Discovery of novel benzothiazolesulfonamides as potent inhibitors of HIV-1 protease

Article abstract of DOI:10.1016/j.bmc.2003.07.001

The human immunodeficiency virus (HIV) has been shown to be the causative agent for AIDS. The HIV virus encodes for a unique aspartyl protease that is essential for the production of enzymes and proteins in the final stages of maturation. Protease inhibitors have been useful in combating the disease. The inhibitors incorporate a variety of isosteres including the hydroxyethylurea at the protease cleavage site. We have shown that the replacement of t-butylurea moiety by benzothiazolesulfonamide provided inhibitors with improved potency and antiviral activities. Some of the compounds have shown good oral bioavailability and half-life in rats. The synthesis of benzothiazole derivatives led us to explore other heterocycles. During the course of our studies, we also developed an efficient synthesis of benzothiazole-6-sulfonic acid via a two-step procedure starting from sulfanilamide.

Full text of DOI:10.1016/j.bmc.2003.07.001

Bioorganic & Medicinal Chemistry 11 (2003) 4769–4777
Discovery of Novel Benzothiazolesulfonamides as
Potent Inhibitors of HIV-1 Protease
Srinivasan R. Nagarajan,a,* Gary A. De Crescenzo,a Daniel P. Getman,a
Hwang-Fun Lu,a James A. Sikorski,a,y Jeffrey L. Walker,a Joseph J. McDonald,a
Kathryn A. Houseman,b Geralyn P. Kocan,b Nandini Kishore,a Pramod P. Mehta,a
Christie L. Funkes-Shippya and Lisa Blystonea
aPfizer Global Research and Development, Pfizer Inc., 700 Chesterfield Parkway West, Chesterfield, MO 63017, USA
bPfizer Global Research and Development, Pfizer Inc., 4901 Searle Parkway, Skokie, IL 60077, USA
Received 31 May 2003; revised 24 July 2003; accepted 25 July 2003
Abstract—The human immunodeficiency virus (HIV) has been shown to be the causative agent for AIDS. The HIV virus encodes
for a unique aspartyl protease that is essential for the production of enzymes and proteins in the final stages of maturation. Protease
inhibitors have been useful in combating the disease. The inhibitors incorporate a variety of isosteres including the hydroxy-
ethylurea at the protease cleavage site. We have shown that the replacement of t-butylurea moiety by benzothiazolesulfonamide
provided inhibitors with improved potency and antiviral activities. Some of the compounds have shown good oral bioavail-
ability and half-life in rats. The synthesis of benzothiazole derivatives led us to explore other heterocycles. During the course of
our studies, we also developed an efficient synthesis of benzothiazole-6-sulfonic acid via a two-step procedure starting from
sulfanilamide.
# 2003 Elsevier Ltd. All rights reserved.
Introduction
and others are at various stages of clinical trials (Tipra-
navir,8c KNI-272,8d Mozenavir,8e and Atazanavir,8f).
The use of protease drugs in combination with other
anti-viral drugs has greatly diminished mortality due to
AIDS in developed countries, although in many parts of
the world the spread of the disease continues unabated.
The human immunodeficiency virus type-1 (HIV-1) has
been shown to be the causative agent for the disease
Acquired Immune Deficiency Syndrome (AIDS). The
HIV-1 virus encodes for a unique aspartyl protease, and
the protease is essential for cleavage of the viral gag and
gag/pol poly peptide precursors into individual enzymes
and proteins during the final stages of maturation.1
Inactivation of this enzyme has been shown to result in
the production of non-infectious virons.2 Therefore, the
HIV-1 protease represents an attractive target for the
design of therapeutic agents for the treatment of AIDS.3
In an effort to combat this epidemic, many protease inhi-
bitors have been discovered which arrest the replication of
the virus. Some of the protease inhibitors have been
approved for clinical use (Indinavir,4 Nelfinavir,5 Rito-
navir,6 Saquinavir,7 and Amprenavir,8a Lopinavir8b),
Potent inhibitors of HIV-1 protease incorporating a
variety of isosteres at the cleavage site have been repor-
ted.9 Efforts in our laboratories led to the discovery of
several protease inhibitors containing the hydroxy-
ethylurea isosteres.10a The t-butyl urea 1 (Z=carbo-
benzyloxy, IC50=112 nM) was one of the key inhibitors
identified based on the hydroxyethylurea isoster. In
order to identify new classes of compounds with better
inhibitory activity and pharmacokinetic properties, we
chose to modify the functional groups in the inhibitor
and then vary and optimize the moieties that are
attached to it. The t-butyl urea in 1 was replaced by a
sulfonamide group, followed by optimization of moi-
eties at P20 and P10 to give compound 2 (IC50=6 nM),
which was shown to be a better protease inhibitor.10b
Optimization of the phenyl group attached to the
sulfonamide moiety by varying the substitutions on the
*Corresponding author. Tel.:+1-636-247-7305; fax:+1-636-247-4362;
e-mail: srinivasan.nagarajan@pfizer.com
yCurrent address: AtheroGenics, Inc., 8995 Westside Parkway,
Alpharetta, GA 30004, USA.
0968-0896/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2003.07.001

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We then synthesized other isomers of benzothiazole to
identify the optimal position for the sulfonamide moi-
ety. The 3-aminobenzenesulfonamide 10, which was
synthesized as shown in Scheme 3, when subjected to
the above reaction with KSCN, afforded two isomers of
the 2-aminobenzothiazolesulfonamide 11 and 12. These
two isomers were easily separated by chromatography
and have been shown to be not very potent (IC50 for 11,
47 nM; 12, 1000 nM) compared to 7. Since only the
benzothiazole-6-sulfonamide analogue was potent, we
focused our efforts to optimize the groups (Z-replace-
ment) in 7 and 8 that would fit in the P2 position.
These derivatives fall into two broad categories: amides
and carbamates, both of which maintain the crucial car-
bonyl group for hydrogen bonding. The benzoic acids
chosen for the P2 position were those containing groups
in the 3-position that enhance hydrogen bond formation
(the 3-hydroxy and 3-amino toluic acids). The 3-
hydroxy-2-methylbenzoyl moiety has been successfully
employed in the design of Nelfinavir.5 The coupling of
3-hydroxy-2-methylbenzoic as well as 3-amino-2-
methylbenzoic acids with 6 was accomplished using
HOBT/EDC as shown in Scheme 4. The products have
potent enzyme activity (IC50’s for 22, 2 nM; 23, 3 nM)
and antiviral activity (EC50’s for 22, 14 nM; 23, 9 nM).
However, these compounds have no significant oral
bioavailability. We also synthesized simple o-toluamide
for comparison. The activity of this compound 24 (IC50,
3 nM; EC50, 12 nM) is surprisingly similar to that of 22
and 23 with no improvement in oral bioavailability,
indicating that the presence of either the hydroxy or the
amino groups in the 3-position does not provide a sig-
nificant advantage in activity in this class of compounds.
The sulfone moiety of methylsulfonylpropionic acid also
would enhance the hydrogen bond formation and the
corresponding amide was synthesized starting from
2(R)-methyl-3-methylsulfonylpropionic acid. The pro-
duct 25 was shown to be very potent (IC50, 2 nM, EC50,
84 nM), again with no improved oral bioavailability.
Scheme 1.
phenyl ring led to the discovery of a compound
containing p-aminophenylsulfonamide 3 (IC50=12 nM),
among other analogues (Scheme 1).
Results and Discussion
The p-aminophenyl group can be further modified to
incorporate fused heteroaromatic sulfonamides instead
of simple sulfonamides. The synthesis of benzothiazole-
sulfonamide was accomplished as described in Scheme
2. p-Nitrophenylsulfonyl chloride was reacted with 410b
to give the corresponding sulfonamide and the p-nitro
group was reduced with Pd/C to the p-amino com-
pound. The amino compound was then protected as the
BOC-derivative to afford 5 in very good yield. This
compound served as the key intermediate for the synth-
esis of benzothiazoles. The aminophenylsulfonamide 5
was then reacted with CuSO4/KSCN11 to afford 6. The
BOC-group was also removed under the reaction con-
ditions. The sulfonamide 6, obtained above was treated
with Z-OSuto afford the Z-derivative 7. The deamina-
tion of 7 was accomplished by treating it with isoamyl
nitrite in dioxane at 85 ꢀC to afford 8. Both 2-amino-
benzothiazole 7 (IC50, 2 nM; EC50, 15 nM) and the des-
amino analogue 8 (IC50, 3 nM) have been shown to be
very potent inhibitors of the enzyme HIV-1 protease
compared to 2 (6 nM).
We next wanted to compare the activity of these com-
pounds with the des-amino analogues. Isoamylnitrite
Scheme 2. Reagents and conditions: (a) p-nitrobenzenesulfonylchloride/NEt3; (b) Pd/C, H2; (c) BOC-ON; (d) CuSO4/KSCN, methanol, reflux;
(e) Z-OSu; (f) isoamylnitrite, dioxane, 85 ꢀC.

S. R. Nagarajan et al. / Bioorg. Med. Chem. 11 (2003) 4769–4777
4771
Scheme 3. Reagents and conditions: (a) Pd/C, H2; (b) Z-OSu; (c) CuSO4, KSCN, MeOH, reflux.
was used for the removal of the amino group as shown
in Scheme 4. Since the use of isoamylnitrite is not com-
patible with existing functionality in 22 and 23, a dif-
ferent procedure was used for the synthesis of 36 and 37
(Scheme 5). The aminobenzothiazole 6 was reacted with
BOC-ON to give the BOC-protected aminobenzothia-
zole. The amino group at the 2-position was then
removed using the technique described above, and the
BOC-protective group was removed with dioxane/HCl
to afford the desired des-amino compound 35 in very
good yield. This was used for coupling 3-hydroxy and 3-
amino-substituted toluic acids and 2(R)-methyl-3-
methylsulfonylpropionic acid to afford 36 (IC50, 2 nM;
EC50, 7 nM) and 37 (IC50, 6 nM; EC50, 21 nM) and 31
(IC50, 2 nM; EC50, 22 nM), respectively. Of these, only
31 showed oral bioavailability (22%). This is in sharp
contrast to 21 and 29 where the des-amino compound
(29) had no oral bioavailability compared to its 2-amino
analogue (21) with a bioavailability of 13% (Table 1).
The P2 moieties of carbamate analogues that were syn-
thesized have been shown to be high affinity ligands by
Table 1. Protease inhibitors and their IC50, antiviral activity and oral
bioavailability values
Compd
IC50 (nM)
EC50 (nM)
%BA in rat (@20 mpk)b
1
2
3
7
112
6
12
2
NDa
ND
ND
15
ND
102
ND
3
14
9
12
84
5
8
3
11
12
21
22
23
24
25
26
27
28
29
30
31
32
33
34
36
37
47
1000
2
13
2
3
3
2
4
3
2
4
4
2
4
5
4
2
6
11
8
3
4
42
13
22
11
9
9
7
21
22
28
20
5
aNot determined.
Scheme 4. Reagents and conditions: (a) R-COOH (13–17), EDC,
HOBt; (b) R-OH (18–20), DSC, pyridine; (c) isoamylnitrite, in diox-
ane, reflux.
bUnless indicated, the compounds did not show significant oral
bioavailability.

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S. R. Nagarajan et al. / Bioorg. Med. Chem. 11 (2003) 4769–4777
Scheme 5. Reagents and conditions: (a) BOC-ON; (b) isoamylnitrite/dioxane, 85 ꢀC; (c) dioxane/HCl; (d) R-COOH/EDC/HOBt.
Scheme 6. Reagents and conditions: (a) NH4SCN; (b) Br2/CHCl3; (c) isoamylnitrite, dioxane; (d) SOCl2/DMF, dichloroethane; (e) 4/N-methyl-
morpholine.
various research groups. The pyridyl, thiazolyl and
tetrahydrofuranyl moieties have been successfully used
in the synthesis of very potent inhibitors. The carbinols
were first activated with DSC and the activated carbi-
nols were then treated with the amine 6 to afford the
desired carbamate analogues (Scheme 4). The amino
group in the 2-position of benzothiazole moiety was
removed using isoamyl nitrite as described above.
mide (39) was treated with isoamylnitrite in DMF at
110 ꢀC, we obtained the benzothiazole-6-sulfonic acid in
very good yield (Scheme 6). The acid chloride was syn-
thesized by treatment with thionyl chloride in dichlor-
oethane. Treatment of the sulfonyl chloride with the
amine 4, afforded the desired sulfonamide 8 in very
good yield. The product is identical in all respects to the
one obtained by the route described in Scheme 3. This
route provides easy access to the desired sulfonamides
in fewer steps.
The new carbamate analogues synthesized are very
potent inhibitors of HIV-1 protease and are potently
antiviral (26, IC50, 4 nM, EC50, 5 nM; 27, IC50, 3 nM,
EC50, 3 nM; 28, IC50, 2 nM; EC50, 4 nM). In general,
the des-aminobenzothiazoles are slightly less potent
compared to the 2-amino isomers (32, IC50, 4 nM, EC50,
11 nM; 33, IC50, 5 nM, EC50, 9 nM; 34, IC50, 4 nM;
EC50, 9 nM). These carbamates, 32, 33 and 34 also
showed good oral bioavailability in rats compared to
their 2-amino analogues.
Conclusions
We have shown that the replacement of the urea moiety
by benzothiazolesulfonamide provided inhibitors of
HIV-1 protease with improved potency and antiviral
activities. Certain members of the class showed good
oral bioavailability in rats, most notably compounds 31,
32, and 33. The synthesis of benzothiazole derivatives
also led us to explore other heterocycles and the results
will be reported elsewhere. During the course of our
studies, we also developed a synthesis of benzothiazole-
6-sulfonic acid via a two-step procedure starting from
sulfanilamide 38.
During the course of this study, we also developed a
two-step synthesis of benzothiazole-6-sulfonic acid
starting from p-aminobenzenesulfonamide (38).
a
A
review of the literature indicated that simple
synthesis of a benzothiazole-6-sulfonic acid has not
been reported in the literature. The introduction of
sulfonic acid moiety on a pre-formed benzothiazole
proved to be difficult as it gave intractable products
or mixture of isomers. However, the synthesis of 2-
aminobenzothiazolesulfonamide is described in the lit-
erature.12 We envisioned the removal of the 2-amino
group using isoamylnitrite and then converting the sul-
fonamide to the desired benzothiazole-6-sulfonic acid.
Interestingly, when 2-aminobenzothiazole-6-sulfona-
Experimental
General
Unless otherwise stated, starting materials were
obtained from commercial sources and were used with-
out further purification. All reactions were performed in

S. R. Nagarajan et al. / Bioorg. Med. Chem. 11 (2003) 4769–4777
4773
anhydrous conditions in an atmosphere of nitrogen.
Nuclear magnetic resonance spectra were recorded on a
Varian XL-300 spectrometer and chemical shifts are
reported in ppm relative to TMS internal standard. Low
resolution mass spectra were recorded on a VG40-250T
instrument and the high resolution mass spectra were
recorded on a Finnigan MAT 90 spectrometer operat-
ing in the FAB mode. All final compounds were ana-
lyzed by analytical hplc (gradient 5–100% acetonitrile in
water containing 0.01% TFA) and peaks were mon-
itored both at 210 and 254 nM for purity. All final
compounds have been shown to be single peaks by
HPLC. Details of enzyme, and antiviral assay have been
provided in an earlier publication.10
solid. The solid was re-crystallized from hexane/ethyl
acetate. The crystalline solid was filtered and dried to
afford 5.7 g, (75%) of the product. H NMR (CDCl3) d
0.86 (2d, 6H, J=6.84 Hz), 1.94 (m, 1H), 2.8–3.2 (m,
6H), 3.6 (s, 1H), 3.9 (s, 2H), 5.05(s, 2H), 7.2–7.4 (m,
10H), 7.9, 8.3 (AB quartet, 4H). Anal. calcd for
C28H33N3O7S: Mr 556.2118. Found: Mr 556.2119
(M+H, HRFABMS).
1
3-S-(N-Butyloxyformamido)-[2R-hydroxy-1-[(4-amino-
phenylsulfonyl) (2 - methylpropyl)amino]-4-phenylbutane
(5). Palladium/C (6.0 g, 10%) was added to a solution
of 5a (8.0 g, 14.41 mmol) in ethyl acetate (100 mL) and
the mixture was subjected to hydrogenolysis. The cata-
lyst was filtered off and the filtrate was concentrated to
afford 5.30 g (70%) of the desired product 5b as a solid.
1H NMR (CD3OD) d (2d, 6H, J=6.8 Hz), 1.94 (m,
1H), 2.51 (dd, 1H, J=9.7, 9 Hz), 2.80–3.1 (m, 5H), 3.75
(m, 1H), 6.69, 7.48 (AB quartet, 4H, J=8.7 Hz), 7.18–
7.32 (m, 5H). A mixture of (3.7 g 9.45 mmol) and BOC-
ON (2.33 g, 9.45 mmol) and triethylamine (0.954 g, 9.45
mmol) in tetrahydrofuran (60 mL) was stirred for 16 h
and concentrated in vacuo. The residue was dissolved in
dichloromethane (200 mL), washed with sodium
hydroxide (1 N, 100 mL), citric acid (5%, 100 mL),
dried (MgSO4), and concentrated to afford 1.18 g (94%)
Animal pharmacokinetic studies
Under metofane anesthesia, the femoral artery (all eight
rats) and femoral vein (only four of eight rats) were
isolated and canulated with PE50 tubing and secured
with 3.0 silk sutures. The procedure required two
catheters, with the venous line being used for infusion of
compound (in the group of rats that received compound
iv), and the arterial line being used for collection of
blood samples. The rats were then placed in restraining
cages, which allow minimal movement and allowed to
recover from anesthesia for approximately 30 min. At
time 0, blood samples (400 mL) were collected from
arterial cannula. One group of rats (four rats per group)
received compound via the oral route (18G, 3-inch
curved gavage needle) at a dosing volume of 2 mL/kg
(10 mg/mL, dissolved in 0.5% methyl-cellulose, 0.1%
Tween 20), while the other group of rats received com-
pound via the intravenous cannula, at a dosing volume
of 2 mL/kg (10 mg/kg, dissolved in 10% EtOH, 50%
PEG 400, 40% saline). The blood samples were col-
lected from the arterial cannula at 15, 30, 60, 120, 240,
and 360 min with an additional 3- min sample being
collected from iv group. After each sample, the cannulas
were flushed with PBS containing 10-units/mL heparin.
At 6 h, the animals were terminated with excess of
anesthesia or by CO2 asphyxiation. The plasma was
obtained by immediate centrifugation and kept frozen
(ꢁ20 ꢀC) until analyzed. Plasma proteins were pre-
cipitated with acetonitrile and subjected to centrifuga-
tion. The supernatant containing compound was
evaporated under nitrogen and reconstituted in DMSO.
To ensure complete extraction, a standard compound at
various concentrations was mixed with control rat
plasma and extracted. The concentration of the inhi-
bitor present in the plasma was determined using the
protease enzyme (assay described above).
1
of the product as a white solid. H NMR (CD3OD) d
(0.87, 0.90, 2d, 6H, J=6.84 Hz), 1.15 and 1.28 (2S, 9H),
1.98 (m, 1H), 2.5–3.2 (m, 6H), 3.6–3.8 (m, 2H), 6.69,
7.48 (AB quartet, 4H, J=8.7 Hz), 7.18–7.23 (m, 5H).
Anal. calcd for C25H37N3SO5: Mr 492.2532. Found: Mr
492.2546 (M+H, HRFABMS).
3-S-Amino-2R-hydroxy-1-[(2-aminobenzothiazol-6-sulfo-
nyl) (2 - methylpropyl)amino]-4-phenylbutane (6). Pow-
dered 5 (37.8 g, 76.9 mmol) was added to a mixture of
anhydrous copper sulfate (151.0 g) and potassium thio-
cyanate (189.1 g) followed by dry methanol (1.1 L) and
the resulting black-brown suspension was stirred with a
mechanical stirrer and was heated at reflux for 2 h. The
reaction mixture turned gray. The reaction mixture was
filtered and the filtrate was diluted with water (1.6 L)
and heated at reflux. Ethanol was added to the reaction
mixture, cooled and filtered. The filtrate was con-
centrated and was diluted with water (1L) then was
made basic with ammonium hydroxide. The basic reac-
tion mixture was then extracted with ethyl acetate (5ꢂ1
L). The organic layer was successively washed with
ammonium chloride (saturated, 2ꢂ500 mL), brine (500
mL), dried (MgSO4) and was concentrated to afford
32.2 g (93%) of the compound as a solid. 1H NMR
(CD3OD) d 0.85, 0.88 (2d, 6H, J=6.7 Hz), 1.96 (m,
1H), 2.54 (m, 1H), 2.89–3.15 (m, 5H), 3.38–3.44 (m,
1H), 3.72–3.77 (m, 1H), 7.18–7.32 (m, 5H), 7.50 (d, 8.5
Hz), 7.68 (dd, 1H, J=8.5 and 2 Hz), 8.08 (d, 1H, J=1.8
Hz). Anal. calcd for C21H28N4O3S2: Mr 449.1681.
Found: Mr 449.1664 (M+H, HRFABMS).
3-S-(N-Benzyloxyformamido)-[2R-hydroxy-1-[(2-methyl-
propyl)(4 - nitrophenylsulfonyl)amino] - 4-phenylbutane
(5a). Small portions of p-nitrobenzenesulfonyl chloride
(3.295 g, 14.865 mmol) were added to a solution of 4
(5.0 g, 13.514 mmol) and triethylamine (4.09 g, 40.54
mmol) in dichloromethane at 0–5 ꢀC for 30 min and at
rt for 1 h. The reaction mixture was diluted with di-
chloromethane (200 mL), washed with citric acid (5%,
200 mL), sodium bicarbonate (200 mL, saturated), brine
(200 mL), dried (MgSO4) and concentrated to afford a
3-S-(N-Benzyloxyformamido)-2R-hydroxy-1-[(2-amino-
benzothiazol-6-sulfonyl) (2-methylpropyl)amino]-4-phe-
nylbutane (7). A mixture of 6 (0.229 g, 0.5094 mmol)
and Z-OSu(0.127 g, 0.5054 mmol), and triethylamine
(0.4 mL) in dimethylformamide (5 mL) was stirred at

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S. R. Nagarajan et al. / Bioorg. Med. Chem. 11 (2003) 4769–4777
room temperature for 18 h. The reaction mixture was
concentrated and the residue was dissolved in dichloro-
methane (100 mL). The dichloromethane solution was
washed with sodium hydroxide (1N, 100 mL), citric acid
(5%, 100 mL) dried (Mg SO4) and concentrated to
afford a residue, which was recrystallized from ethyl
acetate/hexane to afford 0.16 g (54%) of the product as
3-S-{N-2-(2,6-Dimethylphenoxymethylcarboxamido)}-2R-
hydroxy-1-[(2-aminobenzothiazol-6-sulfonyl) (2-methyl-
propyl)amino]-4-phenylbutane (21). A mixture of 2-(2,6-
dimethylphenoxy)acetic acid (0.408 g, 2.27 mmol),
HOBt (0.307 g, 2.27 mmol), and EDC (0.435 g, 2.27
mmol) in dimethylformamide (20 mL) was stirred at rt
for 1 h. Then 6 (1.02 g, 2.27 mmol) was added and the
reaction mixture was stirred for 18 h. The solvent was
removed in vacuo and the residue was dissolved in di-
chloromethane (100 mL), washed with citric acid (5%,
100 mL), sodium bicarbonate (saturated, 100 mL), brine
(100 mL), dried and concentrated. The residue obtained
was purified by chromatography (20% hexane in ethyl
acetate) to afford 0.520 g (38%) of the product. 1H
NMR (CD3OD) d 0.88 and 0.93 (2d, 6H, J=6.6 Hz),
2.06 (m, 1H), 2.13 (s, 6H), 2.75–3.53 (m, 6H), 3.89 (m,
1H), 3.94–4.52 (m, 3H), 6.88–6.99 (m, 3H), 7.15–7.29
(m, 5H), 7.45 (d, 1H, J=8.5 Hz), 7.70 (dd, 1H, J=2, 8.6
Hz), 8.09 (d, 1H, J=2 Hz). Anal. calcd for
C31H38N4O5S2: Mr 610.2362. Found: Mr 611.2367
(M+H, HRFABMS).
1
a solid. H NMR (CD3OD) d 0.85,0.89 (2d, 6H, J=6.6
Hz), 1.98 (m, 1H), 2.61 (m, 1H), 2.84 (m, 5H), 3.71–3.82
(m, 2H), 4.93 (q, 2H, J=4 Hz), 6.98 (m, 1H), 7.14–7.24
(m, 10H), 7.44 (d, 1H, J=8.7 Hz), 7.67 (dd, 1H, J=8.7
and 1.8 Hz), 8.06 (d, 1H, J=1.6 Hz). Anal. calcd for
C29H34N4O5S2: Mr 582.2049. Found: Mr 583.2026
(M+H, HRFABMS).
3-S-(N-Benzyloxyformamido)-2R-hydroxy-1-[(benzothia-
zol - 6 - sulfonyl) (2 - methylpropyl)amino]-4-phenylbutane
(8). Isoamylnitrite (70 mL) was added to a solution of
7 (0.15 g) in dioxane (3 mL) and the mixture was
heated at 85 ꢀC. After the cessation of evolution of
nitrogen, the reaction mixture was concentrated and
the residue was purified by chromatography (hexane–
ethyl acetate 5:3) to afford 0.90 g (53%) of the product
3-S–{N-(3-Hydroxy-2-methylphenylcarboxamido)}-[2R-
hydroxy-1-[(2-aminobenzothiazole-6-sulfonyl)-(2-methyl-
propyl)amino]-4-phenylbutane (22). This compound was
obtained using the procedure described above for com-
pound 21 and replacing the acid with 2-methyl-3-
hydroxybenzoic acid to afford the product. Yield: 60%.
1H NMR (CD3OD) d 0.89, 0.94 (2d, 6H, J=6.6 Hz),
1.77 (s, 3H), 2.06 (m, 1H), 2.64 (m, 1H), 2.92–3.57 (m,
4H), 3.88 (m, 1H), 4.26 (m, 1H), 6.49 (dd, 1H, J=0.6,
7.5 Hz), 6.74 (dd, 1H, J=0.6, 7.5 Hz), 6.93 (t, 1H,
J=7.9 Hz), 7.17–7.27 (m, 5H), 7.45 (d, 1H, J=8.7 Hz),
7.70 (dd, 1H, J=8.6, 2.0 Hz), 8.10 (d, 1H, J=1.8 Hz).
Anal. calcd for C29H34N4O5S2: Mr 582.2049. Found: Mr
583.2012 (M+H, HRFABMS).
1
as a solid. H NMR (CD3OD) d 0.84, 0.88 (2d, 6H,
J=6.6 Hz), 1.99 (m, 1H), 2.59 (m, 1H), 2.91–3.48 (m,
5H), 3.77–3.83 (m, 2H), 4.92 (m, 2H), 7.13–7.25 (m,
10H), 7.94 (dd, 1H, J=1.6, 8.7 Hz), 8.16 (d, 1H,
J=8.7 Hz), 8.59 (d, 1H, J=1.6 Hz), 9.41 (s, 1H). Anal.
calcd for C29H33N3O5S2: Mr 567.1940. Found: Mr
568.1933 (M+H, HRFABMS).
3-S-(N-Benzyloxyformamido)-2R-hydroxy-1-[(2-amino-
benzothiazol-5-sulfonyl) (2-methylpropyl)amino]-4-phe-
nylbutane (11) and 3-S-(N-benzyloxyformamido)-2R-
hydroxy-1-[(2-aminobenzothiazol-7-sulfonyl) (2-methyl-
propyl)amino]-4-phenylbutane (12). The amine 10 (syn-
thesized as described for 5, starting from 4 and m-
nitrobenzenesulfonyl chloride) (0.36 g, 0.685 mmol) was
added to a well mixed powder of anhydrous copper
sulfate (1.44 g) and potassium thiocyanate (1.80 g) fol-
lowed by dry methanol (10 mL) and the resulting black-
brown suspension was heated at reflux for 2 h. The
reaction mixture turned gray. The reaction mixture was
filtered and the filtrate was diluted with water (5 mL)
and heated at reflux. Ethanol was added to the reaction
mixture, cooled and filtered. The filtrate upon concen-
tration afforded a residue which was purified by chro-
matography (ethyl acetate–hexane 1:1) to afford 0.18 g
(45%) of the 7-isomer (12) as a solid. 1H NMR
(CD3OD) d 0.81 (2d, 6H, J=7.05 Hz), 1.96 (m, 1H),
2.58 (m, 1H), 3.07–3.3 (m, 4H), 3.58–3.81 (m, 3H), 4.94
(q, 2H, J=3.6 Hz), 6.87 (dd, 1H, J=8.6 and 2.6 Hz),
7.12–7.32 (m, 11H), 7.52 (d, 1H, 8.66 Hz). Anal. calcd
for C29H34N4O5S2: Mr 582.2049. Found: Mr 583.2034
(M+H, HRFABMS). Further elution of the column
with (ethyl acetate–hexane 3:2) afforded 0.80 g (20%)
afforded the 5-isomer (11) as a solid. 1H NMR
(CD3OD) d 0.87 (m, 6H), 1.96 (m, 1H), 2.58 (m, 1H),
2.89–3.45 (m, 5H), 3.68–3.89 (m, 2H), 4.92 (q, 2H,
J=3.6 Hz), 7.46 (dd, 1H, J=8.4,1.7 Hz), 7.12–7.23 (m,
11H), 7.68 (d, 1H, J=8.5 Hz), 7.78 (d, 1H, J=1.4 Hz).
Anal. calcd for C29H34N4O5S2: Mr 582.2049. Found: Mr
583.2034 (M+H, HRFABMS).
3-S-{N-(3-Amino-2-methylphenylcarboxamido)} - [2R -
hydroxy-1-[(2-aminobenzothiazole-6-sulfonyl)-(2-methyl-
propyl)amino]-4-phenylbutane (23). This compound was
obtained employing the above procedure described for
compound 21 and using 2-methyl-3-aminobenzoic acid
1
to afford the product. Yield: 60%. H NMR (CD3OD)
d 0.89, 0.94 (2d, 6H, J=6.6 Hz), 1.71 (s, 3H), 2.01 (m,
1H), 2.63 (m, 1H), 2.92–3.16 (m, 3H), 3.54 (m, 1H), 3.88
(m, 1H), 4.27 (m, 1H), 6.38 (dd, 1H, J=0.8, 7.4 Hz),
6.71 (dd, 1H, J=0.8, 7.4 Hz), 6.89 (t, 1H, J=7.8 Hz),
7.16–7.28 (m, 5H), 7.45 (d, 1H, J=8.5 Hz), 7.70 (dd,
1H, J=2, 8.6 Hz), 8.10 (d, 1.8 Hz). Anal. calcd for
C29H35N5O4S2: Mr 581.2209. Found: Mr 582.2199
(M+H, HRFABMS).
3-S-{N-(2-Methylphenylcarboxamido)}-[2R-hydroxy-1-
[(2 - aminobenzothiazole - 6 - sulfonyl)-(2-methylpropyl)-
amino]-4-phenylbutane (24). This compound was
obtained using the above procedure described for
compound 21 and replacing the acid with 2-methyl-
benzoic acid to afford the product. Yield: 60%.
1H NMR (CD3OD) d 0.88, 0.94 (2d, 6H, J=6.6 Hz),
1.95 (s, 3H), 2.07 (m, 1H), 2.66 (m, 1H), 2.92–3.59 (m,
4H), 3.91 (m, 1H), 4.29 (m, 1H), 6.99–7.28 (m, 9H),
7.44 (d, 1H, J=8,5 Hz), 7.69 (dd, 1H, J=1.8, 8.4 Hz),
8.09 (d, 1H, J=1.8 Hz). Anal. calcd for

S. R. Nagarajan et al. / Bioorg. Med. Chem. 11 (2003) 4769–4777
4775
C29H34N4O4S2: Mr 566.2100. Found: Mr 567.2053
(M+H, HRFABMS).
(m, 1H), 2.10 (s, 6H), 2.75–4.28 (m, 11H), 6.86–6.95 (m,
3H), 7.14–7.27 (m, 5H), 7.97 (dd, 1H, J=1.8, 8.6 Hz),
8.18 (d, 1H, J=8.6 Hz), 8.62 (d, 1H, J=1.6 Hz), 9.4 (s,
1H). Anal. calcd for C31H37N3O5S2: Mr 595.2253.
Found: Mr 596.2245 (M+H, HRFABMS).
3-S-(N-5-Thiazolylmethyloxyformamido)-2R-hydroxy-1-
[(2 - aminobenzothiazole - 6 - sulfonyl)(2 - methylpropyl)-
amino] - 4 - phenylbutane (27). Pyridine (0.198 g, 7.5
mmol) was added to a solution of thiazole-5-carbinol
(0.2875 g, 2.5 mmol) in acetonitrile (12 mL) followed by
DSC (0.640 g, 2.5 mmol). After 30 min, the reaction
mixture became clear and the 3-S-amino-2R-hydroxy-1-
[(2-aminobenzothiazole-6-sulfonyl)-(2-methylpropyl)a-
mino]-4-phenylbutane (1.12 g, 2.5 mmol) was added and
the reaction mixture was stirred at rt for 16 h. The
reaction mixture was concentrated and the residue was
dissolved in dichloromethane (100 mL), washed with
sodium hydroxide (25 mL), brine (25 mL), dried
(MgSO4) and concentrated. The residue obtained was
purified by chromatography (16% hexane in ethyl ace-
tate) to afford the 0.90 g (61%) of the product. 1H
NMR (CD3OD) d 0.84, 0.88 (2d, 6H, J=6.6 Hz), 1.97
(m, 1H), 2.53–3.40 (m, 6H), 3.71–3.83 (m, 2H), 5.14 (s,
2H), 7.08–7.16 (m, 5H), 7.45 (d, 1H, J=8.5 Hz), 7.67
(dd, 1H, J=1.8, 8.6 Hz), 7.74 (s, 1H), 8.07 (d, 1H,
J=1.8 Hz), 8.87 (s, 1H). Anal. calcd for C26H31N5O5S3:
Mr 589.1566. Found: Mr 590.1580 (M+H,
HRFABMS).
3-S-{N-(2-Methylphenylcarboxamido)}-[2R-hydroxy-1-
[(2 - aminobenzothiazole-6-sulfonyl)-(2-methylpropyl)a-
mino]-4-phenylbutane (30). Starting with the amino-
benzothiazole 24 and using the procedure described
above for 29, the product 30 was obtained. Yield: 59%.
1H NMR (CD3OD) d 0.88, 0.94 (2d, 6H, J=6.6 Hz),
1.94 (s, 3H), 2.08 (m, 1H), 2.65 (m, 1H), 2.99–3.65 (m,
4H), 3.89 (m, 1H), 4.28 (m, 1H), 6.99–7.27 (m, 9H), 7.98
(dd, 1H, J=1.8, 8.4 Hz), 8.19 (d, 1H, J=8.5 Hz), 8.64
(d, 1H, J=1.8 Hz) 9.44 (s, 1H). Anal. calcd for
C29H33N3O4S2: Mr 551.1991. Found: Mr 552.1995
(M+H, HRFABMS).
3-S-(N-5-Thiazolylmethyloxyformamido)-[2R-hydroxy-1-
[(benzothiazole-6-sulfonyl) (2-methylpropyl)amino]-4-phe-
nylbutane (33). Using the procedure described above for
29 and starting with the aminobenzothiazole 27, the
1
product was obtained. Yield: 93%. H NMR (CD3OD)
d 0.85, 0.89 (2d, 6H, J=6.6 Hz), 1.99 (m, 1H), 2.56 (m,
1H), 2.92–3.45 (m, 4H), 3.67–3.82 (m, 2H), 5.15 (s, 2H),
7.09–6.17 (m, 5H), 7.75 (s, 1H), 7.95 (dd, 1H, J=1.8,
8.6 Hz), 8.20 (d, 1H, J=8.7 Hz), 8.61 (s, 1H, J=1.6
Hz), 8.88 (s, 1H), 9.45 (s, 1H). Anal. calcd for
C26H30N4O5S3: Mr 547.1457. Found: Mr 575.1460
(M+H, HRFABMS).
3-S-(N-3-Pyridylmethyloxyformamido)-2R - hydroxy - 1 -
[(2 - aminobenzothiazole - 6 - sulfonyl) (2 - methylpropyl)a-
mino]-4-phenylbutane (26). Obtained using the proce-
dure described for 27 above and pyridine-3-carbinol
instead of thiazole-5-carbinol to afford the product.
1
Yield: 68%. H NMR (CD3OD) d 0.84, 0.89 (2d, 6H,
3-S-(N-3-Pyridylmethyloxyformamido) - 2R - hydroxy - 1 -
[(benzothiazole-6-sulfonyl)(2-methylpropyl)amino]-4-phe-
nylbutane (32). Starting with the aminobenzothiazole
26 and using the procedure described above for 29, the
product was obtained in 58% yield. 1H NMR (CD3OD)
d 0.84, 0.89 (2d, 6H, J=0.4 Hz), 1.99 (m, 1H), 2.58 (m,
1H), 2.96–3.51 (m, 5H), 3.72–3.84 (m, 2H), 4.98 (q, 2H,
J=13 Hz), 7.08–7.18 (m, 5H), 7.31 (m, 1H), 7.59 (d, 1H,
J=7.9 Hz), 7.95 (dd, 1H, J=6.8, 8.6 Hz), 8.18 (d, 1H,
J=8.7 Hz), 8.41 (s, 1H), 8.60 (d, 1H, J=1.6 Hz), 9.42 (s,
1H). Anal. calcd for C28H32N4O5S2: Mr 568.1892.
Found: Mr 569.1894 (M+H, HRFABMS).
J=6.45 Hz), 1.98 (m, 1H), 2.59 (m, 1H), 2.84–3.45 (m,
5H), 3.71–3.85 (m, 2H), 4.98 (q, 1H, J=13 Hz), 7.10–
7.18 (m, 5H), 7.31 (t, 1H, J=5 Hz), 7.44 (d, 1H, J=8.5
Hz), 7.58 (d, 1H, J=7,9 Hz), 7.67 (dd, 1H, J=1.8, 8.4
Hz), 8.07 (dd, 1H, J=1.8 Hz), 8.40 (s, 1H). Anal. calcd
for C28H33N5O5S2: Mr 583.2001. Found: Mr 584.2012
(M+H, HRFABMS).
3-S-(N-3-Tetrahydrofuranyloxyformamido)-2R-hydroxy-
1-[(2-aminobenzothiazole-6-sulfonyl) (2-methylpropyl)a-
mino]-4-phenylbutane (28). This compound was synthe-
sized using the procedure above for 27 and 3-
hydroxytetrahydrofuran to afford the product. Yield:
3-S-(N-3-Tetrahydrofuranyloxyformamido)-2R-hydroxy-
1-[(benzothiazole-6-sulfonyl) (2-methylpropyl)amino]-4-
phenylbutane (34). Starting with the aminobenzothia-
zole 28 and using the procedure described above for 29,
the desired product was obtained in 89% yield. 1H
NMR (CD3OD) d 0.85, 0.90, (2d, 6H, J=6.6 Hz), 1.86–
2.09 (m, 3H), 2.56 (m, 1H), 2.92–3.88 (m, 13H), 4.98 (m,
1H), 7.11–7.20 (m, 5H), 7.96 (dd, 1H, J=1.8, 8.7 Hz),
8.19 (d, 1H, J=8.7 Hz), 8.61 (d, 1H, J=1.8 Hz), 9.42 (s,
1H). Anal. calcd for C26H33N3O6S2: Mr 547.1889.
Found: Mr 548.1869 (M+H, HRFABMS).
1
50%. H NMR (CD3OD) d 0.87, 0.92 (2d, 6H, J=6.6
Hz), 1.98–2.06 (m, 3H), 2.56 (m, 1H), 2.87–3.82 (m,
13H), 4.98 (m, 1H), 7.14–7.22 (m, 5H), 7.46 (d, 1H,
8.7 Hz), 7.68 (dd, 1H, J=1.8, 8.4 Hz), 8.08 (d, 1H,
J=1.6 Hz). Anal. calcd for C26H34N4O6S: Mr
562.1998. Found: Mr 563.2014 (M+H, HRFABMS).
3-S-{N-2-(2,6-Dimethylphenoxymethylformamido)} - 2R -
hydroxy-1-[(2-benzothiazol-6-sulfonyl) (2-methylpropy-
l)amino]-4-phenylbutane (29). Isoamylnitrite (0.149 mL,
1.11 mmol) was added to a solution of the amino-
benzothiazole (0.34 g, 0.557 mmol) in refluxing dioxane
(5 mL). After the evolution of nitrogen had ceased (1 h),
the reaction mixture was concentrated in vacuo and the
residue was purified by chromatography (ethyl acetate–
3-S-(N-t-Butyloxyformamido)-2R-hydroxy-1-[(2-amino-
benzothiazol-6-sulfonyl) (2-methylpropyl)amino]-4-phe-
nylbutane (42). The amino compound 6 (32.2 g, 71.63
mmol), BOC-ON (17.7 g, 71.63 mmol), and triethyl-
amine (7.219 g, 71.63 mmol) in tetrahydrofuran (330
mL) were stirred at room temperature for 18 h. The
1
hexane, 1:1) to afford 0.21 g (64%) of the product. H
NMR (CD3OD) d 0.86, 0.91 (2d, 6H, J=6.6 Hz), 2.05

4776
S. R. Nagarajan et al. / Bioorg. Med. Chem. 11 (2003) 4769–4777
reaction mixture was concentrated and the residue was
dissolved in dichloromethane (1 L). The dichloro-
methane solution was washed with sodium hydroxide (1
N, 500 mL), citric acid (5%, 500 mL) dried (Mg SO4)
and concentrated to afford a residue, which was recrys-
tallized from ethyl acetate–hexane to afford 30.0 g
esis of 21 was used for the coupling of 35 and 2(R)
methyl-3-sulfonyl)propionic acid to afford the product.
Yield: 43%. H NMR (CD3OD) d 0.85, 0.90 (2d, 6H,
J=6.6 Hz), 1.15 (d, 3H, J=6.6 Hz), 2.03 (m, 1H), 2.44
(s, 3H), 2.65 (m, 2H), 2.81–3.51 (m, 9H), 3.82 (m, 1H),
4.06 (m, 1H), 7.14–7.25 (m, 5H), 7.97 (dd, 1H, J=1.8,
8.6 Hz), 8.21 (d, 1H, J=8.6 Hz), 8.63 (d, 1H, J=1.8
Hz), 9.45 (s, 1H). Anal. calcd for C26H35N3O6S3: Mr
582.1766. Found: Mr 582.1744 (M+H, HRFABMS).
1
1
(75%) of the product as a solid. H NMR (CD3OD) d
0.88, 0.92 (2d, 6H, J=6.6 Hz), 1.28 (s, 9H), 2.04 (m,
1H), 2.56 (m, 1H), 2.88–3.43 (m, 4H, 3.60–3.76 (m, 2H),
7.14–7.23 (m, 5H), 7.46 (d. 1H, J=8.5 Hz), 7.69 (dd,
1H, 1.8, 8.6 Hz), 8.08 (d, 1H, J=1.8 Hz). Anal. calcd
for C26H36N4O5S2: Mr 549.2205. Found: Mr 549.2173.
Benzothiazole-6-sulfonic acid (40). A suspension of 2-
amino-6-sulfonamido benzothiazole (Prepared as repor-
ted in the literature,12 10.0 g, 43.67 mmol) in dioxane
(300 mL) was heated at reflux. Isoamylnitrite (24 mL)
was added in two portions to the reaction mixture. Vig-
orous evolution of gas was observed (the reaction was
conducted behind a blast shield as a precaution) and
after 2 h, a red precipitate was deposited in the reaction
vessel. The reaction mixture was filtered hot, and the
solid was washed with dioxane and was dried. The solid
was recrystallized from methanol-water. Only small
amount of a solid was formed after 2 days. This pre-
cipitate was filtered off and the mother liquor was con-
centrated in vacuo to afford pale red-orange solid (8.0 g,
2R-Hydroxy-1-[(benzothiazol-6-sulfonyl) (2-methylpro-
pyl)amino]-4-phenylbutane (35). Portions of 42 (25.0 g,
45.49 mmol) were added to a solution of isoamylnitrite
(12.35 mL) in dioxane (300 mL) and the mixture was
heated at 85 ꢀC. After the cessation of evolution of
nitrogen, the reaction mixture was concentrated and the
residue was purified by chromatography (hexane–ethyl
acetate 1:1) to afford 20.5 g (84%) of the product as a
solid. The crude product from the above reaction mix-
ture (11.8 g, 22.07 mmol) was added dioxane–HCl (4 N,
40 mL) and was stirred at room temperature for 2 h and
concentrated. Excess HCl was chased with toluene to
afford 11.0 g (quantitative yield) of the desired product.
1H NMR (CD3OD) d 0.83, 0.92 (2d, 6H, J=6.6 Hz),
1.95 (m, 1H), 2.84–3.29 (m, 4H), 3.50–3.74 (m, 2H), 4.16
(m, 1H), 7.29–7.39 (m, 5H), 7.96 (dd, 1H, J=1.8, 8.6
Hz), 8.24 (d, 1H, J=8.7 Hz), 8.64 (d, 1H, J=1.6 Hz),
9.50 (s, 1H). Anal. calcd for C21H27N3O3S2: Mr
435.1650. Found: Mr 435.1641 (M+H, HRFABMS).
1
85%). H NMR (CD3OD) d 7.87 (dd, 1H, J=1.4, 8.4
Hz), 7.99 (d, 1H, J=8.5 Hz), 8.41 (d, 1H, J=1.6 Hz),
9.34 (s, 1H). Anal. calcd for C7H5NO3S2: Mr 215.9789.
Found: Mr 215.9790 (M+H, HRFABMS).
3-S-(N-Benzyloxyformamido)-2R-hydroxy-1-[(2-amino-
benzothiazol-6-sulfonyl) (2-methylpropyl)amino]-4-phe-
nylbutane (8). Thionyl chloride (4 mL) was added to a
suspension of the benzothiazole-6-sulfonic acid (0.60 g,
2.79 mmol) in dichloroethane (15 mL) and the reaction
mixture was heated at reflux. The sulfonic acid did not
dissolve in the reaction mixture. Addition of dimethyl-
formamide (5 mL) to the reaction mixture resulted in a
clear solution. After 1.5 h at reflux, the solvent was
removed in vacuo and excess HCl and thionyl chloride
was chased by evaporation with dichloroethane. The
residue in ethyl acetate (100 mL) was added the Z-
amino alcohol 4 (1.03 g, 2.78 mmol) followed by N-
methylmorpholine (4 mL). After stirring at room tem-
perature for 18 h, the reaction mixture was diluted with
ethyl acetate (100 mL), washed with citric acid (5%, 100
mL), sodium bicarbonate (saturated, 100 mL), and
brine (100 mL), dried (MgSO4) and concentrated. The
residue was purified by chromatography (silica gel, ethyl
acetate–hexane 1:1) to afford 0.340 g (23%) the product
3-S-{N-(3-Hydroxy-2-methylphenylamido)}-2R-hydroxy-
1-[(benzothiazole-6-sulfonyl)-(2-methylpropyl)amino]-4-
phenylbutane (36). The procedure for the synthesis of
21 was used for the coupling of 35 and 2-methyl-3-
hydroxybenzoic acid to afford the product. Yield: 81%.
1H NMR (CD3OD) d 0.87, 0.91 (2d, 6H, J=6.6 Hz), 1.76
(s, 3H), 2.08 (m, 1H), 2.66 (m, 1H), 2.99–3.64 (m, 5H),
3.89 (m, 1H), 4.28 (m, 1H), 6.49 (d, 1H, J=7.3 Hz), 6.74
(d, 1H, J=7.5 Hz), 6.92 (t, 1H, J=7.9 Hz), 7.17–7.26 (m,
5H), 7.98 (d, 1H, J=8.7 Hz), 8.18 (d, 1H, J=8.7 Hz),
8.62 (s, 1H) 9.41 (s, 1H). Anal. calcd for C29H33N3O5S2:
Mr 568.190. Found: Mr 568.1919 (M+H, HRFABMS).
3-S-{N-(3-Amino-2-methylphenylcarboxamido)} - [2R -
hydroxy-1-[(benzothiazole-6-sulfonyl)-(2-methylpropyl)a-
mino]-4-phenylbutane (37). The procedure for the synth-
esis of 21 was used for the coupling of 35 and 2-methyl-
3-aminobenzoic acid to afford the product. Yield: 60%.
1H NMR (CD3OD) d 0.88, 0.94 (2d, 6H, J=6.6 Hz),
1.70 (s, 3H), 2.08 (m, 1H), 2.67 (m, 1H), 2.98–3.64 (m,
5H), 3.87 (m, 1H), 4.25 (m, 1H), 6.38 (d, 1H, J=6.9
Hz), 6.70 (d, 1H, J=7.5 Hz), 6.88 (t, 1H, J=7.9 Hz),
7.17–7.26 (m, 5H), 7.99 (dd, 1H, J=7.8, 1.8 Hz), 8.21
(d, 1H, J=8.7 Hz), 8.64 (d, 1H, J=1.6 Hz) 9.44 (s, 1H).
Anal. calcd for C29H34N4O4S2: Mr 567.2099. Found: Mr
567.2127 (M+H, HRFABMS).
in pure form. This product was identical (1H NMR, 13
C
NMR, mass spectrum, and HPLC) to an authentic
1
sample of 8. H NMR (CD3OD) d 0.84, 0.88 (2d, 6H,
J=6.6 Hz), 1.99 (m, 1H), 2.59 (m, 1H), 2.91–3.48 (m,
5H), 3.77–3.83 (m, 2H), 4.92 (m, 2H), 7.13–7.25 (m,
10H), 7.94 (dd, 1H, J=1.6, 8.7 Hz), 8.16 (d, 1H, J=8.7
Hz), 8.59 (d, 1H, J=1.6 Hz), 9.41 (s, 1H). Anal. calcd
for C29H33N3O5S2: Mr 567.1940. Found: Mr 568.1933
(M+H, HRFABMS).
References and Notes
3-S-[N-2-{2(R)methyl-3-methylsulfonyl}propionyl] - 2R -
hydroxy-1-[(2-benzothiazol-6-sulfonyl) (2-methylpropy-
l)amino]-4-phenylbutane. The procedure for the synth-
1. (a) Blundell, T. L.; Lapatto, R.; Wilderspin, A. F.; Hem-
mings, A. M.; Hobart, P. M.; Danley, D. E.; Whittle, P. J.

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Trends Biol. Sci. 1990, 15, 425. (b) Debouck, C.; Metcalf,
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Bacheler, L. T.; Rayner, M. M.; Klabe, R. M.; Shum, L.;
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