Entrapment and kinetic resolution of stabilized axial and equatorial conformers of spiro-β-lactams

Article abstract of DOI:10.1021/jo200363x

The facile synthesis of the stabilized axial and equatorial conformers of spiro-β-lactams was achieved via entrapment of cyclohexanone imines (Schiff bases) with acetoxyacetyl chloride in a [2 + 2]-cycloaddition reaction followed by their kinetic resolution. The immobilization of the racemic substrates on an inert solid support significantly reduced the reaction time and improved the enantioselectivity of conformers during kinetic resolution. The mechanism of the formation of the spiro-β-lactams was explored using B3LYP/6-31+G* level quantum chemical calculations.

Full text of DOI:10.1021/jo200363x

ARTICLE
pubs.acs.org/joc
Entrapment and Kinetic Resolution of Stabilized Axial and Equatorial
Conformers of Spiro-β-lactams
Naveen Anand,†,# Bhahwal A. Shah,† Munish Kapoor,† Rajinder Parshad,† Rattan L. Sharma,‡
Maninder S. Hundal,§ Ajay P. S. Pannu,§ Prasad V. Bharatam,§,^ and Subhash C. Taneja*,†
†Indian Institute of Integrative Medicine, Canal Road, Jammu, 180 001, J&K, India
‡Department of Chemistry, University of Jammu, Jammu, 180 005, J&K, India
§Department of Chemistry, Guru Nanak Dev University, Amritsar, 143 005, Punjab, India
^Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER),
SAS Nagar À160 062, India
S Supporting Information
b
ABSTRACT: The facile synthesis of the stabilized axial and
equatorial conformers of spiro-β-lactams was achieved via
entrapment of cyclohexanone imines (Schiff bases) with acet-
oxyacetyl chloride in a [2 + 2]-cycloaddition reaction followed
by their kinetic resolution. The immobilization of the racemic
substrates on an inert solid support significantly reduced the
reaction time and improved the enantioselectivity of conformers during kinetic resolution. The mechanism of the formation of the
spiro-β-lactams was explored using B3LYP/6-31+G* level quantum chemical calculations.
’ INTRODUCTION
spirane ring formation. The synthesized conformers of 4-sub-
stituted spiro[5.3]-2-azanonanone (spiro azetidinones) are stable at
room temperature and could easily be separated in pure crystal-
line forms. The restricted conformers were also kinetically resolved
using lipases. The use of inert solid support for the substrates
substantially improved the efficacy of lipase-catalyzed hydrolysis
of the corresponding acetates, affording the products with ∼99%
enantiopurity. The confirmations of all the structures and relative
conformational analysis was achieved by NMR and single crystal
X-ray crystallography, besides determining the absolute config-
uration of one of the enantiomers. The reaction mechanism was
explored using density functional (DFT) methods. As men-
tioned earlier similar kind of molecules have reportedly exhibited
interesting biological activities;8 in addition, the optically active
spiro-β-lactams may be used as precursors of optically active
unnatural β-(tertiary) amino acids (Figure 1). Relatively few efforts
have been devoted toward the synthesis of cyclohexylidine-derived
spiro-β-lactams;9 besides, we have not come across the reports of
their kinetic resolutions. It therefore became apparent that the
synthesis and biocatalytic resolution of spiro-β-lactams may be
an interesting as well as challenging task due to their conforma-
tional ambiguity and strained nature.
The importance of β-lactam antibiotics for the treatment of
bacterial infections is very well documented.1 The development
of new synthetic methodologies and ever-growing new applica-
tions of 2-azetidinones in the fields ranging from enzyme in-
hibition to gene activation have triggered a renewed interest in
the building of novel β-lactam systems.2 Spirocyclic β-lactams in
particular behave as β-turn mimetics as well as cholesterol absorp-
tion inhibitors and are precursors of R-substituted β-amino
acids.3 Efficient methods have been developed to synthesize such
unusual amino acids and one such method was published by
Kambara et al.4 Alonso et al.3 combined the features of a spiro
system and R,R-disubstituted β-lactams to propose the intro-
duction of a [5.4]-spirolactam. More recently, various research
groups have shown their interest in the synthesis of proline-
derived stereoselective synthesis of spiro-β-lactams.5
The entrapment, separation, and stability of both the axial and
the equatorial conformers in a cyclic system (e.g., cyclohexane)
are interesting challenges for chemists. For example in mono-
alkyl-substituted cyclohexanes, significant potential energy dif-
ferences between the axial and the equatorial conformers make it
virtually impossible to detect and separate both at room temper-
ature.6 However, at low temperatures, even the less stable
conformer may be easily frozen and detected by spectral (e.g.,
dynamic NMR) or other means.7 The size of the alkyl group, the
steric factors, and electrostatic interactions play important roles
in the predominant formation and stability of a particular con-
former, e.g., the bulkier substituents generally are more stabilized
in equatorial conformations.6
’ RESULTS AND DISCUSSION
Spiro-β-lactams were prepared using Staudinger chemistry
with some modifications.10 In our synthetic strategy we envi-
saged condensation of Schiff bases (b) derived from 4-alkyl-sub-
stituted cyclohexanones (a) and p-anisidine with acetoxyacetyl
In the present article, we report the first entrapment of both
conformers of 4-alkyl-substituted cyclohexanones (imines) through
Received: March 7, 2011
Published: June 13, 2011
r
2011 American Chemical Society
5999
dx.doi.org/10.1021/jo200363x J. Org. Chem. 2011, 76, 5999–6006
|

The Journal of Organic Chemistry
ARTICLE
chloride (AAC, c) (Figure 1). The cycloalkanones were first
condensed with p-anisidine in the presence of p-TSA in a DeanÀ
Stark apparatus to obtain Schiff bases (b). The Schiff bases were
subjected to [2 + 2] cycloaddition reactions with AAC to produce
the desired racemic products in moderate to good yields. Using
cyclohexanone as the model substrate, the reaction conditions were
optimized and the cycloaddition reaction was performed at À78 ꢀC
in dichloromethane in the presence of triethylamine. The formation
of racemic spiro-β-lactam 1 was smooth, and the product obtained
as brown oil was purified by column chromatography. The structure
of (()-1 was also confirmed from the spectral data.
The Schiff bases prepared from 4-methylcyclohexanone and
4-ethylcyclohexanone with p-anisidine in toluene were reacted
under similar conditions. The product mixture was easily sepa-
rated by column chromatography into its components, i.e., 2a
(98%), 2b (2%), 3a (98.5%), and 3b (1.5%). The separation of
the entrapped conformers was carried out on a silica gel column
using ethyl acetate/hexane/heptane as eluent. In the NMR of 2a
and 2b the equatorial and axial methyl signals were positioned at
δ 0.92 (C 21.9) and δ 0.95 (C 17.8), respectively. The NMR data
(Table 1 and Supporting Information) together with 2D correlation
experiments led to the structure assignment of 2a as (()-3-ace-
toxy-1-(4-methoxyphenyl)-7(e)-methyl-2-oxo-1-azaspiro[3.5]-
nonane and 3-acetoxy-1-(4-methoxyphenyl)-7(a)-methyl-2-oxo-1-
azaspiro[3.5]nonane 2b, respectively. The proposed structures 2a
and 2b were finally confirmed by X-ray diffraction (XRD) (Sup-
porting Information). Similarly, in the NMR of 3a and 3b, the
C-7 methyl proton signal of the ethyl substituent was assigned at
δ 0.86 (C, 37.9) and δ 0.88 (C, 34.1) respectively. The NMR
data (Table 1) together with 2D correlation experiments (HSQC
and HMBC) led to the structure assignment as (()-3-acetoxy-
1-(4-methoxyphenyl)-7(e)-ethyl-2-oxo-1-azaspiro[3.5]nonane
3a and 3-acetoxy-1-(4-methoxyphenyl)-7(a)-ethyl-2-oxo-1-azas-
piro[3.5]nonane 3b, respectively. The proposed structures of
spiro-β-lactams 3a and 3b were also confirmed by XRD.
The stability at ambient temperature of the both pairs of con-
formers, i.e., 2a, 2b and 3a, 3b can also be explained on the basis
of their calculated relative energies (Table 1). The energy dif-
ference between 2a and 2b using the B3LYP/6-31+G* level is
2.14 kcal/mol; this is sufficiently different to distinguish the two
species. However, the energy difference between the two isomers
3a and 3b is only on the order of 0.94 kcal/mol. It is apparent that
very small energy differences between the isomers make both
pairs highly stable at room temperature, though expectedly, the
axial conformers with low population are at comparatively higher
energy levels than their equatorial counterparts.
The next objective was to explore the most suitable lipase for
catalyzing the enantioselective hydrolysis of spiro-β-lactams for
their kinetic resolution. To achieve this objective, a panel of nine
lipases and whole cell preparations obtained from commercial
sources as well as an institutional repository were screened. The
racemic spiro-β-lactam 2b was not available in sufficient quan-
tities and 4b could not be detected; therefore, they could not be
subjected to kinetic resolution studies. Thus, only spiro-β-lactams 1,
2a, 3a, 3b, and 4a were subjected to biocatalytic kinetic resolutions.
From the preliminary screening experiments it is evident that
AS lipase (Amano) hydrolyzed the racemates 3a and 4a only (Sup-
porting Information). The lipases from Amano PS and PS-C
showed satisfactory hydrolysis of racemic 3a though slow reac-
tion with 4a. On the other hand, the whole cell preparation from
native strain Arthrobacter sp. lipase (ABL, MTCC 5125) hydro-
lyzed all the substrates satisfactorily. Chiral HPLC analysis con-
firmed that Amano AS, PS, and PS-C were able to hydrolyze the
given substrates with moderate to low enantioselectivity, while
ABL was the most selective.
The racemic 3-acetoxy-1-(4-methoxyphenyl)-2-oxo-1-azaspiro-
[3.5]nonane 1 was incubated with ABL in aqueous in 0.1 M
phosphate buffer, pH 7 at 25 ꢀC. The reaction was sluggish;
therefore, the use of cosolvents was attempted but without any
success. The addition of emulsifier (TWEEN 80) showed a sign
of some improvement (∼49% hydrolysis in 18À20 h), though
not sufficient. It was therefore envisaged that the adsorption of
the substrate over an inert solid support could be a useful alternative
to improve the efficacy of the resolution. Hence, the racemic 1
was adsorbed on Celite support (200 mg on 2 g, 10 g/L) and sub-
jected to enzymatic hydrolysis as above. Gratifyingly, the rate of
hydrolysis was considerably improved and the hydrolysis time
reduced from 20 h to just 4 h (conversion 49%), resulting in the
formation of hydrolyzed alcohol (À)-5 in 99% ee and the unhy-
drolyzed ester (+)-1 in >97% ee (Scheme 1).
The cycloaddition reaction of 4-tert-butylcyclohexanone and
p-anisidine Schiff base under similar experimental conditions re-
sulted in the isolation of one product 4a only. The NMR signals
displayed a nine-proton singlet at δ 0.84 (C, 27.5). The NMR
spectra (Table 1) together with 2D correlation experiments led
to the structural assignment (()-3-acetoxy-1-(4-methoxyphenyl)-
7(e)-tert-butyl-2-oxo-1-azaspiro[3.5]nonane also confirmed by XRD.
Similarly, the racemic 3-acetoxy-1-(4-methoxyphenyl)-7(e)-
methyl-2-oxo-1-azaspiro[3.5]nonane 2a and 3-acetoxy-7(e/a)-
ethyl-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]nonane 3a/b were
also successfully resolved using ABL employing the immobilization
Figure 1. Retrosynthetic pathway for the synthesis of spiro-β-lactams.
Table 1. NMR Data and the Calculated Energy Differences between the Isomers
NMR data
entry
1H (δ)
13C (δ)
21.9 (eq methyl), 31.1 (C7)
ΔEa
2a
2b
3a
3b
4a
0.92 (3H, d, J = 6.42 Hz eq methyl), 1.40 (C7-H, m)
0.00
2.14
0.0
0.95 (3H, d, J = 6.73 Hz ax. methyl), 1.79 (C7-H, m)
17.8 (ax. methyl), 25.0 (C7)
0.86 (3H, t, J = 7.40 Hz, C7-CH2CH3), 1.21 (1H, m, C7-H)
0.88 (3H, t, J = 7.19, C7-CH2CH3), 1.32 (2H, q, J = 6.82, CH2), 1.81 (1H, m, C7-H)
0.84 (9H, s, tert-butyl), 1.03 (1H, m, C7-H)
11.4 (C-7 CH2CH3), 33.5 (C-7 CH2CH3), 37.9 (C-7).
12.1 (C-7 CH2CH3), 24.7 (C-7 CH2CH3), 34.1 (C-7).
27.5 (CH3)3-, 32.3 (ÀC(CH3)3), 46.5 (C-7).
0.97
À
a Relative energies are estimated using the density functional B3LYP/6-31+G* values; the corresponding absolute energy values are given in Supporting
Information.
6000
dx.doi.org/10.1021/jo200363x |J. Org. Chem. 2011, 76, 5999–6006

The Journal of Organic Chemistry
ARTICLE
Scheme 1. Lipase-Catalyzed Kinetic Resolution
Table 2. Effect of Solid Support on Enzymatic Hydrolysis of
1, 2a, 3a, 3b, and 4a
compd enzyme support time convn, % ee(OH), % ee(OAc), %
1
ABL
ABL
ABL
ABL
ABL
ABL
ABL
AS
nil
20 h
49
49
35.5
41
48
45
41
44
42
99
99
56
65
99
81
58
39
67
99
97
99
99
99
99
98
50
98.5
1
Celite 4 h
2a
2a
3a
3a
3b
4a
4a
nil
24 h
Celite 4 h
Figure 2. Possible formation of diastereomers.
nil
36 h
Celite 5 h
the possible eight, four isomers should have nitrogen oc-
cupying the equatorial position (AÀD) and the remaining four
isomers with nitrogen occupying the axial position (EÀH). How-
ever, it was found that only four isomers were formed with methyl
and ethyl substitutions, whereas only two enantiomers were de-
tected in the case of tert-butylcycloheaxane, all exhibiting N-equa-
torial orientation (Figure 3).
Interestingly, the outcome of the reaction may be rationalized
on the basis of the following possible reaction mechanism. From
the conformational analysis of cyclohexanones, it may be estab-
lished that any substitution at C-4 in cyclohexanone may possibly
occupy predominantly an equatorial position which is more
stable than the axial one.12 The synthesis of spiro-β-lactams was ac-
complished in two steps, and the intermediate Schiff bases generally
existed in a dynamic equilibrium between equatorial and axial
conformers through a flipping mechanism, the former being dom-
inant. In 4-tert-butylcyclohexanone this equilibrium may shift
entirely in favor of the equatorial conformer because of its more
bulky nature.
In the Schiff bases obtained from 4-methyl- and 4-ethylcyclo-
hexanones, a ketene can interact from two sides: (i) the equatorial
side approach will result in the formation of an axial product, i.e.,
the N would occupy an axial position; (ii) the axial approach will
lead to the equatorial product, i.e., the N would occupy an equatorial
position.
The mechanism of the Staudinger reaction has been explained
previously.13 It involves a two-step mechanism which is initiated
by the nucleophilic attack of the iminic nitrogen on the electron-
deficient carbon of the ketene followed by a four-electron
conrotatory electrocyclization that is subject to torquoelectonic
effects.13 The electrocyclic ring closure takes place to form the
CC bond. The mechanism of this reaction was explored using
quantum chemical methods, and the possible structures of the
intermediates and the transition states on the reaction path have
been discussed in literature.13,14 In the present case, B3LYP/
6-31+G* calculations indicate that the intermediate on this path
leading to the formation of 2a is found to be about 3.06 kcal/mol
silica
nil
5.5 h
8 days
6 h
AS
silica
methodology (Scheme 1, Table 2). The conversion time in all the
reactions significantly reduced with an improvement in the
enantioselectivity (Supporting Information).
Kinetic resolution of racemic 4a on the other hand was quite
slow, and only the Amano AS and PS were able to hydrolyze it.
Incubation for a period of 8 days with Amano AS showed con-
version of 44% (50% ee), whereas with PS it was <5% for the
product. The native lipase ABL also proved to be a complete
failure for this substrate. Adsorption of 4a over silica again proved
to be very effective with Amano AS, furnishing the hydrolyzed
product of 98.5% ee in 6 h (Supporting Information). These
observations with lipase AS also support the results of earlier
studies carried out to understand the steric requirements of lipases
where it was indicated that lipases such as those belonging to genus
Pseudomonas, Candida, Mucor, etc., are capable of accepting only
small to medium size groups, while lipase from Aspergillus niger
can accommodate comparatively larger groups.11
X-ray crystallographic data collected using a single crystal of
the hydrolyzed enantiomer (À)-3-hydroxy-1-(4-methoxyphenyl)-
2-oxo-1-azaspiro[3.5]nonane (À)-5 (Supporting Information)
obtained as a result of enzymatic resolution, established the ab-
solute configuration as 3S. Therefore, the unreacted ester is as-
signed 3R as the absolute configuration.
If viewed critically, the cycloaddition reaction of substituted
cycohexanone imine with ketene may result in the formation two
groups of diastereomeric products, i.e., I and II (Figure 2).
In the case of unsubstituted cycloalkanes each of these diaster-
eomers should give two pairs of enantiomers (four enantiomers).
Similarly 4-substituted cyclohexanones with two stereogenic
centers and additional molecular asymmetry originated from
spiro structure should always result in the formation of four pairs
of products (eight enantiomers, i.e., AÀH, Figure 2). Thus, out of
6001
dx.doi.org/10.1021/jo200363x |J. Org. Chem. 2011, 76, 5999–6006

The Journal of Organic Chemistry
ARTICLE
Figure 3. Formation of all the possible conformers of spiro-β-lactams.
Figure 4. The potential energy surfaces for the formation of 2a and 2b.
The relative energies are plotted in this graph. The graphs are exactly
parallel, the y-axis representing energy (does not carry any scale). The
relative values are estimated using B3LYP/6-31+G(d) level of quantum
chemical calculations.
Figure 5. The 3D structures of the intermediates and the transition
states on the paths of formation of 2a and 2b. Important bond distances
are shown in angstroms.
more stable than the corresponding starting material. The barrier
for the formation of 2a from the intermediate is found to be
approximately 7.03 kcal/mol. The formation of 2a from the
corresponding starting material is found to be highly exothermic
(40.91 kcal/mol). The energy profile for the formation of the 2a
and 2b are given in Figure 4. The 3D structures of the inter-
mediates on the reaction path leading to the formation of 2a and
2b are given in Figure 5. The energy profiles are quite parallel,
indicating that the reaction mechanism does not dictate the final
thermodynamic preferences of the products.
The origin of preferential formation of 2a over 2b can be
traced to the thermodynamic preferences of the starting material
and that of the products. The energy differences between the equa-
torial and axial alternatives of the starting imine are found to
provide some clues (Table 3). For example, the energy difference
between imines leading to 2 is 2.0 kcal/mol, favoring the equatorial
configuration. Similarly equatorial configuration of the imine leading
to the formation of 3 is 0.85 kcal/mol. On the other hand, the
energy difference between the two configurations of the imine
leading to the formation of 4 is 5.27 kcal/mol. Because of the
large energy difference between the two forms of the imine, 4a is
Table 3. The Relative Energies (B3LYP/6-31+G(d); kcal/mol)
of Various Structures on the Path Leading to the Formation of
Final Spiro-β-lactams
structures
ΔE (equatorial À axial)
imines (2a vs 2b)
imines (3a vs 3b)
imines (4a vs 4b)
intermediates (2a vs 2b)
transition states (2a vs 2b)
2a vs 2b
1.99
0.85
5.27
1.89
2.04
2.14
0.97
3a vs 3b
the only product found. When the energy difference between the
axial and equatorial forms of the imine is small, both axial and
equatorial products are formed (as in the case of 2 and 3). Also
the thermodynamic stability of the equatorial product is more in
6002
dx.doi.org/10.1021/jo200363x |J. Org. Chem. 2011, 76, 5999–6006

The Journal of Organic Chemistry
ARTICLE
Figure 6. Possible mechanism of axial approach in β-lactam formation.
the product. Hence, it can be concluded that thermodynamic
preferences in the starting imine as well as the thermodynamic
stabilities of the final product both dictate the preferential for-
mation of equatorial product in the reactions.
’ EXPERIMENTAL SECTION
General Method for Preparation of Imines. A solution of
cyclic ketone (50.0 mmol) and p-anisidine (6.15 g, 50.0 mmol) were
refluxed in 100 mL of toluene, and the water formed was removed
azeotropically using DeanÀStark apparatus. An excess of solvent was
removed, and the imine was used without further purification.
Further support for the formation of N-equatorial spiro-β-
lactams also came from what is now known as the Cieplak effect,15
which is the theoretical basis for the stereochemical outcome in
the irreversible addition of nucleophiles to compounds such as
cycohexanones, postulating that hyperconjugative σ assistance
favors the axial approach because CH bonds are better electron
donors. In the first place, it appears that the Cieplak effect may
not be applicable in this case, as the imine itself is the nuceleo-
phile. However, in the a two-step concerted addition reaction
between the imine and the ketene, initial attack of the imine on
the ketene carbon results in the formation of the intermediate
(a), which is then followed by intramolecular axial side attack of
the vinyl carbon (which may act as a nucleophile) on the sp2
carbon of the cyclohexane ring, resulting in the formation of
exclusively N-equatorial product (Figure 6). Consequently, there
is a 50% reduction in the total number of isomers formed. Thus,
the intramolecular Cieplak effect also provides a possible ratio-
nalization for the stereochemical outcome of the final product.
(()- 3-Acetoxy-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]-
nonane 1. Triethylamine (6.06 g, 60.0 mmol) was added to a stirred
mixture of imine (4.06 g, 20.0 mmol) in dry dichloromethane (150 mL)
at À78 ꢀC. To this stirred solution was added acetoxyacetyl chloride (3.3
g, 24.0 mmol) dissolved in 50 mL of dichloromethane over a period of 30
min, maintaining the temperature at À78 ꢀC. The reaction temperature
was slowly raised to room temperature, and stirring was continued for 8
h. After the reaction was complete (TLC), the mixture was successively
washed with 5% aqueous sodium bicarbonate (50 mL), 5% HCl (50 mL)
and water (3 Â 50 mL). The organic layer was dried and evaporated
under reduced pressure. The oily product was purified using column
chromatography (230À400 mesh silica gel and dichloromethane and
hexane) to obtain 1. Yield: 5.2 g (86%), IR (Neat), 2938, 2861, 1748,
1
1513, 1447, 1384, 1296, 1221, 1185, 1097, 831. H NMR (200 MHz,
CDCl3): δ 1.08À1.25 (2H, m, CH2), 1.30À1.87 (5H, m, CH2),
1.96À2.14 (3H, m, CH2), 2.2 (3H, s, OCOCH3), 3.80 (3H, s, OCH3),
5.68 (1H, s, C3-H), 6.88 (2H, d, J = 9.1 Hz, Ar-H), 7.41 (2H, d,
J = 9.1 Hz, Ar-H). 13C NMR (50 MHz): δ 20.8, 23.4, 24.5, 29.9, 34.0,
55.4, 67.8, 79.6, 114.4, 122.0, 128.9, 157.2, 162.8, 169.6. MS (m/z): 303,
244, 200, 205, 215, 160, 149, 112. Anal. Calcd for C17H21NO4: C, 67.31;
H, 6.98; N, 4.62. Found: C, 67.11; H, 6.92; N, 4.56.
’ CONCLUSIONS
In conclusion, the entrapment and kinetic resolution of stabilized
conformers of 4-alkyl-substituted cyclohexanones (imines) was
successfully achieved via spiro-β-lactam formation. In the case of
4-methyl and 4-ethyl substituents, both the equatorial and axial
conformers were stable and easily separated. Three of these stable
conformers were also kinetically resolved. Furthermore, only an
equatorial conformer was isolated and resolved for the 4-tert-
butyl-substituted spiro-β-lactam. The unsubstituted cyclohexa-
none-derived spiro-β-lactams were also kinetically resolved, and
the absolute configuration of the hydrolyzed product was deter-
mined by XRD. The confirmation of structures of all the products
was accomplished by single crystal X-ray studies. Quantum chemical
analysis suggests that the thermodynamical preference of the
starting imines and the theromodyanamic preference of the final
products lead to the observed preferential formation of the
equatorial product rather than the kinetic control of the reaction
mechanism of the Staudinger reaction.
(()- 3-Hydroxy-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]-
nonane 5. To a stirred mixture of 1 M KOH (50 mL) and THF
(30 mL) at 0 ꢀC was added 3-acetoxy-1-(4-methoxyphenyl)-2-oxo-1-
azaspiro[3.5]nonane (0.9 g, 3.0 mmol) dissolved in 10 mL of THF
dropwise over a period of 1 h. The reaction mixture was further stirred
for another 1 h, and after completion of the reaction, it was diluted with
30 mL of THF and saturated solution of NaHCO3. Extraction with ethyl
acetate (3 Â 50 mL), washing with water, drying, and evaporation under
reduced pressure gave 5. Yield: 712 mg (91%), mp 157À9 ꢀC, IR (KBr),
3353, 2919, 1718, 1511, 1393, 1358, 1248, 1207, 1150, 1113. 1H NMR
(200 MHz, CDCl3) δ 1.15À2.27 (10H, m, CH2), 3.77 (3H, s, OCH3),
4.58 (1H, s, C3-H), 5.03 (1H, s, OH), 6.82 (2H, d, J = 9.0 Hz, Ar-H), 7.37
(2H, d, J = 9.0 Hz, Ar-H). 13C NMR (50 MHz) δ 23.5, 24.1, 24.9, 29.7,
34.5, 55.4, 68.5, 81.8, 114.3, 121.8, 129.3, 156.9, 167.7. ESI-MS ( m/z):
284 (M+ + Na), 226, 172, 135.
(()-3-Acetoxy-1-(4-methoxyphenyl)-7(e)-methyl-2-oxo-1-
azaspiro[3.5]nonane 2a. Compound 2 was prepared from imine
6003
dx.doi.org/10.1021/jo200363x |J. Org. Chem. 2011, 76, 5999–6006

The Journal of Organic Chemistry
ARTICLE
(4.34 g, 20.0 mmol), triethylamine (6.06 g, 60.0 mmol), and acetox-
yacetyl chloride (3.3 g, 24.0 mmol) following the procedure described
for 1. Yield: 4.8 g (76%), mp 108À9 ꢀC. IR (KBr): 2954, 2925, 2856,
(93%), mp 112À3 ꢀC. IR (KBr): 3285, 2951, 2925, 2866, 1703, 1511,
1
1441, 1344, 1247, 1151, 1118, 1088, 1075, 1036, 833. H NMR (500
MHz, CDCl3): δ 0.93 (3H, d, J = 6.0 Hz, C7-CH3), 1.26 (2H, m, CH2),
1.43 (2H, m, C H2), 1.68À1.75 (3H, m, CH2), 1.98À2.21 (3H, m, CH2),
3.77 (3H, s, OCH3), 4.61 (1H, s, C-3H), 6.83 (2H, d, J = 9.0 Hz, Ar-H),
7.38 (2H, d, J = 9.0 Hz, Ar-H). 13C NMR (125 MHz): δ 21.9, 29.5, 31.5,
32.0, 32.4, 34.1, 55.4, 68.5, 81.4, 114.3, 121.8, 129.2, 157.0, 168.0. MS (m/
z): 275, 257, 247, 229, 218, 202, 186, 160, 149, 126, 108, 93. Anal. Calcd for
C16H21NO3: C, 69.79; H, 7.69; N, 5.09. Found: C, 69.53; H, 7.53; N, 5.13.
(()-7(e)-Ethyl-3-hydroxy-1-(4-methoxyphenyl)-2-oxo-1-
azaspiro[3.5]nonane 7. Compound 7 was prepared by stirring a
mixture of 1 M KOH (50 mL) in THF (30 mL), and 3-acetoxy-7(e)-
ethyl-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5] nonane 3a (1.0 g,
3.0 mmol) following the procedure described for 5. Yield: 800 mg
(92%), mp 100À1 ꢀC. IR (KBr): 3353, 3023, 2961, 2940, 2846, 1730,
1
1736, 1512, 1349, 1225, 1142, 1114, 1090, 1032, 936. H NMR (500
MHz, CDCl3): δ 0.83 (1H, dq, CH2), 0.92 (3H, d, J = 6.4 Hz, C7-CH3),
1.31 (1H, m, C H2), 1.40 (1H, m, C H), 1.75À1.86 (3H, m, C H2),
2.05À2.15 (3H, m, C H2), 2.22 (3H, s, OCOCH3), 5.73 (1H, s, C-3H),
6.89 (2H, d, J = 9.0 Hz, Ar-H), 7.43 (2H, d, J = 9.0 Hz, Ar-H). 13C NMR
(125 MHz): δ 20.8, 21.9, 29.6, 31.1, 31.7, 31.9, 33.8, 55.5, 79.7, 114.7,
121.9, 129.0, 157.2, 162.7, 169.6. MS (m/z): 317, 259, 229, 217, 214,
200, 186, 168, 160, 149, 126.
(()-3-Acetoxy-1-(4-methoxyphenyl)-7(a)-methyl-2-oxo-1-
azaspiro[3.5]nonane 2b. Compound 2b was obtained as a minor
product in the synthesis of 2a. Yield: 95 mg (2%), mp 93 ꢀC. IR (KBr):
2952, 1746, 1511, 1383, 1246, 1228. 1H NMR(500 MHz, CDCl3): δ 0.95
(2H, d, J = 6.7 Hz, C7 CH3), 1.43 (3H, m, CH2), 1.73À1.82 (4H, m,
CH2), 2.17 (1H, m, CH2), 2.19 (3H, s, OCOCH3), 2.28 (1H, m, CH2),
3.80 (3H, s, OCH3), 5.59 (1H, s, C-3H), 6.89 (2H, d, J = 8.5 Hz, Ar-H),
7.36 (2H, d, J = 8.5 Hz, Ar-H). 13C NMR (125 MHz): δ 18.3, 20.7, 25.9,
26.9, 29.2, 29.3, 29.8, 55.5, 67.8, 80.1, 114.6, 123.7, 128.9, 157.8, 163.3,
169.8. MS (m/z): 317, 257, 229, 217, 214, 168, 160, 149, 126.
(()-3-Acetoxy-7(e)-ethyl-1-(4-methoxyphenyl)-2-oxo-1-
azaspiro[3.5]nonane 3a. Compound 3a was prepared from imine
(4.62 g, 20.0 mmol), triethylamine (6.06 g, 60.0 mmol), and acetox-
yacetyl chloride (3.3 g, 24.0 mmol) following the procedure described
for 1. Yield: 5.0 g (75%), mp 65À66 ꢀC. IR (KBr): 2935, 1755, 1513,
1
1414, 1393, 1296, 1253, 1128, 1096, 1032, 947, 923, 808. H NMR
(500 MHz, CDCl3): δ 0.86 (3H, t, J = 7.5 Hz, C7-CH2CH3), 1.12À1.41
(5H, m, CH2), 1.69À1.81 (3H, m, CH2), 1.94À2.19 (3H, m, CH2), 3.75
(3H, s, OCH3), 4.58 (1H, s, C-3H), 6.81 (2H, d, J = 9.0 Hz, Ar-H), 7.37
(2H, d, J = 9.0 Hz, Ar-H). 13C NMR (125 MHz): δ 12.1, 29.6, 29.8, 30.1,
30.4, 34.4, 38.6, 55.8, 69.2, 81.9, 114.7, 122.1, 129.7, 157.2, 168.4. MS (m/
z): 289, 232, 160, 149, 140, 134, 122, 93. Anal. Calcd for C17H23NO3: C,
70.56; H, 8.01; N, 4.84. Found: C, 70.81; H, 7.99; N, 4.76.
(S)-(À)-3-Hydroxy-7(a)-ethyl-1-(4-methoxyphenyl)-2-oxo-
1-azaspiro[3.5]nonane (À)-8. Compound 8 was obtained by re-
solution of 3b, mp 144À46 ꢀC. 1H NMR (400 MHz, CDCl3): δ 0.88
(3H, t, J = 7.5 Hz, C7-CH2CH3), 1.25À1.40 (5H, m, CH2), 1.69À1.81
(3H, m, C H2), 1.95À2.22 (3H, m, CH2), 3.78 (3H, s, OCH3), 4.55 (1H,
s, C-3H), 6.83 (2H, d, J = 9.2 Hz, Ar-H), 7.34 (2H, d, J = 9.2 Hz, Ar-H).
13C NMR (100 MHz): δ 12.6, 24.2, 25.2, 26.9, 27.4, 29.7, 33.7, 55.5,
68.4, 81.8, 114.4, 122.6, 129.2, 157.2, 167.4. MS (m/z): (M+ + 1) 290,
161, 149, 140, 135, 94. Anal. Calcd for C17H23NO3: C, 70.56; H, 8.01; N,
4.84. Found: C, 70.69; H, 7.97; N, 4.79.
1
1463, 1443, 1484, 1248, 1222, 1032, 914, 858. H NMR (500 MHz,
CDCl3): δ 0.77 (1H, dq, J = 3.9, 7.8 Hz, CH2), 0.84 (3H, t, J = 7.5 Hz,
C7-CH2CH3), 1.15 (1H, m, C7- H), 1.20À1.26 (3H, m, C H2), 1.82
(3H, m, CH2), 2.05 (1H, dq, J = 4.5 Hz, CH2), 2.19 (3H, s, OCOCH3),
3.79 (3H, s, OCH3), 5.67 (1H, s, C-3H), 6.87 (2H, d, J = 8.9 Hz, Ar-H),
7.41 (2H, d, J = 8.9 Hz, Ar-H). 13C NMR (125 MHz): δ 11.4, 20.8, 29.2,
29.3, 29.6, 29.8, 33.8, 37.9, 68.0, 114.5, 122.0, 129.1, 157.2, 162.7, 169.6.
MS (m/z): 331, 272, 243, 219, 182, 160, 149, 140.
(() 3-Acetoxy-7(a)-ethyl-1-(4-methoxyphenyl)-2-oxo-1-
azaspiro[3.5]nonane 3b. Compound 3b was obtained as a minor
product in the synthesis of 3a. Yield: 135 mg (1.5%), mp 102À3 ꢀC, IR
(KBr): 2953, 1741, 1512, 1384, 1250, 1229, 1115, 1098, 1016, 940, 832.
1H NMR (500 MHz, CDCl3): δ 0.88 (3H, t, J = 7.2 Hz, C7-CH2CH3),
1.32 (2H, quin, J = 6.8 Hz, CH2), 1.41À1.52 (4H, m, C H2), 1.70À1.82
(3H, m, CH2), 2.07À2.15 (1H, m, CH2), 2.20 (3H, s, OCOCH3), 2.25
(1H, m, CH2), 3.80 (3H, s, OCH3), 5.59 (1H, s, C-3H), 6.89 (2H, d, J =
8.2 Hz, Ar-H), 7.35 (2H, d, J = 8.2 Hz, Ar-H). 13C NMR (125 MHz):
δ 12.0, 20.7, 24.8, 26.1, 26.9, 27.0, 30.1, 34.1, 55.5, 67.9, 80.1, 114.6,
123.7, 128.9, 157.8, 163.3, 169.8. MS (m/z): (M+ + 1) 332, 273, 183,
160, 149, 140.
(()-3-Acetoxy-7(e)-(1,1-dimethylethyl)-1-(4-methoxyphe-
nyl)-2-oxo-1-azaspiro[3.5]nonane 4a. Compound 4a was pre-
pared from imine (5.18 g, 20.0 mmol), triethylamine (6.06 g, 60.0 mmol),
and acetoxyacetyl chloride (3.3 g, 24.0 mmol) following the procedure
described for 1. Yield: 6.1 g (85%), mp 127À9 ꢀC. IR (KBr): 2968, 2937,
2866, 1745, 1513, 1388, 1297, 1244, 1221, 1118, 1035, 1015. 1H NMR
(500 MHz, CDCl3): δ 0.84 (9H, s, tert-butyl), 0.91 (1H, m, CH2), 1.03
(1H, m, CH2), 1.84À1.91 (3H, m, CH2), 2.02À2.16 (3H, m, CH2), 2.19
(3H, s, OCOCH3), 3.79 (3H, s, OCH3), 5.67 (1H, s, C-3H), 6.87 (2H,
d, J = 8.5 Hz, Ar-H), 7.42 (2H, d, J = 8.5 Hz, Ar-H). 13C NMR (125
MHz): δ 20.7, 24.2, 24.3, 27.5, 29.9, 32.3, 34.2, 46.6, 55.5, 67.9, 79.7,
114.5, 121.8, 129.1, 157.1, 162.7, 169.4. MS (m/z): 359, 301, 284, 272,
260, 242, 216, 200, 168, 149, 94.
(()-7(e)-(1,1-Dimethylethyl)-3-hydroxy-2-oxo-1-(4-meth-
oxyphenyl)-1-azaspiro[3.5]nonane 9. Compound 9 was pre-
pared by stirring a mixture of 1 M KOH (40 mL), THF (25 mL), and
3-acetoxy-7(e)-(1,1-dimethylethyl)-1-(4-methoxyphenyl)-2-oxo-1-aza-
spiro[3.5]nonane 4a (718 mg, 2.0 mmol) following the procedure de-
scribed for 5. Yield: 650 mg (91%), mp 180 ꢀC. IR (KBr): 3426, 2931,
1
1722, 1513, 1392, 1297, 1249, 1080. H NMR (500 MHz, CDCl3):
δ 0.84 (9H, s, tert-butyl), 1.02 (1H, t, CH2), 1.24 (1H, q, CH2), 1.49
(1H, m, CH2), 1.76À1.88 (3H, m, CH2), 1.95 (1H, dt, J = 3.8 Hz, CH2),
2.08 (1H, dt, J = 3.31, CH2), 2.25 (1H, dd, J = 2.03 Hz, 2.17, CH2), 3.77
(3H, s, OCH3), 4.59 (1H, s, C-3H), 6.83 (2H, d, J = 8.8 Hz, Ar-H), 7.39
(2H, d, J = 8.9 Hz, Ar-H). 13C NMR (125 MHz): δ 24.6, 25.0, 27.6, 29.8,
32.6, 34.5, 47.0, 55.4, 68.5, 81.6, 114.3, 121.7, 129.3, 156.9, 168.0. MS
(m/z): 317, 168, 160, 149, 134, 94. Anal. Calcd for C19H27NO3: C,
71.89; H, 8.57; N, 4.41. Found: C, 71.79; H, 8.49; N, 4.46.
Methods for Enzyme-Catalyzed Resolution of Spiro-β-
lactams. (R)-(+)-3-Acetoxy-1-(4-methoxyphenyl)-2-oxo-1-azaspiro-
[3.5]nonane (+)-1. (()-3-Acetoxy-1-(4-methoxyphenyl)-2-oxo-1-aza-
spiro[3.5]nonane (0.4 g) was added to aqueous phosphate buffer
(40 mL, 0.1 M, pH 7.0) and Tween 80 (1.0 g). To the above solution
was added a wet pallet of a whole cell preparation of ABL (0.4 g, 1100
units/mg) with continuous shaking at 200 rpm. During the course of the
reaction, the temperature was maintained at 30 ( 1 ꢀC. Thin layer
chromatography (TLC) and chiral high performance liquid chromatog-
raphy (HPLC) were carried out to monitor the progress of the reaction.
After completion of the reaction (18À20 h approx., 49% conversion),
the reaction was terminated by adding ethyl acetate and was extracted
with ethyl acetate (3 Â 30 mL). The organic layer was combined and
washed with water. The combined organic solvent layer was then dried
and evaporated under reduced pressure to furnish a mixture comprising
hydrolyzed alcohol and unhydrolyzed ester, which was separated by column
(()-3-Hydroxy-1-(4-methoxyphenyl)-7(e)-methyl-2-oxo-1-
azaspiro[3.5]nonane 6. Compound 6 was prepared by stirring a
mixture of 1 M KOH (50 mL), THF (30 mL), and 3-acetoxy-1-
(4-methoxyphenyl)-7(e)-methyl-2-oxo-1-azaspiro[3.5]nonane 2a (951
mg, 3.0 mmol) following the procedure described for 5. Yield: 775 mg
6004
dx.doi.org/10.1021/jo200363x |J. Org. Chem. 2011, 76, 5999–6006

The Journal of Organic Chemistry
ARTICLE
chromatography (230À400 mesh silica gel) using dichloromethane and
hexane as eluent giving (R)-(+)-3-acetoxy-1-(4-methoxyphenyl)-2-oxo-
1-azaspiro[3.5]nonane (+)-1 (180 mg, 90%) ee 99%, [R]D +35.0
(R)-(+)-3-Acetoxy-7(a)-ethyl-1-(4-methoxyphenyl)-2-oxo-1-azaspiro-
[3.5]nonane (+)-3b. Compound (+)-3b was resolved using the proce-
dure mentioned for (+)-3a from (()-3-acetoxy-7(a)-ethyl-1-(4-meth-
oxyphenyl)-2-oxo-1-azaspiro[3.5]nonane (50 mg) adsorbed on silica/
Celite (125 mg), aqueous phosphate buffer (2 mL, 0.1 M, pH 7.0), and
lipase AS/ABL (50 mg) at 300 rpm and 24 ( 1 ꢀC. After a certain degree
of conversion (5.5 h approx., 33% conversion), the reaction was terminated
by adding ethyl acetate. The usual workup gave (R)-(+)-3-acetoxy-7(a)-
ethyl-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]nonane (+)-3b (29 mg,
78%) ee 33%, [R]D25 +7.0 (c 1, CHCl3) and (S)-(À)-3-hydroxy-7(a)-
ethyl-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]-nonane (À)-8 (11.5 mg,
25
(c 1.0, CHCl3) and (S)-(À)-3-hydroxy-1-(4-methoxyphenyl)-2-oxo-1-
25
azaspiro[3.5]nonane (À)-5 (160 mg, 92%) ee 99% (chiral HPLC),
[R]D À46.0 (c 1.0, CHCl3).
(R)-(+)-3-Acetoxy-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]nonane
(+)-1. (()-3-Acetoxy-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]non-
ane 1 (100 mg) adsorbed on Celite (400 mg) and phosphate buffer
(10 mL, 0.1M. pH 7.0) was placed in a 25 mL culture tube. To the above
suspension was added a wet pallet of a whole cell preparation of ABL
(100 mg) and was kept in orbital shaker at 200 rpm. During the course of
the reaction, temperature was maintained at 25 ( 1 ꢀC. Thin layer
chromatography (TLC) and chiral high performance liquid chromatogra-
phy (HPLC) were carried out to monitor the progress of the reaction after
every hour. After completion of the reaction (4 h approx., 49% conversion),
the reaction was terminated. The usual workup and separation by CC gave
(3R)-(+)-3-acetoxy-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]nonane
(+)-1 (47 mg, 94%) ee 99%, [R]D25 +35.0 (c 1.0, CHCl3) and (3S)-(À)-
3-hydroxy-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]nonane (À)-5
25
92%) ee 98% (chiral HPLC), [R]D À35.5 (c 0.5, CHCl3).
(R)-(+)-3-Acetoxy-7(e)-(1,1-dimethylethyl)-1-(4-methoxyphenyl)-
2-oxo-1-azaspiro[3.5]nonane (+)-4a. Compound (+)-4a was resolved
using the procedure mentioned for (+)-1 from (()-3-acetoxy-7(e)-(1,1-
dimethylethyl)-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]nonane
(100 mg) adsorbed on silica (500 mg), aqueous phosphate buffer (5 mL,
0.1M. pH 7.0), and lipase Amano AS (200 mg). The reaction mixture
was shaken at 300 rpm and 23 ( 1 ꢀC. After a certain degree of
conversion (5 h approx., 42% conversion), the reaction was terminated
by adding ethyl acetate. The usual workup gave (R)-(+)-3-acetoxy-
7(e)-(1,1-dimethylethyl)-1-(4-methoxyphenyl)-2-oxo-1-azaspiro-[3.5]-
25
(39 mg, 91%) ee 97% (chiral HPLC), [R]D À46.0 (c 1.0, CHCl3).
(R)-(+)-3-Acetoxy-7(e)-methyl-1-(4-methoxyphenyl)-2-oxo-1-azas-
piro[3.5]nonane (+)-2a. (()-3-Acetoxy-7(e)-methyl-1-(4-methoxy-
phenyl)-2-oxo-1-azaspiro[3.5]nonane (100 mg) adsorbed on Celite
(500 mg) was suspended in an aqueous phosphate buffer (5 mL, 0.1
M, pH 7.0). To the above solution was added 100 mg of a whole cell
preparation of ABL. The reaction mixture was continuously shaken in an
orbital shaker at 200 rpm and 25 ( 1 ꢀC. The progress of the reaction
was monitored by TLC and chiral HPLC every hour. The reaction was
terminated after a certain degree of conversion (4 h approx., 41%
conversion), and the usual workup gave (R)-(+)-3-acetoxy-7(e)-meth-
yl-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]nonane (+)-2a (50 mg,
25
nonane (+)-4a (53 mg, 91%) ee 67%, [R]D +14.6 (c 1, CHCl3) and
(S)-(À)-3-hydroxy-7(e)-(1,1-dimethylethyl)-1-(4-methoxyphenyl)-2-oxo-
25
1-azaspiro[3.5]nonane (À)-9 (32 mg, 86%) ee 98.5% (chiral HPLC),
[R]D À60.0 (c 0.5, CHCl3).
X-ray Crystallography. Compounds 2a, 2b, 3a, 3b, 4a, and (À)-5
were crystallized in CH2Cl2 at room temperature. The data were collected
at 298 K on a Siemens P4 single crystal X-ray diffractometer using the
XSCANSpackage. Thedatawere collectedbytheθÀ2θ scan modewitha
variable scan speed up to a maximum of 2θ = 60ꢀ using graphite
monochromatized Mo KR radiations (λ = 0.71073 Å). To monitor the
stability of the crystal, 3 standard reflections were measured after every 97
reflections. The data were corrected for Lorentz and polarization effects.
The structures were solved by direct methods using SIR9716 and
refined by full-matrix least-squares refinement techniques on F2 using
SHELXL-9717 in the WINGX package18 of programs. All non-hydrogen
atoms were refined anisotropically. All hydrogen atoms were attached,
geometrically riding on their respective carrier atoms with Uiso being 1.5,
1.2, and 1.2 times the Uiso of their carrier methyl, methylene, and aromatic
carbon atoms, respectively. The crystal data and refinement details are
given in Supporting Information.
25
92%) ee 65%, [R]D +21.5 (c 0.4, CHCl3) and (S)-(À)-3-hydroxy-
7(e)-methyl-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]nonane (À)-6
(39 mg, 92%) ee 99%, [R]D25 -66.2 (c 1.0, CHCl3).
(R)-(+)-3-Acetoxy-7(e)-ethyl-1-(4-methoxyphenyl)-2-oxo-1-azaspiro-
[3.5]nonane (+)-3a. (()-3-Acetoxy-7(e)-ethyl-1-(4-methoxyphenyl)-
2-oxo-1-azaspiro[3.5]nonane (50 mg) was suspended in aqueous phos-
phate buffer (5 mL, 0.1 M, pH 7.0). To the above solution were added
100 mg of a wet pallet of a whole cell preparation of ABL and 0.5 mL of
DMF. The reaction mixture was stirred at 22 ꢀC. The progress of the
reaction was monitored by TLC and chiral HPLC. The reaction was
terminated after a certain degree of conversion (36 h approx., 48%
conversion), and the usual workup gave (R)-(+)-3-acetoxy-7(e)-ethyl-
1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]nonane (+)-2a (22 mg,
Computational Methods. Ab initio density functional calcula-
tions (DFT)19 have been performed to obtain absolute energies of the
important species referred to in this article. Complete optimizations
have been performed on all the structures using the B3LYP method20
and 6-31+G(d) basis set using the Gaussian03 software.21
25
85%) ee 99%, [R]D +30.4 (c 0.44, CHCl3) and (S)-(À)-3-hydroxy-
25
7(e)-ethyl-1-(4-methoxyphenyl)-2-oxo-1-azaspiro[3.5]nonane (À)-7
(19 mg, 92%) ee 99% (chiral HPLC), [R]D À60.8 (c 0.38, CHCl3).
(R)-(+)-3-Acetoxy-7(e)-ethyl-1-(4-methoxyphenyl)-2-oxo-1-azaspiro-
[3.5]nonane (+)-3a. (()-3-Acetoxy-7(e)-ethyl-1-(4-methoxyphenyl)-
2-oxo-1-azaspiro[3.5]nonane (60 mg) adsorbed on Celite (250 mg) was
suspended in an aqueous phosphate buffer (5 mL, 0.1 M, pH 7.0). To
the above solution were added 200 mg of a whole cell preparation of
ABL and 0.5 mL of acetonitrile. The reaction mixture was continuously
shaken in an orbital shaker at 300 rpm and 22 ( 1 ꢀC. Thin layer
chromatography (TLC) and chiral high performance liquid chromatog-
raphy (HPLC) were carried out to monitor the progress of the reaction
after every hour. After a certain degree of conversion (5 h approx., 43%
conversion), the reaction was terminated by adding ethyl acetate. The
’ ASSOCIATED CONTENT
S
Supporting Information. Experimental procedures, spec-
b
tral data, X-ray structures, computational data, and cif files. This
material is available free of charge via the Internet at http://
pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: sctaneja@iiim.ac.in.
usual workup and CC gave (R)-(+)-3-acetoxy-7(e)-ethyl-1-(4-methoxy-
25
phenyl)-2-oxo-1-azaspiro[3.5]nonane (+)-3a (23 mg), ee 82%, [R]D
+
Present Addresses
#Department of Chemistry, Govt. College for Women,
Gandhi Nagar, Jammu, 180 005, J&K, India.
36.3 (c 0.5, CHCl3) and (S)-(À)-3-hydroxy-7(e)-ethyl-1-(4-meth-
25
oxyphenyl)-2-oxo-1-azaspiro[3.5]nonane (À)-7 (19 mg, 92%), ee 99%
(chiral HPLC), [R]D À61 (c 0.5, CHCl3).
6005
dx.doi.org/10.1021/jo200363x |J. Org. Chem. 2011, 76, 5999–6006

The Journal of Organic Chemistry
ARTICLE
’ ACKNOWLEDGMENT
(11) Itoh, T.; Kuroda, K.; Tomosada, M.; Takagi, Y. J. Org. Chem.
1991, 56, 797–804.
The authors thank Dr. G. N. Qazi, ex-director of the institute,
for supporting the work, Dr. S. Koul, scientist, for some useful
suggestions.
(12) (a) Taskinen, E. Struct. Chem. 1998, 9, 411–18. (b) Alan, R.;
Potts, A. R.; Baer, T. J. Mol. Struct.: THEOCHEM 1997, 419, 11–18. (c)
Lightner, D. A.; Crist, B. V. Appl. Spectrosc. 1979, 33, 307–10.
(13) (a) Cossio, F. P.; Arrieta, A.; Sierra, M. A. Acc. Chem. Res. 2008,
41, 925–36. and the references cited therein. (b) Liang, Y.; Jiao, L.;
Zhang, S.; Yu, Z. X.; Xu, J. J. Am. Chem. Soc. 2009, 131, 1542–49.
(c) Pacansky, J.; Chang, J. S.; Brown, D. W.; Schwarz, W. J. Org. Chem.
1982, 47, 2233–34. (d) Moore, H. W.; Hughes, G.; Srinivasachar, K.;
Fernandez, M.; Nguyen, N. V.; Schoon, D.; Tranne, A. J. Org. Chem.
1985, 50, 4231–38. (e) Lynch, J. E.; Riseman, S. M.; Laswell, W. L.;
Tschaen, D. M.; Volante, R. P.; Smith, G. B.; Shinkai, I. J. Org. Chem.
1989, 54, 3792–96. (f) Venturini, A.; Gonzalez, J. J. Org. Chem. 2002,
67, 9089–92.
(14) (a) Bharatam, P. V.; Kumar, R. S.; Mahajan, M. P. Org.
Lett. 2000, 2, 2725–27. (b) Qi, H.; Li, X.; Xu, J. Org. Biomol. Chem.
2011, 9, 2702–14. (c) Assfeld, X.; RuizÀlopez, M. F.; Gonzalez, J.;
Lopez, R.; Sordo, J. A.; Sordo, T. L. J. Comput. Chem. 1994, 15, 479.
(d) Compomanes, P.; Menendez, M. I.; Sordo, T. L. J. Phys. Chem. A
2005, 109, 11022–26.
’ REFERENCES
(1) (a) Alcaide, B.; Almendros, P.; Campo, T. M.; Acebes, R. R.
Tetrahedron Lett. 2004, 45, 6429–31. (b) Setti, E. L.; Micetich, R. G.
Curr. Med. Chem. 1998, 5, 101–14. (c) The Organic Chemistry of
β-Lactams; Georg, G. I., Ed.; VCH: New York, 1993.
(2) (a) Page, M. I.; Laws, A. P. Tetrahedron 2000, 56, 5631–38.
(b) Bonneau, P. R.; Hasani, F.; Plouffe, C.; Malenfant, E.; LaPlante, S. R.;
Hopkins, J. L.; Morelock, M. M.; Cordingley, M. G.; Deziel, R. J. Am.
Chem. Soc. 1999, 121, 2965–73. (c) Vaccaro, W. D.; Davis, H. R. Bioorg.
Med. Chem. Lett. 1998, 8, 313–18. For reviews, see: (d) Alcaide, B.;
Almendros, P. Synlett 2002, 381–93. (e) Alcaide, B.; Almendros, P.
Chem. Soc. Rev. 2001, 30, 226–40. (f) Palomo, C.; Aizpurua, J. M.;
Ganboa, I.; Oiarbide, M. Synlett 2001, 1813–27. (g) Ojima, I.; Delaloge,
F. Chem. Soc. Rev. 1997, 26, 377–87. (h) Manhas, M. S.; Wagle, D. R.;
Chiang, J.; Bose, A. K. Heterocycles 1988, 27, 1755–1802. (i) Banik, B. K.;
Samajdar, S.; Becker, F. F. Mol. Med. Rep. 2010, 3, 319–21. (j) O’Boyle,
N. M.; Greene, L. M.; Bergin, O.; Fichet, J. B.; McCabe, T.; Lloyd, D. G.;
Zisterer, D. M.; Meegan, M. J. Bioorg. Med. Chem. 2011, 19, 2306–25.
(k) He, P.; Nie, Y. B.; Wu, J.; Ding, M. W. Org. Biomol. Chem. 2011,
9, 1429–36. (l) Li, X.; Yin, Q.; Jiao, L.; Qin, Z.; Feng, J.; Chen, H.; Zhang,
J.; Meng, M. Carbohydr. Res. 2011, 346, 401–09. (m) Chen, H.; Zhao, J.;
Li, Y.; Shen, F.; Li, X.; Yin, Q.; Qin, Z.; Yan, X.; Wang, Y.; Zhang, P.;
Zhang, J. Bioorg. Med. Chem. Lett. 2011, 21, 574–76. (n) Ibrahim, Y. A.;
Al-Azemi, T. F.; Abd El-Halim, M. D. J. Org. Chem. 2010, 75, 4508–13.
(o) Feroci, M.; Chiarotto, I.; Orsini, M.; Inesi, A. Chem. Commun. 2010,
46, 4121–23. (p) Banik, B. K.; Banik, I.; Becker, F. F. Eur. J. Med. Chem.
2010, 45, 846–48. (q) Ibrahim, Y. A.; Al-Azemi, T. F.; Abd El-Halim,
M. D.; John, E. J. Org. Chem. 2009, 74, 4305–10. (r) Burꢀes, J.; Martín, M.;
Urpí, F.; Vilarrasa, J. J. Org. Chem. 2009, 74, 2203–6. (s) Zhang, Y. R.;
He, L.; Wu, X.; Shao, P. L.; Ye, S. Org. Lett. 2008, 10, 277–80. (t)
Charafeddine, A.; Dayoub, W.; Chapuis, H.; Strazewski, P. Chemistry
2007, 13, 5566–84. (u) Jiao, L.; Liang, Y.; Xu, J. J. Am. Chem. Soc. 2006,
128, 6080.
(3) (a) Alonso, E.; Lopez-Ortiz, F.; del Pozo, C.; Macias, A.;
Gonzalez, J. J. Org. Chem. 2001, 66, 6333–38. (b) Alonso, E.; del Pozo,
C.; Gonzalez, J. Synlett 2002, 69–72.
(4) Kambara, T.; Tomioka, K. J. Org. Chem. 1999, 64, 9282–85.
(5) (a) Khasanov, A. B.; Ramirez-Weinhouse, M. M.; Webb, T. R.;
Thiruvazhi, M. J. Org. Chem. 2004, 69, 5766–69. (b) Chowdari, N. S.;
Suri, J. T.; Barbas, C. F., III. Org. Lett. 2004, 6, 2507–10. (c) Macias, A.;
Alonso, E.; del Pozo, C.; Venturini, A.; Gonzalez, J. J. Org. Chem. 2004,
69, 7004–12. (d) Arora, R.; Venugopalan, P.; Bari, S. S. J. Chem. Sci.
2010, 122, 125.
(6) (a) Conformational Behavior of Six-Membered Rings; Juaristi, E.,
Ed.; VCH: New York, 1995. (b) Eliel, E. L.; Wilen, S. H. Stereochemistry
of Organic Compounds; JohnWiley & Sons: New York, 1994. (c) Han,
S.; Yoo, H. S.; Kim, S. K. J. Phys. Chem. A. 2010, 114, 10005–10.
(7) Gill, G.; Pawar, D. M.; Noe, E. A. J. Org. Chem. 2005, 70,
10726–31.
(15) Cieplack, A. S. J. Am. Chem. Soc. 1981, 103, 4540–52.
(16) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115.
(17) Sheldrick, G. M. SHELXS-97, Program for the Solution of Crystal
Structures, University of G€ottingen, Germany, 1997.
(18) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(19) (a) Parr, R. G.; Yang, W. Density Functional Theory of Atoms and
Molecules; Oxford University Press: New York, 1989. (b) Bartolotti, L. J.;
Fluchick, K. In Reviews in Computational Chemistry; Lipkowitz, K. B.;
Boyd, D. B., Eds.; VCH Publishers: New York, 1996; Vol. 7, p 187.
(20) (a) Becke, A. D. J. Chem. Phys. 1993, 98, 5648. (b) Lee, C.;
Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785. (c) Perdew, J. P.; Wang,
Y. Phys. Rev. B 1992, 45, 13244.
(21) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.;
Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.;
Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson,
G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.;
Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.;
Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich,
S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.;
Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.;
Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.;
Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham,
M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian
03, Revision C.02, Gaussian, Inc., Wallingford, CT, 2004.
(8) (a) Dugar, S.; Clader, J. W.; Chan, T.-M.; Davis, H., Jr. J. Med.
Chem. 1995, 38, 4875–77. (b) Burnett, D. A.; Caplen, M. A.; Davis,
H. R., Jr.; Burrier, R. E.; Clader, L. W. J. Med. Chem. 1994, 37, 1733–36.
(c) Wu, G.; Tormos, W. J. Org. Chem. 1997, 62, 6412–14. (d)
Cremonesi, G.; Croce, P. D.; Fontana, F.; Rosa, C. L. J. Org. Chem.
2010, 75, 2010–17.
(9) (a) Moriconi, E. J.; Kelly, J. F. J. Am. Chem. Soc. 1966, 88, 365–66.
(b) Moriconi, E. J.; Kelly, J. F. J. Org. Chem. 1968, 33, 3036–46. (c)
Moriconi, E. J.; Kelly, J. F. Tetrahedron Lett. 1968, 24, 1435–39. (d)
Manhas, M. S.; Chib, J. S.; Chiang, Y. H.; Bose, A. K. Tetrahedron Lett.
1969, 25, 4421–26.
(10) Staudinger, H. Justus Liebigs Ann. Chem. 1907, 356, 51–123.
6006
dx.doi.org/10.1021/jo200363x |J. Org. Chem. 2011, 76, 5999–6006