Journal of Medicinal Chemistry
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filtered through a pad of Celite and evaporated to produce 3.015 g of
crude amine ( )-4 as a colorless oil (97% yield). This product was
used in the next step without further purification. Rf = 0.44 (CH2Cl2/
MeOH/Et3N; 20:2:1, v/v/v). 1H NMR (400 MHz, CDCl3): δ =
1.00−1.14 (1 H, m), 1.37−1.49 (10 H, m), 1.60−1.80 (5 H, m), 2.25−
2.37 (1 H, m), 2.51−2.58 (1 H, m), 2.95−3.00 (2 H, m), 3.13−3.25 (1
H, m), 3.28−3.38 (5 H, m), 3.44−3.52 (2 H, m). HRMS (ESI+): m/z
calcd for C14H29N2O3 273.2178; found 273.2174.
Synthesis of 1H-Inden-2(3H)-one (5). A mixture of pyridinium
chlorochromate (6.426 g, 29.811 mmol, 2.0 equiv) and silica gel
(6.426 g, 70−230 mesh) was ground to a fine powder using a pestle
and mortar. The light-orange mixture was added to a 250 mL round-
bottomed flask with a stirring bar, and CH2Cl2 (80 mL) was added.
The resulting orange suspension was stirred at room temperature, and
2-indanol (2.000 g, 14.905 mmol, 1.0 equiv) was added in small
portions. After 130 min, the resulting dark-brown suspension was
diluted with Et2O (60 mL) and filtered under suction through a
was added again, and this procedure was repeated two more times.
After the final supernatant was removed, the solid residue was dried at
reduced pressure. Water (15 mL) and a stirring bar were added, and
the resulting solution was cooled to 0 °C and adjusted to pH 12 with 1
M aqueous NaOH. The mixture was transferred into a 50 mL
separating funnel, extracted with CH2Cl2 (2× 30 mL), dried over
anhydrous Na2SO4, and evaporated to produce 0.750 g of crude
secondary amine ( )-7 as a slightly brown oil (84% yield). This
product was used in the next step without further purification. Rf =
0.38 (CH2Cl2/MeOH/Et3N, 40:4:1, v/v/v). 1H NMR (400 MHz,
CDCl3): δ = 0.90−1.00 (1 H, m), 1.57−1.83 (6 H, m), 1.94−2.01 (1
H, m), 2.55 (2 H, d, J = 6.40 Hz), 2.77 (2 H, t, J = 5.15 Hz), 2.89−
2.98 (3 H, m), 3.03−3.21 (4 H, m), 3.36 (3 H, s), 3.50 (2 H, t, J =
5.14 Hz), 7.11−7.19 (4 H, m). HRMS (ESI+): m/z calcd for
C18H29N2O 289.2280; found 289.2273.
Synthesis of ( )-N-((1-(2,3-Dihydro-1H-inden-2-yl)piperidin-3-yl)-
methyl)-N-(2-methoxyethyl)-2-naphthamide [( )-1]. To a 50 mL
round-bottomed flask with a stirring bar, 2-naphthoic acid (0.423g,
2.457 mmol, 1.0 equiv) and CH2Cl2 (20 mL) were added at room
temperature. The resulting suspension was stirred, and Et3N (0.685
mL, 4.914 mmol, 2.0 equiv) was added dropwise. The solution was
stirred for 5 min before O-(benzotriazol-1-yl)-N,N,N′,N′-tetramethy-
luronium tetrafluoroborate (TBTU; 0.789 g, 2.457 mmol, 1.0 equiv)
was added in small portions. After 30 min, a solution of ( )-7 (0.709
g, 2.458 mmol, 1.0 equiv) in CH2Cl2 (10 mL) was added dropwise,
and the reaction mixture was stirred for 19 h. The solvent was
evaporated, the residue dissolved in EtOAc (60 mL), transferred into a
250 mL separating funnel, and extracted with H2O (2× 50 mL) and
then aqueous saturated NaHCO3 solution (50 mL), and dried over
anhydrous Na2SO4 and evaporated. The residue was purified by flash
column chromatography using CH2Cl2/MeOH (20:1, v/v) as the
eluent and then precipitated from Et2O to produce 0.391 g of amide
( )-1 as a white solid (36% yield). Rf = 0.48 (CH2Cl2/MeOH, 10:1,
Buchner funnel layered with silica gel (70−230 mesh) and Celite. The
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dark-brown precipitate was washed thoroughly with Et2O (3× 20 mL).
The combined filtrates were evaporated. The residue was purified by
flash column chromatography using Et2O/petroleum ether (1:4, v/v)
as the eluent, to produce 1.302 g of ketone 5 as a slightly golden oil
that solidified into a slightly yellow solid after cooling (66% yield). Rf =
0.46 (Et2O/petroleum ether, 1:1, v/v); mp 51−53 °C (lit.75 mp 52−
54 °C). 1H NMR (400 MHz, CDCl3): δ = 3.58 (4 H, s), 7.21−7.32 (4
H, m).
Synthesis of ( )-tert-Butyl (1-(2,3-Dihydro-1H-inden-2-yl)-
piperidin-3-yl)methyl(2-methoxyethyl)carbamate [( )-6]. To a 100
mL round-bottomed flask with a stirring bar, ( )-4 (1.094 g, 4.016
mmol, 1.0 equiv) and 1,2-dichloroethane (50 mL) were added at room
temperature. The resulting solution was stirred and agitated with a
stream of argon for 15 min. NaBH(OAc)3 (1.596 g, 7.530 mmol, 1.875
equiv), 5 (0.531 g, 4.018 mmol, 1.0 equiv), and AcOH (0.230 mL,
4.018 mmol, 1.0 equiv) were added, and the resulting suspension was
stirred under an atmosphere of argon for 72 h. The reaction mixture
was opened to the air and quenched with saturated aqueous NaHCO3
solution (50 mL). The mixture was transferred into a 250 mL
separating funnel, and CH2Cl2 (20 mL) was added. The separating
funnel was shaken vigorously, and the organic phase was separated,
dried over anhydrous Na2SO4, and evaporated. The residue was
purified by flash column chromatography using CH2Cl2/ MeOH
(30:1, v/v) as the eluent to produce 1.292 g of amine ( )-6 as a
slightly golden oil (83% yield). Rf = 0.50 (CH2Cl2/MeOH, 10:1, v/v);
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v/v); mp 54−57 °C [α]D 0.0 (c 0.285, CHCl3). IR (KBr): 3546,
3209, 2929, 2144, 1622, 1487, 1418, 1301, 1112, 827, 748, 482 cm−1.
1H NMR (400 MHz, DMSO-d6, 60 °C): δ = 0.93 (1 H, bs), 1.44−1.46
(1 H, m), 1.63 (2 H. bs), 1.98 (2 H, bs), 2.67−2.79 (4 H, m), 2.95−
3.00 (2 H, m), 3.15 (3 H, s), 3.23 (2 H, bs), 3.44 (6 H, bd), 7.08−7.13
(2 H, m), 7.16−7.21 (2 H, m), 7.40−7.43 (1 H, m), 7.54−7.60 (2 H,
m), 7.88 (1 H, s), 7.94−7.98 (3 H, m). 13C NMR (100 MHz, DMSO-
d6, 60 °C): δ = 24.00, 27.85, 34.24, 35.84, 35.90, 51.01, 54.68, 57.75,
65.98, 69.28, 123.75, 123.80, 124.06, 125.44, 125.79, 126.25, 126.43,
127.27, 127.53, 127.79, 131.93, 132.47, 134.25, 141.14, 141.16, 170.76.
HRMS (ESI+): m/z calcd for C29H35N2O2 443.2699; found 443.2696.
HPLC purity, 99% at 254.16 nm (method A, tR = 18.11 min).
Separation of (+)-1 and (−)-1 by Semipreparative Reverse-Phase
Chiral HPLC. The resolution of ( )-1 was accomplished by 65 runs of
method C. Eluates corresponding to the two chromatographic peaks
were pooled and evaporated to about 5 mL and then transferred to a
50 mL separating funnel. Water (6 mL) and aqueous saturated
NaHCO3 solution (6 mL) were added and extracted with CH2Cl2 (25
mL). The organic phase was dried over anhydrous Na2SO4 and
evaporated to produce 30.6 mg of the first-eluted enantiomer as a
colorless oil and 31.7 mg of the second-eluted enantiomer as a
colorless oil. Analytical reversed-phase chiral HPLC analysis (method
B, λ = 254.16 nm) of the first-eluted enantiomer gave an enantiomeric
excess (ee) of 100%, whereas the ee of the second-eluted enantiomer
was 98%. The specific rotation of the first-eluted enantiomer was
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[α]D 0.0 (c 0.300, CHCl3). IR (NaCl): 2930, 2359, 1692, 1463,
1
1414, 1365, 1170, 1117, 1010, 867, 743, 526 cm−1. H NMR (400
MHz, DMSO-d6, 60 °C): δ = 0.90−0.99 (1 H, m), 1.40 (9 H, s),
1.56−1.67 (2 H, m), 1.77−1.88 (2 H, m), 2.01−2.07 (1 H, m), 2.73−
2.81 (4 H, m), 2.95−3.02 (2 H, m), 3.10 (2 H, d, J = 6.90 Hz), 3.14−
3.15 (3 H, m), 3.25 (3 H, s), 3.28−3.31 (1 H, m), 3.41−3.44 (2 H, m),
7.07−7.12 (2 H, m), 7.15−7.19 (2 H, m). 13C NMR (100 MHz,
DMSO-d6, 60 °C): δ = 24.08, 27.70, 27.85, 35.92, 36.02, 46.29, 51.18,
54.95, 57.67, 66.13, 78.09, 123.76, 125.78, 141.04, 141.10, 154.52.
HRMS (ESI+): m/z calcd for C23H37N2O3 389.2804; found 389.2798.
HPLC purity, 99% at 210.16 nm (method A, tR = 19.61 min).
Synthesis of ( )-N-((1-(2,3-Dihydro-1H-inden-2-yl)piperidin-3-yl)-
methyl)-2-methoxyethanamine [( )-7]. To a 100 mL round-
bottomed flask equipped with a stirring bar, ( )-6 (1.203 g, 3.096
mmol, 1.0 equiv) and CH2Cl2 (50 mL) were added at room
temperature. The resulting solution was stirred and TFA (2.371 mL,
30.960 mmol, 10.0 equiv) was added dropwise. After 22 h, the reaction
mixture was evaporated. The residue was coevaporated with CH2Cl2
(2× 40 mL), followed by n-hexane (2× 50 mL). Et2O (50 mL) was
added to the oily residue, and the flask was placed in an ultrasonic bath
for 15 min. During this time, the oily residue transformed into a white
solid. The flask was removed from the ultrasonic bath, and the
precipitate was allowed to settle to the bottom of the flask. The
supernatant was removed, Et2O (30 mL) was added, and the flask was
placed back in the ultrasonic bath for 1 min. The flask was removed
from the ultrasonic bath, and the precipitate was allowed to settle to
the bottom of the flask. The supernatant was removed, Et2O (30 mL)
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[α]D −23.82 (c 0.250, CHCl3), while the specific rotation of the
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second-eluted enantiomer was [α]D +24.52 (c 0.260, CHCl3). The
analytical reversed-phase chiral HPLC retention times were (method
B, λ = 254.16 nm): (−)-1, 21.09 min; (+)-1, 22.36 min.
In Vitro Enzyme Inhibition Studies. Inhibitory Activity against
the Cholinesterases. The inhibitory activity of the compounds was
determined using the method of Ellman.51 5,5′-Dithiobis (2-
nitrobenzoic acid) (Ellman’s reagent, DTNB), butyrylthiocholine
(BTC), and acetylthiocholine (ATC) iodides were purchased from
Sigma-Aldrich (Steinheim, Germany). The lyophilized powders of
murine (m)AChE and recombinant huBChE were dissolved in 10 mM
MES buffer (pH 6.5) to give an enzyme stock solution of 4 mg/mL.
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dx.doi.org/10.1021/jm501195e | J. Med. Chem. 2014, 57, 8167−8179