Synthesis of deuterium-labelled (-)-galanthamine

Article abstract of DOI:10.1002/jlcr.1510

The synthesis of deuterium-labelled galanthamine is reported. 6-[ ²H₃]methoxy-N-[²H₃]methyl-(-)- galanthamine was obtained in seven steps from galanthamine. The synthesis was carried out by selective O- and N-de

Full text of DOI:10.1002/jlcr.1510

Research Article
Received 9 January 2008,
Revised 31 January 2008,
Accepted 2 February 2008
Published online 27 March 2008 in Wiley Interscience
(www.interscience.wiley.com) DOI: 10.1002/jlcr.1510
Synthesis of deuterium-labelled (ꢀ)-
galanthamine
Ã
Julien Rouleau, and Catherine Guillou
The synthesis of deuterium-labelled galanthamine is reported. 6-[2H3]methoxy-N-[2H3]methyl-(ꢀ)-galanthamine was
obtained in seven steps from galanthamine. The synthesis was carried out by selective O- and N-demethylations. The [2H3]-
N-methyl and [2H3]-O-methyl-groups were introduced by selective aminoreduction and O-methylation.
Keywords: deuterium labelling; galanthamine; sanguinine; norsanguinine
(ꢀ)-galanthamine 8, which could be a useful compound for
biological studies.
Introduction
(ꢀ)-Galanthamine 1,1 a tertiary alkaloid isolated from Amarylli-
daceae, is a centrally acting, competitive and reversible inhibitor
of acetylcholinesterase that enhances cognitive functions in
Alzheimer’s patients.2 Furthermore, galanthamine is also an
allosteric potentiating ligand of nicotinic receptor.3 This drug is
the most recently approved acetylcholinesterase inhibitor for
use in the United States and Europe. In continuation of our work
in the galanthamine series, we report the synthesis of
deuterium-labelled (ꢀ)-galanthamine, which will be useful for
biological studies. The introduction of six atoms of deuterium on
galanthamine would permit a better detection of this com-
pound by a method based on deuterium’s analysis.
Experimental
General
Proton nuclear magnetic resonance (1H NMR) spectra were
acquired at 300 MHz and 13C NMR were acquired at 75 MHz on a
Bruker Avance-300 spectrometer. Chemical shifts (d) are
reported in ppm relative to CHCl3 (7.27 and 77.0 ppm). Mass
spectra (MS) and high-resolution mass spectra (HRMS) were
determined on an electrospray ionization-time-of-flight (ESI-
TOF) Thermoquest AQA Navigator mass spectrometer. Infrared
(IR) spectra were recorded using a Fourier Perkin Elmer
Spectrum BX Fourier transform-infrared (FT-IR) spectrometer.
All reactions were performed in anhydrous solvents under an
inert atmosphere (argon). Dichloromethane was distilled from
P2O5, tetrahydrofuran (THF) from sodium/benzophenone and
DMF from MgSO4. MeOH, EtOH and all reagents were of the
highest commercially available purity. All separations were
carried out under flash chromatographic conditions on Merck
silica gel 60 (70-230 mesh) at medium pressure (200 mbar). Thin-
layer chromatography (TLC) was performed on Merck silica gel
plates (60F254) with a fluorescent indicator.
Results and discussion
During the preparation of hexadeuterated (ꢀ)-galanthamine,
the formation of a quaternary ammonium must be avoided.
Thus, (ꢀ)-galanthamine 1 was first selectively demethylated by
reaction with L-selectride to give 6-demethylgalanthamine 2
(sanguinine) in high yield (98%).4 The second step of the
synthesis is the previously unknown N-demethylation of
sanguinine 2. Sanguinine 2 was first quantitatively converted
into its N-oxide 3 by oxidation with m-chloroperbenzoic acid
(mCPBA) in dichloromethane at room temperature. Subsequent
treatment of 3 with a (2/1) mixture of ferrous sulphate
heptahydrate and ferric chloride in methanol at 101C provided
norsanguinine 4.5 Protection of the amine function of 4 with di-
tert-butyl dicarbonate furnished compound 5 (81%). Alkylation
of 5 with (CD3O)2SO in dimethylformamide (DMF) in the
presence of cesium carbonate afforded N-BocOCD3 norgalantha-
mine 6. After removal of the N-Boc group of 6, the resulting
amine 7 was treated with deuterated formaldehyde, acetic acid-
d and NaBD4 to afford hexadeuterated (ꢀ)-galanthamine 8
quantitatively.
Synthesis of (4aS,6R,8aS)-11-methyl-5,6,9,10,11,12-hexahydro-4aH-
[1]benzofuro[3a,3,2-ef][2]benzazepine-3,6-diol or sanguinine (2)
A suspension of galanthamine hydrobromide 1 (654 mg) in
CH2Cl2 was washed with saturated aqueous NaHCO3 (30 ml). The
aqueous layer was extracted three times with CH2Cl2 (30 ml).
The organic layers were combined, dried over MgSO4 and
evaporated. The residue was dissolved in THF (20 ml) and a
CNRS, Institut de Chimie des Substances Naturelles, Bt 27, Avenue de la Terrasse,
91198 Gif-sur-Yvette, France
In summary, hexadeuterated (ꢀ)-galanthamine 8 was synthe-
sized in seven steps with an overall yield of 25% from natural
(ꢀ)-galanthamine 1. This is the first synthesis of hexadeuterated
*Correspondence to: Catherine Guillou, CNRS, Institut de Chimie des Substances
Naturelles, Bt 27, Avenue de la Terrasse, 91198 Gif-sur-Yvette, France.
E-mail: guillou@icsn.cnrs-gif.fr
J. Label Compd. Radiopharm 2008, 51 236–238
Copyright r 2008 John Wiley & Sons, Ltd.

J. Rouleau and C. Guillou
O
CH3
N
CH3
N
CH3
N
L-Selectride
mCPBA
CH2Cl2
OH
OH
OH
THF
98%
O
O
O
OH
OCH3
OH
2
1 : (-)-galantamine
3
Fe(II)/Fe(III)
MeOH
51%
Boc
N
Boc
N
H
N
(CD3O)2SO
Boc2O
OH
OH
OH
Cs2CO3, DMF
MeOH
81%
O
80%
O
O
OCD3
OH
OH
6
5
4
CH2Cl2/TFA
76%
CD3
N
H
N
CD2O, CH3COOD
NaBD4
OH
OH
O
O
100%
OCD3
OCD3
8
7
solution 1 M of L-selectride (8.8 ml, 8.8 mmol) in THF was slowly and the mixture was allowed to warm up to 101C. After 3 h,
added at room temperature. The mixture was stirred at 651C for saturated aqueous NaHCO3 (1 ml) was added and the mixture
24 h. After cooling, the excess of L-selectride was neutralized was filtered through a pad of celite. After removal of the
with methanol and then with water. After a filtration on celite, solvents, the residue was purified by silica gel flash-column
the solvents were evaporated under vacuum. Silica gel flash- chromatography (elution with CH2Cl2/MeOH/28% aqueous
column chromatography (CH2Cl2/MeOH/28% aqueous ammo- ammonia: 89/10/1) to give the desired compound 4 as an
1
nia: 94/5/1) of the residue afforded the desired compound 2 as a amorphous solid (38 mg; 51% yield). H NMR (300 MHz, CD3OD)
colourless oil (478 mg; 98%). 1H NMR (300 MHz, CDCl3) d: 6.56 d: 6.54 (2H, m, H71H8), 6.08 (1H, d, J1–2 = 10.1 Hz, H1), 5.88 (1H,
(1H, d, J8–7 = 8.0 Hz, H8), 6.50 (1H, d, J7–8 = 8.0 Hz, H7), 6.09 (1H, d, d, J2–1 = 10.1, J2–3 = 4.5 Hz, H2), 4.48 (1H, bs, H4a), 4.14 (1H, bt,
J1–2 = 10.3 Hz, H1), 5.88 (1H, dd, J2–1 = 10.3, J2–3 = 4.8 Hz, H2), 4.49 J = 4.5 Hz, H3), 4.08 (1H, d, Jgem = 15.4 Hz, H9a), 3.92 (1H, d,
(1H, bs, H4a), 4.13 (1H, bt, J = 4.8 Hz, H3), 4.04 (1H, d, gem = 15.4 Hz, H9b), 3.28 (2H, m, H11a1H11b), 2.47 (1H, dm,
J
J
gem = 15.0 Hz, H9a), 3.62 (1H, d, Jgem = 15.0 Hz, H9b), 3.20 (1H, J = 14.8 Hz, H4a), 2.07 (1H, dm, Jgem = 14.8 Hz, H4b), 1.83 (2H, m,
m, H11a), 2.99 (1H, dm, Jgem = 14.5 Hz, H11b), 2.48 (1H, dm, H12a, H12b). 13C NMR (75 MHz, CD3OD) d: 147.2 (C6), 142.8
J = 15.6 Hz, H4a), 2.35 (3H, s, NMe), 2.02 (2H, m, H4b, H12a), 1.62 (C5a), 134.2 (C8b), 129.5 (C8a), 128.6 (C1), 128.2 (C2), 122.2 (C8),
(1H, dm, J = 13.9 Hz, H12b). 13C NMR (75 MHz, CDCl3) d: 146.7 116.8 (C7), 88.5 (C4a), 62.4 (C3), 53.7 (C9), 49.8 (C4b), 47.4 (C11),
(C6), 142.3 (C5a), 134.2 (C8b), 128.6 (C2), 128.1 (C1), 128.0 (C8a), 39.3 (C12), 31.2 (C4). MS (ESI, m/z) 260.1 (M1H). HRMS (ESI)
123.1 (C8), 116.7 (C7), 88.8 (C4a), 62.5 (C3), 61.5 (C9), 55.1 (C11), calcd. for C15H18NO13 : 260.1287, found: 260.1284. IR n (cmꢀ1):
49.3 (C4b), 42.9 (NMe), 35.3 (C12), 31.3 (C4). MS (ESI, m/z) 274.1 3220, 3025, 2920, 2847, 1616, 1234.
(M1H). HRMS (ESI) calcd. for C16H20NO13 : 274.1443, found:
274.1430. IR n (cmꢀ1): 3030, 2920, 2888, 1621, 1235.
Synthesis of tert-butyl(4aS,6R,8aS)-3,6-dihydroxy-5,6,9,10-tetrahy-
dro-4aH-[1]benzofuro[3a,3,2-ef][2]benzazepine-11 (12H)-carboxy-
late or N-Boc-sanguinine (5)
Synthesis of (4aS,6R,8aS)-5,6,9,10,11,12-hexahydro-4aH- [1]benzo-
furo[3a,3,2-ef] [2]benzazepine-3,6-diol or N-desmethylsanguinine
(4)
Di-tert-butyl dicarbonate (289 ml, 1.3 mmol) was added to a
solution of N-desmethylsanguinine 4 (292 mg, 1.1 mmol) in
ethanol (1 ml). The mixture was stirred at room temperature
overnight. After evaporation of the solvent, the residue was
dissolved in CH2Cl2 (20 ml) and washed with saturated aqueous
NaHCO3 (20 ml) and then brined (20 ml). The organic layer was
separated and each aqueous layer was extracted three times
mCPBA (71 mg, 0.29 mmol) was added to
a solution of
sanguinine 2 (79 mg, 0.29 mmol) in CH2Cl2 (8 ml) at 01C. The
mixture was stirred at 01C for 1 h. Methanol (2 ml), FeSO4
(161 mg, 0.58 mmol) and FeCl3 (78 mg, 0.29 mmol) were added
J. Label Compd. Radiopharm 2008, 51 236–238
Copyright r 2008 John Wiley & Sons, Ltd.
www.jlcr.org

J. Rouleau and C. Guillou
with CH2Cl2 (20 ml). The organic layers were combined, dried ddd,
over MgSO4 and evaporated. Silica gel flash-column chromato-
J
gem = 13.8, J = 3.8, J = 2.4 Hz, H12a), 1.75 (1H, ddd,
J
gem = 13.8, J = 11.7, J = 3.6 Hz, H12b). 13C NMR (75 MHz, CDCl3)
graphy (elution with CH2Cl2/MeOH/28% aqueous ammonia: 97/ d: 146.2 (C6), 144.1 (C5a), 133.1 (C8b), 132.1 (C2), 127.7 (C1),
2/1) of the residue afforded the expected compound 5 as an 126.8 (C8a), 120.8 (C8), 111.1 (C7), 88.5 (C4a), 61.9 (C3), 53.5 (C9),
amorphous solid (327 mg; 81%). 1H NMR (333 K, 300 MHz, 48.6 (C4b), 46.8 (C11), 39.8 (C12), 29.9 (C4). MS (ESI, m/z) 277.1 (M
CD3CN) d: 6.58 (2H, m, H7, H8), 6.01 (1H, d, J1–2 = 10.3 Hz, H1), 1H). HRMS (ESI) calcd. for C16H217H3NO31: 277.1631, found:
5.90 (1H, dd, J2–1 = 10.3, J2–3 = 4.5 Hz, H2), 4.66 (1H, m, H9a), 4.51 277.1629. IR n (cmꢀ1): 2920, 1682, 1274.
(1H, bs, H4a), 4.16 (1H, m, H9b), 4.10 (1H, m, H11a), 4.08 (1H, m,
H3), 3.37 (1H, m, H11b), 2.46 (1H, dm, Jgem = 15.7 Hz, H4a), 2.05 (4aS,6R,8aS)-3-[2H3]methoxy-11-[2H3]methyl-5,6,9,10,11,12-hexa-
hydro-4aH-[1] benzofuro[3a,3,2-ef][2]benzazepin-6-ol or (ꢀ)-6-
(1H, ddd, Jgem = 15.7, J = 5.3, J = 2.6 Hz, H4b), 1.84 (1H, m, H12a),
1.71 (1H, m, H12b), 1.35 (9H, s, H30, H40, H50). 13C NMR (333 K,
75 MHz, CD3CN) d: 156.0 (C10), 147.1 (C6), 141.8 (C5a), 133.9
(C8b), 130.9 (C8a), 128.9 (C2), 128.3 (C1), 122.2 (C8), 116.6 (C7),
89.1 (C4a), 80.2 (C20), 62.7 (C3), 52.4 (C9), 49.9 (C4b), 46.5 (C11),
38.0 (C12), 31.4 (C4), 29.0 (C30, C40, C50). MS (ESI, m/z) 382.1 (M1
Na). HRMS (ESI) calcd. for C20H25NO5Na1: 382.1630, found:
382.1635. IR n (cmꢀ1): 2976, 2925, 1688, 1682, 1237.
[2H3]methoxy-N-[2H3]methyl-galanthamine (8)
Formaldehyde-d2 (30 ml, 0.45 mmol, 30% in water) and acetic
acid-d (26 ml, 0.45 mmol) were added to a solution of 6-
[2H3]methoxynorsanguinine 7 (25 mg; 0.09 mmol) in MeOH
(0.5 ml). The mixture was heated at 651C during 2 h and then
cooled to 01C. NaBD4 (11 mg, 0.27 mmol) was added and the
mixture was stirred for an additional 1 h at 01C. The reaction was
quenched by the addition of saturated aqueous NaHCO3. The
mixture was extracted with CH2Cl2. The combined organic layers
were washed with water, brined, dried (MgSO4) and evaporated
to yield the desired compound 8 as a colourless oil (26.5 mg;
Synthesis of tert-butyl(4aS,6R,8aS)-6-hydroxy-3-[2H3]methoxy-
5,6,9,10-tetrahydro-4aH-[1]benzofuro[3a,3,2-ef][2]benzazepine-11
(12H)-carboxylate or 6-[2H3]methoxy-N-Boc-norsanguinine (6)
Dimethylsulphate-d6 (41 ml, 0.45 mmol) and Cs2CO3 (405 mg, 100%). 1H NMR (300 MHz, CDCl3) d: 6.70 (1H, d, J8–7 = 8.2 Hz, H8),
1.2 mmol) were added to a solution of N-Boc-sanguinine 5 6.68 (1H, d,
J
J7–8 = 8.2 Hz, H7), 6.06 (1H, dd, J2–1 = 10.2,
(149 mg, 0.41 mmol) in DMF (3 ml). The mixture was stirred at 2–3 = 4.9 Hz, H2), 6.01 (1H, d, J1–2 = 10.2 Hz, H1), 4.64 (1H, bs,
room temperature overnight. After evaporation of the solvent, H4a), 4.27 (1H, d, Jgem = 15.3 Hz, H9a), 4.16 (1H, bt, J = 4.6 Hz, H3),
the residue was dissolved in CH2Cl2 (20 ml). The combined 3.86 (1H, d, Jgem = 15.3 Hz, H9b), 3.45 (1H, dd, Jgem = 13.4,
organic layers were washed with saturated aqueous NaHCO3 J = 13.1 Hz, H11a), 3.20 (1H, dm, Jgem = 13.4 Hz, H11b), 2.71 (1H,
(20 ml), brined (20 ml), dried (MgSO4) and evaporated. Silica gel dm, J = 15.9 Hz, H4a), 2.12 (1H, ddd,
Jgem = 13.4, J = 13.1,
flash-column chromatography (elution with CH2Cl2/MeOH/28% J = 2.7 Hz, H12a), 2.02 (1H, ddd, Jgem = 15.9, J = 5.2, J = 2.4 Hz,
aqueous ammonia: 94/5/1) of the residue afforded the expected H4b), 1.73 (1H, dm, Jgem = 13.4 Hz, H12b). 13C NMR (75 MHz,
compound 6 as an amorphous solid (125 mg; 80%). 1H NMR CDCl3) d: 146.0 (C6), 144.9 (C5a), 132.8 (C8b), 128.5 (C2), 125.8
(333 K, 300 MHz, CD3CN) d: 6.70 (2H, m, H7, H8), 6.03 (1H, d, (C1, C8a), 122.9 (C8), 111.6 (C7), 88.6 (C4a), 61.8 (C3), 59.4 (C9),
J
1–2 = 10.4 Hz, H1), 5.91 (1H, dd, J2–1 = 10.4, J2–3 = 4.5 Hz, H2), 4.69 53.1 (C11), 47.8 (C4b), 32.5 (C12), 29.8 (C4). MS (ESI, m/z) 316.2 (M
(1H, d, Jgem = 15.5 Hz, H9a), 4.52 (1H, bs, H4a), 4.20 (1H, d, 1Na), 294.2 (M1H). HRMS (ESI) calcd. for C117H125H6NO3Na1:
Jgem = 15.5 Hz, H9b), 4.12 (1H, m, H11a), 4.09 (1H, m, H3), 3.39 316.1796, found: 316.1793. IR n (cmꢀ1) 3026, 2913, 2856, 1621,
(1H, m, H11b), 2.46 (1H, m, H4a), 2.07 (1H, m, H4b), 1.85 (1H, m, 1288, 1265.
H12a), 1.73 (1H, m, H12b), 1.35 (9H, s, H30, H40, H50). 13C NMR
(333 K, 75 MHz, CD3CN) d: 156.6 (C10), 148.9 (C6), 146.2 (C5a),
134.7 (C8b), 132.4 (C8a), 129.9 (C2), 128.8 (C1), 122.7 (C8), 114.1
Acknowledgements
(C7), 89.7 (C4a), 81.1 (C20), 63.2 (C3), 53.1 (C9), 50.3 (C4b), 47.2
(C11), 38.9 (C12), 32.2 (C4), 29.6 (C30, C40, C50). MS (ESI, m/z) 399.2
The authors thank the CNRS for the financial support. Professor
J. Y. Lallemand is gratefully acknowledged for his interest in our
work. We would also like to thank R. H. Dodd for carefully
(M1Na). HRMS (ESI) calcd. for C121H224H3NO5Na1: 399.1975,
found: 399.1962. IR n (cmꢀ1): 2973, 2925, 1686, 1682, 1237.
reading the article and for his helpful comments.
Synthesis of (4aS,6R,8aS)-3-[2H3]methoxy-5,6,9,10,11,12-hexahy-
dro-4aH-[1]benzofuro[3a,3,2-ef][2]benzazepin-6-ol or 6-[2H3]meth-
oxynorsanguinine (7)
Trifluoroacetic acid (TFA) (3 ml) was added to a solution of 6-
[2H3]methoxy-N-Boc-norsanguinine
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of solvent under reduced pressure afforded the desired
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Copyright r 2008 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2008, 51 236–238