Design, synthesis, and biological and structural evaluations of novel HIV-1 protease inhibitors to combat drug resistance

Article abstract of DOI:10.1021/jm300238h

A series of new HIV-1 protease inhibitors (PIs) were designed using a general strategy that combines computational structure-based design with substrate-envelope constraints. The PIs incorporate various alcohol-derived P2 carbamates with acyclic and cyclic heteroatomic functionalities into the (R)-hydroxyethylamine isostere. Most of the new PIs show potent binding affinities against wild-type HIV-1 protease and three multidrug resistant (MDR) variants. In particular, inhibitors containing the 2,2-dichloroacetamide, pyrrolidinone, imidazolidinone, and oxazolidinone moieties at P2 are the most potent with K_i values in the picomolar range. Several new PIs exhibit nanomolar antiviral potencies against patient-derived wild-type viruses from HIV-1 clades A, B, and C and two MDR variants. Crystal structure analyses of four potent inhibitors revealed that carbonyl groups of the new P2 moieties promote extensive hydrogen bond interactions with the invariant Asp29 residue of the protease. These structure-activity relationship findings can be utilized to design new PIs with enhanced enzyme inhibitory and antiviral potencies.

Full text of DOI:10.1021/jm300238h

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Article
Design, Synthesis, Biological and Structural Evaluations of
Novel HIV-1 Protease Inhibitors to Combat Drug Resistance
Maloy K Parai, David J Huggins, Hong Cao, Madhavi N.L. Nalam,
Akbar Ali, Celia A. Schiffer, Bruce Tidor, and Tariq M. Rana
J. Med. Chem., Just Accepted Manuscript • DOI: 10.1021/jm300238h • Publication Date (Web): 18 Jun 2012
Downloaded from http://pubs.acs.org on June 26, 2012
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Design, Synthesis, Biological and Structural
Evaluations of Novel HIV-1 Protease Inhibitors to
Combat Drug Resistance
Maloy Kumar Parai,1 David J. Huggins,2 Hong Cao,3 Madhavi N. L. Nalam,4 Akbar Ali,3 Celia A.
Schiffer,4 Bruce Tidor,2 and Tariq M. Rana1, 3*
1Program for RNA Biology, SanfordꢀBurnham Medical Research Institute, La Jolla, CA 92037;
2Department of Biological Engineering and Computer Science and Artificial Intelligence Laboratory,
Massachusetts Institute of Technology, Cambridge, MA 02139; 3Chemical Biology Program,
Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical
School, Worcester, MA 01605, 4Department of Biochemistry and Molecular Pharmacology, University
of Massachusetts Medical School, Worcester, MA 01605.
RECEIVED DATE (to be automatically inserted after your manuscript is accepted if required
according to the journal that you are submitting your paper to)
*To whom correspondence should be addressed. Tel: (858) 795ꢀ5325, Fax: (858) 795ꢀ5328
Eꢀmail: trana@sanfordburnham.org
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Abstract
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A series of new HIVꢀ1 protease inhibitors (PIs) were designed using a general strategy that combines
computational structureꢀbased design with substrateꢀenvelope constraints. The PIs incorporate various
alcoholꢀderived P2 carbamates with acyclic and cyclic heteroatomic functionalities into the (R)ꢀ
hydroxyethylamine isostere. Most of the new PIs show potent binding affinities against wildꢀtype HIVꢀ1
protease and three multidrug resistant (MDR) variants, in particular inhibitors containing 2,2ꢀ
dichloroacetamide, pyrrolidinone, imidazolidinone, and oxazolidinone moieties at P2 are the most
potent with Ki values in the picomolar range. Several new PIs exhibit nanomolar antiviral potencies
against patientꢀderived wildꢀtype viruses from HIVꢀ1 clades A, B, and C and two MDR variants. Crystal
structure analyses of four potent inhibitors revealed that carbonyl groups of the new P2 moieties
promote extensive hydrogen bond interactions with the invariant Aspꢀ29 residue of the protease. These
structureꢀactivity relationship findings can be utilized to design new PIs with enhanced enzyme
inhibitory and antiviral potencies.
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Introduction
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The human immunodeficiency virus type 1 (HIVꢀ1) protease plays an important role in the viral
replication by processing the viral Gag and GagꢀPol polyproteins into functional and structural proteins
essential for viral assembly and maturation. Inhibition of HIVꢀ1 protease leads to the generation of
immature virus particles. Hence, HIVꢀ1 protease has emerged as a promising target for therapeutic
intervention in HIV/AIDS patients. The addition of protease inhibitors (PIs) to the highly active
antiretroviral therapy (HAART) with reverseꢀtranscriptase inhibitors resulted in an unprecedented
success of HIV/AIDS chemotherapy.1ꢀ4 However, rapid emergence of drugꢀresistant HIVꢀ1 variants,
transmission of these resistant viral strains and the adverse effects of currently used HIVꢀ1 PIs remain
critical factors limiting the clinical effectiveness of antiretroviral therapies.5ꢀ7 Therefore, to alleviate
these problems, there is a need for the development of new PIs with improved activity against drug
resistant variants and excellent pharmacokinetic and safety profiles.
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Crystal structure analyses of HIVꢀ1 protease in complex with its peptide substrates suggest that
substrate specificity depends on matching a defined shape within the binding site. This shape has been
termed as the substrate envelope.8 Among the FDA approved PIs, amprenavir9 (1, APV, Figure 1)
containing tetrahydrofuran (THF) as the P2 ligand fits reasonably well within the substrate envelope.
The structurally similar nonꢀpeptidic PI, darunavir10ꢀ13 (2, DRV, Figure 1) with bisꢀtetrahydrofuran (bisꢀ
THF) as the P2 ligand exerts high in vitro and in vivo antiviral potency against wildꢀtype HIVꢀ1 as well
as multidrug resistant (MDR) strains. It is reasoned that the additional interactions of bisꢀTHF moiety in
inhibitor 2 with the backbone atoms of Aspꢀ29 and Aspꢀ30 residues in protease result in its potent
activity against MDR HIVꢀ1 variants.13, 14 However, inhibitor 2, though significantly more potent than
1, contains a structurally complex and stereochemically defined P2 ligand, requiring multiple steps for
synthesis. In addition to inhibitor 2, a number of highly potent PIs incorporate the bisꢀTHF moiety or
similar bicyclic ether and flexible polyꢀether based P2 ligands that mimic bisꢀTHF.15ꢀ20
We have been pursuing a general strategy combining structureꢀbased design with substrateꢀenvelope
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constraints to develop novel HIVꢀ1 PIs against clinically relevant MDR protease variants with reduced
structural complexity and hence cost effectiveness. We have recently reported a series of novel PIs that
incorporate stereochemically defined Nꢀphenyloxazolidinoneꢀ5ꢀcarboxamides as P2 ligands into the (R)ꢀ
(hydroxyethylamino)sulfonamide isostere, the core scaffold of inhibitors 1 and 2, and possess
impressive enzyme affinities and antiviral activity against both wildꢀtype and a panel of MDR HIVꢀ1
variants.21, 22 Moreover, crystal structure analysis of the inhibitor 3 in complex with wildꢀtype HIVꢀ1
protease confirmed that the carbonyl group of the oxazolidinone ring mimics the hydrogenꢀbond
interactions of THF/bisꢀTHF moieties of inhibitors 1 and 2, respectively.
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Since the carbonyl oxygen of ester, amide, and lactone functionalities can also act as hydrogen bond
acceptors, it is expected that the above functionalities could mimic the critical hydrogen binding
interactions of bisꢀTHF with the protease enzyme, and the presence of other heteroatoms in the ligand
would make additional interactions with the side chain residues of the protease in the S2 binding pocket.
Thus, we envisioned that P2 ligands containing ester, amide, urea and lactone with flexible carbon chain
may accommodate amino acid side chain variations and interact strongly with enzyme backbone. Based
on this precept, we selected as P2 ligands alcohols 6a-j containing structurally related five membered
heterocyclic structures pyrrolidone, dihydrofuranone, imidazolidone, oxazolidone and some acyclic
ketone, ester, amide subunits for the design of new PIs. To investigate the potential of these
functionalized P2 ligands in combination with (R)ꢀ(hydroxyethylamino)sulfonamide isostere, we have
designed and synthesized a series of new PIs (Figure 1).
In the present study, we report the structureꢀbased computational design, synthesis and biological
evaluation of a series of HIVꢀ1 PIs incorporating a variety of P2 carbamates derived from acyclic and
cyclic alcohols. Structureꢀactivity relationship (SAR) studies with variations at P2, P22 and P12
positions resulted in the generation of several highly potent HIVꢀ1 PIs. Compounds with potent
enzymatic activity have been further evaluated against a panel of MDR HIVꢀ1 protease variants and for
antiviral activity in cellular assays against patient derived wildꢀtype HIVꢀ1 viruses from clades A, B,
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and C and two MDR HIVꢀ1 variants. Crystal structures of the four most potent new inhibitors 13c, 13g,
13f and 14j in complex with wildꢀtype HIVꢀ1 protease are also discussed.
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NH2
NH2
H
O
O
O
O
O
O
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O
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O
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N
H
O
H
H
OH
OH
2
1
OCH3
O
O
O
S
N
H
N
N
O
O
OH
O
(3, Ki = 0.8 pM)
New Design
R2
O
R2
O
O
O
S
S
Y
R3
O
N
N
X
O
N
N
n
Z
n
O
O
H
H
R1
R1
OH
OH
n = 1, 2
4
n = 0, 1, 2
5
R1 = (S)-2-methylbutyl, n-pentyl
R2 = 4-OCH3, 3,4-S-CH=N-
X = CH, NH
Y = CO, NH
Z = CO, O, NH
R3 = ketone, amide, ester, carbamate
Figure 1. Chemical structures of amprenavir 1, darunavir 2, lead compound 3, and designed inhibitors 4
and 5.
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Computational Design
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The aim of inverse design is to consider a large combinatorial library of potential inhibitors and
identify a set of molecules with high affinity against a protein target that are capable of binding within
the substrate envelope. The first step in the inverse design procedure is to select and prepare the protein
target structure. Previous work on HIVꢀ1 protease has shown that improved results can be achieved by
using a crystal structure containing a ligand that is similar to the molecules in the combinatorial
library.23 The ligand is removed from the complex to yield a structure that is amenable for inverse
design. In this work, based on the (R)ꢀhydroxyethylamine isostere of inhibitors 1 and 2, the 2ꢀbound
HIVꢀ1 protease structure (PDB accession code 1T3R) was used.
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Once selected, the protein structure was subjected to a standard preparation protocol. Coordinates
were taken from the PDB and the ligand was removed from the bound state. Three tightly bound water
molecules (HOH1201, HOH1202, and HOH1203) were retained, with all other water molecules
removed. The protein and water hydrogenꢀatom positions were then built using the HBUILD facility of
the CHARMM27 program package24 with the CHARMM22 energy function.25 Histidine residues were
checked for orientations and protonation state, which resulted in the two His69 residues being flipped
and assigned as epsilon protonated. The residues lysine, arginine, aspartate, glutamate, cysteine and
tyrosine were also analyzed to check their protonation state. There was no evidence of any unusual
protonation states and thus all lysine and arginine residues were assigned as positively charged, all
aspartate and glutamate residues were assigned as negatively charged, and all cysteine and tyrosine
residues were assigned as neutral. After minimization of the hydrogenꢀatom positions, the resultant
structures were then rotated into a new coordinate frame and the protein atoms were assigned PARSE
charges26 for use with Delphi.27, 28 The next stage involved creating van der Waals and electrostatic
grids for gridꢀbased energy calculations. The primary scoring function contains three components: a van
der Waals term, a screened electrostatic interaction term, and desolvation penalties for the ligand and
the protein. Grids for van der Waals energies are computed by placing every type of parameterized
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CHARMM atom type at each gridꢀpoint and computing its van der Waals interaction energy with the
protein. For any charged atoms at the grid points, the electrostatic binding free energy was calculated
using the linearized Poisson–Boltzmann equation29 using a locally modified version of the DelPhi
computer program.30
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The next step in the inverse design procedure is to generate the volume in which the designed
inhibitors must lie. When attempting to design molecules that are not susceptible to resistance
mutations, this volume is the substrate envelope. The substrate envelope is generated from the
consensus volume of a set of naturally occurring substrates. In this case, the substrate envelope was
created from five aligned HIVꢀ1 protease−substrate peptide complexes and then transferred to a 2ꢀ
bound HIVꢀ1 protease structure.23 After selecting and preparing the protein structure and the design
shape, the next stage is to place the core scaffold in an ensemble of lowꢀenergy conformations within
the site. The core scaffold in this case is the (R)ꢀhydroxyethylamine isostere shown in Figure 1. A
systematic set of conformations was created by rotating each rotatable torsion angle in increments of
30°. Each conformation was then subjected to systematic placement in the active site with a
translational enumeration of 0.25 Å and a rotational enumeration such that the maximum arc length of
atoms from the centroid swept out a distance of 1.0 Å between orientations. Scaffold placements were
accepted if all atom centers were contained within the substrate envelope, but discarded if their
calculated van der Waals binding energy was greater than zero or any two nonbonded atoms' 0.75ꢀ
scaled radii overlapped.
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Each designed inhibitor is comprised of the (R)ꢀhydroxyethylamine isostere with three side group
substituents, termed R1, R2 and R3. These substituents are derived from primary amines, sulfonyl
chlorides, and alcohols respectively (Scheme 2). The substituents used in the inverse design procedure
were taken from the ZINC database of commercially available compounds.31 Every acceptable scaffold
pose was used for a separate design with the set of side group substituents at R1, R2 and R3 using the
guaranteed combinatorial search algorithms deadꢀend elimination (DEE)32 and A*.33 The DEE/A*
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algorithm places all side group substituents in all conformations and combinations on each scaffold pose
to yield an energyꢀranked list of 1000 unique molecules. The ranked list was then reduced to a
computationally feasible size by removing compounds with an energy of 25.0 kcal/mol or higher than
the lowest energy result. The resulting topꢀranked compounds from the combinatorial search were reꢀ
evaluated using more accurate physicsꢀbased energy functions to identify candidate molecules for
synthesis and testing. The most sophisticated energy function included a geometry optimization using
CHARMM, performed on the ligand in a rigid protein structure for 1,000,000 steps using the adopted
basis NewtonꢀRaphson method. The binding free energies were then estimated using a molecular
mechanics and Poisson–Boltzmann/Surface Area (MMꢀPB/SA) method.30 This includes the sum of van
der Waals interactions with the protein, an electrostatic binding free energy calculated by solving the
linearized Poisson–Boltzmann equation in both the bound and unbound states and a surface area burial
term. A surface tension of 5 cal/Å2 was used for the surface area burial term.30 The compounds
proposed for synthesis were among the highest scoring compounds using the most sophisticated energy
function.
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Chemistry
As outlined in Scheme 1, activated mixed carbonates 7a-j of cyclic and acyclic alcohols used in the
synthesis of designed inhibitors were prepared following the literature procedure.19 It is to be noted that
attempts to use one standard activation condition was not very efficient and resulted in poor yields.
Therefore, depending on the functional groups present in the P2 alcohol fragment, two different
activating agents have been used. Accordingly, alcohols 6a-c, 6f-j were reacted with pꢀ
nitrophenylchloroformate and Nꢀmethylmorpholine in THF at 25 °C to provide corresponding
carbonates 7a-c, 7f-j in 58–79% yields. Alcohols 6d-e were converted to corresponding succinimidyl
carbonates 7d-e by treatment with N,N’ꢀsuccinimidylcarbonate and triethylamine in acetonitrile in 35–
41% isolated yields.
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Scheme 1. Synthesis of Activated Carbonate Intermediates 7a-ja
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2
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4
5
O
a
R3 OH
R3
O
O
NO2
6
7
8
6a-c, 6f-j
7a-c, 7f-j
9
R3 =
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H
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Cl2HC
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O
O
6a
6b
6c
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HN
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N
O
N
MeO
6f
6g
6h
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O
O
H
6i
6j
O
O
b
R3
O
O N
R3 OH
6d-e
7d-e
O
H
N
R3 =
O
O
O
6d
6e
aReagents and conditions: (a) Nꢀmethylmorpholine, pꢀnitrophenylchloroformate, 0 °C to rt, 1 h; (b)
N,N’ꢀdisuccimidyl carbonate, Et3N, CH3CN, 0 °C to rt, 8 h.
The synthesis of (R)ꢀ(hydroxyethylamino)sulfonamide isosteres 12 was carried out following the
reported methods21, 23 as outlined in Scheme 2. Regioselective ring opening of commercially available
epoxide 8, (1S,2S)ꢀ(1ꢀoxiranylꢀ2ꢀphenylethyl)carbamic acid tertꢀbutyl ester, with two primary amines,
(S)ꢀ2ꢀmethylbutyl amine and nꢀpentyl amine, in ethanol provided βꢀamino alcohols 10a-b, respectively.
Depending upon the chemical properties of selected sulfonyl chlorides, two different methods were used
for the synthesis of (R)ꢀ(hydroxyethylamino)sulfonamide intermediates 12a-d. Reactions of the amino
alcohols 10a-b with pꢀ(methoxy)phenylsulfonyl chloride 11a were carried out using aqueous sodium
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carbonate (Na2CO3) and 6ꢀbenzothiazolesulfonyl chloride 11b using diisopropylethylamine in
anhydrous CH2Cl2, and furnished the corresponding sulfonamides 12a-d. Subsequent removal of the
Boc protection using trifluoroacetic acid in CH2Cl2 furnished the corresponding free amino alcohols.
Selective alkoxycarbonylation of the aliphatic amines in amino alcohols 12a-d using either activated pꢀ
nitrophenyl carbonate or succinimidyl carbonate 7a-j of selected alcohols under basic conditions
provided the desired inhibitors 13a-j–16a-j in 49–81% yields (Scheme 2).
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Scheme 2. Synthesis of Designed Protease Inhibitors 13a-j–16a-ja
a
R1
R1-NH2
+
BocHN
N
H
BocHN
O
OH
+
9a-b
8
10a-b
R2
SO2Cl
O
b or c
R2
S
RHN
N
O
OH R1
11a-b
12a R1 = 2-(S)-2-methylbutyl, R2 = 4-OCH3
12b R1 = n-pentyl,
R2 = 4-OCH3
12c R1 = 2-(S)-2-methylbutyl, R2 = 3,4-S-CH=N-
12d R1 = n-pentyl,
R2 = 3,4-S-CH=N-
O
O
R = Boc
R = H
R3
R4
d
e
O
(activated carbonates 7a-j)
R2
O
O
O
R3
S
N
N
O
H
OH R1
13a-j
14a-j
R1 = 2-(S)-2-methylbutyl, R2 = 4-OCH3
R1 = 2-(S)-2-methylbutyl, R2 = 3,4-S-CH=N-
15a-b,d-j R1 = n-pentyl,
R2 = 4-OCH3
16a-j
R1 = n-pentyl,
R2 = 3,4-S-CH=N-
aReagents and conditions: (a) EtOH, 80 °C, 3 h; (b) aq. Na2CO3, CH2Cl2, 0 °C to rt, 6 h; (c) Et3N,
CH2Cl2, 0 °C to rt, 5 h; (d) TFA, CH2Cl2, rt, 1 h; (e) Et3N, THF, 0 °C to rt, 4–8 h.
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Results and Discussion
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We used computational structureꢀbased design combined with substrateꢀenvelope constraints to
design a series of novel HIVꢀ1 PIs. The designed PIs incorporate various alcoholꢀderived P2 carbamates
with acyclic and cyclic heteroatomic functionalities into the (R)ꢀhydroxyethylamine isostere to enhance
the ligandꢀreceptor interactions in the S2 binding pocket of the protease. The (S)ꢀ2ꢀmethylbutyl and nꢀ
pentyl groups were used as P1’ ligands in combination with 4ꢀmethoxyphenyl and 6ꢀbenzothiazole
groups as P2’ ligands. Inhibitory activities of new PIs were determined against wildꢀtype HIVꢀ1
protease (Q7K) using a fluorescence resonance energy transfer (FRET) method34 in a semiꢀhigh
throughput format. Chemical structures of all new inhibitors along with their inhibitory activities (Ki
values) are presented in Table 1; each Ki value denotes the mean of at least three independent
determinations.
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As predicted, introduction of cyclic and acyclic P2 carbamates with multiple hydrogen bond donor
and acceptor parts provided a series of highly potent HIVꢀ1 PIs. Compounds 13-16c, 13-16g and 13-
16h, and 13-16j, containing 2,2ꢀdichloroacetamide, imidazolidinone, oxazolidinone, and pyrrolidinone
moities, respectively, and an extended carbon chain at P2, were highly potent against wildꢀtype protease
with Ki vales in the low nanomolar (nM) to low picomolar (pM) range. In particular, compounds 13c
and 16c showed impressive protease inhibitory activities with Ki values of 0.003 nM and 0.001 nM,
respectively, which are comparable to that of structurally related drugs 1 and 2. Inhibitors 13-15h with
an oxazolidinone substituent at P2 also displayed highly potent inhibitory activities against wildꢀtype
HIVꢀ1 protease (Ki = 0.003, 0.005, and 0.008 nM, respectively). Similarly, inhibitors 14g and 14J with
imidazolidinone, and pyrrolidinone moities, respectively, also showed highly potent inhibitory
activities. Conversely, introduction of trifluoromethylacetamide, (R)ꢀ5ꢀhexanꢀ2ꢀone and
dihydrofuranone groups at the P2 carbamate in 13-16b, 13-16d and 13-16i resulted in weak inhibitory
activity. Among the inhibitors 13-16a and 13-16f containing carbamates of (R)ꢀmethyl 3ꢀ
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hydroxybutanoate and its positional isomer, (R)-methyl 3ꢀhydroxyꢀ2ꢀmethylpropanoate, respectively,
only compounds 13-16f showed better enzyme inhibitory potency. Same trend was observed for
compounds 13-16e which incorporate bisꢀcarbamate P2 substituent. These SAR data suggest that
flexible heterocyclic moieties are preferred at P2.
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A subset of compounds with high binding affinity against wildꢀtype protease was further tested
against three MDR protease variants. These MDR variants were selected by examining the Stanford
HIVꢀ1 Drug Resistance Database (http://hivdb.stanford.edu), which contains sequences of viral isolates
from HIVꢀ1ꢀinfected patients. The selected MDR variants (M1: L10I, G48V, I54V, L63P, V82A; M2:
L10I, L63P, A71V, G73S, I84V, L90M; M3: I50V, A71V) represent the pattern of resistance mutations
observed under the selective pressure of three or more currently prescribed PIs.35 The Ki values of
selected inhibitors are presented in Table 2 with drugs 1, 2 used as control. Most of the PIs in the current
series retained high affinity against the three mutant variants (M1ꢀM3), consistent with their wildꢀtype
protease inhibitory activities. Importantly, compounds 13c, 13f, 13j and 14j exhibited excellent
potencies in the low nM ranges against all three MDR protease variants. In particular, compound 14j
with Ki value of 0.003 nM against wildꢀtype HIVꢀ1 protease exhibited consistently higher potencies
against all three MDR variants (MDR Ki = 0.240–0.377 nM).
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Selected PIs were further examined for antiviral potency in cellular assays against patient derived
wildꢀtype viruses from HIVꢀ1 clades A, B, C and two MDR HIVꢀ1 variants; drugs 1 and 2 were used as
controls (Table 3). Most of the tested compounds exhibited significant antiviral potencies with the EC50
values in the low nM range against both wildꢀtype and drugꢀresistant HIVꢀ1 strains. Among these, three
close analogues 13f, 13j and 14g exhibited modest antiviral potency. Compounds 16 with the most
potent protease binding affinity showed lower activity in cellular assays against both wildꢀtype and
MDR HIVꢀ1 variants. Interestingly, compound 14j with a cyclic pyrrolidinone group at the P2 position
and 6ꢀbenzothiazole sulfonamide at the P2’ position was the most potent against all the viruses tested
(EC50 = 15.5–35.6 nM).
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Journal of Medicinal Chemistry
In general, inhibitors with a flexible heterocyclic moiety at P2 were considerably more potent than
1
2
their inflexible and acyclic counterparts in both enzyme inhibitory and antiviral assays. These results
revealed the compatibility of most of the selected P2 substituents with established P12 and P22
substituents. Thus, further optimization of these potent compounds may lead to the development of
novel HIVꢀ1 protease inhibitors active against drugꢀresistant HIVꢀ1.
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Crystal Structures of HIV-1 Protease Complexes.
Crystal structures of four potent inhibitors 13c, 13f, 13g and 14j have been determined in complex
with wildꢀtype HIVꢀ1 protease. The R3 group in the 13cꢀprotease complex was disordered and the R1
and R2 groups have similar interactions as in 13f and 13g, hence this structure is not discussed in detail.
The backbone atoms of the protease in the three structures, 13f, 13g and 14j, superpose well within 2.12
Å to 2.59 Å. The scaffold of the inhibitors along with the R1 and R2 groups also superpose well onto
each other. The conformation of the protease, including the orientations of the side chains, is similar in
the regions where the three inhibitors superpose well onto each other. Both the benzothiazole and the 4ꢀ
methoxyphenyl R2 substituents in the three structures form hydrogen bonding interactions with the
backbone amide NH of the Aspꢀ30 residue as predicted computationally and previously observed
(Figure 2).
The R3 groups of 13f, 13g and 14j make different contacts in each case, providing interesting
structural basis for their distinct enzymatic activities. Compound 13f contains a methyl ester at R3 which
forms a bifurcated hydrogen bond with the backbone amide NHs of Aspꢀ29 and Aspꢀ30 through its
carbonyl oxygen (See Figure 2a). The methyl group of the ester packs within the hydrophobic P2 pocket
containing residues Valꢀ32, Ileꢀ47 and Ile84. The side chains of Val32 and Ile84 in 13f adopt a different
conformation compared to 13g and 14j structures, probably to accommodate the methyl group while the
backbone of the protease is similar in all the structures. The ester oxygen atom of 13f does not make a
hydrogen bond and thus it would be interesting to test the corresponding keto compound. Compound
13g contains a cyclic urea at R3 in which the carbonyl group forms two hydrogen bonds, one with the
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backbone amide NH of Aspꢀ29 and one with a structural water molecule held in place by the backbone
carbonyl of Gly27 as shown in Figure 2b. The nitrogen NH of the urea appears to be less important.
Compound 14j contains a pyrrolidone in which the carbonyl group also forms hydrogen bonds with the
backbone amide NH of Aspꢀ29 and with the structural water molecule held by Glyꢀ27. This structural
water could be considered in future design efforts. In addition, the pyrrolidinone NH forms bridging
hydrogen bond interactions through a water molecule to the backbone amide NH of Aspꢀ30. Overall, the
three picomolar inhibitors, 13f, 13g and 14j, appear to lock in the active site by forming hydrogen bonds
to both sides of the floor of the active site at Asp29 and/or Asp30, which was also observed for other
picomolar inhibitors from previous studies.36
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HIVꢀ1 protease is highly plastic and adapts to the conformation of the inhibitor to which it binds.
The conformation of the protease in all the three structures is similar except minor differences in the
side chains where the R3 groups of the inhibitors are different and have different conformations. The
number of hydrogen bonds is similar in all the three inhibitor complexes. The binding affinities of the
three inhibitors can not be explained by the number of hydrogen bonds alone, emphasizing that the
binding affinity is a product of both enthalpic interactions (both hydrophilic and hydrophobic) and the
entropy of binding.37, 38
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Figure 2. Hydrogen bond interactions between the wildꢀtype protease and inhibitors in complexes of (a)
13f, (b) 13g and (c) 14j. The two monomers of the protease and the inhibitor are shown in cyan,
magenta, and orange, respectively; nitrogen, oxygen, and sulfur atoms are in blue, red, and yellow,
respectively.
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1
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Conclusions
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In summary, we have described a series of highly potent HIVꢀ1 PIs based on the
(hydroxyethylamino)sulfonamide isostere that incorporate various P2 carbamates of acyclic and cyclic
alcohols. A number of analogues possessing the (R)ꢀ2ꢀmethylpropanoate, (S)ꢀ5ꢀ(methyl)pyrrolidinꢀ2ꢀ
one, ethyloxazolidinꢀ2ꢀone and ethylimidazolidinꢀ2ꢀone at the P2 exhibited excellent binding affinities
against wildꢀtype HIVꢀ1 protease and a panel of three MDR variants. In general, PIs incorporating the
flexible cyclic P2 moieties with multiple polar atoms showed highly potent inhibitory activities against
wildꢀtype protease and MDR variants. Moreover, several compounds exhibited antiviral activities with
EC50 values in the nM range. Notably, inhibitor 14j with the (S)ꢀ5ꢀ(methyl)pyrrolidinꢀ2ꢀone P2 moiety
consistently exhibited potent activity in both enzymatic and cellular assays. The Xꢀray crystal structure
analysis of 14j bound to HIVꢀ1 protease revealed enhanced backbone interactions with the protease
enzyme. The carbonyl oxygen and NH of the pyrrolidone P2 ligand are involved in direct and waterꢀ
mediated hydrogen bonding interactions with the backbone NHs of Aspꢀ29 and Aspꢀ30 in the S2
subsite. These extensive interactions of 14j may be responsible for its impressive activity against MDR
protease variants and for its antiviral potency in cellular assays. The results from the current study
support the compatibility of many selected P2 ligands and the structureꢀactivity relationship data can be
utilized to design new protease inhibitors with better enzyme inhibitory and antiviral potencies.
Experimental Section
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General. Thinꢀlayer chromatography (TLC) was performed on silica gel (60 Fꢀ254) coated plates
(Merck KGA) and spots were visualized with UV light. Flash column chromatography was performed
using silica gels (230–400 mesh, Merck KGA). Proton and carbon nuclear magnetic resonance (1H
NMR and 13C NMR) spectra were normally carried out in CDCl3 solutions on a JEOL JNMꢀECS
1
13
spectrometer, operating at 400 MHz for H NMR and 100 MHz for C NMR. Trimethylsilane (TMS)
was used as an internal standard. Chemical shifts are given in ppm relative to the trimethylsilane (TMS)
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Journal of Medicinal Chemistry
solvent signal and coupling constant (J) values are reported in Hertz (Hz). Lowꢀresolution mass spectra
(ESI) were obtained using Waters Micromass Model ZQ 4000 using methanol solvent. Tetrahydrofuran
(THF) was distilled from sodium/benzophenone. Anhydrous dichloromethane, benzene, toluene and
N,Nꢀdimethylformamide (DMF), and all other solvents and reagents were purchased from commercial
vendors and were used as received. Analytical reversedꢀphase high performance liquid chromatography
(HPLC) was performed on a Waters Separation Module 2695 system equipped with an autoꢀsampler
and a Waters 996 photodiode array detector. Purity of the final compounds was determined using
chromatographic systems: column, YMCꢀPack Pro C18 (particle size = 5 ꢁm, pore size = 12 nm,
dimensions = 150 mm x 4.6 mm); mobile phase A, water; mobile phase B, methanol. Using a flow rate
of 1.0 mL/min, gradient elution was performed from 20% B to 100% B over 10 min. In every case, 10
ꢀL of a 1 mM solution was injected. Purity data and the corresponding retention times of all final
compounds have been presented in the Supporting Information.
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(R)-methyl
phenylbutan-2-yl)carbamoyl)oxy)butanoate (13a). To a solution of the tertꢀbutyl ((2S,3R)ꢀ3ꢀ
hydroxyꢀ4ꢀ(4ꢀmethoxyꢀNꢀ((S)ꢀ2ꢀmethylbutyl)phenylsulfonamido)ꢀ1ꢀphenylbutanꢀ2ꢀyl)carbamate 12a
3-((((2S,3R)-3-hydroxy-4-(4-methoxy-N-((S)-2-methylbutyl)phenylsulfonamido)-1-
(0.02 g, 0.384 mmol) in CH2Cl2 (7 mL) was added trifluoroacetic acid (2 mL) and the resulting mixture
was stirred at room temperature for 1.5 h. After completion of reaction, the reaction mixture was
concentrated under reduced pressure, and the residue was dissolved in toluene (10 mL) and again
evaporated under reduced pressure to dryness. The resulting deꢀprotected amine product was dissolved
in dry CH2Cl2 (6 mL) and the solution was cooled 0 °C. Diisopropylethyl amine (0.2 mL, 1.21 mmol)
was added and after 10 min the activated carbonate 7a solution in dry CH2Cl2 was slowly added. The
resulting reaction mixture was stirred at 0 °C for 4 h, allowed to warm to room temperature, and stirred
until reaction was complete. Water (5 mL) and EtOAc (20 mL) were added and layers were separated;
the organic layer was washed with saturated aqueous NaCl solution (10 mL), dried (Na2SO4), filtered,
and concentrated. The residue was purified by flash chromatography on silica gel, eluting with a
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mixture of 1:3 EtOAc/hexane, to afford the target compound 13a (0.17 g, 81%) as a colorless semiꢀ
solid. 1H NMR (400 MHz, CDCl3) δ 7.68ꢀ7.62 (m, 2H), 7.25ꢀ7.13 (m, 5H), 6.94ꢀ6.88 (m, 2H), 5.87 (d,
J = 8.5 Hz, 1H), 5.19ꢀ5.10 (m, 1H), 4.13ꢀ4.03 (m, 2H), 3.84ꢀ3.74 (m, 4H), 3.61 (s, 3H), 3.05 (dd, J =
14.9, 4.3 Hz, 1H), 2.99 (d, J = 8.5 Hz, 1H), 2.97ꢀ2.86 (m, 2H), 2.75 (dd, J = 13.4, 7.3 Hz, 1H), 2.58ꢀ
2.51 (m, 1H), 2.51ꢀ2.44 (m, 1H), 2.43ꢀ2.37 (m, 1H), 2.36ꢀ2.30 (m, 1H), 2.29ꢀ2.19 (m, 1H), 1.15 (d, J =
1
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4.8 Hz, 3H), 1.01ꢀ0.96 (m, 1H), 0.82ꢀ0.73 (m, 6H); C NMR (100 MHz, CDCl3) δ 170.67, 162.97,
155.71, 137.49, 129.75, 129.53 (2C), 129.45 (2C), 128.47 (2C), 126.46, 114.30 (2C), 72.32, 67.97,
57.33, 55. 58, 54.84, 53.62, 51.63, 40.72, 35.47, 33.39, 26.35, 20.07, 16.84, 11.00; MS (ESI) m/z 587.16
(M + Na)+.
2-(2,2,2-trifluoroacetamido)ethyl
((2S,3R)-3-hydroxy-4-(4-methoxy-N-((S)-2-
methylbutyl)phenylsulfonamido)-1-phenylbutan-2-yl)carbamate (13b). The title compound was
obtained from 12a and 7b as described for 13a in 71% yield after flashꢀchromatography (1:4
1
EtOAc/hexane) as an amorphous white solid. H NMR (400 MHz, CDCl3) δ 7.82 (d, J = 8.5 Hz, 1H),
7.66ꢀ7.59 (m, 2H), 7.23ꢀ7.11 (m, 5H), 6.92ꢀ6.87 (m, 2H), 4.29 (t, J = 7.8 Hz, 1H), 4.11ꢀ3.97 (m, 1H),
3.86ꢀ3.83 (m, 1H), 3.81ꢀ3.74 (m, 4H), 3.57ꢀ3.41 (m, 1H), 3.13 (dd, J = 15.2, 9.2 Hz, 1H), 3.05ꢀ2.79 (m,
4H), 2.73ꢀ2.67 (m, 1H), 2.44ꢀ2.31 (m, 1H), 1.75 (bs, 1H), 1.57ꢀ1.48 (m, 1H), 1.44ꢀ1.35 (m, 1H), 1.20ꢀ
13
1.14 (m, 1H); 1.04ꢀ0.92 (m, 1H), 0.85ꢀ0.72 (m, 6H); C NMR (100 MHz, CDCl3) δ 162.95, 155.42,
151.56, 137.28, 129.43, 129.36 (2C), 129.24 (2C), 128.42 (2C), 128.39, 126.53, 114.28 (2C), 72.26,
62.25, 55.53, 54.73, 53.21, 42.30, 35.86, 33.33, 29.62, 26.39, 16.84, 10.94; MS (ESI) m/z 626.31 (M +
Na)+.
2-(2,2-dichloroacetamido)ethyl
(2S,3R)-3-hydroxy-4-(4-methoxy-N-((S)-2-
methylbutyl)phenylsulfonamido)-1-phenylbutan-2-ylcarbamate (13c). The title compound was
obtained from 12a and 7c as described for 13a in 57% yield after flashꢀchromatography (1:4
1
EtOAc/hexane) as a colorless viscous liquid. H NMR (400 MHz, CDCl3) δ 7.63 (d, J = 9.2 Hz, 2H),
7.24ꢀ7.09 (m, 5H), 6.99 (bs, 1H), 6.91 (d, J = 8.5 Hz, 2H), 5.89 (s, 1H), 5.04 (d, J = 9.2 Hz, 1H), 4.09ꢀ
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3.97 (m, 2H), 3.86ꢀ3.76 (m, 5H), 3.74ꢀ3.56 (m, 2H), 3.47ꢀ3.33 (m, 2H), 3.14ꢀ2.67 (m, 5H), 1.67ꢀ1.46
(m, 2H), 1.05ꢀ0.95 (m, 1H), 0.83ꢀ0.70 (m, 6H); 13C NMR (100 MHz, CDCl3) δ 164.30, 163.05, 156.36,
137.46, 129.63 (2C), 129.42 (2C), 128.84 (2C), 128.48, 126.58, 114.33 (2C), 72.24, 66.22, 63.01, 57.13,
1
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55.60, 55.07, 53.35, 40.28, 35.34, 33.34, 26.41, 16.86, 11.00; MS (ESI) m/z 640.19 (Mꢀ1+ Na)+ 642.19
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,
9
(M+1+ Na)+.
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(R)-5-oxohexan-2-yl ((2S,3R)-3-hydroxy-4-(4-methoxy-N-((S)-2-methylbutyl)phenylsulfonamido)-
1-phenylbutan-2-yl)carbamate (13d). The title compound was obtained from 12a and 7d as described
1
for 13a in 69% yield after flashꢀchromatography (1:3 EtOAc/hexane) as an amorphous white solid. H
NMR (400 MHz, CDCl3) δ 7.66ꢀ7.60 (m, 2H), 7.25ꢀ7.10 (m, 5H), 6.95ꢀ6.86 (m, 2H), 4.69 (d, J = 7.9
Hz, 1H), 4.63ꢀ4.54 (m, 1H), 3.88ꢀ3.67 (m, 6H), 3.10ꢀ2.89 (m, 4H), 2.89ꢀ2.67 (m, 2H), 2.35 (t, J = 6.7
13
Hz, 1H), 2.02 (s, 3H), 1.79ꢀ1.50 (m, 4H), 1.47ꢀ1.36 (m, 1H), 1.09ꢀ0.93 (m, 4H), 0.84ꢀ0.72 (m, 6H); C
NMR (100 MHz, CDCl3) δ 207.90, 163.00, 156.21, 137.63, 129.78, 129.44 (4C), 128.47 (2C), 126.47,
114.31 (2C), 79.35, 72.36, 70.93, 57.23, 55.60, 54.88, 53.50, 39.47, 35,27, 33.39, 29.88, 26.40, 20.18,
16.88, 11.01; MS (ESI) m/z 585.40 (M + Na)+.
2-((tert-butoxycarbonyl)amino)ethyl
((2S,3R)-3-hydroxy-4-(4-methoxy-N-((S)-2-
methylbutyl)phenylsulfonamido)-1-phenylbutan-2-yl)carbamate (13e). The title compound was
obtained from 12a and 7e as described for 13a in 51% yield after flashꢀchromatography (1:3
EtOAc/hexane) as an amorphous white solid. 1H NMR (400 MHz, CDCl3) δ 7.66 (d, J = 8.5 Hz, 2H),
7.30ꢀ7.12 (m, 5H), 6.93 (d, J = 7.9 Hz, 2H), 5.15ꢀ4.92 (m, 1H), 4.80 (bs, 1H), 4.01ꢀ3.88 (m, 2H), 3.85ꢀ
3.73 (m, 5H), 3.65ꢀ3.61 (m, 1H), 3.43ꢀ3.29 (m, 1H), 3.28ꢀ3.15 (m, 3H), 3.08ꢀ2.91 (m, 4H), 1.58ꢀ1.44
13
(m, 1H), 1.43ꢀ1.28 (m, 10H), 1.03ꢀ0.93 (m, 1H), 0.85ꢀ0.69 (m, 6H); C NMR (100 MHz, CDCl3) δ
162.96, 156.45, 155.81, 137.63, 131.01, 129.72 (2C), 129.40 (2C), 128.41 (2C), 126.46, 114.26 (2C),
79.51, 72.27, 62.36, 57.09, 55.54, 53.34, 43.03, 41.96, 35.27, 33.30, 28.30 (3C), 26.40, 16.83, 10.96;
MS (ESI) m/z 630.52 (M + Na)+.
(R)-methyl
3-((((2S,3R)-3-hydroxy-4-(4-methoxy-N-((S)-2-methylbutyl)phenylsulfonamido)-1-
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phenylbutan-2-yl)carbamoyl)oxy)-2-methylpropanoate (13f). The title compound was obtained from
12a and 7f as described for 13a in 63% yield after flashꢀchromatography (1:3 EtOAc/hexane) as an
amorphous white solid. 1H NMR (400 MHz, CDCl3) δ 7.64ꢀ7.60 (m, 2H), 7.25ꢀ7.11 (m, 5H), 6.92ꢀ6.88
(m, 2H), 4.82ꢀ4.79 (m, 1H), 4.08ꢀ3.97 (m, 2H), 3.80 (s, 3H), 3.77ꢀ3.60 (m, 3H), 3.57 (s, 3H), 3.07ꢀ2.79
(m, 5H), 2.75ꢀ2.58 (m, 2H), 1.58ꢀ1.35 (m, 2H), 1.04 (d, J = 6.7 Hz, 3H), 1.02ꢀ0.93 (m, 1H), 0.83ꢀ0.72
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(m, 6H); C NMR (100 MHz, CDCl3) δ 174.23, 162.96, 156.05, 137.43, 129.70, 129.46 (2C), 129.43
(2C), 128.46 (2C), 126.56, 114.26 (2C), 72.27, 65.96, 57.26, 55.56, 54.92, 53.57, 51.79, 39.23, 35.36,
33.36, 26.33, 16.82, 13.51, 10.95; MS (ESI) m/z 587.35 (M + Na)+.
2-(2-oxoimidazolidin-1-yl)ethyl
((2S,3R)-3-hydroxy-4-(4-methoxy-N-((S)-2-
methylbutyl)phenylsulfonamido)-1-phenylbutan-2-yl)carbamate (13g). The title compound was
obtained from 12a and 7g as described for 13a in 51% yield after flashꢀchromatography (1:4
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EtOAc/hexane) as an amorphous white solid. H NMR (400 MHz, CDCl3) δ 7.64 (d, J = 8.5 Hz, 2H),
7.23ꢀ7.07 (m, 5H), 6.89 (d, J = 8.5 Hz, 2H), 5.30 (m, 1H), 5.00 (bs, 1H), 4.17ꢀ3.97 (m, 2H), 3.96ꢀ3.88
(m, 1H), 3.87ꢀ3.79 (m, 2H), 3.78 (s, 3H), 3.35ꢀ3.16 (m, 6H), 3.06ꢀ2.97 (m, 2H), 2.96ꢀ2.84 (m, 2H),
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2.83ꢀ2.69 (m, 2H), 1.63ꢀ1.48 (m, 1H), 1.41ꢀ1.26 (m, 1H), 1.05ꢀ0.85 (m, 1H), 0.81ꢀ0.70 (m, 6H); C
NMR (100 MHz, CDCl3) δ 162.80, 162.75, 155.98, 137.86, 129.97, 129.38 (2C), 129.27 (2C), 128.28
(2C), 126.24, 114.15 (2C), 72.04, 62.10, 56.76, 55.50, 55.00, 52.96, 45.25, 42.80, 38.09, 34.98, 33.18,
26.46, 16.79, 10.96; MS (ESI) m/z 599.32 (M + Na)+.
2-(2-oxooxazolidin-3-yl)ethyl
((2S,3R)-3-hydroxy-4-(4-methoxy-N-((S)-2-
methylbutyl)phenylsulfonamido)-1-phenylbutan-2-yl)carbamate (13h). The title compound was
obtained from 12a and 7h as described for 13a in 68% yield after flashꢀchromatography (1:3
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EtOAc/hexane) as a colorless viscous liquid. H NMR (400 MHz, CDCl3) δ 7.69ꢀ7.67 (m, 2H), 7.25ꢀ
7.14 (m, 5H), 6.95ꢀ6.63 (m, 2H), 5.05 (d, J = 7.9 Hz, 1H), 4.34ꢀ3.99 (m, 4H), 3.93ꢀ3.66 (m, 6H), 3.48ꢀ
3.27 (m, 4H), 3.14ꢀ2.92 (m, 4H), 2.91ꢀ2.73 (m, 2H), 2.68ꢀ2.50 (m, 1H), 1.51ꢀ1.34 (m, 1H), 1.13ꢀ0.91
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(m, 1H), 0.94ꢀ0.74 (m, 6H); C NMR (100 MHz, CDCl3) δ 162.90, 158.51, 155.83, 137.64, 129.86,
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Journal of Medicinal Chemistry
129.38 (2C), 129.32 (2C), 128.36 (2C), 126.35, 114.23 (2C), 72.06, 61.82, 57.02, 55.55, 55.00, 53.16,
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44.81, 43.60, 35.21, 33.28, 26.38, 20.92, 16.78, 10.96; MS (ESI) m/z 599.86 (M + Na)+.
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(R)-2-oxotetrahydrofuran-3-yl
((2S,3R)-3-hydroxy-4-(4-methoxy-N-((S)-2-
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methylbutyl)phenylsulfonamido)-1-phenylbutan-2-yl)carbamate (13i). The title compound was
obtained from 12a and 7i as described for 13a in 64% yield after flashꢀchromatography (1:3
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EtOAc/hexane) as a colorless viscous liquid. H NMR (400 MHz, CDCl3) δ 7.76ꢀ7.69 (m, 2H), 7.31ꢀ
7.15 (m, 5H), 7.02ꢀ6.96 (m, 2H), 4.60 (t, J = 5.5 Hz, 1H), 4.33ꢀ4.21 (m, 1H), 3.87 (s, 3H), 3.84ꢀ3.76 (m,
1H), 3.75ꢀ3.56 (m, 2H), 3.38ꢀ3.14 (m, 3H), 3.13ꢀ3.01 (m, 1H), 2.99ꢀ2.80 (m, 2H), 2.10ꢀ1.96 (m, 1H),
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1.95ꢀ1.65 (m, 3H), 1.63ꢀ1.51 (m, 1H), 1.50ꢀ1.36 (m, 1H), 1.13ꢀ0.97 (m, 1H), 0.91ꢀ0.78 (m, 6H); C
NMR (100 MHz, CDCl3) δ 173.73, 163.05, 155.59, 136.73, 129.88, 129.59 (2C), 129.22, 129.09,
128.65 (2C), 127.00, 114.36 (2C), 76.35, 70.88, 57.21, 55.64, 52.79, 33.45, 32.90, 32.61, 32.13, 31.95,
26.64, 16.84, 10.08; MS (ESI) m/z 571.34 (M + Na)+.
((S)-5-oxopyrrolidin-2-yl)methyl
((2S,3R)-3-hydroxy-4-(4-methoxy-N-((S)-2-
methylbutyl)phenylsulfonamido)-1-phenylbutan-2-yl)carbamate (13j). The title compound was
obtained from 12a and 7j as described for 13a in 59% yield after flashꢀchromatography (1:3
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EtOAc/hexane) as an amorphous white solid. H NMR (400 MHz, CDCl3) δ 7.67 (d, J = 8.5 Hz, 2H),
7.32ꢀ7.11 (m, 6H), 6.92 (d, J = 8.5 Hz, 2H), 5.60 (d, J = 8.5 Hz, 1H), 4.15ꢀ3.99 (m, 2H), 3.69ꢀ3.60 (m,
7H), 3.18ꢀ2.68 (m, 4H), 2.38ꢀ2.18 (m, 2H), 2.15ꢀ2.04 (m, 1H), 1.71ꢀ1.28 (m, 4H), 1.11ꢀ0.86 (m, 2H),
0.89ꢀ0.71 (m, 6H); 13C NMR (100 MHz, CDCl3) δ 178.63, 162.76, 155.82, 137.84, 129.96, 129.34 (2C),
129.28 (2C), 128.24 (2C), 126.25, 114.12 (2C), 72.01, 67.20, 56.65, 55.45, 55.15, 53.20, 52.95, 34.95,
33.14, 29.64, 26.44, 22.67, 16.78, 10.92; MS (ESI) m/z 584.01 (M + Na)+.
(R)-methyl
3-((((2S,3R)-3-hydroxy-4-(N-((S)-2-methylbutyl)benzo[d]thiazole-6-sulfonamido)-1-
phenylbutan-2-yl)carbamoyl)oxy)butanoate (14a). The title compound was obtained from 12b and 7a
as described for 13a in 46% yield after flashꢀchromatography (1:2 EtOAc/hexane) as colorless viscous
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liquid. H NMR (400 MHz, CDCl3) δ 9.13 (s, 1H), 8.40 (d, J = 1.8 Hz, 1H), 8.17 (d, J = 8.5 Hz, 1H),
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7.83 (dd, J = 8.5, 1.8 Hz, 1H), 7.25–7.15 (m, 5H), 6.02 (d, J = 7.9 Hz, 1H), 5.18ꢀ5.09 (m, 1H), 4.14ꢀ4.05
(m, 2H), 3.82ꢀ3.76 (m, 1H), 3.60 (s, 3H), 3.10 (dd, J = 14.9, 3.9 Hz, 1H), 3.08ꢀ3.03 (m, 1H), 3.02ꢀ2.92
(m, 1H), 2.94ꢀ2.83 (m, 2H), 2.76 (dd, J = 14.1, 7.0 Hz, 1H), 2.56ꢀ2.47 (m, 1H), 2.42ꢀ2.35 (m, 1H), 2.29ꢀ
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2.19 (m, 1H), 1.44ꢀ1.32 (m, 1H), 1.13 (d, J = 6.1 Hz, 3H), 1.01ꢀ0.96 (m, 1H), 0.83ꢀ0.73 (m, 6H); C
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NMR (100 MHz, CDCl3) δ 172.05, 170.72, 157.89, 155.46, 137.66, 135.87, 134.26, 129.31 (2C),
128.54 (2C), 126.58, 124.84, 124.25, 122.24, 72.29, 67.57, 57.10, 54.17, 53.06, 51.78, 40.29, 35.03,
33.35, 26.47, 19.70, 16.79, 11.03; MS (ESI) m/z 614.26 (M + Na)+.
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2-(2,2,2-trifluoroacetamido)ethyl ((2S,3R)-3-hydroxy-4-(N-((S)-2-methylbutyl)benzo[d]thiazole-6-
sulfonamido)-1-phenylbutan-2-yl)carbamate (14b). The title compound was obtained from 12b and
7b as described for 13a in 66% yield after flashꢀchromatography (1:2 EtOAc/hexane) as a colorless
viscous liquid. 1H NMR (400 MHz, CDCl3) δ 9.14 (s, 1H), 8.40 (d, J = 1.8 Hz, 1H), 8.17 (d, J = 8.5 Hz,
1H), 7.85ꢀ7.78 (m, 2H), 7.23ꢀ7.11 (m, 6H), 4.30 (t, J = 8.0 Hz, 2H), 4.07ꢀ3.99 (m, 1H), 3.88ꢀ3.78 (m,
3H), 3.56 (d, J = 3.7 Hz, 1H), 3.15 (dd, J = 15.3, 9.2 Hz, 1H), 3.06ꢀ2.94 (m, 2H), 2.89ꢀ2.78 (m, 2H),
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1.57ꢀ1.49 (m, 1H), 1.44ꢀ1.36 (m, 1H), 1.06ꢀ0.94 (m, 2H), 0.87ꢀ0.70 (m, 6H); C NMR (100 MHz,
CDCl3) δ 157.94, 155.50, 155.44, 151.66, 137.35, 134.32, 132.74, 129.43 (2C), 129.23, 128.50 (2C),
126.65, 124.88, 124.31, 122.34, 71.90, 62.27, 57.03, 54.83, 53.11, 42.30, 35.95, 33.27, 26.37, 16.86,
10.98; MS (ESI) m/z 653.37 (M + Na)+.
2-(2,2-dichloroacetamido)ethyl
((2S,3R)-3-hydroxy-4-(N-((S)-2-methylbutyl)benzo[d]thiazole-6-
sulfonamido)-1-phenylbutan-2-yl)carbamate (14c). The title compound was obtained from 12b and
7c as described for 13a in 61% yield after flashꢀchromatography (1:2 EtOAc/hexane) as foam. 1H NMR
(400 MHz, CDCl3) δ 9.14 (s, 1H), 8.37 (d, J = 2.1 Hz, 1H), 8.17 (dd, J = 8.5, 2.4 Hz, 1H), 7.81 (dd, J =
8.5, 1.8 Hz, 1H), 7.31ꢀ7.08 (m, 5H), 6.98 (bs, 1H), 5.81 (s, 1H), 5.12 (bs, 1H), 5.07 (d, J = 7.9 Hz, 1H),
4.09ꢀ3.97 (m, 2H), 3.87ꢀ3.81 (m, 1H), 3.75ꢀ3.58 (m, 2H), 3.47ꢀ3.33 (m, 2H), 3.14ꢀ2.67 (m, 5H), 1.66ꢀ
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1.45 (m, 2H), 1.06ꢀ0.93 (m, 1H), 0.86ꢀ0.72 (m, 6H); C NMR (100 MHz, CDCl3) δ 163.43, 157.20,
156.87, 154.57, 135.52, 135.02, 133.42, 128.50, 128.28, 127.92, 127.60, 126.48, 123.81, 123.44,
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Journal of Medicinal Chemistry
121.25, 72.24, 65.37, 63.43, 56.02, 54.80, 54.71, 47.29, 34.97, 25.91, 16.95, 14.16, 11.32; MS (ESI) m/z
666.99 (Mꢀ1+ Na)+, 668.93 (M+1+ Na)+.
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(R)-5-oxohexan-2-yl ((2S,3R)-3-hydroxy-4-(N-((S)-2-methylbutyl)benzo[d]thiazole-6-sulfonamido)-
1-phenylbutan-2-yl)carbamate (14d). The title compound was obtained from 12b and 7d as described
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for 13a in 55% yield after flashꢀchromatography (1:2 EtOAc/hexane) as an amorphous white solid. H
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NMR (400 MHz, CDCl3) δ 9.14 (s, 1H), 8.39 (d, J = 1.2 Hz, 1H), 8.17 (d, J = 9.2 Hz, 1H), 7.82 (dd, J =
8.5, 1.8 Hz, 1H), 7.23ꢀ7.06 (m, 6H), 4.72 (d, J = 7.9 Hz, 1H), 4.63ꢀ4.55 (m, 1H), 3.87ꢀ3.67 (m, 3H),
3.15ꢀ2.99 (m, 3H), 2.97ꢀ2.91 (m, 1H), 2.89ꢀ2.79 (m, 1H), 2.33 (t, J = 7.3 Hz, 1H), 2.00 (s, 3H), 1.79ꢀ
1.51 (m, 4H), 1.45ꢀ1.34 (m, 1H), 1.07ꢀ0.92 (m, 4H), 0.85ꢀ0.72 (m, 6H); 13C NMR (100 MHz, CDCl3) δ
207.93, 157.96, 156.23, 155.47, 137.56, 135.76, 134.28, 129.40 (2C), 128.49 (2C), 126.53, 124.80,
124.30, 122.22, 72.22, 71.02, 56.98, 55.01, 53.24, 39.44, 35.20, 33.33, 29.83, 29.77, 26.39, 20.14,
16.83, 11.00; MS (ESI) m/z 612.06 (M + Na)+.
2-((tert-butoxycarbonyl)amino)ethyl
((2S,3R)-3-hydroxy-4-(N-((S)-2-
methylbutyl)benzo[d]thiazole-6-sulfonamido)-1-phenylbutan-2-yl)carbamate (14e). The title
compound was obtained from 12b and 7e as described for 13a in 49% yield after flashꢀchromatography
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(1:2 EtOAc/hexane) as a colorless viscous liquid. H NMR (400 MHz, CDCl3) δ 9.14 (s, 1H), 8.38 (m,
1H), 8.14 (d, J = 8.5 Hz, 1H), 7.82 (dd, J = 8.5, 1.8 Hz, 1H), 7.24ꢀ7.11 (m, 5H), 4.86 (d, J = 6.7 Hz,
1H), 4.65 (bs, 1H), 3.98ꢀ3.88 (m, 2H), 3.86ꢀ3.74 (m, 2H), 3.70 (bs, 1H), 3.30ꢀ2.92 (m, 6H), 2.89ꢀ2.75
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(m, 2H), 1.62ꢀ1.47 (m, 2H), 1.36 (s, 9H), 1.06ꢀ0.93 (m, 1H), 0.85ꢀ0.73 (m, 6H); C NMR (100 MHz,
CDCl3) δ 157.95, 156.27, 155.78, 155.56, 137.47, 135.67, 134.34, 129.47 (2C), 128.58 (2C), 126.68,
124.83, 124.38, 122.26, 79.51, 72.20, 64.36, 57.14, 55.09, 53.41, 39.95, 35.27, 33.40, 28.35 (3C), 26.41,
16.87, 11.02; MS (ESI) m/z 657.37 (M + Na)+.
(R)-methyl
3-((((2S,3R)-3-hydroxy-4-(N-((S)-2-methylbutyl)benzo[d]thiazole-6-sulfonamido)-1-
phenylbutan-2-yl)carbamoyl)oxy)-2-methylpropanoate (14f). The title compound was obtained from
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12b and 7f as described for 13a in 68% yield after flashꢀchromatography (1:2 EtOAc/hexane) as an
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amorphous white solid. H NMR (400 MHz, CDCl3) δ 9.13 (s, 1H), 8.37 (d, J = 1.2 Hz, 1H), 8.17 (d, J
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= 8.5 Hz, 1H), 7.82 (dd, J = 8.5, 1.8 Hz, 1H), 7.24ꢀ7.11 (m, 5H), 4.86 (d, J = 7.9 Hz, 1H), 4.08ꢀ3.97 (m,
2H), 3.82ꢀ3.68 (m, 3H), 3.56 (s, 3H), 3.14ꢀ2.92 (m, 4H), 2.89ꢀ2.72 (m, 2H), 2.69ꢀ2.57 (m, 1H), 1.62ꢀ
1.47 (m, 1H), 1.46ꢀ1.36 (m, 1H), 1.06ꢀ0.96 (m, 4H), 0.82ꢀ0.70 (m, 6H); 13C NMR (100 MHz, CDCl3) δ
174.21, 157.98, 156.11, 155.45, 137.36, 135.62, 134.25, 129.41 (2C), 128.49 (2C), 126.54, 124.80,
124.25, 122.20, 72.23, 66.01, 57.11, 55.05, 53.41, 51.83, 39.21, 35.35, 33.33, 26.34, 16.78, 13.48,
10.95; MS (ESI) m/z 614.30 (M + Na)+.
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2-(2-oxoimidazolidin-1-yl)ethyl
((2S,3R)-3-hydroxy-4-(N-((S)-2-methylbutyl)benzo[d]thiazole-6-
sulfonamido)-1-phenylbutan-2-yl)carbamate (14g). The title compound was obtained from 12b and
7g as described for 13a in 57% yield after flashꢀchromatography (1:2 EtOAc/hexane) as an amorphous
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white solid. H NMR (400 MHz, CDCl3) δ 9.13 (s, 1H), 8.41ꢀ8.38 (m, 1H), 8.16 (d, J = 9.2 Hz, 1H),
7.84 (dd, J = 8.5, 1.8 Hz, 1H), 7.24ꢀ7.09 (m, 6H), 5.28 (m, 1H), 4.81 (bs, 1H), 4.20ꢀ4.00 (m, 2H), 3.97ꢀ
3.55 (m, 3H), 3.48ꢀ3.21 (m, 5H), 3.19ꢀ3.06 (m, 2H), 3.01ꢀ2.87 (m, 3H), 2.79ꢀ2.71 (m, 1H), 1.64ꢀ1.44
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(m, 1H), 1.37ꢀ3.25 (m, 1H), 1.07ꢀ0.82 (m, 1H), 0.85ꢀ0.70 (m, 6H); C NMR (100 MHz, CDCl3) δ
162.77, 157.93, 156.05, 155.36, 137.78, 136.03, 134.20, 129.28 (2C), 128.39 (2C), 126.39, 124.89,
124.16, 122.27, 71.76, 61.85, 56.54, 55.15, 52.71, 45.10, 42.86, 38.11, 34,89, 33.18, 26.50, 16.83,
11.03; MS (ESI) m/z 626.34 (M + Na)+.
2-(2-oxooxazolidin-3-yl)ethyl
((2S,3R)-3-hydroxy-4-(N-((S)-2-methylbutyl)benzo[d]thiazole-6-
sulfonamido)-1-phenylbutan-2-yl)carbamate (14h). The title compound was obtained from 12b and
7h as described for 13a in 55% yield after flashꢀchromatography (1:2 EtOAc/hexane) as a colorless
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semiꢀsolid. H NMR (400 MHz, CDCl3) δ 9.12 (s, 1H), 8.46 (d, J = 1.4 Hz, 1H), 8.22 (d, J = 8.7 Hz,
1H), 7.89 (dd, J = 8.7, 1.8 Hz, 1H), 7.34ꢀ7.14 (m, 6H), 5.07 (d, J = 8.6 Hz, 1H), 4.30ꢀ4.07 (m, 3H),
4.08ꢀ3.94 (m, 1H), 3.94ꢀ3.77 (m, 1H), 3.56ꢀ3.36 (m, 3H), 3.24ꢀ3.13 (m, 2H), 3.10ꢀ3.05 (m, 1H), 3.02ꢀ
2.97 (m, 2H), 2.94ꢀ2.83 (m, 2H), 1.69ꢀ1.54 (m, 1H), 1.51ꢀ1.32 (m, 1H), 1.10ꢀ0.89 (m, 1H), 0.85ꢀ0.78
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Journal of Medicinal Chemistry
(m, 6H); 13C NMR (100 MHz, CDCl3) δ 158.57, 157.95, 155.90, 155.42, 137.52, 135.88, 134.24,
129.35 (2C), 128.83, 128.46, 126.48, 124.86, 124.21, 122.24, 71.78, 61.79, 56.86, 55.10, 54.72, 52.95,
44.60, 43.65, 35.15, 33.29, 26.39, 16.79, 11.01; MS (ESI) m/z 626.90 (M + Na)+.
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((2S,3R)-3-hydroxy-4-(N-((S)-2-methylbutyl)benzo[d]thiazole-6-
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sulfonamido)-1-phenylbutan-2-yl)carbamate (14i). The title compound was obtained from 12b and 7i
as described for 13a in 62% yield after flashꢀchromatography (1:2 EtOAc/hexane) as a colorless viscous
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liquid. H NMR (400 MHz, CDCl3) δ 9.15 (s, 1H), 8.45 (d, J = 3.7 Hz, 1H), 8.18 (dd, J = 8.5, 5.5 Hz,
1H), 7.87ꢀ7.81 (m, 1H), 7.26ꢀ7.12 (m, 6H), 4.58 (d, J = 4.9 Hz, 1H), 4.50ꢀ4.36 (m, 1H), 4.36ꢀ4.23 (m,
1H), 3.85ꢀ3.56 (m, 3H), 3.37ꢀ3.07 (m, 3H), 3.05ꢀ2.91 (m, 2H), 1.61 (bs, 1H), 1.50ꢀ1.33 (m, 2H), 1.27ꢀ
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1.19 (m, 1H), 1.12ꢀ0.96 (m, 2H), 0.87ꢀ0.73 (m, 6H); C NMR (100 MHz, CDCl3) δ 173.72, 158.10,
155.55, 155.46, 136.59, 135.82, 134.31, 129.06 (2C), 128.65 (2C), 127.03, 124.88, 124.30, 122.43,
76.34, 70.77, 57.04, 52.66, 33.37, 32.50, 32.17, 29.66, 28.68, 26.58, 16.79, 11.05; MS (ESI) m/z 598.32
(M + Na)+.
((S)-5-oxopyrrolidin-2-yl)methyl ((2S,3R)-3-hydroxy-4-(N-((S)-2-methylbutyl)benzo[d]thiazole-6-
sulfonamido)-1-phenylbutan-2-yl)carbamate (14j). The title compound was obtained from 12b and 7j
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as described for 13a in 60% yield after flashꢀchromatography (1:2 EtOAc/hexane) as a white solid. H
NMR (400 MHz, CDCl3) δ 9.12 (s, 1H), 8.39 (s, 1H), 8.14 (d, J = 8.5 Hz, 1H), 7.82 (d, J = 8.5 Hz, 1H),
7.24ꢀ7.09 (m, 6H), 5.62 (d, J = 9.2 Hz, 1H), 4.16ꢀ3.94 (m, 2H), 3.93ꢀ3.51 (m, 3H), 3.24ꢀ3.03 (m, 2H),
3.01ꢀ2.83 (m, 3H), 2.81ꢀ2.69 (m, 1H), 2.33ꢀ1.98 (m, 4H), 1.69ꢀ1.42 (m, 2H), 1.39ꢀ1.26 (m, 1H), 1.06ꢀ
0.89 (m, 1H), 0.80ꢀ0.69 (m, 6H); 13C NMR (100 MHz, CDCl3) δ 177.85, 156.99, 155.01, 154.27,
136.75, 134.97, 133.13, 128.92 (2C), 128.09 (2C), 125.37, 123.83, 123.04, 121.16, 71.81, 66.25, 55.37,
54.22, 52.23, 51.67, 33.86, 32.09, 28.68, 25.47, 21.82, 16.06, 10.16; MS (ESI) m/z 611.29 (M + Na)+.
(R)-methyl 3-((((2S,3R)-3-hydroxy-4-(4-methoxy-N-pentylphenylsulfonamido)-1-phenylbutan-2-
yl)carbamoyl)oxy)butanoate (15a). The title compound was obtained from 12c and 7a as described
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for 13a in 63% yield after flashꢀchromatography (1:3 EtOAc/hexane) as an amorphous white solid. H
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NMR (400 MHz, CDCl3) δ 7.69ꢀ7.62 (m, 2H), 7.21ꢀ7.12 (m, 5H), 6.92ꢀ6.86 (m, 2H), 6.01 (d, J = 8.5
Hz, 1H), 5.20ꢀ5.12 (m, 1H), 4.16ꢀ3.97 (m, 2H), 3.86ꢀ3.76 (m, 4H), 3.60 (s, 3H), 3.20 (dd, J = 14.6, 4.9
Hz, 1H), 3.05ꢀ2.87 (m, 3H), 2.54ꢀ2.42 (m, 3H), 1.50ꢀ1.31 (m, 2H), 1.25ꢀ1.10 (m, 8H), 0.78 (t, J = 6.7
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Hz, 3H); C NMR (100 MHz, CDCl3) δ 171.95, 167.71, 162.92, 137.87, 130.46, 129.31 (2C), 129.25
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(2C), 128.49 (2C), 126.48, 114.28 (2C), 72.27, 67.57, 55.57, 54.41, 51.77, 50.41, 40.35, 35.04, 30.99,
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29.62, 28.81, 21.26, 19.76, 13.93; MS (ESI) m/z 587.16 (M + Na)+.
2-(2,2,2-trifluoroacetamido)ethyl ((2S,3R)-3-hydroxy-4-(4-methoxy-N-pentylphenylsulfonamido)-
1-phenylbutan-2-yl)carbamate (15b). The title compound was obtained from 12c and 7b as described
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for 13a in 56% yield after flashꢀchromatography (1:3 EtOAc/hexane) as a colorless viscous liquid. H
NMR (400 MHz, CDCl3) δ 7.81 (d, J = 8.5 Hz, 1H), 7.68ꢀ7.59 (m, 2H), 7.24ꢀ7.12 (m, 5H), 6.92ꢀ6.86
(m, 2H), 4.29 (t, J = 7.9 Hz, 1H), 4.08ꢀ3.96 (m, 1H), 3.91ꢀ3.75 (m, 5H), 3.57ꢀ3.42 (m, 1H), 3.14ꢀ3.07
(m, 1H), 3.05ꢀ2.96 (m, 2H), 2.94ꢀ2.77 (m, 3H), 2.44ꢀ2.33 (m, 1H), 1.68 (bs, 1H), 1.48ꢀ1.32 (m, 2H),
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1.22ꢀ1.09 (m, 5H), 0.77 (t, J = 7.8 Hz, 3H); C NMR (100 MHz, CDCl3) δ 162.92, 155.42, 151.65,
137.39, 130.31, 129.43 (2C), 129.36 (2C), 129.24, 128.42 (2C), 126.53, 114.28 (2C), 72.00, 62.52,
55.58, 54.75, 52.13, 50.34, 42.29, 35.80, 28.69, 28.13, 22.13, 13.89; MS (ESI) m/z 626.32 (M + Na)+.
(R)-5-oxohexan-2-yl
((2S,3R)-3-hydroxy-4-(4-methoxy-N-pentylphenylsulfonamido)-1-
phenylbutan-2-yl)carbamate (15d). The title compound was obtained from 12c and 7d as described
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for 13a in 71% yield after flashꢀchromatography (1:3 EtOAc/hexane) as an amorphous white solid. H
NMR (400 MHz, CDCl3) δ 7.66ꢀ7.61 (m, 2H), 7.25ꢀ7.10 (m, 5H), 6.94ꢀ6.86 (m, 2H), 4.89ꢀ4.81 (m, 1H),
4.75 (d, J = 7.7 Hz, 1H), 4.64ꢀ4.56 (m, 1H), 3.92ꢀ3.67 (m, 5H), 3.18ꢀ2.99 (m, 3H), 2.98ꢀ2.92 (m, 1H),
2.89ꢀ2.79 (m, 1H), 2.36 (t, J = 7.3 Hz, 1H), 2.03 (s, 3H), 1.75ꢀ1.58 (m, 2H), 1.48ꢀ1.35 (m, 2H), 1.53ꢀ
1.25 (m, 2H), 1.26ꢀ1.04 (m, 4H), 1.02 (d, J = 6.1 Hz, 3H), 0.78 (t, J = 7.3 Hz, 3H); 13C NMR (100 MHz,
CDCl3) δ 207.96, 168.71, 162.97, 151.14, 137.74, 130.30, 129.44, 129.31 (2C), 128.44 (2C), 126.74,
114.30 (2C), 79.35, 72.27, 71.06, 55.50, 52.23, 50.40, 39.46, 38,56, 35.20, 29.86, 28.74, 25.42, 22.17,
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Journal of Medicinal Chemistry
19.81, 13.90; MS (ESI) m/z 585.40 (M + Na)+.
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2-((tert-butoxycarbonyl)amino)ethyl
((2S,3R)-3-hydroxy-4-(4-methoxy-N-
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pentylphenylsulfonamido)-1-phenylbutan-2-yl)carbamate (15e). The title compound was obtained
from 12c and 7e as described for 13a in 62% yield after flashꢀchromatography (1:3 EtOAc/hexane) as a
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colorless viscous liquid. H NMR (400 MHz, CDCl3) δ 7.64 (d, J = 8.5 Hz, 2H), 7.26ꢀ7.13 (m, 5H),
6.90 (d, J = 9.2 Hz, 2H), 5.03ꢀ4.76 (m, 1H), 4.68 (bs, 1H), 3.99ꢀ3.87 (m, 2H), 3.85ꢀ3.73 (m, 5H), 3.66ꢀ
3.59 (m, 1H), 3.44ꢀ2.92 (m, 7H), 2.89ꢀ2.78 (m, 1H), 1.46ꢀ1.31 (m, 10H), 1.25ꢀ1.06 (m, 5H), 0.78 (t, J =
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7.3 Hz, 3H); C NMR (100 MHz, CDCl3) δ 162.98, 156.36, 155.78, 137.67, 130.23, 129.46 (2C),
129.32 (2C), 128.49 (2C), 126.54, 114.32 (2C), 79.48, 72.20, 64.23, 55.59, 55.07, 52.27, 50.43, 39.93,
35.27, 28.74, 28.34 (3C), 28.17, 22.17, 13.90; MS (ESI) m/z 630.53 (M + Na)+.
(R)-methyl 3-((((2S,3R)-3-hydroxy-4-(4-methoxy-N-pentylphenylsulfonamido)-1-phenylbutan-2-
yl)carbamoyl)oxy)-2-methylpropanoate (15f). The title compound was obtained from 12c and 7f as
described for 13a in 61% yield after flashꢀchromatography (1:3 EtOAc/hexane) as an amorphous white
1
solid. H NMR (400 MHz, CDCl3) δ 7.66ꢀ7.60 (m, 2H), 7.25ꢀ7.11 (m, 5H), 6.92ꢀ6.86 (m, 2H), 4.87 (d,
J = 7.9 Hz, 1H), 4.09ꢀ3.97 (m, 2H), 3.83ꢀ3.71 (m, 5H), 3.69ꢀ3.61 (m, 1H), 3.57 (s, 3H), 3.11ꢀ2.90 (m,
4H), 2.87ꢀ2.78 (m, 1H), 2.68ꢀ2.56 (m, 1H), 1.45ꢀ1.34 (m, 2H), 1.24ꢀ1.07 (m, 5H), 1.04 (d, J = 7.3 Hz,
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3H), 0.77 (t, J = 7.0 Hz, 3H); C NMR (100 MHz, CDCl3) δ 174.25, 162.93, 156.18, 137.55, 130.21,
129.44 (2C), 129.30 (2C), 128.45 (2C), 126.43, 114.27 (2C), 72.22, 65.99, 55.56, 55.01, 52.36, 51.80,
50.45, 39.24, 35.31, 28.71, 28.18, 22.14, 13.87, 13.52; MS (ESI) m/z 587.36 (M + Na)+.
2-(2-oxoimidazolidin-1-yl)ethyl ((2S,3R)-3-hydroxy-4-(4-methoxy-N-pentylphenylsulfonamido)-1-
phenylbutan-2-yl)carbamate (15g). The title compound was obtained from 12c and 7g as described for
13a in 70% yield after flashꢀchromatography (1:3 EtOAc/hexane) as a white solid. 1H NMR (400 MHz,
CDCl3) δ 7.66 (d, J = 9.2 Hz, 2H), 7.24ꢀ7.10 (m, 5H), 6.89 (d, J = 9.2 Hz, 2H), 5.16 (d, J = 8.5 Hz, 1H),
4.75 (bs, 1H), 4.14ꢀ4.02 (m, 2H), 3.95ꢀ3.89 (m, 1H), 3.86ꢀ3.79 (m, 2H), 3.78 (s, 3H), 3.39ꢀ3.13 (m, 5H),
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3.05ꢀ2.99 (m, 1H), 2.95ꢀ2.71 (m, 3H), 2.68ꢀ2.59 (m, 1H), 1.54ꢀ1.26 (m, 2H), 1.23ꢀ0.99 (m, 6H), 0.73 (t,
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J = 7.3 Hz, 3H); C NMR (100 MHz, CDCl3) δ 162.94, 162.74, 156.23, 137.92, 130.61, 129.41 (2C),
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38.20, 34.95, 28.84, 28.12, 22.24, 13.98; MS (ESI) m/z 599.38 (M + Na)+.
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2-(2-oxooxazolidin-3-yl)ethyl
((2S,3R)-3-hydroxy-4-(4-methoxy-N-pentylphenylsulfonamido)-1-
phenylbutan-2-yl)carbamate (15h). The title compound was obtained from 12c and 7h as described
for 13a in 67% yield after flashꢀchromatography (1:3 EtOAc/hexane) as a colorless semiꢀsolid. 1H NMR
(400 MHz, CDCl3) δ 7.71ꢀ7.67 (m, 2H), 7.27ꢀ7.17 (m, 5H), 6.96ꢀ6.62 (m, 2H), 5.10 (d, J = 8.2 Hz, 1H),
4.25ꢀ4.12 (m, 3H), 3.92ꢀ3.78 (m, 5H), 3.74ꢀ3.65 (m, 1H), 3.52ꢀ3.31 (m, 4H), 3.21ꢀ2.95 (m, 5H), 2.92ꢀ
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2.79 (m, 1H), 1.59ꢀ1.42 (m, 2H), 1.28ꢀ1.12 (m, 5H), 0.82 (t, J = 6.7 Hz, 3H); C NMR (100 MHz,
CDCl3) δ 162.92, 158.59, 155.98, 137.77, 130.40, 129.36, 129.31 (3C), 128.41 (2C), 126.40, 114.29
(2C), 71.94, 61.87, 55.57, 55.14, 51.93, 50.28, 44.85, 43.68, 38.84, 35.17, 28.75, 28.11, 22.16, 13.90;
MS (ESI) m/z 599.86 (M + Na)+.
(R)-2-oxotetrahydrofuran-3-yl ((2S,3R)-3-hydroxy-4-(4-methoxy-N-pentylphenylsulfonamido)-1-
phenylbutan-2-yl)carbamate (15i). The title compound was obtained from 12c and 7i as described for
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13a in 50% yield after flashꢀchromatography (1:3 EtOAc/hexane) as a colorless semiꢀsolid. H NMR
(400 MHz, CDCl3) δ 7.76ꢀ7.69 (m, 2H), 7.30ꢀ7.15 (m, 5H), 7.01ꢀ6.96 (m, 2H), 4.62 (t, J = 5.5 Hz, 1H),
4.53ꢀ4.41 (m, 1H), 4.34ꢀ4.21 (m, 1H), 3.87 (s, 3H), 3.78ꢀ3.64 (m, 2H), 3.36ꢀ3.18 (m, 3H), 3.17ꢀ3.00 (m,
3H), 2.14ꢀ1.76 (m, 3H), 1.54ꢀ1.40 (m, 2H), 1.31ꢀ1.10 (m, 5H), 0.85 (t, J = 7.3 Hz, 3H); 13C NMR (100
MHz, CDCl3) δ 173.80, 163.01, 155.67, 136.72, 130.40, 129.43 (2C), 129.09 (2C), 128.65 (2C),
127.00, 114.34 (2C), 76.38, 70.99, 57.19, 56.88, 56.64, 51.69, 50.34, 32.36, 32.15, 28.77, 28.17, 22.21,
13.95; MS (ESI) m/z 571.34 (M + Na)+.
((S)-5-oxopyrrolidin-2-yl)methyl ((2S,3R)-3-hydroxy-4-(4-methoxy-N-pentylphenylsulfonamido)-
1-phenylbutan-2-yl)carbamate (15j). The title compound was obtained from 12c and 7j as described
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Journal of Medicinal Chemistry
1
for 13a in 56% yield after flashꢀchromatography (1:3 EtOAc/hexane) as a white solid. H NMR (400
MHz, CDCl3) δ 7.65 (d, J = 8.5 Hz, 2H), 7.23ꢀ7.09 (m, 5H), 6.93ꢀ6.86 (m, 3H), 5.47 (d, J = 7.9 Hz,
1H), 4.10ꢀ3.93 (m, 2H), 3.91ꢀ3.81 (m, 2H), 3.81ꢀ3.70 (m, 4H), 3.65 (dd, J = 11.0, 7.3 Hz 1H), 3.16ꢀ2.99
(m, 3H), 2.94 (dd, J = 14.0, 4.3 Hz 1H), 2.82ꢀ2.71 (m, 1H), 2.31ꢀ2.15 (m, 2H), 2.14ꢀ2.02 (m, 1H), 1.66ꢀ
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CDCl3) δ 178.75, 162.92, 156.03, 138.96, 129.91, 129.56 (2C), 129.49 (2C), 128.36 (2C), 126.43,
114.30 (2C), 71.27, 66.36, 54.61, 54.25, 52.35, 50.85, 49.11, 36.03, 28.74, 27.81, 27.02, 21.86, 21.21,
13.06; MS (ESI) m/z 583.88 (M + Na)+.
(R)-methyl 3-((((2S,3R)-3-hydroxy-4-(N-pentylbenzo[d]thiazole-6-sulfonamido)-1-phenylbutan-2-
yl)carbamoyl)oxy)butanoate (16a). The title compound was obtained from 12d and 7a as described for
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13a in 51% yield after flashꢀchromatography (1:2 EtOAc/hexane) as a colorless semiꢀsolid. H NMR
(400 MHz, CDCl3) δ 9.14 (s, 1H), 8.43 (d, J = 1.8, Hz, 1H), 8.18 (d, J = 8.5 Hz, 1H), 7.87 (dd, J = 8.5,
1.8 Hz, 1H), 7.26ꢀ7.11 (m, 5H), 6.03 (d, J = 8.5, Hz, 1H), 5.21ꢀ5.11 (m, 1H), 4.18ꢀ4.09 (m, 2H), 3.87ꢀ
3.79 (m, 1H), 3.60 (s, 3H), 3.29 (dd, J = 14.6, 4.8 Hz, 1H), 3.06ꢀ2.86 (m, 3H), 2.62ꢀ2.50 (m, 1H), 2.45ꢀ
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2.21 (m, 2H), 1.50ꢀ1.36 (m, 2H), 1.24ꢀ1.03 (m, 8H), 0.76 (t, J = 7.3 Hz, 3H); C NMR (100 MHz,
CDCl3) δ 172.27, 170.75, 157.86, 155.49, 137.77, 136.30, 134.32, 129.30 (2C), 128.60 (2C), 126.62,
124.78, 124.33, 122.16, 72.18, 67.62, 54.68, 51.81, 50.39, 40.34, 35.13, 29.66, 28.79, 28.21, 22.18,
19.75, 13.90; MS (ESI) m/z 614.26 (M + Na)+.
2-(2,2,2-trifluoroacetamido)ethyl ((2S,3R)-3-hydroxy-4-(N-pentylbenzo[d]thiazole-6-sulfonamido)-
1-phenylbutan-2-yl)carbamate (16b). The title compound was obtained from 12d and 7b as described
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for 13a in 63% yield after flashꢀchromatography (1:2 EtOAc/hexane) as a white solid. H NMR (400
MHz, CDCl3) δ 9.14 (s, 1H), 8.40 (d, J = 1.8 Hz, 1H), 8.17 (d, J = 8.5 Hz, 1H), 7.85ꢀ7.80 (m, 2H), 7.23ꢀ
7.13 (m, 5H), 4.30 (t, J = 7.9 Hz, 2H), 4.08ꢀ4.00 (m, 1H), 3.88ꢀ3.80 (m, 3H), 3.51 (d, J = 3.1 Hz, 1H),
3.21ꢀ2.98 (m, 5H), 1.50ꢀ1.37 (m, 2H), 1.22ꢀ0.99 (m, 6H), 0.73 (t, J = 7.3 Hz, 3H); 13C NMR (100 MHz,
CDCl3) δ 157.92, 155.49, 155.44, 152.86, 137.28, 136.17, 134.31, 129.44 (2C), 128.51 (3C), 126.66,
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