Diastereoisomeric salt formation and enzyme-catalyzed kinetic resolution as complementary methods for the chiral separation of cis-/trans-enantiomers of 3-aminocyclohexanol

Article abstract of DOI:10.1021/op1002424

This contribution demonstrates the preparative-scale synthesis of (1S,3S)-3-aminocyclohexanol by either enzymatic kinetic resolution of Cbz-protected 3-aminocyclohexanols or direct diastereoisomeric salt formation with (R)-mandelic acid. The salt formation demonstrates how a single enantiomer, (1S,3S)-3-aminocyclohexanol (R)-mandelate, can be effectively isolated from the cis/trans racemic mixture and subsequently converted to the free amine, (1S,3S)-3-aminocyclohexanol, by ion-exchange chromatography. We have also demonstrated how the other three enantiomers of 3-aminocyclohexanol can be prepared by either diastereoisomeric salt formation or enzymatic kinetic resolution.

Full text of DOI:10.1021/op1002424

Organic Process Research & Development 2011, 15, 294–300
Diastereoisomeric Salt Formation and Enzyme-Catalyzed Kinetic Resolution as
Complementary Methods for the Chiral Separation of cis-/trans-Enantiomers of
3-Aminocyclohexanol
Cara E. Brocklehurst,*,† Kurt Laumen,† Luigi La Vecchia,† Duncan Shaw,*,‡ and Markus Vo¨gtle†
Global DiscoVery Chemistry, NoVartis Institutes for Biomedical Research, Preparations Laboratories, Klybeckstrasse 141,
4057 Basel, Switzerland, and NoVartis Horsham Research Centre, Wimblehurst Road, Horsham,
West Sussex RH12 5AB, United Kingdom
Abstract:
enantiomers have been published (Figure 1).2,3 The two
groups describe how enantiomerically pure 3-aminocy-
clohexanols were prepared by enzyme-catalyzed kinetic
resolution of N-benzoyl-O-acetylated-2 or Cbz-protected-
3-aminocyclohexanols.3 In the first publication by Ber-
nardelli et al., the enantiomers were separated by a
Candida antarctica lipase-catalyzed hydrolysis of trans-
N-benzoyl-O-acetylated-3-aminocyclohexanol. The addi-
tion and removal of N-benzoyl- and O-acetyl-protecting
groups adds four steps to the synthesis, and (1R,3R)-3-
aminocyclohexanol 2 was obtained in 2.2% overall yield
over six steps. In the second publication by Levy et al.,
Cbz-protected trans-3-aminocyclohexanol (see (()-8, later
in the paper) was prepared by Mitsonobu inversion of the
cis-phthalimide of 3-aminocyclohexanol, prepared by a
slight modification of a method by Sammes et al.4 After
Cbz-protection, the enantiomers were separated by a
Candida antarctica lipase-catalyzed esterification to give
(1R,3R)-3-aminocyclohexanol 2 in 4.8% overall yield for
a 10-step synthesis starting from 2-cyclohexenol. Both of
the syntheses include a number of chromatographic
purification steps which would add a level of complication
should these steps be further scaled up.
This contribution demonstrates the preparative-scale synthesis of
(1S,3S)-3-aminocyclohexanol by either enzymatic kinetic resolution
of Cbz-protected 3-aminocyclohexanols or direct diastereoisomeric
salt formation with (R)-mandelic acid. The salt formation dem-
onstrates how a single enantiomer, (1S,3S)-3-aminocyclohexanol
(R)-mandelate, can be effectively isolated from the cis/trans racemic
mixture and subsequently converted to the free amine, (1S,3S)-
3-aminocyclohexanol, by ion-exchange chromatography. We have
also demonstrated how the other three enantiomers of 3-aminocy-
clohexanol can be prepared by either diastereoisomeric salt
formation or enzymatic kinetic resolution.
Introduction
Aminocyclohexanols are important motifs which exhibit
a wide range of properties as bioactive molecules.1 The
2-amino- and 4-aminocyclohexanols are readily available
from commercial sources in all the possible enantiomeric
and diastereomeric forms. In contrast, the asymmetric
synthesis of 3-aminocyclohexanols has received relatively
little synthetic attention and only two routes to their
* Authors to whom correspondence should be addressed. (C.E.B.) E-mail:
cara.brocklehurst@novartis.com. Telephone: +41 61 6962970. Fax: +41 61
6968016. (D.S.) E-mail: duncan.shaw@novartis.com. Telephone: +41 14703
323078.
Overall, the limited information in the literature regard-
ing the preparation of the cis and trans racemic
3-aminocyclohexanols5-12 has restricted the number of
approaches towards the individual enantiomers. In this
communication we will discuss how it is possible to access
all four enantiomers of 3-aminocyclohexanol 1-4 by
† Novartis Institutes for Biomedical Research.
‡ Novartis Horsham Research Centre.
(1) In the following examples from 2009, 3-aminocyclohexanol is
contained in the core structure of drug-like molecules: (a) Shaw, D.;
Leblanc, C.; Lizos, D.; Ritchie, C.; Furminger, V.; Lewis, S.;
Hornsperger, B.; Stiefl, N. J.; Weiler, S. PCT Int. Appl. WO
2009050183 A2, 2009. (b) Anandan, S. K.; Webb, H. K.; Do, Z. N.;
Gless, R. D. Bioorg. Med. Chem. Lett. 2009, 19, 4259–4263. (c) Bruce,
I.; Dunstan, A.; Hunt, T. A.; Howsham, C. U.S. Pat. Appl. Publ.
2009163463 A1, 2009; (d) Arnold, W. D.; Bounaud, P.; Chen, C.;
Eastman, B.; Gosberg, A.; Gradl, S. N.; Hopkins, S.; Li, Z.; McDonald,
I.; Sprengeler, P. A.; Steensma, R. W.; Wilson, M. E. U.S. Pat. Appl.
Publ. 2009143352 A1, 2009; (e) Humphries, P. S.; Lafontaine, J. A.;
Agree, C. S.; Alexander, D.; Chen, P.; Do, Q. Q. T.; Li, L. L. Y.;
Lunney, E. A.; Rajapakse, R. J.; Siegel, K.; Timofeevski, S. L.; Wang,
T. L.; Wilhite, D. M. Bioorg. Med. Chem. Lett. 2009, 19, 2099–2102.
(f) Swinnen, D.; Jorand-Lebrun, C.; Grippi-Vallotton, T.; Muzerelle,
M.; Royle, A.; Macritchie, J.; Hill, R.; Shaw, J. P. PCT Int. Appl.
WO/2009/027283 A1, 2009; (g) Hauel, N.; Ceci, A.; Doods, H.;
Kauffmann-Hefner, I.; Konetzki, I.; Schuler-Metz, A.; Walter, R. PCT
Int. Appl. WO/2009/021945 A1, 2009; (h) Abbot, S. C.; Boice, G. N.;
Gong, L.; Tan, Y.-C., PCT Int. Appl. WO 2009015917 A2, 2009;(i)
Roughton, A. L.; Ho, K.-K.; Ohlmeyer, M.; Neagu, I.; Kultgen, S. G.;
Ansari, N.; Rong, Y.; Ratcliffe, P. D.; Palin, R., PCT Int. Appl. WO
2009016241 A1, 2009; (j) Bruce, I.; Dunstan, A.; Hunt, T. A.;
Howsham, C. PCT Int. Appl. WO/2009/013348 A2, 2009.
(2) Bernardelli, P.; Bladon, M.; Lorthiois, E.; Manage, A. C.; Vergne,
F.; Wrigglesworth, R. Tetrahedron: Asymmetry 2004, 15, 1451–1455.
(3) Levy, L. M.; de Gonzalo, G.; Gotor, V. Tetrahedron: Asymmetry 2004,
15, 2051–2056.
(4) Sammes, P. G.; Thetford, D. J. Chem. Soc., Perkin Trans. 1 1989,
655–661.
(5) Burford, R. R.; Hewgill, F. R.; Jefferies, P. R. J. Chem. Soc. 1957,
2937–2942.
(6) Burckhardt, U.; Grob, C. A.; Kiefer, H. R. HelV. Chim. Acta 1967,
50, 231–244.
(7) Greenhill, J. V.; Ramli, M.; Tomassini, T. J. Chem. Soc., Perkin Trans.
1 1975, 588–591.
(8) Traynelis, V.; Daduar, J. G. J. Org. Chem. 1961, 26, 1813–1818.
(9) Bartoli, G.; Cimarelli, C.; Palmieri, G. J. Chem. Soc., Perkin Trans.
1 1994, 537–543.
(10) Johnson, A. P.; Luke, R. W. A.; Boa, A. N. J. Chem. Soc., Perkin
Trans. 1 1996, 895–905.
(11) May, H. E.; Boose, R.; Reed, D. J. Biochemistry 1975, 14, 4723–
4730.
(12) Hall, H. K. J. Am. Chem. Soc. 1958, 80, 6412–6420.
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10.1021/op1002424  2011 American Chemical Society
Published on Web 11/15/2010

Figure 1. Previously published routes to chiral 3-aminocyclohexanols.
Scheme 1. Synthesis of (1S,3S)-3-aminocyclohexanol 1
either selective salt formation or enzymatic kinetic resolu-
tion of cis- or trans-Cbz-protected 3-aminocyclohexanols.
Results and Discussions
In the course of our studies (1S,3S)-3-aminocyclohexanol 1
was required on preparative scale for lead optimization and
profiling purposes. The available chemicals directory contains
a number of entries for enantiomerically pure (1S,3S)-3-
aminocyclohexanol 1; however, after a number of attempts, we
were only able to get our hands on mixtures of cis- and trans-
3-aminocyclohexanol, of varying ratios and quality, through the
listed commercial sources. For this reason, (1S,3S)-3-aminocy-
clohexanol 1 was synthesized on larger scale using the synthesis
outlined in Scheme 1.
3-Amino-2-cyclohexen-1-ol 5 was hydrogenated with Raney
nickel according to a procedure by Greenhill et al.,7 and as
reported by Bernardelli et al.,2 the ratio varied between 1:2 and
1:1 for cis:trans on kilogram scale. After a preliminary screen
of chiral acids we found that we were able to obtain clean trans-
3-aminocyclohexanol mandelate (()-7 by crystallization of cis-/
trans-3-aminocyclohexanol 6 with (()-mandelic acid. Resolu-
tion of the corresponding trans-2-(N-benzyl)aminocyclohexanol
by sequential use of (R)- and (S)-mandelic acid was recently
reported by Bolm et al.13,14
The kilogram scale batch of the cis/trans mixture 6 (48:52
cis/trans by NMR) was crystallized with (()-mandelic acid to
give a 44% yield of the desired trans-aminocyclohexanol
mandelate (()-7. Mandelate salt (()-7 was subsequently
protected with a Cbz-group to give racemate (()-8, however,
with lower yield than expected. Significant material was lost
on crystallization of the protected product and removal of
byproduct carried through from the hydrogenation step. High-
purity material was required in order to avoid poisoning of the
biocatalyst in the next step.
Racemate (()-8 was subjected to enzyme-catalyzed kinetic
resolution with Candida antarctica lipase (CAL-B) according
to literature precedence.3 The desired (1S,3S)-Cbz protected
aminocyclohexanol 10 was obtained in 37% yield, and 99.8%
enantiomeric excess by crystallization of the mixture obtained.
The structure of intermediate 10 was confirmed by X-ray
crystallography. Hydrogenation to remove the Cbz-protecting
group gave (1S,3S)-3-aminocyclohexanol 1 in 7.7% overall yield
for five steps from 3-amino-2-cyclohexen-1-ol 5.
The synthesis outlined above was used to provide sufficient
material for our preliminary needs; however, in order to provide
more material we sought to simplify and shorten the synthesis,
providing chirally pure material by the shortest possible route
and avoiding unnecessary protection and deprotection steps
wherever necessary.
(13) Schiffers, I.; Rantanen, T.; Schmidt, F.; Bergmans, W.; Zani, L.; Bolm,
C. J. Org. Chem. 2006, 71, 2320–2331.
Selective Diastereoisomeric Salt Formation. The shortened
synthesis of (1S,3S)-3-aminocyclohexanol 1 is shown in Scheme
(14) Schiffers, I.; Bolm, C. Org. Synth. 2008, 85, 106–117.
Vol. 15, No. 1, 2011 / Organic Process Research & Development
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295

Scheme 2. Direct diastereoisomeric salt formation with
(R)-mandelic acid and subsequent ion-exchange
chromatography to give (1S,3S)-3-aminocyclohexanol 1
Scheme 3. Crystallisation of acetate (()-14 followed by
enzymatic kinetic resolution of cis-racemate (()-15
2. When cis/trans mixture 6 was subjected to direct diastere-
oisomeric salt formation with (R)-mandelic acid, the required
(1S,3S)-enantiomeric salt 11 was obtained in high diastereoi-
someric excess (>95%) and yield comparable to those of the
previous syntheses described herein. The structure of mandelate
salt 11 was confirmed by X-ray crystallography. The possibility
of reaching high diastereoisomeric excess in one single crystal-
lization step compensated for the approximate 50% yield of
the theoretical maximum amount of this single isomer. The
remainder of the required isomer was lost in the highly dilute
crystallization solution, which was required in order to obtain
high diastereoisomeric excess. Ion-exchange chromatography
with Isolute Separtis SCX-2 resin from Biotage, furnished
(1S,3S)-3-aminocyclohexanol 1 in 10% yield over three steps
from 3-amino-2-cyclohexen-1-ol 5.
Table 1. Lipase-catalyzed kinetic resolution of cis-racemate
(()-15
Crystallization of cis/trans mixture 6 with the opposite
enantiomer, (S)-mandelic acid, led to the opposite (1R,3R)-
enantiomeric salt in high enantiomeric excess (>95%) and 11%
yield.
entry
1
lipase
conversiona/% ee 16/% ee 17/%
Eb
Candida
antarctica
Pseudomonas
fluorescens
Thermomyces
lanuginosus
50.6
50.5
50.4
95.4
98.6
99.9
93.0
96.7
98.4
∼100
2
3
∼300
Manipulation of the Mother Liquors To Give cis-
Enantiomers. Scheme 3 outlines how the mother liquors
obtained from crystallization to give trans-aminocyclohexanol
mandelate (()-7 were recycled to give chirally pure cis-isomers.
The mother liquors from previous salt formations were con-
centrated and crystallized to remove residual trans-mandelate
salt to give an oil containing predominantly cis-3-aminocyclo-
hexanol (()-12. Unfortunately, it was not possible to further
crystallize either cis-3-aminocyclohexanol (()-12 or Cbz-
protected-3-aminocyclohexanol (()-13 past a cis/trans ratio of
approximately 85:15. However, when Cbz-protected aminocy-
clohexanol (()-13 was protected as acetate (()-14, the product
easily crystallized and gave pure cis-racemate (()-15 after
removal of the acetate group.
cis-Racemate (()-15 was subjected to enzyme-catalyzed
kinetic resolution with a range of lipases (shown in Table 1)
including Candida antarctica lipase according to literature
precedence (Table 1, entry 1).3 (1R,3S)-Cbz protected ami-
nocyclohexanol 16 (whose structure was confirmed by X-ray
crystallography) and acetic acid (1R,3S)-3-benzyloxycarbonyl-
amino-cyclohexyl ester 17 were obtained in high yield and
enantiomeric excess after column chromatography of the
mixtures was obtained. Thermomyces lanuginosus lipase showed
superior selectivity over Candida antarctica lipase, and by using
this enzyme it was possible to stop the reaction at just over
>1000
a As measured by HPLC. b Enantiomeric ratio.15
50% conversion, giving both enantiomers in high enantiomeric
excess (Table 1, entry 3).
Conclusions
In summary, we have developed a quick and easy method
to obtain (1S,3S)-3-aminocyclohexanol 1 in high enantiomeric
excess (>96%) in three steps starting from commercially
available 3-amino-2-cyclohexen-1-ol 5. The method is advanta-
geous compared to previously reported routes because not only
is it higher yielding, but it also avoids a chromatographic
separation of mixtures from enzyme-catalyzed kinetic resolution
and the use of N-Cbz-, O-acetyl-, or N-benzoyl protecting
groups. We have also demonstrated how the other three
enantiomers of 3-aminocyclohexanol can be prepared by either
diastereoisomeric salt formation or enzymatic kinetic resolution.
Experimental Procedures
All chemicals were purchased from Fluka or Sigma-Aldrich
unless otherwise mentioned. 3-Amino-cyclohex-2-enone was
(15) Chen, C. S.; Fujimoto, Y.; Girdaukas, G.; Sih, C. J. J. Am. Chem.
Soc. 1982, 104, 7294–7299.
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Table 2. Chiral HPLC and chiral GC-MS retention times (please note changes in numbering)
prepared according to a literature procedure for reduction of
3-aminophenol16 or purchased directly from Apollo Scientific.
(R)- or (S)-Mandelic acid was purchased from AK Scientific.
Both Candida antarctica lipase (CAL-B) (as immobilized lipase
preparation, Novozym 435) and Thermomyces lanuginosus
lipase (as immobilized lipase preparation, Novozym TL IM)
were purchased from Novozymes. Pseudomonas fluorescens
lipase (Amano AK) was purchased from Amano. Isolute
Separtis SCX-2 9536 ion-exchange resin (Si-propylsulfonic)
was purchased from Biotage.
retention times for each method are summarized in Table 2 and
Figure 2 below.
NMR was performed using a 400 MHz Varian machine,
AS 400 Oxford. 1H shifts were referenced to d6-DMSO at 2.49
ppm and D2O at 4.79 ppm. 13C shifts were referenced to d6-
DMSO at 39.52 ppm. MS was measured using VG Platform
(Fisons Instruments), Spectraflow 783 Detector, HP 1100 series
HPLC. Melting points were measured using a Bu¨chi, B-545
machine.
cis/trans-3-Aminocyclohexanol 6. 3-Amino-cyclohex-2-
enone 5 (1901 g, 17.1 mol) was dissolved in ethanol (11.5 L)
and NaOH (20% aq, 275 mL) in a 20 L autoclave. Raney nickel
(366 g, 4.28 mol, 0.25 equiv) was added and the reactor purged
with hydrogen. The reaction progress was monitored using TLC
(20% MeOH/CH2Cl2, Rf starting material ) 0.5, Rf product ) 0.14)
until no more starting material was visible, and by hydrogen
update which showed that the reaction was complete after 60 h.
We noted that hydrogenation of 3-amino-cyclohex-2-enone 2,
prepared in house by hydrogenation of 3-aminophenol,16 was
much slower than when commercially available material was
Thin layer chromatography (TLC) was performed on Merck
silica gel plates 60 F-254, Art. Nr. 5729 with detection by UV
(254 nm) or molybdate dip (3 g KMnO4; 20 g K2CO2; 5 mL
5% NaOH; 300 mL H2O). Reverse phase HPLC analyses (for
UV-active Cbz-protected analogues) were performed on an
Agilent-1100 machine using a Zorbax Eclipse XDB-C18, 4.6
mm × 50 mm, 1.8 µm column, acetonitrile and water as eluent
(both containing 0.1% TFA), a column temperature of 35 °C,
a flow rate of 1.0 mL/min, and measuring at 216 nm. The
standard gradient used was 5-100% MeCN over 6 min, 100%
MeCN for 1.5 min, followed by 100 to 5% MeCN over 0.5
min. Normal phase chiral HPLC (for UV-active Cbz-protected
analogues) was performed using a Chiralpak AD-H 250 mm
× 4.6 mm column, an isocratic mixture of 85:15 hexane/ethanol,
a column temperature of 23 °C, with a flow rate of 1.0 mL/
min and measuring at 210 nm over 30 min. Non-UV-active
3-aminocyclohexanols were analyzed by GC-MS after deriva-
tization with trifluoroacetic anhydride. Gas chromatographic
separation was performed using a Carlo Erba Instruments GC
coupled with a Thermo Finnigan TSQ7000 CI/EI mass spec-
trometer and an on-column injector (data acquisition and
evaluation with Excalibur software). Separation was observed
using a Beta DEX 120, Supelco GC column (30 m × 0.25
mm, 0.25 µm film thickness) with hydrogen at 2.5 mL/min
constant flow and 0.4 µL injection volumes. The column was
held at 40 °C for 1 min followed by a ramp of 15 °C/min to 90
°C, 4 °C/min to 150 °C, and 5 °C/min to 200 °C. The TFA
derivates of 3-aminocyclohexanol showed no response with FID
detection; therefore, it is mandatory to analyze these compounds
with GC-MS or GC-ECD. It was possible to derivatize and
analyze both the free base as well as the mandelate salts of
3-aminocyclohexanols using this method. For clarity, the
Figure 2. HPLC trace showing all four isomers of 3-(hydroxy-
cyclohexyl)carbamic acid benzyl ester and all four isomers of
acetic acid 3-benzyloxycarbonylamino-cyclohexyl ester.
(16) Sajiki, H.; Ikawa, T.; Hirota, K. Org. Process Res. DeV. 2005, 9, 219–
220.
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297

used. The reaction mixture was filtered to remove the Raney
nickel and concentrated in Vacuo to give a yellow oil which
crystallized on standing to give a hygroscopic yellow solid (1945
g, 99%). 1H NMR (400 MHz, D2O) δ 0.87-1.79 (8H, m, cis/
trans), 1.79 (0.5H, m, cis), 2.52 (0.5H, m, cis), 2.87 (0.5H, m,
trans), 3.49 (0.5H, m, cis), 3.97 (0.5H, m, trans); cis/trans 48:
52. 13C NMR (101 MHz, D2O) δ 18.7 (d, trans), 21.6 (d, cis),
31.7 (d, trans), 33.6 (d, trans), 33.8 (d, cis), 34.1 (d, cis), 40.6
(d, trans), 43.5 (d, cis), 44.8 (s, trans), 48.1 (s, cis), 66.7 (s,
trans), 61.2 (s, cis), 48:52 cis/trans. HRMS (FAB) calcd for
C6H13NO + H 116.1070, found 116.1070.
C14H19NO3 + H 250.1438, found 250.1438, calcd for
C14H19NO3 + NH4 267.1703, found 267.1703 and calcd for
C14H19NO3 + Na 272.1257, found 272.1256.
(1S,3S)-3-(Hydroxy-cyclohexyl)carbamic Acid Benzyl Es-
ter 10. trans-3-(Hydroxy-cyclohexyl)carbamic acid benzyl ester
(()-8 (660 g, 2.65 mol) was suspended in THF (5.44 L) and
Candida antarctica lipase (Novozym 435, 34 g) was added
followed by vinyl acetate (680 mL, 7.38 mol). The mixture
was stirred at room temperature. After 4.5 days, the conversion
reached 52%, and then the reaction was filtered and the solvent
removed under reduced pressure to give a mixture of acetic
acid (1R,3R)-3-benzyloxy-carbonylamino-cyclohexyl ester 9 and
(1S,3S)-3-(hydroxy-cyclohexyl)carbamic acid benzyl ester 10.
The crude mixture was triturated in 10% dichloromethane/ethyl
acetate (800 mL) and the solid which formed removed by
filtration and dried in the vacuum oven at 40 °C for 1 h to give
(1S,3S)-3-(hydroxy-cyclohexyl)carbamic acid benzyl ester 10
as a bright, white crystalline solid (244 g, 36.8%). The
spectroscopic data were identical to those of racemic starting
trans-3-Aminocyclohexanol (R/S)-Mandelate (()-7. cis/
trans-3-Aminocyclohexanol 6 (1300 g, 1.13 mol) was dissolved
in iPrOH (1.5 M, 7.5 L) at internal temperature 65 °C to give
an fine suspension. (()-Mandelic acid (900 g, 5.92 mol, 0.52
equiv) was added slowly to the hot mixture, and the mixture
was heated to 65 °C overnight. The mixture was cooled to 40
°C to give a white precipitate which was removed by filtration
(room temperature filter funnel) and washed with iPrOH (500
mL) to give a white crystalline solid which was dried in the
vacuum oven at 40 °C overnight (1333 g, 44.2%). Mp
171.1-171.2 °C. 1H NMR (400 MHz, D2O) δ 1.14-1.51 (6H,
m), 1.77-1.84 (2H, m), 3.23 (1H, m), 3.99 (1H, m), 4.81 (1H,
s), 7.19-7.28 (5H, m), 7:93 cis/trans. 13C NMR (101 MHz,
D2O) δ 18.0 (d), 29.5 (d), 30.3 (d), 35.9 (d), 46.2 (s), 65.4 (s),
74.9 (s), 126.9 (s), 128.1 (s), 128.7 (s), 140.4 (q), 179.3 (q).
HRMS (FAB) calcd for C6H13NO + H 116.1070, found
116.1070 and calcd for C8H8O3 - H 151.0408, found 151.0400.
trans-3-(Hydroxy-cyclohexyl)carbamic Acid Benzyl Ester
(()-8. trans-3-Aminocyclohexanol (R/S)-mandelate (()-7 (1333
g, 4.99 mol) was dissolved in saturated aqueous sodium
bicarbonate solution (12 L) and Cbz-Cl (783 mL, 5.49 mol)
added dropwise. A white suspension formed, and the resultant
mixture was stirred at room temperature overnight, after which
time no starting material was visible by TLC. The suspension
was dissolved in ethyl acetate (15 L) and the aqueous phase
diluted with water (2 L). The organic phase was separated and
the aqueous phase washed three more times with ethyl acetate
(3 × 5 L). The combined organic phases were washed with
brine (4 L) and dried over anhydrous sodium sulfate before
concentrating in Vacuo to give a gummy white solid. The crude
solid was triturated in TBME/hexane (1:4, 2 L), the resultant
solid was removed by filtration and washed with TBME/hexane
(1:4, 500 mL). The crystalline solid was subjected to a second
round of crystallization in ethyl acetate/heptane (3:2, 1.5 L) in
which the resultant filtered solid was washed with ethyl acetate/
heptane (3:2, 500 mL). Two crystallizations were required;
otherwise, we observed problems with the subsequent enzyme-
catalyzed kinetic resolution step. The bright, white solid formed
was dried in the vacuum oven at 40 °C for 3 h (596 g, 47.9%).
Mp 130.2-130.4 °C. 1H NMR (400 MHz, DMSO) δ 1.17 (1H,
m), 1.33-1.44 (4H, m), 1.58-1.67 (3H, m), 3.71 (1H, m), 3.89
(1H, br s), 4.40 (1H, d, J ) 3.3), 4.99 (2H, s), 7.12 (2H, d, J
) 8.3), 7.27-7.45 (5H, m). HPLC (Zorbax XDB-C18) rt )
3.96 min; >95% purity. Chiral HPLC (Chiralpak AD-H) 2.5:
97.5 cis/trans. 13C NMR (101 MHz, D2O) δ 19.5 (d), 32.6 (d),
32.9 (d), 40.0 (d), 45.8 (s), 65.0 (s), 65.5 (d), 128.2 (s), 128.2
(s), 128.8 (s), 137.8 (q), 155.8 (q). HRMS (FAB) calcd for
material (()-8. Mp 122.8-122.9 °C [lit. 118-119 °C].3 [R]20
589
) +1.4 (c 1, CHCl3) [lit. [R]20589 ) +4.7 (c 0.5, CHCl3), 78%
ee].3 Chiral HPLC (Chiralpak AD-H) 99.8% ee, >99% trans.
Anal. Calcd for C14H19NO3 + 0.068 equiv H2O C, 67.12; H,
7.70; N, 5.59. Found: C, 67.14; H, 7.71; N, 5.35. Absolute
configuration was confirmed by X-ray crystallography.
The mother liquors from the above crystallization were
concentrated in Vacuo to give a gummy solid, a part of which
was purified by column chromatography on silica, eluting with
ethyl acetate/heptane (2:3) to give acetic acid (1R,3R)-3-
benzyloxycarbonylamino-cyclohexyl ester 9 as an oil which
crystallized on standing. Mp 64.8-64.9 °C [lit. 120-125 °C].3
[R]20 ) -8.8 (c 1, CHCl3) [lit. [R]20 ) -9.6 (c 0.13,
589
589
1
CHCl3), 98% ee].3 H NMR (400 MHz, D2O) δ 1.16 (1H, m),
1.43-1.58 (5H, m), 1.71-1.81 (2H, m), 1.99 (3H, s), 3.62 (1H,
m), 4.99 (3H, br m), 7.27-7.37 (5H, m). HPLC (Zorbax XDB-
C18) rt ) 4.86 min; >99% purity. Chiral HPLC (Chiralpak AD-
H) 97.3% ee, >99% trans. 13C NMR (101 MHz, D2O) δ 19.8
(d), 21.5 (t), 29.4 (d), 31.9 (d), 36.3 (d), 46.0 (s), 65.6 (d), 70.0
(s), 128.2 (s), 128.3 (s), 128.8 (s), 137.7 (q), 155.8 (q),
170.2 (q). HRMS (FAB) calcd for C16H21NO4 + H 292.1543,
found 292.1543, calcd for C16H21NO4 + NH4 309.1809, found
309.1810 and calcd for C16H21NO4 + Na 314.1363, found
314.1361. Anal. Calcd for C16H21NO4 C, 65.96; H, 7.27; N,
4.81. Found: C, 65.92; H, 7.14; N, 4.49.
(1S,3S)-3-Aminocyclohexanol 1 by Hydrogenation. (1S,3S)-
3-(Hydroxy-cyclohexyl)carbamic acid benzyl ester 9 (241.4 g,
968 mmol) was dissolved in ethanol (2 L) in a shaker, and
palladium on carbon (20 g, 18.8 mmol) was added. The flask
was charged with hydrogen and shaken at room temperature
for 10 h after which time complete consumption of hydrogen
was observed and no starting material was observed in the TLC.
The catalyst was removed by filtration and the filtrate concen-
trated in Vacuo to give a white gummy solid which was dried
in high vacuum overnight. The product still contained ethanol
and so was dissolved in water/dioxane and freeze-dried to give
a gummy hygroscopic white solid (127.4 g, >99%). The
analytical data were identical to those of material produced by
the following direct crystallization with (R)-mandelic acid (see
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below). [R]20589 ) +8.0 (c 1, MeOH) [lit. [R]20589 ) +7.5 (c 1,
MeOH), 95.5% ee].2 GC-MS (Beta DEX 120, Supelco) >99%
ee, purity and trans.
filtration to enrich the mother liquors in the cis-racemate to a
maximum of 84:16 cis/trans and 9.5% mandelic acid by NMR.
Alternatively, direct hydrogenation of 3-aminophenol to
3-aminocyclohexanol 6 with the Nishimura catalyst (rhodium
oxide and platinum oxide)17 give cis-enriched material with a
cis/trans ratio of 72:18.
(1S,3S)-3-Aminocyclohexanol (R)-Mandelate 11. cis/trans-
3-Aminocyclohexanol 6 (441.8 g, 3.84 mol) was dissolved in
MeOH/iPrOH (1:1, 2.5 M, 1.53 L) at internal temperature 60
°C to give a fine suspension. (R)-Mandelic acid (152 g, 1.00
mol, 0.26 equiv) was added slowly to the hot mixture, and the
mixture (now dissolved) was heated to 60 °C for 5 min. The
mixture was cooled in an ice bath to 20 °C to give a white
precipitate. Seeding crystals (approximately 5 mg) were added
at 45 °C during the cooling process. After 10 min at room
temperature the solid was removed by filtration (room temper-
ature filter funnel) and washed with iPrOH (560 mL) and TBME
(560 mL) to give a white crystalline solid which was dried under
a filter paper at room temperature overnight (138.8 g, 13.5%).
The spectroscopic data were identical to those of racemic salt
3-(Hydroxy-cyclohexyl)carbamic Acid Benzyl Ester (()-
13 (cis-Enriched). 3-Aminocyclohexanol (()-12 (100 g, 786
mmol) was dissolved in saturated aqueous sodium bicarbonate
solution (1.57 L) and Cbz-Cl (124 mL, 872 mmol) added
dropwise. The orange solution was stirred at room temperature
overnight, after which time no starting material was visible by
TLC and the product had precipitated out of solution. The
mixture was filtered and the solid obtained washed with water
(2 × 200 mL) before drying in the vacuum oven at 30 °C
(caution: melts above 50 °C). The crude solid was triturated in
TBME/hexane (1:3, 300 mL), and the resultant solid wasre-
moved by filtration and washed with hexane (50 mL). The
cream-colored solid formed was triturated a second time in
TBME/hexane (1:3, 300 mL), and the resultant solid was
removed by filtration and washed with hexane (50 mL). The
solid was dried in the vacuum oven at 30 °C for 4 h (120.0 g
g, 55.4%). Further crystallizations led the mixture to higher trans
content. The residual trans-product was removed in crystal-
lization after O-acetylation in the following step. HPLC (Zorbax
XDB-C18) rt (cis) ) 3.90 min; rt (trans) ) 3.96 min; cis/trans
80:20.
(()-7. Mp 187.7-188.1 °C. [R]20 ) -44 (c 1, MeOH).
589
GC-MS (Beta DEX 120, Supelco) 95.9% ee, 98.2% purity
and 1.3:98.7 cis/trans. Anal. Calcd for C14H21NO4 + 0.305
equiv H2O C, 61.64; H, 7.98; N, 5.13. Found: C, 61.62; H,
7.80; N, 5.22. Absolute configuration was confirmed by X-ray
crystallography.
Crystallization was carried out with (S)-mandelic acid at the
same concentrations as given above to give (1R,3R)-3-ami-
nocyclohexanol (S)-mandelate (11.3% yield). The spectroscopic
data were again identical to those of racemic salt (()-7. Mp
191.8-191.9 °C. [R]20589 ) +48 (c 1, MeOH). GC-MS (Beta
DEX 120, Supelco) 97.1% ee, 98.4% purity and 1.6:98.4 cis/
trans.
Acetic Acid cis-3-Benzyloxycarbonylamino-cyclohexyl
Ester (()-14. To a solution of 3-(hydroxy-cyclohexyl)carbamic
acid benzyl ester (()-13 (53.1 g, 213 mmol) in dichloromethane
(700 mL), containing triethylamine (23.7 g, 234 mmol) and
DMAP (100 mg, 0.82 mmol), was added dropwise acetic
anhydride (23.9 g, 234 mmol). After addition, the mixture was
stirred at room temperature for 3 h before quenching with brine
(100 mL). The organic phase was successively washed with 1
N HCl (100 mL), brine (100 mL), and saturated sodium
bicarbonate solution (100 mL) before drying over anyhydrous
magnesium sulfate. The solvent was removed in Vacuo, and
the resulting solid was recrystallized from diethyl ether/pentane
to give a bright, white crystalline solid (50.4 g, 81.2%, 97.5:
2.5 cis/trans). A second recrystallization from diethyl ether/
pentane resulted in almost complete removal of the remaining
trans-material to give a bright, white solid (41.5 g, 66.8%). As
an alternative to using highly flammable solvents such as diethyl
ether or pentane on larger scale, TBME/heptane mixtures have
been shown to be efficient in removing the residual trans-
(1S,3S)-3-Aminocyclohexanol 1 by Ion-Exchange Resin.
(1S,3S)-3-Aminocyclohexanol (R)-mandelate 10 (389.7 g, 1.46
mol) was dissolved in MeOH (7 L) with warming to 50 °C on
the rotorvap to give a pale-yellow solution. A glass column
was filled with Isolute Separtis SCX-2 9536 ion-exchange resin
(3 kg, 1.71 mol, resin loading 0.57 mmol/g). The solution of
product was added to the column (which was preconditioned
with MeOH, 7 L) and pushed onto the resin with nitrogen
pressure. The column was washed with MeOH (7 L) until no
more mandelic acid was visible in the TLC (80% MeCN/water,
Rf mandelic acid ) 0.56, Rf product ) 0.21). The column was flushed
with ammonia in MeOH (2N, 23 L) until no more product
eluted (as observed by TLC). The product was concentrated in
Vacuo to give a foamy solid which was further dried on the
high vacuum for 4 h at room temperature to give a cream-
colored powder (123 g, 73.3%). Mp 70.6-70.9 °C. 1H NMR
(400 MHz, D2O) δ 1.06 (1H, m), 1.33 (1H, m), 1.44 (4H, s),
1.60-1.67 (2H, m), 2.89 (1H, m), 3.98 (1H, s). GC-MS (Beta
DEX 120, Supelco) 96.4% ee, 98.3% purity and 1.7:98.3 cis/
trans. 13C NMR (101 MHz, D2O) δ 18.6 (d), 31.6 (d), 33.6
(d), 40.4 (d), 44.7 (s), 66.8 (s). Anal. Calcd for C6H13NO +
0.162 equiv H2O + 0.002 equiv MeOH C, 61.01; H, 11.37; N,
11.85. Found: C, 61.02; H, 11.18; N, 11.82.
1
material. Mp 85.7-85.9 °C. H NMR (400 MHz, D2O) δ
1.01-1.30 (4H, m), 1.67-1.71 (2H, m), 1.82 (1H, m), 1.96
(3H, s), 2.03 (1H, m), 3.36 (1H, m), 4.59 (1H, m), 4.99 (2H,
s), 7.27-7.37 (5H, m). HPLC (Zorbax XDB-C18) rt ) 4.86
min; >99% purity. Chiral HPLC (Chiralpak AD-H) 99.75:0.25
cis/trans. 13C NMR (101 MHz, D2O) δ 21.4 (d), 21.5 (t), 31.1
(d), 31.9 (d), 38.4 (d), 48.3 (s), 65.6 (d), 71.4 (s), 128.3 (s),
128.6 (s), 128.8 (s), 137.6 (q), 155.7 (q), 170.1 (q). HRMS
(FAB) calcd for C16H21NO4 + H 292.1543, found 292.1543
and calcd for C16H21NO4 + NH4 309.1809, found 309.1810.
3-Aminocyclohexanol (()-12 (cis-Enriched). The mother
liquors from the crystallization of cis/trans-3-aminocyclohexanol
6 with (()-mandelic acid were concentrated in Vacuo to give
a thick oil which crystallized on standing. The solid (trans-3-
aminocyclohexanol (R/S)-mandelate (()-7) was removed by
(17) Nishimura, S. Bull. Chem. Soc. Jpn. 1960, 33, 566–567.
Vol. 15, No. 1, 2011 / Organic Process Research & Development
•
299

cis-3-(Hydroxy-cyclohexyl)carbamic Acid Benzyl Ester
(()-15. A solution of acetic acid cis-3-benzyloxycarbonylamino-
cyclohexyl ester (()-14 (41.8 g, 143.4 mmol), and potassium
carbonate (0.5 g, 3.6 mmol) in MeOH (500 mL) was stirred at
room temperature overnight. The reaction mixture was con-
centrated to remove the methanol, and the crude mixture was
dissolved in ethyl acetate (300 mL) and brine (300 mL). The
organic phase was separated, and the aqueous phase was washed
once more with ethyl acetate (100 mL). The combined organic
phases were dried over anhydrous sodium sulfate before
concentrating in Vacuo. The crude material was crystallized in
dichloromethane/heptane to give a white crystalline solid (28.7
Acetic Acid (1R,3S)-3-Benzyloxycarbonylamino-cyclo-
hexyl Ester 17. The spectroscopic data were identical to those
of racemic material (()-14. Mp 117.6-117.7 °C [lit. 113-115
°C].3 [R]20589 ) +8.3 (c 1, MeOH) [lit. [R]20589 ) +9.1 (c 0.45,
CHCl3), >99% ee].3 Chiral HPLC (Chiralpak AD-H) 96.7%
ee and >99% cis. Anal. Calcd for C16H21NO4 C, 65.96; H, 7.27;
N, 4.81. Found: C, 65.61; H, 7.19; N, 4.96.
(1S,3R)-3-(Hydroxy-cyclohexyl)carbamic Acid Benzyl
Ester 18. A solution of acetic acid (1R,3S)-3-benzyloxycarbo-
nylamino-cyclohexyl ester 17 (11.1 g, 38.1 mmol) and potas-
sium carbonate (0.25 g, 1.81 mmol) in MeOH (150 mL) was
stirred at room temperature overnight. The reaction mixture was
concentrated to remove the methanol, and the crude mixture
was dissolved in ethyl acetate (100 mL). The organic phase
was separated, and the aqueous phase was washed once more
with ethyl acetate (100 mL). The combined organic phases were
dried over anhydrous sodium sulfate before concentrating in
Vacuo. The crude material was crystallized in dichloromethane/
heptane to give a white crystalline solid (9.25 g, 97.4%). The
spectroscopic data were identical to those of racemic starting
1
g, 80.2%). Mp 88.7-88.9 °C [lit. 95-97 °C].3 H NMR (400
MHz, DMSO) δ 0.94-1.19 (4H, m), 1.60-1.75 (3H, m), 1.94
(1H, m), 3.27 (1H, m), 3.36 (1H, m), 4.62 (1H, s), 4.98 (2H,
s), 7.22 (2H, d, J ) 8.3), 7.28-7.37 (5H, m). HPLC (Zorbax
XDB-C18) rt ) 3.90 min; >99% purity. Chiral HPLC
(Chiralpak AD-H) >99% cis. 13C NMR (101 MHz, D2O) δ 22.0
(d), 32.3 (d), 35.1 (d), 42.6 (d), 48.7 (s), 65.5 (d), 68.1 (s), 128.2
(s), 128.3 (s), 128.7 (s), 137.7 (q), 155.7 (q). HRMS (FAB)
calcd for C14H19NO3 + H 250.1438, found 250.1438, calcd for
C14H19NO3 + NH4 267.1703, found 267.1703 and calcd for
C14H19NO3 + Na 272.1257, found 272.1256.
material (()-15. Mp 98.7-99.1 °C [R]20 ) -18.6 (c 1,
589
MeOH). Chiral HPLC (Chiralpak AD-H) 97.3% ee and >99%
cis. Anal. Calcd for C14H19NO3 C, 67.45; H, 7.68; N, 5.62.
Found: C, 67.18; H, 7.53; N, 5.81.
Crystallographic Data. Crystallographic data (excluding
structure factors) for the structure have been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication number CCDC 798573 (10), CCDC 798575 (11),
and CCDC 798574 (16). Copies of the data can be obtained,
free of charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [fax: +44 (0)1223 336 033 or email:
deposit@ccdc.cam.ac.uk].
Typical Procedure for Enzymatic Kinetic Resolution of
cis-3-(Hydroxy-cyclohexyl)carbamic Acid Benzyl Ester (()-
15. cis-3-(Hydroxy-cyclohexyl)carbamic acid benzyl ester (()-
15 (20 g, 80.2 mmol) was suspended in vinyl acetate (200 mL),
and Pseudomonas fluorescens lipase (Amano AK) (1.05 g) was
added. The mixture was stirred at room temperature. After about
2 days, the conversion reached 50.5%; thus, the reaction was
filtered, and the vinyl acetate was removed under reduced
pressure to give the crude mixture which was purified by
column chromatography on silica, eluting with 2% methanol
in dichloromethane to yield (1R,3S)-3-(hydroxy-cyclohexyl)-
carbamic acid benzyl ester 16 (9.77 g, 48.8%) and acetic acid
(1R,3S)-3-benzyloxy-carbonylamino-cyclohexyl ester 17 (12.0
g, 51.2%), both as white crystalline solids.
Acknowledgment
We thank Julia Kleinfelder, Paul Schultheiss, Vikki
Furminger, and Claude Haby for technical assistance; Eric
Francotte, Monique Kessler, Andreas Fredenhagen, and Ju¨rgen
Ku¨hno¨l for determining the optical purities; Trixie Wagner for
performing the X-ray analysis; and Christian Guenat for mass
spectrometry analysis.
(1R,3S)-3-(Hydroxy-cyclohexyl)carbamic Acid Benzyl
Ester 16. The spectroscopic data were identical to those of
racemic starting material (()-15. Mp 99.9-100.5 °C [lit. 95-97
°C].3 [R]20 ) +19.1 (c 1, MeOH) [lit. [R]20 ) -11.0 (c
Supporting Information Available
Crystal structures of compounds 10, 11, and 16. This material
is available free of charge via the Internet at http://pubs.acs.org.
589
589
0.52, CHCl3), 28% ee].3 Chiral HPLC (Chiralpak AD-H) 98.6%
ee and >99% cis. Anal. Calcd for C14H19NO3 C, 67.45; H, 7.68;
N, 5.62. Found: C, 67.58; H, 7.91; N, 5.79. Absolute config-
uration was confirmed by X-ray crystallography.
Received for review September 3, 2010.
OP1002424
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