Synthesis of novel benzoic acid derivatives with benzothiazolyl subunit and evaluation as aldose reductase inhibitors

Article abstract of DOI:10.1002/ardp.200500101

Several methyl benzothiazolyloxybenzoates, 5-isosters, and the corresponding benzoic acids were synthesized and tested as aldose reductase inhibitors (ARIs). Out of this series, the ester derivative 2a-7 was found to exhibit the highest enzyme-inhibitoric activity. In order to investigate this unexpected result, further modifications were carried out which allowed us to explain this finding and to open a path to a novel class of ARIs.

Full text of DOI:10.1002/ardp.200500101

Arch. Pharm. Chem. Life Sci. 2005, 338, 411−418
DOI 10.1002/ardp.200500101
411
Synthesis of Novel Benzoic Acid Derivatives with
Benzothiazolyl Subunit and Evaluation as Aldose
Reductase Inhibitors
Dietmar Rakowitza, Barbara Henniga, Marietta Naganoa, Stefan Stegera,
Luca Costantinob, Barbara Matuszczaka
a Institute of Pharmacy, University of Innsbruck, Innsbruck, Austria
b Dipartimento di Scienze Farmaceutiche, Universita di Modena, Modena, Italy
Several methyl benzothiazolyloxybenzoates, S-isosters, and the corresponding benzoic acids were syn-
thesized and tested as aldose reductase inhibitors (ARIs). Out of this series, the ester derivative 2aϪ7
was found to exhibit the highest enzyme-inhibitoric activity. In order to investigate this unexpected
result, further modifications were carried out which allowed us to explain this finding and to open a
path to a novel class of ARIs.
Keywords: Methyl benzothiazolyloxybenzoates; Benzothiazolyloxybenzoic acids; Aldose reductase inhibitors;
Diabetic complications
Received: February 23, 2005; Accepted: March 24, 2005
Introduction
Diabetes mellitus is a group of complex heterogenous
diseases resulting from defects in insulin secretion and/or
action, characterized by chronic hyperglycemia and disturb-
ances in carbohydrate, fat, and protein metabolism.
Recently, compiled data showed that the total number of
people with diabetes is projected to rise from 171 Mio in
the year 2000 to 366 Mio in 2030 [1]. Although insulin ther-
apy has been dramatically effective in prolonging life, it does
not prevent the occurrence of disabling complications such
as neuropathy, nephropathy, retinopathy, and cataracts [2].
Several metabolic pathways have been implicated in the
toxic effects of glucose like elevated nonenzymatic glycation,
increased glycolytic metabolism, and excess flux through the
polyol pathway [3], an alternate route of glucose metab-
olism. The rate-limiting step of this pathway is the reduction
of glucose to sorbitol catalyzed by the enzyme aldose re-
ductase (EC 1.1.1.21, ALR2). Whereas its physiological role
has not been clearly identified it has been hypothesized that
ALR2 activity could be involved in the occurrence of dia-
Figure 1. Aldose reductase inhibitors.
betic complications. These observations have led to the de-
velopment of numerous aldose reductase inhibitors (ARIs).
Since ARIs have to cross several barriers to reach the target
tissues (lens, kidney, nerves) which are differently perfused
by blood, drugs with different properties (e.g. lipophilicity,
acidity, plasma protein binding affinity, etc.) are required.
Although some ARIs are in clinical trials, to date the only
drug already launched on the market is Epalrestat [4].
ARIs can be divided into two major classes Ϫ spirohydanto-
ins and carboxylic acids, representatives thereof are shown
in Figure 1. These compounds possess an acidic proton
which is either attached to the imidic nitrogen or an acetic
acid moiety in the molecule [4cϪe]. In vivo, the carboxylic
acids are generally less active than the imide derivatives
which may be attributed to different pharmacokinetic be-
Correspondence: Dietmar Rakowitz, Leopold-Franzens-Universität,
Institute of Pharmacy, Innrain 52a, Innsbruck A-6020, Austria.
Phone: ϩ43 512 507-5262, Fax: ϩ43 512 507-2940, e-mail:
dietmar.rakowitz@uibk.ac.at
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412
Rakowitz et al.
Arch. Pharm. Chem. Life Sci. 2005, 338, 411−418
Figure 2. Zopolrestat-aldose reductase complex (from [4e]).
Figure 3. Theoretical model of the binding of type I com-
pounds in the active site of the enzyme.
haviour. However, several spirohydantoin derivatives Ϫ in-
cluding sorbinil, the first of its class Ϫ often showed serious
adverse events [5].
In order to proof the model, the influence of the following
moieties on aldose reductase inhibition was studied:
Recently, benzothiazole derivatives have received much at-
tention due to their potent in vitro as well as in vivo aldose
reductase inhibitory activity. The high activity of such com-
pounds led to the suggestion of the presence of a hydro-
phobic pocket in the target enzyme particularly suited for
the benzothiazole moiety [6]. This hypothesis was confirmed
by crystallographic analysis of a Zopolrestat-aldose re-
ductase complex [7].
1) the length of spacer between the benzene core and car-
boxylic acid,
2) the relative position of the (CH2)n and X-benzothiazolyl
groups in the benzene core,
3) the effect of introduction of a heteroatom between the
(hetero)aromatic cores instead of the methylene spacer
given in compounds like Zopolrestat,
4) the effect of an additional substituent R in the benzene
core, and
As shown in Figure 2, binding of Zopolrestat was found
to involve the following contact zones in the active site: a
recognition region for hydrogen-bond acceptors near the co-
enzyme (including the anionic site) and a hydrophobic con-
tact zone in the active site cleft (including the specificity
pocket for the benzothiazole moiety) [4e, 7].
5) the introduction of the 5-CF3 substituent (RЈ) in the
benzothiazole system.
This paper will focus on the synthesis and evaluation of
aldose reductase inhibition of compounds of type II charac-
terized by a benzoic acid substructure (i.e. derivatives of
type I with n ϭ 0). In a subsequent paper, we will present
our findings with compounds bearing a spacer between aro-
matic core and acidic function (derivatives of type I with
n Ն 1).
Based on the results of enzyme ARI interactions described
above and shown in Figure 2, we are proposing to study
the effect of compounds of type I as enzyme inhibitors. As
outlined in Figure 3, these compounds are characterized by
the following pharmacophores [4a, 8]: first, the atoms of the
carboxylate anion should interact with Tyr48, His110, and
Trp111; second, a (substituted) benzene core forming inter-
actions with lipophilic side chains (e.g. with Phe122 and/or
Trp20), and third, the benzothiazole moiety which may lie
between Trp111 and Leu300 depending on the point of at-
tachment to the benzene ring (“specific benzothiazole
pocket”).
Results and discussion
The target compounds were prepared as described in
Scheme 1. Compounds of type 2 became accessible by treat-
ment of the appropriate methoxycarbonyl-substituted phe-
nol or thiophenol derivatives with 2-chlorobenzothiazole
(1a) at 50°C or with 2-chloro-5-trifluoromethylbenzothi-
azole (1b) at room temperature, respectively. However, at-
tempts to prepare the corresponding N-analogue failed.
Whereas stirring of methyl anthranilate with 1a at 50 to
80°C in the presence of potassium carbonate did not result
in any reaction, employment of potassium hydroxide as base
only led to hydrolysis of the ester function.
In compounds of type I, the carboxylic acid function is
either directly bound at the benzene core (n ϭ 0) or through
methylene unit(s), respectively. The benzothiazole and ben-
zene moieties, however, are connected via spacer X which
represents a heteroatom. Considering the chemical struc-
ture, compounds of type I (see Figure 3) represent iminocar-
bonate derivatives [XC(SR)ϭNRЈ] whereas the known com-
pounds like Zopolrestat are imidoester derivatives
[CH2C(SR)ϭNRЈ].
O-Demethylation of compounds 2aϪ6 and 2bϪ6 was
achieved by treatment with boron tribromide in dichloro-
methane at Ϫ70°C. Finally, the desired corresponding car-
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Arch. Pharm. Chem. Life Sci. 2005, 338, 411−418
Benzoic Acid Derivatives as Aldose Reductase Inhibitors
413
Scheme 1. Synthesis of the target compounds. (i): DMF, K2CO3, 50°C (for 1a) or r.t. (for 1b); (ii): 1) NaOH in C2H5OH, r.t.;
2) HCl.
Table 1. Biological data of compounds of type 2 and 3.
boxylic acids became accessible by alkaline hydrolysis. Sur-
prisingly, attempts to prepare the corresponding carboxylic
acids of 2bϪ1 and 2bϪ5 failed. Instead of the desired com-
pounds 3bϪ1 and 3bϪ5, 2-hydroxy- and 4-hydroxy benzoic
acids were isolated, respectively. This, however, should be
explained with the substructure of a vinylogue or phe-
nylogue of a carbonic acid diester given in 2bϪ1 and 2bϪ5.
This unexpected hydrolysis can be observed only in the case
of trifluoromethyl substituted derivatives. The structures of
all novel compounds were confirmed by elemental analyses,
IR, and NMR spectroscopy as well as MS data (see exper-
imental part).
Compound
Enzyme inhibition (concentration)
or IC50 value
2a-1
2a-2
2a-3
2a-4
2a-5
2a-6
2a-7
2a-8
2b-1
2b-2
2b-3
2b-4
2b-5
2b-6
2b-7
2b-8
3a-1
3a-2
3a-3
3a-4
3a-5
3a-6
3a-7
3a-8
3b-2
3b-3
3b-4
3b-6
3b-8
Sorbinil
0% (83 µM)
0% (89 µM)
18% (70 µM)
0% (100 µM)
0% (100 µM)
0% (34 µM)
57.3 µM
26% (100 µM)
0% (16 µM)
0% (100 µM)
13% (19 µM)
0% (11 µM)
27% (100 µM)
0% (10 µM)
35% (50 µM)
0% (7 µM)
26% (146 µM)
18% (137 µM)
26% (142 µM)
26% (138 µM)
21% (100 µM)
16% (63 µM)
19% (131 µM)
10% (1412 µM)
36% (117 µM)
41% (119 µM)
15% (81 µM)
32% (106 µM)
21% (136 µM)
1.8 µM
The compounds were tested for their inhibitory potency
against the enzyme aldose reductase (ALR2) in an in-vitro
assay as described earlier [9]. Calf lenses were used as en-
zyme source. The enzyme activity was measured by moni-
toring the change in absorbance at 340 nm which ac-
companies the oxidation of NADPH catalyzed by ALR2.
Sorbinil was used as reference standard.
The biological results (% inhibition at given concentration
or IC50 values) of the target compounds (3) and of the cor-
responding ester derivatives (2) are given in Table 1.
Compounds bearing a carboxylic acid substructure were
found to inhibit the aldose reductase in a moderate amount.
The following can be summarized concerning structure-ac-
tivity relationships: No significant influence can be ob-
served regarding the position of the benzothiazolyloxy moi-
ety at the benzoic acid. Furthermore, no effect of an ad-
ditional hydroxy, methoxy, or carboxylic acid group in the
benzene core and of the 5-trifluoromethyl substituent in the
benzothiazolyl ring, respectively, was obtained.
formed to study the structural features critical for aldose
reductase inhibition. Since the corresponding 3-methoxy de-
rivative 2aϪ6 showed no effect on this enzyme (0% at
34 µM), we speculated that the phenolic function in 2aϪ7
represents the acidic subunit. It should be noted that the
corresponding compound with carboxylic acid subunit (i.e.
Surprisingly, a compound without a free carboxylic group
but a methyl ester (i.e. 2aϪ7) instead was found to exhibit
enzyme inhibition with an IC50 value of 57.3 µM. The iso-
meric compound 2a-3, however, displays only low enzyme
inhibition (18% at 70 µM). Thus, modifications were per-
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414
Rakowitz et al.
Arch. Pharm. Chem. Life Sci. 2005, 338, 411−418
3aϪ7) exhibits much lower biological activity (19% at
131 µM). In order to get further insight into structure-
activity relationships, compound 4 was prepared by reaction
of pyrocatechine with 1a. Due to the very low aldose re-
ductase inhibition of this derivative (8% at 100 µM), the
ester function seems to be necessary. This positive effect of
the ester should be explained by interactions of this group
with the enzyme and/or with an increase of the acidity of
the phenolic function. The latter effect would also be in
accordance with the significant lower enzyme inhibition of
3aϪ7. Moreover, the increased activity by formal introduc-
tion of a nitro group into the benzene core (i.e. reaction
product of 4-nitropyrocatechine with 1a, IC50 ϭ 24.3 µM)
supports this interpretation. Additional investigations con-
cerning the inhibitory activity of substituted nitrophenols
will be presented in a forthcoming paper.
2-(Benzothiazol-2Ј-yl)oxyphenol (4)
Powdered potassium carbonate (2.51 g, 18.2 mmol) was
added to a solution of pyrocatechine (1.00 g, 9.1 mmol), in
10 mL of dry N,N-dimethylformamide under nitrogen at-
mosphere. After stirring for 30 minutes at room tempera-
ture, 2-chlorobenzothiazole (1a) (0.77 g, 4.54 mmol) was ad-
ded and stirring was continued at 50°C until TLC indicated
no further conversion (reaction time about 24 h). Then, the
mixture was poured into cold 2N HCl (100 mL) and was
extracted with diethyl ether (3 ϫ 25 mL). The organic layer
was washed with water (2 ϫ 25 mL), brine (1 ϫ 25 mL),
dried over anhydrous sodium sulphate, and evaporated to
dryness. The crude product thus obtained was purified by
column chromatography (CH2Cl2/ethyl acetate, 19/1) and
recrystallized (diisopropyl ether/ethyl acetate) to yield 492
mg (45%) of compound 4. C13H9NO2S, mp. 160Ϫ162°C
(155°C [12]), 1H-NMR (DMSO-d6) δ 10.00 (br s, 1H, OH),
7.90Ϫ7.85 (m, 1H, ArH), 7.67Ϫ7.63 (m, 1H, ArH),
7.44Ϫ7.15 (m, 4H, ArH), 7.01Ϫ6.92 (m, 1H, ArH),
6.89Ϫ6.84 (m, 1H, ArH); MS (m/z) 244 (Mϩϩ1).
Experimental
Compounds 2aϪ1 Ϫ 2aϪ6 and 2aϪ8 were prepared simi-
larly, compounds 2bϪ1 Ϫ 2bϪ6 and 2bϪ8 were prepared
in an analogous manner but at room temperature. For data
see Table 2.
Chemistry
Melting points were determined with a Kofler hot-stage
microscope (Reichert, Vienna, Austria) and are uncorrected.
Infrared spectra (KBr pellets) were recorded on a Mattson
Galaxy Series FTIR 3000 spectrophotometer (Mattson In-
struments, Inc., Madison, WI, USA). Mass spectra were
obtained on a Finnigan MAT SSQ 7000 spectrometer (EI,
70 eV) (Thermo Electron Corporation, Bremen, Germany).
All NMR spectra were recorded in DMSO-d6 or CDCl3
solution in 5 mm tubes at 30°C on a Varian Gemini 200
General procedure for compounds 2aϪ7 and 2bϪ7
A solution of the appropriate ester (1 equivalent; 2aϪ6: 3.17
mmol; 2bϪ6: 0.78 mmol) in dry dichloromethane (20 mL)
was cooled to Ϫ70°C and treated with a solution of boron
tribromide (3.94 equivalents; 12.5 mmol or 3.08 mmol,
respectively) in dry dichloromethane (10 mL). The mixture
was stirred for 30 min at Ϫ70°C and then allowed to warm
to room temperature. After hydrolysing with ice water
(100 mL), the mixture was extracted with ethyl acetate
(3 ϫ 50 mL), washed with sodium bicarbonate solution
(1 ϫ 50 mL) and brine (1 ϫ 50 mL), dried over anhydrous
sodium sulphate, and evaporated to dryness under reduced
pressure. The crude products thus obtained were purified
by column chromatography and/or recrystallisation. For
data see Table 2.
1
spectrometer (199.98 MHz for H) (Varian Inc., Palo Alto,
CA, USA) with the deuterium signal of the solvent as the
lock and TMS as internal standard. Chemical shifts are ex-
pressed in parts per million. Reactions were monitored by
TLC using Polygram SIL G/UV254 (Macherey-Nagel,
Düren, Germany) plastic-backed plates (0.25 mm layer
thickness). With exception of 2bϪ7 (RP-18), column chro-
matography was conducted on Merck silica gel 60 (230Ϫ400
mesh) as stationary phase (Merck, Darmstadt, Germany).
The yields given are not optimized. Light petroleum refers
to the fraction of bp. 40Ϫ60°C. Elemental analyses were
performed by Mag. J. Theiner, Institute of Physical Chemis-
try, University of Vienna, Austria.
General procedure for the carboxylic acids of type 3
A solution of the appropriate ester (1 equivalent) in ethanol
(10 mL) was treated with 2N NaOH (1.1 equivalent) and
stirred overnight at room temperature. The solvent was then
evaporated, the residue treated with a small amount of
water and the pH adjusted to 5 with 2N HCl. The reaction
mixture was extracted with ethyl acetate, the organic layer
washed with water and brine, dried over anhydrous sodium
sulfate and evaporated to dryness under reduced pressure.
The crystals thus obtained were purified by column chroma-
tography and/or recrystallisation. For data see Table 2.
2-Chlorobenzothiazole (1a) was prepared in analogy to the
method of the Eastman Kodak patent [10]. 2-Chloro-5-
trifluoromethylbenzothiazole (1b) was readily available by
reaction of 2-chloro-5-trifluoromethylaniline with carbon
disulfide in presence of sodium hydride to give 5-trifluoro-
methyl-2-mercaptobenzothiazole [11], which was sub-
sequently converted into 1b by chlorination with sulfuryl
chloride in analogy to [10]. Compounds not listed below
were commercial samples of good grade.
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Arch. Pharm. Chem. Life Sci. 2005, 338, 411−418
Table 2. Data of compounds of type 2 and 3.
Benzoic Acid Derivatives as Aldose Reductase Inhibitors
415
Compound
2a-1
X
X-BZT
R
RЈ
RЉ
Purification
Yield
Mp. [°C]
Formula‡
MS
Spectroscopic Data
†
O
2
H
H
H
CH3 CH2Cl2
DIPE§
C15H11NO3S
IR (KBr) 1718 cmϪ1 (CϭO)
(m/z) 285 (Mϩ)
1H-NMR (CDCl3) δ 8.08Ϫ8.03 (m, 1H,
ArH), 7.69Ϫ7.59 (m, 3H, ArH), 7.43Ϫ7.20
(m, 4H, ArH), 3.76 (s, 3H, OCH3)
58%
63Ϫ65
2a-2
2a-3
2a-4
O
O
O
3
3
3
H
H
H
CH3 DIPE§
65%
C15H11NO3S
IR (KBr) 1729 cmϪ1 (CϭO)
(m/z) 285 (Mϩ)
1H-NMR (CDCl3) δ 8.05Ϫ7.95 (m, 2H,
ArH), 7.75Ϫ7.48 (m, 4H, ArH), 7.44Ϫ7.35
(m, 1H, ArH), 7.32Ϫ7.24 (m, 1H, ArH),
3.92 (s, 3H, OCH3)
84Ϫ85
5-OH
CH3 CH2Cl2/EA (9/1)† C15H11NO4S
IR (KBr) 1725 cmϪ1 (CϭO)
DIPE§
27%
155Ϫ158
(m/z) 301 (Mϩ)
1H-NMR (CDCl3) δ 7.75Ϫ7.68 (m, 2H,
ArH), 7.51Ϫ7.50 (m, 1H, ArH), 7.45Ϫ7.27
(m, 4H, ArH and OH), 7.00 (t, J ϭ 2.2 Hz,
1H, ArH), 3.89 (s, 3H, OCH3)
5-COOCH3
CH3 DIPE/LP§
86%
C17H13NO5S
IR (KBr) 1728 cmϪ1 (CϭO)
(m/z) 343 (Mϩ)
1H-NMR (CDCl3) δ 8.62 (t, J ϭ 1.5 Hz,
1H, phenyl H-2), 8.24 (d, J ϭ 1.5 Hz, 2H,
phenyl H-4/H-6), 7.75Ϫ7.69 (m, 2H, ArH),
7.45Ϫ7.26 (m, 2H, ArH), 3.96 (s, 6H,
2 ϫ OCH3)
88Ϫ91
†
2a-5
2a-6
2a-7
2a-8
2b-1
O
O
O
S
4
4
4
2
2
H
H
H
H
H
CH3 CH2Cl2
C15H11NO3S
IR (KBr) 1714 cm-1 (CϭO)
§
DIPE
75%
(m/z) 285 (Mϩ)
1H-NMR (CDCl3) δ 8.18Ϫ8.10 (m, 2H,
ArH), 7.78Ϫ7.69 (m, 2H, ArH), 7.50Ϫ7.26
(m, 4H, ArH), 3.94 (s, 3H, OCH3)
99Ϫ102
§
3-OCH3
3-OH
H
CH3 DIPE
C16H13NO4S·0.2 H2O IR (KBr) 1718 cmϪ1 (CϭO)
62%
(m/z) 315 (Mϩ)
1H-NMR (CDCl3) δ 7.76Ϫ7.65 (m, 4H,
ArH), 7.43Ϫ7.22 (m, 3H, ArH), 3.94 (s,
3H, OCH3), 3.87 (s, 3H, OCH3)
110Ϫ112
CH3 DIPE/EA§
32%
C15H11NO4S
IR (KBr) 1708 cmϪ1 (CϭO)
1H-NMR (CDCl3) δ 8.83 (br s, 1H, OH),
8.11Ϫ7.14 (m, 7H, ArH), 3.89 (s, 3H,
OCH3)
(m/z) 301 (Mϩ)
138Ϫ144
†
CH3 CH2Cl2
C15H11NO2S2·0.3 H2O IR (KBr) 1712 cmϪ1 (CϭO)
80%
oil
(m/z) 301 (Mϩ)
1H-NMR (CDCl3) δ 8.02Ϫ7.96 (m, 2H,
ArH), 7.80Ϫ7.75 (m, 1H, ArH), 7.55Ϫ7.32
(m, 5H, ArH), 3.92 (s, 3H, OCH3)
†
O
H
CF3 CH3 CH2Cl2
95%
C16H10F3NO3S
IR (KBr) 1720 cmϪ1 (CϭO)
(m/z) 353 (Mϩ)
1H-NMR (CDCl3) δ 8.09 (dd, J ϭ 1.8 Hz,
J ϭ 7.8 Hz, 1H, ArH), 7.92 (“s”, 1H, ArH),
7.79 (d, J ϭ 8.4 Hz, 1H, ArH), 7.71Ϫ7.62
(m, 1H, ArH), 7.52Ϫ7.38 (m, 3H, ArH),
3.77 (s, 3H, OCH3)
44Ϫ45
†
2b-2
O
3
H
CF3 CH3 CH2Cl2
C16H10F3NO3S
IR (KBr) 1719 cmϪ1 (CϭO)
1H-NMR (CDCl3) δ 8.06Ϫ7.99 (m, 3H,
ArH), 7.81 (d, J ϭ 8.4 Hz, 1H, ArH),
7.64Ϫ7.51 (m, 3H, ArH), 3.94 (s, 3H,
OCH3)
DIPE§
58%
(m/z) 353 (Mϩ)
149Ϫ153
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Table 2. (continued).
Compound X X-BZT
R
RЈ RЉ
Purification
Yield
Formula‡
MS
Spectroscopic Data
Mp. [°C]
2b-3
2b-4
O
O
3
3
5-OH
CF3 CH3 CH2Cl2/EA(19/1)† C16H10F3NO4S
IR (KBr) 1722 cmϪ1 (CϭO)
DIPE§
62%
(m/z) 369 (Mϩ)
1H-NMR (CDCl3) δ 10.43 (s, 1H, OH), 8.21
(d, J ϭ 8.4 Hz, 1H, ArH), 8.06 (“s”, 1H,
ArH), 7.67 (dd, J ϭ 1.8 Hz, J ϭ 8.4 Hz,
1H, ArH), 7.41Ϫ7.35 (m, 2H, ArH), 7.13 (t,
J ϭ 2.2 Hz, 1H, ArH), 3.84 (s, 3H, OCH3)
166Ϫ169
5-COOCH3 CF3 CH3 DIPE§
88%
C18H12F3NO5S
IR (KBr) 1734 cm-1 (CϭO)
(m/z) 411 (Mϩ)
1H-NMR (CDCl3) δ 8.64 (t, J ϭ 1.5 Hz, 1H,
phenyl H-2), 8.25 (d, J ϭ 1.5 Hz, 2H, phenyl
H-4/H-6), 7.99 (“s”, 1H, ArH), 7.83 (d,
J ϭ 8.4 Hz, 1H, ArH), 7.58Ϫ7.53 (m, 1H,
ArH), 3.98 (s, 6H, 2 ϫ OCH3)
104Ϫ105
2b-5
2b-6
O
O
4
4
H
CF3 CH3 CH2Cl2/LP (1/1)† C16H10F3NO3S
IR (KBr) 1720 cmϪ1 (CϭO)
DIPE§
84%
(m/z) 353 (Mϩ)
1H-NMR (CDCl3) δ 8.19Ϫ8.12 (m, 2H,
ArH), 8.01 (br s, 1H, ArH), 7.82 (d, J ϭ
8.4 Hz, 1H, ArH), 7.57Ϫ7.44 (m, 3H, ArH),
3.94 (s, 3H, OCH3)
102Ϫ104
3-OCH3
CF3 CH3 DIPE/LP§
C17H12F3NO4S
IR (KBr) 1730 cmϪ1 (CϭO)
87%
87
(m/z) 383 (Mϩ)
1H-NMR (CDCl3) δ 7.96 (“s”, 1H, ArH),
7.81Ϫ7.73 (m, 3H, ArH), 7.52 (dd, J ϭ
1.8 Hz, J ϭ 8.4 Hz, 1H, ArH), 7.42Ϫ7.38
(m, 1H, ArH), 3.95 (s, 3H, OCH3), 3.88
(s, 3H, OCH3)
2b-7
O
4
3-OH
CF3 CH3 MeOH/H2O (9/1)† C16H10F3NO4S·0.2 HCl IR (KBr) 1717 cm-1 (CϭO)
DIPE/LP §
52%
(m/z) 369 (Mϩ)
1H-NMR (DMSO-d6) δ 7.86Ϫ7.64 (m, 5H,
ArH), 7.44, 7.40 (s, 1H, OH of 2b-7·HCl and
OH of 2b-7), 7.04Ϫ6.98 (m, 1H, ArH), 3.82,
3.78 (s, 3H, OCH3 of 2b-7·HCl and OCH3
of 2b-7)
117Ϫ118
†
2b-8
3a-1
S
2
2
H
H
CF3 CH3 CH2Cl2
C16H10F3NO2S2·0.5 H2O IR (KBr) 1727 cm-1 (CϭO)
§
DIPE/LP
61%
(m/z) 369 (Mϩ)
1H-NMR (CDCl3) δ 8.21 (“s”, 1H, ArH),
8.03Ϫ7.98 (m, 1H, ArH), 7.86 (d, J ϭ8.4 Hz,
1H, ArH), 7.69Ϫ7.42 (m, 4H, ArH), 3.91
(s, 3H, OCH3)
86
§
O
H
H
DIPE
C14H9NO3S
IR (KBr) 1706 cmϪ1 (CϭO)
62%
(m/z) 271 (Mϩ)
1H-NMR (DMSO-d6) δ 8.01Ϫ7.96 (m, 1H,
ArH), 7.94Ϫ7.89 (m, 1H, ArH), 7.78Ϫ7.69
(m, 1H, ArH), 7.63Ϫ7.58 (m, 1H, ArH),
7.53Ϫ7.25 (m, 4H, ArH)
122Ϫ125
3a-2
3a-3
O
O
3
3
H
H
H
H
H
DIPE§
81%
163Ϫ165
C14H9NO3S·0.7 H2O·
0.1 DIPE
IR (KBr) 1704 cmϪ1 (CϭO)
1H-NMR (DMSO-d6) δ 7.97Ϫ7.91 (m, 3H,
ArH), 7.76Ϫ7.60 (m, 3H, ArH), 7.47Ϫ7.39
(m, 1H, ArH), 7.37Ϫ7.29 (m, 1H, ArH)
(m/z) 271 (Mϩ)
§
5-OH
EA/THF
65%
244Ϫ246
C14H9NO4S
IR (KBr) 1689 cmϪ1 (CϭO)
(m/z) 287 (Mϩ)
1H-NMR (DMSO-d6) δ 10.35 (br s, 1H, OH),
7.97Ϫ7.92 (m, 1H, ArH), 7.73Ϫ7.68 (m,
1H, ArH), 7.48Ϫ7.29 (m, 4H, ArH), 7.05
(t, J ϭ 2.4 Hz, 1H, ArH)
 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Arch. Pharm. Chem. Life Sci. 2005, 338, 411−418
Table 2. (continued).
Benzoic Acid Derivatives as Aldose Reductase Inhibitors
417
Compound X X-BZT
R
RЈ RЉ
Purification
Yield
Formula‡
MS
Spectroscopic Data
Mp. [°C]
3a-4
O
3
5-COOH H
H
EA/MeOH §
29%
277Ϫ279
C15H9NO5S
IR (KBr) 1722 cmϪ1 (CϭO)
(m/z) 315 (Mϩ)
1H-NMR (DMSO-d6) δ 8.42 (t, J ϭ 1.5 Hz, 1H,
phenyl H-2), 8.16 (d, J ϭ 1.5 Hz, 2H, phenyl
H-4/H-6), 8.00Ϫ7.96 (m, 1H, ArH), 7.73Ϫ7.68
(m, 1H, ArH), 7.48Ϫ7.31 (m, 2H, ArH)
3a-5
3a-6
O
O
4
4
H
H
H
H
H
DIPE/EA§
39%
186Ϫ190
C14H9NO3S
IR (KBr) 1677 cmϪ1 (CϭO)
(m/z) 271 (Mϩ)
1H-NMR (DMSO-d6) δ 8.11Ϫ7.95 (m, 2H,
ArH), 7.74Ϫ7.69 (m, 1H, ArH), 7.61Ϫ7.54
(m, 2H, ArH), 7.49Ϫ7.31 (m, 2H, ArH)
3-OCH3
DIPE/EA§
43%
C15H11NO4S·0.4 H2O IR (KBr) 1687 cmϪ1 (CϭO)
(m/z) 301 (Mϩ)
1H-NMR (DMSO-d6) δ 7.97Ϫ7.90 (m, 1H,
190-192
ArH), 7.72Ϫ7.63 (m, 3H, ArH), 7.54 (d,
J ϭ 8.4 Hz, 1H, ArH), 7.45Ϫ7.37 (m, 1H, ArH),
7.35Ϫ7.27 (m, 1H, ArH), 3.83 (s, 3H, OCH3)
§
3a-7
O
4
3-OH
H
H
DIPE/THF
46%
235Ϫ238
C14H9NO4S
IR (KBr) 1677 cmϪ1 (CϭO)
(m/z) 287 (Mϩ)
1H-NMR (DMSO-d6) δ 7.93Ϫ7.88 (m, 1H,
ArH), 7.83Ϫ7.77 (m, 2H, ArH and OH),
7.67Ϫ7.60 (m, 1H, ArH), 7.47Ϫ7.26 (m,
3H, ArH), 7.10 (d, J ϭ 8.0 Hz, 1H, ArH)
3a-8
3b-2
S
2
3
H
H
H
H
H
DIPE/EA§
29%
150Ϫ155
C14H9NO2S2
IR (KBr) 1687 cm-1 (CϭO)
(m/z) 287 (Mϩ)
1H-NMR (DMSO-d6) δ 8.05Ϫ7.94 (m, 3H,
ArH), 7.59Ϫ7.39 (m, 5H, ArH)
O
CF3
CH2Cl2/EA (9/1)† C15H8F3NO3S
IR (KBr) 1692 cmϪ1 (CϭO)
DIPE/LP§
40%
(m/z) 339 (Mϩ)
1H-NMR (DMSO-d6) δ 8.22 (d, J ϭ 8.4 Hz,
1H, ArH), 8.06Ϫ8.05 (m, 1H, ArH), 7.97Ϫ7.92
(m, 2H, ArH), 7.79Ϫ7.62 (m, 3H, ArH)
165Ϫ170
3b-3
3b-4
O
O
3
3
5-OH
CF3
H
H
DIPE/EA§
98%
236Ϫ240
C15H8F3NO4S
IR (KBr) 1701 cmϪ1 (CϭO)
(m/z) 355 (Mϩ)
1H-NMR (DMSO-d6) δ 10.40 (br s, 1H, OH),
8.21 (d, J ϭ 8.4 Hz, 1H, ArH), 8.06 (“s”, 1H,
ArH), 7.67 (“d”, J ϭ 8.4 Hz, 1H, ArH), 7.37Ϫ7.36
(m, 2H, ArH), 7.08 (t, J ϭ 2.2 Hz, 1H, ArH)
5-COOH CF3
3-OCH3 CF3
DIPE/LP§
92%
275
C16H8F3NO5S·0.8 H2O IR (KBr) 1719 cmϪ1 (CϭO)
(m/z) 383 (Mϩ)
1H-NMR (DMSO-d6) δ 8.43 (t, J ϭ 1.3 Hz,
1H, phenyl H-2), 8.26Ϫ8.19 (m, 3H, phenyl
H-4/H-6 and ArH), 8.06 (“s”, 1H, ArH),
7.68 (“d”, J ϭ 8.4 Hz, 1H, ArH)
3b-6
3b-8
O
S
4
2
H
H
DIPE/EA§
66%
176Ϫ177
C16H10F3NO4S
IR (KBr) 1684 cmϪ1 (CϭO)
(m/z) 369 (Mϩ)
1H-NMR (DMSO-d6) δ 8.20 (d, J ϭ 8.0 Hz,
1H, ArH), 8.02 (s, 1H, ArH), 7.73Ϫ7.56
(m, 4H, ArH), 3.83 (s, 3H, OCH3)
H
CF3
DIPE/LP§
77%
166
C15H8F3NO2S2
IR (KBr) 1688 cmϪ1 (CϭO)
(m/z) 355 (Mϩ)
1H-NMR (DMSO-d6) δ 8.28 (s, 1H, ArH),
8.23 (s, 1H, ArH), 8.00Ϫ7.95 (m, 1H, ArH),
7.75Ϫ7.53 (m, 4H, ArH)
†
solvent for column chromatography
recrystallisation solvent (DIPE: diisopropyl ether; EA: ethyl acetate; LP: light petroleum)
All compounds were analyzed for C, H, N. Analytical results obtained for these elements were within 0.4% of the theoretical values.
§
‡
 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

418
Rakowitz et al.
Arch. Pharm. Chem. Life Sci. 2005, 338, 411−418
Aldose reductase inhibitory assay
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 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim