Synthesis of the γ-Secretase Modulator MK-8428

Article abstract of DOI:10.1021/acs.joc.6b02979

The synthesis of the γ-secretase modulator MK-8428 (1) is described. The synthesis is highlighted by an enzyme-catalyzed reaction to access 3,4,5-trifluoro-(S)-phenylglycine, a 1-pot activation/displacement/deprotection sequence to introduce the aminooxy functionality and a dehydrative intramolecular cyclization under mild conditions to form the oxadiazine heterocycle of 1. In situ reaction monitoring was employed to understand the deleterious role of water during the formation of a methanesulfonate ester in the 1-pot activation/displacement/deprotection sequence.

Full text of DOI:10.1021/acs.joc.6b02979

Article
pubs.acs.org/joc
Synthesis of the γ‑Secretase Modulator MK-8428
Steven P. Miller,* William J. Morris,* Robert K. Orr, Jeffrey Eckert, Jay Milan, Mathew Maust,
Cameron Cowden, and Jian Cui
Department of Process Research, MRL, Merck & Co., Inc., Rahway, New Jersey 07065, United States
S
* Supporting Information
ABSTRACT: The synthesis of the γ-secretase modulator MK-8428 (1) is described.
The synthesis is highlighted by an enzyme-catalyzed reaction to access 3,4,5-trifluoro-
(S)-phenylglycine, a 1-pot activation/displacement/deprotection sequence to introduce
the aminooxy functionality and a dehydrative intramolecular cyclization under mild
conditions to form the oxadiazine heterocycle of 1. In situ reaction monitoring was
employed to understand the deleterious role of water during the formation of a
methanesulfonate ester in the 1-pot activation/displacement/deprotection sequence.
INTRODUCTION
RESULTS AND DISCUSSION
■
■
The retrosynthesis of 1 is presented in Figure 1. The key
oxadiazine pharmacophore5 was generated via intramolecular
dehydrative cyclization of an intermediate aminooxy nucleo-
phile derived from carbinol 2. This carbinol was accessible after
coupling of α,β-unsaturated acid 3 with amino-alcohol 4. Acid 3
was formed via Horner−Wadsworth−Emmons olefination of
aldehyde 5, and the amino-alcohol 4 was prepared via an
enzyme-mediated conversion of an α-keto carboxylic acid 6 to
an optically pure α-amino acid followed by reduction of the
carboxylic acid.
The route employed to produce α,β-unsaturated acid 3 is
shown in Scheme 1. 3-Hydroxy-4-nitro benzoic acid (7)
underwent bis-alkylation with dimethylsulfate to generate 8.
The nitro group was reduced in the presence of Raney-Ni to
provide aniline 9. This aniline was formylated and subsequently
alkylated with chloroacetone to yield 11, which upon treatment
with ammonium acetate in acetic acid underwent dehydrative
cyclization to afford 4-methyl-imidazole 12. The methyl ester
was subsequently converted to aldehyde 56 using a two-step
reduction/oxidation sequence. Aldehyde 5 was coupled to
phosphonate 135a under Horner−Wadsworth−Emmons7 con-
ditions, yielding a mixture of olefin isomers (E:Z 4.7:1). Finally,
exposure to trifluoroacetic acid resulted in the cleavage of the
tert-butyl ester to afford the trifluoroaceate salt of 3.
The synthesis of the amino-alcohol coupling partner 4 is
shown in Scheme 2. Readily available 5-bromo-1,2,3-trifluor-
obenzene (15) was acylated with diethyl oxalate, and the
resulting ester was hydrolyzed to yield α-keto carboxylic acid 6.
In a key transformation, exposure of 6 to an amino acid
dehydrogenase (L-AADH-108)8 produced 3,4,5-trifluoro-(S)-
phenylglycine 16 in high yield and with excellent enantiose-
lectivity (>99% ee). Glucose and glucose dehydrogenase were
used to regenerate the NADH cofactor from NAD+, producing
D-glucono-1,5-lactone (Figure 2) in the process. The carboxylic
Alzheimer’s disease (AD) is a neurodegenerative disorder that
results in gradual loss of memory and impairment of vocal and
motor control before ultimately resulting in death. By 2025, it is
estimated that greater than 7 million Americans will be
suffering from AD, a number that represents a 40% increase
from the number of Americans living with the disease in 2015.1
The current standard of care involves treatment with a
cholinesterase inhibitor to improve cognition, but there are
currently no disease-modifying therapies available to treat AD.
Patients suffering from AD possess two distinctive biomarkers:
extracellular amyloid plaques and intracellular neurofibrillary
tangles, both of which are believed to result in the loss of
neurons in the cerebral cortex. The amyloid plaques are formed
when amyloid precursor protein (APP) is cleaved sequentially
by proteases BACE1 and γ-secretase, leading to the formation
of Aβ42. Novel inhibitors or modulators of the γ-secretase
protease can therefore be assessed as possible treatments for
AD.2
During the course of their clinical evaluation, γ-secretase
inhibitors were found to lead to higher incidence of adverse
events, likely due to the promiscuity of the γ-secretase enzyme,
which possesses a range of endogenous substrates and is
involved in a variety of key cellular processes.3 To mitigate
these concerns, a new class of molecules was developed that
changes the enzyme’s interaction with APP without further
cellular impact. These new molecules, γ-secretase modulators,
alter the APP specificity and result in the elevated formation of
the shorter, less toxic Aβ37 and Aβ38 fragments, resulting in
lower levels of Aβ42.4 MK-8428 (1) was identified as a novel γ-
secretase modulator possessing favorable in vitro activity and an
excellent pharmacokinetic profile and was subsequently
targeted for further development. To support preclinical and
early clinical development of this compound, a robust and
efficient synthesis of 1 was required.
Received: December 13, 2016
© XXXX American Chemical Society
A
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Figure 1. Retrosynthesis of 1.
Scheme 1. Preparation of α,β-Unsaturated Acid 3
Scheme 2. Preparation of Amino Alcohol 4
to previously disclosed routes to 4 with respect to overall yield
and stereocontrol.5
e
Amino-alcohol 4 was coupled to unsaturated acid 3 under
HOBT/EDC conditions, resulting in the formation of amide
17 (Scheme 3). Treatment of amide 17 with NaOMe
promoted the intramolecular alkylation, yielding the δ-lactam
2. Assembly of the aminooxy moiety was carried out in a 2-step
sequence beginning with the addition of N-hydroxyphthalimide
after activation of 2 as the methanesulfonate ester10 to yield 18.
It was determined that isolation of 18 was not required, as
direct addition of aqueous hydroxylamine resulted in the
cleavage of the phthalimide to provide 19. Hydroxylamine was
chosen as the nucleophile for this transformation, as the
byproduct of the reaction (N-hydroxyphthalimide) was easily
separated from 19 by washing with aqueous base during the
reaction workup. The overall yield from 2 to 19 was 86% and
Figure 2. Enzymatic mediated conversion of keto-acid 6 to amino acid
16.
acid of 16 was then reduced to provide 4, which was isolated as
the mandelate salt.9 The targeted amino alcohol was prepared
in 3 steps with an overall yield of 42% and provided advantages
B
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Scheme 3. Installation of the Aminooxy Moiety
Table 1. Impact of Water on the Activation/Displacement Approach to 18
a
b
b
entry
H2O content (mol %)
age time (h)
2 (%)
18 (%)
c
1
2
3
4
60
0.5
0.5
3
3.7
0.3
91.9
97.2
81.2
96.7
d
6
60
5
11.0
0.3
3
a
b
Time between the end of the MsCl addition and the N-hydroxyphtalimide charge. Content was recorded after reaction was deemed complete by
c
HPLC. Numbers shown are HPLC area percents. KF values were recorded for individual components (2 and THF, respectively) for this analysis.
d
KF value was the solution of 2 in THF.
yielded the precursor for the pivotal oxadiazine formation (vide
infra).
The impact of water on the conversion of 2 to 18 was further
explored using in situ IR spectroscopy.11 In situ IR provided a
tool to monitor the formation of the methanesulfonate ester 20,
as this reactive intermediate was unstable under reverse phase
HPLC conditions.12 An experiment was carried out where
water removal by azeotropic distillation was omitted (Table 1,
entry 3). Following the addition of methanesulfonyl chloride,
the batch was aged for 3 h. The IR spectroscopy data showed
initial formation of the of the methanesulfonate ester (Figure 3,
orange band), which was followed by clear decomposition of
this reactive intermediate during the course of the 3 h holding
period (Figure 3, red band). N-Hydroxyphthalimide was then
added to the reaction, and the final content of 2 was observed
to be 11% by HPLC.
During the course of our optimization work on installing the
N-hydroxyphthalimide group of 18, it was observed that small
amounts of 2 persisted at the end of the reaction (Table 1,
entry 1). Given the stoichiometry of the methanesulfonyl
chloride employed (1.5 equiv), we considered it unlikely that
the carbinol was not fully converted to the methanesulfonate
ester. A more plausible scenario was that adventitious water
reacted with the newly formed methanesulfonate ester 20 to
return carbinol 2. To evaluate this hypothesis, water introduced
from 2 and THF was azeotropically removed prior to addition
of the methanesulfonyl chloride and triethylamine. This
operation reduced the measured water content to 6 mol %
(Table 1, entry 2). Following formation of the methanesulfo-
nate ester and addition of the N-hydroxyphthalimide, the
amount of 2 observed was lowered to 0.3% by HPLC with a
concomitant increase in the purity of 18 by HPLC.
A subsequent experiment was conducted in which water was
removed by azeotropic distillation (Table 1, entry 4). Following
completion of the methanesulfonyl chloride addition, the
reaction was again aged for 3 h (Figure 4, pink band). In stark
C
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Figure 3. IR spectrum from mesylation of 2 without distillation prior to reaction (3 h hold). Formation of the intermediate methanesulfonate ester
20 was established by monitoring the appearance of the S−O stretch in the IR spectrum. Unlabeled stretches represent time points prior to the
completion of the MsCl addition.
Figure 4. IR spectrum from mesylation of 2 with distillation prior to reaction (3 h hold). Formation of the intermediate methanesulfonate ester 20
was established by monitoring the appearance of the S−O stretch in the IR spectrum. Unlabeled stretches represent time points prior to the
completion of the MsCl addition.
contrast to the experimental data shown in Figure 3, no
discernible mesylate decomposition was observed by IR when
the water was removed prior to the addition of methanesulfonyl
chloride and triethylamine (Figure 4, light blue band).
Following completion of the reaction, the final content of 2
was determined to be 0.3% by HPLC. Taken together, the
water titration and in situ IR data provided strong support that
water dramatically impacts the conversion of 2 to 18
presumably by reacting with the intermediate mesylate to
regenerate carbinol 2.
polyphosphate byproducts13 which complicated the isolation of
1. Acids were screened to determine their effectiveness in
promoting the conversion of 19 to 1 (Table 2). While the
conversion in the presence of most acids was high, the assay
yields of the desired oxadiazine product were low due to the
competing side reactions. Gratifyingly, we discovered that when
treating a solution of 19 with hexamethyldisilazane (HMDS)
and catalytic amounts of trimethylsilyl trifluormethanesulfonate
(TMSOTf), the desired intramolecular cyclization took place in
high yield.14 This silyl-mediated dehydration provided a milder
alternative to Brønsted acids and a new approach to access this
interesting heterocycle (1). Finally, isolation as the hemi-
fumarate salt provided access to our targeted γ-secretase
modulator 1 (Scheme 4).
With an understanding of the conversion of 2 to 19 in place,
we were poised to introduce the oxadiazine heterocycle using
an intramolecular dehydrative cyclization. Previously reported
conditions using P2O5 in EtOH5a led to the formation of
D
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Table 2. Acid Screen for Intramolecular Dehydration
a
b
entry
acid
conversion (%)
assay yield of 1 (%)
1
1
2
3
4
5
6
7
none
0
0
42
65
54
52
70
68
75
HCl
60
MsOH
AcOH
TFA
98
98
99
HBF4
H3PO4
Tf2NH
99.5
99.5
99.8
c
8
HMDS/TMSOTf
99.9
92
a
b
c
Entries 1−7 were run using EtOH as a solvent under reflux conditions for 14 h. Based on HPLC area percent of 19. Reaction solvent was 2-Me-
THF, and reaction temperature was 30 °C.
Scheme 4. End Game Approach to 1
preclinical development of this potentially important disease-
modifying therapy for AD.
CONCLUSION
■
A convergent synthesis of γ-secretase modulator 1 was
described. Highlights of this synthesis included an enzyme-
mediated conversion of an α-keto carboxylic acid to access an
enantiopure 3,4,5-trifluoro-(S)-phenylglycine (16). In situ
reaction monitoring was employed to understand the
deleterious role of water on the 1-pot mesylation/displacement
sequence that was employed to introduce the aminooxy
functionality. Finally, mild dehydration conditions were
identified to form the key oxadiazine heterocycle in high
yield. The route described enabled production of 1 to support
EXPERIMENTAL SECTION
■
General Information. All reactions were carried out under a
nitrogen atmosphere in dried glassware with either magnetic stirring or
overhead agitation. 1H NMR spectra were recorded on either a 500 or
400 MHz spectrometer and are reported in ppm using deuterated
solvent as an internal standard. Data are reported as ap = apparent, s =
singlet, d = doublet, t = triplet, q = quartet, m = multiplet, b = broad;
coupling constant(s) in Hz; integration. Proton-decoupled 13C NMR
spectra were recorded on a 125 or 100 MHz spectrometer and are
E
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reported in ppm using deuterated solvent as an internal standard.
Electrospray mass spectra (ESI-MS) were obtained using a triple
quadrupole mass spectrometer. L-AADH-108 and GDH-105 were
purchased from Codexis.
NH4Cl (3.18 g, 59.7 mmol) were dissolved in pH 7 kPi buffer (75
mL), and the pH was adjusted to pH 8 using NH4OH. Glucose (8.1 g,
45 mmol) and NAD (195 mg, 0.3 mmol) were then added to this
solution. The solution containing L-AADH-108 and GDH-105 was
added to the keto acid solution, resulting in a pH drop to 7.4. The pH
was adjusted back to pH 8 using 2 M NaOH, and the reaction was
aged for 10 h at 25 °C. MeOH (24 mL) was added to the mixture, and
the reaction was heated to 70 °C for 1 h. The reaction was cooled to
25 °C over 1 h and further stirred for 1 h. 1-Butanol was added (50
mL), and the mixture was distilled at 70 °C under vacuum to 20 mL
total volume. The solids were collected by filtration and dried over
(E)-1-(4-(2-Carboxy-5-chloropent-1-en-1-yl)-2-methoxyphenyl)-
4-methyl-1H-imidazol-3-ium 2,2,2-trifluoroacetate (3). To a round-
bottom flask at 5 °C were added potassium tert-butoxide (3.5 g, 31.1
mmol) and THF (100 mL). A solution of tert-butyl diethylphospho-
noacetate (7.5 g, 29.7 mmol) in THF (19 mL) was added to the
potassium tert-butoxide solution at a rate to maintain the internal
temperature <10 °C. After the addition was complete, the solution was
warmed to 25 °C and aged for 45 min. 1-Bromo-3-chloropropane (9.4
g, 59.4 mmol) was added to the anion solution of tert-butyl
diethylphosphonoacetate at 25 °C. The reaction was warmed to 60
°C and aged for 3 h. The reaction was cooled to 25 °C, and aldehyde 5
(5.78 g, 21.6 mmol) was charged in a single portion. The reaction was
further cooled to −5 °C, and a solution of potassium tert-butoxide
(3.02 g, 26.9 mmol) was added to the reaction at a rate to maintain the
internal temperature <0 °C. The reaction was aged for 60 min at 0 °C.
Ethyl acetate (100 mL) was added to the reaction; the temperature
was raised to 25 °C, and the reaction mixture was transferred to a
separatory funnel. The organic layer was washed with water (90 mL),
and the resulting aqueous layer was extracted with ethyl acetate (50
mL). The combined organic layers were washed with brine (90 mL)
and treated with activated charcoal (500 mg) for 30 min at 25 °C. The
activated charcoal was removed by filtration over Celite, and the ethyl
acetate solution was dried over Na2SO4. The Na2SO4 was removed by
filtration, and the resulting solution was concentrated to dryness. The
unpurified tert-butyl ester 14 was dissolved in dichloromethane (50
mL), cooled to 0 °C, and treated with trifluoroacetic acid (12 mL, 156
mmol). The reaction was warmed to 25 °C and aged for 3 h. The
dichloromethane was removed by evaporation; ethyl acetate (30 mL)
was added, and the residue was stirred for 1 h. The solids were filtered
and dried over nitrogen, yielding TFA salt 3 (4.33g, 45%), mp 163−
166 °C. 1H NMR (DMSO-d6, 500 MHz) δ: 9.38 (s, 1H), 7.76 (s, 1H),
7.71 (s, 1H), 7.67 (m, 1H), 7.37 (s, 1H), 7.25 (m, 1H), 3.94 (s, 3H),
3.71 (t, J = 6.3 Hz, 2H), 2.65 (t, J = 7.9 Hz, 2H), 2.39 (s, 3H), 2.01
(quintuplet, J = 6.3 Hz, 2H); 13C NMR (DMSO-d6, 125 MHz) δ
169.1, 159.1 (q, J = 35.8 Hz), 152.6, 138.8, 137.7, 136.1, 134.7, 130.0,
126.6, 123.8, 121.9, 120.1, 116.4 (q, J = 292.4 Hz), 114.2, 56.8, 45.8,
31.9, 25.4, 9.9. HRMS calcd. for C17H20ClN2O3 ([M + H]+) 335.1157,
found 335.1162.
1
nitrogen, yielding amino acid 16 (4.5 g, 75%), mp 201−202 °C. H
NMR (D2O, 500 MHz) δ 7.18 (m, 2H), 5.10 (s, 1H); 13C NMR
(CDCl3, 125 MHz) δ 169.6, 151.2 (ddd, J = 249.8, 10.0, 4.0 Hz),
140.6 (dt, J = 252.4, 14.9 Hz), 127.5 (td, J = 8.0, 5.0 Hz), 113.2 (dd, J
= 17.6, 6.0 Hz), 55.3. HRMS calcd. for C8H5F3NO2 ([M − H]−)
204.0278, found 204.0276. Chiral analysis performed using Zwix (−)
column (150 × 3 mm, 3 μm); mobile phase: isocratic elution (49%
MeOH, 49% MeCN, 2% water, 50 mM formic acid, 25 mM
diethylamine), 0−6 min, 0.75 mL/min, 45 °C, 99% ee.
(S)-2-Hydroxy-1-(3,4,5-trifluorophenyl)ethan-1-aminium-(R)-2-
hydroxy-2-phenylacetate (4). NaBH4 (1.33 g, 35.2 mmol) and THF
(60 mL) were added to a round-bottom flask, and the solution was
cooled to 0 °C. A solution of iodine (3.72 g, 14.6 mmol) in THF (14
mL) was slowly added to this solution at a rate to maintain the internal
temperature, <5 °C. 3,4,5-Trifluoro-(S)-phenylglycine (3 g, 14.6
mmol) was added in 1 portion, and the mixture was warmed to 55 °C
for 16 h. The mixture was cooled to 23 °C, and MeOH was added
until the batch became clear. The mixture was concentrated, and
EtOAc (12 mL) was added. In a separate flask, (R)-mandelic acid (2.4
g, 15.8 mmol) was dissolved in EtOAc (24 mL) and MeOH (0.8 mL)
and heated to reflux. The EtOAc solution containing amino alcohol
was added to the mandelic acid solution and heated to reflux for 1 h
before being cooled to 10 °C over 3 h. The solids were collected by
vacuum filtration and dried over nitrogen, yielding mandelate salt 4 as
a white solid (3.4 g, 68%), mp 163−165 °C. 1H NMR (DMSO-d6, 500
MHz) δ 7.40 (m, 4H), 7.27 (s, 2H), 7.20 (m, 1H), 6.68 (bs, 4H), 4.72
(s, 1H), 7.08 (m, 1H), 6.64 (s, 1H), 4.57 (s, 1H), 4.16 (dd, J = 5.7, 4.4
Hz, 1H), 3.61 (dd, J = 11.2, 5.0 Hz, 1H), 3.54 (dd, J = 10.7, 6.3 Hz,
1H); 13C NMR (DMSO-d6, 125 MHz) δ 175.5, 150.4 (ddd, J = 246.8,
9.7, 3.7 Hz), 142.9, 138.5 (dt, J = 248.8, 15.8 Hz), 137.2, 128.1, 127.1,
126.9, 112.7 (dd, J = 17.2, 4.6 Hz), 73.6, 64.6, 55.6. HRMS calcd. for
C8H9F3NO ([M + H]+) 192.0631, found 192.0632. Chiral analysis
performed on the free base of 4 using Chiralcel AD-RH column (4.6 ×
150 mm, 3 um); isocratic elution (17% MeCN, 83% 5 mM Na2B4O7,
pH 9.2), 0−8 min, 1.00 mL/min, 25 °C, 99% ee.
(S,E)-5-Chloro-N-(2-hydroxy-1-(3,4,5-trifluorophenyl)ethyl)-2-(3-
methoxy-4-(4-methyl-1H-imidazol-1-yl)benzylidene)pentanamide
(17). Mandelate salt 4 (3.3 g, 9.62 mmol) was slurried in EtOAc (25
mL) and treated with 1 M NaOH (10 mL, 10 mmol) for 30 min. The
stirring was stopped, and the aqueous layer was removed. To the
resulting EtOAc layer containing the free base of 4 was added 3 (4.33
g, 9.64 mmol) at 25 °C. HOBT hydrate (738 mg, 4.82 mmol), N,N′-
diisopropylethylamine (9.21 mL, 53 mmol), and EDCI-HCl (6.2 g,
67.5 mmol) were added at 25 °C. The reaction was stirred at 25 °C for
90 min. The reaction mixture was transferred to a separatory funnel
and washed with saturated NaHCO3 (3 × 30 mL), water (2 × 20 mL),
and brine (1 × 20 mL) and dried over Na2SO4. The drying agent was
removed by filtration, and the organic layer was concentrated to afford
a pale yellow solid. The solid was treated with MTBE (20 mL) and
stirred at 20−24 °C for 30 min. The solid material was collected by
filtration and dried over nitrogen, yielding 17 as a white solid (4.06 g,
83%), mp 151−152 °C. 1H NMR (CDCl3, 500 MHz) δ 7.64 (s, 1H),
7.37 (m, 1H), 7.07 (m, 4H), 6.91 (m, 3H), 5.03 (dd, J = 5.3 Hz, 1H),
4.03 (dd, J = 11.5, 3.6 Hz, 1H), 3.91 (dd, J = 11.6, 5.0 Hz, 1H), 3.83
(s, 3H), 3.56 (t, J = 6.1 Hz, 2H), 2.70 (t, J = 4.7 Hz, 2H); 2.26 (s, 3H),
1.98 (quintuplet, J = 6.2 Hz, 2H); 13C NMR (CDCl3, 125 MHz) δ
169.4, 151.9, 151.2 (ddd, J = 250.1, 10.0, 3.7 Hz), 138.9 (dt, J = 251.0,
15.3 Hz), 138.1, 137.5, 136.9 (td, J = 4.4 Hz), 136.7, 135.9, 132.3,
125.8, 124.6, 121.6, 116.7, 112.8, 111.0 (dd, J = 16.7, 5.1 Hz), 64.5,
2-Oxo-2-(3,4,5-trifluorophenyl)acetic Acid (6). To a solution of
isopropylmagnesium chloride−lithium chloride in THF (50.8 mL,
66.2 mmol) at −10 °C was added 5-bromo-1,2,3-trifluorobenzene
(13.9 g, 66 mmol). After being stirred for 4 h at −10 °C, the solution
was cooled to −70 °C, and diethyl oxalate (19.4 g, 132 mmol) was
added dropwise. The reaction was warmed to room temperature over
4 h and then quenched into saturated ammonium sulfate. The ester
was extracted with MTBE (200 mL), washed with water (100 mL) and
1 M HCl (100 mL), and concentrated in vacuo to afford a crude oil.
The crude oil was then charged to a flask and then dissolved in 40 mL
of THF with stirring. The mixture was cooled to 0 °C, and NaOH (40
mL, 198 mmol) was added dropwise. After being warmed to room
temperature and stirred overnight, 1 M HCl was added to the solution
until the pH was 2−3. The product was then extracted with
dichloromethane (200 mL), and the solvent was removed. The
crude oil was then crystallized from dichloromethane (20 mL) and
heptane (20 mL) to afford 6 as a white solid (9.44 g, 70%). This crude
solid was used in the downstream processing without further
purification. For analytical purposes, the material was chromato-
graphed on a SiO2 ISCO cartridge using 100% hexane to 30% EtOAc
1
over 12 column volumes, mp 164−165 °C. H NMR (CDCl3, 500
MHz) δ 7.88 (t; J = 7.47 HZ; 2 H); 13C NMR (CDCl3, 125 MHz) δ
115.2 (dd, J = 5.62, 17.1 Hz), 128.9 (td; J = 3.9, 6.4 Hz), 143.6 (dt; J =
15.3, 259.6 Hz), 150.8 (dd; J = 3.2, 10.3, 250.7 Hz), 164.3, 184.9.
HRMS calcd. for C8H2F3O3 ([M − H]−) 202.9962, found 202.9959.
(S)-2-Amino-2-(3,4,5-trifluorophenyl)acetic Acid (16). L-AADH-
108 (450 mg) and GDH-105 (150 mg) were dissolved in pH 7 kPi
buffer (75 mL). In a separate flask, keto acid 6 (6 g, 29 mmol) and
F
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56.0, 55.0, 44.9, 31.5, 25.8, 13.3. HRMS calcd. for C25H26ClF3N3O3
([M + H]+) 508.1609, found 508.1604.
under vacuum at 45 °C for 12 h, yielding 1 as a white solid (2.5 g, 4.7
mmol), mp 164−168 °C. 1H NMR (DMSO-d6, 500 MHz) δ 13.16 (s,
1H), 7.80 (s, 1H), 7.38 (m, 2H), 7.25 (m, 3H), 7.15 (s, 1H), 7.08 (m,
1H), 6.64 (s, 1H), 4.57 (s, 1H), 3.93 (dd, J = 91.4, 11.1 Hz, 2H), 3.86
(s, 3H), 3.09 (m, 2H), 2.78 (m, 2H), 2.16 (s, 3H), 1.78 (m, 2H); 13C
NMR (DMSO-d6, 125 MHz) δ 166.5, 152.1, 151.5, 150.7 (ddd, J =
247.9, 9.8, 3.6 Hz), 138.5 (dt, J = 248.5, 15.7 Hz), 138.4 (td, J = 3.9
Hz), 137.2, 137.0, 134.5, 130.4, 126.7, 125.5, 125.3, 122.4, 117.1,
114.5, 112.0 (dd, J = 16.8, 4.5 Hz), 68.6, 59.2, 56.5, 48.0, 25.7, 23.1,
(S,E)-1-(2-Hydroxy-1-(3,4,5-trifluorophenyl)ethyl)-3-(3-methoxy-
4-(4-methyl-1H-imidazol-1-yl)benzylidene)piperidin-2-one (2). To a
solution of 17 (3.5 g, 6.9 mmol) in THF (35 mL) was added NaOMe
(559 mg, 10.4 mmol) at 25 °C. The reaction was stirred for 2 h at 25
°C. Saturated aqueous NaHCO3 (40 mL) was added at 25 °C, and the
reaction mixture was aged for 30 min (pH 8−9). The aqueous layer
was extracted with ethyl acetate (3 × 25 mL), and the combined
organic layers were dried over Na2SO4. The drying agent was removed
by filtration, and the filtrate was concentrated to 10 mL, at which time
the product crystallized from solution. The slurry was cooled to 10 °C
and stirred for 12 h. The solids were collected by filtration and dried
over nitrogen, yielding lactam 2 as a pale yellow solid (3.2 g, 97%), mp
+
13.9. HRMS calcd. for C25H24F3N4O2 ([M + H]+) 469.1846, found
469.1861.
ASSOCIATED CONTENT
■
S
1
* Supporting Information
158−160 °C. H NMR (CDCl3, 500 MHz) δ 7.85 (s, 1H), 7.73 (s,
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.joc.6b02979.
1H), 7.26 (s, 1H), 7.02 (m, 4H), 6.94 (s, 1H), 5.76 (dd, J = 6.5, 6.3
Hz, 1H), 4.19 (dd, J = 11.6, 5.2 Hz, 1H), 4.12 (dd, J = 11.5, 8.0 Hz,
1H), 3.86 (s, 3H), 3.42 (m, 1H), 3.18 (m, 1H), 2.82 (m, 1H), 2.30 (s,
3H), 1.83 (m, 3H); 13C NMR (CDCl3, 125 MHz) δ 165.9, 151.9,
151.2 (ddd, J = 250.6, 9.9, 3.8 Hz), 139.0 (dt, J = 252.1, 15.1 Hz),
137.8, 136.7, 136.1, 135.4, 133.7 (td, J = 6.8, 4.7 Hz), 130.3, 126.2,
124.6, 122.1, 116.2, 113.7, 111.9 (dd, J = 16.6, 5.2 Hz), 61.4, 58.8,
55.7, 44.3, 26.3, 22.9, 13.4. HRMS calcd. for C25H24F3N3O3 ([M +
H]+) 472.1842, found 472.1843.
Spectroscopic data for compounds 6, 16, 4, 3, 17, 2 and
1 (PDF)
AUTHOR INFORMATION
■
Corresponding Authors
*E-mail: steven.miller@merck.com.
*E-mail: william.morris2@merck.com.
(S,E)-1-(2-(Aminooxy)-1-(3,4,5-trifluorophenyl)ethyl)-3-(3-me-
thoxy-4-(4-methyl-1H-imidazol-1-yl)benzylidene)piperidin-2-one
(19). Lactam 2 (3.0 g, 6.4 mmol) in THF (60 mL) was
atmospherically distilled to 30 mL (internal temperature 64−67 °C)
to reduce water content to 6 mol %. Triethylamine (5.4 mL, 38.4
mmol) was added, and the batch was cooled to −25 °C.
Methanesulfonyl chloride (0.74 mL, 9.6 mmol) was added as a
solution in THF (1 mL) at a rate such that the internal temperature
did not exceed −15 °C. After addition was complete, the reaction
mixture was stirred for 30 min between −25 and −15 °C. N-
Hydroxyphthalimide (1.57 g, 9.6 mmol) was added as a solid in a
single portion at −10 °C. The batch was warmed to 25 °C and aged
for 18 h. Hydroxylamine (50% wt. solution in water, 0.75 mL) was
added at 25 °C and aged for 2 h. 2-Methyltetrahydrofuran (2-Me-
THF) was added (40 mL) at 25 °C, and the contents of the reaction
were transferred to a separatory funnel. The mixture was washed with
5% aqueous NaHCO3 (15 mL) at 25 °C followed by 5% aqueous
NaCl (15 mL). The organic layer was treated with 15 g of 4 Å
molecular sieves (8−12 mesh) for 18 h (KF < 0.1%). The molecular
sieves were removed by filtration, and the 2-Me-THF was removed by
vacuum distillation to a volume of 24 mL (internal temperature <30
°C) and maintained as a solution in 2-Me-THF for the next step. Yield
in solution: 2.67 g, 86%.
(S,E)-1-(2-Methoxy-4-((4-(3,4,5-trifluorophenyl)-3,4,7,8-
tetrahydropyrido[2,1-c][1,2,4]oxadiazin-9(6H)-ylidene)methyl)-
phenyl)-4-methyl-1H-imidazol-3-ium-hemi-(E)-3-carboxyacrylate
(1). To a solution of hexamethyldisilazane (2.2 mL, 10.8 mmol) in 2-
Me-THF(5 mL) was added trimethylsilyl trifluoromethanesulfonate
(1.95 mL, 10.8 mmol) at a rate to maintain an internal reaction
temperature <20 °C. The solution of 19 (2.67 g, 5.4 mmol) in 2-Me-
THF (24 mL) was added to the HMDS/TMSOTf solution at a rate to
maintain the internal reaction temperature <20 °C. The reaction was
warmed to 30 °C and aged for 12 h. HCl (3 N, 8 mL) was slowly
added while maintaining the batch temperature below 30 °C. The
resulting aqueous layer was extracted with MTBE 3 times (150 mL
total), and the these combined aqueous layers were discarded.
Isopropyl acetate (50 mL) was added to the aqueous layer followed by
the addition of K3PO4 (30 g). The organic layer was removed, and the
aqueous layer was extracted with IPAc (50 mL). The combined IPAc
layers were washed with water and concentrated under vacuum.
Isopropyl alcohol (10 mL) was added followed by a solution of
fumaric acid (313 mg, 2.7 mmol) in isopropyl alcohol (4 mL). The
mixture was heated to 60 °C and aged for 30 min. The solution was
cooled to 40 °C and aged for 30 min, at which time the product
crystallized from solution. The slurry was further cooled to 0 °C over 3
h, aged for 1 h at 0 °C, and then filtered. Hemifumarate 1 was dried
ORCID
William J. Morris: 0000-0003-4322-4509
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank Wendy Zhong and Xiaoxia Qian (Merck)
for HRMS data, Alexi Makarov and Leo Joyce for chiral HPLC
method development, and Louis-Charles Campeau for helpful
discussions.
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