Preparation of shortened norbelladine analogs

Article abstract of DOI:10.3390/71000743

The preparation of N-[(2-bromo-5-hydroxy-4-methoxyphenyl)methyl]-N-[(4- hydroxyphenyl)methyl]formamide (5) and 2-bromo-5-hydroxy-α-[(4- hydroxyphenyl)-methyl]-4-methoxypropaneamide (10) is reported.

Full text of DOI:10.3390/71000743

Molecules 2002, 7, 743-750
molecules
ISSN 1420-3049
http://www.mdpi.org
Preparation of Shortened Norbelladine Analogs
Matthias Treu, Johannes Fröhlich and Ulrich Jordis*
Institute of Applied Synthetic Chemistry, Vienna University of Technology, A-1060 Vienna,
Getreidemarkt 9/163, Austria; Tel. +43 (1) 58801.15460, Fax +43(1)58801.15499,
* Author to whom correspondence should be addressed; email: ujordis@pop.tuwien.ac.at.
Received: 1 November 2001; in revised form 23 September 2002 / Accepted: 30 September 2002 /
Published: 31 October 2002
Abstract: The preparation of N-[(2-bromo-5-hydroxy-4-methoxyphenyl)methyl]-N-[(4-
hydroxyphenyl)methyl]formamide (5) and 2-bromo-5-hydroxy-α-[(4-hydroxyphenyl)-
methyl]-4-methoxypropaneamide (10) is reported.
Keywords: O-dealkylation, norbelladine analogs.
Introduction
One of the key steps of the industrial synthesis [1] of the anti-Alzheimer drug galanthamine
(Reminyl®, Nivalin®) [2] comprises a K3[Fe(CN)6] induced phenol oxidation tandem cyclization [3]. In
this reaction the 5-6-6-7 ring system is formed in one step starting from a suitable norbelladine
derivative. We tried to extend this cyclization reaction towards the construction of 5-6-6-6 ring systems
and prepared both N-[(2-bromo-5-hydroxy-4-methoxyphenyl)methyl]-N-[(4-hydroxyphenyl)methyl]-
formamide (5) and 2-bromo-5-hydroxy-α-[(4-hydroxyphenyl)methyl]-4-methoxypropaneamide (10) as
necessary intermediates. These intermediates were subjected to the conditions of the tandem
cyclization [1], however the desired ring contracted galanthamine analog could not be obtained.

Molecules, 2002, 7
744
OH
OH
H
O
OH
H
O
MeO
HO
HO
N
H
MeO
G
N
Me
norbelladine
(-)-galanthamine
desired galanthamine analogs
G = NMe, CHCONH2
The synthesized open chained norbelladine analogs 3 – 5, which retain the partial structure of
substituted benzylamines and thus are of potential pharmaceutical interest prompted this publication.
Results and Discussion
For the synthesis of diphenol compound (5) 1-bromo-2-(chloromethyl)-5-methoxy-4-(1-
methylethoxy)benzene (1) [4] was converted into an amine by reaction with potassium phthalimide
with subsequent hydrazinolysis and isolated as hydrochloride salt (2) with 79% yield. Reductive
amination of 4-hydroxybenzaldehyde with the free base of 2 using sodium borohydride gave rise to the
secondary amine (3) with 84% yield, which was reacted with ethyl formate in presence of catalytic
amount of 4-(N,N-dimethylamino)pyridine to give the amide (4) with 74% yield. Isopropyl ether
cleavage was performed under mild conditions in presence of the aryl-methy-ether substructure using
boron trichloride with 98% yield (see Scheme 1) to give diphenol 5 as colorless crystals.
Scheme 1
1. potassium
phthalimide
2. hydrazine
hydrate
1. 4-hydroxy-
benzaldehyde
2. NaBH4
Cl
HCl
NH2
Br
Br
Br
N
R2
79%
iPrO
OMe
HO
84%
iPrO
OMe
OMe
OR1
3 R1 = iPr, R2 = H
4 R1 = iPr, R2 = CHO
5 R1 = H, R2 = CHO
1
2
HCOOEt 74%
BCl3 98%
10 was prepared starting from 1-(chloromethyl)-4-(1-methylethoxy)benzene (6) [5]. Reaction with
dimethyl malonate and potassium carbonate gave 7 with a yield of 78%. The second alkylation step
using 1-bromo-2-(chloromethyl)-5-methoxy-4-(1-methylethoxy)benzene (1) gave the ester (8) which
was saponified and decarboxylated using a Kugelrohr apparatus. The obtained acid was converted into

Molecules, 2002, 7
745
the amide (9) by subsequent treatment with thionyl chloride and a saturated solution of ammonia in dry
formamide. Deprotection of 9, isolated as colorless crystals with 76% yield, using boron trichloride for
a selective isopropyl-aryl-ether cleavage gave rise to the norbelladine analog (10) with 93% yield (see
Scheme 2).
Scheme 2
dimethyl
malonate
COOMe
K2CO3
78%
Cl
COOMe
iPrO
iPrO
6
7
1. KOH
2.160 °C
3. SOCl2
Br
Br
COOMe
COOMe
CONH2
1, K2CO3
4. NH3
7
MeO
MeO
78%
82%
OiPr
OR
OiPr
OR
8
9 R = iPr
10 R = H
BCl3 93%
Tandem cyclization of 5 and 10 employing the conditions found to be optimal in the galanthamine
synthesis [1] failed (see Scheme 3).
Scheme 3
O
H
O
K3[Fe(CN)6]/
K2CO3
HO
MeO
G
MeO
G
Br
OH
Br
5 G = NCHO
10 CHCONH2
Conclusions
In summary, we have developed efficient and high yielding routes towards the preparation of N-[(2-
bromo-5-hydroxy-4-methoxyphenyl)methyl]-N-[(4-hydroxyphenyl)methyl]formamide (5) and 2-
bromo-5-hydroxy-α-[(4-hydroxyphenyl)methyl]-4-methoxypropaneamide (10). Attempts to convert

Molecules, 2002, 7
746
both 5 and 10 into their corresponding bromoformylnarwedine analogs failed. Scope and limitations of
this tandem cyclization were summarized elsewhere [6].
Experimental
General
1
Melting points were determined on a Kofler melting point apparatus. H- and 13C-NMR-spectra
were recorded on a Bruker AC-200 (200 MHz) pulse Fourier-transform NMR spectrometer in CDCl3
or DMSO-d6 using tetramethylsilane as an internal standard. Thin layer chromatography (TLC) was
performed on precoated plates (Merck TLC aluminum sheets silica 60 F254) with detection by UV light
or with phosphomolybdic acid in aqueous EtOH by heating. All reactions were magnetically stirred
under an argon atmosphere. MPLC (medium pressure liquid chromatography) was performed using
SiO2 (Baker), a LC-8A pump (Shimadzu), a SPD-6AV UV-detector (Shimadzu) and Büchi glass
columns.
2-Bromo-4-methoxy-5-(1-methylethoxy)benzenemethanamine hydrochloride (2). 1-Bromo-2-(chloro-
methyl)-5-methoxy-4-(1-methylethoxy)benzene (1) (5.00 g, 17.0 mmol) and potassium phthalimide
(3.47 g, 18.7 mmol) were stirred in dry DMF (60 mL) for 12 h at 60 °C. The suspension was filtered
and concentrated in vacuo, and the residue was partitioned between water (150 mL) and Et2O (150
mL). The aqueous layer was extracted with Et2O (2 x 100 mL), the combined organic layer was washed
with water (3 x 200 mL) and brine (1 x 200 mL), dried over Na2SO4, filtered and concentrated in
vacuo. The residue was refluxed with hydrazine hydrate (1.28 g, 25.5 mmol) in dry EtOH (100 mL) for
24 h, cooled to ambient temperature and filtered. The residue was extracted with boiling EtOH (2 x 25
mL), the combined extracts were added to the filtrate and concentrated in vacuo. The residue was
dissolved in Et2O (10 mL), cooled to 0 °C and treated with HCl/Et2O (satd. at 0 °C). The precipitated
hydrochloride salt was collected by filtration and triturated with dry Et2O (3 x 50 mL). Yield: colorless
needles (4.15 g, 79%), mp. 235-237 °C. TLC: Rf = 0.7 (CHCl3 - MeOH - conc. NH3 = 89:10:1); Anal.
Calcd for C11H16BrNO2*HCl: C, 42.54; H, 5.52; N, 4.51. Found: C, 42.24; H, 5.40; N, 4.36. 1H-NMR
(DMSO-d6): δ 8.73 (b, 3H), 7.41 (s, 1H), 7.18 (s, 1H), 4.61 (septet, J = 6.3 Hz, 1H), 4.03 (s, 2H),
3.86(s, 3H), 3.47(s, 2H), 1.22 (d, J = 6.3 Hz, 6H); 13C-NMR (DMSO-d6): δ 150.5 (s), 146.4 (s), 124.95
(s), 117.05 (s), 115.85 (d), 113.55 (d), 70.8 (d), 56.1 (q), 41.7 (t), 21.9 (2 q).
4-[[[2-Bromo-4-methoxy-5-(1-methylethoxy)phenylmethyl]amino]methyl]phenol (3). 2-Bromo-4-
methoxy-5-(1-methylethoxy)benzenemethanamine (2.28 g. 7.30 mmol, extracted from 2 by partitioning
the salt between CHCl3 and conc. NH3) and 4-hydroxybenzaldehyde (0.89 g, 7.30 mmol) in dry EtOH
(60 mL) were stirred under reflux for 6 h. The mixture was cooled to 0 °C, then sodium borohydride
(1.36 g, 36.5 mmol) was added and stirred for 30 min at this temperature and 1 h under reflux. 2 N HCl
(10 mL) was added, the mixture was concentrated to a volume of 5 mL, neutralized with satd. NaHCO3

Molecules, 2002, 7
747
and extracted with CHCl3 (4 x 50 mL). The combined organic layer was washed with satd. NaHCO3 (2
x 100 mL), water (1 x 100 mL) and brine (1 x 100 mL), dried over Na2SO4, filtered and concentrated in
vacuo. The residue was purified by MPLC (100 g SiO2, CHCl3 : MeOH : conc. NH3 = 89 : 10 : 1).
Yield: colorless crystals (2.34 g, 84%). An analytical sample was converted into the hydrochloride salt
by treatment with HCl/Et2O to give colorless crystals (mp. 211 - 215 °C). TLC: Rf = 0.55 (CHCl3 -
MeOH - conc. NH3 = 89:10:1); Anal. Calcd for C18H22BrNO3*HCl: C, 51.88; H, 5.56; N, 3.36. Found:
C, 51.93; H, 5.56; N, 3.31. 1H-NMR (DMSO-d6): δ 9.82 (b, 3H), 7.54 (s, 1H), 7.39 (d, J = 8.9 Hz, 2H),
7.17 (s, 1H), 6.82 (d, J = 8.9 Hz, 2H), 4.61 (septet, J = 6,7 Hz, 1H), 4.10 (s, 2H), 4.06 (s, 2H), 3.80 (s,
3H), 1.26 (d, J = 6,7 Hz, 6H); 13C-NMR (DMSO-d6): δ 158.1 (s), 150.8 (s), 146.3 (s), 131.8 (d), 123.1
(s), 121.5 (s), 117.7 (s), 115.8 (d), 115.4 (d), 114.4 (d), 70.8 (d), 56.0 (q), 49.4 (t), 48.3 (t), 21.9 (q).
N-[[2-Bromo-4-methoxy-5-(1-methylethoxy)phenyl]methyl]-N-[(4-hydroxyphenyl)-methyl]formamide
(4). Compound 3 (1.50 g, 3.94 mmol), 4-(dimethylamino)pyridine (50 mg), ethyl formate (1.4 mL),
formic acid (0.4 mL) and DMF (1.5 mL) were refluxed in dry dioxane for 6 h. The mixture was
concentrated in vacuo, and the residue was partitioned between water (50 mL) and EtOAc (50 mL).
The aqueous layer was extracted with EtOAc (3 x 20 mL), the combined organic layer was washed
with 2 N HCl (3 x 50 mL), water (1 x 50 mL), satd. NaHCO3 (2 x 50 mL) and brine (1 x 100 mL),
dried over Na2SO4, filtered and concentrated in vacuo. The residue was triturated with tert.-
butylmethylether (5 mL). Yield: colorless crystals (1.19 g, 74%), mp. 125 - 128 °C. TLC: Rf = 0.5
(CHCl3 - MeOH - conc. NH3 = 89:10:1); Anal. Calcd for C19H22BrNO4: C, 55.89; H, 5.43; N, 3.43.
1
Found: C, 55.91; H, 5.43; N, 3.44. H-NMR (DMSO-d6): δ 9.46 and 9.38 (s, 1H), 8.46 and 8.40 (s,
1H), 7.12 and 7.10 (s, 1H), 7.03 and 6.99 (d, J = 13.3 Hz, 2H), 6.78 (s, 1H), 6.73 and 6.99 (d, J = 13.3
13
Hz, 2H), 4.55 - 4.12 (m, 5H), 3.76 (s, 3H), 1.32 - 1.12 (m, 6H); C-NMR (DMSO-d6): δ 163.5 and
163.3 (d), 157.0 and 156.6 (s), 150.4 and 150.0 (s), 146.3 (s), 129.1 (s), 127.0 and 126.7 (d), 126.9 and
126.6 (s), 117.2 and 116.4 (s), 116.2 and 116.1 (d), 115.4 and 115.2 (d), 113.7 and 113 (d), 70.9 (d),
55.9 (q), 49.7 (t), 44.4 and 43.9 (t), 21.8 and 21.7 (q).
N-[(2-Bromo-5-hydroxy-4-methoxyphenyl)methyl]-N-[(4-hydroxyphenyl)methyl]formamide (5). To 4
(1.0 g, 2.45 mmol) in dry CH2Cl2 (5 mL) BCl3 (10 mL, 10 mmol, 1 M in CH2Cl2) was added at -78 °C
and stirred for 4 h at ambient temperature. Water (20 mL) was added dropwise, and the mixture was
concentrated in vacuo to a volume of 15 mL. The precipitate was collected by filtration and triturated
with water (6 x 20 mL) and iPr2O (2 x 10 mL). Yield: colorless crystals (879 mg, 98%), mp. 94 - 96
°C. TLC: Rf = 0.2 (CHCl3 - MeOH - conc. NH3 = 89:10:1); Anal. Calcd for C16H16BrNO4: C, 52.84; H,
1
4.40; N, 3.82. Found: C, 52.65; H, 4.61; N, 3.67. H-NMR (DMSO-d6): δ 9.50 (b, 1H), 9.40 (b, 1H),
8.50 and 8.40 (s, 1H), 7.31 - 6.81 (m, 3H), 6.81 - 6.55 (m, 3H), 4.51 - 4.11 (m, 4H), 3.79 (s, 3H);
13C-NMR (DMSO-d6): δ 163.5 and 163.3 (d), 157.1 and 156.7 (s), 148.3 and 147.9 (s), 146.5 (s)129.3
and 129.2 (s), 127.2 and 127.1(d), 126.6 and 126.5 (s), 116.7 and 116.3 (s), 116.0 and 115.8 (d), 115.5
and 115.4 (d), 111.1 and 110.6 (d), 56.1 (q), 49.5 and 49.2 (t), 43.7 and 43.6 (t).

Molecules, 2002, 7
748
2-[4-(1-Methylethoxy)phenylmethyl]propandioic acid dimethylester (7). 1-(Chloromethyl)-4-(1-
methylethoxy)benzene (6) (20.5 g, 111 mmol), dimethyl malonate (102.5 g, 776 mmol) and potassium
carbonate (46.5 g, 332 mmol, anhydrous, freshly ground) in dry DMF (250mL) were stirred for 24 h at
70 °C. The suspension was filtered and concentrated, and the residue was partitioned between water
(250 mL) and Et2O (250 mL). The aqueous layer was extracted with Et2O (2 x 50 mL), the combined
organic layer was washed with water (3 x 200 mL) and brine (1 x 150 mL), dried over Na2SO4, filtered
and concentrated in vacuo. The excess of dimethylmalonate was removed by distillation (160 °C/15
mbar), and the crude product was purified by kugelrohr distillation (130 °C/0.001 mbar). Yield:
colorless oil (23.6 g, 78%). TLC: Rf = 0.8 (petroleum ether - EtOAc = 9:1); Anal. Calcd for C15H20O5:
C, 64.27; H, 7.19. Found: C, 64.28; H, 7.07. 1H-NMR (CDCl3): δ 7.07 (d, J = 7.6 Hz, 2H), 6.76 (d, J =
7.6 Hz, 2H), 4.48 (septet, J = 6.0 Hz, 1H), 3.67 (s, 6H), 3.61 (t, J = 8.0 Hz, 1H), 3.12 (d, J = 8.0 Hz,
2H), 1.29 (d, J = 6.0 Hz, 6H); 13C-NMR (CDCl3): δ 169.1 (s), 156.6 (s), 129.6 (d), 129.4 (s), 115.8 (d),
69.6 (d), 53.7 (d), 52.3 (q), 33.8 (t), 21.9 (q).
2-[[2-Bromo-4-methoxy-5-(1-methylethoxy)phenyl]methyl]-2-[[4-(1-methylethoxy)phenyl]methyl]-
propanedioic acid dimethylester (8). Compound 7 (2.50 g, 8.92 mmol), 1-bromo-2-chloromethyl-5-
methoxy-4-(1-methylethoxy)benzene (1) (2.62 g, 8.92 mmol) and potassium carbonate (3.71 g, 26.8
mmol, anhydrous, freshly ground) in dry acetonitrile (100 mL) were stirred for 24 h at 60 °C. The
suspension was filtered and concentrated, and the residue was partitioned between water (100 mL) and
Et2O (100 mL). The aqueous layer was extracted with Et2O (1 x 50 mL), the combined organic layer
was washed with water (3 x 100 mL) and brine (1 x 100 mL), dried over Na2SO4, filtered and
concentrated in vacuo. The crude product was purified by kugelrohr distillation (180 °C/0.01 mbar).
Yield: colorless oil (3.93 g, 82%). TLC: Rf = 0.5 (petroleum ether - EtOAc = 9:1); 1H-NMR (CDCl3): δ
7.02 (d, J = 8.1 Hz, 2H), 7.00 (s, 1H), 6.89 (s, 1H), 6.78 (d, J = 8.1 Hz, 2H), 4.58 - 4.31 (m, 2H), 3.78
(s, 3H), 3.59 (s, 6H), 3.37 (s, 2H), 3.26 (s, 2H), 1.37 - 1.26 (m, 12H); 13C-NMR (CDCl3): δ 171.2 (s),
156.8 (s), 149.5 (s), 146.1 (s), 130.9 (d), 128.1 (s), 127.8 (s), 118.0 (s), 116.1 (s), 115.8 (d), 115.5 (d),
71.3 (d), 69.7 (d), 60.2 (s), 56.0 (q), 52.2 (q), 39.9 (t), 38.6 (t), 22.0 (q), 21.9 (q).
2-Bromo-4-methoxy-5-(1-methylethoxy)-α-[[4-(1-methylethoxy)phenyl]methyl]-benzenepropanamide
(9). Compound 8 (3.93 g, 7.31 mmol) and KOH (1.50 g, 26.8 mmol) were stirred in EtOH (50
mL)/water (5 mL) under reflux for 12 h. The solution was concentrated to 5 mL in vacuo, a pH < 1 was
adjusted by dropwise addition conc. HCl, and the mixture was partitioned between water (100 mL) and
Et2O (100 mL). The aqueous layer was extracted with Et2O (2 x 50 mL), the combined organic layer
was washed with water (3 x 100 mL) and brine (1 x 100 mL), dried over Na2SO4, filtered and
concentrated in vacuo. The residue was decarboxylated using a kugelrohr apparatus (160 °C, 30 min),
and the formed carboxylic acid was purified by subsequent distillation (165 °C/0.01 mbar). The
distillate was dissolved in thionyl chloride (10 mL), then DMF (100 µL) was added and stirred for 6 h

Molecules, 2002, 7
749
at ambient temperature. The mixture was concentrated in vacuo, dissolved in dry formamide, cooled to
0 °C and treated with a solution of NH3 in formamide (20 mL, saturated at 0 °C). The mixture was
stirred for 1 h and poured into water (500 mL). The precipitate was collected by filtration and triturated
with water (5 x 100 mL). Yield: colorless crystals (2.58 g, 76%), mp. 129 - 131 °C. TLC: Rf = 0.7
(CH2Cl2 - MeOH = 9:1); Anal. Calcd for C23H30BrNO4: C, 59.49; H, 6.51; N, 3.02. Found: C, 59.22;
H, 6.24; N, 2.90. 1H-NMR (DMSO-d6): δ 7.22 (b, 1H), 7.10 (d, J = 8.1 Hz, 2H), 7.07 (s, 1H), 6.88 (s,
1H), 6.80 (d, J = 8.1 Hz, 2H), 6.71 (b, 1H), 4.76 - 4.46 (m, 2H), 3.39 (s, 3H), 2.98 - 2.34 (m, 5H), 1.38
- 1.07 (m, 12H); 13C-NMR (DMSO-d6): δ 175.5 (s), 155.8 (s), 149.1 (s), 145.8 (s), 131.4 (s), 131.0 (s),
129.9 (d), 118.1 (s), 115.9 (d), 115.4 d), 114.1 (d), 70.7 (d), 69.0 (d), 55.8 (q), 48.0 (d), 37.6 (t), 37.0
(t), 22.0 (q), 21.9 (q), 21.8 (q).
2-Bromo-5-hydroxy-α-[(4-hydroxyphenyl)methyl]-4-methoxypropanamide (10). To 9 2.00 g, 4.31
mmol) in dry CH2Cl2 (30 mL) BCl3 (10 mL, 16 mmol, 1.6 M in CH2Cl2) was added at -78 °C and
stirred for 1 h at this temperature and for additional 2 h at ambient temperature. Water (100 mL) was
added dropwise, and the mixture was concentrated in vacuo to a volume of 80 mL. The precipitate was
collected by filtration and triturated with water (6 x 50 mL) and iPr2O (2 x 10 mL). Yield: colorless
crystals (1.52 g, 93%), mp. 174 - 176 °C. TLC: Rf = 0.4 (CH2Cl2 - MeOH = 9:1); Anal. Calcd for
C17H18BrNO4: C, 53.70; H, 4.77; N, 3.68. Found: C, 53.48; H, 4.66; N, 3.50. 1H-NMR (DMSO-d6): δ
9.21 (b, 2H), 7.21 (b, 1H), 7.13 - 6.89 (m, 3H), 6.87 - 6.51 (m, 4H), 3.72 (s, 3H), 2.93 - 2.30 (m, 5H);
13C-NMR (DMSO-d6): δ 175.9 (s), 155.6 (s), 147.1 (s), 145.8 (s), 131.4 (s), 130.0 (d), 129.9 (s), 118.0
(s), 115.9 (d), 115.1 (d), 112.0 (d), 56.0 (q), 48.2 (d), 37.7 (t), 37.1 (t).
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