A convenient chemoenzymatic synthesis of (4aS,5S)-(+)-4,4a,5,6,7,8-hexahydro-5-hydroxy-4a-methylnaphthalen-2(3H)-one

Article abstract of DOI:10.1021/jo015998a

We have developed a convenient chemoenzymatic method for the preparation of (4aS,5S)-4,4a,5,6,7,8-hexahydro-5-hydroxy-4a-methylnaphthalen-2(3H)-one by taking advantage of the excellent enantioselectivity of alcalase. Four different esters were compared, and the butanoate ester was found to be the best substrate. The stereochemistry of the product is the same as the one predicted from the binding model of alcalase. A simple extraction/partition procedure was used to separate the hydroxyenone product from the remaining ester. This practical procedure would be very useful in a gram-scale operation for securing the title compound in high optical purity.

Full text of DOI:10.1021/jo015998a

282
J . Org. Chem. 2002, 67, 282-285
Notes
A Con ven ien t Ch em oen zym a tic Syn th esis
of (4a S,5S)-(+)-4,4a ,5,6,7,8-Hexa h yd r o-
5-h yd r oxy-4a -m eth yln a p h th a len -2(3H)-on e
Lee-Chiang Lo,* J ung-J ing Shie, and Tzyy-Chao Chou
Department of Chemistry, National Taiwan University,
Taipei 106, Taiwan
F igu r e 1. Structures of Wieland-Miescher ketone 1, hy-
droxyenone 2, and racemic ester derivatives 3-6.
lclo@ccms.ntu.edu.tw
Received August 2, 2001
Sch em e 1. Asym m etr ic Cycliza tion of Tr ion e 7 in
th e P r esen ce of (S)-p r olin e To F or m (S)-1
Abstr a ct: We have developed a convenient chemoenzymatic
method for the preparation of (4aS,5S)-4,4a,5,6,7,8-hexahy-
dro-5-hydroxy-4a-methylnaphthalen-2(3H)-one by taking
advantage of the excellent enantioselectivity of alcalase.
Four different esters were compared, and the butanoate
ester was found to be the best substrate. The stereochem-
istry of the product is the same as the one predicted from
the binding model of alcalase. A simple extraction/partition
procedure was used to separate the hydroxyenone product
from the remaining ester. This practical procedure would
be very useful in a gram-scale operation for securing the title
compound in high optical purity.
70%).3,6 A more recent example of this cyclization using
catalytic antibodies,7 which gave Wieland-Miescher
ketone in high optical purity, is yet to be applied to large-
scale processes. The other two approaches also have room
for improvement, as they would require either careful
manipulations of the incubation medium and microbes
or tedious crystallization procedures. The first step in
many synthetic applications of (S)-1 often involved its
regio- and diastereoselective reduction with NaBH4 to
give (4aS,5S)-(+)-4,4a,5,6,7,8-hexahydro-5-hydroxy-4a-
methylnaphthalen-2(3H)-one (2).8 Therefore, this hy-
droxyenone intermediate (4aS,5S)-2 becomes an inter-
esting target and could also serve as a starting point for
future applications. Since compound 2 carries a second-
ary hydroxyl group, we envision that it would be well
suited for enzyme-catalyzed kinetic resolution. We hereby
report a convenient chemoenzymatic method using alca-
lase as an alternative approach for the preparation of
(4aS,5S)-2 (Scheme 2).
Alcalase,9 prepared from submerged fermentation of
a selected strain of Bacillus licheniformis, is an inexpen-
sive additive widely used in detergent formulations and
the food industry. Its major enzyme component is a serine
protease, subtilisin Carlsberg. Alcalase also possesses
esterase activity with a high turnover rate and shows
good stability in various organic solvents.10 In the mean-
time, the mechanism of subtilisin action in water and in
various anhydrous solvents has been thoroughly studied
Optically pure Wieland-Miescher ketone (1)1 (Figure
1) and its enantiomer are important starting materials
for the syntheses of a variety of natural products,
including terpenoids and steroids.2 A number of recent
publications have focused on how to secure large quanti-
ties of optically active 1. Three different approaches,
including asymmetric synthesis,3 enantioselective micro-
bial reduction,4 and classical resolution through a hemi-
phthalate derivative,5 are currently utilized for this
purpose. In the first approach, asymmetric cyclization of
achiral 2-methyl-2-(3-oxobutyl)-1,3-cyclohexanedione (7)
in the presence of (S)-(-)-proline would offer optically
enriched Wieland-Miescher ketone (1) (Scheme 1). How-
ever, the process is time consuming (3-5 days), and the
optical purity of the product is frequently variable (40-
(1) Wieland, P.; Miescher, K. Helv. Chim. Acta 1950, 33, 2215-2228.
(2) Examples from (S)-1: (a) Smith, A. B., III; Kingery-Wood, J .;
Leenay, T. L.; Nolen, E. G.; Sunazuka, T. J . Am. Chem. Soc. 1992,
114, 1438-1449. (b) Danishefsky, S. J .; Masters, J . J .; Young, W. B.;
Link, J . T.; Snyder, L. B.; Magee, T. V.; J ung, D. K.; Isaacs, R. C. A.;
Bornmann, W. G.; Alaimo, C. A.; Coburn, C. A.; Di Grandi, M. J . J .
Am. Chem. Soc. 1996, 118, 2843-2859. (c) An, J .; Wiemer, D. F. J .
Org. Chem. 1996, 61, 8775-8779. Examples from (R)-1: (d) Harada,
N.; Sugioka, T.; Ando, Y.; Uda, H.; Kuriki, T. J . Am. Chem. Soc. 1988,
110, 8483-8387. (e) Paquette, L. A.; Wang, H.-L. J . Org. Chem. 1996,
61, 5352-5357. (f) Paquette, L. A.; Backhaus, D.; Braun, R.; Underiner,
T. L.; Fuchs, K. J . Am. Chem. Soc. 1997, 119, 9662-9671.
(3) (a) Eder, U.; Sauer, G.; Wiechert, R. Angew. Chem., Int. Ed. Engl.
1971, 10, 496-497. (b) Hajos, Z. G.; Parrish, D. R. J . Org. Chem. 1974,
39, 1615-1621. (c) Gutzwiller, J .; Buchschacher, P.; Fu¨rst, A. Synthesis
1977, 167-168. (d) Buchschacher, P.; Fu¨rst, A. Org. Synth. 1985, 63,
37-43.
(6) Rajagopal, D.; Rajagopalan, K.; Swaminathan, S. Tetrahedron:
Asymmetry 1996, 7, 2189-2190.
(7) (a) Zhong, G.; Hoffmann, T.; Lerner, R. A.; Danishefsky, S.;
Barbas, C. F., III. J . Am. Chem. Soc. 1997, 119, 8131-8132. (b)
Hoffmann, T.; Zhong, G.; List, B.; Shabat, D.; Anderson, J .; Grama-
tikova, S.; Lerner, R. A.; Barbas, C. F., III. J . Am. Chem. Soc. 1998,
120, 2768-2779.
(8) (a) Yeo, S.-K.; Hatae, N.; Kanematsu, K. Tetrahedron 1995, 51,
3499-3506. (b) Cheung, W. S.; Wong, H. N. C. Tetrahedron 1999, 55,
11001-11016.
(9) Alcalase, available from Novo Nordisk Biochem North America,
Inc., Franklinton, NC, was a gift from Trump Chemical Corp., Taipei,
Taiwan. The enzyme activity is expressed in Anson Units per gram
(AU/g). http://www.novozymes.com/eventure/demo/b1145a-gb.pdf.
(4) (a) Prelog, V.; Acklin, W. Helv. Chim. Acta 1956, 39, 748-757.
(b) Fuhshuku, K.; Funa, N.; Akeboshi, T.; Ohta, H.; Hosomi, H.; Ohba,
S.; Sugai, T. J . Org. Chem. 2000, 65, 129-135. (c) Hioki, H.; Hashimoto,
T.; Kodama, M. Tetrahedron: Asymmetry 2000, 11, 829-834.
(5) Newkome, G. R.; Roach, L. C.; Montelaro, R. C.; Hill, R. K. J .
Org. Chem. 1972, 37, 2098-2101.
10.1021/jo015998a CCC: $22.00 © 2002 American Chemical Society
Published on Web 12/11/2001

Notes
J . Org. Chem., Vol. 67, No. 1, 2002 283
Sch em e 2. Alca la se-Ca ta lyzed Hyd r olysis of Ra cem ic Ester s 3-6
Ta ble 1. Resu lts of Alca la se-Ca ta lyzed Hyd r olysis of
Ra cem ic Ester s 3-6
enantiomeric excessb
(%)
time conversiona (1R,8aR)
E
esters
R
(h)
(%)
ester
(4aS,5S)-2 valuec
3
4
4
4
4
5
6
CH3
48
6
12
24
48
NR
17
27
45
52
n-C3H7
n-C3H7
n-C3H7
n-C3H7
n-C5H11 48
n-C7H15 48
20
36
73
90
>99
>99
90
84
F igu r e 2. Preferred binding of (S)-substrate in the active site
of subtilisin; L stands for the large substituent and M for the
medium-sized substituent.
43
41
NR
NR
and found to be the same.11 The enantiopreference of
subtilisin for the resolution of secondary alcohols was
reported to be largely determined by the relative size of
the two substituents.12 The preferred binding of S-
substrate in the active site is depicted in Figure 2, where
L stands for the large substituent and M for the medium
substituent. The extensive information about the enan-
tiopreference of alcalase together with its readily avail-
ability have made it a useful reagent in organic synthe-
sis.13 Based on this binding model, we predict that the
secondary alcohol (4aS,5S)-2 would meet the stereochem-
ical requirement in the binding pocket of alcalase. We
therefore prepared a series of four racemic esters 3-6
and carried out a preliminary screening using these
substrates for alcalase-catalyzed hydrolytic reactions
(Scheme 2). Esters 3-6, including acetate 3, butanoate
4, hexanoate 5, and octanoate 6, are mainly different in
the length of their carboxylate moiety (Figure 1). Their
syntheses were achieved by acylation of the racemic
alcohol 2 with suitable acylating agents in high yields.
The hydrolytic reactions were performed by incubating
individual racemic ester substrate (50 mM) with Alcalase
(2.4 AU/g)9 in 0.3 M phosphate buffer (pH 7.0) containing
15% DMF at 37 °C. Reactions were stopped at intervals
to check the conversions as well as the enantiomeric
excess of the remaining ester and the hydroxyenone
product 2. Under this screening condition, those four
esters displayed a dramatic difference in their rates
toward hydrolysis (Table 1). Only butanoate 4 gave a
reasonable conversion after 12 h (∼26%), whereas the
other three substrates (3, 5, and 6) showed no appreciable
a
NR indicates no reaction when checked with TLC. The
conversions for ester 4 were calculated from the equation c ) ees/
(ees + eep),14 where ees and eep represent the enantiomeric excess
b
of ester starting material and alcohol product, respectively. The
enantiomeric excess was determined by HPLC with a Chiralcel
OJ column. The retention times for the two pairs of enantiomers
4 and 2 are shown in parentheses (min); (1S,8aS)-4 (7.36),
(1R,8aR)-4 (8.20), (4aR,5R)-2 (18.47), and (4aS,5S)-2 (23.76). c E
(enantioselectivity) ) ln[1 - c(1 + eep)]/ln[1 - c(1 - eep)].
reactions even after 48 h when checked with TLC. This
interesting result indicates that the carboxylate moiety
also plays a critical role in the rate of hydrolysis in
addition to the steric requirement for the substituents
of the alcohol. This observation is not uncommon in
enzyme-catalyzed reactions, as in some cases the rate and
specificity could be manipulated by partially altering the
structure of the substrates.15 Since the reaction only
occurred with butanoate 4, the results were further
examined.
Butanoate 4 is a good substrate for alcalase-catalyzed
hydrolysis, and it also exhibits excellent enantioselectiv-
ity14 as inferred from the optical purity of both remaining
ester and hydroxyenone product 2 (Table 1). Determina-
tion of the enantiomeric excess was achieved by using
HPLC with a Chiralcel OJ column. The absolute config-
uration of the major hydroxyenone product was estab-
lished by comparing its optical rotation with that of
authentic sample. The optical purity of (4aS,5S)-2 re-
mained high (ee > 99%) at the conversion of 27%. It
slightly dropped to 90% when the conversion reached 45%
and further dropped to 84% when the conversion was
over 52%. The calculated E values14 were larger than 40,
favoring the formation of (4aS,5S)-(+)-2. The influence
of DMF content on the rate and enantioselectivity was
also studied, and the results showed that the enzyme still
performed well in the presence of 15-35% DMF.
Since alcalase has great enantioselectivity on bu-
tanoate 4 (E > 40), we then combine this feature with
(10) (a) Chen, S.-T.; Wang, K.-T.; Wong, C.-H. Chem. Commun. 1986,
1514-1516. (b) Zaks, A.; Klibanov, A. M. J . Biol. Chem. 1988, 263,
3194-3201. (c) Chen, S.-T.; Chen, S.-Y.; Wang, K.-T. J . Org. Chem.
1992, 57, 6960-6965.
(11) (a) Kanerva, L. T.; Klibanov, A. M. J . Am. Chem. Soc. 1989,
111, 6864-6865. (b) Adams, K. A. H.; Chung, S.-H. Klibanov, A. M. J .
Am. Chem. Soc. 1990, 112, 9418-9419.
(12) (a) Fitzpatrick, P. A.; Klibanov, A. M. J . Am. Chem. Soc. 1991,
113, 3166-3171. (b) Kazlauskas, R. J .; Weissfloch, A. N. E. J . Mol.
Catal. B: Enzymol. 1997, 3, 65-72.
(13) (a) Chen, S.-T.; Wang, K.-T. Synthesis 1987, 581-582. (b) Chen,
S.-T.; Chen, S.-Y.; Hsiao, S.-C.; Wang, K.-T. Biotch. Lett. 1991, 13, 773-
778. (c) Wong, C.-H.; Whitesides, G. M. In Enzymes in Synthetic
Organic Chemistry; Baldwin, J . E., Magnus, P. D., Eds.; Elsevier:
Oxford, 1994; pp 41-131. (d) Chen, S.-T.; Wang, K.-T. J . Chin. Chem.
Soc. 1999, 46, 301-311.
(14) (a) Chen, C.-S.; Fujimoto, Y.; Girdaukas, G.; Sih, C. J . J . Am.
Chem. Soc. 1982, 104, 7294-7299. (b) Sih, C. J .; Wu, S.-H. Top.
Stereochem. 1989, 19, 63-125.
(15) (a) Oberhauser, T.; Bodenteich, M.; Faber, K.; Penn, G.; Griengl,
H. Tetrahedron 1987, 43, 3931-3944. (b) Scilimati, A.; Ngooi, T. K.;
Sih, C. J . Tetrahedron Lett. 1988, 29, 4927-4930. (c) Wu, S.-H.; Lo,
L.-C.; Chen, S.-T.; Wang, K.-T. J . Org. Chem. 1989, 54, 4220-4222.

284 J . Org. Chem., Vol. 67, No. 1, 2002
Notes
removed under reduced pressure. The residual oil was dissolved
in EtOAc and washed consecutively with NaHCO3 (×3), 5% citric
acid (×3), H2O (×2), and brine (×1). After drying over anhydrous
Na2SO4 and filtration, the desired ester 3 (890 mg, 95%) was
purified by silica gel column chromatography eluted with
hexane/EtOAc (80/20). Rf ) 0.35 (hexane/EtOAc ) 65/35). 1H
NMR (400 MHz, CDCl3): δ 5.80 (d, J ) 1.9 Hz, 1 H), 4.64 (dd,
J ) 11.1, 4.1 Hz, 1 H), 2.48-2.28 (m, 3 H), 2.22 (m, 1 H), 2.07
(s, 3 H), 1.98-1.62 (m, 5 H), 1.49 (m, 1 H), 1.26 (s, 3 H). 13C
NMR (100 MHz, CDCl3): δ_198.9, 170.3, 166.7, 125.8, 79.2, 40.4,
34.0, 33.5, 31.8, 26.9, 22.9, 21.1, 16.6. IR (neat): 2959, 2873,
1732, 1679, 1626, 1461, 1169, 1090,1003, 864 cm-1. HRMS: calcd
for C13H19O3 (M + 1)+ 223.1334, found 223.1332.
Gen er a l P r oced u r e for th e P r ep a r a tion of Ra cem ic
Ester s 4-6. The procedure is similar to that for acetate 3, except
suitable acyl chlorides (butanoyl, hexanoyl, and octanoyl) instead
of anhydrides were used as the acylating agents. The desired
esters 4-6 were purified by silica gel column chromatography
eluted with hexane/EtOAc (8/2 f 6/4).
Bu ta n oic Acid (1S*,8a S*)-(()-8a -Meth yl-6-oxo-1,2,3,4,6,7,
8,8a -octa h yd r on a p h th a len -1-yl Ester (4). Yield: 98%. Mp:
43-44 °C. Rf ) 0.47 (hexane/EtOAc ) 65/35). 1H NMR (400
MHz, CDCl3): δ 5.77 (d, J ) 1.9 Hz, 1 H), 4.62 (dd, J ) 12.0, 4.1
Hz, 1 H), 2.45-2.14 (m, 6 H), 1.98-1.58 (m, 7 H), 1.46 (m, 1 H),
1.24 (s, 3 H), 0.93 (t, J ) 7.3 Hz, 3 H). 13C NMR (100 MHz,
CDCl3): δ 198.9, 172.9, 166.8, 125.8, 78.9, 40.4, 36.5, 34.0, 33.5,
31.8, 26.9, 22.9, 18.6, 16.7, 13.7. IR (neat): 2952, 1737, 1673,
1241, 1038 cm-1. HRMS: calcd for C15H23O3 (M + 1)+ 251.1647,
found 223.1644. Optically enriched (1S,8aS)-4 was similarly
prepared from (4S,5aS)-enriched 2.
the availability of (1S,8aS)-enriched ester 4 to develop a
practical method for the large-scale preparation of enan-
tiomerically pure (4aS,5S)-2. For a gram-scale operation,
the condition for the resolution was the same as the one
depicted in Scheme 2, except (1S,8aS)-enriched butanoate
4 (58% ee) instead of the racemate was used as the
substrate. Optically enriched (S)-13,6 (Scheme 1) was first
reduced to hydroxyenone 2, which was subjected to
acylation with butanoyl chloride to offer (1S,8aS)-
enriched butanoate 4 (58% ee). After enzymatic hydroly-
sis, both (4aS,5S)-2 and the remaining ester were ex-
tracted from the mixture with EtOAc. These two com-
pounds could easily be separated by partitioning in
n-hexane/H2O. The remaining ester goes to the hexane
layer, while (4aS,5S)-2 stays in the aqueous phase. This
simple extraction/partition procedure is especially con-
venient and suitable for a large-scale operation. It avoids
the need of extensive chromatography for the separation
of (4aS,5S)-2 from the remaining ester. Hydroxyenone
(4aS,5S)-2 of high optical purity (>97% ee) could thus
be obtained in 57% yield.
In conclusion, we have developed a convenient chemo-
enzymatic method for the preparation of (4aS,5S)-4,-
4a,5,6,7,8-hexahydro-5-hydroxy-4a-methylnaphthalen-
2(3H)-one (2) by taking advantage of the excellent
enantioselectivity of alcalase. Butanoate 4 was found to
be the best substrate, and it gave a product with the
predicted absolute stereochemistry. The carboxylate moi-
ety of butanoate 4 not only plays an important role in
the rate of alcalase-catalyzed hydrolysis, it also offers the
advantage of simplifying the purification procedure after
enzymatic resolution. Although only alcalase was studied
in this report, its low cost and readily availability would
make this procedure very useful in a gram-scale opera-
tion for securing (4aS,5S)-(+)-2 in high optical purity. We
are currently surveying other hydrolytic enzymes, includ-
ing esterases and lipases, for the hydrolysis of the
butanoate 4. It is interesting to note that lipases might
display a reverse enantiopreference for this substrate,
based on the knowledge of the binding pocket of lipases.12b
A recent example of lipase-catalyzed transesterification
on a structurally similar secondary alcohol also supports
this prediction.16 We will report the results in due course.
Hexa n oic Acid (1S*,8a S*)-(()-8a -Meth yl-6-oxo-1,2,3,4,6,7,
8,8a -octa h yd r on a p h th a len -1-yl Ester (5). Yield: 90%. Rf )
0.52 (hexane/EtOAc ) 65/35). 1H NMR (400 MHz, CDCl3): δ
5.76 (d, J ) 1.9 Hz, 1 H), 4.61 (dd, J ) 11.7, 4.1 Hz, 1 H), 2.43-
2.18 (m, 6 H), 1.98-1.55 (m, 7 H), 1.46 (m, 1 H), 1.32-1.27 (m,
4 H), 1.23 (s, 3 H), 0.86 (t, J ) 7 Hz, 3 H). 13C NMR (100 MHz,
CDCl3): δ 198.9, 173.1, 166.8, 125.8, 78.9, 40.4, 34.5, 34.0, 33.5,
31.8, 31.2, 26.9, 24.7, 22.9, 22.3, 16.7, 13.9. IR (neat): 2957, 2864,
1738, 1682, 1240, 1170, 1006, 774 cm-1. HRMS: calcd for
C
17H27O3 (M + 1)+ 279.1960, found 279.1964.
Octa n oic Acid (1S*,8a S*)-(()-8a -Meth yl-6-oxo-1,2,3,4,6,7,
8,8a -octa h yd r on a p h th a len -1-yl Ester (6). Yield: 90%. Rf )
0.60 (hexane/EtOAc ) 65/35). 1H NMR (400 MHz, CDCl3): δ
5.76 (d, J ) 1.8 Hz, 1 H), 4.61 (dd, J ) 12.7, 4.1 Hz, 1 H), 2.37-
2.22 (m, 6 H), 1.98-1.58 (m, 7 H), 1.57-1.36 (m, 1 H), 1.32-
1.27 (m, 11 H), 0.85-0.82 (m, 3 H). 13C NMR (100 MHz,
CDCl3): δ 198.8, 172.9, 166.7, 125.6, 78.7, 40.3, 34.4, 33.8, 33.3,
31.6, 31.5, 28.9, 28.7, 26.7, 24.9, 22.8, 22.4, 16.5, 13.9. IR
(neat): 2934, 2863, 1738, 1684, 1469, 1452, 1166, 1006 cm-1
.
HRMS: calcd for C19H31O3 (M + 1)+ 307.2273, found 307.2271.
Alca la se-Ca ta lyzed Hyd r olysis of Ra cem ic Ester s 3-6
(An a lytica l Sca le). Two stock solutions were first prepared;
solution A contains 0.333 M of individual substrate in DMF and
solution B contains 25% Alcalase 2.4L9 (v/v) in 0.3 M phosphate
buffer (pH 7.0). For each reaction, 60 µL of solution A and 300
µL of phosphate buffer (0.3 M, pH 7.0) were first mixed. A 40
µL portion of solution B (total volume ) 400 µL) was then added
and the mixture placed in a shaker at 37 °C. The reactions were
terminated at 6, 12, 24, and 48 h, respectively, by addition of
EtOAc (20 mL) and H2O (10 mL). The organic layer was collected
and washed with H2O (10 mL ×2) and brine (10 mL ×1). It was
dried over anhydrous Na2SO4, filtered, and concentrated to
dryness. The residue was dissolved in n-hexance/i-PrOH for
HPLC analysis.
Exp er im en ta l Section :
Gen er a l Meth od s. Melting points are uncorrected. 1H and
13C NMR spectra were recorded at 400 and 100 MHz in CDCl3,
respectively. Analytical TLC (silica gel, 60F-54, Merck) and spots
were visualized under UV light and/or phosphomolybdic acid-
ethanol. Flash column chromatography was performed with
silica gel 60 (70-230 mesh, Merck). HPLC was performed on a
Chiralcel OJ column (250 × 4.6 mm, n-hexane/i-PrOH ) 94/6,
1 mL/min) monitored at 235 nm. Both racemic and optically
enriched 2 were prepared according to literature procedures.3,8
Acetic Acid (1S*,8a S*)-(()-8a -Meth yl-6-oxo-1,2,3,4,6,7,
8,8a -octa h yd r on a p h th a len -1-yl Ester (3).17 To an ice-cooled
solution of the racemic hydroxyenone 2 (760 mg, 4.22 mmol) in
6 mL of pyridine was slowly added 0.5 mL of Ac2O (5.29 mmol).
The reaction was kept at room temperature and stirred over-
night. The progress of the reaction was monitored by TLC
(hexane/EtOAc ) 4/6). After the reaction was complete (∼12 h),
a few drops of H2O were added to quench the reaction. The
mixture was stirred for another 30 min, and pyridine was
Alca la se-Ca ta lyzed Hyd r olysis of (1S,8a S)-En r ich ed Bu -
tan oic Acid 8a-Meth yl-6-oxo-1,2,3,4,6,7,8,8a-octah ydr on aph -
th a len -1-yl Ester (4) (Gr a m Sca le). To a solution of (1S,8aS)-
enriched butanoate-4 (1.00 g, 58% ee) in 12 mL of DMF was
added 66 mL of phosphate buffer (0.3 M, pH 7.0) and 2 mL of
alcalase. The mixture was placed in a shaker at 37 °C for 48 h.
After enzymatic hydrolysis, both the hydroxyenone product 2
and the remaining ester 4 were extracted from the mixture with
EtOAc (200 mL ×3). The EtOAc extracts were combined and
concentrated. The residual oil was partitioned between hexane/
H2O. The remaining ester 4 goes to the hexane layer, while the
hydroxyenone product 2 stays in aqueous phase. The aqueous
phase was extracted with EtOAc (x3) and the desired product
(16) Franssen, M. C. R.; J ongejan, H.; Kooijman, H.; Spek, A. L.;
Bell, R. P. L.; Wijnberg, J . B. P. A.; de Groot, A. Tetrahedron:
Asymmetry 1999, 10, 2729-2738.
(17) Harada, N.; Kohori, J .; Uda, H.; Nakanishi, K.; Takeda, R. J .
Am. Chem. Soc. 1985, 107, 423-428.

Notes
J . Org. Chem., Vol. 67, No. 1, 2002 285
was purified by silica gel column chromatography eluted with
(M + 1)+ 181.1228, found 181.1228. The spectroscopic data were
identical to those reported in the literature.4,8
hexane/EtOAc (6/4) to give (4aS,5S)-(+)-2 (0.41 g, 57% yield).
Its ee was found to be 98% by HPLC analysis, [R]25 ) +174 (c
D
Ack n ow led gm en t. This work was supported by the
National Science Council (NSC 90-2113-M-002-028). We
thank Professors Shih-Hsiung Wu and J im-Min Fang
for helpful discussions.
1.0, benzene). 1H NMR (400 MHz, CDCl3): δ 5.76 (d, J ) 1.9
Hz, 1 H), 3.40 (dd, J ) 11.7, 4.4 Hz, 1 H), 2.50-2.22 (m, 3 H),
2.21-2.10 (m, 2 H), 1.90-1.58 (m, 5 H), 1.39 (m, 1 H), 1.17 (s,
3 H). 13C NMR (100 MHz, CDCl3): δ 199.8, 168.8, 125.4, 78.2,
41.6, 34.2, 33.6, 32.0, 30.2, 23.1, 15.2. HRMS: calcd for C11H17O2
J O015998A