Structural optimization of cyclic sulfonamide based novel HIV-1 protease inhibitors to picomolar affinities guided by X-ray crystallographic analysis

Article abstract of DOI:10.1016/j.tet.2014.03.038

Synthesis and HIV-1 protease inhibitory activity of compound 5 based on the structure of a novel cyclic sulfonamide pharmacophore has been recently disclosed from our group. X-ray crystallographic structure of 5 when bound to the HIV-1 protease defined its binding mode. The importance of the geometry of the substitution at C4-Me (S configuration) was emphasized. In the present paper we wish to disclose the design of novel inhibitors 47 and 48 based on the X-ray structure of compound 5 bound to the HIV-1 protease, their synthesis and activity against HIV-1 protease. By making changes at the C4 position and the carbamate linkage the above compounds 47 and 48 were found to be approximately one hundred fold more active compared to 5 and their K_i values are in the picomolar range. An unusual observation regarding the activity and geometry was made with compounds 51 and 52. X-ray results demonstrate that 48 and 52 bind to the same binding pocket with simultaneous change in the conformation of the cyclic sulfonamide ring.

Full text of DOI:10.1016/j.tet.2014.03.038

Tetrahedron 70 (2014) 2894e2904
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Structural optimization of cyclic sulfonamide based novel HIV-1
protease inhibitors to picomolar affinities guided by X-ray
crystallographic analysis
,
a
a
a
Ashit K. Ganguly a , Sesha S. Alluri , Chih-Hung Wang , Alyssa Antropow ,
Alex White a, Danielle Caroccia a, Dipshikha Biswas a, Eunhee Kang a, Li-Kang Zhang b,
Steven S. Carroll c, Christine Burlein c, John Fayc, Peter Orth d, Corey Strickland d
*
a Department of Chemistry, Chemical Biology and Biomedical Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA
b Merck Research Laboratories, Analytical Chemistry, Kenilworth, NJ 07033, USA
c Merck Research Laboratories, In Vitro Science Department, West Point, PA 19486, USA
d Merck Research Laboratories, Structural Chemistry, Kenilworth, NJ 07033, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Synthesis and HIV-1 protease inhibitory activity of compound 5 based on the structure of a novel cyclic
sulfonamide pharmacophore has been recently disclosed from our group. X-ray crystallographic struc-
ture of 5 when bound to the HIV-1 protease defined its binding mode. The importance of the geometry of
the substitution at C4eMe (S configuration) was emphasized. In the present paper we wish to disclose
the design of novel inhibitors 47 and 48 based on the X-ray structure of compound 5 bound to the HIV-1
protease, their synthesis and activity against HIV-1 protease. By making changes at the C4 position and
the carbamate linkage the above compounds 47 and 48 were found to be approximately one hundred
fold more active compared to 5 and their Ki values are in the picomolar range. An unusual observation
regarding the activity and geometry was made with compounds 51 and 52. X-ray results demonstrate
that 48 and 52 bind to the same binding pocket with simultaneous change in the conformation of the
cyclic sulfonamide ring.
Received 20 December 2013
Received in revised form 19 February 2014
Accepted 12 March 2014
Available online 19 March 2014
Keywords:
HIV-1 protease inhibitors
X-ray crystallography
Absolute inhibition constant (Ki)
Stereoselective synthesis
Radical cyclization
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
more potent with a Ki of 29 nM. Indeed for optimal potency it is
important that the C4eMe group has (S) configuration (compound
In our previous publication1a we have disclosed the synthesis of
a novel class of HIV-1 protease inhibitors represented by structure
1. These inhibitors were designed based on a novel pharmacophore
containing conformationally restricted sulfonamides. Our expec-
tation is that the cyclic sulfonamides would assume fewer confor-
mations when bound to the HIV-1 protease compared with the
corresponding open chain sulfonamides,2e4 which might also
translate into advantages in potency and possibly pharmacokinetic
properties. An unusual radical cyclisation1b process yielded the
above novel cyclic sulfonamides. In HIV-1 protease assay, our initial
lead compound 2 was found to have Ki value of 470 nM (Fig. 1). In
order to optimize the potency we decided to suitably substitute
both the aliphatic and aromatic rings in compound 2. Following the
sequence of steps as in our earlier publication, the diastereoisomers
3 and 4 were synthesized. The HIV-1 protease inhibitory activities
of the diastereoisomers showed that compound 3 was significantly
3) as the diastereoisomer with C4eMe with (R) configuration was
found to be essentially inactive with Ki of 1000 nM (compound 4).
We have synthesized several analogs to establish the structur-
eeactivity relationship and found that compound 5 was the most
potent in this series with a Ki of 20 nM (Fig. 1). The X-ray crystal-
lographic analysis of compound 5 bound to the HIV-1 protease1a
revealed that compound 5 binds to the same cavity as the clinical
drug darunavir and that it makes hydrogen bonding to the catalytic
aspartic acid residues Asp 25 and Asp 250 through the 20 hydroxyl
group. The sulfonamide and the carbamate carbonyl form hydrogen
bonds with a structural water molecule, which in turn hydrogen-
bonds with Ile50 and Ile500 of the protease backbone. In addition
to these favorable interactions, C4eMe (S configuration) fits into
a hydrophobic pocket containing Val82, Leu23, Ile84. Furthermore,
ꢀ
C4eMe (S configuration) in compound 5 is 2.9 A away from the
carbonyl oxygen of Gly270. If the C4eMe configuration is changed to
(R) instead of (S), an unfavorable repulsion would be created
between the C4eMe and the Gly270 carbonyl group and the in-
teractions to the hydrophobic pocket would be lost. These are the
* Corresponding author. Tel.: þ1 201 216 5540; fax: þ1 201 216 8240; e-mail
address: akganguly1@aol.com (A.K. Ganguly).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.03.038

A.K. Ganguly et al. / Tetrahedron 70 (2014) 2894e2904
2895
Fig. 1. Novel HIV-1 protease inhibitors.
reasons for the improved activity of compound 5 when compared
with the initial lead compound 2.
the compounds possessing tetrahydrofuran carbamate moiety
were more potent in the HIV-1 protease inhibitory activity when
compared with compounds possessing t-butyl carbamate. In ad-
dition the molecular modeling studies also suggested that a phenyl
group could be accommodated at the C4 position, although not as
tightly as the alkyl groups in the same pocket. As a test case we
synthesized compound 49 and found that it had good activity al-
though it was not as active as the alkyl substituted compounds.
Thus in the present study we identified compounds 47 and 48 as
the most potent inhibitors with Ki values of 360 pM and 260 pM,
respectively, which are approximately a hundred fold more potent
than compound 5 described in our earlier paper. As discussed above
in the C4eMe series only the diastereoisomers with (S) stereo-
chemistry at this center were active and it was also true when the
methyl group was displaced with ethyl and n-propyl groups.
However when the methyl group was replaced with isopropyl or
tertiary butyl groups both the distereoisomers were active. Thus 51
and 52 were active although much less so when compared with 47
and 48, respectively. X-ray crystallographic analysis of 52 bound to
the HIV-1 protease provided a clue to this unexpected result, which
is described later in the paper.
2. Present study
The X-ray crystallographic analysis of compound 5 also sug-
gested that C4eMe group could be further extended in order to
maximize the interactions with the hydrophobic pocket, thus en-
hancing potency. Hence we decided to study the effect of various
alkyl groups on the cyclic sulfonamide ring for their activities
against HIV-1 protease. In addition, the molecular modeling sug-
gested that the tetrahydrofuran carbamates similar to amprenavir
and different than darunavir would provide stronger binding to the
protease backbone through hydrogen bonding of Asp 290 and
Asp300. In our earlier publication we noted that fluorine sub-
stitution of the aromatic sulphonamide ring was optimum for ac-
tivity. Thus we synthesized compounds represented by the
structure 6 (Fig. 2) incorporating all the above ideas. As predicted
2.1. Synthesis of C4-substituted derivatives
Synthesis of newer analogs is summarized in Scheme 1. It in-
volves steps we have disclosed in our earlier publication, however it
Fig. 2. Novel cyclic sulfonamides.
Scheme 1. Synthesis of cyclic sulfonamides 20e23.

2896
A.K. Ganguly et al. / Tetrahedron 70 (2014) 2894e2904
has been modified to incorporate novel structural features in the
molecules disclosed in the present study. Thus the treatment of 2-
bromo-4 fluorobenzenesulfonyl chloride with 4-methoxybenzyl
amine gave the sulfonamide 7.
respectively with (S)-2,5-dioxopyrrolidin-1-yl (tetrahydrofuran-3-
yl) carbonate (46)7 and triethylamine in dichloromethane yielded
47e49. Treatment of 40 with tert-butyl isocyanate in the presence
of magnesium bromide using 1,4-dioxane as solvent gave the urea
50. Although the less polar diastereoisomers were inactive in pre-
vious cases,1a compounds 35 and 36, when converted into tetra-
hydrofuran carbamates, 51 and 52, respectively, were found to be
active. It should be noted that in every case studied, it is the more
polar diastereoisomeric amines when converted to the carbamates
show activity.
Allylation of 7 with substituted bromo compounds 8e11 using
sodium iodide and cesium carbonate in DMF as solvent yielded the
N-allyl sulfonamides 12e15, respectively. Removal of the 4-
methoxybenzyl group in the presence of ceric ammonium nitrate
and acetonitrile:water (5:1) as solvent provided the radical pre-
cursors 16e19. Radical cyclization of compounds 16e19 with trib-
utyltin hydride (TBTH) and azobisisobutyronitrile (AIBN) as radical
initiator in toluene under reflux conditions gave the radical cyclized
products 20e23, respectively. The bromo intermediates 8e11, in
turn were synthesized following Scheme 2.5 Thus substituted
acroleins 8ae11a were reduced by sodium borohydride in presence
of methanol and ether to give the corresponding alcohols 8be11b,
which were then converted to the desired bromo intermediates
using phosphorous tribromide in ether at 0 ꢀC.
2.2. HIV-1 protease activity and X-ray crystallographic
analysis
The results of HIV-1 protease inhibitory assay of compounds
43e45, 47e52 are summarized in Table 1. Compound 43 with
C4eEt (S) on the cyclic sulfonamide ring was found to have the Ki
value of 11 nM, which was a slight improvement in potency when
compared with C4eMe (S) substitution as in compound 5. C4-Pr (S)
compound 44 had the Ki value of 28 nM. With the introduction of
C4eiPr (R) group in compound 45 there was nearly 6-fold increase
in the potency with Ki of 2.8 nM when compared to compound 5.
The urea derivative 50 was also found to be active with a Ki of
6.4 nM. The activity improved significantly in compound 47 when
the tetrahydrofuran carbamate was made with a Ki of 360 pM. With
the introduction of C4et-butyl (R) group as in compound 48 there
was further increase in activity when compared with compound 47.
Indeed compound 48 is the most potent analog in this series of
cyclic sulfonamides with a Ki of 260 pM. We have also made the
diastereoisomers 51 and 52 and to our surprise found them to be
also active with a Ki value of 19 nM and 14 nM, respectively. Al-
though 51 was considerably less active than 47 and 52 much less
active than 48, however, when these results are compared with the
activities of the C4eMe diastereoisomers, in which case (S) di-
astereoisomer was active and the (R) diastereoisomer was essen-
tially inactive, the above observations were surprising. The potent
Scheme 2. Synthesis of bromo intermediates 8e11.
The C4-phenyl substituted sulfonamide was prepared follow-
ing Scheme 3. Treatment of 2-bromo-4 fluorobenzenesulfonyl
chloride with 2-phenylallylamine (24)6 in the presence of pyri-
dine yielded the radical precursor 25, which when treated with
AIBN, TBTH in toluene under reflux provided the desired com-
pound 26.
Scheme 3. Synthesis of C4-phenyl sulfonamide 26.
Treatment of 20e23, 26 with the commercially available chiral
epoxide 27 in the presence of cesium carbonate and DMF yielded
mixtures of diastereoisomers 28e32, respectively, which could not
be separated (Scheme 4). However, 28 on treatment with tri-
fluoroacetic acid in dichloromethane yielded the diastereoisomers
33 and 38, which could be separated using preparatory TLC. Simi-
larly, 29 gave 34 and 39, 30 gave 35, and 40, 31 gave 36 and 41, 32
gave 37 and 42. The absolute configuration in the C4eMe (S) di-
astereoisomer series was established by X-ray crystallography of
the corresponding amine and corroborated further by X-ray crystal
structure of compound 5 bound to the protease as disclosed in our
previous publication.1a The more polar (6% Methanol in Chloro-
form) diastereoisomers 38e40 were treated with di-tert-butyl
dicarbonate and diisopropylethylamine to give the final products
43e45, respectively, which showed potent activity as HIV-1 pro-
tease inhibitors. The corresponding derivatives obtained from the
less polar diastereoisomers 33, and 34 were inactive and not re-
ported in the paper. Treatment of the diastereoisomers 40e42,
activity of 51 and 52 were indeed unexpected and needed an ex-
planation. X-ray analysis of 48 and 52 when bound to the HIV-1
protease unequivocally demonstrated that both these compounds
bind to the same hydrophobic pocket as the C4eMe (S) di-
astereoisomer and have similar interactions involving Asp 25, Asp
250, Ile50, and Ile500. X-ray results also demonstrated that 48 and
52 assume different conformations of the seven membered sul-
fonamide rings (Fig. 5). The same explanation we suspect holds
good for 47 and 51. Although the inactive C4eMe (R) di-
astereoisomer could not be soaked into HIV protease apo crystals,
molecular modeling suggests that the methyl group in this case was
pushed away from the important hydrophobic binding site. The
above X-ray crystallography results also confirmed the absolute
stereochemistry of 47, 48, 51, and 52. Perhaps it should also be
noted that the absolute stereochemistry at C20 and C30 were derived
from the absolute stereochemistry of the epoxide 27 and the
remaining asymmetric center was defined from compound 46 used
in the preparation of the carbamate.

A.K. Ganguly et al. / Tetrahedron 70 (2014) 2894e2904
2897
O
O
H
Ph
O
O
N
(S)
(S)
Ph
O2
S
O2
S
N
O
N
NH
H
1. TFA, DCM
27
OH
2. Separation by
prep TLC
F
F
CS2CO3, DMF
R
R
28 R = -CH2-CH3 (49%)
20 R = -CH2-CH3
21 R = -CH2-CH2-CH3
22 R = -CH(CH3)2
23 R = -C(CH3)3
26 R = -Ph
Ph
O
29 R = -CH2-CH2-CH3 (44%)
30 R = -CH(CH3)2 (45%)
31 R = -C(CH3)3 (57%)
O2
S
N
O
N
H
Di-tert-butyl
dicarbonate
32 R = -Ph (35%)
OH
F
(iPr)2NEt
R
43 R = -CH2-CH3 (4S,2'R,3'S) (40%)
44 R = -CH2-CH2-CH3 (4S,2'R,3'S) (40%)
45 R = -CH(CH3)2 (4R,2'R,3'S) (27%)
Ph
Ph
O2
S
2'
O2
S
NH2
3'
NH2
OH
O
O
N
N
+
OH
Ph
O
N
O
O
4
F
O2
S
F
O
O
N
O
S
46
R
R
N
H
OH
33 R = -CH2-CH3 (4R,2'R,3'S) (31%)
34 R = -CH2-CH2-CH3 (4R,2'R,3'S) (30%)
35 R = -CH(CH3)2 (4S,2'R,3'S) (16%)
36 R = -C(CH3)3 (4S,2'R,3'S) (15%)
37 R = -Ph (4S,2'R,3'S) (18%)
Et3N
38 R = -CH2-CH3 (4S,2'R,3'S) (33%)
39 R = -CH2-CH2-CH3 (4S,2'R,3'S) (29%)
40 R = -CH(CH3)2 (4R,2'R,3'S) (40%)
41 R = -C(CH3)3 (4R,2'R,3'S) (15%)
42 R = -Ph (4R,2'R,3'S) (24%)
O
F
R
47 R = -CH(CH3)2 (4R,2'R,3'S) (43%)
48 R = -C(CH3)3 (4R,2'R,3'S) (45%)
49 R = -Ph (4R,2'R,3'S) (80%)
O
N
O
Ph
O
Ph
O
tert-Butyl
O2
S
O2
S
O
O
N
N
isocyanate
N
O
S
N
H
H
N
H
O
O
46
OH
OH
MgBr2
O
F
F
Et3N
R
R
50 R = -CH(CH3)2 (4R,2'R,3'S) (55%)
51 R = -CH(CH3)2 (4R,2'R,3'S) (50%)
52 R = -C(CH3)3 (4R,2'R,3'S) (49%)
Scheme 4. Synthesis of novel HIV-1 protease inhibitors 43e45, 47e52.
Table 1
Summary of biological activity in HIV-1 protease assay
Table 1 (continued )
Compound
Structure
Ki (nM)
<0.02
Compound
Structure
Ki (nM)
Darunavir
48
49
50
0.26ꢁ0.05
34ꢁ5.1
6.4ꢁ1
Amprenavir
0.08ꢁ0.02
11ꢁ1.1
43
44
45
28ꢁ6
51
19ꢁ1.6
14ꢁ0.6
2.8ꢁ1.9
3a
52
47
0.36ꢁ0.1
0.43a
a
Replicate of HIV-1 assay at a different time.

2898
A.K. Ganguly et al. / Tetrahedron 70 (2014) 2894e2904
The X-ray crystal structure of compound 47 bound to the HIV-1
protease is shown in Fig. 3. It was found that in addition to the
binding interactions shown by compound 5, the tetrahydrofuran
group in compound 47 forms a hydrogen bond with Asp 290 and
Asp300. The isopropyl group extends deeper into the hydrophobic
pocket of Val82, Leu23, Ile84. It is partially disordered by rotation
of the isopropyl group placing the two methyl groups at three
positions. The additional interactions are responsible for much
improved activity of 47. The t-butyl group in compound 48 elim-
inates the disorder of compound 47 and further maximizes the
interactions with the hydrophobic pocket, which makes it the
most potent analog in this series of compounds. Fig. 4 shows
overlay of compounds 47, 50, and 5. Fig. 5 shows the overlay of 48
and 52.
Fig. 5. Overlay of X-ray crystallographic structures of compounds 48 (red) and 52
(blue).
these favorable interactions, the tetrahydrofuran group in com-
pound 47 shows hydrogen-bonding interactions with Asp 290 and
Asp300 of the protease backbone. The isopropyl group extends
deeper into the hydrophobic pocket of Val82, Leu23, and Ile84.
These factors contribute to the picomolar activity of compound
47 and we believe that in the case of the t-butyl group at C4
position as in compound 48 the hydrophobic interactions are
further maximized. In HIV-1 protease assay compound 47
showed Ki of 360 pM and compound 48 showed Ki of 260 pM,
which were a hundred fold more active than our previously re-
ported compound 5. To our greatest surprise we have found that
both the C4eiPr (S), C4et-butyl (S), 51 and, 52 diastereoisomers
were active although much less so when compared to the cor-
responding (R) isomers. X-ray studies demonstrated that when
bound to the HIV-1 protease they occupy the same pocket as the
C4eMe (S) diastereoisomer, excepting that in the case of 51 and
52 the seven membered sulfonamide rings assume different
conformations. In spite of our best effort we have not been able to
get our compounds screened against resistant organisms. Once
Fig. 3. X-ray crystal structure of compound 47 bound to HIV-1 protease.
we are successful we shall report the results in
publication.
a future
4. Experimental section
4.1. General
All the reactions were performed under a nitrogen atmosphere
with magnetic stirring. Air and moisture-sensitive reagents were
transferred via disposable syringes. Anhydrous solvents and com-
mercially available chemicals were used without further drying.
TLC was performed on Analtech silica gel glass plates (250 m) and
visualized with a UV lamp. NMR spectra were recorded with Varian
400 MHz spectrometer using CDCl3 as solvent unless otherwise
noted. The purity of the compounds was established using various
chromatographic techniques including HPLC and were judged to be
>95%.
Fig. 4. Overlay of X-ray crystallographic structures of compound 5 (gray), compound
47 (green), and compound 50 (orange).
3. Conclusion
In conclusion, the compounds with C4-alkyl substitution, i.e.,
isopropyl or t-butyl groups were found to be significantly more
active than the C4-phenyl substitution. The X-ray crystallographic
analysis of compound 47 bound to the HIV-1 protease revealed
that it binds to the same cavity as the C4eMe (S) diastereoisomer
and that it makes hydrogen bonding to the catalytic aspartic acid
residues Asp 25 and Asp 250 through the 20 hydroxyl group. The
sulfonamide and the carbamate carbonyl form hydrogen bonds
with a structural water molecule, which in turn hydrogen-bonds
with Ile50 and Ile500 of the protease backbone. In addition to
4.2. A general procedure for sulfonamide formation (7) and
(25)
2-Bromo-4-fluoro-N-(4-methoxybenzyl)benzenesulfonamide
(7). To a solution of 4-methoxybenzylamine (1.0 g, 3.66 mmol) in
dichloromethane (DCM) (5 mL) were added, pyridine (0.59 mL,
7.32 mmol) followed by
a
solution of 4-fluoro-2-
bromobenzenesulfonyl chloride (0.52 mL, 4.02 mmol) in DCM
(2 mL). The reaction mixture was stirred at room temperature for
8e10 h. TLC was monitored to check the progress of the reaction.

A.K. Ganguly et al. / Tetrahedron 70 (2014) 2894e2904
2899
After the reaction was complete, the reaction mixture was diluted
35.01, 20.45, 13.69. HRMS calcd for
456.0639; found 456.0628.
C
20H24BrFNO3S [MþH]þ
with DCM and washed with 15% HCl (2ꢂ10 mL). The organic layer
was dried over anhydrous sodium sulfate, filtered, and evaporated
to dryness to yield the crude compound, which was purified by
column chromatography using 15% ethyl acetate in hexane to yield
the pure compound. Crystals were obtained from DCM and hexane
4.3.3. 2-Bromo-4-fluoro-N-(4-methoxybenzyl)-N-(3-methyl-2-
methylenebutyl)benzene sulfonamide (14). The title compound was
prepared following the general procedure for N-allylation using
compound 7 and 2-(bromomethyl)-3-methylbut-1-ene (10). Crys-
tals were obtained from DCM and hexane (1:4). Yield: 91%. Mp
(1:4). Yield: 59%. Mp 85e87 ꢀC. 1H NMR (400 MHz, CDCl3)
d ppm
8.17e8.03 (m, 1H), 7.41 (d, J¼7.9 Hz, 1H), 7.16e7.05 (m, 3H), 6.76 (d,
J¼8.3 Hz, 2H), 5.32 (t, J¼5.7 Hz, 1H), 4.04 (d, J¼6.1 Hz, 2H), 3.76 (s,
65e67 ꢀC. 1H NMR (400 MHz, CDCl3)
d
ppm 8.15 (dd, J¼8.9, 5.9 Hz,
3H); 13C NMR (400 MHz, CDCl3)
d
ppm 165.38, 162.80, 159.36,
1H), 7.46 (dd, J¼8.0, 2.6 Hz, 1H), 7.10 (ddd, J¼8.9, 7.5, 2.6 Hz, 1H),
7.03 (d, J¼8.7 Hz, 2H), 6.78 (d, J¼8.7 Hz, 2H), 4.91 (s, 1H), 4.86 (s,
1H), 4.40 (s, 2H), 3.84 (s, 2H), 3.77 (s, 3H), 2.08 (m, 1H), 0.89 (d,
135.26, 133.63, 133.55, 129.37, 127.46, 122.46, 122.20, 120.97, 120.86,
114.93, 114.73, 55.26, 47.02. HRMS calcd for C14H14BrFNO3S [MþH]þ
371.9700; found 371.9690.
J¼6.8 Hz, 6H); 13C NMR (400 MHz, CDCl3)
d ppm 165.28, 162.70,
159.22, 149.40, 134.40, 134.31, 130.10, 127.39, 122.89, 122.64, 121.97,
121.87, 114.63, 114.42, 113.82, 111.01, 55.22, 50.67, 49.80, 30.38,
21.43. HRMS calcd for C20H24BrFNO3S [MþH]þ 456.0639; found
456.0627.
4.2.1. 2-Bromo-4-fluoro-N-(2-phenylallyl)benzenesulfonamide
(25). The title compound was prepared starting from 246 and 2-
bromo-4-fluorobenzenesulfonyl chloride following the general
procedure for sulfonamide formation. Yield: 73%. 1H NMR
(400 MHz, CDCl3)
d
ppm 8.12 (dd, J¼8.8, 5.8 Hz, 1H), 7.35 (dd, J¼7.9,
4.3.4. 2-Bromo-N-(3,3-dimethyl-2-methylenebutyl)-4-fluoro-N-(4-
methoxybenzyl)benzene sulfonamide (15). The title compound was
prepared following the general procedure for N-allylation using
compound 7 and 2-(bromomethyl)-3,3-dimethylbut-1-ene (11).
Crystals were obtained from DCM and hexane (1:4). Yield: 58%. Mp
2.5 Hz, 1H), 7.31e7.24 (m, 3H), 7.24e7.10 (m, 3H), 5.34 (s, 1H), 5.21
(b, 2H), 4.04 (d, J¼6.1 Hz, 2H); 13C NMR (400 MHz, CDCl3)
d
ppm 165.40, 162.83, 142.58, 137.48, 135.38, 133.45, 128.72, 128.32,
125.95, 125.88, 122.48, 122.23, 121.26, 121.16, 115.79, 114.86, 114.65,
47.36. HRMS calcd for C15H14BrFNO2S [MþH]þ 369.9907; found
369.9902.
75e76 ꢀC. 1H NMR (400 MHz, CDCl3)
d
ppm 8.14 (dd, J¼8.9, 5.8 Hz,
1H), 7.46 (dd, J¼8.0, 2.5 Hz,1H), 7.13e7.06 (m, 1H), 6.99 (d, J¼8.6 Hz,
2H), 6.77 (d, J¼8.6 Hz, 2H), 4.94 (s,1H), 4.86 (s,1H), 4.43 (s, 2H), 3.96
(s, 2H), 3.77 (s, 3H), 0.96 (s, 9H); 13C NMR (400 MHz, CDCl3)
d ppm
4.3. A general procedure for N-allylation 12e15
165.18, 162.61, 159.27, 150.23, 136.43, 136.39, 134.27, 134.17, 130.05,
127.27, 122.86, 122.61, 114.62, 114.41, 113.81, 107.48, 55.22, 49.79,
To a solution of compound 7 (1.35 g, 3.62 mmol) in N,N-dimethyl
formamide (DMF) (3 mL) were added sodium iodide (1.08 g,
7.24 mmol) and cesium carbonate (2.35 g, 7.24 mmol), followed by
substituted allyl bromides, 8e11 (1.18 g, 7.24 mmol). The reaction
mixture was allowed to stir for 10e12 h at room temperature under
nitrogen. TLC was checked to monitor the progress of the reaction.
The reaction mixture was diluted with water and extracted with
ethyl acetate. The combined organic layer was dried over anhy-
drous sodium sulfate, filtered, and evaporated to dryness to yield
crude product, which was purified by column chromatography in
15% ethyl acetate in hexane to yield the pure compound.
47.63, 34.99, 29.02. HRMS calcd for
470.0795; found 470.0781.
C
21H26BrFNO3S [MþH]þ
4.4. A general procedure for synthesis of substituted allyl
bromides 8e115
Substituted acroleins 8ae11a (1.0 g, 11.89 mmol) were dissolved
in a solution of diethyl ether and methanol (8 mL:2 mL) and cooled
to 0 ꢀC. Sodium borohydride (0.44 g, 11.89 mmol) was added por-
tion wise, and the reaction was stirred at 0 ꢀC for 1 h and at room
temperature 3e4 h. TLC showed the disappearance of starting
material. The reaction mixture was diluted with diethyl ether and
washed with water. The organic layer was dried over sodium sul-
fate, filtered, and evaporated to 1/4 volume to yield the substituted
allyl alcohols 8be11b, which were used for the next step without
further purification.
To a solution of compounds 8be11b (1.02 g, 11.89 mmol) in
diethyl ether (10 mL) was added phosphorus tribromide (0.82 mL,
8.76 mmol) drop wise at 0 ꢀC. Then the reaction mixture was stirred
at room temperature for 8e10 h. The reaction mixture was cooled
to 0 ꢀC and quenched with ice water. The organic layer was then
washed sequentially with water, saturated sodium bicarbonate, and
brine solution. The combined organic layer was dried over sodium
sulfate, filtered, and evaporated to 1/4 volume to yield substituted
allyl bromides 8e11. These crude products were used for N-allyla-
tion reaction without further purification.
4 . 3 .1. 2 - B ro m o - 4 - fl u o ro - N - ( 4 - m e t h o x y b e n z yl ) - N - ( 2 -
methylenebutyl)benzenesulfonamide (12). The title compound was
prepared following the general procedure for N-allylation using
compound 7 and 2-(bromomethyl)but-1-ene (8). Crystals were
obtained from DCM and hexane (1:5). Yield: 85%. Mp 50e52 ꢀC. 1H
NMR (400 MHz, CDCl3)
d
ppm 8.15 (td, J¼9.3, 4.7 Hz, 1H), 7.46 (td,
J¼8.0, 3.0 Hz, 1H), 7.11 (ddd, J¼9.1, 7.7, 2.5 Hz, 1H), 7.03 (d, J¼8.7 Hz,
2H), 6.78 (d, J¼8.6 Hz, 2H), 4.92 (s,1H), 4.87 (s,1H), 4.39 (s, 2H), 3.81
(s, 2H), 3.78 (s, 3H), 1.87 (q, J¼7.3 Hz, 2H), 0.90 (t, J¼7.4 Hz, 3H). 13
C
NMR (400 MHz, CDCl3) d ppm 165.27, 162.69, 159.19, 145.05, 134.37,
130.09, 129.96, 127.32, 122.87, 122.62, 121.88, 114.62, 113.80, 112.87,
55.24, 51.67, 49.64, 25.78, 11.78. HRMS calcd for C19H22BrFNO3S
[MþH]þ 442.0482; found 442.0474.
4 . 3 . 2 . 2 - B ro m o - 4- flu o ro - N - ( 4 - m e t h o xy b e n z yl ) - N - ( 2 -
methylenepentyl)benzenesulfonamide (13). The title compound was
prepared following the general procedure for N-allylation using
compound 7 and 2-(bromomethyl)pent-1-ene (9). Yield: 82%. 1H
4.5. A general procedure for ceric ammonium nitrate reaction
(CAN) reaction 16e19
NMR (400 MHz, CDCl3)
d
ppm 8.16 (dd, J¼8.9, 5.9 Hz, 1H), 7.47 (dd,
Compound 12 (0.84 g, 1.89 mmol) was dissolved in an acetoni-
trile:water solution (5 mL : 1 mL) to which ceric ammonium nitrate
(4.16 g, 7.59 mmol) was added portion wise (3 portions) with in-
tervals of 10 min. The reaction mixture was allowed to stir at room
temperature for 10e12 h. TLC was monitored to check the progress
of the reaction. The reaction mixture was quenched with 10%
aq sodium bicarbonate (5 mL) solution and extracted with ethyl
J¼8.0, 2.5 Hz, 1H), 7.15e7.08 (m, 1H), 7.06 (d, J¼8.5 Hz, 2H), 6.79 (d,
J¼8.5 Hz, 2H), 4.91 (s, 1H), 4.86 (s, 1H), 4.42 (s, 2H), 3.78 (s, 3H), 3.76
(s, 2H), 1.81 (t, J¼7.5 Hz, 2H), 1.24 (dd, J¼14.9, 7.4 Hz, 2H), 0.80 (t,
J¼7.3 Hz, 3H); 13C NMR (400 MHz, CDCl3)
d ppm 165.24, 162.67,
159.15, 143.23, 136.28, 134.33, 134.24, 130.06, 127.35, 122.85, 122.60,
121.99, 121.89, 114.57, 114.36, 114.00, 113.78, 55.18, 51.26, 49.65,

2900
A.K. Ganguly et al. / Tetrahedron 70 (2014) 2894e2904
acetate. The combined organic layer was washed with water, dried
over anhydrous sodium sulfate, and evaporated to dryness to yield
the crude mixture, which was purified by column chromatography
using 15% ethyl acetate in hexane to yield the product (0.80 g).
According to NMR data, the product at this stage contained p-
methoxybenzaldehyde as a byproduct. The product mixture (0.80 g,
5.87 mmol) was dissolved in methanol and cooled to 0 ꢀC. To this
mixture sodium borohydride (0.33 g, 8.81 mmol) was added slowly.
The reaction was allowed to stir for 4e6 h at room temperature
under nitrogen. TLC was used to monitor the progress of the re-
action. The reaction mixture was quenched with water and
extracted with DCM. The combined organic layer was dried over
anhydrous sodium sulfate, filtered, and evaporated to dryness to
yield the crude mixture, which was purified by column chroma-
tography using 15% ethyl acetate in hexane to yield the pure
product 16 (0.54 g) and p-methoxybenzyl alcohol as a byproduct.
(18.39 mg, 0.11 mmol). The above solution was heated to about
60e70 ꢀC and then tributyltin hydride (TBTH) (0.16 mL, 0.61 mmol)
was added slowly under nitrogen. After the addition was complete,
the reaction mixture was refluxed for 4e6 h. Upon completion
(followed by TLC), the reaction mixture was evaporated to dryness.
The residue was extracted with DCM and washed with water. The
organic layers were combined, dried over sodium sulfate, filtered,
and concentrated to yield the crude compound, which was further
purified by column chromatography using ethyl acetate and hexane
to yield the pure compound 20 (93 mg).
4.6.1. 4-Ethyl-7-fluoro-2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine 1,1-
dioxide (20). The title compound was prepared starting from 16
following the general procedure for radical reaction. Crystals were
obtained from DCM and hexane (1:4). Yield: 69%. Mp 114e116 ꢀC.
1H NMR (400 MHz, CDCl3)
d ppm 7.88 (m, 1H), 6.95e6.84 (m, 2H),
4.57 (s, 1H), 3.42e3.10 (m, 2H), 1.61e6.52 (m, 2H), 1.35e1.25 (m,
4.5.1. 2-Bromo-4-fluoro-N-(2-methylenebutyl)benzenesulfonamide
(16). The title compound was prepared from compound 12 fol-
lowing the general procedure for CAN reaction. Yield: 89%. 1H NMR
1H), 1.27e1.14 (m, 2H), 0.960 (t, J¼7.4 Hz, 3H). 13C NMR (400 MHz,
CDCl3)
d ppm 165.72, 163.20, 138.53, 129.60, 129.51, 128.56, 126.99,
119.23, 119.01, 113.21, 112.99, 49.47, 40.20, 33.01, 26.25, 11.46. HRMS
(400 MHz, CDCl3)
d
ppm 8.15 (dd, J¼8.8, 5.7 Hz, 1H), 7.48e7.36 (m,
calcd for C11H15FNO2S [MþH]þ 244.0802; found 244.0796.
1H), 7.17e7.09 (m, 1H), 5.09 (s, 1H), 4.88e4.79 (m, 2H), 3.48 (d,
J¼6.4 Hz, 2H), 2.01 (q, J¼7.7 Hz, 2H), 0.987 (t, J¼7.4 Hz, 3H). 13C NMR
4.6.2. 7-Fluoro-4-propyl-2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine
1,1-dioxide (21). The title compound was prepared starting from 17
following the general procedure for radical reaction. Crystals were
obtained from DCM and hexane (1:4). Yield: 87%. Mp 101e102 ꢀC.
(400 MHz, CDCl3)
d ppm 165.40, 162.33, 152.42, 134.98, 133.66,
133.55, 122.61, 120.93, 120.83, 115.05, 114.83, 110.07, 48.11, 26.38,
11.81. HRMS calcd for C11H14BrFNO2S [MþH]þ 321.9907; found
321.9896.
1H NMR (400 MHz, CDCl3)
d
ppm 7.90 (dd, J¼8.50, 6.08 Hz, 1H),
7.02e6.90 (m, 2H), 4.51 (t, J¼6.0 Hz, 1H), 3.79e2.91 (m, 4H),
1.84e1.68 (m, 1H), 1.45e1.27 (m, 2H), 1.25e1.05 (m, 2H), 0.89 (t,
4.5.2. 2-Bromo-4-fluoro-N-(2-methylenepentyl)benzenesulfonamide
(17). The title compound was prepared from compound 13 fol-
lowing the general procedure for CAN reaction. Yield: 79%. 1H NMR
J¼7.3 Hz, 3H). 13C NMR (400 MHz, CDCl3)
d ppm 165.90, 163.38,
138.51, 129.64, 129.54, 119.19, 118.98, 113.23, 113.02, 49.73, 40.48,
32.78, 26.75, 20.01, 14.02. HRMS calcd for C12H17FNO2S [MþH]þ
258.0959; found 258.0953.
(400 MHz, CDCl3)
d
ppm 8.15 (dd, J¼8.6, 5.9 Hz, 1H), 7.48 (dd, J¼7.9,
2.2 Hz, 1H), 7.21e7.12 (m, 1H), 5.09 (t, J¼5.2 Hz, 1H), 4.93 (s, 1H),
4.84 (s, 1H), 3.46 (d, J¼6.4 Hz, 2H), 1.96 (t, J¼7.5 Hz, 2H), 1.45e1.30
(m, 2H), 0.86 (t, J¼7.3 Hz, 3H). 13C NMR (400 MHz, CDCl3)
d
ppm
4.6.3. 7-Fluoro-4-isopropyl-2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine
1,1-dioxide (22). The title compound was prepared starting from
18 following the general procedure for radical reaction. Crystals
were obtained from DCM and hexane (1:4). Yield: 87%. Mp
165.48, 162.90, 143.99, 133.64, 133.55, 122.58, 122.33, 120.99,
120.89, 115.04, 114.82,112.60, 47.99, 35.63, 20.52,13.65. HRMS calcd
for C12H16BrFNO2S [MþH]þ 336.0064; found 336.0056.
158e161 ꢀC. 1H NMR (400 MHz, CDCl3)
d
ppm 7.90 (dd, J¼8.3,
4.5.3. 2-Bromo-4-fluoro-N-(3-methyl-2-methylenebutyl)benzene-
sulfonamide (18). The title compound was prepared from com-
pound 14 following the general procedure for CAN reaction. Yield:
5.8 Hz, 1H), 6.96 (dd, J¼12.8, 4.5 Hz, 2H), 4.46 (t, J¼6.5 Hz, 1H),
3.64e3.51 (m, 1H), 3.16e3.03 (m, 3H), 1.54e1.43 (m, 2H), 0.955 (d,
J¼6.6 Hz, 6H); 13C NMR (400 MHz, CDCl3)
d ppm 165.72, 163.20,
52%. 1H NMR (400 MHz, CDCl3)
d
ppm 8.14 (dd, J¼8.8, 5.8 Hz, 1H),
138.46, 138.43, 129.69, 129.59, 118.91, 118.69, 113.11, 112.90, 48.16,
43.33, 38.25, 19.65, 19.19. HRMS calcd for C12H17FNO2S [MþH]þ
258.0959; found 258.0954.
7.47 (dd, J¼7.9, 2.5 Hz, 1H), 7.16 (ddd, J¼8.8, 7.6, 2.5 Hz, 1H),
5.07e4.87 (m, 1H), 4.88 (d, J¼16.1, 2H), 3.50 (d, J¼6.3, 2H),
2.24e2.14 (m, 1H), 0.982 (d, J¼6.9 Hz, 6H); 13C NMR (400 MHz,
CDCl3)
d
ppm 165.47, 162.89, 150.17, 135.21, 135.17, 133.64, 133.55,
4.6.4. 4-(tert-Butyl)-7-fluoro-2,3,4,5-tetrahydrobenzo[1,2-f]thiaze-
pine 1,1-dioxide (23). The title compound was prepared starting
from 19 following the general procedure for radical reaction.
Crystals were obtained from DCM and hexane (1:4). Yield: 88%. Mp
122.58, 122.32, 120.97, 115.04, 114.82, 110.38, 46.95, 31.42, 21.39.
HRMS calcd for C12H16BrFNO2S [MþH]þ 336.0064; found 336.0055.
4.5.4. 2-Bromo-N-(3,3-dimethyl-2-methylenebutyl)-4-
fluorobenzenesulfonamide (19). The title compound was prepared
from compound 15 following the general procedure for CAN re-
action. Crystals were obtained from DCM and hexane (1:4). Yield:
196e198 ꢀC. 1H NMR (400 MHz, CDCl3)
d
ppm 7.94 (dd, J¼8.3,
5.8 Hz, 1H), 6.96 (dd, J¼10.8, 4.5 Hz, 2H), 4.38e4.21 (m, 1H),
3.71e3.61 (m, 1H), 3.59e3.40 (m, 2H), 2.95e2.85 (m, 1H),
1.41e1.1.38 (m, 1H), 0.98 (s, 9H); 13C NMR (400 MHz, CDCl3)
d ppm
87%. Mp 65e67 ꢀC. 1H NMR (400 MHz, CDCl3)
d
ppm 8.15 (dd, J¼8.8,
165.83, 163.31, 142.98, 129.59, 129.50, 118.27, 118.05, 113.09, 112.88,
48.27, 47.35, 36.88, 33.07, 27.35. HRMS calcd for C13H19FNO2S
[MþH]þ 272.1115; found 272.1110.
5.8 Hz, 1H), 7.48 (dd, J¼7.9, 2.5 Hz, 1H), 7.22e7.14 (m, 1H), 5.04 (t,
J¼5.6 Hz, 1H), 4.98 (d, J¼11.1 Hz, 2H), 3.52 (d, J¼6.1 Hz, 2H), 1.02 (s,
9H); 13C NMR (400 MHz, CDCl3)
d ppm 165.45, 162.87, 152.42,
134.98, 134.95, 133.64, 133.55, 122.61, 122.35, 120.93, 115.05, 114.83,
110.07, 44.36, 35.35, 28.98. HRMS calcd for C13H18BrFNO2S [MþH]þ
350.0220; found 350.0205.
4.6.5. 7-Fluoro-4-phenyl-2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine
1,1-dioxide (26). The title compound was prepared starting from 25
following the general procedure for radical reaction. Yield: 94%. 1H
NMR (400 MHz, CDCl3)
d
ppm 7.96 (dd, J¼8.6, 5.6 Hz, 1H), 7.36 (m,
4.6. A general procedure for radical reaction 20e23 and 26
2H), 7.29 (t, J¼6.8 Hz, 1H), 7.21 (d, J¼7.6 Hz, 2H), 7.07e6.90 (m, 2H),
4.69 (dd, J¼9.1, 4.4 Hz, 1H), 4.10 (dd, J¼13.7, 11.9 Hz, 1H), 4.03e3.86
(m, 1H), 3.41 (d, J¼14.7 Hz, 1H), 3.03 (d, J¼14.7 Hz, 1H), 2.91 (dt,
Compound 16 (180 mg, 0.55 mmol) was dissolved in toluene
(12 mL) and to it was added azobisisobutyronitrile (AIBN)
J¼11.3, 3.1 Hz, 1H); 13C NMR (400 MHz, CDCl3)
d ppm 165.82,

A.K. Ganguly et al. / Tetrahedron 70 (2014) 2894e2904
2901
163.29, 142.55, 141.55, 141.46, 138.64, 138.61, 129.79, 129.04, 127.35,
126.80, 119.11, 118.89, 113.43, 113.22, 51.41, 44.48, 42.10. HRMS calcd
for C15H15FNO2S [MþH]þ 292.0802; found 292.0797.
4.8.1. (R)-2-((2R,3S)-3-Amino-2-hydroxy-4-phenylbutyl)-4-ethyl-7-
fluoro-2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine 1,1-dioxide (33) and
(S)-2-((2R,3S)-3-amino-2-hydroxy-4-phenylbutyl)-4-ethyl-7-fluoro-
2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine 1,1-dioxide (38). The title
compounds were prepared following general procedure for TFA
reaction starting from compound 28. Compound 33 is less polar
than compound 38.
4.7. A general procedure for epoxide reaction 28e32
To a solution of compound 20 (182 mg, 0.70 mmol) in N,N-di-
methyl formamide (DMF) (2 mL) was added (2S,3S)-1,2-epoxy-3-
(Bocamino)-4-phenylbutane (27) (186 mg, 0.70 mmol) followed by
the addition of cesium carbonate (461 mg, 1.41 mmol). The reaction
mixture was stirred for 10e12 h at room temperature under ni-
trogen. TLC was checked to monitor the progress of the reaction.
The reaction mixture was filtered, diluted with ethyl acetate, and
then washed with water. The combined organic layer was dried
over anhydrous sodium sulfate, filtered, and evaporated to yield the
crude compound, which was purified by column chromatography
using 25% ethyl acetate in hexane to yield the product (180 mg).
Compound 33. Yield: 31%. 1H NMR (400 MHz, CDCl3)
d ppm 7.92
(dd, J¼8.9, 5.3 Hz, 1H), 7.30e7.15 (m, 5H), 7.00e6.96 (m, 2H),
3.91e3.81 (m,1H), 3.65e3.40 (m,1H), 3.52e3.28 (m,1H), 3.23e3.03
(m, 3H), 2.98e2.84 (m, 3H), 2.95e2.53 (m, 1H), 2.59e2.48 (m, 1H),
2.16e1.97 (m, 2H), 1.85e1.69 (m, 1H), 1.41e1.26 (m, 2H), 0.99 (t,
J¼7.2 Hz, 3H); 13C NMR (400 MHz, CDCl3)
d ppm 165.98, 163.46,
138.73, 135.08, 131.59, 131.50, 129.33, 129.23, 128.58, 126.45, 119.07,
118.84, 113.16, 112.95, 73.59, 56.67, 55.14, 49.84, 40.74, 38.47, 34.53,
26.89, 11.27. HRMS calcd for C21H28FN2O3S [MþH]þ 407.1799; found
407.1795.
Compound 38. Yield: 33%. 1H NMR (400 MHz, CDCl3)
d ppm 7.94
(dd, J¼8.9, 5.3 Hz, 1H), 7.29e7.07 (m, 5H), 6.94e6.80 (m, 2H),
4.01e3.87 (m, 1H), 3.89e3.71 (m, 1H), 3.53e3.40 (m, 2H), 3.13 (d,
J¼11.2 Hz, 2H), 2.97 (d, J¼12.5 Hz, 1H), 2.89e2.72 (m, 2H), 2.41 (m,
1H), 2.99e2.87 (m, 2H), 1.80e1.70 (m, 1H), 1.41e1.29 (m, 3H), 0.99
4.7.1. tert-Butyl ((2S,3R)-4-(4-ethyl-7-fluoro-1,1-dioxido-4,5-
dihydrobenzo[1,2-f]thiazepin-2(3H)-yl)-3-hydroxy-1-phenylbutan-2-
yl)carbamate (28). The title compound was prepared starting from
20 following the general procedure for epoxide reaction. Yield: 49%.
Mixture of diastereoisomers. NMR data were consistent with the
proposed structure.
(t, J¼7.2 Hz, 3H); 13C NMR (400 MHz, CDCl3)
d ppm 165.99, 163.46,
138.75, 135.10, 131.60, 131.50, 129.34, 129.30, 128.60, 126.45, 119.09,
118.86, 113.17, 112.96, 73.61, 56.65, 55.14, 49.84, 40.72, 38.44, 34.51,
26.89, 11.27. HRMS calcd for C21H28FN2O3S [MþH]þ 407.1799; found
407.1792.
4.7.2. tert-Butyl((2S,3R)-4-(7-fluoro-1,1-dioxido-4-propyl-4,5-
dihydrobenzo[1,2-f] thiazepin-2(3H)-yl)-3-hydroxy-1-phenylbutan-
2-yl)carbamate (29). The title compound was prepared starting
from 21 following the general procedure for epoxide reaction.
Yield: 44%. Mixture of diastereoisomers. NMR data were consistent
with the proposed structure.
4.8.2. (R)-2-((2R,3S)-3-Amino-2-hydroxy-4-phenylbutyl)-7-fluoro-
4-propyl-2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine 1,1-dioxide (34)
and (S)-2-((2R,3S)-3-amino-2-hydroxy-4-phenylbutyl)-7-fluoro-4-
propyl-2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine 1,1-dioxide
(39). The title compounds were prepared following general pro-
cedure for TFA reaction starting from compound 29. Compound 34
is less polar than compound 39.
4.7.3. tert-Butyl((2S,3R)-4-(7-fluoro-4-isopropyl-1,1-dioxido-4,5-
dihydrobenzo[1,2-f] thiazepin-2(3H)-yl)-3-hydroxy-1-phenylbutan-
2-yl)carbamate (30). The title compound was prepared starting
from 22 following the general procedure for epoxide reaction.
Yield: 45%. Mixture of diastereoisomers. NMR data were consistent
with the proposed structure.
Compound 34. Yield: 30%. 1H NMR (400 MHz, CDCl3)
d ppm 7.93
(dd, J¼9.3, 5.5 Hz, 1H), 7.31e7.19 (m, 5H), 7.12e6.91 (m, 2H),
4.09e4.79 (m, 2H), 3.61e3.32 (m, 2H), 3.19e3.01 (m, 2H),
2.99e2.89 (m, 1H), 2.75e2.61 (m, 2H), 2.43e2.31 (m, 1H), 2.12e1.82
(m, 3H), 1.91e1.74 (m, 1H), 1.51e1.35 (m, 2H), 1.32e1.20 (m, 2H),
4.7.4. tert-Butyl ((2S,3R)-4-(4-(tert-butyl)-7-fluoro-1,1-dioxido-4,5-
dihydrobenzo[1,2-f]thiazepin-2(3H)-yl)-3-hydroxy-1-phenylbutan-2-
yl)carbamate (31). The title compound was prepared starting from
23 following the general procedure for epoxide reaction. Yield: 57%.
Mixture of diastereoisomers. NMR data were consistent with the
proposed structure.
0.99 (t, J¼7.3 Hz, 3H). 13C NMR (400 MHz, CDCl3)
d ppm 165.95,
163.41, 138.69, 135.08, 131.52, 129.29, 129.18, 128.56, 126.42, 119.06,
118.83, 113.09, 112.93, 73.60, 55.15, 49.87, 41.14, 38.41, 36.11, 34.15,
32.78, 19.87, 14.05. HRMS calcd for
421.1956; found 421.1944.
C
22H30FN2O3S [MþH]þ
Compound 39. Yield: 29%. 1H NMR (400 MHz, CDCl3)
d ppm 7.93
(dd, J¼9.3, 5.5 Hz, 1H), 7.31e7.19 (m, 5H), 7.12e6.91 (m, 2H),
4.09e4.79 (m, 2H), 3.61e3.32 (m, 2H), 3.19e3.01 (m, 2H),
2.99e2.89 (m, 1H), 2.75e2.61 (m, 2H), 2.43e2.31 (m, 1H), 2.12e1.82
(m, 3H), 1.91e1.74 (m, 1H), 1.51e1.35 (m, 2H), 1.32e1.20 (m, 2H),
4.7.5. tert-Butyl ((2S,3R)-4-(7-fluoro-1,1-dioxido-4-phenyl-4,5-
dihydrobenzo[1,2-f] thiazepin-2(3H)-yl)-3-hydroxy-1-phenylbutan-
2-yl)carbamate (32). The title compound was prepared starting
from 26 following the general procedure for epoxide reaction. Yield
76%. Mixture of diastereoisomers. NMR data were consistent with
the structure.
0.99 (t, J¼7.3 Hz, 3H). 13C NMR (400 MHz, CDCl3)
d ppm 165.96,
163.43, 138.72, 135.08, 131.55, 129.32, 129.21, 128.56, 126.42, 119.06,
118.83, 113.14, 112.93, 73.62, 55.15, 49.87, 41.11, 38.42, 36.08, 34.20,
32.78, 19.90, 14.07. HRMS calcd for
421.1956; found 421.1950.
C
22H30FN2O3S [MþH]þ
4.8. A general procedure for TFA reaction 33e42
4.8.3. (S)-2-((2R,3S)-3-Amino-2-hydroxy-4-phenylbutyl)-7-fluoro-
4-isopropyl-2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine 1,1-dioxide (35)
and (R)-2-((2R,3S)-3-amino-2-hydroxy-4-phenylbutyl)-7-fluoro-4-
isopropyl-2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine 1,1-dioxide
(40). The title compounds were prepared following general pro-
cedure for TFA reaction starting from compound 30. Compound 35
is less polar than compound 40.
Compound 28 (87 mg, 0.17 mmol) was dissolved in a mixture of
DCM and trifluoroacetic acid (TFA) (5 mL:1 mL) and stirred at room
temperature under nitrogen for 3e4 h. TLC was checked to monitor
the progress of the reaction. After the reaction was complete, the
reaction mixture was basified with sodium hydroxide solution
(50%) and extracted with ethyl acetate. The combined organic layer
was dried with anhydrous sodium sulfate and evaporated to yield
the crude compound. Compounds 33 (22 mg) and 38 (23 mg) were
separated by preparative TLC (6% methanol in chloroform).
Compound 35. Isolated yield: 16%. 1H NMR (400 MHz, CDCl3)
d
ppm 7.89 (dd, J¼9.2, 5.6 Hz, 1H), 7.33e7.25 (m, 2H), 7.23e7.14 (m,
3H), 7.03e6.93 (m, 2H), 4.09e4.00 (m, 1H), 3.65e3.47 (m, 2H),

2902
A.K. Ganguly et al. / Tetrahedron 70 (2014) 2894e2904
3.27e3.02 (m, 3H), 2.89 (dd, J¼13.8, 4.3 Hz, 2H), 2.67 (d, J¼14.2 Hz,
1H), 2.51 (dd, J¼13.5, 9.4 Hz, 1H), 2.17e1.80 (m, 3H), 1.78e1.57 (m,
2H), 1.00 (d, J¼6.8 Hz, 3H), 0.93 (d, J¼6.8 Hz, 3H). 13C NMR
113.47, 113.26, 73.82, 57.85, 55.15, 49.66, 42.01, 39.21, 38.66. HRMS
calcd for C25H28FN2O3S [MþH]þ 455.1799; found 455.1797.
(400 MHz, CDCl3)
d ppm 165.95, 163.42, 143.14, 143.06, 138.43,
134.86, 131.56, 131.47, 129.16, 128.55, 126.43, 118.83, 118.61, 113.16,
112.94, 72.21, 54.85, 53.34, 49.56, 39.45, 37.88, 31.69, 19.26, 18.45.
HRMS calcd for C22H30FN2O3S [MþH]þ 421.1956; found 421.1953.
4.9. A general procedure for t-Boc carbamate formation
43e45
Compound 40. Yield: 40%. 1H NMR (400 MHz, CDCl3)
d
ppm 7.93
To an ice cold solution of compound 38 (20 mg, 0.05 mmol) in
THF (2 mL), diisopropylethylamine (DIPEA) (10.73 mg, 0.05 mmol)
was added followed by the addition of di-tert-butyl dicarbonate
(0.01 mL, 0.05 mmol) in THF (1 mL). The reaction mixture was
slowly allowed to reach room temperature and stirring was con-
tinued for 10e12 h under nitrogen. The progress of the reaction was
monitored by TLC. When the reaction was complete, the reaction
mixture was diluted with water and extracted with chloroform. The
combined organic layer was dried over anhydrous sodium sulfate
and evaporated to yield the crude compound. The crude compound
was purified by column chromatography using ethyl acetate and
hexane.
(dd, J¼9.3, 5.5 Hz, 1H), 7.31e7.19 (m, 5H), 7.12e6.91 (m, 2H),
4.19e4.01 (m, 1H), 3.83e3.71 (m, 1H), 3.65e3.51 (m, 1H), 3.49e3.35
(m, 1H), 3.21e3.10 (m, 2H), 3.05e2.89 (m, 1H), 2.90e2.81 (m, 1H),
2.74e2.62 (m, 1H), 2.51e2.40 (m, 1H), 1.61e1.50 (m, 5H), 0.98 (dd,
J¼21.7, 6.8 Hz, 6H). 13C NMR (400 MHz, CDCl3)
d ppm 165.95,163.42,
143.36, 143.28, 138.78, 134.94, 134.91, 131.64, 131.55, 129.32, 128.55,
126.39, 118.80, 118.58, 113.03, 73.68, 55.27, 55.19, 49.68, 38.47,
37.86, 31.72, 19.40, 18.30. HRMS calcd for C22H30FN2O3S [MþH]þ
421.1956; found 421.1946.
4.8.4. (S)-2-((2R,3S)-3-Amino-2-hydroxy-4-phenylbutyl)-4-(tert-bu-
tyl)-7-fluoro-2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine 1,1-dioxide
(36) and (R)-2-((2R,3S)-3-amino-2-hydroxy-4-phenylbutyl)-4-(tert-
butyl)-7-fluoro-2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine 1,1-dioxide
(41). The title compounds were prepared following general pro-
cedure for TFA reaction starting from compound 31. Compound 36
is less polar than compound 41.
4.9.1. tert-Butyl((2S,3R)-4-((S)-4-ethyl-7-fluoro-1,1-dioxido-4,5-
dihydrobenzo[1,2-f] thiazepin-2(3H)-yl)-3-hydroxy-1-phenylbutan-
2-yl)carbamate (43). The title compound was prepared following
the general procedure for t-Boc carbamate formation starting from
compound 38. Yield: 40%. 1H NMR (400 MHz, CDCl3)
d ppm 7.90
Compound 36. Isolated yield: 15%. 1H NMR (400 MHz, CDCl3)
(dd, J¼5.6, 9.3 Hz, 1H), 7.34e7.14 (m, 5H), 7.03e6.94 (m, 2H),
4.70e4.64 (m, 1H), 4.11e4.03 (m, 1H), 3.86e3.75 (m, 3H), 3.51e3.27
(m, 2H), 3.11e2.90 (m, 4H), 2.76e2.64 (m, 2H), 1.71e1.52 (m, 2H),
d
ppm 7.98e7.84 (m, 1H), 7.33e7.14 (m, 5H), 6.97 (d, J¼8.4 Hz, 2H),
4.01 (t, J¼13.3 Hz, 1H), 3.66e3.41 (m, 4H), 3.22e3.05 (m, 3H),
2.97e2.83 (m, 3H), 2.48 (dd, J¼13.0, 10.2 Hz, 1H), 1.47 (t, J¼11.0 Hz,
1H), 1.30e1.22 (m, 1H), 1.04e0.92 (m, 9H). 13C NMR (400 MHz,
1.35 (s, 9H), 0.98 (t, J¼7.4 Hz, 3H). 13C NMR (400 MHz, CDCl3)
d ppm
165.78, 163.42, 143.19, 137.99, 134.75, 131.66, 129.52, 128.44, 126.46,
118.81, 118.62, 113.07, 112.83, 107.90, 72.87, 67.66, 55.14, 54.84,
36.99, 34.91, 32.12, 29.06, 28.18, 19.42, 12.01. HRMS calcd for
CDCl3)
d ppm 166.25, 163.72, 143.77, 143.69, 138.69, 135.29, 135.26,
131.62, 129.42, 128.83, 126.71, 118.92, 118.69, 113.40, 113.19, 72.73,
55.16, 52.55, 49.85, 42.30, 39.75, 37.02, 33.00, 27.64. HRMS calcd for
C
26H36FN2O5S [MþH]þ 507.2323; found 507.2322.
C
23H32FN2O3S [MþH]þ 435.2112; found 435.2109.
Compound 41. Isolated yield: 15%. 1H NMR (400 MHz, CDCl3)
ppm 7.95e7.87 (m, 1H), 7.34e7.15 (m, 5H), 6.97 (d, J¼9.2 Hz, 2H),
4.9.2. tert-Butyl ((2S,3R)-4-((S)-7-fluoro-1,1-dioxido-4-propyl-4,5-
dihydrobenzo[1,2-f]thiazepin-2(3H)-yl)-3-hydroxy-1-phenylbutan-2-
yl)carbamate (44). The title compound was prepared following the
general procedure for t-Boc carbamate formation starting from
d
4.09e3.97 (m, 1H), 3.82e3.74 (m, 1H), 3.67 (d, J¼14.1 Hz, 1H),
3.58e3.44 (m, 3H), 3.11 (d, J¼13.0 Hz, 2H), 2.99 (d, J¼13.7 Hz, 1H),
2.87 (d, J¼14.4 Hz, 1H), 2.83e2.73 (m, 2H), 2.48e2.36 (m, 1H),
compound 39. Yield: 40%. 1H NMR (400 MHz, CDCl3)
d ppm 7.91
1.53e1.37 (m, 1H), 0.99 (s, 9H). 13C NMR (400 MHz, CDCl3)
d
ppm
(dd, J¼5.6, 9.3 Hz, 1H), 7.32e7.14 (m, 5H), 7.05e6.93 (m, 2H), 5.58
(dd, J¼1.1, 5.5 Hz, 1H), 4.68 (d, J¼6.9 Hz, 1H), 4.30e4.00 (m, 1H),
3.98e3.71 (m, 2H), 3.52e3.21 (m, 1H), 3.12e2.89 (m, 3H),
2.72e2.65 (m, 2H), 2.09e1.92 (m, 2H), 1.93e1.80 (m, 2H),
1.77e1.70 (m, 2H), 1.34 (s, 9H), 0.98 (t, J¼7.4 Hz, 3H). 13C NMR
166.41, 163.51, 143.75, 143.69, 138.70, 135.29, 135.21, 131.62, 129.39,
128.83, 126.69, 118.92, 118.69, 113.43, 113.19, 72.73, 55.16, 52.53,
49.85, 42.30, 39.75, 37.05, 33.07, 27.61. HRMS calcd for
C
23H32FN2O3S [MþH]þ 435.2112; found 435.2109.
(400 MHz, CDCl3)
d ppm 165.94, 163.44, 143.20, 137.89, 134.77,
4.8.5. (S)-2-((2R,3S)-3-Amino-2-hydroxy-4-phenylbutyl)-7-fluoro-
4-phenyl-2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine 1,1-dioxide (37)
and (R)-2-((2R,3S)-3-amino-2-hydroxy-4-phenylbutyl)-7-fluoro-4-
phenyl-2,3,4,5-tetrahydrobenzo[1,2-f]thiazepine 1,1-dioxide
(42). The title compounds were prepared starting from 32 fol-
lowing the general procedure for TFA reaction.
131.66, 129.51, 128.42, 126.49, 118.82, 118.60, 113.05, 112.87, 107.94,
72.87, 67.65, 55.09, 49.75, 37.72, 34.92, 32.78, 29.09, 28.18, 19.93,
14.04. HRMS calcd for C27H38FN2O5S [MþH]þ 521.2480; found
521.2477.
4.9.3. tert-Butyl((2S,3R)-4-((R)-7-fluoro-4-isopropyl-1,1-dioxido-
4,5-dihydrobenzo[1,2-f] thiazepin-2(3H)-yl)-3-hydroxy-1-
phenylbutan-2-yl)carbamate (45). The title compound was pre-
pared following the general procedure for t-Boc carbamate for-
mation starting from compound 40. Yield: 27%. 1H NMR (400 MHz,
Compound 37. Isolated yield: 18%. 1H NMR (400 MHz, CDCl3)
d
ppm 7.98 (dd, J¼8.5, 5.6 Hz, 1H), 7.45e7.11 (m, 11H), 7.03 (m, 2H),
4.35e4.25 (m, 1H), 4.18 (dd, J¼14.1, 11.6 Hz, 1H), 3.78e3.43 (m, 1H),
3.05 (m, 8H), 2.54 (dd, J¼13.6, 9.3 Hz, 1H); 13C NMR (400 MHz,
CDCl3)
d
ppm 166.03, 163.49, 142.27, 141.98, 141.89, 138.30, 135.16,
CDCl3)
d
ppm 7.90 (dd, J¼5.6, 9.3 Hz, 1H), 7.35e7.20 (m, 5H),
135.13, 131.70, 131.61, 129.16, 129.06, 128.58, 127.37, 126.83, 126.47,
119.36, 113.6, 113.42, 72.27, 56.31, 54.91, 49.94, 41.98, 39.73, 38.92.
HRMS calcd for C25H28FN2O3S [MþH]þ 455.1799; found 455.1796.
Compound 42. Isolated yield: 24%. 1H NMR (400 MHz, CDCl3)
7.01e6.92 (m, 2H), 5.58 (dd, J¼1.1, 5.5 Hz, 1H), 4.69 (d, J¼6.9 Hz, 1H),
4.17e4.00 (m, 1H), 3.99e3.90 (m, 1H), 3.87e3.76 (m, 1H), 3.53 (dd,
J¼11.2, 13.9 Hz, 1H), 3.24 (d, J¼15.2 Hz, 1H), 3.15e2.87 (m, 2H),
2.70e2.59 (m, 1H), 2.09e1.96 (m, 1H), 1.95e1.81 (m, 1H), 1.80e1.65
(m, 2H), 1.34 (s, 9H), 0.98 (d, J¼6.6 Hz, 3H), 0.92 (d, J¼6.9 Hz, 3H).
d
ppm 7.99 (dd, J¼8.6, 5.6 Hz, 1H), 7.44e7.12 (m, 11H), 7.11e6.96 (m,
2H), 4.39e4.24 (m, 1H), 4.17 (dd, J¼14.1, 11.9 Hz, 1H), 3.83e3.74 (m,
1H), 3.51 (d, J¼14.9 Hz, 1H), 3.24 (dd, J¼14.8, 3.4 Hz, 1H), 3.19e2.87
(m, 6H), 2.42 (dd, J¼13.3, 10.1 Hz, 1H); 13C NMR (400 MHz, CDCl3)
13C NMR (400 MHz, CDCl3)
d ppm 165.99, 163.46, 158.62, 143.24,
137.89, 134.77, 131.66, 129.53, 128.42, 126.46, 118.82, 118.60, 113.05,
112.83, 107.90, 72.87, 67.65, 55.14, 49.75, 37.71, 31.68, 29.09, 28.18,
d
ppm 165.99, 163.45, 142.49, 142.11, 142.03, 138.71, 135.11, 135.08,
23.88, 19.42, 18.26. HRMS calcd for
521.2480; found 521.2479.
C
27H38FN2O5S [MþH]þ
131.80, 131.70, 129.28, 129.05, 128.96, 128.55, 126.89, 126.40, 119.33,

A.K. Ganguly et al. / Tetrahedron 70 (2014) 2894e2904
2903
4.10. A general procedure for urea formation. 1-(tert-Butyl)-
3-((2S,3R)-4-((R)-7-fluoro-4-isopropyl-1,1-dioxido-4,5-
dihydrobenzo[1,2-f]thiazepin-2(3H)-yl)-3-hydroxy-1-
phenylbutan-2-yl)urea (50)
(m, 7H), 3.59e3.40 (m, 2H), 3.13e2.98 (m, 2H), 2.95e2.80 (m, 2H),
2.67e2.57 (m, 1H), 2.13e2.05 (m, 1H), 1.98e1.81 (m, 1H), 1.47e1.36
(m, 1H), 0.98 (s, 9H); 13C NMR (400 MHz, CDCl3)
d ppm 166.03,
163.50, 156.56, 143.65, 143.57, 137.56, 137.19, 134.82, 131.41, 129.44,
128.49, 126.57, 118.70, 118.48, 113.02, 112.80, 75.48, 73.09, 72.73,
66.85, 55.29, 49.94, 36.81, 36.73, 35.10, 32.74, 32.69, 22.61, 14.09.
HRMS calcd for C28H38FN2O6S [MþH]þ 549.2429; found 549.2422.
To a solution of 2-isocyanato-2-methylpropane (0.005 mL,
0.05 mmol) in 1,4-dioxane (1 mL), was added magnesium bromide
(0.87 mg, 0.005 mmol) followed by compound 40 (20 mg,
0.05 mmol) in 1,4 dioxane (1 mL). The reaction mixture was stirred
at room temperature for 10e12 h under nitrogen. TLC was checked
to monitor the progress of the reaction. The reaction mixture was
evaporated to dryness. The residue was extracted with DCM and
washed with water. The combined organic layer was dried over
sodium sulfate, filtered, and evaporated to dryness to yield the
crude compound, which was purified by column chromatography
using 15% ethyl acetate in hexane to give the title compound 50.
4.11.3. (S)-Tetrahydrofuran-3-yl((2S,3R)-4-((R)-4-(4-fluorophenyl)-
1,1-dioxido-4,5-dihydrobenzo[1,2-f]thiazepin-2(3H)-yl)-3-hydroxy-
1-phenylbutan-2-yl)carbamate (49). The title compounds were
prepared starting from 42 following the general procedure for THF
carbamate formation. Yield: 80%. 1H NMR (400 MHz, CDCl3)
d ppm
7.96 (dd, J¼8.6, 5.6 Hz, 1H), 7.42e7.15 (m, 10H), 7.10e6.95 (m, 2H),
5.13e5.06 (m, 1H), 5.03e4.79 (m, 1H), 4.41e4.26 (m, 1H), 4.13 (m,
2H), 3.95e3.62 (m, 5H), 3.40e3.27 (m, 1H), 3.22e3.12 (m, 1H),
Yield 55%. 1H NMR (400 MHz)
d
ppm 7.89 (dd, 1H, J¼5.4, 9.1 Hz, 1H),
3.07e2.73 (m, 5H), 2.19e2.05 (m,1H), 2.04 (m, 1H),1.87 (m,1H); 13
C
7.32e7.16 (m, 5H), 7.01e6.93 (m, 2H), 5.39 (s, 1H), 4.69e4.60 (m,
1H), 4.37e4.33 (m, 1H), 4.04e3.92 (m, 2H), 3.85e3.49 (m, 1H),
3.54e3.46 (m, 1H), 3.26e3.04 (m, 2H), 2.98e2.90 (m, 2H),
2.69e2.56 (m, 2H), 1.76e1.64 (m, 2H), 1.25 (s, 9H), 0.99 (d, J¼6.5 Hz,
NMR (400 MHz, CDCl3) d ppm 166.09, 163.55, 156.67, 142.24, 142.10,
142.02, 137.57, 134.92, 134.90, 131.80, 129.41, 129.05, 128.54, 127.39,
126.87, 126.62, 119.44, 119.22, 113.52, 113.30, 75.58, 73.04, 72.74,
66.84, 57.47, 55.42, 50.04, 42.04, 39.09, 34.85, 32.78. HRMS calcd for
3H), 0.92 (d, J¼6.6 Hz, 3H). 13C NMR (400 MHz, CDCl3)
d
ppm 166.01,
C
30H34FN2O6S [MþH]þ 569.2116; found 569.2113.
163.47, 158.68, 143.32, 143.24, 138.48, 134.78, 131.39, 131.31, 129.39,
129.24, 128.48, 126.41, 118.85, 113.13, 112.92, 72.29, 56.32, 53.71,
50.53, 48.87, 37.62, 37.03, 35.40, 31.68, 29.31, 19.44, 18.22. HRMS
calcd for C27H39FN3O4S [MþH]þ 520.2640; found 520.2636.
4.11.4. (S)-Tetrahydrofuran-3-yl((2S,3R)-4-((S)-7-fluoro-4-isopropyl-
1,1-dioxido-4,5-dihydrobenzo[1,2-f]thiazepin-2(3H)-yl)-3-hydroxy-
1-phenylbutan-2-yl)carbamate (51). The title compound was pre-
pared following the general procedure for THF carbamate starting
4.11. A general procedure for tetrahydrofuran (THF) carba-
from compound 35. Yield: 50%. 1H NMR (400 MHz, CDCl3)
d ppm
mate formation 47e49 and 51e52
7.87 (dd, J¼9.2, 5.6 Hz, 1H), 7.31e7.12 (m, 5H), 7.10e6.93 (m, 2H),
5.15e5.02 (m, 1H), 5.01e4.94 (m, 1H), 4.06e3.95 (m, 1H), 3.79e3.60
(m, 5H), 3.62e3.42 (m, 3H), 3.15e3.01 (m, 1H), 2.97e2.86 (m, 3H),
2.71e2.60 (m, 2H), 2.07e2.00 (m, 1H), 1.91e1.79 (m, 1H), 1.70e1.65
(m, 1H), 1.57e1.50 (m, 1H), 0.97 (d, J¼6.8 Hz, 3H), 0.91 (d, J¼6.8 Hz,
To a solution of (S)-2,5-dioxopyrrolidin-1-yl (tetrahydrofuran-3-
yl) carbonate (12.6 mg, 0.06 mmol) and triethylamine (0.01 mL,
0.1 mmol) in DCM (2 mL), was added compound 40 (20 mg,
0.05 mmol) dissolved in DCM (1 mL). The reaction mixture was
stirred at room temperature for 10e12 h under nitrogen. After the
completion of the reaction, monitored by TLC, the reaction mixture
was diluted with DCM, and washed with saturated aq sodium bi-
carbonate solution. The aqueous layer was again extracted with
DCM. The combined organic layer was dried over anhydrous so-
dium sulfate, filtered, and evaporated to dryness to give the crude
compound, which was purified by column chromatography using
20% ethyl acetate in hexane to give the pure compound 47 (11 mg).
3H). 13C NMR (400 MHz, CDCl3)
d ppm 166.00, 163.47, 155.86,
143.09, 143.00, 137.29, 134.61, 131.55, 131.45, 129.36, 128.42, 126.50,
118.92,118.69,113.21, 112.99, 75.23, 73.10, 71.45, 66.78, 54.56, 53.74,
50.74, 37.75, 35.46, 32.64, 31.61, 19.25, 18.34. HRMS calcd for
C
27H36FN2O6S [MþH]þ 535.2273; found 535.2251.
4.11.5. (S)-Tetrahydrofuran-3-yl((2S,3R)-4-((S)-4-(tert-butyl)-7-
fluoro-1,1-dioxido-4,5-dihydrobenzo[1,2- f]thiazepin-2(3H)-yl)-3-
hydroxy-1-phenylbutan-2-yl)carbamate (52). The title compound
was prepared following the general procedure for THF carbamate
starting from compound 36. Yield: 49%. 1H NMR (400 MHz, CDCl3)
4.11.1. (S)-Tetrahydrofuran-3-yl((2S,3R)-4-((R)-7-fluoro-4-isopropyl-
1,1-dioxido-4,5-dihydrobenzo[1,2-f]thiazepin-2(3H)-yl)-3-hydroxy-
1-phenylbutan-2-yl)carbamate (47). The title compound was pre-
pared following the general procedure for THF carbamate starting
d
ppm 7.99e7.82 (m, 1H), 7.32e7.14 (m, 5H), 7.05e6.92 (m, 2H),
5.13e5.05 (m, 1H), 4.91e4.83 (m, 1H), 4.15e4.08 (m, 1H), 4.02e3.93
(m, 1H), 3.87e3.66 (m, 4H), 3.59 (d, J¼10.4 Hz, 1H), 3.53e3.42 (m,
2H), 3.36 (d, J¼14.3 Hz, 1H), 2.99e2.82 (m, 4H), 2.76e2.65 (m, 1H),
2.14e2.02 (m, 1H), 1.95e1.81 (m, 1H), 1.42e1.29 (m, 1H), 0.96 (s,
from compound 40. Yield: 43%. 1H NMR (400 MHz, CDCl3)
d ppm
7.90 (dd, J¼9.3, 5.6 Hz, 1H), 7.25 (m, 5H), 6.98 (m, 2H), 5.12 (m, 1H),
4.89 (m, 1H), 4.08 (m, 1H), 3.86 (m, 5H), 3.68 (m, 1H), 3.53 (m, 1H),
3.22 (m, 1H), 3.05 (m, 1H), 2.84 (m, 1H), 2.64 (m, 2H), 2.09 (m, 1H),
1.90 (m, 1H), 1.72 (m, 1H), 1.58 (m, 2H), 1.28 (m, 1H), 0.99 (d,
J¼6.9 Hz, 3H), 0.87 (d, J¼6.8 Hz, 3H); 13C NMR (400 MHz, CDCl3)
9H); 13C NMR (400 MHz, CDCl3)
d ppm 166.09, 163.55, 155.89,
143.50, 143.41, 137.18, 134.75, 131.50, 131.40, 129.46, 128.50, 126.59,
118.79, 118.57, 113.24, 113.03, 75.28, 73.20, 71.70, 66.84, 54.52,
52.87, 51.01, 42.39, 36.73, 35.63, 32.70, 27.38, 18.34. HRMS calcd for
d
ppm 166.06, 163.53, 156.69, 143.25, 137.61, 134.68, 131.70, 129.46,
C
28H38FN2O6S [MþH]þ 549.2429; found 549.2421.
128.54, 126.62, 118.93, 118.70, 114.68, 113.10, 112.89, 75.58, 73.10,
72.64, 66.87, 55.43, 54.92, 49.90, 37.81, 35.03, 32.78, 25.44, 19.40,
18.34. HRMS calcd for C27H36FN2O6S [MþH]þ 535.2273; found
535.2265.
4.12. In vitro HIV-1 protease assay
Compounds were evaluated for the ability to inhibit the enzy-
matic activity of HIV-1 protease in an in vitro assay modified for
product quantitation with use of mass spectrometric analysis.8
Protease activity was assessed in reactions catalyzed by purified
HIV-1 protease at 20 pM in buffer (50 mM sodium acetate, pH 5.5,
100 mM NaCl, 1 mg/mL bovine serum albumin) using a peptide
4.11.2. (S)-Tetrahydrofuran-3-yl((2S,3R)-4-((R)-4-(tert-butyl)-7-
fluoro-1,1-dioxido-4,5-dihydrobenzo[1,2-f]thiazepin-2(3H)-yl)-3-
hydroxy-1-phenylbutan-2-yl)carbamate (48). The title compound
was prepared following the general procedure for THF carbamate
starting from compound 41. Yield: 45%. 1H NMR (400 MHz, CDCl3)
substrate with sequence Val-Ser-Gln-Asn-(
Ile-Val at 450 M in a final volume of 25
stock were added to a final DMSO concentration of 2.5% and
b
-naphthylalanine)-Pro-
d
ppm 7.98e7.81 (m, 1H), 7.38e7.15 (m, 5H), 7.06e6.89 (m, 2H),
m
mL. Compounds in DMSO
5.15e5.07 (m, 1H), 4.95e4.83 (m, 1H), 4.13e3.96 (m, 1H), 3.96e3.58

2904
A.K. Ganguly et al. / Tetrahedron 70 (2014) 2894e2904
preincubated with enzyme prior to the initiation of the reaction by
addition of substrate. Inhibitor dose titrations were used to de-
termine IC50 values. Reactions were incubated at 30 ꢀC for 60 min
4.14. Accession codes
The X-ray crystal structure of inhibitors 47, 48, 50, and 52 bound
to HIV-1 protease have been deposited within the Protein Databank
with access code 4mc9, 4mc6, 4mc2, and 4mc1, respectively.
and were then quenched by the addition of 30 mL of 0.04% formic
acid and 250 nM indinavir as an internal standard. The amount of
product formed was determined using high performance liquid
chromatography with a Zorbax Eclipse XDB-C18 column and mass
spectrometric detection of product on an Agilent API4000 mass
spectrometer. Percent inhibition was determined relative to control
samples without inhibitor, and IC50 values were determined using
a standard four parameter fit to the inhibition data. Ki values were
determined from Eq. 1 for competitive inhibitors,
Acknowledgements
We thank Stevens Institute of Technology, Hoboken, NJ, for
generous financial support.
References and notes
IC50 ¼ Kið1 þ ½Sꢃ=KMÞ
with a KM of 90 M.
(1)
1. (a) Ganguly, A. K.; Alluri, S. S.; Caroccia, D.; Biswas, D.; Wang, C.-H.; Kang, E.;
Zhang, Y.; McPhail, A. T.; Carroll, S. S.; Burlein, C.; Munshi, V.; Orth, P.; Strickland,
C. J. Med. Chem. 2011, 54, 7176e7183; (b) Biswas, D.; Samp, L.; Ganguly, A. K.
Tetrahedron Lett. 2010, 51, 2681e2684.
2. (a) Turner, S. R.; Strohbach, J. W.; Tommasi, R. A.; Aristoff, P. A.; Johnson, P. D.;
Skulnick, H. I.; Dolak, L. A.; Seest, E. P.; Tomich, P. K.; Bohanon, M. J.; Horng, M.
M.; Lynn, J. C.; Chong, K. T.; Hinshaw, R. R.; Watenpaugh, K. D.; Janakiraman, M.
N.; Thaisrivongs, S. J. Med. Chem. 1998, 41, 3467e3476; (b) De Meyer, S.; Azijn, H.;
Surleraux, D.; Jochmans, D.; Tahri, A.; Pauwels, R.; Wigerinck, P.; de Bethune, M.
P. Antimicrob. Agents Chemother. 2005, 49, 2314e2321.
3. (a) Ghosh, A. K.; Chapsal, B. D.; Baldridge, A.; Steffey, M. P.; Walters, D. E.; Koh, Y.;
Amano, M.; Mitsuya, H. J. Med. Chem. 2011, 54, 622e634; (b) Ali, A.; Kiran Kumar
Reddy, G. S.; Nalam, M. N. L.; Anjum, S. G.; Cao, H.; Schiffer, C. A.; Rana, T. M. J.
Med. Chem. 2010, 53, 7699e7708.
4. He, G.-X.; Yang, Z.-Y.; Williams, M.; Callebaut, C.; Cihlar, T.; Murray, B. P.; Yang, C.;
Mitchell, M. L.; Liu, H.; Wang, J.; Arimilli, M.; Eisenberg, E.; Stray, K. M.; Tsai, L. K.;
Hatada, M.; Chen, X.; Chen, J. M.; Wang, Y.; Lee, M. S.; Strickley, R. G.; Iwata, Q.;
Zheng, X.; Kim, C. U.; Swaminathan, S.; Desai, M. C.; Lee, W. A.; Xu, L. Med. Chem.
Commun. 2011, 2, 1093e1098.
m
4.13. X-ray crystallography
The triple mutant Q7K L33I L63I was used because of its higher
stability against autoproteolysis. HIV-1 protease crystals were
grown by the hanging-drop vapor diffusion method against 0.7 M
NaCl, acetate buffer, pH 5.5. Plate-shaped crystals belong to space
ꢀ
ꢀ
group P21212 with unit cell dimensions of a¼58.6 A, b¼85.9 A,
ꢀ
c¼46.2 A and one dimer per asymmetric unit. Crystals were soaked
in the reservoir solution in the presence of 1 mM inhibitor. 25%
glycerol was added for cryoprotection, and crystals were flash-
frozen in liquid nitrogen. High resolution limits lay between 1.18
ꢀ
and 1.56 A. Data sets with atleast 97% completeness were collected
5. Cheng, B.; Sunderhaus, J. D.; Martin, S. F. Org. Lett. 2010, 12, 3622e3625.
6. (a) Reed, S. F., Jr. J. Org. Chem. 1965, 30 3258e3258; (b) Osby, J. O.; Martin, M. G.;
Ganem, B. Tetrahedron Lett. 1984, 25, 2093e2096; (c) Sasaki, T.; Minamoto, K.;
Itoh, H. J. Org. Chem. 1978, 43, 2320e2325.
7. Hohlfeld, K.; Tomassi, C.; Wegner, J. K.; Kesteleyn, B.; Linclau, B. ACS Med. Chem.
Lett. 2011, 2, 461e465.
at the APS beamline ID17 (Argonne, IL) and processed using auto-
Proc. Rmerge and I/s were atleast 6.9% and 15.9 for the whole data
set and were 63.4% and 2.5 for the highest resolution shell, re-
spectively. The structures were refined using Buster and manually
refitted using Coot, resulting in final Rwork (Rfree) of 20.0% (20.7%)
and excellent geometry. Figures were generated using Pymol.
8. Olsen, D.; Stahlhut, M.; Rutkowski, C.; Schock, H.; vanOlden, A.; Kuo, L. C. J. Biol.
Chem. 1999, 274, 23699e23701.