A novel series of non-carboxylic acid, non-hydantoin inhibitors of aldose reductase with potent oral activity in diabetic rat models: 6-(5-Chloro-3- methylbenzofuran-2-sulfonyl)-2H-pyridazin-3-one and congeners

Article abstract of DOI:10.1021/jm050462t

Discovery of a highly selective, potent, and safe non-carboxylic acid, non-hydantoin inhibitor of aldose reductase (AR) capable of potently blocking the excess glucose flux through the polyol pathway that prevails under diabetic conditions has been a long-standing challenge. In response, we did high-throughput screening of our internal libraries of compounds and identified 6-phenylsulfonylpyridazin-2H-3-one, 8, which showed modest inhibition of AR, both in vitro and in vivo. Initial structure-activity relationships concentrated on phenyl substituents and led to 6-(2,4-dichlorophenylsulfonyl)-2/f-pyridazin- 3-one, 81, which was more potent than 8, both in vitro and in vivo. Incorporation of extant literature findings with other aldose reductase inhibitors, including zopolrestat, resulted in the title inhibitor, 19m, which is one of the most potent and highly selective non-carboxylic acid, non-hydantoin inhibitors of AR yet described (IC₅₀, 1 nM; ED ₉₀ vs sciatic nerve sorbitol and fructose, respectively, 0.8 and 4.0 mg/kg). In rats, its oral bioavailability is 98% and it has a favorable plasma t_1/2 (26 ± 3 h).

Full text of DOI:10.1021/jm050462t

6326
J. Med. Chem. 2005, 48, 6326-6339
A Novel Series of Non-Carboxylic Acid, Non-Hydantoin Inhibitors of Aldose
Reductase with Potent Oral Activity in Diabetic Rat Models:
6-(5-Chloro-3-methylbenzofuran-2-sulfonyl)-2H-pyridazin-3-one and Congeners
Banavara L. Mylari,* Sandra J. Armento, David A. Beebe, Edward L. Conn, James B. Coutcher,
Michael S. Dina, Melissa T. O’Gorman, Michael C. Linhares, William H. Martin, Peter J. Oates, David A. Tess,
Gregory J. Withbroe, and William J. Zembrowski
Pfizer Global Research and Development, Pfizer Inc., Groton, Connecticut 06340
Received May 16, 2005
Discovery of a highly selective, potent, and safe non-carboxylic acid, non-hydantoin inhibitor
of aldose reductase (AR) capable of potently blocking the excess glucose flux through the polyol
pathway that prevails under diabetic conditions has been a long-standing challenge. In response,
we did high-throughput screening of our internal libraries of compounds and identified
6-phenylsulfonylpyridazin-2H-3-one, 8, which showed modest inhibition of AR, both in vitro
and in vivo. Initial structure-activity relationships concentrated on phenyl substituents and
led to 6-(2,4-dichlorophenylsulfonyl)-2H-pyridazin-3-one, 8l, which was more potent than 8,
both in vitro and in vivo. Incorporation of extant literature findings with other aldose reductase
inhibitors, including zopolrestat, resulted in the title inhibitor, 19m, which is one of the most
potent and highly selective non-carboxylic acid, non-hydantoin inhibitors of AR yet described
(IC50, 1 nM; ED90 vs sciatic nerve sorbitol and fructose, respectively, 0.8 and 4.0 mg/kg). In
rats, its oral bioavailability is 98% and it has a favorable plasma t1/2 (26 ( 3 h).
Introduction
high intracellular glucose flux through the polyol path-
way5,6 (Figure 1, shaded in blue), viz., cellular osmotic
stress7 and pseudohypoxia-linked oxidative stress.8
Diabetes mellitus has become pandemic and according
to reports, including a forecast by the World Health
Organizations, there will be a sharp increase in the total
number of cases worldwide by 2030, especially in the
two most populous countries, China and India.1 In fact,
India could be bracing itself for the dubious distinction
of becoming the diabetes capital of the world. This is
an ominous forecast, because managing the long-term
complications of the disease, which include nephropa-
thy, neuropathy, retinopathy, and cardiovascular com-
plications, will have a serious impact on public health
budgets. For example, an American Diabetes Associa-
tion estimate puts the total costs for diabetes care in
the United States in 2002 at $132 billon. Direct medical
expenditures alone totaled $91.8 billion, of which $24.6
billion accounted for chronic complications attributable
to diabetes.2 These include hospital and in-patient care
to provide for limb amputation (a complication of serious
neuropathy), cataract surgery, retinal coagulation
therapy, and kidney dialysis. Results of the Diabetes
Control and Complications Trial (DCCT)3 and the
United Kingdom Perspective Diabetes Study (UK PDS)4
have underscored the link between chronically elevated
blood glucose levels and the severity of the consequent
diabetic complications as well as the critical importance
of controlling and maintaining near normal blood glu-
cose excursions. While the exact mechanism(s) underly-
ing the pathological consequences of chronically high
blood glucose levels is not yet fully understood, consid-
erable attention has focused on one aspect of metabolic
research that pertains to the primary consequences of
Figure 1 also calls attention to several other down-
stream events tied to the polyol pathway, for example,
protein kinase stress and glycation stress. From a
potential successful therapeutic approach, a robust
blockade of excess glucose flux through both steps of the
polyol pathway, with a powerfully effective aldose
reductase inhibitor (ARI), to completely normalize both
cellular sorbitol and fructose pools, would not only
address the osmotic and the oxidative stress hypotheses
but also the other downstream markers. It is noteworthy
that, in the streptozotocin diabetic rat model, suppres-
sion of nerve fructose lags behind that of sorbitol by a
factor of 3-20-fold, confirming that just inhibition of
sorbitol is not a satisfactory marker for robust control
of glucose flux through the polyol pathway.6d Animal
data with sorbitol dehydrogenase inhibitors further
confirms that flux through the polyol pathway is quite
active, even in the nondiabetic state, e.g., in normal
rats.9 In other words, near normalization of fructose
levels requires near overnormalization of sorbitol levels.
Strong support for this notion derives from dose titration
using different ARIs, aimed at studying relationships
between polyol pathway metabolites and tissue function.
For example, a nearly full correction of the nerve
conduction velocity deficit (NCV) in diabetic rats re-
quires doses of ARIs that not only overnormalize nerve
sorbitol levels but also suppress nerve fructose levels
g90%.10,11 In retrospect, clinical dose selection for all
ARIs, including tolrestat, Ponalrestat, zopolrestat, and
sorbinil (Chart 1), which were taken into placebo
controlled phase III neuropathy studies in the United
States and Europe, was based exclusively on safety and
* To whom correspondence should be addressed. Phone: (860) 691-
2033. Fax: (860) 739-7450. E-mail: blmylari@aol.com.
10.1021/jm050462t CCC: $30.25 © 2005 American Chemical Society
Published on Web 09/10/2005

Novel Inhibitors of Aldose Reductase
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20 6327
Figure 1. Polyol pathway network.
Chart 1
Because there is as yet no safe and effective ARI
therapy available worldwide, the question has been
raised whether the polyol approach to diabetic compli-
cations merits continued medicinal chemistry attention
and whether one can discover an ARI of distinct chemi-
cal structure with sufficient potency and duration of
action to effectively block the excess flux at safe doses
in the clinic. We believe there are several compelling
new findings to justify continued diligence and opti-
mism. (1) Strong support comes from results of AR
knockout mouse studies15 and from reports that several
allelic variants of the human AR gene that are associ-
ated with overexpression of AR are also associated with
a significant increase in the risk of development of
microvascular complications.16 (2) Exciting clinical re-
sults have been obtained with the spiroimide ARI
ranirestat (AS-3201),17 in a just completed placebo-
controlled 12-week study, in diabetic neuropathic pa-
tients. Ranirestat is reported to penetrate the human
sural nerve sufficiently well to inhibit both sorbitol and
fructose accumulation and, concomitantly, markedly
improve nerve function as well as clinical measures of
neuropathy in a dose-dependent manner.18 (3) Also,
there is an extremely encouraging earlier report that
minalrestat, another spiroimide, in an open label, short-
term clinical study strongly suppressed both sorbitol
and fructose in sural nerve biopsy samples, as well as
improved NCV, at very low doses.19 (4) For the first time
with any ARI, encouraging positive results have been
obtained with zopolrestat in a placebo-controlled, double-
blind clinical trial aimed at treating cardiac abnormali-
ties in diabetic patients with neuropathy, particularly
under an exercise regimen.20 These contemporary find-
ings have lent strong timely support for an initiative
that we undertook some years ago to discover a novel
chemical class of ARIs with potency clearly superior to
both sorbinil and zopolrestat. In a previous publication
in this journal,21 we have given a preliminary account
of a highly selective, orally potent non-carboxylic acid,
non-hydantoin inhibitor of AR that normalized elevated
levels of both sorbitol and fructose in the sciatic nerve
of chronically diabetic rats at very low doses. Herein,
we present the details of that account, including SAR
sorbitol suppression end point in diabetic rat models.
In fact, none of the inhibitors has been shown to effect
robust suppression of fructose in human tissues, for
example, sural nerve biopsy samples, in a placebo-
controlled large-scale efficacy trial. Furthermore, these
ARIs were either carboxylic acids or spirohydantoins
(broadly referred to as spiroimides). The major short-
coming of carboxylic acids is their poor tissue penetra-
tion, inherent to the conspicuous difference between
their pKas (between 3 and 4) and blood pH (∼7.4),
resulting in poor distribution from blood to the tissues,
and that of hydantoins is the phenytoin-like hypersen-
sitivity safety issue, both of which are well docu-
mented.12 In view of the clinical dose selection issue and
the dearth of new ARI chemotypes, perhaps it is not
too surprising that no inhibitor has reached the market
broadly yet. While the potential of ARIs in complications
of cardio-renal tissues has long been recognized,13,14 so
far only feeble attempts have been made in clinical
follow up. Major preoccupation on neuropathy may have
detracted attention away from investigating clinical
potential of ARIs in nephropathy and cardiac abnor-
malities. The positive effects seen in animal models with
ARIs in the kidney13 and the heart14 warrant more
focused and dedicated future follow up clinical investi-
gations.

6328 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20
Mylari et al.
Scheme 1a
a Reagents and conditions: (a) Na/MeOH, PhMe or KHCO3/Ac2O or KOt-Bu/DMF. (b) MCPBA/CH2Cl2. (c) dioxane-HCl. (d) iPO/H2O.
Scheme 2a
starting with 2-mercaptoindole. In the case of other
indoles, sulfonyl-protected derivatives (cf. 17, Y ) NSO2-
Ph) were used in the lithiation step. The SO2Ph was
freed by base hydrolysis prior to unmasking the meth-
oxy group to obtain the pyridazinones with indole side
chains.
a Reagents and conditions: (a) iPO/H2O.
Scheme 3a
Biology
Full details of the biological methods employed are
included in the Experimental Section. Primary in vitro
screening of potential inhibitors was conducted using
human recombinant AR. Coefficient of variation for the
screening assay based on 21 determinations each with
inhibitors zopolrestat, sorbinil, and compound 18m was
102%. Selectivity vs aldehyde reductase (ALR) was
determined using rat kidney ALR and a highly specific
AR inhibitor.25 Sufficiently potent in vitro AR inhibitors
were evaluated in streptozotocin-induced diabetic rats
with two protocols. The acute test (also referred to as
prevention test), a 27-h model with tid dosing, measured
the preventive ability of the inhibitors to normalize the
excess accumulation of metabolites, sorbitol as well as
fructose, in the sciatic nerve. The chronic test, employ-
ing once-a-day dosing of the inhibitor for 5 days follow-
ing 1 week of untreated diabetes, assessed the potential
of acute test active inhibitors to normalize already
elevated levels of the same metabolites in the same
tissue. The blood glucose levels in diabetic control rats
in the acute and chronic tests, respectively, were in the
range of 300-350 and 600-650 mg/dL. As a general
approach, unless an inhibitor nearly normalized either
sorbitol or fructose in the acute test, it was not pro-
gressed to the chronic test. Potent activity in the chronic
test was taken as an encouraging sign that the inhibitor
may show good pharmacokinetics in other species,
including humans. Selected inhibitors were tested for
effect on accumulation of sorbitol in lens, in both test
protocols. All in vivo inhibition responses included in
Tables1-3 were statistically significant at p e 0.05 vs
diabetic control values, except for values indicted. This
is the first full report in which nerve fructose has been
included as a critical part of the primary in vivo
screening criteria for blocking flux through the polyol
pathway, rather than merely sorbitol, as has routinely
been done until now.
a Reagents and conditions: (a) thiourea/MEK (b) NaH/DMF (c)
MCPBA/CH2Cl2 (d) dioxane-HCl.
investigations within the core family of novel sulfo-
nylpyridazinones.
Chemistry
The synthetic route for the phenyl-substituted ana-
logues is shown in Scheme 1. Benzenethiols with desired
substituents, 2, were reacted with 3-chloro-6-methoxy-
pyridazine, 1, in the presence mild or strong bases, to
obtain compound 3. Controlled or complete sulfoxidation
using MCPBA, followed by hydrolysis of the resulting
4 or 5, in the presence of aqueous HCl, gave 7 or the
target compound, 8.22 Hydrolysis of 3 under similar
conditions gave 6. Compound 8 was also prepared in
one step starting from aryl sulfinic acid salt, 11, as
shown in Scheme 2. 8j was prepared by the standard
palladium-catalyzed coupling of 4-bromophenyl sulfone,
8b, with phenylboronic acid.
Sulfonylmethyl compounds 15 were prepared starting
from the known 3-mercapto-4-methoxy pyridazine23 12
and allowed to react with benzyl halides 13 (X ) Cl,
Br), to obtain the sulfenymethyl compound 14 (Scheme
3). Peracid oxidation of 14 followed by acid hydrolysis
of the resulting 14 (n ) 2) gave the target compounds
1524 (cf. Scheme 1).
Scheme 4 depicts the method used for the preparation
of pyridazinones with a heterocyclic side chain. Lithi-
ated heterocycle prepared from deprotonation of het-
erocycles 17 with n-BuLi was added to the sulfonyl
fluoride23 16 to obtain 18, which was hydrolyzed under
acidic conditions to obtain the target compound 19.
Reversing the order of addition of the reactants signifi-
cantly improved the yield of 19. Depending on the access
to mercapto heterocycles, Scheme 1 could also be used.
For example, the parent indole 19a was prepared
Results and Discussion
High-throughput screening of internal libraries of
compounds has proved to be an expedient avenue to
search for potential new leads. However, the eventual
success in delivering potential clinical candidates with

Novel Inhibitors of Aldose Reductase
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20 6329
Scheme 4a
a Reaction conditions: (a) KHF2/Cl2(g)-MeOH/H2O. (b) n-BuLi, THF, -78 °C. (c) dioxane/HCl (concd).
satisfactory pharmaceutical properties appears to hinge,
in large part, on the initial criteria set for identification
of leads and working strategies employed for optimiza-
tion of structure-activity relationships (SAR). Our
target was low molecular weight non-carboxylic acid,
non-hydantoin structures with no readily discernible
toxic pharmacophore and with good in vitro activity vs
human r-AR at e1 µM. Our extensive library yielded
only one hit with this set of credentials, with an IC50 of
0.6 µM, except that the compound was registered in the
file with structure 10, featuring a very unattractive,
labile bis-sulfone, signaling potential chemical stability
and safety issues. It could have been easily rejected to
terminate the project, but the length of time spent on
in vitro screening justified at least a preliminary in vivo
test of the compound, against the conventional sorbitol
end point. Surprisingly, 10 showed good sorbitol inhibi-
tion activity in the sciatic nerve of diabetic rats in the
acute test. To our knowledge of the ARI literature and
in our own experience, this was the first time that a
compound with no measurable pKa, specifically on the
acidic side, showed both in vitro and in vivo activities.
It was hard to reconcile the new finding with the
repository of X-ray structures of the AR-cofactor-ARI
complexes, where every ARI is lodged deep inside the
anion well.26 A simple solubility test in aqueous sodium
hydroxide confirmed that the inhibitor was at least
weakly acidic. Acidification of the basic solution gave a
precipitate as would have been expected, and seren-
dipitously, the precipitate was sufficiently crystalline
for a single-crystal X-ray, which proved beyond a doubt
that the inhibitor was indeed 6-phenylsulfonylpyridazin-
2H-3-one, 8.22 It has low molecular weight (236) and is
weakly acidic (pKa, 7.1). In our new screening paradigm,
it normalized elevated nerve sorbitol levels by 95% and
fructose levels by 89%, albeit at a high dose of 300 mg/
kg, in the sciatic nerve of acutely diabetic rats. In
subsequent dose titration in the acute test, 8 showed
ED50s of 15 and 25 mg/kg, against sorbitol and fructose
end points, respectively. Just to trace the genesis of
structure misassignment, it is instructive to see how it
was prepared. Reaction of 3,6-dichloropyridazine gives
the corresponding bis-sulfide, which when oxidized with
peracid leads to the bis-sulfone. However this labile bis-
sulfone undergoes hydrolysis under conditions of aque-
ous workup, resulting in 8 (Scheme 1). Strong support
for this view comes from the rapid in situ hydrolysis of
the electron-withdrawing 3-Cl, following peracid oxida-
tion of 3-chloro-8-phenylsulfenylphthalazine to the ph-
thalazinone analogue 8y (see Experimental Section).
through a systematic SAR pursuit around 8. As an
expedient strategy toward the objective, the resource
demanding in vivo tests were run at a maximum dose
no higher than 20 mg/kg, with only a very few excep-
tions. A down side of this strategy was that sharper SAR
insights into the relative ranking of inhibitors that were
not sufficiently potent at 20 mg/kg could not be dis-
cerned.
Because the phthalazinone template had already been
deployed to design potent ARIs such as ponalrestat and
zopolrestat, sulfonyl phthalazinone 8y, with a 41,51
benzo substituent (see Table 1), was prepared very early
on, but it showed little AR inhibition activity. Conse-
quently, the first phase of our investigation focused on
SAR, which encompassed deletion of the SO2 linker,
replacement of the linker by CO, extension of the linker
by CH2 (i.e. SO2-CH2), and substituents on the phenyl
ring. The first two modifications, 2027 and 21,28 showed
no AR inhibition activity, even at 10 µM. Furthermore,
the methoxy sulfone 5 (n ) 2, no measurable pKa) also
showed no AR inhibition activity, even at 32 µM.
We will now discuss SAR relative to substituents on
the phenyl ring of 8 and homologues of 8 featuring the
SO2-CH2 linker. Phenyl substituents were chosen to
probe the influence of orientation, lipophilicity, electron
withdrawal, electron release, and steric bulk. In general,
compact, electron-withdrawing F and Cl substituents
that are reasonably lipophilic gave potent compounds
both in vitro and in vivo. Compounds with one Cl (8c-
e), two Cl (8k-o), and one Cl with one F (8s), especially
at the 2- and 2,4-positions, showed the most attractive
in vivo activity. Among these, 8l was the best (vide
infra). However, 8t, which features the effective 2F, 4Br
substituent pattern present in ponalrestat,29 zenar-
estat,11 and minalrestat,19 was less potent than 8l in
vivo. IC50s for this group of compounds were in the range
of 50-400 nM. Electron-releasing substituents (e.g.,
OMe and Me, 8h and 8i) and bulky groups, especially
at the 2-position (e. g., Ph, 8j), had unfavorable effect
on in vitro potency. However, unlike 8j, which could
have many degrees of rotation around the 2-phenyl
bond, rigid naphthalenes, 8w and 8x, were more potent
than 8, suggesting the scope of permissible space for
activity. Table 1 summarizes SAR in the phenylsulonyl
pyridazinone series. 6-(2,4-Dichloro-phenylsulfonyl)-2H-
pyridazin-3-one, 8l (pKa, 6.9; IC50, 190 nM), was the
most potent inhibitor in the chronic test; it was 2 times
more potent than zopolrestat in normalizing both sciatic
With a novel lead of desired profile in hand, our goal
was to seek an inhibitor at least 10 times more potent
than zopolrestat in the chronic diabetic rat model
against the targeted nerve fructose end point (ED90),

6330 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20
Mylari et al.
Table 1. In Vitro and in Vivo Data for Phenyl-Substituted
Sulfonylpyridazinones
Table 2. In Vitro and in Vivo Data for Benzyl-Substituted
Sulfonylpyridazinones
% inhibitiona
% inhibitiona
acute
test
chronic
test
acute
test
chronic
test
IC50
dose
IC50
(nM)
dose
(mg/kg)
compd
sub.
(nM)
(mg/kg)
s
f
s
f
compd
sub.
s
f
s
f
15
600
118
422
500
72
35
52
257
667
26
54
44
60
c
c
c
20
20
10
20
c
20
20
20
73
b
8
600
50
25
10
95
73
40
15
55
26f
74
49
14f
25
b
15a
15b
15c
15d
15e
15f
15g
15h
15i
15j
2-Cl
2-F
2-CF3
h
ED50
3-CF3
88
65
42
82
70
48
24d
51
65
42
8a
8b
8c
2-Br
4-Br
2-Cl
210
350
170
50
50
20
10
c
10
20
10
50
c
2, 3-Cl2
2,6-Cl2
2,3-F2
101 81
96
68
2-F, 4-Br
2-Cl, 6-F
2F, 3-Cl
2-F, 3-CF3
8d
8e
8f
3-Cl
4-Cl
2-F
240
380
540
42
74
61
45
64
56
65
91
79
81
52
56
34
b
15k
a s ) sorbitol. f ) fructose. b Not measured. c Not tested. d Not
statistically significant at p e 0.05.
8g
8h
8i
8j
8k
4-F
474
74
89
b
4-OMe
4-Med
2-Ph
2.0 µM
1.9 µM
2.2 µM
55
c
c
it is understandable why 8l, with a much higher pKa
than zopolrestat (6.9 vs 3.8), would be more effective.
We investigated the impact of increasing the length
of the linker by one methylene group, as in 15. SAR
exploration was guided by experience in the phenyl
series, but it was confounding. While several halogen-
substituted compounds were found to be more potent
in vitro than the best inhibitors in the phenyl series,
they were, by and large, less potent in vivo, and no
inhibitor more potent than 8l could be identified. While
we did not study the pharmacokinetics/metabolism
issues in this series, we surmise that metabolic oxida-
tion at the methylene carbon (common to all inhibitors)
may have been a key factor for the lack of good
correlation between in vitro and in vivo potency.
As we had not yet achieved our in vivo potency goal
(10 times zopolrestat), we explored activity-potentiating
replacements for the phenyl in 8 with selected hetero-
cycles. On the basis of previous SAR experience with
zopolrestat30a and related analogues,30b the X-ray struc-
ture information from the AR-NADPH(NADP+)-zopol-
restat ternary complex,31 and a literature example, 20
(M-16209),32 we targeted a new family of compounds of
general formula 19.
2,3-Cl2
20
10
5
ED50
20
10
30
20
98
77
55
0.8
79
65
81
b
b
b
81
g
8l
8m
2,4-Cl2
2,5-Cl2
190
73
3
67
36
b
8n
2,6-Cl2
50
75
50
b
b
10
8o
58
98
84
91
68
b
3,4-Cl2
3,5-Cl2
2,3-F2
2,4-F2
20
10
20
5
30
10
c
20
10
10
20
20
10
20
10
20
85
60
8p
8q
49 73 38
32 63 30
390
870
b
b
81
50
8r
8s
2-Cl, 4-F 280
106 97
95
81
45
67
44
95
88
87
8t
8u
8v
2-F, 4-Br 140
3-CF3
4-CF3
67
175
360
17f
24f
10f
8w
8x
2,3-benzo 150
3,4-benzo 360
55 70 43
49 60 31
74 51
The rank order of in vitro potency (IC50), at least
numerically, among the parent heterocycles was ben-
zofuran (19h) (150 nM) ∼ benzothiophene (19w) (180
nM) > benzothiazole (19z) (450 nM) > indole (19a) (590
nM). None had the desired in vivo potency, and also a
number of SAR probes around 19a did not improve the
status quo. However, on the basis of the in vitro potency
of 19h, literature data for 20, and the potential vulner-
ability of 19w for metabolic oxidation of the sulfur atom,
we decided to focus SAR around the benzofuran 19h.
We thought that we needed to increase lipophilicity for
better tissue penetration. There is very sparse knowl-
edge about the metabolism of benzofuran with an
electron-withdrawing group at the 5-position. Neverthe-
less, it appeared that the strategy of blocking the highly
electrophilic 5-position with a lipophilic Cl substituent
would be a good probe to address both issues. More
significantly, zopolrestat with a 5-CF3 on the benzothia-
sorbinil
140
4
e
e
g
zopolrestat
a s ) sorbitol. f ) fructose. b Not measured. c Not tested. d Chem.
Abstr. 1960, 5714. e See Figures 1-3 for in vivo comparative data.
f Not statistically significant at p e 0.05. g See Figures 3-5. h In
mg/kg.
nerve sorbitol (ED90, 5 vs 10 mg/kg) and fructose (ED90,
20 mg/kg vs ∼40 mg/kg) levels. Even though 8l is nearly
25-fold less potent than zopolrestat (IC50, 190 nM vs 4
nM), it is markedly more effective than zopolrestat in
suppressing lens sorbitol levels (94% vs 30% at 20 mg/
kg), suggesting that the new class of ARIs penetrate the
diabetic target tissues far more efficiently that a typical
carboxylic acid ARI (cf. Figures 3-5). Because xenobi-
otics can penetrate into the avascular lens tissue from
systemic blood only by diffusion of uncharged species,

Novel Inhibitors of Aldose Reductase
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20 6331
Table 3. In Vitro and in Vivo Data for Sulfonylpyridazinones
with Heterocyclic Side Chains
% inhibitiona
acute
test
chronic
test
IC50
dose
compd
X
Y
sub.
(nM) (mg/kg)
s
f
s
f
19a
CH NH
590
20
10
c
100 82 67 50
75 58
19b CH NH 5-Cl
19c CH NH 6-Cl
19d CH NH 7-Cl
19e
19f
19g
19h CH
19i
19j
1.1 µM
645
450
1.4 µM
c
20
c
c
c
10
10
20
10
20
10
40 44
CH NH 6-F
CH NH 5,6-OCH2O 3.8 µM
CH NH 5,7-Cl2
200
150
25
O
O
O
b
b
b
b
34
39
56
43
CH
CH
5-Cl
Figure 3. Chronic test: nerve sorbitol data.
3-Me
140
19k CH
19l CH
19m CH
19n CH
19o
O
O
O
O
O
5-OMe
5, 7-Cl2
3-Me, 5-Cl
230
87
1
49 34
32 39
f
ED50 0.2 0.8 e
3-Me, 6-Cl 190
10
10
3
40 28d
CH
3-Me, 5-F
3
84 62 100 90
66 42 86 64
47 11d 52 17d
1
ED50 1.2 5.8
1
2.4
19p CH
O
3-Me, 5-CF3
5
10
3
1
101 97 102 100
91 79 95 81
43 19d 75 54
ED50 1.3 2.0 <1
1
19q CH
O
O
O
O
O
O
S
3, 5-Me2
3-Et, 5-Cl
3-iPr,5C l
3-Ph
3-(4-F)-Ph
3-Ph, 5-Cl
13
6
10
10
10
c
21d 18d
c
19r
19s
19t
CH
CH
CH
b
b
b
b
48 24d
48 14d
92
23
49
34
180
160
55
19u CH
19v CH
19w CH
19x
19y
10
20
20
20
10
3
66 50
27d 20d
46 22d
c
c
c
c
c
c
Figure 4. Chronic test: nerve fructose data.
CH
CH
S
5-Me
3Me, 5-Cl
b
7d
S
83 51
49 29d
19z
S
N
450
c
a s ) sorbitol. f ) fructose. b Not measured. c Not tested. d Not
statistically significant at p e 0.05. e See Figures 3-5. f In mg/
kg.
Figure 2. In vitro AR inhibition dose-response.
Figure 5. Chronic test: lens sorbitol data.
zole was >20 times more potent than its 6-CF3 congener
in vitro, and it turns out that the strategically placed
5-CF3 cooperatively aided in the binding of zopolrestat
within the anion well, through powerful hydrogen-bond-
accepting fluorine atoms, two of which are in close
contact with Thr113 and Cys303 in the X-ray structure
of AR-cofactor-zopolrestat ternary complex.31 Also, a
similar strong interaction between the bromine in the
ARI 21 (IDD 594) and Thr113 has been depicted.26 So
hydrogen-bond-accepting halogens at the 5-position of
the benzofuran side chain became immediate targets.
19i (IC50, 25 nM) was found to be more potent in vitro
than 19h, but it was still not very potent in vivo, even
though it gave good serum levels when administered
orally (data not shown).
Faced with a potency impasse, it is not uncommon
for medicinal chemists to draw lessons from disparate
drug series. We noticed that whenever benzofuran had
been employed in other medicinal chemistry projects, a
3-substituent had played a remarkable role in enhanc-
ing in vivo potency. In addition to a 3-bromo substituent
in 20 (Chart 2),32 we were particularly impressed by the
role of the same substituent in the benzofuran-based

6332 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20
Mylari et al.
Chart 2
AII blocker 22 (GR-117289)33 in providing efficacy in
blood pressure lowering, in rat models.
output relative to normal rats.36 Selectivity profiling of
19m against aldehyde reductase37 and alcohol,38 fruc-
tose,39 and sorbitol dehydrogenases9b showed respec-
tively the following IC50s (nM): 930, 18 000, 25 000, and
>100 000. This selectivity profile makes CP-744,809, to
our knowledge, the most selective orally active ARI. Its
pKa, log P, and log D (pH 7.4) respectively are 6.9, 3.05,
and 2.46. A higher log D/log P value of 0.81, for 19m, is
in stark contrast with the value of 0.16, for zopolrestat,30a
and is consistent with more effective penetration of 19m
into the lens tissue. It is very well absorbed in rats, with
oral bioavailability of 98% (plasma Cmax, 9 ( 3 µg/mL
at 2 mg/kg, po), and shows a favorable plasma t1/2 (26
( 3 h). These desirable physicochemical and pharma-
cokinetic properties of 19m, taken together with its
stability toward P450 enzymes and excellent Caco-2
transcellular permeability (>10-5 cm/s), bode well for
potential once-a-day dosing in the clinic.
So we appended a 3-substituent to the best benzofu-
ran in hand, 19i. We preferred to incorporate a methyl
group, rather than an additional halogen atom, leading
to 19m, which is one of the most potent ARIs yet
described in the literature. Before we return to the
detailed laboratory profile of 19m, we turn our attention
to additional SAR around 19m. Replacing the 5-Cl in
19m by F or CF3 led to inhibitors 19o or 19p, respec-
tively, which retained a significant portion of the in vitro
and in vivo potencies of 19m, but neither was quite
equal to 19m, although 19p was closer to 19m. On the
other hand, the 5-Me congener 19q was considerably
less potent than 19m, 19o, or 19p in vivo. As speculated
above, the 6-Cl analogue 19n was markedly less potent
than 19m (IC50, 0.8 nM vs 190 nM), suggesting perhaps
a nonoptimum orientation for the 6-Cl to interact with
a hydrogen-bond-accepting residue in the AR. Again, it
is interesting to note that, even in the zopolrestat series,
the 6-Cl congener was less potent (10 times) than the
5-Cl congener. The progressively more lipophilic 3-sub-
stituted compounds 19r-v were all less potent than
19m. Among these, the least lipophilic, 19r, was the
most potent. The observed in vivo potency difference
between 19p and 19r with nearly the same IC50s is
rather difficult to explain, except to invoke facile bio-
hydroxylation of the ethyl group, leading to greater
clearance and/or decreased sciatic nerve penetration.
The first possibility has support from the experimentally
measured lower activation energy for P450 oxidation of
ethyl benzene over toluene and the reported lower CYP2
Km for ethyl benzene vs toluene.34,35 The early choice of
focusing SAR on the benzofuran template is borne out
by a comparison of benzothiophene 19y with 19m. Even
though 19y has the same substitution pattern as in
19m, it is ∼50-fold less potent than 19m in vitro.
The best inhibitor, 19m (CP-744809), was selected for
further laboratory characterization. Its IC50 vs r-human
AR is 1 nM (n ) 168, Figure 2). For its low molecular
weight (324), it is the most potent AR inhibitor in vitro.
In a side-by-side evaluation, its ED90 for normalization
of fructose in the chronic test (Figure 4) is lower than
that of zopolrestat (13 times) and of sorbinil (3 times).
The dose-response of 19m for inhibition of sorbitol
(Figure 3) and fructose reiterates the greater sensitivity
for sorbitol over fructose and should raise caution in
targeting just sorbitol as a robust marker of flux through
the polyol pathway. Inhibitor 19m, in contrast to
zopolrestat, shows remarkable potency in suppressing
sorbitol in lens (Figure 5). In fact, it is the most potent
inhibitor in lens relative to comparators, including
sorbinil, the previous best in our hands. Recently, it has
been reported that 19m shows positive effects in the
diabetic kidney. In a diabetic rat model, it shows a near
normalization of elevated (2.5-fold) urinary albumin
Conclusion
High-throughput screening of internal libraries of
compounds targeted toward a structurally distinct non-
hydantoin, non-carboxylic acid ARI, with potential to
robustly block the flux through the polyol pathway,
yielded a weak inhibitor, 8. Nearly complete normaliza-
tion of elevated fructose (rather than just sorbitol) levels
(ED90) in the sciatic nerve of rats with established
diabetes was used as the primary biochemical marker
for effective blockade of flux. A systematic SAR pursuit
around 8, with initial focus on the phenyl ring substitu-
tion, yielded 8l, which was 2 times more potent than
zopolrestat in the chronic test against the fructose end
point. Spurred by this significant finding and applying
lessons learned from literature on extant ARIs, espe-
cially zopolrestat, and monitoring the profile of newly
prepared analogues for lipophilicity (both log P and D),
movement across Caco-2 cell monolayer via transcellu-
lar mechanism, and pharmacokinetics in rats led to the
title compound 6-(5-chloro-3-methylbenzofuran-2-sulfo-
nyl)-2H-pyridazin-3-one, 19m. It is a novel, highly
selective ARI with unprecedented in vitro potency (1
nM, n ) 168) and remarkable potency in the sciatic
nerve, as well as in the lens of chronically diabetic rats,
in normalizing polyol metabolites. It is reported to show
positive effects in a diabetic rat model of proteinuria,
and it is well absorbed in diabetic rats with sustained
plasma t1/2 of 26 ( 3 h.
Experimental Section
All target compounds gave elemental analyses data for C,
H, and N in compliance with the commonly acceptable range
(see Supporting Information). All reactions were carried out
1
using commercial grade reagents and solvents. The H NMR
spectra were recorded on a Varian Unity Inova 400 MHz
spectrometer at 400 MHz with chemical shifts (δ) reported in
ppm downfield relative to tetramethylsilane internal standard.

Novel Inhibitors of Aldose Reductase
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20 6333
Anhydrous Na2SO4 was used as the drying agent. Chemical
J ) 8 Hz, 1H), 7.81 (d, J ) 9 Hz, 1H), 8.0 (dd, J ) 8 Hz, 2 Hz,
1H), 8.06(d, J ) 9 Hz, 1H), 8.20 (d, J ) 2 Hz, 1H), 13.89 (b,
1H).
6-(2,6-Dichlorobenzenesulfonyl)-2H-pyridazin-3-one
(8n) (81%): mp 219-220 °C; 1H NMR, DMSO-d6, δ 7.15 (d, J
) 10 Hz, 1H), 7.74 (m, 3H), 8.0 (d, J ) 10 Hz, 1H), 13.80 (b,
1H).
abbreviations: MCPBA ) m-chloroperoxybenzoic acid.
6-(3-Chlorobenzenesulfonyl)-2H-pyridazin-3-one (8d).
Step 1. Sodium metal (218 mg, 9.5 mmol) was dissolved in
MeOH (10 mL). 3-Chlorothiophenol (1.12 g, 7.7 mmol) was
added and the mixture stirred for 1 h at room temperature.
The excess MeOH was evaporated and to the dry residue were
added toluene (20 mL) and 3-chloro-6-methoxypyridazine (1.1
g, 7.7 mmol). The reaction mixture was refluxed for 4 h, cooled
to room temperature, and then poured into H2O (30 mL). The
pH of the solution was first adjusted to 10 with 20% KOH and
extracted with EtOAc. The aqueous layer from the extraction
was collected. The aqueous portion was acidified to pH 3 with
concentrated HCl acid and then extracted with EtOAc. The
EtOAc extract was evaporated and the residue was purified
by silica gel chromatography to afford 3-(3-chloro-phenylsul-
fanyl)-6-methoxypyridazine.
Step 2. A mixture of 3-(3-chlorophenylsulfanyl)-6-methoxy-
pyridazine (529 mg, 1.5 mmol), MCPBA (760 mg, 4.4 mmol),
and CHCl3 (20 mL) was prepared and stirred at room tem-
perature for 2 h. The reaction mixture was diluted with 5%
sodium thiosulfate (20 mL) followed by H2O (30 mL). The
CHCl3 layer was collected, dried, and filtered, and the dried
CHCl3 portion was evaporated to dryness. The resulting solid
residue was purified by silica gel chromatography (3:1 hexane/
EtOAc as eluent) to obtain 3-(3-chloro-benzenesulfonyl)-6-
methoxypyridazine (29%, 173 mg).
6-(3,4-Dichlorobenzenesulfonyl)-2H-pyridazin-3-one
1
(8o) (55%): mp166-168 °C; H NMR, DMSO-d6, δ 7.09 (d, J
) 9 Hz, 1H), 7.74 (m, 2H), 8.0 (d, J ) 9 Hz, 1H), 8.21 (d, J )
2 Hz, 1H), 13.87 (s, 1H).
6-(3,5-Dichlorobenzenesulfonyl)-2H-pyridazin-3-one
(8p) (42%): mp 231-232 °C; 1H NMR, DMSO-d6, δ 7.01 (d, J
) 9 Hz, 1H), 7.80 (d, J ) 9 Hz, 1H), 7.89 (s, 1H), 8.35 (s, 2H),
13.76 (b, 1H).
6-(2,3-Difluorobenzenesulfonyl)-2H-pyridazin-3-one (8q)
(%): mp >225 °C; 1H NMR, DMSO-d6, δ 7.08 (d, J ) 9 Hz,
1H), 7.60 (d, J ) 8 Hz, 1H), 7.87 (d, J ) 8 Hz, 1H), 8.07 (d, J
) 9 Hz, 1H), 8.33 (m, 1H), 13.85 (s, 1H).
6-(2,4-Difluorobenzenesulfonyl)-2H-pyridazin-3-one (8r)
1
(41%): mp 186-188 °C; H NMR, DMSO-d6, δ 7.09 (d, J ) 8
Hz, 1H), 7.72 (d, J ) 8 Hz, 1H), 7.93 (m, 3H), 13.84 (s, 1H).
6-(2-Chloro-4-fluorobenzenesulfonyl)-2H-pyridazin-3-
1
one (8s) (74%): mp 205-208 °C; H NMR, DMSO-d6, δ 7.13
(d, J ) 9 Hz, 1H), 7.60 (dd, J ) 8 Hz, 2 Hz, 1H), 7.87 (dd, J )
8 Hz, 2 Hz, 1H), 8.02 (d, J ) 9 Hz, 1H), 8.33 (m, 1H), 13.82 (s,
1H).
Step 3. A mixture of 3-(3-chlorobenzenesulfonyl)-6-meth-
oxypyridazine (148 mg, 0.52 mmol), dioxane (2 mL), and
concentrated HCl (0.5 mL) was prepared and refluxed for 30
min. The reaction mixture was then evaporated to dryness and
the residue was extracted with EtOAc. The EtOAc mixture
was collected, dried, and filtered, and the filtrate was evapo-
rated to dryness to afford 8d as white solid (38%, 61 mg): mp
222-223 °C; 1H NMR, DMSO-d6, δ 7.11 (d, J ) 8 Hz, 1H),
7.74 (s, 1H), 7.86-8.04 (m, 4H), 13.86(s, 1H). The following
examples were prepared from the appropriate starting materi-
als in a manner analogous to the method of example 8d.
6-(4-Trifluoromethylbenzenesulfonyl)-2H-pyridazin-3-
one (8v) (47%): mp 214-222 °C; 1H NMR, DMSO-d6, 7.02
(d, J ) 11 Hz, 1H), 7.55-7.65 (m, 4H), 7.75 (m, 1H), 13.90 (s,
1H).
6-(r-Naphthylmethylbenzenesulfonyl)-2H-pyridazin-
3-one (8w) (16%): mp 225-226 °C; 1H NMR, DMSO-d6, δ 7.05
(d, J ) 9 Hz, 1H), 7.67-7.84 (m, 3H), 8.02 (d, J ) 9 Hz, 1H),
8.17 (dd, J ) 8 Hz, 1H), 8.40-8.51 (m, 3H), 13.76 (s, 1H).
6-(â-Naphthylmethylbenzenesulfonyl)-2H-pyridazin-
1
3-one (8x) (49%): mp 232-233 °C; H NMR, DMSO-d6, δ δ
7.01 (d, J ) 9 Hz, 1H), 7.80 (d, J ) 9 Hz, 1H), 7.89 (s, 1H),
6-(2-Bromobenzenesulfonyl)-2H-pyridazin-3-one (8a)
8.35 (s, 2H), 13.76 (s, 1H).
1
(38%): mp 210-213 °C; H NMR, DMSO-d6, δ 7.15 (d, J ) 8
6-(2-Fluorobenzenesulfonyl)-2H-pyridazin-3-one (8f).
Step 1. To a clear solution of 4-fluorothiophenol (20 mmol,
2.58 g) and t-BuOK (2.24 20 mmol) in DMF (10 mL) was added
3-chloro-6-methoxypyridazine (20 mmol, 2.85 g) and the
mixture stirred at room temperature for 1 h. The reaction
mixture was quenched with H2O (30 mL) and extracted with
EtOAc (50 mL). The EtOAc layer was collected and washed
with H2O, and the organic portion was collected, dried, and
filtered, and the filtrate was evaporated to obtain crude 3-(2-
fluorophenylsulfanyl)-6-methoxy-pyridazine (85%): mp 58-
62 °C.
Hz, 1H), 7.72 (m. 2H), 7.91 (m, 1H), 8.04 (d, J ) 8 Hz, 1H),
8.79 (m, 1H), 13.80 (s, 1H).
6-(4-Bromobenzenesulfonyl)-2H-pyridazin-3-one (8b)
(21%): mp >200 °C: 1H NMR DMSO-d6, δ 7.08 (d, J ) 9 Hz,
1H), 7.77 (d, J ) 9 Hz, 2H), 7.98 (m, 2H), 7.98 (m, 1H), 13.82
(s, 1H).
6-(2-Chlorobenzenesulfonyl)-2H-pyridazin-3-one 8c
(28%): mp 222 °C; 1H NMR (DMSO, 300 MHz) δ 7.25 (d, J )
8 Hz, 1H), 7.72 (m. 2H), 7.91 (m, 1H), 8.04 (d, J ) 8 Hz, 1H),
8.91 (m, 1H), 13.80 (s, 1H).
6-(4-Chlorobenzenesulfonyl)-2H-pyridazin-3-one (8e)
(35%): mp >220 °C: 1H NMR, DMSO-d6, δ 7.08 (d, J ) 9 Hz,
1H), 7.77 (d, J ) 9 Hz, 2H), 7.98 (m, 2H), 7.98 (m, 1H), 13.82
(s, 1H).
6-(4-Fluorobenzenesulfonyl)-2H-pyridazin-3-one (8g)
(37%): mp >225 °C; 1H NMR, DMSO-d6, δ 7.08 (d, J ) 9 Hz,
1H), 7.77 (d, J ) 9 Hz, 2H), 7.98 (m, 2H), 7.98 (m, 1H), 13.82
(s, 1H).
6-(4-Methoxybenzenesulfonyl)-2H-pyridazin-3-one (8h)
(45%): mp 111-113 °C; 1H NMR, DMSO-d6, δ 3.87 (s. 3H),
7.06 (d, J ) 9 Hz, 1H), 7.20 (d, J ) 8 Hz, 1H), 7.90 (d, J ) 8
Hz, 1H), 7.95 (d, J ) 9 Hz, 1H), 13.71 (b, 1H).
Step 2. A mixture of 3-(2-fluorophenylsulfanyl)-6-methoxy-
pyridazine (500 mg, 1.9 mmol), MCPBA (1.04 g, 7.3 mmol),
and CH2Cl2 (10 mL) was prepared and stirred at room
temperature for 2 h. The reaction mixture was diluted with
CH2Cl2 and the CH2Cl2 layer was washed with saturated
sodium bicarbonate (10 mL) and then with H2O. The CH2Cl2
layer was collected, dried, and filtered, and the filtrate was
evaporated to dryness. The residue was purified by silica gel
chromatography (3:1 EtOAc/hexane as eluent) to obtain 3-(2-
fluorobenzenesulfonyl)-6-methoxypyridazine as a white solid
(51%): 1H NMR, DMSO-d6, δ 4.19 (s, 3H), 7.13 (d, J ) 8 Hz,
1H), 7.21 (d, J ) 8 Hz, 1H), 8.13 (m, 4H).
Step 3. A mixture of 3-(2-fluorobenzenesulfonyl)-6-meth-
oxypyridazine (200 mg, 0.84 mmol) and concentrated HCl (2
mL) was prepared and refluxed for 1h. The reaction mixture
was cooled and diluted with H2O (20 mL). Sufficient 40%
aqueous NaOH was then added to adjust the pH of the mixture
to 3 and the mixture was extracted with EtOAc. The EtOAc
extracts were collected, combined, dried, and filtered. The
filtrate was evaporated to obtain 8f as a white solid (80 mg,
45%): mp 189-191 °C; 1H NMR, DMSO-d6, 7.06 (d, J ) 8 Hz,
1H), 7.23 (m, 1H), 7.3 (m, 1H), 7.89 (d, J ) 8 Hz,1H), 8.02 (m,
2H) and 13.82 (s, 1H).
6-(2,3-Dichlorobenzenesulfonyl)-2H-pyridazin-3-one
(8k) (76%): 224-225 °C; 1H NMR, DMSO-d6, δ 7.13 (d, J ) 9
Hz, 1H), 7.60 (dd, J ) 2 Hz, 8 Hz, 1H), 7.87 (dd, J ) 2 Hz, 8
Hz, 1H), 8.02 (d, J ) 9 Hz, 1H), 8.33 (m, 1H), 13.86 (s, 1H).
6-(2,4-Dichlorobenzenesulfonyl)-2H-pyridazin-3-one (8l)
1
(87%): mp 202-203 °C; H NMR, DMSO-d6, δ 7.15 (d, J ) 9
Hz, 1H), 7.81 (dd, J ) 8 Hz, 1 Hz, 1H), 8.03 (m, 2 H), 8.25 (d,
J ) 9 Hz, 1H), 13.88 (b, 1H).
6-(2,5-Dichlorobenzenesulfonyl)-2H-pyridazin-3-one
(8m) (72%): mp 229-232 °C: 1H NMR, DMSO-d6, δ 7.15 (d,

6334 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20
Mylari et al.
6-(Biphenylyl-2-sulfonyl)-2H-pyridazin-3-one (8j). Step
1. 6-(Biphenylyl-2-sulfonyl)-6-methoxypyridazine. A mix-
ture of benzene-2-boronic acid (157 mg, 1.2 mmol), 6-(4-
bromobenzenesulfonyl)-6-methoxypyridizine (247 mg, 0.8 mmol),
K2CO3 (207 mg), Pd[P(Ph)3]4 (87 mg), toluene (4 mL), EtOH
(2 mL), and H2O (1.5 mL) was prepared and refluxed for 4 h.
The mixture was cooled and H2O was added (10 mL). The
mixture was then filtered, and the resulting filtrate was
extracted with EtOAc (20 mL). The EtOAc extract was washed
with H2O and the EtOAc portion was collected, dried, and
filtered. The filtrate was collected and evaporated to dryness
to afford the title product of step 1.
Step 2. The product of step 1 was treated with concentrated
HCl according to step 3 of example 8d to obtain the title
compound (40%): mp 207-208 °C; 1H NMR, DMSO-d6, δ 7.25
(d, J ) 9 Hz, 1H), 7.05 (m, 4H), 7.27-7.41 (b, 5H), 8.28 (d, J
) 9 Hz, 1H), 13.57 (s, 1H).
6-(4-Bromo-2-fluorobenzenesulfonyl)-2H-pyridazin-3-
one (8t). Step 1. A mixture of 2-fluoro-4-bromothiophenol (300
mg, 1.6 mmol), 3,6-dichloro-pyridazine (149 mg, 1.0 mmol), K2-
CO3 (400 mg), and acetone (6 mL) was prepared and refluxed
for 2 h. The acetone from the mixture was evaporated and the
resulting residue was dissolved in a solution of methanol (3
mL) and sodium metal (166 mg, 7.2 mmol). The resulting
solution was refluxed for 1 h. Evaporation of methanol afforded
3-(4-bromo-2-fluorophenylsulfanyl)-6-methoxypyridazine, which
was not isolated but was immediately used in step 2.
Step 2. The product of step 1 (400 mg, 1.3 mmol) was
dissolved in CHCl3 (10 mL), and MCPBA (770 mg, 4.5 mmol)
was added to the resulting solution. The reaction mixture was
stirred overnight at room temperature. The solvent was
evaporated and the resulting residue was purified by silica
gel chromatography (90% hexane/10% EtOAc as eluent) to
obtain 3-(4-bromo-2-fluorobenzenesulfonyl)-6-methoxypyridazine
(60%).
1H), 8.08 (m, 3H), 8.34 (d. J ) 8 Hz, 1H0, 8.52 (d, J ) 8 Hz,
1H0, 13.31 (s, 1H).
The following, 15a-k, were prepared according to the
method of Kukolja et al.24 using the requisite benzyl ha-
lides.
6-(2-Cl-phenylmethanesulfonyl)-2H-pyridazin-3-one
(15a) (63%): mp 175-176 °C; 1H NMR, DMSO-d6, δ 4.98 (s,
2H), 7.03 (d, J ) 9.9 Hz, 1H), 7.61-7.65 (m, 4H), 7.75 (m, 1H),
13.89 (s, 1H).
6-(2-F-phenylmethanesulfonyl)-2H-pyridazin-3-one
1
(15b) (72%): mp 181-182 °C; H NMR, DMSO-d6, δ 4.94 (s,
2H), 7.08 (d, J ) 9.9 Hz, 1H), 7.25-7.43 (m, 2H), 7.46-7.54
(m, 2H), 7.75 (d, J ) 9.9 Hz, 1H), 13.82 (s, 1H).
6-(2-CF3-phenylmethanesulfonyl)-2H-pyridazin-3-
one (15c) (54%): mp 190-191 °C; 1H NMR, DMSO-d6, δ 4.99
(s, 2H), 7.03 (d, J ) 9.9 Hz, 1H), 7.55-7.65 (m, 4H), 7.75 (m,
1H), 13.89 (s, 1H).
6-(3-CF3-phenylmethanesulfonyl-2H-pyridazin-3-one
1
(15d), (64%): mp 227-228 °C; H NMR, DMSO-d6, δ 4.92(s,
2H), 7.02 (d, J ) 10 Hz, 1H), 7.42 (m, 2H), 7.48-7.59 (m, 2H),
7.75 (d, J ) 10 Hz, 1H), 13.89 (s, 1H).
6-(2,3-Cl2-phenylmethanesulfonyl)-2H-pyridazin-3-
one (15e) (72%): mp >230 °C; 1H NMR, DMSO-d6, δ 5.01 (s,
2H), 7.01 (d, J ) 9.9 Hz, 1H), 7.42-7.47 (m, 2H), 7.62-7.71
(m, 1H), 7.78 (d, J ) 9.9 Hz, 1H), 13.83 (s, 1H).
6-(2,6-Cl2-phenylmethanesulfonyl)-2H-pyridazin-3-
one (15f) (76%): 1H NMR, DMSO-d6, δ 4.99 (s, 2H), 7.03 (d,
J ) 9.9 Hz, 1H), 7.62-7.71 (m, 3H), 7.78 (d, J ) 9.9 Hz, 1H),
13.89 (s, 1H).
6-(2,3-F2-phenylmethanesulfonyl)-2H-pyridazin-3-
one (15g) (47%): 1H NMR, DMSO-d6, δ 4.94 (s, 2H), 7.01 (d,
J ) 10 Hz, 1H), 7.42 (m, 1H), 7.44-7.54 (m, 2H), 7.72 (d, J )
10 Hz, 1H), 13.84 (s, 1H).
6-(2F,4Br-phenylmethanesulfonyl)-2H-pyridazin-3-
one (15h) (53%): 1H NMR, DMSO-d6, δ 4.98 (s, 2H), 7.03 (d,
J ) 9.9 Hz, 1H), H), 7.38 (m, 1H), 7.62-7.71 (m, 2H), 7.78 (d,
J ) 9.9 Hz, 1H).
Step 3. A mixture of 3-(4-bromo-2-fluorobenzenesulfonyl)-
6-methoxypyridazine (260 mg), dioxane (5 mL), and concen-
trated HCl (1 mL) was prepared and refluxed for 2 h. The
reaction mixture was then evaporated to dryness. The result-
ing residue was triturated with H2O and the precipitated solid
was collected and air-dried to obtain the title compound
(90%): mp >220 °C; 1H NMR, DMSO-d6, δ 7.05 (d, J ) 8 Hz,
1H), 7.7 (d, J ) 8 Hz, 1H), 7.9 (m, 3H), 13.8 (s, 1H).
6-(2Cl,6F-phenylmethanesulfonyl)-2H-pyridazin-3-
1
one (15i) (68%): mp >230 °C; H NMR, DMSO-d6, δ 4.99 (s,
2H), 7.03 (d, J ) 9.9 Hz, 1H), 7.42 (m, 1H), 7.62-7.71 (m, 2H),
7.78 (d, J ) 9.9 Hz, 1H), 13.89 (s, 1H).
6-(2F,3-Cl-phenylmethanesulfonyl)-2H-pyridazin-3-
one (15j) (49%): 1H NMR, DMSO-d6, δ 4.99 (s, 2H), 7.03 (d,
J ) 9.9 Hz, 1H), 7.62-7.71 (m, 3H), 7.78 (d, J ) 9.9 Hz, 1H),
13.89 (s, 1H).
6-(2F,3-CF3-phenylmethanesulfonyl)-2H-pyridazin-3-
one (15k) (47%): mp 188-191 °C; 1H NMR, DMSO-d6, δ 4.99
(s, 2H), 7.03 (d, J ) 9.9 Hz, 1H), 7.62-7.71 (m, 3H), 7.78 (d, J
) 9.9 Hz, 1H), 13.89 (s, 1H).
6-(Indole-2-sulfonyl)-2H-pyridazin-3-one (19a). Method
1. Step 1. To a solution of 2-mercaptoindole (6.7 mmol, 1.0 g)
in acetone (20 mL) was added 3-chloro-6-methoxypyridazine
(144 mmol, 1.52 g) and K2CO3 (70 mmol, 0.98 g), and the
mixture was refluxed for 2 h. Excess acetone was removed and
the residue was partitioned between CHCl3 and H2O. The
CHCl3 layer was collected, dried, and filtered, and the filtrate
was evaporated to a residue, which was purified by silica gel
chromatography (eluent, hexanes-EtOAc/4:1) to obtain 6-(in-
dole-2-sulfenyl)-3-methoxypyridazine (31%, 534 mg).
Step 2. To a solution of 6-(indole-2-sulfenyl)-3-methoxypy-
ridazine (1.9 mmol, 488 mg) in CHCl3 (20 mL) was added
MCPBA (4.1 mmol, 1.0 g), and the reaction stirred overnight
at room temperature. The reaction was filtered and the filtrate
was washed with saturated sodium bicarbonate solution (20
mL) and H2O (20 mL). The CHCl3 layer was collected, filtered,
and dried and the filtrate was evaporated to a residue, which
was purified by silica gel chromatography (eluent, hexanes-
EtOAc/3:1) to obtain the desired product, 6-(indole-2-sulfonyl)-
3-methoxypyridazine (33%, 180 mg).
6-(3-Trifluoromethylbenzenesulfonyl)-2H-pyridazin-3-
one (8u). A mixture of 3,6-dichloropyridazine (30 mmol, 4.4
g), 3-trifluoromethylphenylsulfinic acid sodium salt (30 mmol,
6.9 g), 2-propanol (30 mL), and H2O (1 mL) was prepared and
refluxed for 18 h. The reaction mixture was then cooled and
diluted with H2O (100 mL), and the precipitated solid was
collected. The solid was triturated with n-propanol and the
solid was collected to obtain the title compound (25%): mp
1
>230 °C; H NMR, DMSO-d6, δ 7.10 (d, J ) 11 Hz, 1H), 8.01
(d, J ) 11 Hz, 1H), 8.10 (d, J ) 8 Hz, 2H), 8.21 (d, J ) 8 Hz,
2H), 13.90 (s, 1H).
8-Phenylsulfonylphthalazin-2H-3-one (8y). Step 1. To
a solution of sodium metal (15 mmol, 0.345 g) in MeOH (10
mL) was added thiophenol (12.5 mmol, 1.38 g, 1.3 mL) and
stirred for 30 min. The solution was evaporated to dryness
and to the solid residue was added toluene (20 mL), followed
by 1,4-dichlorophthalazine (10.0 mmol, 1.99 g), and the
mixture refluxed for 1.5 h. Excess toluene was evaporated and
the residue was chromatographed over silica gel. Elution with
hexane/EtOAc (1:1) and evaporation of solvents gave 3-chloro-
8-phenylsulfenylphthalazine (23%, 590 mg): mp 173-177 °C.
This was used in step 2.
Step 2. A mixture of 3-chloro-8-phenylsulfenylphthalazine
(2.32 mmol), MCPBA (4.1 mmol, 1.07 g), and CHCl3 (30 mL)
was stirred at room temperature for 3 h. The reaction mixture
was diluted with CHCl3 and washed with saturated aqueous
Na2CO3, the organic portion was dried and evaporated to
dryness, and the residue was crystallized from IPO to obtain
Step 3. A mixture of 6-(indole-2-sulfonyl)-3-methoxypy-
ridazine (0.58 mmol, 290 mg), concentrated HCl (0.5 mL), and
dioxane (3 mL) was heated at 100 °C for 2 h. The reaction
was cooled and evaporated to dryness. H2O (10 mL) was added
to the residue, and the resulting solid, 6-(indole-2-sulfonyl)-
1
8y (47%, 310 mg): mp > 225 °C; H NMR, DMSO-d6, δ 7.72
(d, J ) 8 Hz, 2H), 7.81 (d, J ) 8 Hz, 1H), 8.00 (d, J ) 8 Hz,

Novel Inhibitors of Aldose Reductase
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20 6335
2H-pyridazin-3-one (19a), was collected (83%, 133 mg): mp
248-249 °C; 1H NMR, DMSO-d6, δ 7.3 (d, J ) 8 Hz, 1H), 7.40
(m, 1H), 7.60 (m, 2H), 7.80 (m, 2H), 8.0 (d, J ) 8 Hz, 1H),
13.84 (s, 1H).
to it was added n-BuLi (2.5 M in hexane, 1.47 mmol, 0.6 mL)
dropwise. The reaction was stirred for 30 min and 3-fluoro-
sulfonyl-6-methoxypyridazine (1.34 mmol, 257 mg) was added
to it. The reaction was allowed to come to room temperature
overnight and was diluted with EtOAc (20 mL) and H2O (10
mL). The organic portion was collected, dried, and filtered, and
the filtrate was evaporated to dryness to obtain a brown oil,
6-(3-methylbenzofuran-2-sulfonyl)-3-methoxypyridazine (52%,
212 mg).
Step 2. A mixture of 6-(3-methylbenzofuran-2-sulfonyl)-3-
methoxypyridazine (0.73 mmol, 212 mg), concentrated HCl (2
mL), and dioxane (3 mL) was heated at 100 °C for 2 h. The
reaction was cooled and evaporated to dryness to obtain a
crude product, which was purified by silica gel chromatography
(eluent, EtOAc-hexanes, 1:1), to obtain 6-(3-methylbenzofu-
ran-2-sulfonyl)-2H-pyridazin-3-one (31%, 65 mg): mp 182-
183 °C; 1H NMR, DMSO-d6, δ 2.6 (s, 3H), 7.1 (d, J ) 8 Hz,
1H), 7.4 (m, 1H), 7.55(m, 2H), 7.75 (m, 1H), 8.0 (d, J ) 8 Hz,
1H), 13.86 (s, 1H).
6-(5-Chloro-3-methylbenzofuran-2-sulfonyl)-2H-py-
ridazin-3-one (19m). Method 1. Step 1. n-Butyllithium (2.5
M in hexane, 0.09 mol, 33 mL) was added dropwise over 15
min to a solution of 5-chloro-3-methylbenzofuran41 (0.09 mol,
15g) in THF (160 mL), cooled to -78 °C. To this was added
sulfur powder (0.09 mol, 2.7 g) and the mixture stirred for 10
min. The reaction was allowed to come to room temperature
and then quenched with Et2O (200 mL) and H2O (500 mL).
Sufficient 10% HCl was added to adjust the pH to 7. The ether
layer was collected, dried, and filtered, and the filtrate was
evaporated to dryness to obtain a pale yellow solid, 5-chloro-
2-mercapto-3-methylbenzofuran (90%, 15.1 g).
Step 2. To a solution containing 5-chloro-2-mercapto-3-
methylbenzofuran (10 mmol, 1.98 g) and 3-chloro-6-methoxy
pyridazine (10 mmol, 1.44 g) in DMF (10 mL) was added K2-
CO3 (20 mmol, 2.76 g), and the reaction was stirred at room
temperature for 3 h. The reaction was quenched with H2O (200
mL), the precipitated yellow solid was collected, and the solid
was purified by silica gel chromatography (eluent, hexanes-
EtOAc, 9:1) to obtain 6-(5-chloro-3-methylbenzofuran-2-sulfe-
nyl)-3-methoxypyridazine (93%, 2.87 g): mp 131-134 °C.
Step 3. A mixture of 6-(5-chloro-3-methylbenzofuran-2-
sulfenyl)-3-methoxypyridazine (1.6 mmol, 500 mg), concen-
trated HCl (1 mL), and dioxane (5 mL) was heated at 100 °C
for 2 h. The reaction was cooled and evaporated to dryness.
H2O (10 mL) was added to the residue, and the resulting white
precipitate was collected and crystallized from EtOH to obtain
the desired product, 6-(5-chloro-3-methylbenzofuran-2-sulfe-
nyl)-2H-pyridazin-3-one (73%, 113 mg).
Step 4. To a mixture of 6-(5-chloro-3-methylbenzofuran-2-
sulfenyl)-2H-pyridazin-3-one and AcOH (30 mL) was added
peracetic acid (33 mmol, 7.8 mL). The reaction was allowed to
stir overnight and the precipitated solid was collected and
washed with H2O. The solid was air-died and crystallized from
MeOH to give 6-(5-chloro-3-methylbenzofuran-2-sulfonyl)-2H-
pyridazin-3-one, (37%, 1.81 g): mp 247-248 °C; 1H NMR,
DMSO-d6, δ 2.6 (s, 3H), 7.1 (d, J ) 8 Hz, 1H), 7.55 (m, 2H),
7.8 (s, 1H), 8.0 (d, J ) 8 Hz, 1H), 13.84 (s, 1H).
6-(5-Chloro-3-methylbenzofuran-2-sulfonyl)-2H-py-
ridazin-3-one (19m). Method 2. Step 1. n-BuLi (2.5 M in
hexane, 1.2 mmol, 0.48 mL) was added dropwise over 15 min
to a solution of 5-chloro-3-methylbenzofuran (1.92 mmol, 320
mg) in THF (6 mL) cooled to -78 °C. To this was added
3-fluorosulfonyl-6-methoxypyridazine (1.92 mmol, 369 mg) and
the mixture stirred for 30 min. The reaction was allowed to
come to room temperature overnight and then quenched with
EtOAc (20 mL) and H2O (10 mL). The organic portion was
collected, dried, and filtered, and the filtrate was evaporated
to dryness to obtain a crude product, which was purified by
silica gel chromatography (eluent, hexanes-EtOAc, 3:2) to
obtain 6-(5-chloro-3-methylbenzofuran-2-sulfonyl)-3-methoxy-
pyridazine (22%, 166 mg).
6-(Indole-2-sulfonyl)-2H-pyridazin-3-one (19a). Method
2. Step 1. t-BuLi (2.5 M in hexane, 6.5 mmol, 4.3 mL) was
added dropwise over 15 min to a solution of N-sulfonylphenyl
indole (2.88 mmol, 520 mg) in THF (8 mL) cooled to -78 °C.
To this was added 3-fluorosulfonyl-6-methoxypyridazine (5.2
mmol, 1.0 g) and stirred for 30 min. The reaction was allowed
to come to room temperature overnight and then quenched
with EtOAc (20 mL) and H2O (10 mL). The organic portion
was collected, dried, and filtered, and the filtrate was evapo-
rated to dryness to obtain a crude product, which was purified
by silica gel chromatography (eluent, hexanes-EtOAc, 7:1) to
obtain 3-methoxy-6-(N-phenylsulfonyliindole-2-sulfonyl)py-
ridazine (39%, 867 mg).
Step 2. To a solution of sodium metal (18.6 mmol, 428 mg)
dissolved in MeOH (8 mL) was added a solution of 3-methoxy-
6-(N-phenylsulfonyliindole-2-sulfonyl)pyridazine (1.86 mmol,
850 mg) and the reaction was stirred for 10 min. The reaction
was quenched with H2O (10 mL) and CHCl3 (25 mL). The
CHCl3 layer was collected, dried, and filtered, and the filtrate
was evaporated to obtain 6-(indole-2-sulfonyl)-3-methoxypy-
ridazine (82%, 440 mg).
Step 3. A mixture of 6-(indole-2-sulfonyl)-3-methoxypy-
ridazine (1.03 mmol, 300 mg), concentrated HCl (1 mL), and
dioxane (6 mL) was heated at 100 °C for 2 h. The reaction
was cooled and evaporated to dryness. H2O (10 mL) was added
to the residue, and the resulting solid was triturated with
MeOH (2 mL) to yield 6-(indole-2-sulfonyl)-2H-pyridazin-3-one,
19a (37%).
6-(5-Chloroindole-2-sulfonyl)-2H-pyridazin-3-one (19b)
was prepared according to the method for 19a, starting from
5-chloro-N-p-tolylsulfonyl indole (64%): mp >250 °C; 1H NMR,
DMSO-d6, δ 7.06 (d,1H, J ) 10 Hz), 7.29 (s, 1H), 7.32 (d, 1H,
J ) 8 Hz), 7.46 (d, 1H, J ) 8 Hz), 7.77 (s,1H), 7.92 (d,1H, J )
10 Hz), 12.74 (s,1H), 13.80 (s, 1H).
The following were prepared according to procedures for
19a, method 2, starting from appropriate starting materials
and reagents.
6-(6-Chloroindole-2-sulfonyl)-2H-pyridazin-3-one (19c)
was prepared according to the method for 19a, starting from
6-chloro-N-p-tolylsulfonylindole (95%): mp >250 °C; 1H NMR,
DMSO-d6, δ 7.05 (d, J ) 10 Hz, 1H), 7.15 (d, J ) 8 Hz, 1H),
7.34 (s, 1H), 7.46 (s, 1H), 7.72 (d, J ) 8 Hz, 1H), 7.92 (d, J )
10 Hz, 1H), 12.69 (s,1H), 13.80 (s, 1H).
6-(7-Chloroindole-2-sulfonyl)-2H-pyridazin-3-one (19d)
was prepared according to the method for 19a starting from
1
7-chloro-N-p-tolylsulfonyl indole (76%): mp 248-250 °C; H
NMR, DMSO-d6, δ 7.07-7.16 (m, 2H), 7.41-7.45 (m, 2H), 7.69
(d, J ) 8 Hz, 1H), 8.01 (d, J ) 10 Hz, 1H), 12.83 (s, 1H), 13.74
(s, 1H).
6-(6-Fluoroindole-2-sulfonyl)-2H-pyridazin-3-one (19e)
was prepared according to the method for 19a, starting from
6-fluoro-N-p-tolylsulfonylindole (90%): mp >250 °C; 1H NMR,
DMSO-d6, δ 7.03 (m, 2H), 7.17 (d, J ) 8 Hz, 1H), 7.34 (s, 1H),
7.74 (d, J ) 8 Hz, 1H), 7.92 (d, J ) 10 Hz, 1H), 12.63 (s, 1H),
13.78 (s, 1H).
6-(5,6-Methylenedioxyindole-2-sulfonyl)-2H-pyridazin-
3-one (19f) was prepared according to the method for 19a,
starting from 5,6-methylenedioxy-N-p-tolylsulfonyl indole
(67%): mp 250 °C; 1H NMR, DMSO-d6, δ 5.99 (s, 2H), 6.86 (s,
1H), 7.04 (d, J ) 10 Hz, 1H), 7.08 (s, 1H), 7.14 (s, 1H), 7.88 (d,
J ) 10 Hz, 1H), 12.34 (s, 1H), 13.71 (s, 1H).
6-(5,7-Dichloroindole-2-sulfonyl)-2H-pyridazin-3-one
(19g) was prepared according to the method for 19a starting
from 5,7-dichloro-N-p-tolylsulfonyl indole (80%): mp >250 °C;
1H NMR, DMSO-d6, δ 7.15(d, J ) 10 Hz, 1H), 7.42 (s, 1H),
7.56 (s, 1H), 7.80 (s,1H), 8.20 (d, J ) 10 Hz, 1H), 13.15 (s,1H),
13.78 (s, 1H).
6-(3-Methylbenzofuran-2-sulfonyl)-2H-pyridazin-3-
one (19j). Step 1. A solution of 2-bromo-3-methylbenzofuran
(1.34 mmol, 283 mg) in THF (5 mL) was cooled to -78 °C and
Step 2. A mixture of 6-(5-chloro-3-methylbenzofuran-2-
sulfonyl)-3-methoxypyridazine (0.5 mmol, 162 mg), concen-
trated HCl (1 mL), and dioxane (3 mL) was heated at 100 °C

6336 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20
Mylari et al.
for 2 h. The reaction was cooled and evaporated to dryness.
H2O (10 mL) was added to the residue, and the resulting yellow
precipitate was collected and crystallized from EtOH to obtain
6-(5-chloro-3-methylbenzofuran-2-sulfonyl)-2H-pyridazin-3-
one (73%, 113 mg).
ridazine (11 mmol, 2.11 g) and the mixture stirred for 30 min.
The reaction was allowed to come to room temperature
overnight and then quenched with EtOAc (40 mL) and H2O
(10 mL). The organic portion was collected, dried, and filtered,
and the filtrate was evaporated to dryness to obtain a crude
product, which was purified by silica gel chromatography
(eluent, hexanes-EtOAc, 4:1) to obtain the desired product,
6-(5-fluoro-3-methylbenzofuran-2-sulfonyl)-3-methoxypyrid-
azine (22%, 781 mg).
6-(5-Chloro-3-methylbenzofuran-2-sulfonyl)-2H-py-
ridazin-3-one (19m). Method 3. Step 1. n-Butyllithium (2.5
M in hexane, 33 mmol, 13.2 mL) was added dropwise over 15
min to a solution of 5-chloro-3-methylbenzofuran (30.0 mmol,
5 g) in THF (30 mL) cooled to between -50 and -35 °C. This
was transferred into a cold-jacketed addition funnel and added
dropwise to a solution of 3-fluorosulfonyl-6-methoxypyridazine
(30 mmol, 5.76 g) in THF (30 mL) over 10 min. The reaction
was allowed to come to room temperature, excess solvents were
removed, and the residue was quenched with H2O (500 mL).
The granulated product was filtered and air-dried to obtain
6-(5-chloro-3-methylbenzofuran-2-sulfonyl)-3-methoxypyrid-
azine (75%, 7.62 g).
Step 2. A mixture of 6-(5-chloro-3-methylbenzofuran-2-
sulfonyl)-3-methoxypyridazine (22.2 mmol, 7.5 g), concentrated
HCl (5 mL), and dioxane (50 mL) was heated at 100 °C for 2
h. The reaction was cooled and evaporated to dryness. H2O
(20 mL) was added to the residue, the resulting precipitate
was collected and crystallized from EtOH to obtain 6-(5-chloro-
3-methylbenzofuran-2-sulfonyl)-2H-pyridazin-2H-pyridazin-3-
one, 19n (89%, 6.42 g).
Step 4. A mixture of 6-(5-fluoro-3-methylbenzofuran-2-
sulfonyl)-3-methoxypyridazine (2.4 mmol, 775 mg), concen-
trated HCl (1.5 mL), and dioxane (3 mL) was heated at 100
°C for 2 h. The reaction was cooled and evaporated to dryness.
The dried residue was triturated with H2O (10 mL) and filtered
to obtain 6-(5-fluoro-3-methylbenzofuran-2-sulfonyl)-2H-py-
ridazin-3-one (84%, 620 mg): mp 232-233 °C; 1H NMR,
DMSO-d6, δ 2.6 (s, 3H), 7.1 (d, J ) 8 Hz, 1H), 7.3 (m, 1H), 7.5
(m, 1H), 7.6 (m, 1H), 8.0 (d, J ) 8 Hz, 1H), 13.84 (s, 1H).
6-(6-Chloro-3-methylbenzofuran-2-sulfonyl)-2H-py-
ridazin-3-one (19n) was prepared according to the method
for 19o, starting from 4-chloro-2-hydroxyacetophenone (42%):
1
mp >240 °C; H NMR, DMSO-d6, δ 2.55 (s, 3H), 7.04 (d, J )
10 Hz, 1H), 7.45 (m, 1H), 7.79-7.95 (m, 2H), 7.8 (d, J ) 10
Hz, 1H), 13.82 (s, 1H).
6-(5-Trifluoromethyl-3-methylbenzofuran-2-sulfonyl)-
2H-pyridazin-3-one (19p). 5-Trifluoromethyl-3-methylben-
zofuran was prepared following a procedure described by
Larock et al.41
6-(Benzofuran-2-sulfonyl)-2H-pyridazin-3-one (19h) was
prepared according to example 19m, method 2, but staring
from benzofuran (10%): mp 210-211 °C; 1H NMR, DMSO-d6,
δ 7.1 (d, J ) 8 Hz, 1H), 7.35 (m, 1H), 7.56 (m, 2H), 7.82 (mm,
2H), 8.0 (d, J ) 8 Hz, 1H), 13.9 (s, 1H).
Step 1. A mixture of iodine (91.6 mmol, 23.2 g) and Na2-
CO3 (91.6 mmol, 7.7 g) was added to a solution of R,R,R-
trifluoro-p-cresol (83.3 mmol, 13.5 g) in THF (90 mL) and H2O
(90 mL), and the reaction was allowed to stand at room
temperature overnight. Sufficient thiourea (5% solution) was
added to remove the excess I2, as indicated by the color change
of the reaction from deep violet to brown. The reaction mixture
was extracted with Et2O, the extract was dried and filtered,
and the filtrate was concentrated to obtain a brown oil. This
oil was distilled (bp, 105 °C at 44 mmHg) to obtain R,R,R-
trifluoro-o-iodo-p-cresol (4.1 g, 75% pure, admixed with the
starting R,R,R-trifluoro-p-cresol).
Step 2. To a mixture of the above 75% pure R,R,R-trifluoro-
o-iodo-p-cresol (4.1 g, 17 mmol), K2CO3 (7.7 g), and DMF (120
mL) was added allyl bromide (6.8 g). After 3 h the reaction
mixture was poured into H2O (100 mL) and extracted with
Et2O. The Et2O layer was collected, dried, and filtered, and
the filtrate was concentrated to obtain a brown oil. This oil
was distilled (bp 95-100 °C at 20 mmHg) to obtain a mixture
(3:1) of allyl compounds.
6-(5-Chlorobenzofuran-2-sulfonyl)-2H-pyridazin-3-
one (19i) was prepared according to example 19m, method
3, but staring from 5-chlorobenzofuran (68%): mp 246-247
°C; 1HNMR, DMSO-d6, δ 7.15 (d, J ) 8 Hz, 1H), 7.50 (m, 2H),
7.82 (d, J ) 4 Hz, 2H), 8.0 (d, J ) 8 Hz, 1H), 13.82 (s, 1H).
6-(5-Methoxybenzofuran-2-sulfonyl)-2H-pyridazin-3-
one (19k) was prepared according to example 19m, method
3, but staring from 5-methoxybenzofuran (28%): mp 222-223
1
°C; H NMR, DMSO-d6, δ 3.8 (s, 3H), 7.05 (d, J ) 8 Hz, 1H),
7.15 (dd, 1H, J ) 2, 6 Hz), 7.5 (d, J ) 6 H), 75 (s, 1H), 8.0 (d,
J ) 8 Hz, 1H), 13.82 (s, 1H).
6-(5,7-Dichlorobenzofuran-2-sulfonyl)-2H-pyridazin-3-
one (19l) was prepared according to example 19m, method 3,
but staring from 5,7-dichloro-benzofuran: mp 240-245 °C; 1H
NMR, DMSO-d6, δ 7.15 (d, J ) 8 Hz, 1H), 7.65 (d, J ) 2 Hz,
1H), 7.78 (d, J ) 2 Hz, 1H), 7.85 (d, J ) 2 Hz, 1H), 8.0 (d, J )
8 Hz, 1H), 13.82 (s, 1H).
Step 3. To a mixture of the above allyl compounds (3.9 g,
8.83 mmol of the desired), Na2CO3 (22.1 mmol, 2.3 g), HCO2-
Na (8.83 mmol, 0.81 g), n-BuNH4Cl (9.72 mmol, 2.7 g), and
DMF (15 mL) was added Pd(OAc)2 (0.44 mmol, 0.1 g). The
reaction was heated to 80 °C and maintained at that temper-
ature overnight. After bringing the reaction to room temper-
ature, the mixture was filtered, the filtrate was dried and
evaporated to give a crude product, which was purified by silica
gel chromatography (eluent, hexanes) to obtain 3-methyl-5-
trifluoromethylbenzofuran as a clear oil (44%, 780 mg).
Step 4. n-BuLi (2.5 M in hexane, 4.2 mmol, 1.7 mL) was
added dropwise over 15 min to a solution of 3-methyl-5-
trifluoromethylbenzofuran (3.82 mmol, 765 mg) in THF (10
mL) cooled to -78 °C. To this was added 3-fluorosulfonyl-6-
methoxypyridazine (3.82 mmol, 734 mg) and the mixture
stirred for 30 min. The reaction was allowed to come to room
temperature overnight and was then quenched with EtOAc
(20 mL) and H2O (10 mL). The organic portion was collected,
dried, and filtered, and the filtrate was evaporated to dryness
to obtain a crude product, which was purified by silica gel
chromatography (eluent, hexanes-EtOAc, 3:1) to obtain 6-(tri-
fluoromethyl-3-methylbenzofuran-2-sulfonyl)-3-methoxypy-
ridazine (35%, 501 mg).
6-(5-Fluoro-3-methylbenzofuran-2-sulfonyl)-2H-py-
ridazin-3-one (19o). Step 1. Chloroacetic acid (99.3 mmol,
9.4 g) was added to a suspension of 5-fluoro-2-hydroxyac-
etophenone (33.1 mmol, 5.1 g) in H2O (60 mL) containing
NaOH (165.4 mmol, 6.6 g), and the mixture was refluxed for
3.5 h. The reaction was cooled to room temperature and poured
into a separatory funnel, and the oily liquid at the bottom of
the funnel was discarded. The aqueous top layer was collected,
cooled to 0 °C, and acidified with concentrated HCl. The white
precipitate was collected and air died. The dry solid was
crystallized from toluene to obtain 2-acetyl-4-fluorophenoxy
acetic acid (57%, 4.3 g).
Step 2. Anhydrous NaOAc (139.3 mmol, 11.4 g) was added
to a solution of the product of step 1 (3.24 mmol, 1.6 g) in acetic
anhydride (70 mL) and heated for 3 h at 110 °C. After cooling,
the reaction mixture was poured into H2O (100 mL) and stirred
for 1 h. The aqueous solution was extracted with Et2O and
washed with 3% aqueous KOH and H2O. The washed Et2O
layer was collected, dried, and filtered, and the filtrate was
evaporated to a brown residue, which was purified by silica
gel chromatography (eluent, hexanes) to obtain 5-fluoro-3-
methylbenzofuran (59%, 1.65 g).
Step 3. n-BuLi (2.5 M in hexane, 11 mmol, 4.83 mL) was
added dropwise over 15 min to a solution of 5-fluoro-3-
methylbenzofuran (11 mmol, 1.65 g) in THF (20 mL) cooled to
-78 °C. To this was added 3-fluorosulfonyl-6-methoxypy-
Step 5. A mixture of 6-(trifluoromethyl-3-methylbenzofuran-
2-sulfonyl)-3-methoxypyridazine (1.34 mmol, 500 mg), concen-
trated HCl (2 mL), and dioxane (4 mL) was heated at 100 °C

Novel Inhibitors of Aldose Reductase
Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20 6337
for 2 h. The reaction was cooled and evaporated to dryness.
H2O (10 mL) was added to the residue, the resulting white
solid was collected and air-dried to obtain the desired product,
6-(5-trifluoromethyl-3-methylbenzofuran-2-sulfonyl)-2H-py-
ridazin-3-one (56%, 270 mg): mp 244-245 °C; 1H NMR,
DMSO-d6, δ 2.6 (s, 3H), 7.1 (d, J ) 8 Hz, 1H), 7.75 (d, J ) 6
Hz, 1H), 7.85 (d, J ) 6 Hz,1H), 8.0 (d, J ) 8 Hz, 1H), 8.2 (s,
1H), 13.89 (s, 1H).
6-(3,5-Dimethylbenzofuran-2-sulfonyl)-2H-pyridazin-
3-one (19q) was prepared according to example 19m, method
3, but staring from 3,5-dimethylbenzofuran (68%): mp 246-
247 °C; 1H NMR, DMSO-d6, δ 2.6 (s, 3H), 2.8 (s, 3H), 7.1 (d, J
) 8 Hz, 1H), 7.4 (m, 2H), 7.5 (s,1H), 8.0 (d, J ) 8 Hz, 1H),
13.78 (s, 1H).
6-(5-Chloro-3-ethylbenzofuran-2-sulfonyl)-2H-pyridazin-
3-one (19r). Step 1. To a solution of 4-chlorophenol in THF
(75 mL) and H2O (75 mL) was added a mixture of crushed I2
(78.7 mmol, 20 g) and Na2CO3 (78.7 mmol, 6.6 g). The reaction
was stirred at room temperature overnight and then quenched
with sufficient 5% sodium thiosulfate solution to turn the color
of the reaction mixture from deep violet to light yellow and
extracted with ether. The ether layer was collected and washed
with H2O, the washed ether layer was dried and filtered, and
the filtrate was evaporated to a crude product, which was
purified by distillation to obtain 4-chloro-2-iodo phenol (7%,
1.3 g): mp 79-82 °C.
dried, and filtered and the filtrate was evaporated to dryness
to obtain a crude product, which was purified by silica gel
chromatography (eluent, hexanes-EtOAc, 4:1) to obtain the
desired product, 6-(5-chloro-3-isopropylbenzofuran-2-sulfonyl)-
3-methoxypyridazine (21%, 283 mg).
Step 2. A mixture of 6-(5-chloro-3-isopropylbenzofuran-2-
sulfonyl)-3-methoxypyridazine (0.77 mmol, 283 mg), concen-
trated HCl (1.5 mL), and dioxane (3 mL) was heated at 100
°C for 2 h. The reaction was cooled and evaporated to dryness.
The dried residue was triturated with H2O (10 mL) and filtered
to obtain the desired product, 6-(5-chloro-3-isopropylbenzofu-
ran-2-sulfonyl)-2H-pyridazin-3-one (79%, 215 mg): mp 211-
1
212 °C; H NMR, DMSO-d6, δ 1.4 (d, J ) 6 Hz, 6H), 7.2 (d, J
) 8 Hz, 1H), 7.5 (m, 1H), 7.6 (m, 1H), 8.0 (d, J ) 8 Hz, 1H),
13.82 (s, 1H).
6-(3-Phenylbenzofuran-2-sulfonyl)-2H-pyridazin-3-
one (19t) was prepared according to example 19m, method
1
3, starting from 3-phenylbenzofuran (65%): mp >220 °C; H
NMR, DMSO-d6, δ 7.02 (d, J ) 10 Hz, 1H), 7.49-7.55 (m, 8H),
7.65 (m, 1H), 7.75 (d, J ) 10 Hz, 1H), 13.82 (s, 1H).
6-(3-[4-Fluorophenyl]benzofuran-2-methylsulfonyl)-
2H-pyridazin-3-one (19u) was prepared according to ex-
ample 19m, method 3, (46%): mp >240 °C; 1H NMR, DMSO-
d6, δ 7.02 (d, J ) 9.9 Hz, 1H), 7.35 (m, 2H), 7.43 (m, 1H), 7.56-
7.65 (m, 4H), 7.77-7.82 (m, 2H). The starting material,
4-fluorophenylbenzofuran, was prepared as follows.
Step 2. To a mixture of 4-chloro-2-iodophenol (5.11 mmol,
1.3 g) in DMF (40 mL) and K2CO3 (10 mmol, 1.4 g) was added
crotyl bromide (10.2 mmol, 1.6 g) and the reaction was stirred
at room temperature for 1 h. The reaction was quenched with
H2O (100 mL) and extracted with EtOAc. The EtOAc layer
was collected, dried, and filtered, and the filtrate was evapo-
rated to obtain 4-chloro-2-iodo-o-crotylphenol (94%, 1.5 g).
Step 3. To a mixture of 4-chloro-2-iodo-o-crotylphenol (1.5
g, 4.86 mmol of the desired), Na2CO3 (12.2 mmol, 1.3 g), HCO2-
Na (4.86 mmol, 330 mg), n-BuNH4Cl (5.34 mmol, 1.5 g), and
DMF (10 mL) was added Pd(OAc)2 (0.24 mmol, 55 mg). The
reaction was heated to 80 °C and maintained at that temper-
ature overnight. After bringing the reaction to room temper-
ature, the mixture was filtered, and the filtrate was dried and
evaporated to give a crude product, which was purified by silica
gel chromatography (eluent, hexanes) to obtain 5-chloro-3-
ethylbenzofuran as a clear oil (60%, 530 mg).
Step 4. n-BuLi (2.5 M in hexane, 3.2 mmol, 1.3 mL) was
added dropwise over 15 min to a solution of 5-chloro-3-
ethylbenzofuran (2.88 mmol, 520 mg) in THF (8 mL) cooled
to -78 °C. To this was added 3-fluorosulfonyl-6-methoxy-
pyridazine (2.88 mmol, 553 mg), and the mixture stirred for
30 min. The reaction was allowed to come to room tempera-
ture overnight and then quenched with EtOAc (20 mL) and
H2O (10 mL). The organic portion was collected, dried, and
filtered, and the filtrate was evaporated to dryness to obtain
a crude product, which was purified by silica gel chromatog-
raphy (eluent, hexanes-EtOAc, 4:1) to obtain the desired
product, 6-(5-chloro-3-ethylbenzofuran-2-sulfonyl)-3-methoxy-
pyridazine (35%, 352 mg).
To an ice-cold solution of 3-coumaranone (10 mmol, 1.34 g)
in Et2O (20 mL) was added 4-fluorophenylmagnesium bromide
(2 M in Et2O, 20 mmol, 10 mL), and the reaction stirred for
3.5 h. The reaction was quenched with H2O (10 mL), the pH
adjusted to 7 with sufficient 10% HCl, and reaction extracted
with Et2O. The ether extract was collected, dried, filtered, and
evaporated to dryness. The residue was purified by silica gel
chromatography (eluent, hexanes) to obtain 4-fluorophenyl-
benzofuran.
6-(5-Chloro-3-phenylbenzofuran-2-sulfonyl)-2H-py-
ridazin-3-one (19v) was prepared according to example 19h,
method 2, starting from 5-chloro-3-phenylbenzofuran: mp
>240 °C; 1H NMR, DMSO-d6, δ 7.02 (d, J ) 9.9 Hz, 1H), 7.49-
7.55 (m, 6H), 7.65 (m, 1H), 7.75 (d, J ) 9.9 Hz, 1H), 7.86 (d, J
) 8.7 Hz, 1H), 13.84 (s, 1H).
6-(5-Chloro-3-methylbenzothiophene-2-sulfonyl)-2H-
pyridazin-3-one (19y). Step 1. n-BuLi (2.5 M in hexane, 2.1
mmol, 0.84 mL) was added dropwise over 15 min to a solution
of 5-chloro-3-methylbenzothiophene43 (1.91 mmol, 348 mg) in
THF (6 mL) cooled to -78 °C. To this was added 3-fluorosul-
fonyl-6-methoxypyridazine (1.91 mmol, 366 mg) and the
mixture stirred for 30 min. The reaction was allowed to come
to room temperature overnight and then quenched with EtOAc
(20 mL) and H2O (10 mL). The organic portion was collected,
dried, and filtered, and the filtrate was evaporated to dryness
to obtain a crude product, which was purified by silica gel
chromatography (eluent, hexanes-EtOAc, 4:1) to obtain the
desired product, 6-(5-chloro-3-methylbenzothophene-2-sulfo-
nyl)-3-methoxypyridazine (29%, 197 mg).
Step 2. A mixture of 6-(5-chloro-3-methylbenzothophene-
2-sulfonyl)-3-methoxypyridazine, (0.55 mmol, 197 mg), con-
centrated HCl (1 mL), and dioxane (3 mL) was heated at 100
°C for 2 h. The reaction was cooled and evaporated to dryness.
H2O (10 mL) was added to the residue, and the resulting yellow
precipitate, 6-(5-chloro-3-methylbenzothiophene-2-sulfonyl)-
2H-pyridazin-3-one was collected (29%, 55 mg): mp 258-259
Step 5. A mixture of 6-(5-chloro-3-ethylbenzofuran-2-sul-
fonyl)-3-methoxypyridazine (1.04 mmol, 352 mg), concentrated
HCl (1.5 mL), and dioxane (3 mL) was heated at 100 °C for 2
h. The reaction was cooled and evaporated to dryness. H2O
(10 mL) was added to the residue, and the resulting solid, 6-(5-
chloro-3-ethylbenzofuran-2-sulfonyl)-2H-pyridazin-3-one, was
1
1
°C; H NMR, DMSO-d6, δ 2.9 (s, 3H), 7.1 (d, J ) 10 Hz, 1H),
collected (46%, 155 mg): mp 209-210 °C; H NMR, DMSO-
7.55 (d, J ) 9 Hz, 1H), 7.9 (d, J ) 9 Hz, 1H), 7.95 (s, 1H), 8.0
(d, J ) 10 Hz, 1H), 13.78 (s, 1H).
d6, δ 1.1 (m, 3H), 2.45 (m, 2H), 7.2 (d, J ) 8 Hz, 1H), 7.5 (m,
1H), 7.6 (m, 1H), 8.0 (d, J ) 8 Hz, 1H) 13.82 (s, 1H).
6-(Benzothiophene-2-sulfonyl)-2H-pyridazin-3-one(19w)
6-(5-Chloro-3-isopropylbenzofuran-2-sulfonyl)-2H-py-
ridazin-3-one (19s). Step 1. n-BuLi (2.5 M in hexane, 4.04
mmol, 1.62 mL) was added dropwise over 15 min to a solution
of 5-chloro-3-isopropylbenzofuran42 (3.67 mmol, 715 mg) in
THF (10 mL) cooled to -78 °C. To this was added 3-fluoro-
sulfonyl-6-methoxypyridazine (3.67 mmol, 706 mg) and the
mixture stirred for 30 min. The reaction was allowed to come
to room temperature overnight and then quenched with EtOAc
(20 mL) and H2O (10 mL). The organic portion was collected,
was prepared according to the method for 19y, starting from
1
benzothiophene (42%): mp 209-210 °C; H NMR, DMSO-d6,
δ 7.1 (d, J ) 10 Hz, 1H), 7.5 (m, 2H), 8.0 (d, J ) 10 Hz, 1H),
8.1 (m, 3H), 8.2 (s, 1H), 13.80 (s, 1H).
6-(5-Methylbenzothiophene-2-sulfonyl)-2H-pyridazin-
3-one (19x) was prepared according to the method for 19y,
starting from 5-methylbenzothiophene (62%): mp 240-242 °C;
1H NMR, DMSO-d6, δ 2.4 (s, 3H), 7.1 (d, J ) 10 Hz, 1H), 7.4

6338 Journal of Medicinal Chemistry, 2005, Vol. 48, No. 20
Mylari et al.
(d, J ) 9 Hz, 1H), 7.8 (d, J ) 9 Hz, 1H), 7.85 (s, 1H), 7.9 (d, J
) 9 Hz, 1H), 8.0 (d, J ) 10 Hz, 1H), 8.25 (s, 1H).
for fructose analysis at a later date, using the methods
described above.
6-(Benzothiazole-2-sulfonyl)-2H-pyridazin-3-one (19z)
was prepared according to the method of Kukolja et al.,24 but
starting from 2-chlorobenzothiazole and 3-mercapto-4-meth-
Supporting Information Available: Elemental analysis
data. This material is available free of charge via the Internet
at http://pubs.org.
1
oxypyridazine, 12 (15%): mp 187 °C; H NMR, DMSO-d6, δ
7.1 (d, J ) 9 Hz, 1H), 7.40 (m, 1H), 7.56 (m, 2H), 7.82 (m, 1H),
8.0 (d, J ) 8 Hz, 1H), 13.84 (s, 1H).
References
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dissolving TC in 20 µL of 20% dimethyl sulfoxide (DMSO) and
diluting with 100 mM potassium phosphate buffer, pH 7.0, to
various TC concentrations, typically ranging from 5 mM to 1
µM. A “zero TC” solution was prepared that started with only
20 µL of DMSO (no TC).
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The assay for AR activity was performed in a 96-well plate.
Initiation of the reaction (with substrate) was preceded by a
10-min preincubation at 24 °C of 200 µL of 100 mM potassium
phosphate buffer, pH 7.0, containing 125 µM NADPH and 12.5
nM human recombinant aldose reductase (Wako Chemicals,
Inc., #547-00581) with 25 µL of TC solution. The reaction was
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model LS50B fluorescence spectrophotometer). After the ap-
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