Access to optically pure 4- and 5-substituted lactones: A case of chemical-biocatalytical cooperation

Article abstract of DOI:10.1021/jo026605q

Optically pure or highly enantiomerically enriched 4- and 5-substituted lactones are rather difficult to obtain. Chemical or enzymatic syntheses alone are not particularly successful. A combination of chemical catalysis and biocatalysis, however, provides a convenient route to a variety of these useful chiral compounds. In this paper we describe the synthesis of several optically pure 4- and 5-substituted lactones obtained via whole cell-catalyzed Baeyer-Villiger oxidations of highly enantiomerically enriched 3-alkyl cyclic ketones. Such chiral ketones are readily accessed by recently developed copper-catalyzed asymmetric conjugate reductions of the corresponding enones. A very high proximal regioselectivity and complete chirality transfer was obtained by employing biological Baeyer-Villiger oxidations, using recombinant E. coli strains that overexpress cyclopentanone monooxygenase (CPMO). A comparative study showed that CPMO gives superior results to those obtained with cyclohexanone monooxygenase (CHMO) catalyzed oxidations.

Full text of DOI:10.1021/jo026605q

Access to Op tica lly P u r e 4- a n d 5-Su bstitu ted La cton es: A Ca se of
Ch em ica l-Bioca ta lytica l Coop er a tion
Shaozhao Wang and Margaret M. Kayser*
Department of Physical Sciences, University of New Brunswick, Saint J ohn, N.B. E2L 4L5, Canada
Valdas J urkauskas
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
kayser@unbsj.ca
Received October 24, 2002
Optically pure or highly enantiomerically enriched 4- and 5-substituted lactones are rather difficult
to obtain. Chemical or enzymatic syntheses alone are not particularly successful. A combination of
chemical catalysis and biocatalysis, however, provides a convenient route to a variety of these useful
chiral compounds. In this paper we describe the synthesis of several optically pure 4- and
5-substituted lactones obtained via whole cell-catalyzed Baeyer-Villiger oxidations of highly
enantiomerically enriched 3-alkyl cyclic ketones. Such chiral ketones are readily accessed by recently
developed copper-catalyzed asymmetric conjugate reductions of the corresponding enones. A very
high proximal regioselectivity and complete chirality transfer was obtained by employing biological
Baeyer-Villiger oxidations, using recombinant E. coli strains that overexpress cyclopentanone
monooxygenase (CPMO). A comparative study showed that CPMO gives superior results to those
obtained with cyclohexanone monooxygenase (CHMO) catalyzed oxidations.
In tr od u ction
cyclohexanones to divergent regioisomers.5 Such diver-
gent behavior of enantiomers was noted earlier by
Furstoss and co-workers in CHMO-catalyzed oxidation
of racemic bicyclo[3.2.0]heptenones and dihydrocarvone.7
The corresponding oxidations of 3-methyl, ethyl, propyl,
and allyl cyclopentanones were nonselective and pro-
duced racemic mixtures of both regioisomers.6
In the case of 3-cyclohexanones substituted with the
propyl or butyl groups, and 3-cyclopentanones with
chains longer than four carbon atoms, only the proximal
regioisomers were formed, with modest enantioselectivity
favoring (R) configuration for ꢀ-caprolactones,5 and no
significant enantioselectivity for δ-valerolactones.6 Thus,
the access to optically pure 4- and 5-substituted lactones
is not easy by either chemical or biological routes.
Since several synthetic methods have been developed
to afford optically pure or highly enantioenriched ketones,
the combination of chemical synthesis and enzymatic
Baeyer-Villiger oxidation allows for regio- and enan-
tioselective synthesis of 4- and 5-substituted lactones.
Here we report the preparation of these compounds
achieved through the cooperation of chemical and biologi-
cal catalysis.
Chemical Baeyer-Villiger oxidations of racemic 3-sub-
stituted cyclic ketones are not particularly useful reac-
tions since they generally lead to the formation of two
enantiomeric pairs of regioisomeric lactones;1,2 the cor-
responding transformations mediated by cyclohexanone
monooxygenase (CHMO) or cyclopentanone monooxyge-
nase (CPMO) are more selective.3,4 We have observed in
the past that the products of CHMO-catalyzed oxidations
of 3-substituted cyclohexanones and cyclopentanones
depended on the size of the substituents.5,6 Thus CHMO
cleanly converted the antipodes of 3-methyl and 3-ethyl
* Corresponding author. Phone: (506) 648-5576. Fax: (506) 648-
5650.
(1) For reviews on chemical Baeyer-Villiger oxidations, see: (a)
Strukul, G. Angew. Chem., Int. Ed. 1998, 37, 1199-1209. (b) Renz,
M.; Meunier, B. Eur. J . Org. Chem. 1999, 737-750.
(2) For recent examples on chemical Baeyer-Villiger oxidations,
see: (a) Neimann, K.; Neumann, R. Org. Lett. 2000, 2, 2861-2863.
(b) Lambert, A.; Elings, J . A.; Macquarrie, D. J .; Carr, G.; Clark, J . H.
Synlett 2000, 1052-1054. (c) ten Brink, G.-J .; Vis, J .-M.; Arends, I.
W. C. E.; Sheldon, R. A. J . Org. Chem. 2001, 66, 2429-2433. (d) Corma,
A.; Nemeth, L. T.; Renz, M.; Valencia, S. Nature 2001, 412, 423-425.
(e) Berkessel, A.; Andreae, M. R. M. Tetrahedron Lett. 2001, 42, 2293-
2295. (f) Bolm, C.; Palazzi, C.; Francio, G.; Leitner, W. Chem. Commun.
2002, 1588-1589. (g) Murahashi, S.-I.; Ono, S.; Imada, Y. Angew.
Chem., Int. Ed. 2002, 41, 2366-2368. (h) Watanabe, A.; Uchida, T.;
Ito, K.; Katsuki, T. Tetrahedron Lett. 2002, 43, 4481-4485.
(3) For reviews on enzyme-catalyzed Baeyer-Villiger oxidations,
see: (a) Stewart, J . D. Curr. Org. Chem. 1998, 2, 195-216. (b) Leonida,
M. D. Curr. Med. Chem. 2001, 8, 345-369.
Resu lts a n d Discu ssion
Chemical Baeyer-Villiger oxidations of 3-substituted
cyclic ketones lead to the formation of two enantiomeric
(4) For recent examples on enzyme-catalyzed Baeyer-Villiger oxida-
tions, see: (a) Sheng, D.; Ballou, D. P.; Massey, V. Biochemistry 2001,
40, 11156-11167. (b) Colonna, S.; Del Sordo, S.; Gaggero, N.; Carrea,
G.; Pasta, P. Heteroatom Chem. 2002, 13, 467-473.
(5) Stewart, J . D.; Reed, K. W.; Martinez, C. A.; Zhu, J .; Chen, G.;
Kayser, M. M. J . Am. Chem. Soc. 1998, 120, 3541-3548.
(6) Kayser, M. M.; Chen, G.; Stewart, J . D. J . Org. Chem. 1998, 63,
7103-7106.
(7) (a) Alphand, V.; Archelas, A.; Furstoss, R. Tetrahedron Lett.
1989, 30, 3663-3664. (b) Alphand, V.; Furstoss, R. Tetrahedron:
Asymmetry 1992, 3, 379-382.
10.1021/jo026605q CCC: $25.00 © 2003 American Chemical Society
Published on Web 07/15/2003
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J . Org. Chem. 2003, 68, 6222-6228

Access to Optically Pure 4- and 5-Substituted Lactones
SCHEME 1
corresponding enones. This recently developed method
employs catalytic amounts of CuCl, NaOt-Bu, and a
chiral bis-phosphine ligand with polymethylhydrosilox-
ane (PMHS), as a stoichiometric reductant, to generate
a highly enantioselective catalyst for 1,4-reduction.11
The Baeyer-Villiger oxidations were performed with
two engineered E. coli strains, one expressing cyclohex-
anone monooxygenase (CHMO)13 and the other express-
ing cyclopentanone monooxygenase (CPMO).14 The con-
structions of the E. coli strain expressing CHMO from
Acinetobacter sp. NCIB 9871 and CPMO from Comamo-
nas sp. NCIB 9872 have been described in detail else-
where.13,14 Both constructs have a strong promoter and
produce an excess of the desired proteins when induced
by adding isopropyl thio â-D-galactoside (IPTG) to the
growth media. The maintenance of the recombinant
organisms and the fermentations are simple to perform.
All biotransformations discussed in this paper were
carried out in a standard organic laboratory without
specialized equipment.
pairs of regioisomeric lactones. In contrast to 2-alkyl-
substituted ketones, there is no electronic preference for
migration of one of the two carbon-carbon bonds. We
have reported earlier5 that oxidations of 3-substitued
cyclopentanones and cyclohexanones by CHMO-express-
ing engineered baker’s yeast were more selective and
produced one or the other regioisomer depending on the
size of a substituent. However, at the outset of this study,
the CPMO-catalyzed Baeyer-Villiger oxidations of 3-sub-
stituted cyclic ketones5 were not known.
Our preliminary experiments with CPMO-catalyzed
oxidations of several racemic substrates yielded the
proximal regioisomer exclusively, regardless of the size
of the tether. Unfortunately, no enantio-preference could
be detected in any of the CPMO reactions. Although
kinetic resolution8 of 3-alkylcyclohexanones, particularly
with longer alkyl chains, can be achieved in the course
of the CHMO-catalyzed reactions, the process is tedious
and the yields are low.5,6 Furthermore, no kinetic resolu-
tion of 3-alkylcyclopentanones was observed.
All reactions, monitored by chiral-phase GC, were
completed within 18-28 h. In the case of racemic
compounds 4c and 4e, CHMO-catalyzed biotransforma-
tions were allowed to proceed to ca. 50% conversion to
assess the degree of kinetic resolution obtainable in
isolated products. The parallel reactions mediated by
CPMO were allowed to reach 100% conversion since no
enantiopreference was observed in the course of these
transformations. Control experiments in which the host
strains (E.coli BL21 and E.coli DH5R) were used instead
of the plasmid-containing strains were run routinely and
showed no lactone formation, confirming that CHMO or
CPMO was indeed responsible for the observed Baeyer-
Villiger reactions.
In contrast to CHMO-mediated Baeyer-Villiger oxida-
tions of ketones to lactones, small quantities of corre-
sponding hydroxy acids were obtained when CPMO
catalyst was used, resulting in lower isolated yields of
the desired products.15 The control experiments with two
E. coli carrier strains [DH5R] vs [BL21] showed that the
E. coli [DH5R] contains an enzyme or enzymes that can
slowly hydrolyze the proximal valerolactones but not
caprolactones. There was no lactone hydrolysis observed
with the E. coli [BL21] strain.
Thus, neither of the two enzymes provides a convenient
route to optically pure ꢀ-caprolactones and δ-valerolac-
tones from racemic 3-substituted cyclic ketones. An
obvious way to circumvent this problem was to use
optically pure or highly enantioenriched 3-alkyl cyclic
ketones. Recently, the latter compounds became more
readily available through enantioselective conjugate ad-
dition of organometallic reagents9,10 to R,â-unsaturated
cyclic ketones and asymmetric conjugate reduction of
cyclic enones.11 The marriage of chemical and biological
catalytic methods provided a convenient route to optically
pure 3- and 4-substituted lactones (Scheme 1).
The enantioenriched cyclic ketones12 used in this study
were prepared via asymmetric conjugate reduction of the
In addition to compounds listed in Tables 1 and 2, two
other optically pure 3-substituted cyclopentanones (S)-
4g and (S)-4h were tested as possible substrates (Figure
1). In both cases no reaction was observed after 24 h of
fermentation with either CHMO or CPMO, and ketones
were recovered unchanged.
As in the “designer yeast”- mediated reactions reported
earlier,5 the E. coli (CHMO)-catalyzed oxidation of (R)-
3-methylcyclohexanone 1a gave exclusively the proximal
lactone 2a while its antipode (S)-1a was converted to the
distal lactone 3a . Highly enantiomerically enriched (R)-
1b (81% ee) and (S)-1c (83% ee) yielded (R)-2b (94% ee)
and (S)-2c (56% ee), respectively. The results obtained
(8) Leading references on kinetic resolution: (a) Kagan, H. B.; Fiaud,
J . C. Top. Stereochem. 1988, 18, 249-330. (b) Kagan, H. B. Tetrahedron
2001, 57, 2449-2468. (c) Keith, J . M.; Larrow, J . F.; J acobsen, E. N.
Adv. Synth. Catal. 2001, 343, 5-26. (d) Blackmond, D. G. J . Am. Chem.
Soc. 2001, 123, 545-553. For recent treatment of biocatalytic aspects
of kinetic resolution see: Faber, K.; Kroutil, W. Tetrahedron: Asym-
metry 2002, 13, 377-382.
(9) Reviews on conjugate addition: (a) Feringa, B. L. Acc. Chem.
Res. 2000, 33, 346-353. (b) Krause, N.; Hoffmann-Ro¨der, A. Synthesis
2001, 171-196. (c) Hayashi, T. Synlett 2001, 879-887.
(10) For recent examples of enantioselective conjugate addition to
cyclic enones, see: (a) Arnold, L. A.; Imbos, R.; Mandoli, A.; de Vries,
A. H. M.; Naasz, R.; Feringa, B. L. Tetrahedron 2000, 56, 2865-2878.
(b) Escher, I. H.; Pfaltz, A. Tetrahedron 2000, 56, 2879-2888. (c)
Chataigner, I.; Gennari, C.; Ongeri, S.; Piarulli, U.; Ceccarelli, S. Chem.
Eur. J . 2001, 7, 2628-2634. (d) Degrado, S. J .; Mizutani, H.; Hoveyda,
A. H. J . Am. Chem. Soc. 2001, 123, 755-756. (e) Reetz, M. T.; Gosberg,
A.; Moulin, D. Tetrahedron Lett. 2002, 43, 1189-1191.
(11) Moritani, Y.; Appella, D. H.; J urkauskas, V.; Buchwald, S. L.
J . Am. Chem. Soc. 2000, 122, 6797-6798. For application of asym-
metric conjugate reduction to disubstituted cyclopentenones, see:
J urkauskas, V.; Buchwald, S. L. J . Am. Chem. Soc. 2002, 124, 2892-
2893.
(12) Compounds (R)-1b and (R)-4b were a gift from Drs. Escher and
Pfaltz, who synthesized them via 1,4-additions of organozinc reagents
to cyclic enones. See ref 10b.
(13) Mihovilovic, M. D.; Chen, G.; Wang, S.; Kyte, B.; Rochon, F.;
Kayser, M. M.; Stewart, J . D. J . Org. Chem. 2001, 66, 733-738.
(14) Iwaki, H.; Hasegawa, Y.; Wang, S. Z.; Kayser, M. M.; Lau, P.
C. K. Appl. Environ. Microbiol. 2002, 68, 5671-5684.
(15) The hydroxy acids were not detectable on GC since at high
temperature they undergo condensation to yield the corresponding
lactones.
J . Org. Chem, Vol. 68, No. 16, 2003 6223

Wang et al.
TABLE 1. CHMO- a n d CP MO-Ca ta lyzed Oxid a tion s of 3-Alk ylcycloh exa n on es
E. coli CHMO
2:3 ratio
E. coli CPMO
2:3 ratio
reactant
(abs configur)
conv, %
conv, %
R
(isolated yield, %)
2 (% ee)a
3 (% ee)
(isolated yield, %)
2 (% ee)
3 (% ee)
Me
(R)-1a (100 % ee)
(S)-1a (100 % ee)
(R)-1b (81 % ee)
(S)-1c (83 % ee)
100 (77)
100 (60)
100 (89)
38 (ND)
>99
(100 R)
-
-
100 (75)
>99
-
(100 R)
ND
Me
Et
99
ND
(100 S)
94
6
100 (87)
100 (85)
>99
-
-
(94 R)
>99
(>99 S)
(80 R)
>99
n-Bu
-
(56 S)
(83 S)
a
The ee of starting materials and products were determined by chiral GC.
TABLE 2. CHMO- a n d CP MO-Ca ta lyzed Oxid a tion s of 3-Alk ylcyclop en ta n on es
E. coli CHMO
5:6 ratio
E. coli CPMO
5:6 ratio
reactant
(abs configur)
conv, %
(isolated yield, %)
5
6
conv, %
(isolated yield, %)
5
6
R
(% ee)a
(% ee)
(% ee)
(% ee)
Me
Me
Et
(R,S)-4a (racemic)
(R)-4a (>99% ee)
(R,S)-4b (racemic)
(R)-4b (86% ee)
(R,S)-4c (racemic)
(S)-4d (87% ee)
(R,S)-4e (racemic)
(S)-4e (90% ee)
100 (95)
100 (88)
86 (80)
ND
13
(9 R)
10
(99 R)
20
(12 R)
ND
87
(36 S)
90
(99 R)
80
(32 S)
100 (68)
>99
-
-
-
-
-
-
-
-
-
(racemic)
100
100
(62)
100 (78)
(>99 R)
100
(racemic)
>99
Et
100 (69)
100 (70)
100 (75)
100 (76)
95 (84)
(86 R)
>99
n-Pr
53 (44)b
65 (58)c
44 (34)d
100 (88)
81 (80)e
83
(60 S)
33
(97 R)
>99
(38 S)
95
(90 S)
>99
(99 S)
17
(33 R)
67
(93 S)
-
(racemic)
>99
i-Pr
(87 R)
>96
n-Bu
(racemic)
>99
n-Bu
5
(92 S)
>99
(CH2)2Ph
(S)-4f (88% ee)
-
100 (80)
(88 S)
a
b
The ee values of starting materials and products were determined by chiral GC. The remaining ketone was 25% ee (R). The absolute
configuration in this case was tentatively assigned by comparing the chiral GC traces of the n-propyl-substituted ketones and lactones
with those with 3-butyl substitution. c The remaining ketone was 84% ee. The remaining ketone was 25% ee (R). e The remaining ketone
d
was 42% ee.
are consistent with our diamond lattice-active site model
for cyclohexanone monooxygenase.5 This model, illus-
trated in Figure 2, incorporates effects of the conforma-
tional equilibrium of a substrate within the active site
on enantioselectivity of CHMO-catalyzed reactions.5,6
Here, for example, while 3-ethyl substituted (R)-1b (81%
ee) is converted completely and rapidly to a mixture of
lactones (R)-2b and (S)-2b, both of higher optical purity
F IGURE 1. Compounds (S)-4g and (S)-4h are not suitable
substrates for CHMO and CPMO.
than the substrate, the 3-n-butyl-substituted ketone (S)-
1c (83% ee) reacts slowly (38% conversion after 24 h) to
give the proximal lactone (S)-2c with diminished ee (56%
ee). The remaining unreacted ketone (S)-2b is signifi-
cantly enantiomerically enriched (99% ee vs 83% ee) in
the process.
6224 J . Org. Chem., Vol. 68, No. 16, 2003

Access to Optically Pure 4- and 5-Substituted Lactones
F IGURE 2. Diamond lattice active site model for cyclohexanone monooxygenase (CHMO). (A) According to the model, the major
(R) enantiomer (90.5%) in equatorial conformation is the preferred (faster reacting) substrate and yields enantioselectively enriched
lactone 2b during fermentation. The antipode (S) (9.5%) is preferentially converted to the distal lactone 3b, which is also
enantiomerically enriched in the process. (B) In the case of 3-n-butylcyclohexanone, the (S)-enantiomer is disfavored. The n-butyl
chain in the equatorial position (see box) does not fit into the enzyme’s active site pocket. Conversely, the n-butyl group in the
axial position is conformationally disfavored and reacts more slowly than the (R)-enantiomer. As a result, only 38% conversion
is achieved after 24 h. The minor enantiomer (R) reacts faster and is completely converted to the lactone during that time. This
process results in enantiomeric enrichment of the remaining (S)-ketone; the optical purity of the lactone, however, is diminished.
Compared to 3-alkylcyclohexanones, 3-alkylcyclopen-
tanones show lower selectivity. This behavior has been
linked to the near equivalence of pseudoaxial and pseu-
doequatorial conformations.6 In the present study, similar
effects are evident. The conformational considerations
may apply but the effects are weak due to the intrinsic
flexibility of five-member rings and the resulting small
differences in energy between axial and equatorial sub-
stituents. The lack of such preferences is clearly evident
in the case of conversions of (S)-4d to (R)-5d and (S)-4f
to (S)-5f, where both lactones have higher optical purity
than the original ketones. This may be the result of
favorable stabilizing interactions between the substitu-
ents and the active site of the enzyme.
active site model available at present. The Baeyer-
Villiger oxidations with CPMO (whole cells, partly puri-
fied enzyme, or an overexpression E. coli system) indicate
that transformations of 2- and 4-alkyl-substituted cyclic
ketones tend to be less enantioselective than the corre-
sponding reactions performed with CHMO.15,16 The no-
table exceptions are prochiral bicyclo[4.3.0]ketones which
upon fermentation with CHMO produce (+) lactones in
excellent enantiomeric excess (>99%).17 CPMO-mediated
oxidations of 3-substituted cyclohexanones (Table 1) and
cyclopentanones (Table 2) are usually faster than the
corresponding CHMO transformations and reach 100%
conversion in less than 28 h.
(16) Wang, S. Z.; Chen, G.; Kayser, M. M.; Iwaki, H.; Lau, P. C. K.;
Hasegawa, Y. Can. J . Chem. 2002, 80, 613-621.
(17) Mihovilovic M. D.; Mu¨ller, B.; Kayser, M. M.; Stanetty, P.
Synlett 2002, 700-703.
In contrast to CHMO, the selectivity of CPMO in the
Baeyer-Villiger oxidations of 3-substituted cyclic ketones
has not been previously investigated and there is no
J . Org. Chem, Vol. 68, No. 16, 2003 6225

Wang et al.
were characterized by 1H NMR, 13C NMR, and IR spectroscopy,
in addition to high-resolution mass spectra (Finnegan MAT
System 8200 spectrometer). Chiral GC analyses were per-
formed on a Shimadzu GC-9A gas chromatograph, using a
Supelco Inc. FILM â-Dex225 column.
All substrates investigated, irrespective of their abso-
lute configurations, were converted to the corresponding
proximal lactones. However, the products formed were
racemic and no enantiopreference was observed in any
of the transformations. The chiral phase GC analyses of
samples collected during the reactions showed that both
enantiomers were converted at approximately the same
rate. This apparent disadvantage of CPMO-catalyzed
oxidations is circumvented when optically pure ketones
are used and is compensated by a very high and predict-
able regioselectivity of these reactions.
Gen er a l P r oced u r e for Cop p er -Ca ta lyzed Asym m etr ic
Con ju ga t e R ed u ct ion s. A chiral bisphosphine (0.1 mmol)
was placed in an oven-dried Schlenk flask and dissolved in
toluene (2.0 mL). The Schlenk flask was then moved into a
nitrogen-filled drybox. In the drybox, NaOt-Bu (10 mg, 0.1
mmol) and CuCl (10 mg, 0.1 mmol) were weighed into a vial.
The toluene solution of chiral bisphosphine was added via pipet
to the vial to dissolve the solids and the resulting solution was
then transferred back into the Schlenk flask. The Schlenk flask
was removed from the drybox, the solution was stirred for 10-
20 min, and PMHS (0.126 mL, 2.1 mmol) was added to the
solution under argon purge and stirred for 10 min at room
temperature. The resulting reddish orange solution was then
cooled to 0 °C. The solution of cyclic enone (2.0 mmol) in 2.5
mL of toluene was added (on the walls of the Schlenk flask)
to the reaction solution. The reaction was stirred for the
indicated period of time. Consumption of cyclic enone was
monitored by GC. The catalyst-free filtrate was concentrated
and analyzed by GC to determine the percent conversion. The
Schlenk flask was opened and water (2 mL) was added. The
resulting solution was diluted with diethyl ether, washed once
with brine, and back extracted with diethyl ether. To the
combined organic extracts was added TBAF (2.0 mL, 1.0 M in
THF) and the resulting solution was stirred for 1 h. The
solution was then washed once with brine and back extracted
with diethyl ether and the organic layer was dried over
anhydrous MgSO4. The solvent was removed in vacuo and the
enantiomerically enriched starting material was purified by
silica column chromatography and analyzed by chiral GC to
determine the enantiomeric excess.
Con clu sion
Although CHMO and CPMO-catalyzed Baeyer-
Villiger oxidations of racemic 3-alkyl-substituted cyclo-
hexanones, and particularly 3-alkyl-substituted cyclo-
pentanones alone, do not provide convenient high-
yielding routes to optically pure lactones, their high and
predictable regioselectities are complementary when
optically pure or enantiomerically enriched ketones,
prepared via chemical enatioselective catalysis, are avail-
able. The combination of two catalytic methodologies,
therefore, allows the synthesis of rather difficult to obtain
but highly desirable chiral 4- and 5-substituted lactones.
Exp er im en ta l Section
Gen er a l Con sid er a tion . Toluene, THF, and Et2O were
purchased from J . T. Baker in CYCLE-TAINER solvent
delivery kegs, which were vigorously purged with argon for 2
h. Toluene was further purified by passing through two packed
columns of neutral alumina and copper(II) oxide under argon
pressure. THF and Et2O were further purified by passing
through a column of neutral alumina.18 For biocatalytical
oxidations, all solvents were purified by fractional distillation.
For asymmetric conjugate reductions, CuCl (99.995%) was
purchased from Strem and NaOt-Bu was purchased from
Aldrich and stored in a nitrogen-filled drybox. PMHS was
purchased from Aldrich, (S)-p-tol-BINAP was purchased from
Strem. All other reagents were available from commercial
sources and were used without further purification, unless
otherwise noted. All manipulations involving air-sensitive
materials were conducted in a Vacuum Atmospheres drybox
under an atmosphere of nitrogen. Unless otherwise stated, all
reactions were conducted in flasks sealed with a rubber septum
under a positive pressure of argon. Analytical thin-layer
chromatography was performed using E.M. Reagents 0.25 mm
silica gel 60 plates. Flash chromatography was performed on
E.M. Science Kieselgel 60 (230-400 mesh). Yields refer to
isolated yields of compounds of greater than 95% purity as
estimated by capillary GC and 1H NMR. Nuclear magnetic
resonance (NMR) spectra were recorded on a Varian XL-200,
or a Varian Mercury 300, or a Varian Unity 300, or a Brucker
AMX-400FT-NMR, or a Varian Inova 500 spectrometer. Split-
ting patterns are designated as follows: s, singlet; d, doublet;
dd, doublet of doublets; t, triplet; td, triplet of doublets; q,
quartet; qd, quartet of doublets; m, multiplet. Infrared (IR)
spectra were recorded on an Asi Applied Systems ReactIR 1000
(liquids and solids were measured neat on a DiComp probe)
or Mattson Satellite FT-IR spectrometer. Gas chromatography
(GC) analyses were performed on a Hewlett-Packard 6890 gas
chromatograph with an FID detector, using a 25 m × 0.20 mm
or a 30 m × 0.32 mm capillary column with cross-linked
methyl siloxane as a stationary phase. All new compounds
Precursors to asymmetric conjugate reductions, 3-alkyl
cyclic enones, were prepared by literature reported proce-
dures.19
3-(S)-n -Bu tylcycloh exa n on e (1c). Following the General
Procedure for the asymmetric conjugate reduction with (S)-
BIPHEMP and 3-butylcyclohexenone (0.304 g, 2.0 mmol) gave,
after 2 d at 0 °C and flash chromatography (8:1 hexanes:ethyl
acetate), the title compound as a clear oil (0.262 g, 85% yield).
Spectroscopic data for the title compound were consistent with
the previously reported data for this compound.20 For ee
determination see the procedure for 2c.
3-(R)-Isop r op ylcyclop en ta n on e (4d ). Following the Gen-
eral Procedure for the asymmetric conjugate reduction with
(S)-p-tol-BINAP and 3-isopropylcyclopentenone (0.248 g, 2.0
mmol) gave, after 4 d at 0 °C and flash chromatography (10:1
pentane:diethyl ether), the title compound as a clear oil (0.219
g, 87% yield). Spectroscopic data for the title compound were
consistent with the previously reported data for this com-
pound.21 For ee determination see the procedure for 6d .
3-(S)-n -Bu tylcyclop en ta n on e (4e). Following the General
Procedure for the asymmetric conjugate reduction with (S)-
p-tol-BINAP and 3-butylcyclopentenone (0.276 g, 2.0 mmol)
gave, after 12 h at 0 °C and flash chromatography (20:1
hexanes:ethyl acetate), the title compound as a clear oil (0.260
g, 93% yield). Spectroscopic data for the title compound were
consistent with the previously reported data for this com-
pound.22 For ee determination see the procedure for 5e.
3-(S)-P h en eth ylcyclop en ta n on e (4f). Following the Gen-
eral Procedure for the asymmetric conjugate reduction with
(S)-p-tol-BINAP and 3-phenethylcyclopentenone (0.372 g, 2.0
(19) Strok, G.; Danheiser, R. L. Org. Chem. 1973, 38, 1775-1776.
(20) J ones, P.; Reddy, C. K.; Knochel, P. Tetrahedron 1998, 54,
1471-1490.
(18) (a) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R.
K.; Timmers, F. J . Organometallics 1996, 15, 1518-1520. (b) Alaimo,
P. J .; Peters, D. W.; Arnold, J .; Bergman, R. G. J . Chem. Educ. 2001,
78, 64.
(21) Barnhart, R. W.; Wang, X.; Noheda, P.; Bergens, S. H.; Whelan,
J .; Bosnich, B. J . Am. Chem. Soc. 1994, 116, 1821-1830.
(22) Stangeland, E. L.; Sammakia, T. Tetrahedron 1997, 53, 16503-
16510.
6226 J . Org. Chem., Vol. 68, No. 16, 2003

Access to Optically Pure 4- and 5-Substituted Lactones
mmol) gave, after 24 h at 0 °C and flash chromatography (10:1
hexanes:ethyl acetate), the title compound as a clear oil (0.323
g, 86% yield). Spectroscopic data for the title compound were
consistent with the previously reported data for this com-
pound.23 For ee determination see the procedure for 5f.
P r op a ga tion of E. coli Str a in s. The E. coli strain BL21-
(DE3)(pMM04) was streaked from a frozen stock on LB-
Ampicillin plates and incubated at 30 °C until colonies were
1-2 mm in size. One colony was used to inoculate 10 mL of
an LB-Ampicillin medium in a 50-mL Erlenmeyer flask and
incubated at 30 °C, 250 rpm overnight. Sterile glycerol (15%
v/v) was added and the mixture was divided into 0.5-mL
aliquots and stored in a -80 °C freezer. The propagation of
the E. coli DH5R(pCMP201) was carried out in the same way.
The carrier strains BL21(DE3) and DH5R were propagated
by using the above protocol except that no ampicillin was used
in the plates and the medium.
Hz), 2.60 (2H, m), 1.88 (2H, m), 1.75 (1H, m), 1.63 (2H, m),
1.41 (2H, m), 1.26 (4H, m), 0.90 (3H, t, J ) 3.0 Hz) ppm. 13C
NMR (100 MHz, CDCl3) δ 176.2, 72.6, 38.6, 34.9, 34.3, 31.3,
29.2, 22.6, 21.3, 14.0 ppm.
(R)-5-Meth yl Tetr ah ydr opyr an -2-on e ((R)-5a).24 Biotrans-
formation according to the general protocol of (R)-3-methyl
cyclopentanone (0.100 g, 1.02 mmol, chiral GC analysis with
a Shimadzu GC-9A column indicated >99% ee) using E. coli
(CPMO) gave, after 28 h and flash chromatography (4:1
hexanes:ethyl acetate), the title compound as a pale yellow
oil (0.072 g, 62% yield). Chiral GC analysis with a Shimadzu
GC-9A column indicated >99% ee. [R]D 17.0 (c 0.72, CH2Cl2).
IR (neat) νmax 2962, 2880, 1732, 1462, 1262, 1177, 1113, 994,
777 cm-1. 1H NMR (400 MHz, CDCl3) δ 4.31 (1H,m), 3.91 (1H,
t, J ) 10 Hz), 2.63 (1H, m), 2.51 (1H, m), 2.07 (1H, m), 1.98
(1H, m), 1.55 (1H, m), 1.01 (3H, d, J ) 6.6 Hz) ppm. 13C NMR
(100 MHz, CDCl3) δ 171.1, 74.8, 29.1, 27.9, 27.5, 16.5 ppm.
(R)-5-Eth yl Tetr a h yd r op yr a n -2-on e ((R)-5b).25 Biotrans-
formation according to the general protocol of (R)-3-ethyltet-
rahydronpyran-2-one (0.050 g, 0.45 mmol, chiral GC analysis
with a Shimadzu GC-9A column indicated 84% ee) mediated
by E. coli (CPMO) gave, after 18 h and flash chromatography
(7:1 hexanes:ethyl acetate), the title compound as a pale yellow
oil (0.030 g, 69% yield). Chiral GC analysis with a Shimadzu
GC-9A column indicated 84% ee. [R]D -2.4 (c 2.3, CH2Cl2). IR
P r otocol for E. coli-Med ia ted Rea ction s. A saturated
culture of E. coli was prepared as above. This culture was used
at
a 1:100 ratio to inoculate an LB-Ampicillin medium
supplemented with 10% glucose in a baffled Erlenmeyer flask.
The culture was incubated at 30 °C, 250 rpm until OD600 was
approximately 0.6. IPTG stock solution (0.84 M/L, 200 mg/
mL) was added (0.1 µL per mL of medium) followed by the
substrate. If cyclodextrin was necessary to alleviate the
solubility problem, it was introduced at this stage. The culture
was agitated at 30 °C at 250 rpm and monitored by GC or
TLC until the reaction was finished. The culture was saturated
with NaCl and extracted with ethyl acetate. Combined extracts
were washed once with NaHCO3 (1%) and NaCl brine and
dried over anhydrous Na2SO4 or MgSO4. The solvent was
removed on a rotary evaporator and the residue was purified
by flash chromatography.
1
(neat) νmax 2967, 2927, 1743, 1262, 1223, 1071 cm-1. H NMR
(400 MHz, CDCl3) δ 4.34 (1H, ddd, J ) 11, 9, 1 Hz), 4.00 (1H,
m), 2.63 (1H, ddd, J ) 17, 6, 2 Hz), 2.51 (1H, m), 2.02 (1H, m),
1.87-1.60 (2H, m), 1.36 (2H, m), 0.97 (3H, t, J ) 7.5 Hz) ppm.
13C NMR (63 MHz, CDCl3) δ 174.0, 73.6, 34.7, 29.9, 25.3, 24.7,
11.5 ppm.
(()-5-n -P r op yl Tetr a h yd r op yr a n -2-on e (5c).6 Biotrans-
formation according to the general protocol of (()-3-n-propy-
lcyclopentanone (0.092 g, 0.73 mmol) mediated by E. coli
(CPMO) gave, after 24 h and flash chromatography (9:1
hexanes:ethyl acetate), the title compound as a colorless oil
(0.079 g, 70% yield). IR (neat) νmax 2960, 2927, 2875, 1743,
(R)-6-Meth yl-2-oxep a n on e ((R)-2a ).5 Biotransformation
according to the general protocol of (R)-3-methyl cyclopen-
tanone (0.050 g, 0.45 mmol, chiral GC analysis with
a
Shimadzu GC-9A column indicated >99% ee) mediated by E.
coli (CPMO) gave, after 20 h and flash chromatography (9:1
hexanes:ethyl acetate), the title compound as colorless oil
(0.043 g, 75% yield). Chiral GC analysis with a Shimadzu GC-
9A column indicated >99% ee. [R]D -33 (c 1.8, CH2Cl2). 1H
NMR (400 MHz, CDCl3) δ 4.10 (1H, dt, J ) 12, 1.2 Hz), 4.00
(1H, dd J ) 12, 8 Hz), 2.65 (1H, t, J ) 3 Hz), 2.61 (1H, t, J )
16 Hz), 1.94 (1H, m), 1.86 (1H, m), 1.67 (1H, m), 1.38 (2H, m),
0.98 (3H, d, J ) 20 Hz) ppm. 13C NMR (100 MHz, CDCl3) δ
176.0, 73.9, 36.9, 34.4, 33.8, 21.6, 17.7 ppm.
1
1190, 1052 cm-1. H NMR (400 MHz, CDCl3) δ 4.31 (1H, ddd,
J ) 15.6, 4.5, 1.9 Hz), 3.91 (1H, t, J ) 9.7 Hz), 2.56 (1H, m),
2.30 (1H, m), 1.94 (2H, m), 1.51 (1H, m), 1.30 (4H, m), 0.89
(3H, t, J ) 6.8 Hz) ppm. 13C NMR (100 MHz, CDCl3) δ 171.6,
73.6, 33.6, 32.5, 29.0, 25.4, 19.9, 14.0 ppm.
(R)-5-Isop r op yl Tetr a h yd r op yr a n -2-on e ((R)-5d ).26 Bio-
transformation according to the general protocol of (S)-3-
isopropyl cyclopentanone (0.050 g, 0.35 mmol, chiral GC
analysis with a Shimadzu GC-9A column indicated 87% ee)
mediated by E. coli (CPMO) gave, after 20 h and flash
chromatography (9:1 hexanes:ethyl acetate), the title com-
pound as a colorless oil (0.038 g, 68% yield). Chiral GC analysis
with a Shimadzu GC-9A column indicated 87% ee. [R]D 37 (c
3.8, CHCl3). IR (neat) νmax 2963, 2877, 1739, 1269, 1123, 1048,
772 cm-1. 1H NMR (250 MHz, CDCl3) δ 4.38 (1H, dq, J ) 18.5,
2.5 Hz), 4.06 (1H, dd, J ) 12.5, 10 Hz), 2.52 (2H, m), 1.96 (1H,
m), 1.80-1.52 (3H, m), 0.96 (6H, d, J ) 7.5 Hz) ppm. 13C NMR
(63 MHz, CDCl3) δ 172.0, 72.2, 42.6, 39.1, 29.2, 22.7, 20.0, 19.7
ppm.
(R)-6-Eth yl-2-oxep a n on e ((R)-2b).5 Biotransformation ac-
cording to the general protocol of (R)-3-ethylcyclohexanone
(0.093 g, 0.74 mmol, chiral GC analysis with a Shimadzu GC-
9A column indicated 81% ee) mediated by E. coli (CPMO) gave,
after 24 h and flash chromatography (9:1 hexanes:ethyl
acetate), the title compound as a colorless oil (0.085 g, 87%
yield). Chiral GC analysis with a Shimadzu GC-9A column
indicated 81% ee. [R]D -26 (c 2.1, CH2Cl2). IR (neat) νmax 2961,
2876, 1734, 1462, 1169 cm-1 1H NMR (400 MHz, CDCl3) δ
.
4.11 (1H, d, J ) 1.2 Hz), 4.01 (1H, dd, J ) 12.6, 7.8 Hz), 2.59
(2H, t, J ) 4.8 Hz), 1.87 (2H, m), 1.63 (2H, m), 1.41 (1H, m),
1.30 (2H, m), 0.92 (3H, t, J ) 7.4 Hz) ppm. 13C NMR (100 MHz,
CDCl3) δ 176.3, 72.7, 40.5, 34.6, 34.5, 24.7, 21.5, 11.6 ppm.
(S)-6-n -Bu tyl-2-oxep a n on e ((S)-2c).5 Biotransformation
according to the general protocol of (S)-3-n-butylcyclohexanone
(0.050 g, 0.32 mmol, chiral GC analysis with a Shimadzu GC-
9A column indicated 83% ee) mediated by E. coli (CPMO) gave,
after 28 h and flash chromatography (9:1 hexanes:ethyl
acetate), the title compound as a colorless oil (0.047 g, 85%
yield). Chiral GC analysis with a Shimadzu GC-9A column
indicated 83% ee. [R]D 2.7 (c 1.0, CH2Cl2). IR (neat) νmax 2927,
(S)-5-n -Bu tyl Tetr ah ydr opyr an -2-on e ((S)-5e).6 Biotrans-
formation according to the general protocol of (S)-3-n-butyl
cyclopentanone (0.048 g, 0.34 mmol, chiral GC analysis with
a Shimadzu GC-9A column indicated >95% ee) mediated by
E. coli (CPMO) gave, after 28 h and flash chromatography (7:1
hexanes:ethyl acetate), the title compound as a colorless oil
(0.045 g, 84% yield). Chiral GC analysis with a Shimadzu
GC-9A column indicated >95% ee. [R]D -1.6 (c 2.3, CH2Cl2).
IR (neat) νmax 2928, 1734, 1457, 1169 cm-1. 1H NMR (400 MHz,
(24) (a) Oikawa, M.; Oikawa, H.; Ichihara, A. Tetrahedron 1995, 51,
6237-6254. (b) Ozegowski, R.; Kunath, A.; Schick, H. Liebigs Ann.
Chem. Engl. 1994, 10, 1019-1023.
1
1735, 1458, 1352, 1273, 1165, 1048 cm-1. H NMR (400 MHz,
CDCl3) δ 4.14 (1H, d, J ) 8.0 Hz), 4.00 (1H, dd, J ) 8.5, 5.0
(25) Ashworth, P.; Belagali, S. L.; Casson, S.; Marczak, A.; Kocienski,
P. Tetrahedron 1991, 47, 9939-9946.
(23) Gadwood, R. C.; Mallick, I. M.; DeWinter, A. J . J . Org. Chem.
1987, 52, 774-782.
(26) Hiratake, J .; Yamamoto, K.; Yamamoto, Y.; Oda, J . Tetrahedron
Lett. 1989, 30, 1555-1556.
J . Org. Chem, Vol. 68, No. 16, 2003 6227

Wang et al.
CDCl3) δ 4.32 (1H, ddd, J ) 11, 5, 2 Hz), 3.93 (1H, t, J ) 10
Hz), 2.59 (1H, m), 2.46 (1H, m), 1.98 (1H, m), 1.87 (1H, m),
1.50 (1H, m), 1.28 (6H, m), 0.87 (3H, t, J ) 6.0 Hz) ppm. 13C
NMR (100 MHz, CDCl3) δ 171.6, 73.8, 32.8, 31.2, 29.0, 28.9,
25.5, 22.7, 13.9 ppm.
ee for 5d . [R]D -21 (c 2.8, CHCl3). IR (neat) νmax 2961, 2876,
1
1731, 1468, 1403, 1259, 1179, 1083 cm-1. H NMR (250 MHz,
CDCl3) δ 4.38 (1H, m), 4.23 (1H, ddd, J ) 11, 10, 2.5 Hz), 2.62
(1H, m), 2.23 (1H, dd, J ) 18, 10 Hz), 1.96 (1H, m), 1.80-1.53
(3H, m), 0.94 (3H, d, J ) 1.5), 0.91 (3H, d, J ) 1.5 Hz) ppm.
13C NMR (63 MHz, CDCl3) δ 172.1, 68.7, 37.8, 34.0, 32.3, 26.3,
19.2, 19.1 ppm.
(S)-5-P h en yleth yl Tetr a h yd r op yr a n -2-on e ((S)-5f). Bio-
transformation according to the general protocol of (S)-3-
phenethyl cyclopentanone (0.030 g, 0.16 mmol, chiral GC
analysis with a Shimadzu GC-9A column indicated 92% ee)
mediated by E. coli (CHMO) gave, after 24 h and flash
chromatography (7:1 hexanes:ethyl acetate), the title com-
pound as a colorless oil (0.026 g, 80% yield). Chiral GC analysis
with a Shimadzu GC-9A column indicated >95% ee. [R]D -0.3
(c 2.3, CH2Cl2). IR (neat) νmax 3026, 2928, 2861, 1732, 1603,
Ack n ow led gm en t. Support by the Natural Sciences
and Engineering Research Council (NSERC) of Canada
is gratefully acknowledged (M.M.K.). V.J. thanks NSERC
of Canada for a predoctoral fellowship and the National
Institutes of Health (GM 46059) for funding. The
authors are in debt to Drs. Andreas Pfaltz and Iris
Escher for the gift of highly enantiomerically enriched
3-(R)-methylcyclopentanone and 3-(R)-ethylcyclohex-
anone and Dr. Rudy Schmid of Hoffmann-LaRoche for
a gift of (S)-BIPHEMP. The authors also thank Profes-
sor Stephen L. Buchwald for helpful discussions. The
NMR spectra were recorded at the Atlantic Regional
Magnetic Resonance Centre at Dalhousie University,
Halifax, Canada, and we would particularly like to
express our thanks for the Centre’s help. Funding for
the Massachusetts Institute of Technology Department
of Chemistry Instrumentation Facility has been pro-
vided in part by the National Science Foundation (CHE-
9808061 and DBI-9729592). The authors also thank
Cerestar, Inc. for supplying the cyclodextrin used in this
study.
1454, 1244, 1179, 1054, 750, 700 cm-1 1H NMR (400 MHz,
.
CDCl3) δ 7.28 (2H, dd, J ) 15, 7.5 Hz), 7.19 (3H, dd, J ) 7.2,
2.0 Hz), 4.35 (1H, m), 3.99 (1H, t, J ) 10 Hz), 2.68 (2H, m),
2.51 (1H, m), 2.04 (1H, m), 1.94 (1H, m), 1.66 (4H, m) ppm.
13C NMR (100 MHz, CDCl3) δ 171.3, 141.2, 128.6, 128.2, 126.2,
73.3, 33.3, 33.0, 32.3, 28.9, 25.4 ppm. HRMS (EI, m/e) calcd
for C13H16O2: 204.1145 (M+). Found: 204.1148.
(S)-4-Isop r op yl Tetr a h yd r op yr a n -2-on e ((S)-6d ).27 Bio-
transformation according to the general protocol of (R)-3-
isopropyl cyclopentanone (0.050 g, 0.35 mmol, chiral GC
analysis with a Shimadzu GC-9A column indicated 87% ee)
mediated by E. coli (CHMO) gave, after 24 h and flash
chromatography (9:1 hexanes:ethyl acetate), the title com-
pound as the major product (2:1, 6d :5d as determined by GC)
as a colorless oil (0.033 g, 60% yield). Chiral GC analysis with
a Shimadzu GC-9A column indicated 93% ee for 6d and 97%
(27) Paquette, L. A.; Dahnke, K.; Doyon, J .; He, W.; Wyant, K.;
Friedrich, D. J . Org. Chem. 1991, 56, 6199-6205.
J O026605Q
6228 J . Org. Chem., Vol. 68, No. 16, 2003