Enantioselective synthesis of (-)- and (+)-conduritol F via enzymatic asymmetrization of cis-cyclohexa-3,5-diene-1,2-diol

Full text of DOI:10.1021/jo960251j

6458
J . Org. Chem. 1996, 61, 6458-6461
Ta ble 1. Ester ifica tion of 1 w ith Vin yl Aceta te in
En a n tioselective Syn th esis of (-)- a n d
ter t-Bu tyl Meth yl Eth er a
(+)-Con d u r itol F via En zym a tic
Asym m etr iza tion of
time, 1, (-)-2, ee,
stereo-
3,
b
b
c
b
entry lipase source
h
%
%
%
preferenced
%
cis-Cycloh exa -3,5-d ien e-1,2-d iol
1
2
3
4
5
6
P. cepacia
2
3
4.5
6
2
10
-
86
89
82
93
51
89
90
>98
91
95
68
R
R
R
4
11
4
7
-
11
Angela Patti, Claudia Sanfilippo, Mario Piattelli, and
Giovanni Nicolosi*
M. mieheie
C. antarcticaf
14
-
Istituto CNR per lo Studio delle Sostanze Naturali di
Interesse Alimentare e Chimico-Farmaceutico,
Via del Santuario 110, 95028 Valverde CT, Italy
49
-
5
70
a
Reaction conditions: lipase 10 mg/mL, substrate 10 mg/mL,
b
vinyl acetate 1 equiv, 40 °C, 300 rpm. Determined by 1H-NMR
Received February 6, 1996
spectrum of the reaction mixture. c Determined by chirospecific
d
In tr od u ction
GC analysis of the corresponding tetrahydro derivative. Assigned
according ref 10. e Immobilized (Lipozyme® IM). f Immobilized
(Novozym® 435).
Conduritols A-F (5-cyclohexene-1,2,3,4-tetrols)1 are a
class of cyclitols of great relevance in the synthesis of
inositol derivatives, such as the antidiabetic (+)-pinitol2
and the putative insulin mimics D-myo-inositol 1,4,5-
triphosphate3 and 6-O-(2-amino-2-deoxy-R-D-glucopyran-
osyl)-1-O-dihydrogenphosphoryl-D-myo-inositol.4 More-
over, conduritols themselves and their epoxides are
inhibitors of D-glucosidases.5 Preparation of these tetrols
is not always simple, and this is particularly true for
those existing as couples of enantiomers (conduritol B,
C, E, and F), the synthesis of which from achiral
precursors obviously requires a resolution step.6 To
overcome this difficulty stereocontrolled syntheses have
been developed, starting from chiral materials, in many
instances cyclic cis-glycols obtained by microbial oxida-
tion of aromatic substrates mediated by Pseudomonas
putida, and thus (-)-C, (+)-C, (-)-E, (+)-E, and (-)-F
conduritols have been synthesized.7 Lipase-mediated
enantiotoposelective esterification or hydrolysis of meso-
compounds derived from 2-cyclohexene-1,4-diol has been
used to obtain chiral intermediates valuable for the
synthesis of conduritols with the desired stereochemis-
try.8 As part of a project aimed at the evaluation of the
synthetic value9 of (1R,2S)-1-acetoxy-2-hydroxycyclohexa-
3,5-diene, (-)-2, prepared by enantiotoposelective esteri-
fication of “benzene cis-glycol” 1 catalyzed by lipase,10 we
report the synthesis of homochiral F-conduritol enanti-
omers via OsO4-catalyzed dihydroxylation of this hydroxy
ester.
course of a study directed to the asymmetrization of cyclic
meso-diols through the enantiotoposelective esterification
mediated by lipases in organic medium,11 we observed
that Mucor miehei lipase (immobilized, Lipozyme IM) in
tert-butyl methyl ether (t-BME) promotes the esterifica-
tion of cis-1,2-dihydroxycyclohexa-3,5-diene (1) to afford
monoester (-)-2.10 In an attempt to optimize the reaction
we screened several lipases (lipases from Candida cylin-
dracea, C. antarctica, Aspergillus niger, Rhizopus jav-
anicus, Pseudomonas cepacia and porcine pancreas).
Among them, only those from P. cepacia and C. antarctica
(immobilized, Novozym 235) were active in the esterifi-
cation of 1 in anhydrous t-BME with vinyl acetate as the
acyl donor. The results, summarized in Table 1, show
that P. cepacia lipase is the most effective. With this
enzyme, conversion reached 90% after 2 h incubation and
the reaction mixture contained (-)-2 (86%) with ee 90%
(entry 1), along with minor amounts (4%) of diester 3.
The ee of the desired product could be improved up to
>98% by prolonging the reaction time beyond the com-
plete conversion of the substrate (entry 2), due to kinetic
amplification;12 in this case about 10% of diester 3 is
formed. Mucor miehei lipase gave comparable results in
terms of chemical and optical yields, but the reaction rate
was lower (entries 3 and 4), while C. antarctica lipase
was definitely the worst (entry 5), yielding a monoester
with low enantiomeric excess which did not improve by
prolonging the reaction time (entry 6). Therefore P.
cepacia lipase was used in a gram scale preparation to
give homochiral (-)-2 in high yield (90%).
Resu lts a n d Discu ssion
En zym a tic P r ep a r a tion of Both En a n tiom er s of
1-Acet oxy-2-h yd r oxycycloh exa -3,5-d ien e. In the
(1) For a review, see: Balci, M.; Su¨tbeyaz, Y.; Sec¸en, H. Tetrahedron
1990, 46, 3715.
(2) (a) Ley, S. V.; Sternfeld, F.; Taylor, S. Tetrahedron Lett. 1987,
28, 225. (b) Hudlicky, T.; Price, J . D.; Rulin, F.; Tsunoda, T. J . Am.
Chem. Soc. 1990, 112, 9439.
(3) Ley, S. V.; Sternfeld, F. Tetrahedron Lett. 1988, 29, 5305.
(4) Ley, S. V.; Yeung, L. L. Synlett. 1992, 997.
(5) Legler, G. Adv. Carbohydr. Chem. Biochem. 1990, 48, 319.
(6) Ley, S. V.; Redgrave, A. J . Synlett. 1990, 393.
(7) (a) Hudlicky, T.; Price, J . D.; Olivo, H. F. Synlett. 1991, 645. (b)
Carless, H. A. J .; Oak, O. Z. J . Chem. Soc., Chem. Commun. 1991, 61.
(c) Hudlicky, T.; Luna, H.; Olivo, H. F.; Andersen, C.; Nugent, T.; Price,
J . D. J . Chem. Soc. Perkin Trans. 1 1991, 2907. (d) Carless, H. A. J .
Tetrahedron: Asymmetry 1992, 3, 795. (e) Carless, H. A. J . Tetrahedron
Lett. 1992, 33, 6379. (f) Carless, H. A. J . J . Chem. Soc., Chem. Commun.
1992, 234.
Monoester (-)-2 is very sensitive to the action of water,
acids, and heat, undergoing loss of acetic acid to afford
phenol. Extensive degradation also occurs on silica gel
and chromatographic purification is only possible on Si
Diol. The corresponding propanoate and benzoate, ob-
tained by biocatalyzed asymmetrization of 1 using vinyl
propanoate or vinyl benzoate, respectively, proved to be
as unstable as (-)-2.
(8) (a) J ohnson, C. R.; Ple`, P. A.; Adams, J . P. J . Chem. Soc., Chem.
Commun. 1991, 1006. (b) Dumortier, L.; Liu, P.; Dobbelaere, S.; Van
der Eycken, J .; Vandewalle, M. Synlett. 1992, 243. (c) Pingli L.,
Vandewalle, M., Tetrahedron 1994, 50, 7061.
(9) Patti, A.; Nicolosi, G.; Piattelli M.; Sanfilippo, C. Tetrahedron:
Asymmetry 1995, 6, 2195.
Since the lipases that catalyze the esterification of 1
all give the same monoester, (-)-2, to obtain the opposite
(11) Nicolosi, G.; Patti, A.; Piattelli M.; Sanfilippo, C. Tetrahedron:
Asymmetry 1995, 6, 519.
(10) Nicolosi, G.; Patti, A.; Piattelli M.; Sanfilippo, C. Tetrahedron
Lett. 1995, 36, 6545.
(12) Wang, Y.-F.; Chen, C.-H.; Girdaukas, G.; Sih, C. J . J .. Am.
Chem. Soc. 1984, 106, 3695.
S0022-3263(96)00251-4 CCC: $12.00 © 1996 American Chemical Society

Notes
J . Org. Chem., Vol. 61, No. 18, 1996 6459
Sch em e 1a
Sch em e 2a
a
Reaction conditions: (a) NMMO; 1% OsO4, CH2Cl2/t-BME, rt;
(b) Ac2O, Py, rt.
enantiomer we resorted to the alcoholysis of diester 3
prepared by chemical esterification of 1. Therefore, when
3 was treated with n-butanol in the presence of P. cepacia
lipase using t-BME as solvent after 24 h, a monoester
(+)-2 with 77% yield and ee 90% was recovered.
Osm yla tion of (-)-2. Dihydroxylation of 1,2-dihy-
droxycyclohexa-3,5-diene derivatives with OsO4 in
stoichiometric7a or catalytic amounts in the presence of
N-methylmorpholine N-oxide13 (NMMO) has been used
successfully in the preparation of conduritol isomers. We
studied the dihydroxylation of (-)-2 in the presence of
OsO4 in catalytic amounts to assess the influence of the
substrate chirality on the regio- and stereoselectivity of
the reaction outcome.
Monoester (-)-2 by treatment with NMMO in the
presence of catalytic amounts of OsO4, under the same
conditions described by Carless for the dihydroxylation
of 1, after 15 h gave a complex mixture containing four
1
monoacetyl tetrols, as evidenced by H NMR analysis.
Complete acetylation of the crude reaction products
afforded conduritol E tetraacetate (+)-4 of low ee (15%)
and meso-conduritol D tetraacetate 5 in a 7:3 ratio (see
Scheme 1). This shows that (-)-2 behaves, as regards
the syn/ anti stereoselectivity, the same as 1.13
In the hope of a more stereoselective course14 we then
considered catalytic osmylation in the presence of H2O2
(Milas’ reagent)15 as a possible alternative for attaining
cis-dihydroxylation, although it is known that the reac-
tion products may undergo further oxidation to an
R-ketol.16
a
Reaction conditions: (a) 2% OsO4 in t-BuOH/H2O2, 0 °C; (b)
Ac2O Py, rt; (c) (EtCO)2O/Py, rt; (d) NaBH4/CeCl3, 0 °C; (d) K2CO3/
MeOH.
The presence of an axial-axial coupling (J ) 11.2 Hz)
between H-5 and H-6 in the spectrum of (+)-7 allows
exclusion of their cis relation, thus defining the relative
stereochemistry at C-6. It is therefore apparent that
OsO4 attacks the diene system in (-)-2 with complete
preference anti with respect to the preexisting oxygen-
ated functions. The presence of the acetyl group origi-
nates a partial regioselectivity, so that the hydroxylation
of the C5 over the C3 double bond is preferred, yielding
the two diastereoismers 6a and 6b. These cannot be
separated by chromatography without partial loss of
optical purity due to intramolecular transacetylation.
Therefore, the reaction mixture was treated with pro-
panoic anhydride to afford the mixed esters (+)-8a and
(-)-8b, which were purified by column chromatography
on Si gel.
When (-)-2 was subjected to this reaction, it did not
give the corresponding tetrahydroxycyclohexene mono-
acetates, but two trihydroxycyclohexenone monoacetates
1
in 3:2 ratio, as deduced from H-NMR analysis. Chemical
acetylation of the crude reaction mixture yielded 4,5,6-
triacetoxycyclohex-2-enone [(+)-7] with 20% ee [1H-NMR
analysis in the presence of Eu(hfc)3], corresponding to the
diastereomeric ratio of the parent ketones (see Scheme
2). This indicates that in this case overoxidation is
complete.
(13) Carless, H. A. J .; Busia K.; Dove Y.; Malik S. S. J . Chem. Soc.
Perkin Trans. 1 1993, 2505.
(14) (a) Cha , J . K.; Christ, W. J .; Kishi, Y. Tetrahedron Lett. 1983,
24, 3943. (b) Cha , J . K.; Christ, W. J .; Kishi, Y. Tetrahedron 1984, 40,
2247.
(15) Milas, N. A.; Sussman, S. J . Am. Chem. Soc. 1936, 58, 1302.
(16) (a) Schro¨der, M. Chem. Rev. 1980, 80, 187. (b)VanRheenen, V.;
Kelly, R. C.; Cha, D. Y. Tetrahedron Lett. 1976, 23, 1973.
Reduction of (+)-8a with NaBH4 in the presence of
CeCl3 occurred stereoselectively, the attack of the hydride

6460 J . Org. Chem., Vol. 61, No. 18, 1996
Notes
°C and 300 rpm. After 24 h the enzyme was removed by
filtration and the reaction mixture, containing (+)-2 (77%) and
3 (23%), processed as above to afford (+)-2 (290 mg, 74%, 90%
ee) ([R]D +197° (c 0.48, C6H6)).
anion to the carbonyl carbon taking place exclusively syn
with respect to the ester at C-6, thus giving, after
treatment with K2CO3 in MeOH, the single tetrol deriva-
tive (+)-9 [(+)-conduritol F] with ee >95%. An analogous
procedure applied to (-)-8b gave the enantiomer (-)-9.
Osm yla tion of (-)-2 w ith NMMO. A solution (10 mL) of
NMMO (320 mg, 2.73 mmol) and OsO4 (7 mg, 0.027 mmol) in
CH2Cl2 was added to a solution of (-)-2 (400 mg, 2.6 mmol) in
t-BME (40 mL). After 15 h of stirring at rt, the reaction was
stopped by evaporation of solvent. Conventional acetylation
(Ac2O/Py) at room temperature of the residue followed by
chromatographic purification (SiO2, acetone-CH2Cl2 1:9) af-
forded (+)-4 (510 mg, 63%) and 5 (220 mg, 27%). The enantio-
meric excess of (+)-4 was determined as 15% after hydrolysis
to (+)-conduritol E ([R]D +50° (c 1, H2O), lit.7c [R]D +330° (c 4.5,
H2O)).
Osm yla tion of (-)-(2) w ith t-Bu OH/H2O2. To a solution
of (-)-2 (0.95 g, 6.17 mmol, >98% ee) in t-BME (95 mL) were
successively added 5 mL of a 6.3% solution of H2O2 in t-BuOH
prepared according to the Milas procedure15 and 6 mL of a 0.5%
solution of OsO4 in t-BuOH. The mixture was stirred at 0 °C
until TLC analysis showed the nearly complete disappearance
of (-)-2 (ca. 12 h), then the reaction was quenched by filtration
on a Sep-pack cartridge and the solvent evaporated under
reduced pressure. 1H-NMR analysis of the residue showed the
presence of two monoesters (6a and 6b) in a 3:2 ratio, as
calculated from the integrated areas of the resonances for the
carboxymethine (δ 5.01 and 5.63, respectively).
Half of the osmylation mixture was submitted to conventional
acetylation followed by chromatography (SiO2, hexane-Et2O 1:1)
to afford (+)-(4S,5S,6R)-4,5,6-t r ia cet oxycycloh ex-2-en on e
(+)-7: (720 mg, 86%, 20% ee), [R]D +13° (c 1, CHCl3); 1H-NMR δ
2.06 (3H, s), 2.14 (3H, s), 2.18 (3H, s), 5.43 (1H, dd, J ) 11.2
and 3.9 Hz), 5.75 (1H, d, J ) 11.2 Hz), 5.80 (1H, dd, J ) 5.9 and
3.9 Hz), 6.27 (1H, d, J ) 9.9 Hz), 6.92 (1H, dd, J ) 9.9 and 5.9
Hz); 13C-NMR δ 20.04, 20.56, 20.62, 65.27, 68.62, 72.01, 131.98,
140.93, 169.60, 169.88, 169.92, 190.93.
The second half of the crude osmylation product was treated
with propanoic anhydride/pyridine in CH2Cl2. After 10 h of
stirring at rt, the solution was extracted with 1 N HCl and taken
to dryness under reduced pressure, and the residue was sub-
jected to column chromatography (Si gel, hexane-Et2O 60:40)
to give (+)-8a (445 mg, 48%) and (-)-8b (295 mg, 32%).
(+)-(4S ,5S ,6R )-5-Ace t oxy-4,6-d ip r op yloxycycloh e x-2-
en on e [(+)-8a ]: [R]D +118°, (c 0.3, CHCl3); 1H-NMR δ 1.18 (3H,
t, J ) 7.6 Hz), 1.19 (3H, t, J ) 7.6 Hz), 2.05 (3H, s), 2.44 (4H,
m), 5.44 (1H, dd, J ) 11.2 and 3.9 Hz), 5.77 (1H, d, J ) 11.2
Hz), 5.84 (1H, dd, J ) 5.9 and 3.9 Hz), 6.28 (1H, d, J ) 10 Hz),
6.93 (1H, dd, J ) 5.9 and 10 Hz); 13C-NMR δ 9.07, 9.13, 20.55,
27.26, 27.38, 65.09, 68.73, 71.84, 132.00, 140.97, 169.59, 173.42,
173.52, 191.11.
(-)-(4R ,5R ,6S )-4-Ace t oxy-5,6-d ip r op yloxycycloh e x-2-
en on e [(-)-8b]: [R]D -82°, (c 0.2, CHCl3); 1H-NMR δ 1.13 (3H,
t, J ) 7.6 Hz), 1.18 (3H, t, J ) 7.5 Hz), 2.14 (3H,s), 2.51 (4H,
m), 5.46 (1H, dd, J ) 3.8 and 11.1 Hz), 5.78 (1H, d, J ) 11.1
Hz), 5.82 (1H, dd, J ) 5.9 and 3.8 Hz), 6.28 (1H, d, J ) 10 Hz),
6.93 (1H, dd, J ) 10 and 5.9); 13C-NMR δ 8.88, 9.06, 20.66, 27.24,
27.28, 65.34, 68.50, 71.84,132.04, 140.88, 169.94, 173.01, 173.39,
191.12.
(+)-Con d u r itol F [(+)-9]. NaBH4 (46 mg) was added por-
tionwise to a stirred solution of (+)-8a (150 mg, 0.5 mmol) in
0.1 M CeCl3 (8 mL, 0.8 mmol) in methanol.17 After 15 min at 0
°C the resulting mixture was poured in water and extracted with
AcOEt. The organic phase was taken to dryness and K2CO3 was
then added to the residue dissolved in MeOH. Hydrolysis
proceeded smoothly to give (+)-9 (66 mg, 90%), the 1H-NMR data
of which were in agreement with the literature values6 ([R]D
+68.5° (c 0.13, CH3OH); lit.6 [R]D +70.8° (c 0.13, CH3OH)).
(-)-Con d u r itol F [(-)-9]. A solution of (-)-8b (150 mg, 0.5
mmol) was treated as above to give (-)-9 (64 mg, 88%) ([R]D
-68.7° (c 0.2, CH3OH); lit.6 [R]D -71.7° (c 0.75, CH3OH)).
Con clu sion s
In brief, enantiotoposelective esterification and alco-
holysis assisted by lipase are convenient ways to obtain
both enantiomers of 1-acetoxy-2-hydroxycyclohexa-3,5-
diene with high chemical and optical yields. This com-
pound is a valuable starting material for the synthesis
of chiral conduritol derivatives. In particular, dihydroxyl-
ation of (-)-2 with H2O2 in the presence of catalytic
amounts of OsO4 is highly stereoselective and moderately
regioselective, yielding the two monoacetates 6a and 6b.
Treatment of the crude reaction mixture with propanoic
anhydride afforded the mixed esters (+)-8a and (-)-8b
that were separated by conventional column chromatog-
raphy and each subjected to NaBH4 reduction followed
by alkaline hydrolysis to give (+)-9 and (-)-9, respec-
tively. Compounds (+)-8a and (-)-8b have structural
features that prelude their use as starting material for
the preparation of other conduritol derivatives.
Exp er im en ta l Section
All chemicals were purchased from Aldrich and used as
received. Vinyl acetate was distilled prior to use. Solvents were
dried according to literature procedures. Column chromatog-
raphy was performed on silica gel or Si Diol; analytical TLC was
carried out on Merck silica gel 60-F254 precoated glass plates
and compounds were visualized by spraying with molybdo-
phosphoric acid. Lipases from C. cylindracea, P. cepacia (PSL),
R. javanicus, and A. niger were from Amano International
Enzyme Co. Lipase from porcine pancreas was obtained from
Sigma. Novozym 435 (immobilized lipase from Candida ant-
arctica) and Lipozyme IM (immobilized lipase from Mucor
miehei) are registred marks from Novo Nordisk. 1H- and 13C-
NMR spectra were recorded in CDCl3 at 250.13 and 62.9 MHz,
respectively. Chemical shifts are in ppm (δ) downfield from
Me4Si . (R)-(-)-1-(9-Anthryl)-2,2,2-trifluoroethanol (Pirkle’s
alcohol) or europium(III) tris-[3-(heptafluoropropyl)hydroxy-
methylene]-(+)-camphorate were used as chiral shift reagents
to determine enantiomeric ratios. Optical rotations were meas-
ured on a DIP 135 J ASCO instrument. GC analyses were
performed on Chiraldex G-DA (dialkyl γ-cyclodextrin) capillary
column.
Gen er a l P r oced u r e for En zym a tic Ester ifica tion of cis-
1,2-Dih yd r oxycycloh exa -3,5-d ien e (1). For a typical enzy-
matic esterification, the lipase of choice (10 mg) and vinyl acetate
(0.02 mL) were added to a solution of 1 (10 mg) in t-BME (1
mL), and the suspension was stirred at 40 °C and 300 rpm.
Substrate conversion was determined by 1H-NMR at regular
time intervals. The enantiomeric excess of (-)-2 was determined
by 1H-NMR in the presence of Pirkle’s alcohol or by chirospecific
GC of the corresponding tetrahydro derivative.11
En zym a tic P r ep a r a tion of (-)-(1R,2S)-1-Acetoxy-2-h y-
d r oxycycloh exa -3,5-d ien e [(-)-(2)]. PSL (0.5 g) was added
to a solution of 1 (0.5 g, 4.46 mmol) and vinyl acetate (1 mL) in
t-BME (50 mL), and the mixture was shaken at 40 °C and 300
rpm. After 3 h the reaction was stopped by filtering off the
enzyme and the solvent evaporated under a stream of N2.
Conversion of substrate and ratio of the products were deter-
mined by 1H-NMR analysis. After purification on Si Diol with
hexane/CH2Cl2 5:95, (-)-2 (580 mg, 85%, >98% ee) ([R]D -215°
(c 1, C6H6)) was recovered.
Ack n ow led gm en t. This work has financially been
supported by Italian National Council of Research under
the scheme “Progetto Strategico: Tecnologie Chimiche
En zym a tic P r ep a r a tion of (+)-(1S,2R)-1-a cetoxy-2-h y-
d r oxycycloh exa -3,5-d ien e [(+)-(2)]. PSL (0.5 g) was added
to a solution of 3 (0.5 g, 2.55 mmol) and n-butanol (0.5 mL) in
t-BME (50 mL), and the resulting suspension was shaken at 40
(17) Le Drian, C.; Vieira, E; Vogel, P. Helv. Chim. Acta 1989, 72,
338.

Notes
J . Org. Chem., Vol. 61, No. 18, 1996 6461
material is contained in libraries on microfiche, immediately
follows this article in the microfilm version of the journal, and
can be ordered from the ACS; see any current masthead page
for ordering information.
Innovative”. The authors thank Amano Co and NOVO
Nordisk for a gift of P. cepacia lipase and M. miehei
lipase (Lipozyme IM) respectively.
Su p p or tin g In for m a tion Ava ila ble: 13C NMR spectra of
compounds (+)-2, (+)-7, (+)-8a , and (-)-8b (4 pages). This
J O960251J