Chemoenzymatic preparation of enantiopure isomers of 4-aminochroman-3-ol and 1-amino-1,2,3,4-tetrahydronaphthalen-2-ol

Article abstract of DOI:10.1002/ejoc.200600385

Enantiomerically pure N-protected cis-4-aminochroman-3-ol (key precursor in the synthesis of novel HIV second-generation protease inhibitors), its trans isomer and both cis- and trans-1-amino-1,2,3,4-tetrahydronaphthalen-2-ol, useful chiral catalysts in o

Full text of DOI:10.1002/ejoc.200600385

FULL PAPER
DOI: 10.1002/ejoc.200600385
Chemoenzymatic Preparation of Enantiopure Isomers of 4-Aminochroman-3-ol
and 1-Amino-1,2,3,4-tetrahydronaphthalen-2-ol
[a]
[a]
[a]
[a]
Verónica Recuero, Gonzalo de Gonzalo, Rosario Brieva, and Vicente Gotor*
Keywords: Antiviral agents / Hydrolases / Enzyme catalysis / Amino alcohols
Enantiomerically pure N-protected cis-4-aminochroman-3-ol
key precursor in the synthesis of novel HIV second-genera-
N-benzyloxycarbonyl-protected derivatives. Of the biocata-
lysts tested, Pseudomonas cepacea and Candida antarctica B
lipases showed excellent enantioselectivities in the acylation
processes depending on the reaction conditions employed.
(
tion protease inhibitors), its trans isomer and both cis- and
trans-1-amino-1,2,3,4-tetrahydronaphthalen-2-ol, useful chi-
ral catalysts in organic synthesis, have been successfully pre-
pared through a lipase-catalyzed kinetic acylation of the
alcohol moiety, employing as substrates the corresponding
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
Introduction
salts with (S)-mandelic acid and selective crystallization of
the mixture.
On the other hand, optically pure vicinal amino alcohols
[
7]
Vicinal amino alcohols have a well-established impor-
tance in organic and pharmaceutical chemistry. They are have been recognized as generally useful and versatile chiral
used as modulators of the potassium channel in cells, as auxiliaries for the preparation of enantiopure compounds.[
intermediates in the synthesis of σ- and κ-opiate receptors The most important applications of these compounds in-
8]
and as core moieties of antiviral agents.[ The amino clude the enantioselective addition of Et Zn to aldehydes,
1]
[9]
2
[
10]
alcohol structure is also found in biologically important the Diels–Alder reaction
and the enantioselective re-
duction of prochiral ketones with BH ·SMe . (1R,2S)-1-
[
2]
[11]
natural products.
3 2
One good example of 1,2-amino alcohols with pharma- Amino-1,2,3,4-tetrahydronaphthalen-2-ol has recently been
[
12]
ceutical properties are the HIV type-1 protease inhibitors. synthesized and applied to this last reaction
These compounds, such as Indinavir and L-754394, repre- (1S,2S) enantiomer has been described as a chiral auxiliary
and the
[
13]
sent a major advance in the treatment of HIV infection and in Reformatsky-type reactions.
[
3]
AIDS. However, a number of patients develop resistance
Taking into account the importance of the enantiopure
[4]
to these inhibitors through viral mutations. So, a second- 1,2-amino alcohol structures, the main aim of this paper
generation of protease inhibitors has been developed with was to develop a biocatalytic method for the preparation of
better pharmacokinetic parameters and improved activity optically pure cis- and trans-1-aminochroman-2-ol and 1-
against resistant mutants. These drugs are also 1,2-amino amino-1,2,3,4-tetrahydronaphthalen-2-ol.
alcohols with a structure similar to Indinavir, but with the
aminoindanol residue having been replaced by other benzo-
fused 1,2-amino alcohols, as for example, the aminochro-
manol analogue.
Results and Discussion
[
5]
Several approaches have been described for the prepara-
Synthesis of Substrates
tion of the optically pure cis-4-aminochroman-3-ol. Hansen
[
6]
et al. achieved an asymmetric synthesis in seven steps in
Racemic cis-1,2-amino alcohols were synthesized accord-
which the absolute stereochemistry of the molecule was de- ing to the procedure described by Davies and co-workers
III
[7]
rived from (salen)Co -catalyzed opening of methyl glycid- (Scheme 1). 4-Chromanone (1) and α-tetralone (5) were
ate with phenol. The enantiomers of (±)-cis-aminochro- converted by Moriarty oxidation into the α-hydroxy
[
14]
manol were separated by formation of the diastereomeric ketones (±)-2 and (±)-6, respectively.
Subsequent reac-
tion with hydroxylamine hydrochloride yielded the corre-
sponding α-hydroxy oximes (±)-3 and (±)-7; cis-selective hy-
Universitario de Biotecnología de Asturias, Universidad de drogenation of the α-hydroxy oximes catalyzed by palla-
[
a] Departamento de Química Orgánica e Inorgánica, Instituto
Oviedo,
dium on carbon using a methanol solution of HBr led to
the corresponding bromide salts of (±)-cis-4 and (±)-cis-8
in good overall yields.
3
3006 Oviedo, Asturias, Spain
Fax: +34-985103448
E-mail: vgs@fq.uniovi.es
4224
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 4224–4230

Enantiopure Isomers of 4-Aminochroman-3-ol and 1-Amino-1,2,3,4-tetrahydronaphthalen-2-ol
FULL PAPER
Scheme 1. Chemical synthesis of (± ±-cis-4 and (± ±-cis-8.
Scheme 2. Synthesis of (± ±-trans-4-(benzyloxycarbonylamino±chroman-3-ol [(± ±-trans-9].
Scheme 3. Chemical procedure for the preparation of (± ±-trans-1-amino-1,2,3,4-tetrahydronaphthalen-2-ol [(± ±-trans-8].
The highest yields for the preparation of racemic trans- the immobilized lipases from Candida antarctica (CAL-A,
4-(benzyloxycarbonylamino±chroman-3-ol
[(± ±-trans-9] CAL-B and CAL-B-L2±, Pseudomonas cepacia (PSL-C±,
were obtained by protection of (± ±-cis-4 with the benzyl- Candida rugosa (CRL± and porcine pancreatic lipase (PPL±.
[
15]
oxycarbonyl group
and Mitsunobu inversion of the cis- CAL-B and PSL-C exhibited the highest enantioselectivities
[
18]
N-protected amino alcohol, as shown in Scheme 2. In the (E = 40 and 63; Entries 2 and 4, respectively±, but moder-
preparation of trans-1-amino-1,2,3,4-tetrahydronaphthalen- ate reaction rates. Depending on the biocatalyst employed,
2-ol [(± ±-trans-8], a better overall yield was obtained by em- an opposite stereochemical preference was observed in the
ploying as starting material 1,2-dihydronaphathalene 10. resolution processes. CAL-A catalyzed the acylation of the
[
12a]
Epoxidation of the corresponding bromohydrin (± ±-11
(+±-(3R,4R± enantiomer, while with the other biocatalysts,
and subsequent epoxide ring opening of (± ±-12 with ammo- product 14 was obtained with the (–±-(3S,4S± configuration,
[
16]
nia in methanol
Scheme 3±.
led to the desired product (± ±-trans-8 with the (+±-(3R,4R± enantiomer of the unreacted substrate
9 remaining.
(
The influence of the organic solvent on the selectivity of
the transesterification reaction of (± ±-cis-9 catalyzed by
CAL-B (Entries 7–10± and PSL-C (Entries 13–16± was ex-
Enzymatic Resolution
The N-(benzyloxycarbonyl± derivatives (± ±-cis- and (± ±- amined under the same reaction conditions as shown be-
trans-9 and -13 were prepared in order to avoid the nonen- fore. The best results in the CAL-B-catalyzed process were
zymatic reaction of the amino group with the acyl donor achieved with vinyl acetate or toluene as solvent. Excellent
during the kinetic resolutions (Scheme 4±.
enantioselectivities (E Ͼ 200± and moderate reaction rates
Taking into account previous results obtained in the bio- were measured (40 and 31% conversion after 96 h, respec-
catalytic resolution of cyclic 1,2-amino alcohols by li- tively±. Vinyl acetate was also the best solvent found for the
[
17]
pases,
our initial experiments were designed to find the PSL-C-catalyzed acylation, obtaining a high enantiomeric
most suitable lipase for catalyzing the acetylation of N-pro- ratio (E Ͼ 200± with a 42% conversion after 100 h reaction
tected cis-4-aminochroman-3-ol (± ±-cis-9 in tBuOMe using time (Entry 14±. Thus, by choosing the appropriate reaction
10 equiv. of vinyl acetate. The enzymatic processes were car- conditions and biocatalyst, it is possible to isolate enantio-
ried out at 30 °C. Table 1 shows the results achieved with pure (3R,4R±-9 and (3S,4S±-14 at conversions close to 50%.
Scheme 4. Enzymatic acetylation of N-protected 1,2-amino alcohols (± ±-cis- and (± ±-trans-9 and -13 employing vinyl acetate and lipases.
4225
Eur. J. Org. Chem. 2006, 4224–4230
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org

V. Recuero, G. De Gonzalo, R. Brieva, V. Gotor
Table 1. Lipase-catalyzed esterification of (± ±-cis-9 with vinyl acetate in organic solvents.[a]
FULL PAPER
c [%][b]
ee
s
[%][c]
ee
p
[%][c]
E[d]
Entry
Lipase
Solvent
T [°C]
t [h]
(
3R,4R±-9
(3S,4S±-14
1
2
3
4
5
6
7
8
9
CAL-A[e]
CAL-B
CAL-B-L2
PSL-C
CRL
tBuOMe
tBuOMe
tBuOMe
tBuOMe
tBuOMe
tBuOMe
acetonitrile
vinyl acetate
THF
toluene
toluene
toluene
acetonitrile
vinyl acetate
THF
30
30
30
30
30
30
30
30
30
30
40
50
30
30
30
30
48
24
24
24
24
48
48
96
120
96
48
248
48
100
120
100
12
30
23
15
4
Յ3
18
40
43
31
45
46
20
42
17
37
5
34
93
75
96
28
–
96
Ն99
3
Ն99
Ն99
46
2
40
9
63
2
–
60
Ͼ200
1
Ͼ200
Ͼ200
4
40
21
18
1
PPL
–
CAL-B
CAL-B
CAL-B
CAL-B
CAL-B
CAL-B
PSL-C
PSL-C
PSL-C
PSL-C
21
67
4
44
82
40
25
71
5
10
11
12
13
14
15
16
96
Ն99
24
62
Ͼ200
2
toluene
54
94
56
[
a] For reaction details, see Exp. Sect. [b] Conversion, c = ee
s s p
/(ee +ee ±. [c] Determined by HPLC. [d] Enantiomeric ratio, E = ln(1–c±[(1–
ee ±]/ln(1–c±[(1+ee ±]. [e] The opposite configuration of substrate and product was observed.
s
s
In order to improve the reaction rate of the CAL-B-cata- 50% after 48 h, as shown in Entries 3 and 4±. Note the
lyzed acetylation in toluene, the temperature was increased marked effect of the organic solvent on the resolution of
to 40 °C. A 45% conversion after 48 h was measured (En- (± ±-cis-13 catalyzed by PSL-C. When using acetonitrile, tol-
try 11± with a significant enhancement of the enantio- uene or 1,4-dioxane, very low enantioselectivities were mea-
selectivity. When the resolution was carried out at 50 °C, sured (Entries 5–7±.
the biocatalyst almost totally lost its selectivity, as shown in
Entry 12.
After the successful resolution of N-protected cis-4-
aminochroman-3-ol and cis-1-amino-1,2,3,4-tetra-
The best reaction conditions found for the enzymatic res- hydronaphthalen-ol, we focused our attention on the trans
olution of (± ±-cis-9 were applied in the enzymatic acety- diastereoisomers (Table 3±. For the N-protected trans-4-
lation of the non-oxygenated N-protected derivative (± ±- aminochroman-3-ol (± ±-trans-9, resolution led to the for-
cis-1-amino-1,2,3,4-tetrahydronaphthalen-2-ol, (± ±-cis-13 mation of (–±-(3R,4S±-14, the alcohol (+±-(3S,4R±-9 remain-
(Table 2±. Under all the conditions tested, the (+±-(1S,2R± ing. A moderate E value was achieved in the CAL-B-cata-
enantiomer of the substrate was acetylated by the biocata- lyzed acetylation in toluene at 40 °C (Entry 1±. In contrast,
lysts, the alcohol with the (–±-(1R,2S± configuration remain- it seemed that PSL-C was more suitable as the biocatalyst in
ing unaltered. As shown in Entry 1, esterification of (± ±- the resolution of (± ±-trans-9. When using PSL-C at 30 °C,
cis-13 catalyzed by CAL-B led to (–±-(1R,2S±-13 and (+±- enantiopure (3S,4R±-9 and (3R,4S±-14 were obtained in a
(1S,2R±-15 with low conversion (14% after 48 h± and mod- process with a conversion near 50% after 24 h (Entry 2±.
erate enantioselectivity (E = 38± when the reaction was car- Also with tBuOMe at 30 °C it was possible to achieve high
ried out in toluene at 40 °C. By employing vinyl acetate as enantioselectivity (E = 73±, but lower than that obtained
the solvent and by lowering the temperature to 30 °C, the with vinyl acetate.
same conversion was obtained after 48 h, but a significant
With (± ±-trans-13, excellent results were achieved when
decrease in the selectivity was observed. In contrast, much using CAL-B as the biocatalyst in toluene or PSL-C in vinyl
better reaction rates and enantiomeric ratios were achieved acetate as the solvent and acyl donor. The same enzyme
in the acetylation reactions catalyzed by PSL-C in vinyl ace- enantiopreference was observed for both biocatalysts
tate or tBuOMe (E Ͼ 200 and conversions were close to (Table 3, Entries 4 and 5±. In this last reaction, a 50% con-
Table 2. Lipase-catalyzed esterification of (± ±-cis-13 with vinyl acetate[a] in organic solvents.
c [%][b]
ee
s
[%][c]
ee
p
[%][c]
E[d]
Entry
Lipase
Solvent
T [°C]
t [h]
(
1R,2S±-13
(1S,2R±-15
1
2
3
4
5
6
7
CAL-B
CAL-B
PSL-C
PSL-C
PSL-C
PSL-C
PSL-C
toluene
vinyl acetate
vinyl acetate
tBuOMe
acetonitrile
toluene
40
30
30
30
30
30
30
48
48
48
48
72
72
72
14
15
42
45
33
48
10
15
16
73
81
37
45
3
94
85
Ն99
Ն99
72
49
28
38
14
Ͼ200
Ͼ200
9
4
2
1,4-dioxane
[
a] For reaction details, see Exp. Sect. [b] Conversion, c = ee
s s p
/(ee +ee ±. [c] Determined by HPLC. [d] Enantiomeric ratio, E = ln(1–c±[(1–
ee ±]/ln[(1–c±[(1+ee ±].
s
s
4226
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 4224–4230

Enantiopure Isomers of 4-Aminochroman-3-ol and 1-Amino-1,2,3,4-tetrahydronaphthalen-2-ol
Table 3. Acetylation of (± ±-trans-9 and (± ±-trans-13 with vinyl acetate in organic solvents catalyzed by CAL-B and PSL-C.[a]
FULL PAPER
Alcohol
Conf. ee
Ester
ee
E[d]
Entry
Substrate
Lipase
Solvent
T [°C]
t [h]
c [%][b]
[%][c]
Conf.
[%][c]
88
Ն99
93
Ն99
Ն99
25
s
p
1
2
3
4
5
6
(± ±-9
(± ±-9
(± ±-9
(± ±-13
(± ±-13
(± ±-13
CAL-B
PSL-C
PSL-C
CAL-B
PSL-C
PSL-C
toluene
vinyl acetate
tBuOMe
toluene
vinyl acetate
tBuOMe
40
30
30
40
30
30
24
24
51
52
17
72
50
43
47
49
50
34
(3S,4R±
(3S,4R±
(3S,4R±
(1S,2S±
(1S,2S±
(1S,2S±
90
75
84
(3R,4S±
(3R,4S±
(3R,4S±
(1R,2R±
(1R,2R±
(1R,2R±
43
Ͼ200
73
Ͼ200
Ͼ200
2
95
Ն99
13
[
a] For reaction details, see Exp. Sect. [b] Conversion, c = ee
s s p
/(ee +ee ±. [c] Determined by HPLC. [d] Enantiomeric ratio, E = ln(1–c±[(1–
ee ±]/ln(1–c±[(1+ee ±].
s
s
version was achieved after 17 h and both substrate (–±- 400.13 MHz; 13C: 100.5 MHz± spectrometers. The chemical shift
values (δ± are given in ppm. Mass spectra were recorded with a
(
1S,2S±-13 and product (+±-(1R,2R±-15 were isolated in
Hewlett-Packard 110 series spectrometer. The enantiomeric ex-
cesses were determined by chiral HPLC analysis with a Hewlett-
their optically pure forms. Employing CAL-B led to lower
reaction rates (c = 49% after 52 h±. Both poor conversion
and enantioselectivity were observed in the process cata-
lyzed by PSL-C in tBuOMe, as shown in Entry 6.
Packard 1100 LC liquid chromatograph equipped with
a
CHIRALCEL OD (Daicel± or a CHIRALCEL OB-H (Daicel±
chiral column.
Determination of Absolute Configurations: Optically active cis- and
trans-N-protected amino alcohols 9 and 13 were converted into the
unprotected derivatives 4 and 8 by treatment with hydrogen in the
Conclusions
In conclusion, we have developed an easy and efficient presence of Pd/C in quantitative yield. The configuration of these
route to the enantiomerically pure cis and trans isomers of compounds was established by comparison of the specific rotations
[
7]
measured with those previously reported: (–±-(3R,4R±-4, (–±-
4
-aminochroman-3-ol and 1-amino-1,2,3,4-tetrahydronaph-
1R,2S±-8[
11a]
and (–±-(1S,2S±-8.
[19]
Compound (–±-(3S,4R±-9 was
(
thalen-2-ol through lipase-catalyzed acetylation reactions.
Good yields and high enantioselectivities can be achieved
by the appropriate choice of biocatalyst (CAL-B and PSL-
C± and reaction conditions. Taking into account the sim-
plicity of lipase-catalyzed reactions, the applicability of this
method to the synthesis of high-added-value compounds,
such as chiral auxiliaries for organic synthesis and potential
antiviral agents, is noteworthy.
converted by a Mitsunobu inversion of the hydroxy group into the
optically pure protected amino alcohol (+±-(3R,4R±-9 and sub-
sequently deprotected to give cis-(–±-(3R,4R±-4 whose specific rota-
[7]
tion was compared with the one previously established.
Synthesis of 3-Hydroxy-2,3-dihydro-4H-chromen-4-one [(± ±-2ꢀ and
,4-Dihydro-2-hydroxy-2H-naphthalen-1-one [(± ±-6ꢀ: The α-hydroxy
ketones were prepared by the method described by Moriarty et
3
[14]
al.
Oxidation of commercially available chroman-4-one and α-
tetralone yielded (± ±-2 (yellow solid, 84% yield± and (± ±-6 (yellow
oil, 90% yield±, respectively.
Experimental Section
Synthesis of the α-Hydroxy Oximes (± ±-3 and (± ±-ꢁ: The corre-
sponding α-hydroxy ketones (± ±-2 and (± ±-6 (1.0 g, 1.0 equiv.± were
treated with hydroxylammonium chloride (1.1 equiv.± in pyridine
(35 mL± at 0 °C. The reaction mixtures were warmed to room tem-
perature and stirred for 16 h. Pyridine was then evaporated under
reduced pressure and the crude product was extracted with ethyl
acetate (3×20 mL±. The organic phases were combined, dried and
concentrated under reduced pressure to afford a yellow oil which
was purified by flash chromatography (dichloromethane/ethyl ace-
General Methods: Enzymatic reactions were carried out in a Gal-
lenkamp incubatory orbital shaker. Immobilized Candida antarc-
–1
tica lipase B, CAL-B Novozym 435 (7300 PLUg ±, was a gift from
Novo Nordisk Co. Candida antarctica lipase B (CAL-B-L2,
–1
CHIRAZYME L-2, c-f, C3, Ն400 Ug ±, Candida rugosa lipase
–
1
(
CRL, CHIRAZYME L-3, Ͼ250 Umg ± and Candida antarctica
–1
lipase A (CAL-A, CHIRAZYME L-5, 1 kUg ± were supplied by
Roche Molecular Biochemicals. Immobilized Pseudomonas cepacia
–1
[7a]
lipase (PSL-C, 783 Ug ± is available commercially from Amano
tate, 1:1± to give (± ±-3 (764.0 mg, 70% yield± or (± ±-ꢁ (1.0 g, 92%
Pharmaceuticals. Porcine pancreas lipase (PPL crude, 100–
yield±.
–1
400 Umg ± is a product from Sigma. Chemical reagents were pur-
(
± ±-3,4-Dihydro-2-hydroxy-2H-naphthalen-1-one Oxime [(± ±-ꢁꢀ:
chased from Aldrich, Fluka, Lancaster or Prolabo and were of the
highest quality grade available. Solvents were distilled from an ap-
propriate desiccant under nitrogen. Flash chromatography was per-
formed using Merck silica gel 60 (230–400 mesh±. Melting points
were measured with a Gallenkamp apparatus on samples in open
capillary tubes and are uncorrected. IR spectra were recorded with
a Perkin-Elmer 1720-X infrared Fourier transform spectrophotom-
eter using KBr pellets. Optical rotations were measured using a
Perkin-Elmer 241 polarimeter and are quoted in units of
–
1
Yellow pale oil. IR (KBr±: ν˜ = 3453, 1649, 1608, 1573, 1477 cm .
1
H NMR (CDCl
m, 2 H±, 3.24 (br. s, 1 H±, 5.15 (t, JHH = 5.6 Hz, 1 H±, 7.14–7.27
m, 4 H±, 7.81 (m, 1 H± ppm. 13C NMR (CDCl
, 75.4 MHz±: δ =
5.9 (CH ±, 29.7 (CH ±, 64.1 (CH±, 124.9 (CH±, 127.0 (CH±, 128.6
CH±, 129.9 (CH±, 132.9 (C±, 140.1 (C±, 155.6 (C=N± ppm. MS
3
, 300 MHz±: δ = 1.90–2.02 (m, 2 H±, 2.91–2.98
3
(
(
2
3
2
2
(
(
+
+
+
ESI ±: m/z (%± = 200 (95± [M+Na] , 178 (10± [M+H] . HRMS:
+
2
calcd. for C10H11NO [M ] 177.07890; found 177.08021.
–1
2
–1
1
13
10
degcm g . H NMR, C NMR and DEPT spectra were re-
Preparation of (± ±-cis-4-(Benzyloxycarbonylamino±chroman-3-ol
[(± ±-cis-9ꢀ and (± ±-cis-1-(Benzyloxycarbonylamino±-1,2,3,4-tetra-
hydronaphthalen-2-ol [(± ±-cis-13ꢀ: Aqueous HBr (2.5 equiv.± and a
corded with TMS (tetramethylsilane± as the internal standard with
1
13
Bruker AC-300 ( H: 300.13 MHz; C: 75.4 MHz±, Bruker AC-300
1
13
1
DPX ( H: 300.13 MHz; C:, 75.5 MHz± and Bruker NAV-400 ( H: catalytic amount of 10% Pd/C were added to a solution of the
Eur. J. Org. Chem. 2006, 4224–4230
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4227

V. Recuero, G. De Gonzalo, R. Brieva, V. Gotor
50.3 (CH±, 65.9 (CH±, 67.8 (CH ±, 67.8 (CH ±, 114.5 (CH±, 120.5
FULL PAPER
corresponding α-hydroxy oximes (± ±-cis-3 or (± ±-cis-ꢁ (500 mg,
2
2
1
.0 equiv.± in methanol (12 mL±. The mixture was stirred at room
(CH±, 125.9 (C±, 126.8 (CH±, 127.1 (CH±, 127.2 (CH±, 128.5 (C±,
129.0 (CH±, 129.5 (CH±, 129.8 (CH±, 142.2 (C±, 155.7 (C±, 156.1
temperature for 12 h and then filtered through a Celite pad in order
to remove the catalyst. The solvent was evaporated under reduced
pressure and the crude free 1,2-amino alcohols (± ±-cis-4 or -8 were
obtained and protected without purification. Benzyl chloroformate
+
(C=O± ppm. MS (ESI±: m/z (%± = 322 (90± [M+Na] , 300 (35±
+
[M+H] .
(
± ±-trans-2-Bromo-1-hydroxy-1,2,3,4-tetrahydronaphthalene
[(± ±-
(
(
2.2 equiv.± was added dropwise to a biphasic system of water
12 mL± and dichloromethane (6 mL± containing the bromine salt
trans-11ꢀ: Prepared from dihydronaphthalene as a white solid
12a]
(
2.89 g, 83% yield± according to ref.[
of the amino alcohol (± ±-cis-4 or -8 (500 mg, 1.0 equiv.± and
Na CO (2.2 equiv.± at 0 °C. After 4 h, the mixture was extracted
with dichloromethane (3×15 mL±. The organic phase was washed
(± ±-trans-1,2-Epoxy-1,2,3,4-tetrahydronaphthalene [(± ±-trans-12ꢀ:
NaOH pellets (200 mg, 5.0 mmol± were added at room temperature
to a solution of (± ±-trans-11 (1.0 g, 4.41 mmol± in diethyl ether
(15 mL±. The mixture was stirred for 4 h. After this time, water
(10 mL± was added and the reaction mixture was extracted with
diethyl ether (3×20 mL±. The organic phases were washed with
2
3
with a 5% aqueous solution of sodium hydrogencarbonate
2 4
(3×20 mL±, dried with Na SO and the solvent evaporated under
reduced pressure. The crude residue was purified by flash
chromatography on silica gel with hexane/ethyl acetate (1:1± to af-
2 4
ford (± ±-cis-9 (542.9 mg, 65% yield± or (± ±-cis-13 (595.7 mg, 71% brine (2×25 mL±, dried with Na SO and the solvent was removed
yield±.
under reduced pressure. The crude residue was purified on a chro-
matographic column using hexane/ethyl acetate (2:1± as eluent to
obtain the epoxide (± ±-trans-12 (441.3 mg± as a colorless oil in a
(± ±-cis-4-(Benzyloxycarbonylamino±chroman-3-ol [(± ±-cis-9ꢀ: White
solid. M.p. 164.7–166.2 °C. IR (KBr±: ν˜ = 3470, 3021, 1690,
6
8% yield. Epoxide (± ±-trans-12 exhibited physical and spectral
–
1 1
1508 cm . H NMR ([D
6
]DMSO, 400 MHz±: δ = 3.94–3.99 (m, 2
[12a]
properties in agreement with those reported previously.
3
4
H±, 4.05–4.15 (m, 2 H±, 4.90 (dd, JHH = 9.3 Hz, JHH = 3.9 Hz, 1
H±, 5.11 (s, 2 H±, 5.30 (br. s, 1 H±, 6.75 (d, JHH = 8.0 Hz, 1 H±,
3
(± ±-trans-1-(Benzyloxycarbonylamino±-1,2,3,4-tetrahydronaph-
thalen-2-ol [(± ±-trans-13ꢀ: A solution of (± ±-12 (500 mg, 3.42 mmol±
in MeOH (20 mL± was cooled to 0 °C and NH3 was bubbled
through the solution for 15 min. After this, the mixture was heated
at 50 °C for 16 h. The crude product obtained containing (± ±-trans-
3
3
6
7
.85 (t, JHH = 7.5 Hz, 1 H±, 7.12 (t, JHH = 7.5 Hz, 1 H±, 7.31–
1
3
.42 (m, 6 H± ppm. C NMR ([D
±, 68.1 (CH
22.8 (C±, 128.2 (CH±, 128.3 (CH±, 128.7 (CH±, 128.8 (CH±, 129.2
6
]DMSO, 100.5 MHz±: δ = 49.7
(CH±, 63.8 (CH±, 65.9 (CH
2
2
±, 116.1 (CH±, 120.7 (CH±,
1
8
2 2
was protected with benzyl chloroformate in CH Cl and water as
(CH±, 137.6 (C±, 154.3 (C±, 157.1 (C=O± ppm. MS (ESI±: m/z (%±
+
+
described before to give (± ±-trans-13 in an overall yield of 71%
(722.1 mg± after purification by flash chromatography using hex-
ane/ethyl acetate (1:1± as eluent. M.p. 102.7–104.0 °C. IR (KBr±: ν˜
=
C
322 (100± [M+Na] , 300 (15± [M+H] . HRMS: calcd. for
+
17
4
H17NO [M] 299.11521; found 299.11442.
(± ±-cis-1-(Benzyloxycarbonylamino±-1,2,3,4-tetrahydronaphthalen-2-
–1 1
=
3
3475, 3035, 1697 cm . H NMR (CDCl , 300 MHz±: δ = 1.83–
ol [(± ±-cis-13ꢀ: Yellow solid. M.p. 91.1–92.5 °C. IR (KBr±: ν˜ = 3473,
1
1
3
=
.94 (m, 1 H±, 2.07–2.15 (m, 1 H±, 2.83–2.89 (m, 2 H±, 3.42 (br. s,
–1 1
3031, 1695, 1509 cm . H NMR (CDCl
3
, 400 MHz±: δ = 1.92–1.97
3
H±, 3.89 (br. s, 1 H±, 4.78 (t, JHH = 7.9 Hz, 1 H±, 5.10–5.15 (m,
(m, 2 H±, 2.39–2.46 (br. s, 1 H±, 2.73–2.81 (m, 1 H±, 2.88–3.02 (m,
13
H±, 7.06–7.41 (m, 9 H± ppm. C NMR (CDCl
3
, 100.5 MHz±: δ
1 H±, 4.15–4.16 (m, 1 H±, 4.91–4.99 (m, 1 H±, 5.15 (s, 2 H±, 5.34–
5
.37 (m, 1 H±, 7.09–7.37 (m, 9 H± ppm. 13C NMR (CDCl
75.4 MHz±: δ = 26.4 (CH ±, 27.7 (CH ±, 54.2 (CH±, 67.9 (CH
69.9 (CH±, 127.2 (CH±, 128.4 (CH±, 128.6 (C±, 128.9 (CH±, 129.0
27.8 (CH ±, 29.9 (CH ±, 58.3 (CH±, 68.0 (CH ±, 73.4 (CH±, 127.0
2 2 2
3
,
(
1
(
CH±, 128.0 (CH±, 128.4 (C±, 128.6 (CH±, 128.7 (CH±, 129.0 (CH±,
29.1 (CH±, 134.9 (C±, 137.0 (C±, 158.0 (C=O± ppm. MS (EI±: m/z
%± = 298 (20± [M+H] , 297 (94± [M] .
2
2
2
±,
+
+
(CH±, 129.4 (CH±, 129.8 (CH±, 135.2 (C±, 136.9 (C±, 158.0 (C=O±
+
Chemical Acetylation of the (± ±-cis- and -trans-N-Protected Amino
Alcohols: Acetic anhydride (2.0 equiv.± was added dropwise at 0 °C
to a solution of the racemic N-protected amino alcohols (± ±-
ppm. MS (ESI±: m/z (%± = 320 (100± [M+Na] , 298 (25±
+
+
[
2
M+H] . HRMS: calcd. for C18
97.13636.
3
H19NO [M] 297.13648; found
2 2
cis/trans-9 or -13 (50 mg, 1.0 equiv.± in CH Cl (5.0 mL± and pyri-
(
± ±-trans-4-(Benzyloxycarbonylamino±chroman-3-ol [(± ±-trans-9ꢀ: 4-
Nitrobenzoic acid (250 mg, 1.50 mmol±, triphenylphosphane
400 mg, 1.50 mmol± and diethyl azodicarboxylate (230 µL,
.50 mmol± were added dropwise to a solution of (± ±-cis-4-(benzyl-
dine (2.0 equiv.± and the mixture stirred for 8 h and washed with
1.0  HCl (3×10 mL±. The organic fraction was dried with
Na SO , filtered and the solvent evaporated under reduced pres-
sure. The crude residue was purified by flash chromatography on
silica gel with hexane/ethyl acetate (1:1± to afford the corresponding
racemic esters (± ±-cis/trans-14 or -15 (75–87% yield±.
(
1
2
4
oxycarbonylamino±chroman-3-ol [(± ±-cis-9] (220 mg, 0.75 mmol± in
THF (10 mL±. The mixture was shaken overnight and the solvent
was evaporated under reduced pressure. The crude residue was
purified by flash chromatography on silica gel (hexane/ethyl ace-
tate, 9:1± to afford a p-nitrobenzoate ester, which was hydrolyzed
in situ by treatment with a 0.2  solution of sodium methoxide
Benzyl (± ±-cis-N-(3-Acetoxychroman-4-yl±carbamate [(± ±-cis-14ꢀ:
White solid. M.p. 147.8–149.6 °C. IR (KBr±: ν˜ = 3040, 1731,
–
1 1
1
3
690 cm . H NMR (CDCl , 300 MHz±: δ = 2.05 (s, 3 H±, 4.21
2
3
2
(dd,
J
HH = 12.1 Hz,
JHH = 3.4 Hz, 1 H±, 4.25 (dd,
J
HH
=
=
(
2.5 mL± in methanol (20 mL± at 0 °C. The reaction mixture was
3
3
1
8
2.1 Hz, JHH = 3.4 Hz, 1 H± 5.19–5.28 (m, 5 H±, 6.86 (d, JHH
.3 Hz, 1 H±, 6.97 (t, JHH = 7.2 Hz, 1 H±, 7.19–7.43 (m, 7 H± ppm.
C NMR (CDCl
CH±, 66.6 (CH ±, 67.2 (CH
27.8 (CH±, 128.1 (CH±, 128.2 (CH±, 128.5 (CH±, 129.1 (CH±, 136.0
stirred for 4 h and then treated with ammonium chloride until the
pH was acidic. The solvent was evaporated and ethyl acetate was
added in order to precipitate the salts formed. The crude residue
was filtered off and the solvent was removed under reduced pres-
sure. The reaction mixture was purified by flash chromatography
using hexane/ethyl acetate (1:1± as eluent to obtain (± ±-trans-9
3
1
3
3
, 75.4 MHz±: δ = 20.9 (CH
3
±, 47.4 (CH±, 65.3
(
1
2
2
±, 116.5 (CH±, 120.1 (CH±, 121.2 (C±,
(
(
C
C±, 154.8 (C±, 156.2 (C=O±, 170.3 (C=O± ppm. MS (ESI±: m/z
+
+
%± = 364 (80± [M+Na] , 342 (20± [M+H] . HRMS: calcd. for
(
156.2 mg, 71% yield±. White solid. M.p. 157.2–159.1 °C. IR (KBr±:
+
–1 1
19
H19NO
5
[M] 341.12631; found 341.12901.
s, 1 H±, 3.77–4.19 (m, 3 H±, 4.95 (m, 1 H±, 5.18 (s, 2 H±, 6.72–7.38 Benzyl (± ±-cis-N-(2-Acetoxy-1,2,3,4-tetrahydronaphthyl±carbamate
m, 9 H±, 8.29 (m, 1 H± ppm. 13C NMR (CDCl
, 100.5 MHz±: δ = [(± ±-cis-15ꢀ: White solid. M.p. 112.9–115.1 °C. IR (KBr±: ν˜ = 3040,
3
ν˜ = 3475, 3022, 1689 cm . H NMR (CDCl , 300 MHz±: δ = 2.37
(
(
3
4228
www.eurjoc.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 4224–4230

Enantiopure Isomers of 4-Aminochroman-3-ol and 1-Amino-1,2,3,4-tetrahydronaphthalen-2-ol
FULL PAPER
±, ee Ն 99%. (+±-(3R,4R±-
1
3
725, 1689 cm . M.p. 112.0–114.1 °C. 1H NMR (CDCl
–1
3
,
35.45 min. [α]
14: HPLC, t
23
D
= –32.4 (c = 1.12, CHCl
3
2
3
00 MHz±: δ = 2.01 (s, 3 H±, 2.19–2.25 (m, 2 H±, 2.76–2.94 (m, 2
R
D 3
= 37.18 min. [α] = +10.3 (c = 1.52, CHCl ±, ee =
H±, 4.39–4.44 (m, 1 H±, 5.06–5.27 (m, 4 H±, 7.09–7.39 (m, 9 H± 34%.
ppm. 13C NMR (CDCl
, 75.4 MHz±: δ = 20.9 (CH ±, 26.1 (CH ±,
6.9 (CH ±, 54.0 (CH ±, 66.1 (CH±, 72.3 (CH±, 126.4 (CH±, 127.6
3
3
2
(
–±-(3R,4S±-14: Determination of the ee by HPLC analysis: Chi-
2
2
2
–
1
R
ralcel OB-H, 35 °C, hexane/2-propanol (90:10±, 0.7 mLmin , t =
(
(
CH±, 128.0 (CH±, 128.1 (CH±, 128.2 (CH±, 128.4 (CH±, 128.5
2
3
3
5.45 min. [α]
D 3
= –83.2 (c = 0.65, CHCl ±, ee Ն 99%.
CH±, 134.6 (C±, 135.7 (C±, 136.2 (C±, 156.0 (C=O±, 171.0 (C=O±
+
ppm. MS (ESI±: m/z (%± = 362 (100± [M+Na] , 340 (15±
(+±-(1S,2R±-15: Determination of the ee by HPLC analysis: Chi-
ralcel OD, 25 °C, hexane/2-propanol (90:10±, 0.5 mLmin , t =
R
+
+
–1
[
M+H] . HRMS: calcd. for C20
39.14551.
H21NO
4
[M] 339.14704; found
2
3
3
35.72 min. [α]
D
= +28.6 (c = 0.75, MeOH±, ee Ն 99%.
Benzyl (± ±-trans-N-(3-Acetoxychroman-4-yl±carbamate [(± ±-trans- (+±-(1R,2R±-15: Determination of the ee by HPLC analysis: Chi-
–
1
1
1
2
4ꢀ: White solid. M.p. 153.1–155.2 °C. IR (KBr±: ν˜ = 3041, 1730,
R
ralcel OD, 25 °C, hexane/2-propanol (90:10±, 0.5 mLmin , t =
28.52 min. [α] = +72.4 (c = 0.52, CHCl ±, ee Ն 99%.
D 3
–1
1
23
689 cm . M.p. 163.1–164.9 °C. H NMR (CDCl
3
, 300 MHz±: δ =
2
3
.02 (s, 3 H±, 4.18 (dd, JHH = 12.0 Hz, JHH = 3.7 Hz, 1 H±, 4.35
General Procedure for the Cleavage of the Benzyloxycarbonyl Group:
Pd/C (10 mg± was added under hydrogen to a solution of N-pro-
tected amino alcohol cis/trans-9 or -13 (100 mg, 1.0 equiv.± in etha-
nol (3 mL± at room temperature. The progress of the reaction was
monitored by TLC using hexane/ethyl acetate (1:1± as eluent. After
4 h, the resulting mixture was filtered through Celite and washed
with ethanol. The solvent was then evaporated under reduced pres-
sure to obtain the corresponding free amino alcohol cis/trans-4 or
2
3
(
(
(
4
(
dd, JHH = 12.0 Hz, JHH = 3.7 Hz, 1 H±, 5.09–5.28 (m, 4 H±, 6.81
3
3
d, JHH = 7.8 Hz, 1 H±, 6.92 (t, JHH = 8.4 Hz, 2 H±, 7.18–7.42
m, 6 H± ppm. 13C NMR (CDCl
, 100.5 MHz±: δ = 20.9 (CH ±,
8.6 (CH±, 67.3 (CH±, 68.7 (CH ±, 69.4 (CH ±, 117.6 (CH±, 123.2
CH±, 125.4 (C±, 129.1 (CH±, 129.2 (CH±, 129.3 (CH±, 129.6 (CH±,
30.3 (CH±, 137.0 (C±, 155.9 (C±, 157.2 (C=O±, 171.3 (C=O± ppm.
3
3
2
2
2
1
+
+
MS (ESI±: m/z (%± = 364 (80± [M+Na] , 342 (20± [M+H] .
Benzyl
mate [(± ±-trans-15ꢀ: White solid. M.p. 103.6–105.9 °C IR (KBr±: ν˜
(± ±-trans-N-(2-Acetoxy-1,2,3,4-tetrahydronaphthyl±carba- -8 (71–88% yield±.
–1
1
=
3038, 1728, 1692 cm . M.p. 100.9–102.6 °C. H NMR (CDCl
3
,
Acknowledgments
300 MHz±: δ = 2.03 (s, 3 H±, 2.09–2.29 (m, 2 H±, 2.90–2.94 (m, 2
13
3
H±, 4.95–5.26 (m, 5 H±, 7.11–7.40 (9 H± ppm. C NMR (CDCl ,
1
3 2 2 2
00.5 MHz±: δ = 20.9 (CH ±, 26.0 (CH ±, 26.5 (CH ±, 53.8 (CH
±, This work was supported by the Principado de Asturias (project
6.8 (CH±, 72.7 (CH±, 126.5 (CH±, 127.6 (CH±, 128.03 (CH±, 128.1 PC04-10±. We express our appreciation to Novo Nordisk Co. for
6
(
CH±, 128.2 (CH±, 128.4 (CH±, 128.5 (CH±, 134.6 (C±, 135.8 (C±, the generous gift of the lipase Novozym 435.
1
3
36.4 (C±, 156.3 (C=O±, 170.7 (C=O± ppm. MS (ESI±: m/z (%± =
62 (100± [M+Na] , 340 (5± [M+H] .
+
+
[
1] a± L. Radesca, W. D. Bowen, L. D. Di Paolo, B. R. Costa, J.
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1
996, 307–308; c± J. Hogarth, D. G. Lloyd, J. Antimicrob.
-
Chemother. 2000, 46, 625–627.
acetate (10 equiv., except when used as the solvent± were added to
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1
994, 59, 5104–5105; b± G. Mahler, G. Serra, E. Manta, Synth.
9
or -13 (50 mg, 1.0 equiv.± in the selected organic solvent (15 mL±
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progress of the reaction was monitored by TLC using hexane/ethyl
acetate (1:1± as eluent. Once the reaction was finished, the enzyme
was filtered off, washed with ethyl acetate and the solvent evapo-
rated under reduced pressure. The crude residue was then purified
by flash chromatography (hexane/ethyl acetate, 1:1± to afford com-
pounds (+±- or (–±-cis/trans-14 or -15 and the corresponding enantio-
mer of the remaining substrate (+±- or (–±-cis/trans-9 or -13.
[
3] a± J. P. Vacca, B. D. Dorsey, W. A. Schleif, R. B. Levin, S. L.
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(
+±-(3R,4R±-9: Determination of the ee by HPLC analysis: Chi-
–
1
[4] a± J. H. Condra, Drug. Resist. Updates 1998, 1, 292–299; b±
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3
R
=
1.95 min. [α]2
3
D 3
= +48.1 (c = 0.78, CHCl ±, ee = 82%. (–±-(3S,4S±-
2
783.
9
: t = 30.17 min, ee = 5%.
R
[
5] a± Y. Cheng, F. Zhang, T. A. Rano, Z. Lu, W. A. Schleif, L.
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(
+±-(3S,4R±-9: Determination of the ee by HPLC analysis: Chi-
–
1
ralcel OD, 25 °C, hexane/2-propanol (90:10±, 0.5 mL min , t
3
R
5.96 min. [α]2
3
D 3
= +78.4 (c = 0.97, CHCl ±, ee 84%.
(
–±-(1R,2S±-13: Determination of the ee by HPLC analysis: Chi-
–
1
ralcel OD, 25 °C, hexane/2-propanol (90:10±, 0.5 mLmin , t
3
R
=
2.30 min. [α]2
3
D
= –41.9 (c = 0.6, MeOH±, ee = 81%.
[
(
–±-(1S,2S±-13: Determination of the ee by HPLC analysis: Chi-
–
1
ralcel OD, 25 °C, hexane/2-propanol (90:10±, 0.5 mLmin , t
3
R
=
6.11 min. [α]2
3
D
= –89.0 (c = 0.82, CHCl ±, ee Ն 99%.
3
(
–±-(3S,4S±-14: Determination of the ee by HPLC analysis: Chi-
–
1
R
ralcel OB-H, 35 °C, hexane/2-propanol (90:10±, 0.7 mLmin , t =
Eur. J. Org. Chem. 2006, 4224–4230
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
4229

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Published Online: July 19, 2006
[
4230
www.eurjoc.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 4224–4230