ACS Chemical Neuroscience
Research Article
(
1
4
151 MHz, CDCl ) (mixture of rotamers) δ 171.7, 154.0, 138.1,
38.0, 116.0, 115.9, 81.2, 81.2, 80.0, 79.7, 64.8, 64.6, 48.7, 47.4, 46.0,
(2S,3S)-3-(3-Hydroxy-4,5-dihydroisoxazol-5-yl)pyrrolidine-2-car-
boxylic acid trifluoroaceate (3f-A). 30A (140 mg, 0.334 mmol) was
dissolved in dioxane (840 μL). To this was added 1 N NaOH (1.70
mL, 1.67 mmol), and the reaction mixture was stirred at 80 °C
overnight. The mixture was allowed to cool to rt. Water (10 mL) and
EtOAc (10 mL) were added and the aqueous layer was acidified with
1 N HCl to pH 2. The aqueous layer was extracted with EtOAc (3 ×
3
5.8, 31.0, 30.4, 28.6, 28.5, and 28.2 ppm. LC-MS (m/z) calcd for
+
+
C H NO [M + H] 298.2, found [M-Boc-tBu-tBu+H] 142.4.
16
27
4
Di-tert-butyl-(2S,3S)-3-((S)-3-bromo-4,5-dihydroisoxazol-5-yl)-
pyrrolidine-1,2-dicarboxylate (30A/B). Alkene 29 (150 mg, 0.503
mmol) was loaded in a vial and dissolved in EtOAc/H O (3 mL, 9:1).
To the colorless solution was added NaHCO (510 mg, 6.04 mmol)
2
10 mL), and the combined organic layers were dried over Na SO ,
3
2 4
and dibromoformaldoxime (410 mg, 2.02 mmol). The reaction
mixture was stirred vigorously at rt overnight. Then, water (10 mL)
was added and the aqueous layer was extracted with EtOAc (3 × 10
filtered, and concentrated in vacuo. The title compound was obtained
as a white foam (80 mg, 78%). The crude product was not further
purified and dissolved in DCM (1 mL) to which was added TFA (1
mL). The reaction mixture was stirred at rt overnight and then
mL). The combined organic layers were dried over MgSO , filtered,
4
and concentrated in vacuo. The crude material was purified by flash
column chromatography on silica gel (heptane:EtOAc, 3:1 v/v) to
afford two C1′ diastereomers of the title compound. The major
diastereomer (30A) was obtained as a colorless oil (139 mg, 0.332
mmol, 66%). The minor diastereomer (30B) was obtained as a
concentrated to dryness. The product was obtained as a white solid
1
(51.0 mg, 0.169 mmol, 51% over 2 steps). H NMR (600 MHz, D
O)
2
δ 5.04 (m, 1H), 4.25 (d, J = 7.4 Hz, 1H), 3.57−3.41 (m, 3H), 3.10
(dd, J = 17.0, 8.6 Hz, 1H), 3.00−2.92 (m, 1H), 2.89 (dd, J = 17.1, 8.5
1
3
Hz, 1H), 2.33 (m, 1H), and 2.15 (m, 1H) ppm. C NMR (151 MHz,
1
D O) δ 173.5, 171.3, 163.0 (q, TFA), 116.3 (q, TFA), 79.9, 60.6,
colorless oil as well (70 mg, 0.166 mmol, 33%). 30A: H NMR (600
2
4
5.7, 45.1, 35.8, and 24.7 ppm. LC-MS (m/z) calcd for C H N O
MHz, CDCl ) (mixture of rotamers) δ 4.70 (m, 0.6H), 4.61 (m,
8 12 2 4
3
+
[M + H] 201.2, found 201.5.
0
.4H), 3.90 (d, J = 4.5 Hz, 0.4H), 3.85 (d, J = 5.0 Hz, 0.6H), 3.65−
(2S,3S)-3-(3-Hydroxy-4,5-dihydroisoxazol-5-yl)pyrrolidine-2-car-
3
.61 (m 0.6), 3.55−3.44 (m, 1.4H), 3.40−3.34 (m, 1H), 3.11−3.04
boxylic acid trifluoroaceate (3f-B). 30B (70.0 mg, 0.167 mmol) was
dissolved in dioxane (842 μL). To this was added 1 N NaOH (0.84
mL, 0.835 mmol), and the reaction mixture was stirred at 80 °C
overnight. The mixture was allowed to reach rt. Water (10 mL) and
EtOAc (10 mL) were added and the aqueous layer was acidified with
1 N HCl to pH 2. The aqueous layer was extracted with EtOAc (3 ×
(
m, 1H), 2.43−2.38 (m, 1H), 2.13−2.02 (m, 1H), 1.99−1.87 (m,
1
H), 1.48 (s, 6H), 1.47 (s, 3H), 1.46 (s, 3H), and 1.44 (s, 6H) ppm.
13
C NMR (151 MHz, CDCl ) (mixture of rotamers) δ 171.3, 171.1,
3
1
6
2
54.4, 153.8, 137.5, 137.3, 82.6, 82.2, 82.0, 80.4, 80.2, 77.4, 77.2, 77.0,
2.1, 61.9, 48.7, 47.5, 45.9, 45.6, 45.6, 45.5, 29.9, 28.5, 28.2, 28.1,
1
6.9, and 25.6 ppm. 30B: H NMR (600 MHz, CDCl ) (mixture of
3
1
0 mL), and the combined organic layers were dried over Na SO ,
2 4
rotamers) δ 4.79−4.75 (m, 0.3H), 4.68 (dt, J = 10.7, 8.0 Hz, 0.7H),
filtered, and concentrated in vacuo. The title compound was obtained
as a white foam (41 mg, 80%). The crude product was not further
purified and dissolved in DCM (1 mL) to which was added TFA (1
mL). The reaction mixture was stirred at rt overnight and then
4
1
1
1
.11 (d, J = 4.0 Hz, 0.7H), 4.08 (d, J = 5.2 Hz, 0.3H), 3.60−3.49 (m,
.7H), 3.46−3.42 (m, 0.3H), 3.34−3.23 (m, 1H), 3.10−3.01 (m,
H), 2.55−2.50 (m, 1H), 2.11−2.04 (m, 1H), 1.78−1.70 (m, 0.3H),
.68−1.62 (m, 0.7H), 1.48 (s, 9H), 1.46 (s, 3H), and 1.44 (s, 6H)
concentrated to dryness. The product was obtained as a white solid
13
ppm. C NMR (151 MHz, CDCl ) (mixture of rotamers) δ 171.6,
1
3
(
25.0 mg, 0.083 mmol, 50% over 2 steps). H NMR (600 MHz, D O)
2
1
54.0, 137.1, 82.2, 81.8, 80.4, 80.1, 61.6, 61.4, 48.03 46.7, 45.8, 45.2,
δ 4.85 (m, 1H), 4.46 (d, J = 5.4 Hz, 1H), 3.49 (m, 2H), 3.12−3.03
4
5.0, 44.5, 29.9, 28.5, 28.2, 28.1, 26.9, and 26.0 ppm. LC-MS (m/z)
(
1
m, 2H), 2.88 (dd, J = 17.0, 8.3 Hz, 1H), 2.37−2.29 (m, 1H), and
+
calcd for C H BrN O [M + H] 419.1 and 421.1, found [M-Boc-
tBu+H] 263.4 and 265.4.
13
17
27
2
5
.95 (m, 1H) ppm. C NMR (151 MHz, D O) δ 176.1, 173.9, 163.0
+
2
(
q, TFA), 116.3 (q, TFA), 83.7, 63.0, 48.2, 47.1, 38.6, and 29.0 ppm.
Di-tert-butyl-(2S,3S)-3-((S)-3-(ethoxycarbonyl)-4,5-dihydroisoxa-
zol-5-yl)pyrrolidine-1,2-dicarboxylate (32A/B). Alkene 29 (100 mg,
+
LC-MS (m/z) calcd for C H N O [M + H] 201.2, found 201.5.
8
12
2
4
5
-((2S,3S)-2-Carboxypyrrolidin-3-yl)-4,5-dihydroisoxazole-3-car-
0
.335 mmol) was loaded into a vial and dissolved in EtOAc (670 μL).
boxylic acid hydrochloride (3g-A). Intermediate 32A (90.0 mg, 0.218
mmol) was dissolved in EtOH (2.20 mL) to which was added 1 N
NaOH (220 μL). The solution was stirred at rt overnight and then
concentrated to dryness. The residue was resuspended in water (10
mL) and EtOAc (10 mL). The aqueous layer was acidified with 1 N
HCl to pH 2 and then with EtOAc (3 × 10 mL). The combined
organic layers were dried over Na SO , filtered, and concentrated in
To this was added NaHCO (370 mg, 4.4 mmol,) and ethyl 2-chloro-
3
2
-(hydroxyimino)acetate (356 mg, 2.35 mmol). The suspension was
vigorously stirred at rt overnight. Water (10 mL) was added to the
reaction mixture, and the aqueous layer was extracted with EtOAc (3
×
10 mL). The combined organic layers were dried over MgSO4,
filtered, and concentrated in vacuo. The crude material was purified by
flash column chromatography on silica gel (heptane:EtOAc, 3:1 v/v)
to afford two C1′ diastereomers of the title compound. The major
diastereomer 32A was obtained as a colorless oil (91.0 mg, 0.221
mmol, 66%). The minor diastereomer 32B was obtained as a colorless
2
4
vacuo to afford the intermediate as a colorless oil (73.0 mg, 0.19
mmol, 86%). The compound was not further purified. The crude
mixture was dissolved in DCM (1 mL) to which was added TFA (1
mL). The reaction was stirred at rt for 20 h and subsequently
concentrated to dryness. 1 N HCl (2 mL) was added and the solution
was concentrated to dryness. The title compound was obtained as the
1
oil as well (46.0 mg, 0.111 mmol, 33%). 32A: H NMR (600 MHz,
CDCl ) (mixture of rotamers) δ 4.83 (m, 0.6H), 4.76 (m, 0.4H), 4.35
3
(
3
(
1
m, 2H), 3.96 (d, J = 4.4 Hz, 0.4H), 3.90 (d, J = 4.9 Hz, 0.6H) 3.65−
.62 (m, 0.6H), 3.56−3.45 (m, 1.4H), 3.38−3.32 (m, 1H), 3.09−3.04
m, 1H), 2.43−2.38 (m, 1H), 2.12−2.01 (m, 1H), 1.99−1.88 (m,
H), 1.48−1.46 (m, 12H), 1.44 (s, 6H), and 1.37 (t, J = 7.1 Hz, 3H)
1
HCl salt as a white solid (50.0 mg, 0.188 mmol, 86% over 2 steps). H
NMR (600 MHz, D O) δ 5.25 (ddd, J = 11.4, 7.5, 3.8 Hz, 1H), 4.19
2
(
d, J = 7.5 Hz, 1H), 3.55−3.47 (m, 2H), 3.43 (m, 1H), 3.16 (dd, J =
1
8.3, 7.5 Hz, 1H), 2.83 (m, 1H), 2.29−2.22 (m, 1H), and 1.89 (m,
13
ppm. C NMR (151 MHz, CDCl ) (mixture of rotamers) δ 171.3,
13
3
1H) ppm. C NMR (151 MHz, D O) δ 172.2, 164.2, 155.6, 82.6,
2
1
6
2
71.1, 160.6, 160.5, 154.4, 153.8, 151.7, 84.2, 83.8, 82.0, 80.4, 80.2,
6
1.9, 46.5, 45.5, 37.7, and 24.1 ppm. LC-MS (m/z) calcd for
2.4, 62.3, 62.1, 62.0, 48.9, 47.7, 45.6, 45.5, 37.9, 37.8, 28.5, 28.2,
+
C H N O [M + H] 229.1, found 229.5.
9
12
2
5
1
8.1, 26.7, 25.5, and 14.3 ppm. 32B: H NMR (400 MHz, CDCl )
3
5-((2S,3S)-2-Carboxypyrrolidin-3-yl)-4,5-dihydroisoxazole-3-car-
(
mixture of rotamers) δ 4.87−4.76 (m, 1H), 4.36 (m, 2H), 4.12−4.08
boxylic acid trifluoroacetate 3g-B). Intermediate 3B (45 mg, 0.109
mmol) was dissolved in EtOH (1.10 mL) to which was added 1 N
NaOH (110 μL). The solution was stirred at rt overnight and then
concentrated to dryness. The residue was resuspended in water (10
mL) and EtOAc (10 mL). The aqueous layer was acidified with 1 N
HCl to pH 2 and then extracted with EtOAc (3 × 10 mL). The
combined organic layers were dried over Na SO , filtered, and
(
1
1
m, 1H), 3.62−3.44 (m, 2H), 3.35−3.25 (m, 1H) 3.07−2.98 (m,
H), 2.54−2.50 (m, 1H), 2.12−2.03 (m, 1H), 1.77−1.63 (m, 1H),
13
.39−1.37 (m, 18H), and 1.36 (t, J = 7.1 Hz, 3H) ppm. C NMR
(
151 MHz, CDCl ) (mixture of rotamers) δ 171.6, 160.6, 154.0,
3
1
4
51.5, 84.2, 84.1, 81.8, 80.4, 80.1, 62.4, 62.3, 61.8, 61.5, 48.3, 47.0,
5.8, 45.2, 37.2, 36.8, 28.5, 28.1, 26.9, 26.0, and 14.3 ppm. LCMS (m/
2
4
+
+
z) calcd for C H N O [M + H] 413.2, found [M-Boc-tBu+H]
concentrated in vacuo to afford the intermediate as colorless oil (36.0
mg, 0.092 mmol, 85%). The compound was not further purified. The
20
32
2
7
2
57.5.
J
ACS Chem. Neurosci. XXXX, XXX, XXX−XXX