One-pot enantioselective synthesis of functionalized pyranocoumarins and 2-amino-4 H -chromenes: Discovery of a type of potent antibacterial agent

Article abstract of DOI:10.1021/jo202020m

Function-oriented design and synthesis of chiral small molecules with novel activity is a key goal in modern organic chemistry. As multiple antibiotic-resistant pathogens are emerging and causing serious diseases, the need for practical routes for the dev

Full text of DOI:10.1021/jo202020m

Article
pubs.acs.org/joc
One-Pot Enantioselective Synthesis of Functionalized
Pyranocoumarins and 2-Amino-4H-chromenes: Discovery of a Type
of Potent Antibacterial Agent
Gen Zhang,† Yaohu Zhang,† Jiexi Yan,† Ru Chen,† Shoulei Wang,† Yunxia Ma,† and Rui Wang*,†,‡
†Key Laboratory of Preclinical Study for New Drugs of Gansu Province, Institute of Biochemistry and Molecular Biology, State Key
Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000 China
‡State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of
Sciences, Lanzhou 730000 China
S
* Supporting Information
ABSTRACT: Function-oriented design and synthesis of chiral
small molecules with novel activity is a key goal in modern
organic chemistry. As multiple antibiotic-resistant pathogens
are emerging and causing serious diseases, the need for
practical routes for the development of new types of
antibacterial agents is very urgent. Herein, we present a highly
efficient process for the synthesis of optically active
pyranocoumarins and 2-amino-4H-chromenes through an
organocatalytic Knoevenagel/Michael/cyclization sequence,
and the preliminary biological studies of these new
heterocyclic compounds revealed potent antibacterial activity.
This study provides a novel strategy for further research and development of new types of antibacterial agents effective against
human pathogens.
privileged heterocycles in enantiomerically pure form are still
surprisingly rare.4 In particular, the evaluation of chiral
pyranocoumarins and 2-amino-4H-chromenes for biological
activities and studies on structure−activity relationships are
scarce and remain a great challenge.
INTRODUCTION
■
Coumarins and pyrans are ubiquitous in many important
biologically active molecules, synthetic drugs, and drug
candidates (Figure 1),1 which have shown biological and
Recently, organocatalytic domino reactions5 where multiple
carbon−carbon bond formations are achieved in a single
operation using simple experimental procedures have become
one of the most powerful methods for the synthesis of useful
organic molecules. As a result, significant advances have been
made in this flourishing area by several groups. Significant
progress has been made using α,β-unsaturated aldehydes,
ketones, esters, imides, and nitroolefins as electrophiles.6 In
contrast, less progress has been made on α,α-dicyanoolefins,
probably because of their high chemical reactivity.7 Considering
that α,α-dicyanoolefins could be readily prepared from a simple
Knoevenagel condensation of aldehydes with malononitrile and
that the nitrile group could be easily transformed to other
important groups, research into a suitable catalytic system for
α,α-dicyanoolefin addition is particularly appealing. On the
other hand, as intramolecular domino reactions have become
one of the most powerful methods for the construction of
useful organic molecules, multiple-component intermolecular
Figure 1. Natural products pyranocoumarins and 2-amino-4H-
chromenes.
pharmacological activities.2 Consequently, the incorporation of
the two structural features into interesting motifs, such as
pyranocoumarins and 2-amino-4H-chromenes, may have some
significance to the design of new therapeutic agents.3 However,
to date, the asymmetric catalytic approaches to construct these
Received: September 29, 2011
Published: December 13, 2011
© 2011 American Chemical Society
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Scheme 1. Strategy for Synthesis of Chiral Pyranocoumarins by Chiral Tertiary Amines
domino reactions with highly enantioselectivity still remain
elusive in current organic synthesis.8
RESULTS AND DISCUSSION
■
As part of our continuous interest in developing new methods
for the synthesis of useful compounds,9 we recently succeeded
in developing a novel class of bifunctional thiourea catalysts
based on abietic acid10 and applied it to enantioselective
synthesis.9a−c Encouraged by these successful efforts and
aiming to demonstrate the efficiency and generality of this
abietic-acid-derived thiourea bifunctional catalysis, we fixed our
recent attention on employing this novel catalysis for the
asymmetric synthesis of optically active pyranocoumarins and
2-amino-4H-chromenes prepared from simple and easily
available starting materials under mild reaction conditions.
We envisioned that in the presence of a chiral tertiary amine-
thiourea, 4-hydroxycoumarins 2 might be activated through a
hydrogen bond between the nitrogen atom of the chiral tertiary
amine-thiourea with the hydrogen of the hydroxyl.11 Then the
electron-rich α-carbon atom of 2 attacks the electron-deficient
cyanoolefins 1 to generate the Micheal adducts A. Sub-
sequently, intramolecular cyclization of A afforded the cyclized
adducts B, and finally, tautomerization of C obtained the
Figure 2. Organocatalysts used in this study.
desired final product 3 (Scheme 1).
To explore the possibility of the proposed Michael addition/
cyclization sequence, initially, we used the reaction of 2-
benzylidenemalononitrile with 4-hydroxycoumarin as a model
reaction, and a variety of bifunctional organocatalysts were
screened at room temperature in toluene for the synthesis of
the optically active pyranocoumarins (Figure 2, Table 1). The
results showed that the bifunctional thiourea catalyst derived
from quinine amine12 based on abietic acid exhibited good
activity and high enantioselectivity (Table 1, entry 6), while
other thiourea catalysts derived from diaminocyclohexane
(Table 1, entries 1−5), and cinchonine or quinine derivatives
(Table 1, entries 7−11) provided disappointing results. Solvent
optimization results showed that ether was a better solvent
according to the enantioselectivity (up to 94% ee, Table 1,
entry 13). Satisfactorily, little decrease in enantioselectivity or
yield was observed when the loading of tertiary amine-thiourea
L6 was lowered to 2.0 mol % (Table 1, entry 15).
With optimal conditions established, we then examined the
scope of the reaction for the construction of various optically
active pyranocoumarins, and the results are summarized in
Table 2. In general, the reaction proceeded smoothly to afford
the desired products in good yields and excellent enantiose-
lectivities. For the reaction with 4-hydroxycoumarin 2a, a wide
range of substituted aromatic α,α-dicyanoolefins 1 were
examined (Table 2, entries 1−10). It was found that α,α-
dicyanoolefins 1 with either electron-withdrawing or electron-
donating groups on the phenyl ring provided good yields (75−
90%) and excellent enantioselectivities (83−98% ee values). In
addition, good results were also obtained by using 2-furyl, 3-
thienyl, and n-hexyl as substituents of α,α-dicyanoolefins 1
(Table 2, entries 11−13). And various substituted 4-
hydroxycoumarins are also suited under this system (Table 2,
entries 14−16). Importantly, this efficient approach can also be
utilized for the asymmetric synthesis of optically pure pyranone
using the reaction of 4-hydroxy-6-methyl-2-pyrone 2e with 2-
benzylidenemalononitrile 1a (Table 2, entry 17). Furthermore,
cyanoacrylates are also suitable to afford the desirable products
(Table 2, entries 18−19). The absolute configuration of
products were determined to be R by using single crystal X-
ray diffraction of 3f.13
Encouraged by the results achieved above, we wished this
effective catalysis system could be extended to the asymmetric
synthesis of other useful organic molecules, such as 2-amino-4-
H-chromenes. Considering their potential versatility as active-
determining building blocks in some biologically active natural
products,14 to date, efficient protocols for construction of the
optically pure form have not been achieved.15 Satisfactorily, as
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Table 1. Catalyst Screening and Optimization of Reaction
Conditions
Table 2. Asymmetric Synthesis of 3,4-
a
Dihydropyrano[c]chromenes via Two-Component
a
Reactions
b
c
entry
catalyst
R
yield (%)
ee (%)
d
1
L1
L2
L3
L4
L5
L6
L7
L8
L9
L10
L11
L6
L6
L6
L6
H
3a/77
3a/74
3a/80
3a/82
<10
44
2
H
H
H
H
H
H
H
H
H
H
CH3
H
H
H
42
d
3
69
b
c
entry
R
sm
yield (%)
ee (%)
4
70
e
1
Ph
1a/2a
1a/2a
1a/2a
1a/2a
1a/2a
1a/2a
1a/2a
1a/2a
1a/2a
1a/2a
1a/2a
1a/2a
1a/2a
1a/2b
1a/2c
1a/2d
1a/2e
1b/2a
1c/2a
3a/90
3b/87
3c/83
3d/89
3e/81
3f/75
3g/78
3h/87
3i/80
3j/81
3k/72
3l/88
3m/69
3n/86
3o/82
3p/81
3q/82
3r/85
3s/83
93
94
98
96
87
90
83
93
88
96
99
95
77
98
96
90
93
80
92
5
n.d.
2
4-ClPh
4-FPh
4-BrPh
3-ClPh
3-BrPh
3-MeOPh
2-FPh
2-BrPh
2-MePh
2-furyl
3-thienyl
n-hexyl
Ph
6
3a/92
3a/81
3a/76
3a/74
3a/70
3a/75
<10
87
39
35
3
7
4
8
d
5
9
53
d
6
10
11
12
37
7
38
e
8
n.d.
f
9
13
3a/90
3a/91
3a/90
94
93
93
fg
14 ,
10
11
12
13
14
15
16
17
18
19
fh
15 ,
a
Unless otherwise specified, the reaction was carried out with 1a (0.2
mmol) and 2a (0.3 mmol) in the presence of an organocatalyst L
b
(0.02 mmol) in toluene (2.0 mL) at rt for 4 h. Isolated yield.
c
d
Ph
Determined by chiral HPLC on a Chiralpak OD column. The
e
f
Ph
opposite configuration. Not determined. The reaction was conducted
in Et2O (2.0 mL). 5.0 mol % of ligand loading for 6 h. 2.0 mol % of
ligand loading for 8 h.
g
h
Ph
Ph
Ph
a
shown in Table 3, in general, the reaction proceeded smoothly
to afford various kinds of 2-amino-4-H-chromenes 5 in good
yields (71−95%) and excellent enantioselectivities (up to 99%
ee). More importantly, when cyclohexane-1,2-dione 4c was
used as nucleophile, the reaction could proceed well to give the
desired product in good yield (67%) and moderate
enantioselectivities (77% ee, Scheme 2). In addition, good
results were also obtained by using naphthalen-1-ol 4d and
naphthalene-1,3-diol 4e as substrates (up to 84% yield and 83%
ee, Scheme 3).
More importantly, pyranocoumarins and 2-amino-4-H-
chromenes could be readily obtained without any loss of
enantioselectivies when the condition was extended to one-pot,
three-component intermolecular domino reactions among
aromatic aldehyde, malononitrile, and 4-hydroxycoumarin or
cyclohexane-1,3-dione (Scheme 4).16
Coumarin and chromen derivatives have been reported to
have various biological activities, such as anticoagulant,
anticancer, anti-HIV, and apoptosis-inducing activities.17
However, other biological activities, such as antibacterial
activity, have not been successfully exploited. So in this study,
some of the synthesized compounds 3a−s and 5a−v were
tested for their antibacterial activities at concentrations of
3.125, 6.25, 12.5, 25.0, 50.0, 100.0, and 200.0 μg/mL using a
standard broth microdilution method.18 Antibacterial activity
studies showed that the coumarin-based compounds, such as
3d, 3g, 3j, 3n, 3q, and 3r, were only very slightly active against
standard reference strains of Staphylococcus aureus (CMCC
26003) and Escherichia coli (CMCC 44102). Interestingly, 2-
amino-4H-chromene derivatives exhibited distinct antibacterial
Unless otherwise specified, the reaction was carried out with 1 (0.2
mmol) and 2 (0.3 mmol) in the presence of an organocatalyst L6
b
(0.02 mmol) and Et2O (2.0 mL) at rt for 8 h. Isolated yield.
c
Determined by HPLC on a Chiralpak AD or OD column, and the
configuration was assigned by comparison of HPLC date and X-ray
crystal data of 3f.
activity against S. aureus (CMCC 26003). As summarized in
Table 4, optically active 5u (MIC = 6.25 μg/mL) was 2 times
more efficient than kanamycin sulfate (MIC = 15.625 μg/mL),
a well-known antibiotic. And 5u with a hydroxyl group at the 5-
position was about 50-fold more active than the lead compound
5t (MIC = 300.0 μg/mL) against S. aureus. This phenomenon
suggests that the hydroxyl is a key functional group of 2-amino-
4H-chromenes that enhances the inhibition effect on the
growth of S. aureus. In addition, the optically active 5u was 4
times more efficient than the racemic form (MIC = 25.0 μg/
mL). The 4-chlorophenyl analogue 5v (MIC = 6.25 μg/mL)
was equally potent as 5u.
Cytotoxicity tests for new a therapeutic agent are necessary
before it can be declared as a potential medicine for any disease.
Having identified a potential agent with antibacterial activity,
the next question is whether this antibacterial agent has
selectivity between bacteria and human cells. We chose a
hemolysis experiment as a model to test the acute cytotoxicity
of these compounds. And the acute cytotoxicity of 5u
(racemic), 5u, and 5v was examined as according to Ryan
and co-workers with a little modification.19 Blood specimens
were freshly collected from mice and different adult human
donors. Solutions of different concentrations were added to the
erythrocytes and incubated for 60 min at 37 °C; 0.2% Triton-X
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Table 3. Asymmetric Synthesis of 2-Amino-4H-chromenes
via Two-Component Reactions
Scheme 2. Asymmetric Synthesis of 2-Amino-4H-chromene
5s via Two-Component Reactions
a
b
c
entry
R
R1
yield (%)
ee (%)
1
Ph
4a/H
4a/H
4a/H
4a/H
4a/H
4a/H
4a/H
4a/H
4a/H
4a/H
4a/H
4a/H
4a/H
4a/H
4a/H
4b/Me
5a/94
5b/90
5c/91
5d/87
5e/95
5f/89
5g/83
5h/86
5i/90
5j/85
5k87
96
95
93
85
80
79
89
97
94
89
99
97
80
75
73
68
Scheme 3. Asymmetric Synthesis of 2-Amino-4H-chromene
5t, 5u, and 5v via Two-Component Reactions
2
4-ClPh
4-BrPh
4-FPh
3
4
5
4-CNPh
4-MeOPh
3-ClPh
3-BrPh
3-MeOPh
3-MePh
2-BrPh
2-FPh
6
7
8
9
10
11
12
13
14
15
16
5l/91
5m/93
5o/84
5p/71
5q/83
enantioslectivities (up to 99% ee). Importantly, preliminary
biological studies of these new heterocyclic compounds showed
antibacterial activity against S. aureus, MIC = 6.25 μg/mL. This
study discloses a novel type of antibacterial agent and may
provide a practical strategy for further developing new types of
potent antibiotics efficient against Gram-positive human
pathogens. Further investigation on these new heterocyclic
compounds is ongoing in our laboratories.
2-MeOPh
2-furyl
n-hexyl
Ph
a
Unless otherwise specified, the reaction was carried out with 1 (0.2
mmol) and 4 (0.3 mmol) in the presence of an organocatalyst L6
(0.02 mmol) in Et2O (2.0 mL) at rt for 4 h. Isolated yield.
Determined by HPLC.
b
c
EXPERIMENTAL SECTION
■
100 and PBS were used as the positive and the negative control,
respectively. The data of these compounds against mice
erythrocytes showed that the release of mice hemoglobin was
less than 5% even at the concentration of 125 μg/mL, which is
about 20 times of the MIC (Figure 3A). And the release of
human hemoglobin was less than 5% even at the concentration
of 250 μg/mL, which is about 40 times of the MIC (Figure 3B).
Besides the acute cytotoxicity assay, the chronic cytotoxicity of
these compounds against human cells was also assayed. Briefly,
human Jurkat and Hela cells were inoculated into 96-well plates
at 8 × 103 cells/well before treatment. After 24 h, the cells were
treated with a range of concentrations of compounds, and PBS
buffer was used as control. All the cells were incubated for 24 h
at 37 °C and 5% CO2. Then, MTT reagent solution was added,
and the 96-well plate was incubated for 4 h at 37 °C. After that,
the supernatant was discarded and the MTT formazan
precipitate was dissolved in 150 μL of DMSO with gentle
shaking. The absorbance was determined at 570 nm. IC50
values for each cell line were evaluated, representing the
concentration at which human cell viability was reduced to 50%
compared with PBS treated cells. The data of these compounds
against human cells showed that the IC50 value of 5u and 5v
was about 4 times the antibacterial MIC (Table 5). These
results showed that these compounds show same selectivity
against bacteria.
All reactions were carried out under an argon atmospheric condition
unless otherwise noted, and solvents were dried according to
established procedures. Reactions were monitored by thin layer
chromatography (TLC); column chromatography purifications were
carried out using silica gel. Proton nuclear magnetic resonance (1H
NMR) spectra were recorded on a 300 MHz spectrometer in CDCl3
unless otherwise noted, and carbon nuclear magnetic resonance (13C
NMR) spectra were recorded on 300 MHz spectrometer in CDCl3
using tetramethylsilane (TMS) as internal standard unless otherwise
noted. Data are presented as follows: chemical shift, integration,
multiplicity (br = broad, s = singlet, d = doublet, t = triplet, q =
quartet, m = multiplet, cm = complex multiplet), and coupling
constant in Hertz (Hz). Infrared (IR) spectra were recorded on a
spectrometer. Optical rotations were recorded on a polarimeter. HR-
MS was measured with a mass spectrometer. Melting points were
measured on a melting point apparatus and were uncorrected. The ee
value determination was carried out using chiral high-performance
liquid chromatography (HPLC) with Daicel Chiracel AD-H column
with a UV-detector.
General Procedure for Asymmetric Synthesis of L6. Carbon
disulfide (15 mmol) and N,N′-dicyclohexylcarbodiimide (DCC, 10
mmol) were added to a solution of dehydroabietic amine (10 mmol)
in dry ether (50 mL) at 0 °C. The reaction mixture was allowed to
warm slowly to room temperature over a period of 3 h and then was
stirred for a further 12 h at room temperature. After separation of the
precipitated thiourea by filtration, the resulting mixture was
concentrated under reduced pressure, and the residue was purified
through column chromatography on silica gel (eluent, ethyl acetate/
hexane 1:50) to give the isothiocyanate as a yellow oil (90% yield).
And then the isothiocyanate (6.0 mmol) was added over a period of
1.5 h to a stirred solution of (R)-quininenamine (5 mmol, 1.14 g) in
dry dichloromethane (30 mL). The reaction mixture was stirred
overnight at room temperature. After the reaction was completed, the
resulting mixture was concentrated under reduced pressure, and the
residue was purified through column chromatography on silica gel
CONCLUSION
■
In conclusion, we have successfully developed a unique
approach to asymmetric synthesis of various optically pure
pyranocoumarins and 2-amino-4H-chromenes catalyzed by a
novel tertiary amine-thiourea with low ligand loading under
one-pot, two-component and three-component intermolecular
domino reactions with high yield (up to 95%) and
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Scheme 4. Asymmetric Synthesis of Pyranocoumarins and 2-Amino-4H-chromenes via One-Pot, Three-Component Domino
Reaction
a
Table 4. Antibacterial Activity of Compounds 3 and 5
MIC (μg/mL)
compounds
3d
S. aureus (CMCC 26003)
E. coli (CMCC 44102)
>100.0
>100.0
>100.0
>100.0
100.0
>100.0
>100.0
>100.0
>100.0
>100.0
25.0
>100.0
>100.0
>100.0
>100.0
>100.0
>100.0
>100.0
>100.0
>100.0
>100.0
>100.0
>100.0
>100.0
62.5−125.0
>64.0
3g
3j
3n
3q
3r
5i
5k
5r
5t
5u (racemic)
5u
6.25
5v
6.25
kanamycin
vancomycin
15.625
1.0
a
MICs were determined by a standard broth microdilution method as
recommended by the NCCLS. Serial 2-fold dilutions of each
compound were made in appropriate broth, the plates were inoculated
with 1 × 106 CFU mL−1 of each strain in a volume of 100 μL, and then
the compounds of different concentrations were added in each well.
Plates were incubated at 35 °C for 18 h, and then the MICs were
scored.
(eluent, ethyl acetate) to give the isothiocyanate L6 as a white solid
(67% yield).
1 - ( ( ( 1 R , 4 a S , 1 0 a R ) - 7 - I s o p r o p y l - 1 , 4 a - d i m e t h y l -
1,2,3,4,4a,9,10,10a-octahydrophenanthren-1-yl)methyl)-3-
((1R)-(6-methoxyquinolin-4-yl)(8-vinylquinuclidin-2-yl)-
methyl)thiourea (L6). White solid: mp 133−134 °C; [α]20 = −70
D
1
(c = 1.0, CHCl3); H NMR (300 MHz, DMSO-d6) δ 8.67 (s, 1 H),
7.89−7.92 (d, J = 5.1 Hz, 2 H), 7.37−7.44 (m, 2 H), 7.10−7.13 (d, J =
8.1 Hz, 1 H), 6.93−6.95 (d, J = 7.8 Hz, 1 H), 6.83 (s, 1 H), 5.72−5.83
(m, 2H), 4.87−4.98 (m, 2 H), 3.90 (s, 3 H), 3.55−3.58 (d, J = 10.5
Hz, 1 H), 3.04−3.14 (m, 4 H), 2.75−2.80 (t, J = 6.6 Hz, 3 H), 2.51−
2.59 (m, 2 H), 2.22 (br, 2 H), 1.54 (br, 1 H), 1.38 (m, 7 H), 1.54−
1.77 (m, 11 H), 1.09 (s, 3 H), 0.78 (s, 3 H) ppm; 13C NMR (75 MHz,
DMSO-d6) δ 158.0, 148.5, 148.1, 145.9, 145.2, 142.9, 135.7, 132.2,
128.9, 127.4, 125.0, 124.5, 122.2, 115.2, 104.2, 56.6, 56.3, 45.1, 41.8,
39.0, 38.4, 37.9, 36.8, 33.9, 30.5, 28.4, 28.1, 26.6, 26.1, 25.1, 24.9, 21.8,
19.8, 19.6, 19.2 ppm; IR (neat) 3328, 3070, 2925, 2864, 1711, 1620,
1536, 1359, 1232, 1026, 726 cm−1; HRMS (ESI) C41H54N4OS [M +
H]+ calcd 651.4091, found 651.4081.
Figure 3. The acute cytotoxicity studies of 5u (racemic), 5u, and 5v
(A) against mice red blood cells and (B) against human red blood
cells. (For experimental details, see the Supporting Information.)
General Procedure for Asymmetric Synthesis Pyranocou-
marins. Typical experimental procedure: To a stirred solution of L6
(0.004 mmol, 2.0 mol %) and 4-hydroxycoumarin 2a or 4-hydroxy-6-
methyl-2-pyrone 2b or 4-hydroxy-1-methyl-1,2- dihydroquinolin-2-one
2c (0.30 mmol) in dry ether (1.0 mL), a solution of α,β-unsaturated
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(R)-2-Amino-4-(3-chlorophenyl)-5-oxo-4,5-dihydropyrano-
[3,2-c]chromene-3-carbonitrile (3e). White solid: mp 227−228
°C; 81% yield; 87% ee determined by HPLC on a Chiralpak AD-H
column (hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254
nm, tmajor = 11.91 min, tminor = 8.51 min); [α]20 = +13 (c = 1.0,
acetone); 1H NMR (300 MHz, DMSO-d6) δ 7.91−D7.93 (d, J = 7.8 Hz,
1 H), 7.70−7.75 (t, J = 7.5 Hz, 1 H), 7.45−7.52 (m, 3 H), 7.26−7.37
(m, 4 H), 4.53 (s, 1 H) ppm; 13C NMR (75 MHz, DMSO-d6) δ 160.0,
158.4, 154.2, 152.6, 146.2, 133.5, 133.4, 130.8, 128.0, 127.6, 127.0,
125.1, 123.0, 119.5, 117.0, 113.4, 103.6, 57.8, 37.1 ppm; IR (neat)
3350, 3185, 2923, 2854, 2196, 1725, 1672, 1603, 1371, 1025, 756
cm−1; HRMS (ESI) C19H11ClN2O3 [M + NH4]+ calcd 368.0796,
found 368.0802.
Table 5. Chronic Cytotoxicity of Compounds against
Human Cells
IC50 (μg/mL)
compounds
Hela
Jurkat
5u (racemic)
25
25
5u
5v
100
25
100
27
nitriles (0.2 mmol) in dry ether (1.0 mL) was added over a period of
10 min. The solution was stirred at room temperature for 8 h. After
the reaction was completed (monitored by TLC), the resulting
mixture was concentrated under reduced pressure, and the residue was
purified through column chromatography on silica gel (eluent, ethyl
acetate/dichloromethane 1:25) to give the pure products. After
filtration, the solvent was removed at reduced pressure to give the pure
products.
(R)-2-Amino-4-(3-bromophenyl)-5-oxo-4,5-dihydropyrano-
[3,2-c]chromene-3-carbonitrile (3f). White solid: mp 247−248 °C;
75% yield; 90% ee determined by HPLC on a Chiralpak AD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
12.76 min, tminor = 9.11 min); [α]20 = +23 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.90−7.93 (dd, J = 1.2 Hz, 7.8 Hz, 1
H), 7.70−7.75 (t, J = 7.2 Hz, 1 H), 7.44−7.53 (m, 5 H), 7.29−7.31
(m, 2 H), 4.51 (s, 1 H) ppm; 13C NMR (75 MHz, DMSO-d6) δ 160.0,
158.4, 154.2, 152.6, 146.5, 133.5, 131.2, 130.9, 130.5, 127.4, 125.1,
123.0, 122.2, 119.5, 117.0, 113.4, 103.6, 57.8, 37.1 ppm; IR (neat)
3321, 3183, 2921, 2852, 2195, 1713, 1672, 1604, 1375, 1054, 761
cm−1; HRMS (ESI) C19H11BrN2O3 [M + H]+ calcd 395.0026, found
395.0036.
( R ) - 2 - A m i n o - 4 - ( 3 - m e t h o x y p h e n y l ) - 5 - o x o - 4 , 5 -
dihydropyrano[3,2-c]chromene-3-carbonitrile (3g). White solid:
mp 233−234 °C; 78% yield; 83% ee determined by HPLC on a
Chiralpak AD-H column (hexane/2-propanol = 80/20, flow rate = 1.0
mL/min, 254 nm, tmajor = 14.62 min, tminor = 10.83 min); [α]20D = +18
(c = 1.0, acetone); 1H NMR (300 MHz, DMSO-d6) δ 7.90−7.93 (d, J
= 7.8 Hz, 1 H), 7.69−7.74 (t, J = 7.5 Hz, 1 H), 7.44−7.52 (m, 3 H),
7.23−7.28 (t, J = 8.4 Hz, 1 H), 6.85 (s, 1 H), 6.82 (s, 2 H), 4.45 (s, 1
H), 3.74 (s, 3 H) ppm; 13C NMR (75 MHz, DMSO-d6) δ 159.5,
159.2, 157.9, 153.4, 152.1, 144.8, 132.9, 129.6, 124.6, 122.4, 119.7,
119.1, 116.5, 113.8, 112.9, 111.9, 103.8, 57.8, 54.9, 36.8 ppm; IR
(neat) 3364, 3313, 3177, 2920, 2850, 2189, 1710, 1668, 1371, 1051,
766 cm−1; HRMS (ESI) C20H14N2O4 [M + H]+ calcd 347.1026, found
347.1031.
(R)-2-Amino-4-(2-fluorophenyl)-5-oxo-4,5-dihydropyrano-
[3,2-c]chromene-3-carbonitrile (3h). White solid: mp 205−206
°C; 87% yield; 93% ee determined by HPLC on a Chiralpak AD-H
column (hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254
nm, tmajor = 16.56 min, tminor = 9.73 min); [α]20 = +21 (c = 1.0,
acetone); 1H NMR (300 MHz, DMSO-d6) δ 7.91−D7.94 (d, J = 7.5 Hz,
1 H), 7.71−7.76 (t, J = 7.2 Hz, 1 H), 7.46−7.54 (dd, J = 7.8 Hz, 15.0
Hz, 3 H), 7.29−7.36 (m, 2 H), 7.14−7.27 (m, 2 H), 4.75 (s, 1 H)
ppm; 13C NMR (75 MHz, DMSO-d6) δ 161.8, 159.4, 158.6, 158.2,
153.8, 152.1, 133.0, 130.2, 129.8 (d, J = 12.0 Hz), 129.2 (d, J = 8.3
Hz), 124.7, 122.4, 119.0, 116.6, 115.5 (d, J = 21.8 Hz), 112.8, 102.6,
56.3, 31.3 ppm; IR (neat) 3370, 2922, 2853, 2188, 1703, 1668, 1598,
1375, 1054, 1027, 749 cm−1; HRMS (ESI) C19H11FN2O3 [M + H]+
calcd 335.0826, found 335.0819.
(R)-2-Amino-5-oxo-4-phenyl-4,5-dihydropyrano[3,2-c]-
chromene-3-carbonitrile (3a). White solid: mp 264−265 °C; 90%
yield; 93% ee determined by HPLC on a Chiralpak OD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
20.52 min, tminor = 27.81 min); [α]20 = +12 (c = 1.0, acetone); H
NMR (300 MHz, DMSO-d6) δ 7.90−D7.93 (d, J = 7.8 Hz, 1 H), 7.69−
7.72 (t, J = 6.9 Hz, 1 H), 7.42−7.52 (m, 3 H), 7.25−7.33 (m, 5 H),
4.46 (s, 1 H) ppm; 13C NMR (75 MHz, DMSO-d6) δ 159.5, 157.9,
153.4, 152.1, 143.3, 132.9, 128.5, 127.6, 127.1, 124.6, 122.4, 119.2,
116.5, 112.9, 104.0, 57.9, 36.9 ppm; IR (neat) 3350, 3320, 2921, 2852,
2195, 1700, 1669, 1603, 1373, 1044, 759 cm−1; HRMS (ESI)
C19H12N2O3 [M + H]+ calcd 317.0921, found 317.0926.
1
(R)-2-Amino-4-(4-chlorophenyl)-5-oxo-4,5-dihydropyrano-
[3,2-c]chromene-3-carbonitrile (3b). White solid: mp 233−234
°C; 87% yield; 94% ee determined by HPLC on a Chiralpak OD-H
column (hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254
nm, tmajor = 13.21 min, tminor = 25.66 min); [α]20 = +13 (c = 1.0,
D
acetone); 1H NMR (300 MHz, DMSO-d6) δ 7.90−7.93 (d, J = 7.5 Hz,
1 H), 7.70−7.75 (t, J = 7.5 Hz, 1 H), 7.45−7.53 (m, 3 H), 7.30−7.39
(dd, J = 8.4 Hz, 19.5 Hz, 4 H), 4.50 (s, 1 H) ppm; 13C NMR (75
MHz, DMSO-d6) δ 160.0, 158.4, 154.0, 152.6, 142.8, 133.5, 132.2,
130.1, 128.9, 125.1, 123.0, 119.5, 117.0, 113.4, 103.9, 58.0, 36.8 ppm;
IR (neat) 3404, 2924, 2255, 2184, 2128, 1704, 1668, 1378, 1026, 1001,
763 cm−1; HRMS (ESI) C19H11ClN2O3 [M + NH4]+ calcd 368.0796,
found 368.0804.
(R)-2-Amino-4-(4-fluorophenyl)-5-oxo-4,5-dihydropyrano-
[3,2-c]chromene-3-carbonitrile (3c). White solid: mp 243−244
°C; 83% yield; 98% ee determined by HPLC on a Chiralpak AD-H
column (hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254
nm, tmajor = 11.10 min, tminor = 7.53 min); [α]20 = +12 (c = 0.5,
acetone); 1H NMR (300 MHz, DMSO-d6) δ 7.90−D7.93 (d, J = 7.8 Hz,
1 H), 7.69−7.74 (t, J = 7.2 Hz, 1 H), 7.44−7.52 (m, 3 H), 7.32−7.36
(dd, J = 5.4 Hz, 8.4 Hz, 2 H), 7.12−7.18 (t, J = 9.0 Hz, 2 H), 4.50 (s, 1
H) ppm; 13C NMR (75 MHz, DMSO-d6) δ 162.8, 159.5 (d, J = 6.8
Hz), 157.8, 153.3, 152.1, 139.4, 132.9, 129.6 (d, J = 8.3 Hz), 124.6,
122.4, 119.1, 116.5, 115.1 (d, J = 21.8 Hz), 112.9, 103.7, 57.7, 36.2
ppm; IR (neat) 3378, 2922, 2852, 2254, 2191, 1714, 1673, 1376, 1025,
1000, 761 cm−1; HRMS (ESI) C19H11FN2O3 [M + H]+ calcd
335.0826, found 335.0834.
(R)-2-Amino-4-(2-bromophenyl)-5-oxo-4,5-dihydropyrano-
[3,2-c]chromene-3-carbonitrile (3i). White solid: mp 247−248 °C;
80% yield; 88% ee determined by HPLC on a Chiralpak AD-H column
(R)-2-Amino-4-(4-bromophenyl)-5-oxo-4,5-dihydropyrano-
[3,2-c]chromene-3-carbonitrile (3d). White solid: mp 228−229
°C; 89% yield; 96% ee determined by HPLC on a Chiralpak AD-H
column (hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254
nm, tmajor = 12.76 min, tminor = 8.46 min); [α]20 = +15 (c = 1.0,
acetone); 1H NMR (300 MHz, DMSO-d6) δ 7.90−D7.92 (d, J = 7.8 Hz,
1 H), 7.70−7.75 (t, J = 7.2 Hz, 1 H), 7.53 (s, 1 H), 7.46−7.50 (dd, J =
6.0 Hz, 7.5 Hz, 4 H), 7.24−7.27 (d, J = 8.4 Hz, 2 H), 4.48 (s, 1 H)
ppm; 13C NMR (75 MHz, DMSO-d6) δ 160.0, 158.3, 154.0, 152.6,
143.2, 133.5, 131.8, 130.5, 125.1, 124.4, 123.0, 120.7, 117.0, 113.4,
103.9, 57.9, 36.9 ppm; IR (neat) 3414, 2925, 2854, 2255, 2193, 2128,
1673, 1378, 1027, 1002, 764 cm−1; HRMS (ESI) C19H11BrN2O3 [M +
NH4]+ calcd 412.0291, found 412.0287.
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor =
17.68 min, tminor = 10.18 min); [α]20 = +14 (c = 1.0, acetone); H
NMR (300 MHz, DMSO-d6) δ 7.91−D7.93 (d, J = 7.5 Hz, 1 H), 7.71−
7.76 (t, J = 7.5 Hz, 1 H), 7.58−7.61 (d, J = 7.8 Hz, 1 H), 7.46−7.54
(m, 3 H), 7.31 (s, 2 H), 7.19−7.21 (m, 1 H), 5.00 (s, 1 H) ppm; 13C
NMR (75 MHz, DMSO-d6) δ 159.3, 157.9, 153.9, 152.2, 141.9, 133.0,
132.7, 130.6, 129.0, 128.3, 124.7, 122.9, 122.5, 118.6, 116.6, 112.8,
103.1, 56.6, 36.4 ppm; IR (neat) 3318, 3176, 2923, 2853, 2194, 1712,
1672, 1604, 1375, 1054, 751 cm−1; HRMS (ESI) C19H11BrN2O3 [M +
H]+ calcd 395.0026, found 395.0035.
1
(R)-2-Amino-5-oxo-4-o-tolyl-4,5-dihydropyrano[3,2-c]-
chromene-3-carbonitrile (3j). White solid: mp 210−211 °C; 81%
yield; 96% ee determined by HPLC on a Chiralpak AD-H column
883
dx.doi.org/10.1021/jo202020m | J. Org. Chem. 2012, 77, 878−888

The Journal of Organic Chemistry
Article
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
3 H), 4.43 (s, 1 H), 2.43 (s, 3 H) ppm; 13C NMR (75 MHz, DMSO-
d6) δ 159.6, 157.9, 157.8, 153.3, 150.2, 143.3, 134.0, 133.7, 128.5,
127.5, 127.1, 122.0, 116.2, 112.5, 103.8, 57.9, 36.9, 20.4 ppm; IR
(neat) 3412, 3308, 3183, 2924, 2855, 2181, 1643, 1598, 1374, 1210,
998 cm−1; HRMS (ESI) C20H14N2O3 [M + H]+ calcd 331.1077, found
331.1067.
(R)-2-Amino-9-methoxy-5-oxo-4-phenyl-4,5-dihydropyrano-
[3,2-c]chromene-3-carbonitrile (3p). White solid: mp 220−221
°C; 81% yield; 90% ee determined by HPLC on a Chiralpak AD-H
column (hexane/2-propanol = 70/30, flow rate = 1.0 mL/min, 254
nm, tmajor = 12.13 min, tminor = 7.69 min); [α]20 = +37 (c = 1.0,
acetone); 1H NMR (300 MHz, DMSO-d6) δ 7.40−D7.43 (d, J = 8.7 Hz,
1 H), 7.37 (s, 1 H), 7.25−7.37 (m, 6 H), 4.45 (s, 1 H), 3.87 (s, 3 H)
ppm; 13C NMR (75 MHz, DMSO-d6) δ 159.6, 157.9, 155.8, 153.1,
146.5, 143.3, 128.5, 127.5, 127.1, 120.3, 119.1, 117.7, 113.3, 104.8,
104.1, 57.8, 55.8, 36.9 ppm; IR (neat) 3425, 3295, 2923, 2853, 2205,
1705, 1673, 1457, 1374, 1235, 1020 cm−1; HRMS (ESI) C20H14N2O4
[M + H]+ calcd 347.1026, found 347.1019.
1
12.60 min, tminor = 7.86 min); [α]20 = +19 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.91−7.94 (dd, J = 1.2 Hz, 7.8 Hz, 1
H), 7.72−7.74 (t, J = 8.4 Hz, 1 H), 7.45−7.53 (dd, J = 7.5 Hz, 15.9 Hz,
2 H), 7.38 (s, 1 H), 7.03−7.16 (m, 4 H), 4.76 (s, 1 H), 2.51 (s, 3 H)
ppm; 13C NMR (75 MHz, DMSO-d6) δ 159.5, 157.7, 153.4, 152.0,
142.2, 135.2, 132.8, 130.0, 127.9, 126.7, 124.6, 122.4, 119.2, 116.5,
112.8, 104.6, 57.8, 32.4, 19.0 ppm; IR (neat) 3402, 2924, 2854, 2255,
2196, 2128, 1673, 1377, 1027, 1003, 764 cm−1; HRMS (ESI)
C20H14N2O3 [M + NH4]+ calcd 348.1343, found 348.1353.
(R)-2-Amino-4-(furan-2-yl)-5-oxo-4,5-dihydropyrano[3,2-c]-
chromene-3-carbonitrile (3k). White solid: mp 268−269 °C; 72%
yield; 99% ee determined by HPLC on a Chiralpak AD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
11.96 min, tminor = 9.62 min); [α]20 = +22 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.88−7.91 (d, J = 7.5 Hz, 1 H), 7.71−
7.76 (t, J = 7.5 Hz, 1 H), 7.47−7.54 (m, 5 H), 6.38−6.40 (t, J = 3.0 Hz,
1 H), 6.28−6.29 (d, J = 3.0 Hz, 1 H), 4.63 (s, 1 H) ppm; 13C NMR
(75 MHz, DMSO-d6) δ 159.3, 158.7, 154.1, 153.9, 152.1, 142.4, 133.1,
124.9, 124.7, 122.3, 116.6, 112.8, 110.6, 106.4, 101.5, 55.2, 30.5 ppm;
IR (neat) 3380, 3192, 2923, 2853, 2200, 1704, 1669, 1607, 1376, 1052,
759 cm−1; HRMS (ESI) C17H10N2O4 [M + Na]+ calcd 329.0533,
found 329.0542.
(R)-2-Amino-7-methyl-5-oxo-4-phenyl-4,5-dihydropyrano-
[4,3-b]pyran-3-carbonitrile (3q). White solid: mp 234−235 °C;
82% yield; 93% ee determined by HPLC on a Chiralpak AD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
17.70 min, tminor = 9.96 min); [α]20D= −17 (c = 1.0, acetone); H
NMR (300 MHz, DMSO-d6) δ 7.29−7.34 (t, J = 7.5 Hz, 2 H), 7.17−
7.25 (m, 4 H), 6.29 (s, 1 H), 4.28 (s, 1 H), 2.22 (s, 3 H) ppm; 13C
NMR (75 MHz, DMSO-d6) δ 162.9, 161.3, 158.1, 158.0, 143.5, 128.4,
127.4, 126.9, 119.3, 100.7, 97.9, 57.8, 36.2, 19.2 ppm; IR (neat) 3399,
3323, 3203, 2923, 2198, 1711, 1675, 1644, 1382, 1260, 1138 cm−1;
HRMS (ESI) C16H12N2O3 [M + H]+ calcd 281.0921, found 281.0914.
(S)-Methyl 2-Amino-5-oxo-4-phenyl-4,5-dihydropyrano[3,2-
c]chromene-3-carboxylate (3r). White solid: mp 164−165 °C; 85%
yield; 80% ee determined by HPLC on a Chiralpak AD-H column
1
(R)-2-Amino-5-oxo-4-(thiophen-3-yl)-4,5-dihydropyrano-
[3,2-c]chromene-3-carbonitrile (3l). White solid: mp 228−229 °C;
88% yield; 95% ee determined by HPLC on a Chiralpak AD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
11.13 min, tminor = 8.52 min); [α]20 = +31 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.88−7.90 (d, J = 7.8 Hz, 1 H), 7.68−
7.74 (t, J = 7.8 Hz, 1 H), 7.43−7.541 (m, 4 H), 7.35 (s, 1 H), 7.02−
7.04 (dd, J = 1.2 Hz, 7.8 Hz, 1 H), 4.60 (s, 1 H) ppm; 13C NMR (75
MHz, DMSO-d6) δ 160.1, 158.7, 153.7, 152.5, 144.3, 133.3, 127.5,
126.9, 125.1, 122.9, 122.6, 119.8, 117.0, 113.5, 104.4, 57.9, 32.4 ppm;
IR (neat) 3394, 2922, 2853, 2253, 2195, 1707, 1666, 1375, 1024, 999,
759 cm−1; HRMS (ESI) C17H10N2O3S [M + NH4]+ calcd 340.0750,
found 340.0759.
(hexane/2-propanol = 70/30, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
11.92 min, tminor = 8.97 min); [α]20 = +15 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.97−8.00 (d, J = 7.2 Hz, 1 H), 7.87
(s, 2 H), 7.67−7.72 (t, J = 7.5 Hz, 1 H), 7.43−7.51 (dd, J = 7.5 Hz,
15.9 Hz, 2 H), 7.24−7.26 (d, J = 3.9 Hz, 4 H), 7.14−7.18 (m, 1 H),
4.72 (s, 1 H), 3.56 (s, 3 H) ppm; 13C NMR (75 MHz, DMSO-d6) δ
167.8, 159.8, 158.6, 153.1, 152.0, 144.8, 132.6, 128.1, 127.7, 126.4,
124.6, 122.4, 116.5, 113.1, 106.9, 76.9, 50.7, 35.0 ppm; IR (neat) 3410,
3305, 2951, 2924, 1719, 1693, 1657, 1374, 1196, 1049, 761 cm−1;
HRMS (ESI) C20H15NO5 [M + H]+ calcd 350.1023, found 350.1022.
(S)-Ethyl 2-Amino-5-oxo-4-phenyl-4,5-dihydropyrano[3,2-
c]chromene-3-carboxylate (3s). White solid: mp 161−162 °C;
83% yield; 92% ee determined by HPLC on a Chiralpak AD-H column
(R)-2-Amino-5-oxo-4-hexyl-4,5-dihydropyrano[3,2-c]-
chromene-3-carbonitrile (3m). White solid: mp 171−172 °C; 69%
yield; 77% ee determined by HPLC on a Chiralpak AD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
11.39 min, tminor = 8.07 min); [α]20 = +11 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.80−7.83 (d, J = 8.1 Hz, 1 H), 7.68−
7.74 (t, J = 8.7 Hz, 1 H), 7.44−7.49 (t, J = 8.1 Hz, 2 H), 7.33 (s, 1 H),
3.42−3.45 (dd, J = 3.9 Hz, 5.4 Hz, 1 H), 1.65−1.99 (m, 1 H), 1.49−
1.60 (m, 1 H), 1.17−1.32 (m, 2 H), 0.84−0.89 (t, J = 6.9 Hz, 3 H)
ppm; 13C NMR (75 MHz, DMSO-d6) δ 160.4, 159.8, 154.5, 152.5,
133.2, 125.0, 122.6, 120.1, 117.0, 113.4, 104.8, 55.6, 36.6, 31.2, 25.6,
14.3 ppm; IR (neat) 3310, 3190, 2925, 2191, 1703, 1667, 1606, 1390,
1313, 1036, 755 cm−1; HRMS (ESI) C16H14N2O3 [M + H]+ calcd
283.1077, found 283.1083.
(hexane/2-propanol = 70/30, flow rate = 1.0 mL/min, 254 nm, tmajor
=
9.06 min, tminor = 7.68 min); [α]20D = +18 (c = 1.0, acetone); 1H NMR
(300 MHz, DMSO-d6) δ 7.98−8.00 (d, J = 7.2 Hz, 1 H), 7.87 (s, 2 H),
7.66−7.72 (t, J = 7.2 Hz, 1 H), 7.43−7.51 (dd, J = 7.5 Hz, 15.6 Hz, 2
H), 7.17−7.25 (m, 5 H), 4.71 (s, 1 H), 3.99−4.03 (dd, J = 6.6 Hz, 13.2
Hz, 2 H), 1.10−1.14 (t, J = 6.3 Hz, 1 H) ppm; 13C NMR (75 MHz,
DMSO-d6) δ 167.5, 159.8, 158.5, 153.1, 152.0, 144.9, 132.6, 127.9,
126.4, 124.5, 122.4, 116.5, 113.1, 106.8, 77.0, 59.0, 35.2, 14.1 ppm; IR
(neat) 3413, 3306, 2924, 2854, 1724, 1691, 1375, 1282, 1197, 1090,
762 cm−1; HRMS (ESI) C21H17NO5 [M + H]+ calcd 364.1179, found
364.1172.
(R)-2-Amino-9-chloro-5-oxo-4-phenyl-4,5-dihydropyrano-
[3,2-c]chromene-3-carbonitrile (3n). White solid: mp 188−189
°C; 86% yield; 98% ee determined by HPLC on a Chiralpak AD-H
column (hexane/2-propanol = 80/20, flow rate = 0.8 mL/min, 254
nm, tmajor = 18.13 min, tminor = 11.09 min); [α]20 = +29 (c = 1.0,
D
acetone); 1H NMR (300 MHz, DMSO-d6) δ 7.94 (s, 1 H), 7.74−7.77
(d, J = 9.0 Hz, 1 H), 7.50−7.53 (d, J = 9.0 Hz, 1 H), 7.42 (s, 1 H),
7.26−7.32 (m, 6 H), 4.45 (s, 1 H) ppm; 13C NMR (75 MHz, DMSO-
d6) δ 159.7, 158.3, 153.0, 151.3, 143.6, 133.1, 131.0, 130.1, 129.3,
128.2, 127.7, 122.4, 119.2, 115.1, 105.4, 58.4, 37.5 ppm; IR (neat)
3395, 3319, 3255, 3191, 2921, 2852, 2199, 1707, 1672, 1375, 1055
cm−1; HRMS (ESI) C19H11ClN2O3 [M + H]+ calcd 351.0531, found
351.0536.
General Procedure for Asymmetric Synthesis of 2-Amino-
4H-chromenes. Typical experimental procedure: To a stirred
solution of L6 (0.004 mmol, 2.0 mol %) and various carbonyl
compounds 4a−4f (0.30 mmol) in dry ether (1.0 mL), a solution of
α,β-unsaturated nitriles (0.2 mmol) in dry ether (1.0 mL) was added
over a period of 10 min. The solution was stirred at room temperature
for 4.0 h. After the reaction was completed (monitored by TLC), the
resulting mixture was concentrated under reduced pressure, and the
residue was purified through column chromatography on silica gel
(eluent, ethyl acetate/dichloromethane 1:25) to give the pure
products. After filtration, the solvent was removed at reduced pressure
to give the pure products.
(R)-2-Amino-9-methyl-5-oxo-4-phenyl-4,5-dihydropyrano-
[3,2-c]chromene-3-carbonitrile (3o). White solid: mp 229−230
°C; 82% yield; 96% ee determined by HPLC on a Chiralpak AD-H
column (hexane/2-propanol = 70/30, flow rate = 1.0 mL/min, 254
nm, tmajor = 9.76 min, tminor = 6.57 min); [α]20 = +58 (c = 1.0,
D
acetone); 1H NMR (300 MHz, DMSO-d6) δ 7.71 (s, 1 H), 7.50−7.52
(d, J = 8.4 Hz, 1 H), 7.42 (s, 1 H), 7.31−7.36 (m, 3 H), 7.25−7.27 (m,
(R)-2-Amino-5-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-chro-
mene-3-carbonitrile (5a). White solid: mp 211−212C; 94% yield;
884
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The Journal of Organic Chemistry
Article
96% ee determined by HPLC on a Chiralpak OD-H column (hexane/
20.3 ppm; IR (neat) 3330, 3212, 3187, 2928, 2193, 1682, 1654, 1367,
1260, 1170, 535 cm−1; HRMS (ESI) C17H16N2O3 [M + H]+ calcd
297.1234, found 297.1232.
2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor = 11.91
1
min, tminor = 10.40 min); [α]20 = +16 (c = 1.0, acetone); H NMR
D
(300 MHz, DMSO-d6) δ 7.25−7.30 (t, J = 7.5 Hz, 2 H), 7.14−7.17
(m, 3 H), 6.99 (s, 2 H), 4.19 (s, 1 H), 2.58−2.61 (m, 2 H), 2.20−2.31
(m, 2 H), 1.84−1.99 (m, 2 H) ppm; 13C NMR (75 MHz, DMSO-d6)
δ 196.3, 164.9, 158.9, 145.2, 128.8, 127.6, 127.0, 120.2, 114.2, 58.7,
36.8, 35.9, 26.9, 20.3 ppm; IR (neat) 3326, 3208, 2923, 2855, 2187,
1678, 1645, 1601, 1361, 994, 692 cm−1; HRMS (ESI) C16H14N2O2 [M
+ H]+ calcd 267.1128, found 267.1131.
(R)-2-Amino-4-(4-chlorophenyl)-5-oxo-5,6,7,8-tetrahydro-
4H-chromene-3-carbonitrile (5b). White solid: mp 239−240 °C;
90% yield; 95% ee determined by HPLC on a Chiralpak OD-H column
(R)-2-Amino-4-(3-chlorophenyl)-5-oxo-5,6,7,8-tetrahydro-
4H-chromene-3-carbonitrile (5g). White solid: mp 223−224 °C;
83% yield; 89% ee determined by HPLC on a Chiralpak OD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
12.38 min, tminor = 9.89 min); [α]20 = +14 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.24−7.35 (m, 2 H), 7.12−7.19 (m.2
H), 7.08 (s, 2 H), 4.22 (s, 1 H), 2.59−2.63 (m, 2 H), 2.28−2.32 (m, 2
H), 1.86−1.99 (m, 2 H) ppm; 13C NMR (75 MHz, DMSO-d6) δ
196.4, 165.3, 158.9, 147.7, 133.4, 130.7, 127.5, 127.1, 126.4, 113.6,
58.0, 36.7, 35.7, 26.9, 20.2 ppm; IR (neat) 3448, 3313, 3154, 2924,
2196, 1682, 1644, 1367, 1212, 1001, 693 cm−1; HRMS (ESI)
C16H13ClN2O2 [M + H]+ calcd 301.0738, found 301.0744.
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
11.00 min, tminor = 9.41 min); [α]20 = +10 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.26−7.54 (dd, J = 1.8 Hz, 6.6 Hz, 2
H), 7.17−7.20 (dd, J = 1.8 Hz, 6.6 Hz, 2 H), 7.05 (s, 1 H), 4.20 (s, 1
H), 2.59−2.63 (m, 2 H), 2.21−2.31 (m, 2 H), 1.85−1.99 (m, 2 H)
ppm; 13C NMR (75 MHz, DMSO-d6) δ 196.3, 165.1, 158.9, 144.2,
131.5, 129.5, 128.7, 120.0, 113.8, 58.1, 36.7, 35.4, 26.9, 20.2 ppm; IR
(neat) 3413, 3334, 3215, 2918, 2194, 1682, 1653, 1365, 1131, 1005,
507 cm−1; HRMS (ESI) C16H13ClN2O2 [M + H]+ calcd 301.0738,
found 301.0743.
(R)-2-Amino-4-(3-bromophenyl)-5-oxo-5,6,7,8-tetrahydro-
4H-chromene-3-carbonitrile (5h). White solid: mp 193−194 °C;
86% yield; 97% ee determined by HPLC on a Chiralpak O−H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
11.74 min, tminor = 8.84 min); [α]20D = +6 (c = 1.0, acetone); 1H NMR
(300 MHz, DMSO-d6) δ 7.38−7.40 (d, J = 7.8 Hz, 1 H), 7.33 (s, 1 H),
7.24−7.29 (t, J = 7.8 Hz, 1 H), 7.16−7.19 (d, J = 7,8 Hz, 1 H), 7.10 (s,
1 H), 4.21 (s, 1 H), 2.58−2.65 (m, 2 H), 2.26−2.32 (m, 2 H), 1.88−
1.99 (m, 2 H) ppm; 13C NMR (75 MHz, DMSO-d6) δ 196.4, 165.3,
158.9, 148.0, 131.1, 130.3, 130.0, 126.8, 122.0, 120.0, 113.6, 57.9, 36.7,
35.7, 26.9, 20.2 ppm; IR (neat) 3324, 3209, 2954, 2922, 2854, 2190,
1674, 1652, 1363, 1206, 1002 cm−1; HRMS (ESI) C16H13BrN2O2 [M
+ H]+ calcd 345.0233, found 345.0225.
(R)-2-Amino-4-(4-bromophenyl)-5-oxo-5,6,7,8-tetrahydro-
4H-chromene-3-carbonitrile (5c). White solid: mp 241−242 °C;
91% yield; 93% ee determined by HPLC on a Chiralpak OD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
11.81 min, tminor = 10.03 min); [α]20 = +18 (c = 1.0, acetone); H
NMR (300 MHz, DMSO-d6) δ 7.46−D7.49 (d, J = 8.4 Hz, 2 H), 7.12−
7.15 (d, J = 8.4 Hz, 2 H), 7.07 (s, 1 H), 4.20 (s, 1 H), 2.61−2.63 (m, 2
H), 2.24−2.31 (m, 2 H), 1.88−1.99 (m, 2 H) ppm; 13C NMR (75
MHz, DMSO-d6) δ 196.3, 165.1, 158.8, 144.7, 131.6, 130.0, 120.1,
113.7, 58.0, 36.7, 35.5, 26.9, 20.2 ppm; IR (neat) 3417, 3331, 3213,
2961, 2195, 1681, 1653, 1363, 1207, 1005, 504 cm−1; HRMS (ESI)
C16H13BrN2O2 [M + H]+ calcd 345.0233, found 345.0243.
1
(R)-2-Amino-4-(3-methoxyphenyl)-5-oxo-5,6,7,8-tetrahydro-
4H-chromene-3-carbonitrile (5i). White solid: mp 195−196 °C;
90% yield; 94% ee determined by HPLC on a Chiralpak OD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
17.15 min, tminor = 13.53 min); [α]20 = +18 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.18−7.28 (t, J = 7.8 Hz, 1 H), 6.99 (s,
1 H), 6.66−6.78 (m, 3 H), 4.16 (s, 1 H), 3.72 (s, 3 H), 2.58−2.64 (m,
2 H), 2.26−2.31 (m, 2 H), 1.87−1.99 (m, 2 H) ppm; 13C NMR (75
MHz, DMSO-d6) δ 195.8, 164.5, 159.2, 158.4, 146.3, 129.4, 119.7,
119.2, 113.6, 113.2, 111.3, 58.0, 54.9, 36.3, 35.2, 26.4, 19.8 ppm; IR
(neat) 3320, 3176, 2942, 2196, 1680, 1605, 1366, 1262, 1210, 1001,
537 cm−1; HRMS (ESI) C17H16N2O3 [M + H]+ calcd 297.1234, found
297.1230.
(R)-2-Amino-4-(4-fluorophenyl)-5-oxo-5,6,7,8-tetrahydro-
4H-chromene-3-carbonitrile (5d). White solid: mp 209−210 °C;
87% yield; 85% ee determined by HPLC on a Chiralpak OD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
11.34 min, tminor = 9.64 min); [α]20 = +13 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.18−7.22 (m, 2 H), 7.07−7.13 (m, 2
H), 7.04 (s, 2 H), 4.21 (s, 1 H), 2.61−2.63 (m, 2 H), 2.27−2.28 (m, 2
H), 1.90−1.99 (m, 2 H) ppm; 13C NMR (75 MHz, DMSO-d6) δ
196.4, 165.0, 163.0, 159.7, 158.9, 141.4, 129.5 (d, J = 8.3 Hz), 120.1,
115.4 (d, J = 21.0 Hz), 114.1, 58.5, 36.7, 35.2, 26.9, 20.2 ppm; IR
(neat) 3414, 3335, 3218, 2928, 2193, 1683, 1654, 1367, 1209, 1002,
533 cm−1; HRMS (ESI) C16H13FN2O2 [M + H]+ calcd 285.1034,
found 285.1043.
(R)-2-Amino-5-oxo-4-m-tolyl-5,6,7,8-tetrahydro-4H-chro-
mene-3-carbonitrile (5j). White solid: mp 211−212 °C; 85% yield;
89% ee determined by HPLC on a Chiralpak OD-H column (hexane/
2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor = 11.90
1
min, tminor = 9.33 min); [α]20 = +10 (c = 1.0, acetone); H NMR
D
(300 MHz, DMSO-d6) δ 7.13−7.19 (t, J = 7.5 Hz, 1 H), 7.00 (s, 1 H),
6.92−6.98 (m, 3 H), 4.14 (s, 1 H), 2.58−2.64 (m, 2 H), 2.21−2.31
(m, 5 H), 1.84−1.99 (m, 2 H) ppm; 13C NMR (75 MHz, DMSO-d6)
δ 196.3, 164.8, 158.8, 145.2, 137.8, 128.7, 128.1, 127.7, 124.7, 120.2,
114.3, 58.7, 36.8, 35.8, 26.9, 21.5, 20.3 ppm; IR (neat) 3319, 3259,
3165, 2924, 2195, 1681, 1648, 1366, 1208, 1001, 537 cm−1; HRMS
(ESI) C17H16N2O2 [M + H]+ calcd 281.1285, found 281.1290.
(R)-2-Amino-4-(2-bromophenyl)-5-oxo-5,6,7,8-tetrahydro-
4H-chromene-3-carbonitrile (5k). White solid: mp 208−209 °C;
87% yield; 99% ee determined by HPLC on a Chiralpak OD-H column
(R)-2-Amino-4-(4-cyanophenyl)-5-oxo-5,6,7,8-tetrahydro-
4H-chromene-3-carbonitrile (5e). White solid: mp 237−238 °C;
95% yield; 80% ee determined by HPLC on a Chiralpak OD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
18.57 min, tminor = 16.46 min); [α]20 = +19 (c = 1.0, acetone); H
NMR (300 MHz, DMSO-d6) δ 7.75−D7.78 (d, J = 8.4 Hz, 2 H), 7.36−
7.39 (d, J = 8.1 Hz, 2 H), 7.13 (s, 2 H), 4.30 (s, 1 H), 2.60−2.63 (m, 2
H), 2.27−2.31 (m, 2 H), 194−1.99 (m, 2 H) ppm; 13C NMR (75
MHz, DMSO-d6) δ 196.3, 165.6, 159.0, 150.7, 132.8, 128.8, 119.8,
119.3, 113.2, 109.9, 57.5, 36.7, 36.2, 26.9, 20.2 ppm; IR (neat) 3419,
3332, 3215, 2921, 2198, 1681, 1653, 1365, 1207, 1004, 555 cm−1;
HRMS (ESI) C17H13N3O2 [M + H]+ calcd 292.1081, found 292.1087.
(R)-2-Amino-4-(4-methoxyphenyl)-5-oxo-5,6,7,8-tetrahydro-
4H-chromene-3-carbonitrile (5f). White solid: mp 206−207 °C;
89% yield; 79% ee determined by HPLC on a Chiralpak OD-H column
1
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
21.92 min, tminor = 17.36 min); [α]20 = +12 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.51−7.54 (d, J = 7.8 Hz, 1 H), 7.28−7.32
(t, J = 7.2 Hz, 1 H), 7.08−7.17 (m, 2 H), 7.03 (s, 2 H), 4.72 (s, 1 H),
2.60−2.62 (m, 2 H), 2.22−2.29 (m, 2 H), 1.94−1.99 (m, 2 H) ppm; 13C
NMR (75 MHz, DMSO-d6) δ 196.2, 165.5, 158.9, 143.9, 133.0, 130.3,
128.8, 128.6, 123.2, 119.6, 113.6, 57.5, 36.8, 35.4, 26.9, 20.3 ppm; IR (neat)
3475, 3315, 3175, 2962, 2187, 1682, 1658, 1595, 1362, 1248, 756 cm−1;
HRMS (ESI) C16H13BrN2O2 [M + H]+ calcd 345.0233, found 345.0239.
(R)-2-Amino-4-(2-fluorophenyl)-5-oxo-5,6,7,8-tetrahydro-
4H-chromene-3-carbonitrile (5l). White solid: mp 217−218 °C;
91% yield; 97% ee determined by HPLC on a Chiralpak OD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
18.01 min, tminor = 12.78 min); [α]20 = +16 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.05−7.08 (dd, J = 1.8 Hz, 6.6 Hz, 2
H), 6.95 (s, 1 H), 6.82−6.85 (dd, J = 2.1 Hz, 6.9 Hz, 2 H), 4.13 (s, 1
H), 3.71 (s, 3 H), 2.60−2.62 (m, 2 H), 2.24−2.30 (m, 2 H), 1.86−1.99
(m, 2 H) ppm; 13C NMR (75 MHz, DMSO-d6) δ 196.3, 164.6, 158.8,
158.4, 137.4, 128.6, 120.3, 114.5, 114.1, 58.9, 55.5, 36.8, 35.0, 26.9,
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
13.59 min, tminor = 11.76 min); [α]20 = +30 (c = 1.0, acetone); H
D
885
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The Journal of Organic Chemistry
Article
NMR (300 MHz, DMSO-d6) δ 7.08−7.24 (m, 4 H), 7.03 (s, 2 H),
4.47 (s, 1 H), 2.60−2.63 (m, 2 H), 2.20−2.33 (m, 2 H), 1.86−
2.02 (m, 2 H) ppm; 13C NMR (75 MHz, DMSO-d6) δ 196.2, 165.5,
159.1 (d, J = 32.3 Hz), 158.7, 131.8 (d, J = 13.5 Hz), 129.9 (d, J = 3.8
Hz), 128.9 (d, J = 7.5 Hz), 124.9 (d, J = 3.8 Hz), 119.9, 115.8 (d, J =
21.8 Hz), 112.9, 57.2, 36.7, 29.9, 26.9, 20.3 ppm; IR (neat) 3324,
3257, 3173, 2928, 2190, 1685, 1646, 1370, 1211, 1167, 761 cm−1;
HRMS (ESI) C16H13FN2O2 [M + H]+ calcd 285.1034, found
285.1030.
ppm; IR (neat) 3425, 3332, 3192, 2930, 2192, 1670, 1633, 1598, 1409,
1557, 702 cm−1; HRMS (ESI) C16H14N2O2 [M + H]+ calcd 267.1128,
found 267.1134.
(S)-2-Amino-4-phenyl-4H-benzo[h]chromene-3-carbonitrile
(5t). White solid: mp 196−197 °C; 84% yield; 75% ee determined by
HPLC on a Chiralpak OD-H column (hexane/2-propanol = 90/10,
flow rate = 1.0 mL/min, 254 nm, tmajor = 27.39 min, tminor = 24.92
1
min); [α]20 = +46 (c = 0.5, acetone); H NMR (300 MHz, DMSO-
d6) δ 8.25−D8.28 (d, J = 7.8 Hz, 1 H), 7.88−7.91 (d, J = 7.5 Hz, 1 H),
7.59−7.65 (t, J = 9.0 Hz, 3 H), 7.11−7.32 (m, 8 H), 4.91 (s, 1 H)
ppm; 13C NMR (75 MHz, DMSO-d6) δ 160.6, 146.1, 143.2, 133.1,
129.2, 128.1, 127.4, 127.2, 127.1, 126.7, 124.4, 123.2, 121.2, 120.9,
118.4, 56.7, 41.3 ppm; IR (neat) 3385, 3323, 3210, 2920, 2195, 1663,
1616, 1399, 1368, 1097, 734 cm−1; HRMS (ESI) C20H14N2O [M +
H]+ calcd 299.1179, found 299.1171.
(R)-2-Amino-4-(2-methoxyphenyl)-5-oxo-5,6,7,8-tetrahydro-
4H-chromene-3-carbonitrile (5m). White solid: mp 191−192 °C;
93% yield; 80% ee determined by HPLC on a Chiralpak AD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
8.45 min, tminor = 14.17 min); [α]20 = +21 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.12−7.18 (m, 1 H), 6.94−6.99 (m, 2
H), 6.80−6.86 (m, 2 H), 4.54 (s, 1 H), 3.76 (s, 3 H), 2.61−2.63 (m, 2
H), 2.22−2.29 (m, 2 H), 1.88−1.99 (m, 2 H) ppm; 13C NMR (75
MHz, DMSO-d6) δ 196.2, 165.5, 159.3, 157.2, 133.0, 128.5, 128.2,
120.9, 120.2, 113.6, 112.1, 58.1, 56.1, 36.9, 30.0, 26.9, 20.4 ppm; IR
(neat) 3373, 3323, 3182, 2929, 2184, 1682, 1646, 1369, 1206, 1001,
753 cm−1; HRMS (ESI) C17H16N2O3 [M + Na]+ calcd 319.1053,
found 319.1046.
(S)-2-Amino-5-hydroxy-4-phenyl-4H-benzo[h]chromene-3-
carbonitrile (5u). White solid: mp 223−224 °C; 70% yield; 83% ee
determined by HPLC on a Chiralpak AD-H column (hexane/2-
propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor = 8.41 min,
1
tminor = 10.06 min); [α]20 = +18 (c = 1.0, acetone); H NMR (300
MHz, DMSO-d6) δ 8.10−D8.13 (d, J = 8.1 Hz, 1 H), 7.67−7.69 (d, J =
8.1 Hz, 1 H), 7.43−7.47 (t, J = 6.9 Hz, 1 H), 7.35−7.40 (t, J = 7.5 Hz,
1 H), 7.24−7.29 (t, J = 7.2 Hz, 2 H), 7.13−7.19 (m, 5 H), 6.91 (s, 1
H), 4.75 (s, 1 H) ppm; 13C NMR (75 MHz, DMSO-d6) δ 160.3,
152.2, 145.4, 144.6, 133.4, 128.3, 127.1, 126.9, 126.4, 125.7, 123.1,
120.7, 120.5, 117.6, 111.3, 104.6, 57.3, 37.1 ppm; IR (neat) 3391,
3176, 2927, 2187, 1660, 1615, 1410, 1284, 1026, 1003, 760 cm−1;
HRMS (ESI) C20H14N2O2 [M + H]+ calcd 315.1128, found 315.1122.
(S)-2-Amino-4-(4-chlorophenyl)-5-hydroxy-4H-benzo[h]-
chromene-3-carbonitrile (5v). White solid: mp 166−167 °C; 65%
yield; 80% ee determined by HPLC on a Chiralpak OD-H column
(R)-2-Amino-4-(furan-2-yl)-5-oxo-5,6,7,8-tetrahydro-4H-
chromene-3-carbonitrile (5o). White solid: mp 224−225 °C; 84%
yield; 75% ee determined by HPLC on a Chiralpak OD-H column
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
13.73 min, tminor = 12.13 min); [α]20 = +15 (c = 0.2, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 7.48−7.49 (t, J = 0.9 Hz, 1 H), 7.08 (s,
1 H), 6.31−6.33 (dd, J = 2.1 Hz, 3.3 Hz, 1 H), 6.05−6.06 (d, J = 3.3
Hz, 1 H), 4.33 (s, 1 H), 2.57−2.61 (m, 2 H), 2.27−2.35 (m, 2 H),
1.85−1.99 (m, 2 H) ppm; 13C NMR (75 MHz, DMSO-d6) δ 195.6,
165.1, 159.2, 155.7, 141.7, 119.5, 111.4, 110.4, 105.1, 55.2, 36.1, 28.9,
26.4, 19.7 ppm; IR (neat) 3398, 3325, 3212, 2925, 2187, 1680, 1603,
1360, 1210, 1012, 536 cm−1; HRMS (ESI) C14H12N2O3 [M + H]+
calcd 257.0921, found 257.0926.
(hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor
=
1
20.24 min, tminor = 16.54 min); [α]20 = +21 (c = 1.0, acetone); H
D
NMR (300 MHz, DMSO-d6) δ 10.18 (br, 1 H), 8.09−8.11 (d, J = 8.4
Hz, 1 H), 7.65−7.68 (d, J = 8.1 Hz, 1 H), 7.41−7.46 (t, J = 7.2 Hz, 1
H), 7.33−7.38 (t, J = 7.5 Hz, 1 H), 7.30−7.33 (d, J = 8.4 Hz, 2 H),
7.13−7.16 (d, J = 8.7 Hz, 2 H), 7.04 (s, 2 H), 6.89 (s, 1 H), 4.76 (s, 1
H) ppm; 13C NMR (75 MHz, DMSO-d6) δ 160.2, 152.2, 144.5, 133.5,
130.9, 129.0, 128.3, 126.9, 125.7, 123.1, 120.7, 120.4, 117.5, 110.7,
104.7, 56.8, 36.6 ppm; IR (neat) 3449, 3335, 3199, 2924, 2854, 2191,
1659, 1380, 1284, 1087, 835 cm−1; HRMS (ESI) C20H13ClN2O2 [M +
H]+ calcd 349.0738, found 349.0734.
(R)-2-Amino-4-hexyl-5-oxo-5,6,7,8-tetrahydro-4H-chro-
mene-3-carbonitrile (5p). White solid: mp 165−166 °C; 71% yield;
73% ee determined by HPLC on a Chiralpak OD-H column (hexane/
2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor = 13.21
1
min, tminor = 11.72 min); [α]20 = +11 (c = 1.0, acetone); H NMR
D
(300 MHz, DMSO-d6) δ 6.88 (s, 1 H), 3.14−3.17 (t, J = 4.2 Hz, 1 H),
2.30−2.47 (m, 2 H), 1.89−1.99 (m, 2 H), 1.74−1.87 (m, 2 H), 1.57−
1.45 (m, 2 H), 1.21−1.33 (m, 2 H), 1.14−1.19 (t, J = 7.8 Hz, 3 H)
ppm; 13C NMR (75 MHz, DMSO-d6) δ 196.9, 165.4, 160.2, 120.7,
114.4, 55.9, 37.8, 36.8, 29.5, 26.8, 20.4, 18.0, 14.4 ppm; IR (neat)
3394, 3319, 3195, 2922, 2853, 2194, 1700, 1666, 1455, 1375, 1055
cm−1; HRMS (ESI) C13H16N2O2 [M + H]+ calcd 233.1285, found
233.1291.
(R)-2-Amino-7,7-dimethyl-5-oxo-4-phenyl-5,6,7,8-tetrahy-
dro-4H-chromene-3-carbonitrile (5q). White solid: mp 208−
209 °C; 83% yield; 68% ee determined by HPLC on a Chiralpak OD-H
column (hexane/2-propanol = 80/20, flow rate = 1.0 mL/min, 254
nm, tmajor = 17.38 min, tminor = 15.41 min); [α]20 = +13 (c = 1.0,
acetone); 1H NMR (300 MHz, DMSO-d6) δ 7.26−D7.31 (t, J = 4.2 Hz,
2 H), 7.13−7.20 (m, 3 H), 7.00 (s 2 H), 4.17 (s, 1 H), 2.51 (s, 2 H),
2.07−2.28 (dd, J = 15.9 Hz, 46.8 Hz, 2 H), 1.04 (s, 3 H), 0.95 (s, 3 H)
ppm; 13C NMR (75 MHz, DMSO-d6) δ 196.1, 162.9, 158.9, 145.2,
128.8, 127.6, 127.0, 120.1, 113.2, 58.8, 55.3, 50.4, 36.0, 32.3, 28.8, 27.2
ppm; IR (neat) 3396, 3325, 3212, 2962, 2199, 1681, 1660, 1602, 1370,
1214, 698 cm−1; HRMS (ESI) C18H18N2O2 [M + H]+ calcd 295.1441,
found 295.1443.
General Procedure for Antibacterial Activity of Pyranocou-
marins and 2-Amino-4H-chromenes. Some of the synthesized
compounds 3a−s and 5a−v were tested for their antibacterial activities
at concentrations of 200.0, 100.0, 50.0, 25.0, 12.5, 6.25, and 3.125 μg/
mL using standard broth microdilution methods. Briefly, a single
colony of Gram negative or Gram positive bacteria was inoculated
into culture medium (Luria−Bertani broth) and cultured overnight at
37 °C. An aliquot of this culture was transferred to 10 mL fresh culture
medium and incubated for an additional 3−5 h at 37 °C to obtain
midexponential phase organisms. Then, the bacteria were inoculated
into 96-well microtiter plates (OD600 = 0.1). A 2-fold dilution series of
compounds were added into each well, and then the plates were
incubated at 37 °C for 16 h. Kanamycin sulfate, vancomycin, and PBS
buffer were used as the positive and negative control, respectively. The
Staphylococcus aureus (CMCC 26003) and Escherichia coli (CMCC
44102) were obtained from Gansu Food and Drug Administration.
The antibacterial activity is expressed as minimal inhibitory
concentration (MIC), and the MIC is defined as the minimal
concentration that inhibits the microbial growth. The reported
minimal inhibitory concentrations are the mean of triplicate
measurements from three independent assays. The result of the
antibacterial activities of pyranocoumarins and 2-amino-4H-chromenes
is shown in Table 5.
(R)-2-Amino-8-oxo-4-phenyl-5,6,7,8-tetrahydro-4H-chro-
mene-3-carbonitrile (5s). White solid: mp 91−92 °C; 67% yield;
77% ee determined by HPLC on a Chiralpak AD-H column (hexane/
2-propanol = 80/20, flow rate = 1.0 mL/min, 254 nm, tmajor = 12.56
1
min, tminor = 20.63 min); [α]20D= −10 (c = 1.0, acetone); H NMR
General Procedure for Acute Cytotoxicity Testing of the
Compounds. The acute cytotoxicity of these compounds was
examined according to Ryan and co-workers with a little modification.
Blood specimens were freshly collected from mice and different adult
donors in heparinized tubes and centrifuged at 1000g for 3 min. The
(300 MHz, DMSO-d6) δ 7.35−7.40 (t, J = 7.5 Hz, 2 H), 7.22−7.25
(m, 3 H), 6.90 (s, 1 H), 4.19 (s, 1 H), 2.25−2.42 (m, 2 H), 2.71−2.99
(m, 4 H) ppm; 13C NMR (75 MHz, DMSO-d6) δ 190.5, 160.0, 143.2,
140.1, 134.9, 129.3, 128.3, 127.9, 120.5, 55.5, 43.4, 37.9, 27.4, 21.8
886
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Article
pellet was washed three times with cold PBS buffer gently and
resuspended in the same buffer to a final erythrocyte concentration of
2%. The RBC suspension (100 μL) was added to a 96-well microtiter
plate. The compound solutions of different concentrations were added
to the erythrocytes and incubated for 60 min at 37 °C. 0.2% Triton-X
100 and PBS were used as the positive and the negative control,
respectively. The release of hemoglobin of the supernatant was
measured after centrifugation (1200g for 15 min) by a microplate
reader (Bio-Rad 680) at 490 nm. The acute cytotoxicity of these
compounds was calculated as the following formulation:
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T − T
A
acute cytotoxicity % =
× 100%
T − T
B
A
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̈
where TA represents the negative control and TB represents the
positive control
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General Procedure for Chronic Cytotoxicity Testing of the
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trazolium bromide) assay with a little modification. Briefly, Human
Jurkat and Hela cells were seeded in a 96-well plate at 8 × 103 cells/
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concentrations of compounds for 24 h at 37 °C in a humidified
atmosphere at 5% CO2. Cells treated with phosphate buffered saline
(PBS) buffer alone were the control. After that, 10 μL of 5 mg/mL
MTT reagent solution was added into each well, and the 96-well plate
was incubated for 4 h at 37 °C. Then, the supernatant was discarded,
and the MTT formazan precipitate was dissolved in 150 μL of DMSO
with gently shaking. The absorbance was determined by a microplate
reader (Bio-Rad 680) at 570 nm. IC50 values for each cell line were
evaluated, representing the concentration at which human cell viability
was reduced to 50% compared with PBS-treated cells.
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Chem. Soc. 2007, 129, 6686. (h) Zu, L. S.; Wang, J.; Li, H.; Xie, H. X.;
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ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental details, compound characterization, and X-ray
crystallographic data (CIF) for 3f. This material is available free
of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: wangrui@lzu.edu.cn.
■
ACKNOWLEDGMENTS
■
We are grateful for the grants from the National Natural
Science Foundation of China (No. 90813012 and 20932003)
and the Key National S & T Program “Major New Drug
Development” of the Ministry of Science and Technology
(2012ZX09504001-003).
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