Synthesis of the β3-adrenergic receptor agonist Solabegron and Analogous N-(2-Ethylamino)-β-amino alcohols from O-acylated cyanohydrins - expanding the scope of minor enantiomer recycling

Article abstract of DOI:10.1021/acs.joc.5b00322

A novel methodology to produce highly enantioenriched N-(2-ethylamino)-β-amino alcohols was developed. These compounds were obtained from O-(α-bromoacyl) cyanohydrins, which were synthesized by the minor enantiomer methodology employing a Lewis acid and a

Full text of DOI:10.1021/acs.joc.5b00322

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Note
Synthesis of the beta3-Adrenergic Receptor Agonist Solabegron and
Analogous N-(2-Ethylamino)-beta-amino Alcohols from O-Acylated
Cyanohydrins – Expanding the Scope of Minor Enantiomer Recycling
Robin Hertzberg, Guillermo Monreal Santiago, and Christina Moberg
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.5b00322 • Publication Date (Web): 17 Feb 2015
Downloaded from http://pubs.acs.org on February 18, 2015
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Synthesis of the β
3
-Adrenergic Receptor Agonist Solabegron and Analogous N-(2-
Ethylamino)-β-amino Alcohols from O-Acylated Cyanohydrins – Expanding the Scope of
Minor Enantiomer Recycling
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Robin Hertzberg, Guillermo Monreal Santiago and Christina Moberg*
KTH Royal Institute of Technology, Department of Chemistry, Organic Chemistry, SE-10044
Stockholm, Sweden
kimo@kth.se
Abstract Graphic:
Abstract: A novel methodology to produce highly enantioenriched N-(2-ethylamino)-β-amino
alcohols was developed. These compounds were obtained from O-(α-bromoacyl) cyanohydrins,
which were synthesized by the minor enantiomer methodology employing a Lewis acid and a
biocatalyst, followed by nucleophilic substitution with amines and reduction. The importance of
the developed methodology was demonstrated by completing a highly enantioselective total
synthesis of the β
3
-adrenergic receptor agonist Solabegron.
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The N-(2-Ethylamino)-β-amino alcohol fragment (Figure 1) is an important structural element
1
present in several biologically active compounds. Examples comprise the α -adrenoreceptor
1
2,3
agonist Midodrine (1) and the β
3
-adrenergic receptor agonist Solabegron (2), as well as
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analogues of the latter compound. Solabegron (2) is currently in clinical trials for both
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,7
overactive bladder (OAB) and irritable bowel syndrome (IBS) with promising results.
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Figure 1. The N-(2-ethylamino)-β-amino alcohol fragment.
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2,8
Solabegron (2) has in previous syntheses been obtained starting from (R)-3-chlorostyrene oxide
3
,9,10
or (R)-3-chloromandelic acid,
which are both commercially available in enantiopure form.
We envisioned an alternative strategy to obtain these types of structures starting from O-(α-
bromoacyl) cyanohydrins. Substitution of the bromide with nitrogen nucleophiles followed by
1
1
reduction of the nitrile group to the amine, accompanied by intramolecular acyl transfer, would
result in a range of highly interesting N-acylated β-amino alcohols (Scheme 1). A special
advantage is that this reaction sequence has a high atom economy since the acyl group becomes a
vital part of the desired target molecule.
Scheme 1. Retrosynthetic Plan for Formation of N-(2-Ethylamino)-β-amino Alcohols
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We have earlier developed a highly efficient and selective Lewis acid/Lewis base catalyzed
method for the preparation of enantioenriched O-acylated cyanohydrins from a variety of acyl
1
2,13
cyanides and aldehydes.
The O-(α-bromoacyl) cyanohydrins are, however, not readily
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available by direct acylcyanation using our dual activation methodology since the highly reactive
α-bromoacyl cyanides are incompatible with the Lewis base present in the reaction, resulting in
low yields of the product. However, the desired compounds can be synthesized using a
combination of chiral metal Lewis acid catalysis and biocatalysis (Scheme 2), conditions which
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4,15
do not require the presence of a Lewis base.
The role of the biocatalyst is to selectively
hydrolyze the minor, undesired, enantiomer obtained in the product-forming step to the free
cyanohydrin, which is in equilibrium with the starting aldehyde. The required coupled exergonic
process to generate chemical energy is provided by the irreversible release of carboxylate ions
14,16
into the aqueous phase during the hydrolysis of the minor product enantiomer.
Scheme 2. Minor Enantiomer Recycling
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O-(α-Bromoacyl) cyanohydrin (R)-4, derived from benzaldehyde, was used as a model substrate
for our initial studies. This compound has previously been obtained with high enantiomeric purity
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using the minor enantiomer recycling methodology with (S,S)-titanium salen dimer 3 as Lewis
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acid and Candida antarctica lipase B (CALB) as biocatalyst.
To our disappointment, substitution of (R)-4 with aniline in the presence of DIPEA as a base
resulted in depletion of the product ee. Fortunately, replacement of the base with an excess of the
nucleophile afforded product (R)-5a in high yield without any racemization. The reaction was
successful with anilines substituted with both electron-donating and electron-withdrawing groups
(Scheme 3), but was, as expected, more efficient and required fewer equivalents of the
nucleophile when the electron-rich nucleophile 3,5-dimethylaniline was used. Acetonitrile was
superior as solvent to THF and DCM, which both resulted in no or little product formation.
Scheme 3. Substitution of (R)-4 with Different Anilines
Primary aliphatic amines, such as propylamine, did not lead to the desired product. Instead the
amine attacked the harder carbonyl carbon with formation of the free cyanohydrin, which
decomposed to aldehyde and HCN. The aldehyde then reacted with another equivivalent of
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propylamine to form the imine, which was attacked by cyanide to give compound 6 (Scheme 4).
Some secondary amines were also tested in the reaction but resulted in products with reduced
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ee.
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Scheme 4. Reaction of 4 with Propylamine
The subsequent reduction was achieved by catalytic hydrogenation using Raney nickel as catalyst
and with 20 bar of H in 1,4-dioxane at 80 °C. Whereas reduction of enantioenriched O-
2
acetylated (S)-mandelonitrile at 120 °C has been shown to result in partial racemization (from
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5% to 75% ee) , our modified conditions gave the desired products (R)-7a-b with practically no
racemization, albeit in low yields (Scheme 5). Reduction of (R)-5c gave a product which we were
not able to obtain in pure form.
Scheme 5. Catalytic Hydrogenation of (R)-5
A more divergent approach to the desired products would be the direct reduction of the bromine-
containing substrate 4 and nucleophilic substitution of the resulting product with the amine.
However, attempts to perform the catalytic hydrogenation of 4 only led to reduction of the
bromide to yield O-acetylated mandelonitrile.
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To demonstrate the usefulness of the developed methodology, a total synthesis of Solabegron (2)
was performed. The synthesis started with the minor enantiomer recycling with 3-
chlorobenzaldehyde and acyl cyanide 8, prepared from CuCN and bromoacetyl bromide (Scheme
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). In the minor enantiomer recycling step a decrease of ee during the addition of acyl cyanide 8
was observed. This annoyance was previously observed with a similar acyl cyanide and was
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attributed to inhibition of the enzyme Candida antarctica lipase B (CALB) by the acyl cyanide.
A comparison of kinetic resolutions with the present substrate, rac-9, with or without acyl
cyanide 8 present showed a significant difference in the performance of the enzyme (see
Supporting Information). In order to counteract the effect of the inhibition larger amounts of the
enzyme were used, which indeed gave a higher final ee of the product. A reaction in preparative
scale gave the product with a final ee of 86%. The addition of an additional portion of CALB to
the reaction mixture, thereby allowing the enzyme to hydrolyze the remaining minor enantiomer,
gave after purification the product (R)-9 in 69% yield and with 98% ee.
Scheme 6. Minor Enantiomer Recycling to Obtain (R)-9
The next step in the synthesis was the reaction of (R)-9 with the aniline derivative 13. This
aniline was efficiently synthesized according to a slightly modified literature procedure
consisting of a one-pot two-step reaction using Pd/C as a catalyst for both the Suzuki coupling
21
between 10 and 11 and hydrogenation of the nitro group (Scheme 7). The substitution gave
product (R)-14 in high yield and practically without any racemization. The drawback with this
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reaction is the need to use three equivalents of the aniline derivative 13; however most of the
remaining compound was possible to recover from the chromatographic purification. In the
catalytic hydrogenation to obtain amino alcohol (R)-15, using conditions identical to those used
for the other substrates, only a slight decrease in enantiomeric excess was observed (97% to
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9
4%). In order to reduce the amide to an amine without reducing the ester functionality we used a
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modified literature procedure employing borane dimethylsulfide complex; this transformation
gave the known compound (R)-16 with an enantiomeric excess of 95%. Final hydrolysis of the
ester function to the carboxylic acid was accomplished following a literature procedure using
3
LiOH. The absolute configuration of 2 was confirmed to be R by comparing the sign of the
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optical rotation with that previously reported.
Scheme 7. Synthesis of Solabegron
In conclusion, we have developed an efficient synthetic procedure for the synthesis of highly
enantioenriched N-(2-ethylamino)-β-amino alcohols. The synthetic importance of the procedure
3
was demonstrated by the synthesis of the β -adrenergic receptor agonist Solabegron.
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Experimental section
General
Dry solvents were taken from a Glass Contour solvent dispensing system, except for 1,4-dioxane
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t
which was distilled over LiAlH
4
prior to use. (S,S)-[(4,6-Bis( butyl)salen)Ti(µ-O)]
2
(3) was
17
-1
prepared according to a published procedure. Immobilized (acrylic resin, >5000 U g ) Candida
antarctica lipase B (CALB, expressed in Aspergillus niger) was purchased from Sigma Aldrich.
3-Chlorobenzaldehyde was distilled prior to use. CuCN is highly toxic and should be handled
1
13
with great care. H and C NMR spectra were recorded at 500 or 400 MHz and 125 or 100 MHz,
1
13
respectively. The H and C chemical shifts are reported in parts per million relative to residual
CHCl or CD HOD in CDCl and CD OD, respectively. GC analyses were conducted with a FID
3
2
3
3
detector and a chiral column: CYCLOSIL B (30 m × 0.25 mm × 0.25 µm). HPLC analyses were
conducted with a UV detector and a chiral column: Daicel Chiralpak IC (0.46 cm × 25 cm),
Daicel Chiralpak IA (0.46 cm × 25 cm) or Daicel Chiralcel OD-H (0.46 cm × 25 cm).
(R)-Cyano(phenyl)methyl phenylglycinate ((R)-5a). (R)-4 (92.7 mg, 0.361 mmol) was
dissolved in acetonitrile (1.4 mL) and put under N -atmosphere. Aniline (99.0 µL, 1.09 mmol)
2
was added and the solution was stirred at room temperature. After 17 h of stirring, additional
aniline (33.0 µL, 0.362 mmol) was added. The solution was stirred another 24 h after which the
solvent was evaporated, the residue was dissolved in EtOAc and washed three times with aq.
HCL (0.1 M). The organic phase was dried over MgSO
4
and the solvent evaporated. The residue
= 0.48) to give (R)-5a
87.9 mg, 0.330 mmol, 90%, >99% ee) as pale yellow crystals. Mp = 105–111 °C. IR: 3389,
was purified by flash chromatography (petroleum ether/EtOAc 4:1, R
f
(
-
1
1
757, 1604, 1184 cm . HPLC (Daicel Chiralpak IC, hexanes/2-propanol 95:5, 0.7 mL/min,
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detection at 254 nm): t
R
(major) 40.6 min, t
R D 2 2
(minor) 56.8 min. [α] -4.7 (c 0.77, CH Cl ). H
NMR (400 MHz, CDCl
3
): δ 7.42–7.51 (m, 5H), 7.20 (t, J = 7.9 Hz, 2H), 6.81 (t, J = 7.7 Hz, 1H),
6.64 (d, J = 7.8 Hz, 2H), 6.49 (s, 1H), 4.08 (A part of AB, J = 18.2 Hz, 1H), 4.03 (B part of AB, J
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13
=
18.2 Hz, 1H). C NMR (100 MHz, CDCl
3
): δ 169.6, 146.1, 131.4, 130.8, 129.6, 129.5, 128.1,
+
1
19.5, 115.8, 113.7, 63.7, 46.1. HRMS (ESI-Orbitrap) m/z: [M + H] calcd for
16 15 2 2
C H N O 267.1128, found 267.1124.
(
R)-Cyano(phenyl)methyl (3,5-dimethylphenyl)glycinate ((R)-5b). (R)-4 (90.9 mg, 0.358
mmol) was dissolved in acetonitrile (1.4 mL) and put under N -atmosphere. 3,5-Dimethylaniline
133 µL, 1.06 mmol) was added and the solution was stirred at room temperature. After 17 h the
solvent was evaporated, the residue dissolved in EtOAc and washed three times with aq. HCl (0.1
M). The organic phase was dried over MgSO and the solvent evaporated. The residue was
purified by flash chromatography (petroleum ether/EtOAc 4:1, R = 0.62) to give (R)-5b (96.5
mg, 0.328 mmol, 92%, >99% ee) as a pale brown oil. IR: 3408, 2917, 1761, 1604, 1161 cm .
2
(
4
f
-
1
HPLC (Daicel Chiralpak IC, hexanes/2-propanol 93:7, 1.0 mL/min, detection at 220 nm): t
R
25
1
(
major) 22.7 min, t
R
(minor) 31.2 min. [α]
D
-5.1 (c 1.9, CH
2
Cl
2
). H NMR (400 MHz, CDCl
3
): δ
7
.41–7.52 (m, 5H), 6.49 (s, 1H), 6.47 (s, 1H), 6.27 (s, 2H), 4.06 (A part of AB, J = 18.1 Hz, 1H),
1
3
4.01 (B part of AB, J = 18.2 Hz, 1H), 2.22 (s, 6H). C NMR (100 MHz, CDCl
3
): δ 169.6, 146.0,
1
39.3, 131.4, 130.7, 129.5, 128.1, 121.7, 115.8, 111.9, 63.6, 46.3, 21.6. HRMS (ESI-Orbitrap)
+
19 2 2
m/z: [M + H] calcd for C18H N O 295.1441, found 295.1434.
(R)-Cyano(phenyl)methyl (4-iodophenyl)glycinate ((R)-5c). (R)-4 (87.1 mg, 0.343 mmol) and
-iodoaniline (297 mg, 1.36 mmol) were dissolved in acetonitrile (1.4 mL) and put under N . The
4
2
mixture was stirred at room temperature for four days after which the precipitate formed was
filtered off on a pad of cotton. The solvent was evaporated, the residue was dissolved in EtOAc
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and the solution was washed three times with aq. HCl (0.1 M). The organic phase was dried over
MgSO
4
and the solvent was evaporated. The residue was purified by flash chromatography
(petroleum ether/EtOAc 4:1, R
f
= 0.63) to give (R)-5c (101 mg, 0.258 mmol, 75%, >99% ee) as
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white crystals. Mp = 98–106 °C Decomp. IR: 3390, 1760, 1590, 1178 cm . HPLC (Daicel
Chiralpak IC, hexanes/2-propanol 95:5, 0.7 mL/min, detection at 254 nm): t
R
(major) 40.8 min, t
): δ 7.42–7.51 (m, 7H),
.48 (s, 1H), 6.38 (d, J = 8.8 Hz, 2H), 4.03 (A part of AB, J = 18.2 Hz, 1H), 3.98 (B part of AB, J
R
2
5
1
(
D 2 2 3
minor) 54.3 min. [α] +4.9 (c 0.8, CH Cl ). H NMR (400 MHz, CDCl
6
1
3
= 18.2 Hz, 1H). C NMR (125 MHz, CDCl
3
): δ 169.4, 146.1, 138.2, 131.3, 130.9, 129.5, 128.1,
+
1
15.7, 115.5, 80.2, 63.8, 45.6. HRMS (ESI-Orbitrap) m/z: [M + H] calcd for
16 2 2
C H14IN O 393.0094, found 393.0084.
General procedure for hydrogenation reactions. Raney-Nickel (4200, slurry in water) was
activated prior to use by treatment with aq. NaOH (0.1 M), washing with water until neutral pH
and finally washing twice with MeOH.
The substrate dissolved in 1,4-dioxane was added to the activated catalyst in an autoclave. The
2
autoclave was sealed and flushed once with H before increasing the pressure to 20 bars. The
mixture was stirred at 80 °C for 3 h, allowed to reach room temperature, filtered through celite
using EtOAc as eluent and the solvents were evaporated. The residue was purified by flash
chromatography.
(
R)-N-(2-Hydroxy-2-phenylethyl)-2-(phenylamino)acetamide ((R)-7a). The general procedure
was followed using (R)-5a (65.1 mg, 0.245 mmol), Raney-Nickel (108 mg) and 1,4-dioxane (1.8
mL). Flash chromatography (petroleum ether/EtOAc 1:4 to 1:9, R = 0.41 (using 1:4 eluent) gave
R)-7a (20.1 mg, 0.0744 mmol, 30%, 99% ee) as a pale yellow solid. Mp = 96–102 °C. IR: 3283,
f
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668, 1603 cm . HPLC (Daicel Chiralcel OD-H, hexanes/2-propanol 90:10, 0.7 mL/min,
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
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5
5
5
5
5
5
5
5
5
6
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5
1
detection at 220 nm): t
R
(major) 64.6 min, t
): δ 7.25–7.32 (m, 5H), 7.21 (dd, J = 7.6, 7.9 Hz, 2H), 7.13 (bs, 1H), 6.84
t, J = 7.3 Hz, 1H), 6.60 (d, J = 8.3 Hz, 2H), 4.82 (dd, J = 3.3, 7.7 Hz, 1H), 3.81 (s, 2H), 3.68
R D
(minor) 84.1 min. [α] -5.3 (c 1.1, MeOH). H
NMR (500 MHz, CDCl
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
(
1
3
ddd, J = 3.4, 6.7, 14.0 Hz, 1H), 3.40 (ddd, J = 5.9, 7.7, 13.8 Hz, 1H). C NMR (125 MHz,
CDCl
3
): δ 172.1, 146.9, 141.7, 129.7, 128.7, 128.0, 125.9, 119.6, 113.6, 73.8, 49.0, 47.4. HRMS
+
(ESI-Orbitrap) m/z: [M + H] calcd for C16
H
19
N
2
O
2
271.1441, found 271.1436.
(
R)-2-((3,5-Dimethylphenyl)amino)-N-(2-hydroxy-2-phenylethyl)acetamide ((R)-7b). The
general procedure was followed using (R)-5b (76.1 mg, 0.259 mmol), Raney-Nickel (114 mg)
and 1,4-dioxane (1.9 mL). Flash chromatography (petroleum ether/EtOAc 1:9, R = 0.47) gave
(R)-7a (25.4 mg, 0.0851 mmol, 33%, >99% ee) as a pale brown gum. IR: 3371, 2918, 1657, 1604
f
-
1
cm . HPLC (Daicel Chiralpak IA, hexanes/2-propanol 95:5, 0.5 mL/min, detection at 220 nm): t
R
2
5
1
(major) 64.3 min, t
R
(minor) 75.3 min. [α]
D
-37 (c 1.2, CH
2
Cl
2
). H NMR (500 MHz, CDCl
3
): δ
7.28–7.33 (m, 4H), 7.24–7.28 (m, 1H), 7.16 (bs, 1H), 6.49 (s, 1H), 6.24 (s, 2H), 4.81 (dd, J = 3.3,
7
1
.8 Hz, 1H), 3.78 (s, 2H), 3.66 (ddd, J = 3.4, 6.7, 14.0 Hz, 1H), 3.40 (ddd, J = 5.8, 7.8, 13.8 Hz,
1
3
H), 2.25 (s, 6H). C NMR (125 MHz, CDCl
3
): δ 172.4, 147.1, 141.7, 139.5, 128.6, 128.0,
+
125.9, 121.5, 111.4, 73.8, 49.0, 47.4, 21.6. HRMS (ESI-Orbitrap) m/z: [M + H] calcd for
18 23 2 2
C H N O 299.1754, found 299.1749.
2
4
2
-Bromoacetyl cyanide (8). Bromoacetyl bromide (5.4 mL, 62.0 mmol) was added to CuCN
(6.7 g, 74.8 mmol) at room temperature under N . The mixture was stirred for 30 min at room
2
temperature after which it was heated to 65 °C for 16 h, then 75 °C for 6 h. The pure product was
collected in a cold trap (-78 °C) by heating the mixture at 50 °C under vacuum (~5 mBar). This
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1
gave 8 (2.21 g, 15.0 mmol, 24%) as a colorless liquid. H NMR (500 MHz, CDCl
3
): δ 4.10 (s,
2
H).
(R)-(3-Chlorophenyl)(cyano)methyl 2-bromoacetate ((R)-9). 3-Chlorobenzaldehyde (140 µL,
.24 mmol) and (S,S)-[(salen)Ti(µ-O)] (3) (75.5 mg, 0.0620 mmol) were dissolved in toluene (5
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
mL), CALB (300 mg) and phosphate buffer (2M, 5 mL) were added to the solution. The mixture
was stirred at room temperature while 8 (550 mg, 3.72 mmol) in cyclopentyl methyl ether (1.80
mL total volume) was added to the organic phase during 48 h using a syringe pump. When the
addition was finished, CALB (100 mg) was added to the mixture which was allowed to stir for 2
h 20 min. The phases were separated and the aqueous phase was extracted with diethyl ether, the
combined organic phases were dried over MgSO
4
and the solvents were evaporated. The residue
= 0.44) to give (R)-9 (246
was purified by flash chromatography (petroleum ether/EtOAc 9:1, R
f
-
1
mg, 0.852 mmol, 69%, 98% ee) as a yellow oil. IR: 1760, 1250, 1129 cm . GC-FID (CYCLOSIL
B, flow rate = 2.0 ml/min, 60 °C for 10 min, 20 °C/min to 100 °C, hold 5 min, 5 °C/min to 180
2
4
1
°C, hold 30 min): t
R R D 2 2
(major) 54.1 min, t (minor) 57.0 min. [α] +1.7 (c 1.7, CH Cl ). H NMR
13
(
400 MHz, CDCl ): δ 7.54 (s, 1H), 7.39–7.49 (m, 3H), 6.42 (s, 1H), 3.92 (s, 2H). C NMR (100
3
MHz, CDCl
3
): δ 165.5, 135.6, 132.8, 131.2, 130.9, 128.2, 126.2, 115.0, 63.7, 24.3. HRMS (ESI-
+
Orbitrap) m/z: [M + H] calcd for C10
H
8
BrClNO
2
287.9421, found 287.9410.
9
25
Methyl 3'-amino-[1,1'-biphenyl]-3-carboxylate (13). 11 (2.87 g, 13.4 mmol) and 3-
nitrophenylboronic acid (10) (2.29 g, 13.7 mmol) were dissolved in MeOH (17 mL) and Na CO
(1.42 g, 13.4 mmol) and Pd/C (10 wt %) (710 mg) were added. The mixture was put under N
2
3
2
and stirred at reflux for 22 h. After allowing the mixture to reach room temperature, EtOAc (34
mL) and Pd/C (10 wt %) (710 mg) were added. The mixture was stirred at room temperature
under H
2
atmosphere for 22 h where after it was filtered through celite and eluted with EtOAc.
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The residue was purified by flash chromatography (petroleum ether/EtOAc 2:1, R
f
= 0.48) to give
1
1
3 (1.88 g, 8.27 mmol, 62%) as a light brown solid. H NMR (500 MHz, CDCl
3
): δ 8.25 (s, 1H),
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
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2
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4
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5
5
6
8.00 (d, J = 7.8 Hz, 1H), 7.76 (d, J = 7.8 Hz, 1H), 7.49 (t, J = 7.7 Hz, 1H), 7.24–7.29 (m, 1H),
.04–7.09 (m, 1H), 6.98–7.03 (m, 1H), 6.75–6.81 (m, 1H), 3.94 (s, 3H).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
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9
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3
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7
8
9
0
7
Methyl (R)-3'-((2-((3-chlorophenyl)(cyano)methoxy)-2-oxoethyl)amino)-[1,1'-biphenyl]-3-
carboxylate ((R)-14). (R)-9 (182 mg, 0.632 mmol) and 13 (432 mg, 1.90 mmol) were dissolved
in acetonitrile (2.5 mL) and put under N
and the solvent was evaporated. The residue was dissolved in EtOAc, washed with water and the
aqueous phase was extracted with EtOAc. The combined organic phases were dried over MgSO
and the solvent was evaporated. The residue was purified by flash chromatography (petroleum
ether/EtOAc 3:1, R = 0.56) to give (R)-14 (206 mg, 0.473 mmol, 75%, 97% ee) as a pale brown
gum. IR: 3407, 1762, 1717, 1607 cm . HPLC (Daicel Chiralpak IC, hexanes/2-propanol 80:20,
2
. The solution was stirred at room temperature for 40 h
4
f
-
1
2
5
0
.7 mL/min, detection at 220 nm): t
R
(major) 37.5 min, t
R D
(minor) 67.2 min. [α] -8.1 (c 1.7,
1
CH
2
Cl
2
). H NMR (400 MHz, CDCl
3
): δ 8.22 (s, 1H), 8.01 (d, J = 7.8 Hz, 1H), 7.72 (d, J = 7.8
Hz, 1H), 7.49 (t, J = 7.7 Hz, 1H), 7.40–7.45 (m, 1H), 7.34–7.39 (m, 2H), 7.31 (t, J = 7.8 Hz, 1H),
.10 (d, J = 7.6 Hz, 1H), 6.91 (s, 1H), 6.71 (d, J = 7.8 Hz, 1H), 6.47 (s, 1H), 4.18 (A part of AB,
7
1
3
J = 18.2 Hz, 1H), 4.14 (B part of AB, J = 18.1 Hz, 1H), 3.95 (s, 3H). C NMR (100 MHz,
CDCl ): δ 168.5, 167.2, 146.6, 141.62, 141.56, 135.4, 133.1, 131.7, 131.0, 130.73, 130.71, 130.1,
28.9, 128.6, 128.4, 128.1, 126.1, 118.5, 115.3, 112.8, 112.3, 62.9, 52.3, 46.0. HRMS (ESI-
3
1
+
2 4
Orbitrap) m/z: [M + H] calcd for C24H20ClN O 435.1106, found 435.1096.
Methyl
(R)-3'-((2-((2-(3-chlorophenyl)-2-hydroxyethyl)amino)-2-oxoethyl)amino)-[1,1'-
biphenyl]-3-carboxylate ((R)-15). The general procedure for hydrogenation was followed using
(R)-14 (177 mg, 0.407 mmol), Raney-Nickel (180 mg) and 1,4-dioxane (3.0 mL). Flash
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chromatography (petroleum ether/EtOAc 1:9, R
3%, 94% ee) as a pale yellow gum. IR: 3357, 1717, 1654, 1605 cm . HPLC (Daicel Chiralcel
OD-H, hexanes/2-propanol 85:15, 1.0 mL/min, detection at 220 nm): t (minor) 44.9 min, t
): δ 8.22 (s, 1H), 7.99
d, J = 7.7 Hz, 1H), 7.72 (d, J = 7.8 Hz, 1H), 7.48 (t, J = 7.7 Hz, 1H), 7.27–7.36 (m, 3H), 7.15–
f
= 0.52) gave (R)-15 (59.3 mg, 0.135 mmol,
-
1
3
R
R
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
26
1
(
D 2 2 3
major) 52.1 min. [α] -30 (c 0.79, CH Cl ). H NMR (400 MHz, CDCl
(
7
1
.22 (m, 3H), 7.12 (d, J = 7.5 Hz, 1H), 6.97 (bs, 1H), 6.72 (bs, 1H), 4.86 (dd, J = 2.7, 7.8 Hz,
H), 3.95 (bs, 2H), 3.91 (s, 3H), 3.68 (ddd, J = 3.0, 6.5, 14.0 Hz, 1H), 3.35 (ddd, 5.8, 7.9, 13.9
1
3
Hz, 1H). C NMR (125 MHz, CD
3
OD): δ 174.3, 168.6, 149.9, 146.2, 143.4, 142.3, 135.3, 132.7,
1
4
31.8, 130.9, 130.8, 130.0, 129.2, 128.9, 128.6, 127.2, 125.6, 117.9, 113.4, 112.6, 72.7, 52.7,
+
2 4
8.96, 47.4. HRMS (ESI-Orbitrap) m/z: [M + H] calcd for C24H24ClN O 439.1419, found
439.1406.
Methyl (R)-3'-((2-((2-(3-chlorophenyl)-2-hydroxyethyl)amino)ethyl)amino)-[1,1'-biphenyl]-
9
3
-carboxylate ((R)-16). (R)-15 (36.4 mg, 0.0829 mmol) was dissolved in THF (0.70 mL) and
2 3 2
put under N . The solution was cooled to 0 °C, BH ·Me S (2M in THF) (83 µL, 0.166 mmol) was
added dropwise and the reaction mixture was heated at 75 °C for 1.5 h. To quench the reaction,
the solution was cooled to 0 °C and aq. HCl (0.5 M, 0.5 mL) was added. The mixture was stirred
at room temperature for 1 h after which aq. NaOH (0.2 M, 1.5 mL) was added. This was followed
by extraction with EtOAc, drying over Na
purified by flash chromatography (EtOAc/MeOH 9:1, R
Et N in EtOAc/MeOH 9:1), to give (R)-16 (15.9 mg, 0.0374 mmol, 45%, 95% ee) as a colorless
oil. HPLC (Daicel Chiralpak IC, hexanes/2-propanol/Et NH 90:10:0.1, 0.8 mL/min, detection at
2
SO
4
and evaporation of the solvents. The residue was
f
= 0.27), using base-washed SiO (1%
2
3
2
2
4
1
R R D
254 nm): t (minor) 47.9 min, t (major) 51.3 min. [α] -10 (c 1.6, MeOH). H NMR (400
MHz, CDCl
3
): δ 8.25 (s, 1H), 8.00 (d, J = 7.7 Hz, 1H), 7.75 (d, J = 7.7 Hz, 1H), 7.48 (t, J = 7.8
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Hz, 1H), 7.37 (s, 1H), 7.17–7.29 (m, 4H), 6.97 (d, J = 7.6 Hz, 1H), 6.85 (s, 1H), 6.65 (dd, J = 1.5,
8
.0 Hz, 1H), 4.76 (dd, J = 3.2, 8.8 Hz, 1H), 3.94 (s, 3H), 3.34 (t, J = 5.7 Hz, 2H), 2.91–3.04 (m,
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
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4
4
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4
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5
5
5
5
5
5
5
5
5
5
6
1
3
3H), 2.77 (dd, J = 9.0, 12.2 Hz, 1H). C NMR (100 MHz, CD
3
OD): δ (Two carbons overlapped)
68.6, 150.6, 146.9, 143.6, 142.2, 135.4, 132.7, 131.7, 131.0, 130.8, 130.0, 129.1, 128.9, 128.6,
27.1, 125.4, 117.0, 113.5, 112.6, 72.5, 57.5, 52.7, 43.8.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
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8
9
0
1
1
(
R)-3'-((2-((2-(3-Chlorophenyl)-2-hydroxyethyl)amino)ethyl)amino)-[1,1'-biphenyl]-3-
9
carboxylic acid (2). (R)-16 (14.5 mg, 0.0341 mmol) was dissolved in MeOH (0.25 mL) and
water (0.15 mL) and LiOH·H
room temperature for 17 h; pH was adjusted to ~7 using aq. HCl (0.5 M), which resulted in a
white precipitate. The mixture was extracted with EtOAc, the organic phase dried over Na SO
2
O (7.2 mg, 0.17 mmol) were added. The mixture was stirred at
2
4
and the solvents were evaporated. The crude material was triturated with DCM, discarding the
24
soluble material, to give 2 (6.9 mg, 0.0168 mmol, 49%) as a white solid. [α]
D
-11 (c 0.69,
9
20
1
MeOH) [lit. [α]
J = 7.5 Hz, 1H), 7.65 (d, J = 7.4 Hz, 1H), 7.47 (s, 1H), 7.40 (t, J = 7.6 Hz, 1H), 7.30–7.37 (m,
H), 7.22 (t, J = 7.9 Hz, 1H), 6.94–6.99 (m, 2H), 6.69 (d, J = 7.7 Hz, 1H), 5.00 (dd, J = 2.5, 10.1
D 3
-20 (c 0.075, MeOH)]. H NMR (500 MHz, CD OD): δ 8.21 (s, 1H), 7.92 (d,
3
Hz, 1H), 3.57 (t, J = 6.0 Hz, 2H), 3.25–3.36 (m, 3H), 3.13 (dd, J = 10.5, 12.4 Hz, 1H).
ASSOCIATED CONTENT
Supporting Information
Characterization of compounds and graphs for hydrolysis experiments are provided. This
material is available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
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Corresponding Author
*
kimo@kth.se
Notes
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The authors declare no competing financial interest.
ACKNOWLEDGMENT
Financial support from the Swedish Research Council (Grant 621-2012-3391) is gratefully
acknowledged. We are grateful to Lorraine Cherrier for her skillful experimental work.
REFERENCES
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(
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8) Cooke, J. W. B.; Glover, B. N.; Lawrence, R. M.; Sharp, M. J.; Tymoschenko, M. F. PCT
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12) Lundgren, S.; Wingstrand, E.; Moberg, C. Adv. Synth. Catal. 2007, 349, 364.
(13) Lundgren, S.; Wingstrand, E.; Penhoat, M.; Moberg, C. J. Am. Chem. Soc. 2005, 127,
1592.
(
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(14) Wingstrand, E.; Laurell, A.; Fransson, L.; Hult, K.; Moberg, C. Chem.–Eur. J. 2009, 15,
12107.
(
15) Fransson, L.; Laurell, A.; Widyan, K.; Wingstrand, E.; Hult, K.; Moberg, C. ChemCatChem
010, 2, 683.
(16) Laurell Nash, A.; Widyan, K.; Moberg, C. ChemCatChem 2014, 6, 3314.
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18) Hertzberg, R.; Moberg, C. J. Org. Chem. 2013, 78, 9174.
2
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(
(19) Diethylamine gave a product with a lower ee, even at decreased temperature. Substitution
with both dibenzylamine and N-benzylmethylamine were successful without racemization, but
the subsequent reduction resulted in depletion of the ee.
(20) This method is superior to a previous method where more expensive TMSCN was used, see
ref. 18.
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21) Dear, A. E.; Liu, H. B.; Mayes, P. A.; Perlmutter, P. Org. Biomol. Chem. 2006, 4, 3778.
(22) Imanishi, M.; Itou, S.; Washizuka, K.; Hamashima, H.; Nakajima, Y.; Araki, T.;
Tomishima, Y.; Sakurai, M.; Matsui, S.; Imamura, E.; Ueshima, K.; Yamamoto, T.; Yamamoto,
N.; Ishikawa, H.; Nakano, K.; Unami, N.; Hamada, K.; Matsumura, Y.; Takamura, F.; Hattori, K.
J. Med. Chem. 2008, 51, 4002.
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(23) Compound 9 was also transformed to the known O-acetylated 3-chloromandelonitrile and
the HPLC elution order and sign of optical rotation were compared to those published.
(24) Herrmann, K.; Simchen, G. Synthesis 1979, 204.
(25) Cary, J. M.; Moore, J. S. Org. Lett. 2002, 4, 4663.
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