethoxyethyl ether, the epoxide 7 was
treated with LiCuMe2 to provide compound 8. The
a-hydroxy ketone 9 was obtained by treatment of 8 with
NBS in CCl4. The chiral alcohol 9 was then condensed
on isopropoxyacetic acid21 in the presence of CMC to
give the ester 10. In turn, the ester 10 was heated in
CH3CN in the presence of DBU and isopropyl tri-
fluoroacetate to provide compound 11 in 59% yield.
The trifluoroethyl analogue 18 was prepared from
2-methyl-4,4,4-triflurobutyric acid 12 (Scheme 2). The
acid was transformed to the acyl chloride 13 followed
by a Friedel–Crafts reaction with thiomethylanisole to
provide ketone 14. The ketone was hydroxylated with
(EtO)3P/potassium tert-butoxide/O222 to give 15 in 50%
yield. After oxidation with mCPBA, the alcohol 16 was
condensed on acetoxyacetyl chloride followed by DBU
Scheme 2.

Y. Leblanc et al. / Bioorg. Med. Chem. Lett. 12 (2002) 3317–3320
3319
treatment to provide 17. The isopropyl moeity was then
introduced by treatment with 2-iodopropane in the pre-
sence of Ag2CO3 to give the final compound 18.
hepatocytes (106 cells, 50 mM substrate, 2 h),20 the ana-
logue 11 was highly metabolized (25–35%) as opposed
to DFP (ꢁ2%). These results are in accordance with
the shorter half-life of 11, 2 h versus 7 h for DFP.12
1
The racemate trifluoroethyl analogue 18 was found to
be four times less potent than DFP in the COX-2
human whole blood assay (COX-2 HWB), as shown in
Table 1. In addition, poor in vivo activity was observed
with compound 18 in the rat paw edema assay (ED50 7.8
mg/kg). The ethyl methyl analogue was found to have
comparable activity to DFP. The R-(19) and S-(11)
enantiomers have similar potency in the COX-2 HWB
assay with IC50’s of 0.5 and 0.4 mM, respectively. Both
enantiomers were found to be very selective with IC50’s
of >100 mM for the R-enantiomer and 86 mM for the
S-enantiomer 11 in the COX-1 HWB assay. However,
the pharmacokinetics and the in vivo profile in rats of
the S-enantiomer 11 were found to be superior com-
pared to the R-enantiomer(19) as described in Tables 2
and 3. As observed with rofecoxib, no gastrointestinal
side effects were observed in rats with analogue 11 as
demonstrated by the 51Cr assay to probe the intestinal
permeability.9c No chromium leakage was observed
with compound 11 at a daily dose of 100 mg/kg bid for
10 days.
LC/MS studies using APCI-MS18 and H NMR experi-
ments on a purified sample of the most significant
metabolite indicated that the major metabolic pathway
for 11 was now occurring on the ethyl side chain at the
methylene position, yielding both possible hydroxy dia-
stereomers (data not shown). In order to predict whe-
ther the half-life of analogue 11 would also be shorter
than DFP in humans, human hepatocyte incubations
were performed with both 11 and DFP. As observed for
rat hepatocyte incubations, 11 was significantly more
metabolized than DFP19 (ꢁ18% for 11 vs <2% for
DFP). The turn-over of 11 in human hepatocytes was
faster than that obtained for etoricoxib (ꢁ8%),23
a
once-a-day COX-2 drug with an apparent terminal half
life of 22 h.24
In conclusion, it has been possible to modulate the
degree of metabolism and therefore the pharmaco-
kinetics of this inhibitor class by adding metabolic soft
sites to DFP, while maintaining the biological proper-
ties essential for a COX-2 inhibitor. The in vitro and in
vivo data of analogue 11 are comparable to DFP. The
incubation with human hepatocytes suggests that the
human half-life of compound 11 should be shorter than
that for DFP.
Studies were performed to evaluate the overall meta-
bolic profile of 11. In standard incubations with rat
Table 1. In vitro potency and selectivity data of DFP(2), 18, 19 and
11
Acknowledgements
The authors would like to acknowledge Dr Marc Bilo-
deau from the Hopital Saint-Luc, Montreal, for pro-
viding human liver tissue.
IC50 (mM)
References and Notes
COX-2 HWB
COX-1 HWB
0.3
>100
1.3
n/a
0.5
>100
0.4
>86
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