Chemoenzymatic synthesis of homochiral (R)- and (S)-karahanaenol from (R)-limonene

Article abstract of DOI:10.1021/jf990531a

Terpinolene oxide, a monoterpene belonging to the p-menthane group, is easily derived from naturally abundant (R)-limonene. It was isomerized with montmorillonite clay catalyst to karahanaenone (2,2,5-trimethylcyclohept-4- en-1-one) by ring enlargement. The enantiomers of the corresponding alcohol, karahanaenol (2,2,5-trimethylcyclohept-4-en-1-ol), known for their individual organoleptic properties, were resolved through Pseudomonas cepacia lipase mediated enantiospecific alcoholysis of its acetate derivative.

Full text of DOI:10.1021/jf990531a

J. Agric. Food Chem. 1999, 47, 5209−5210
5209
Ch em oen zym a tic Syn th esis of Hom och ir a l (R)- a n d
(S)-Ka r a h a n a en ol fr om (R)-Lim on en e
A. Roy†
Plantation Products and Flavor Technology Discipline, Central Food Technological Research Institute,
Mysore 570 013, India
Terpinolene oxide, a monoterpene belonging to the p-menthane group, is easily derived from naturally
abundant (R)-limonene. It was isomerized with montmorillonite clay catalyst to karahanaenone
(2,2,5-trimethylcyclohept-4-en-1-one) by ring enlargement. The enantiomers of the corresponding
alcohol, karahanaenol (2,2,5-trimethylcyclohept-4-en-1- ol), known for their individual organoleptic
properties, were resolved through Pseudomonas cepacia lipase mediated enantiospecific alcoholysis
of its acetate derivative.
Keyw or d s: Karahanaenone; karahanaenol; lipase; Pseudomonas cepacia; enantiospecific alcoholysis
INTRODUCTION
Sch em e 1
A large number of monoterpene hydrocarbons are
readily available from natural sources, and these are
often used as starting material for the synthesis of a
wide variety of oxygenated derivatives that mostly find
application as aroma chemicals (Ohloff, 1994). A com-
mon approach toward such functionalization is the
epoxidation of the respective double bond and rear-
rangement of the resulting three-membered highly
strained epoxide ring (oxiran) system under the influ-
ence of various acid, base, and heterogeneous catalysts
(Smith, 1984). The main rearrangement products thus
obtained are usually alcohols, carbonyl compounds, and
skeletally rearranged products, respectively. On the
other hand, direct addition of small molecules such as
haloacid, alcohol, and water, is also possible across the
double bond in the presence of a suitable catalyst
(Erman, 1985). Following these methods, earlier work-
ers from this laboratory have shown that (R)-limonene
(1), a major citrus byproduct, can be utilized as a
potential source for preparation of some aroma chemi-
cals (Ravindranath, 1983). Now, I report the synthesis
of the enantiomers of karahanaenol in this paper.
Karahanaenol (4) (Scheme 1) is an optically active
monoterpene alcohol and usually obtained in racemic
form by chemical reduction of karahanaenone (3), a
constituent of hop oil (Naya and Kotake, 1968). Re-
cently, the enantiomers of 4 have been obtained by
asymmetric reduction of 3 using various microbial
cultures. It was reported that the individual enanti-
omers differ in their odor (Miyazawa et al., 1995). In
the present case, racemic 4 was resolved through lipase-
catalyzed enantiospecific alcoholysis (transesterifica-
tion) in organic solvent.
Gurudutt, 1997). Racemic karahanaenol was obtained by
reduction of karahanaenone with lithium aluminum hydride
in dry tetrahydrofuran. All of the solvents were distilled prior
to their use and stored over molecular sieves. Candida rugosa
and porcine pancreas lipases were purchased from Sigma,
whereas the remaining lipases were gifts from Amano and
Novo Nordisk, respectively. The gas chromatographic analysis
was carried out on an HP-5734 instrument equipped with an
HP-3380A reporting integrator using a capillary column (6 ft
× 0.125 in. o.d.) packed with 3% OV-17 under the following
conditions: injection port temperature, 200 °C; detector (H2,
FID) temperature, 250 °C; temperature program, 90 °C (5 min
MATERIALS AND METHODS
(R)-(+)-Limonene was obtained from commercial sources
and fractionated. Terpinolene oxide (2) was prepared from (R)-
limonene following the standardized procedure (Roy and
† Present address: Department of Pharmaceutical Technol-
ogy, National Institute of Pharmaceutical Education and
Research, Mohali 160 062, India.
10.1021/jf990531a CCC: $18.00 © 1999 American Chemical Society
Published on Web 12/02/1999

5210 J. Agric. Food Chem., Vol. 47, No. 12, 1999
Roy
hold), raised at 4 °C/min to 180 °C (5 min hold); carrier gas,
nitrogen; flow rate, 40 mL/min. Mass analysis was performed
on a Shimadzu QP 5000 gas chromatography/mass spectros-
copy instrument using a capillary DB-Wax column (30 m ×
0.25 mm i.d.) under similar conditions. The optical rotation
was measured on a Perkin-Elmer 243 polarimeter at 20 °C.
1H NMR analysis was performed on a Bruker AMX 300
MHz, instrument using TMS as internal standard. The enan-
tiomeric excess was determined from the resolution of geminal
methyl group shift using chiral shift reagent Pr(hfc)3 (Sullivan,
1979), and absolute configuration of the enantiomers was
assigned by comparing the optical rotation measurement with
literature values (Miyazawa et al., 1995).
P r ep a r a tion of Ka r a h a n a en on e (3). To a solution of 1.52
g (0.01 mol) of distilled terpinolene oxide in 60 mL of benzene
was added 200 mg of K-10 montmorillonite clay (Sigma), and
the mixture was stirred at 30 °C for 6 h. The clay material
was filtered, and the solvent was removed through rotary
evaporation in vacuo. The residual product was purified by
column (length 30 cm × 20 mm i.d.) chromatography over silica
gel (Glaxo, 60-120 mesh). Isolated yield of 4: 1.05 g (70%);
1H NMR (TMS) δ 1.02 (s, 3H), 1.03 (s, 3H), 1.67 (s, 3H), 2.69
(m, 2H), 1.99-2.31 (m, 4H), 5.58 (m, 1H); MS 152 [M+], 137
(15), 109 (52), 95 (100), 81(46), 41(43).
Lipase-Catalyzed En an tioselective Alcoh olysis of Kar a-
h a n a en ol Aceta te (5). In a 100 mL stoppered Erlenmeyer
flask was dissolved 400 mg of 5 in 15 mL of a diisopropyl ether/
n-butanol mixture (3:1), and 100 mg of P. cepacia lipase was
added. The mixture was incubated at 35 °C, 200 rpm, and
progress of the reaction was monitored by GC at regular
intervals. After 70 h, the enzyme was filtered off and solvent
removed by rotary evaporation. The residual oily mass was
separated and purified over a silica gel (Glaxo, 60-120 mesh)
column (30 cm × 20 mm i.d.) with an ethyl acetate/hexane
(1-10%) solvent gradient. Yield of 4(R): 164 mg (82%); [R]20
) 36.2° (c 0.87, CHCl3); enantiomeric excess 94%. Recovered
unreacted 5(S): 190 mg.
resolve 4 through the lipase-catalyzed irreversible acyl
transfer technique did not show any encouraging re-
sults. The lipases screened were from C. rugosa, porcine
pancreas, Mucor miehei, P. cepacia, Pseudomonas sp.,
and an esterase isolated from hog liver. Only C. rugosa
and P. cepacia indicated some selectivity (48-56% ee).
However, the best results were obtained by carrying out
the alcoholysis of the acetate derivative (Bevinakatti
and Banerji, 1991; Shkolnik and Gutman, 1994) (5) in
a diisopropyl ether/n-butanol (3:1) mixture employing
P. cepacia lipase. The marked increase in enantiospeci-
ficity in changing the reaction conditions from acylation
of 4 to alcoholysis of 5 could be due to steric reasons.
The presence of geminal methyl groups at the C-2
position may facilitate the deacylation process more
than the corresponding acylation at the chiral center
by virtue of their spatial arrangements.
CONCLUSION
The work reported here offers a direct access to the
enantiomers of karahanaenol starting from a naturally
abundant and inexpensive terpene hydrocarbon such as
(R)-limonene. Similarly, R-terpineol derived from the
same hydrocarbon was resolved via lipase catalysis, and
the details of this work will be the subject of another
paper soon.
ACKNOWLEDGMENT
I am thankful to Dr. K. N. Gurudutt for some helpful
discussion. I thank Amano, J apan, and Novo Nordisk,
Denmark, for generous gifts of some lipases and So-
phisticated Instrumentation Facility, Indian Institute
of Science, Bangalore, for recording NMR spectra.
Alk a lin e Hyd r olysis of 5. One hundred milligrams of the
unreacted 5(S) was dissolved in 2 mL of 1 M methanolic NaOH
solution and stirred magnetically at 0-5 °C for 6 h. Usual
workup and purification led to 84% of 4(S): [R]20 ) -28.4° (c
0.53, CHCl3); enantiomeric excess 91%.
LITERATURE CITED
Bevinakatti, H. S.; Banerji, A. A. Practical Chemoenzymatic
Synthesis of Both Enantiomers of Propranolol. J . Org.
Chem. 1991, 56, 5372-5375.
Erman, W. F. Chemistry of Monoterpenes. Parts A and B;
Dekker: New York, 1985.
RESULTS AND DISCUSSION
Terpinolene oxide [p-menth-1-en-4(8)-oxide] is a tet-
rasubstituted spiro oxiran (2,2,6-trimethyl-1-oxa-spira-
[2.5]oct-ene, CAS Registry No. 4584-23-0), and the
inherent reactivity of the molecule has made it an
important intermediate for the synthesis of many flavor
and fragrance chemicals. Rearrangement with Lewis
acids such as zinc bromide, lithium perchlorate, mag-
nesium bromide, and borontrifluoride etherate has led
to a number of products including ring-enlarged kara-
hanaenone (3) and its isomer isokarahanaenone (6) in
almost equal amounts (Roy and Gurudutt, 1997). At-
tempts to increase the formation of 3 and/or 6 by
altering the reaction condition or solvent did not work.
Montmorillonite clay is a noncorrosive solid Lewis acid
in use for a wide variety of organic reactions (Laszlo,
1987). Isomerization of 2 with K-10 montmorillonite
gave 3 in 71% yield. This prochiral ketone with its
characteristic fragrance is very important in the flavor
industry, and the individual enantiomers of the corre-
sponding reduced alcohol 4 are known to possess vary-
ing degrees of fruity and woody odor.
Laszlo, P. Chemical Reactions on Clay. Science 1987, 235,
1473-1477.
Miyazawa, M.; Tsuruno, K.; Kameoka, H. Microbial asym-
metric reduction of karahanaenone. Tetrahedron Asym.
1995, 6 (9), 2121-2122.
Naya, T.; Kotake, M. New Monoterpenoids from Hop Oil.
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Ohloff, G. Scent and Fragrances; Springer-Verlag: Berlin,
Germany, 1994.
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a
byproduct of the citrus industry. J Sci. Ind. Res. 1983, 42
(2), 82-86; Chem. Abstr. 1983, 98, 217540j.
Roy, A.; Gurudutt, K. N. Chemistry of Terpinolene Oxide. J .
Sci. Ind. Res. 1997, 56, 513-517; Chem. Abstr. 1997, 127,
234436q.
Shkolnik, E.; Gutman, A. L. Resolution of racemic sterically
hindered secondary alcohols via enzymatic alcoholysis of
their ester. The first enzymatic preparation of optically pure
2,2,2-trifluoro-1-(9-anthryl) ethanols. Bio-Org. Med. Chem.
1994, 2 (7), 567-572.
Smith, J . G. Synthetically Useful Reactions of Epoxides.
Synthesis 1984, 629-656.
Resolution of racemic alcohols using biocatalysts is
now considered to be one of the best methods. Hydro-
lases are by far the most important class of enzymes
preferred for the preparation of chiral alcohols, and their
application in organic synthesis has developed exten-
sively during the past two decades. Initial efforts to
Received for review May 18, 1999. Revised manuscript received
August 17, 1999. Accepted September 16, 1999. I am grateful
to the Director, CFTRI and CSIR, New Delhi for financial
assistance.
J F990531A