Chemo-enzymatic enantioconvergent approach toward ethyl shikimate from ethyl 5-hydroxy-3,4-isopropylidenedioxycyclohex-1-enecarboxylate

Article abstract of DOI:10.1016/j.tet.2013.05.004

An enantioconvergent route for natural form of ethyl shikimate was achieved from Diels-Alder adduct of furan and acryloyl chloride. The key step was a highly enantioselective (E >500) and efficient acetylation of ethyl (3R*,4S*,5S*)-5-hydroxy-3,4-isopropylidenedioxycyclohex-1- enecarboxylate, which had a diastereomeric relationship with ethyl shikimate, mediated by Burkholderia cepacia lipase (Amano PS-IM). Both of the resolved enantiomers were converted to natural form of ethyl shikimate by inversion at C-5 for the former and at C-3 and C-4 for the latter, respectively.

Full text of DOI:10.1016/j.tet.2013.05.004

Tetrahedron 69 (2013) 6527e6532
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Chemo-enzymatic enantioconvergent approach toward ethyl
shikimate from ethyl 5-hydroxy-3,4-isopropylidenedioxycyclohex-
1-enecarboxylate
*
Yasunobu Yamashita, Kengo Hanaya, Takeshi Sugai, Tohru Mizushima, Mitsuru Shoji
Faculty of Pharmacy, Keio University, 1-5-30 Shibakoen, Minato-ku, Tokyo 105-8512, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 April 2013
Received in revised form 30 April 2013
Accepted 3 May 2013
Available online 13 May 2013
An enantioconvergent route for natural form of ethyl shikimate was achieved from DielseAlder adduct of
furan and acryloyl chloride. The key step was a highly enantioselective (E >500) and efficient acetylation
of ethyl (3R*,4S*,5S*)-5-hydroxy-3,4-isopropylidenedioxycyclohex-1-enecarboxylate, which had a di-
astereomeric relationship with ethyl shikimate, mediated by Burkholderia cepacia lipase (Amano PS-IM).
Both of the resolved enantiomers were converted to natural form of ethyl shikimate by inversion at C-5
for the former and at C-3 and C-4 for the latter, respectively.
Keywords:
Ó 2013 Elsevier Ltd. All rights reserved.
Ethyl shikimate
Enantioconvergent approach
Lipase
Kinetic resolution
Carbacycle
1. Introduction
Ethyl shikimate (1) is well-known intermediate for the synthesis
of oseltamivir phosphate (TamifluÒ), which is a neuraminidase in-
hibitor used in the treatment of both Type A and B human in-
fluenza.1 Shikimic acid (Scheme 1),2 a starting material for the
synthesis of oseltamivir phosphate, has been obtained from the
extracts of Chinese star anis and is recently supplied by bio-
synthesis of engineered microorganism.3 The production from
fermented coffee pulp combined with another microbial trans-
formation is also promising.4 Synthetically, DielseAlder reaction
between furan and acrylic acid or its derivatives is a robust ap-
proach for the construction of cyclohexenecarboxylate framework
in shikimic acid. The DielseAlder reaction and subsequent dia-
stereoselective transformations, however, gave ‘racemic’ form of
the polyoxygenated carbacycles. Pioneering works on enzyme-
catalyzed kinetic resolution,5 asymmetric DielseAlder reaction,6
and ring-closing metathesis7 toward natural type of shikimic acid
have been reported. Herein we describe an enantioconvergent
approach to ethyl shikimate (1) by designing a readily accessible
intermediate via lipase-mediated kinetic resolution of the
cyclohexenol.
Scheme 1. Enantioconvergent retrosynthesis of 1.
2. Results and discussion
In our synthetic plan as illustrated in Scheme 1, both 2 and 3
would be converted to natural form of ethyl shikimate (1) by
regioselective inversion of stereochemistry at C-5 on 2 and at C-3
and C-4 on 3, respectively. Optically active 2 and 3 would be
* Corresponding author. Tel.: þ81 3 5400 2659; fax: þ81 3 5400 2695; e-mail
address: shoji-mt@pha.keio.ac.jp (M. Shoji).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.05.004

6528
Y. Yamashita et al. / Tetrahedron 69 (2013) 6527e6532
obtained via lipase-mediated kinetic resolution of (ꢀ)-4, which
would be produced by DielseAlder reaction between furan and
acryloyl chloride followed by
b
-elimination of bicycloester (ꢀ)-5.
DielseAlder reaction between furan and acryloyl chloride8 and
subsequent quenching with ethanol (EtOH) gave a 1:1.4 mixture of
endo-(ꢀ)-6 and exo-(ꢀ)-7 in 77% yield over two steps (Scheme 2).
Although the endo/exo selectivity was low, these two adducts were
converged on single diastereomer at a later stage. The next dia-
stereoselective dihydroxylation catalyzed by K2OsO2(OH)4
(1 mol %) provided a mixture of (ꢀ)-8 and (ꢀ)-9 quantitatively. In
this dihydroxylation, higher loading of K2OsO2(OH)4 caused the
dihydroxylation from concave face. Protection of diol 8 and 9 as
acetonide afforded a mixture of 10 and 11 in 96% yield over two
steps. Subsequent b-elimination of 10 and 11 with lithium hex-
amethyldisilazide (LHMDS) in tetrahydrofuran (THF) at low tem-
perature furnished (ꢀ)-12 in 93% yield.
Scheme 3. Lipase-catalyzed resolution of racemic 12.
Table 1
Lipase-catalyzed kinetic resolution of (ꢀ)-12 and (ꢀ)-15a
Entry Substrate Lipase
Time/h Conv./% E valueb
1
2
3
4
(ꢀ)-12
(ꢀ)-12
(ꢀ)-12
(ꢀ)-15
C. rugosa (Meito OF)
B. cepacia (Amano PS-IM)
C. antarctica B (Novozym 435) 38
C. rugosa (Meito OF) 16
4
2
50
50
45.8
44.7
>500c
>500c
71d
124c
a
b
c
For detailed conditions, see Experimental section.
Calculated according to Ref. 9.
The (ꢁ)-enantiomer reacted faster.
d
The (þ)-enantiomer reacted faster.
to afford acetate (ꢁ)-13 (8.3 g, 48.5% yield, 99.8% ee) and alcohol
(þ)-12 (7.4 g, 49.3% yield, 98.0% ee). The ee of the latter could fur-
ther be increased by recrystallization.
The next task was the transformation of ‘slow’ enantiomer
(þ)-12 into ethyl shikimate [(ꢁ)-1]. Immediately after the conver-
sion of alcohol 12 into triflate 16, inversion of stereochemistry at C-
5 with KNO2 in N,N-dimethylformamide (DMF) at room tempera-
ture provided (ꢁ)-17 (75% over two steps, Scheme 4).11 Mesylate
and chloromethylsulfonate derived from 12 gave undesired aro-
matized byproduct because higher temperature for the inversion
was required. The absolute configuration of 17 was determined
to be (3R,4S,5R) by the comparison of its sign of optical rotation
Scheme 2. Synthesis of (ꢀ)-12 as a substrate for the enzymatic resolution.
Since the desired (ꢀ)-12 was in hand, lipase-catalyzed acetyla-
tion was investigated with three commercially available enzymes,
such as Candida rugosa lipase (Meito OF), Burkholderia cepacia li-
pase (Amano PS-IM), and Candida antarctica lipase (Novozym 435)
as shown in Scheme 3. The results are summarized in Table 1.
With the former two enzymes, (ꢁ)-12 was acetylated faster than
(þ)-12 (entries 1 and 2) and the reactions proceeded with high
enantioselectivities in both cases (E value9 >500). The bulkier
substituent was isopropylidenedioxy group in case of (ꢁ)-12,10
whereas methoxycarbonyl group was larger in the ‘fast’ enantio-
mer of structurally related substrate (ꢁ)-14.8 Interestingly, C. ant-
arctica lipase showed the opposite enantiomeric preference
compared with the other lipases (entry 3). When bulkier sub-
stituent, such as 3-pentylidenedioxy group was introduced in
(ꢀ)-15, the reactivity of ‘fast’ enantiomer decreased with the result
of low enantioselectivity (E¼124) and incomplete conversion (en-
try 4). The acetylations with B. cepacia and C. antarctica lipases were
almost no reaction.
[[a
]
D
26 ꢁ33.0 (c 0.50, EtOAc)] with the reported value [[
a
]
25 ꢁ31.0 (c
D
3.0, EtOAc)].12
Compared with Meito OF, Amano PS-IM was stable and reliable
because it was immobilized to resin. Based on the result of entry 2
in Table 1, the scaled-up reaction was performed with 15 g of (ꢀ)-12
Scheme 4. Synthesis of natural form of ethyl shikimate (1) from (þ)-12.

Y. Yamashita et al. / Tetrahedron 69 (2013) 6527e6532
6529
Removal of acetonide of 17 worked well by the treatment with
Dowex 50W-X8 (Hþ form) in EtOH to accomplish the synthesis of
natural form of ethyl shikimate [(ꢁ)-1] in 78% yield. Since triol 1
was soluble in aqueous phase, deprotection under acidic condition,
such as pyridinium p-toluenesulfonate in methanol followed by
aqueous workup resulted in a low yield (54%).
Toward the enantioconvergent approach, the next task was the
synthesis of ethyl shikimate (1) from (ꢁ)-13, which was the ‘fast’
isomer of the lipase-catalyzed kinetic resolution. Our first attempt
was the removal of acetonide under acidic condition with Brønsted
acids, such as Dowex 50W-X8 (Hþ form) or PPTS in alcoholic sol-
vents. Those conditions, however, caused solvolysis of acetyl group
along with the removal of acetonide to give the triol (ca. 30%) with
the equal amount of desired 18. The yield of this step was improved
by Lewis acidic condition using FeCl3$6H2O to afford 18 in 87% yield
(Scheme 5).
The enantioconvergent synthesis of (ꢁ)-1 was achieved in 59%
yield over three steps and in 6% yield over six steps from (þ)-12 and
(ꢁ)-13, respectively.
4. Experimental section
4.1. General methods
IR spectra were measured as ATR. 1H and 13C NMR spectra were
measured in CDCl3 at 400 and 100 MHz, respectively. HRMS anal-
ysis was recorded on a FAB-MS mass spectrometer. Column chro-
matography was performed on silica gel.
4.2. Ethyl (1R*,2S*,5S*)-2,5-epoxycyclohex-3-enecarboxylate
(6, endo isomer) and (1R*,2R*,5R*)-2,5-epoxycyclohex-3-
enecarboxylate (7, exo isomer)
To furan (32 mL, 440 mmol) was added acryloyl chloride
(9 mL, 110 mmol) and the mixture was stirred for 72 h at room
temperature. After evaporation of the excess reagents, to the
residue were added pyridine (26 mL) and EtOH (30 mL) and the
mixture was stirred for 1 h at room temperature. The reaction
mixture was cooled to 0 ꢂC, and the reaction was quenched with
water. Organic materials were extracted with EtOAc. The com-
bined extract was washed with 2 M HCl aq solution, saturated
NaHCO3 aq solution and brine, dried over Na2SO4, and concen-
trated in vacuo. The residue was purified by silica gel column
chromatography (100 g). Elution with hexaneeEtOAc (2:1) affor-
ded a mixture of (ꢀ)-6 (endo) and (ꢀ)-7 (exo) as a pale yellow oil
(14.2 g, 77%, endo:exo¼1:1.4). IR 2981, 1722, 1450, 1369, 1317, 1184,
1045, 1020, 906, 875, 703 cmꢁ1 1H NMR (CDCl3)
; d 6.42 (d,
J¼5.9 Hz, 1H, endo), 6.37 (d, J¼5.8 Hz, 1H, exo), 6.33 (d, J¼5.8 Hz,
1H, exo), 6.21 (d, J¼5.9 Hz, 1H, endo), 5.17 (s, 1H, exo), 5.14 (d,
J¼5.5 Hz, 1H, endo), 5.05 (d, J¼4.3 Hz, 1H, exo), 5.00 (d, J¼4.7 Hz,
1H, endo), 4.16 (q, J¼7.2 Hz, 2H, exo), 4.08 (q, J¼7.1 Hz, 2H, endo),
3.08 (dt, J¼8.8, 3.9 Hz, 1H, endo), 2.40 (dd, J¼8.7, 4.0 Hz, 1H, exo),
2.14 (ddd, J¼11.5, 8.7, 4.3 Hz, 1H, exo), 2.07 (ddd, J¼11.6, 8.8,
4.7 Hz, 1H, endo), 1.55 (dd, J¼11.6, 3.9 Hz, 1H, endo), 1.54 (dd,
J¼11.5, 4.0, 1H, exo), 1.25 (t, J¼7.2 Hz, 3H, exo), 1.22 (t, J¼7.1 Hz, 3H,
Scheme 5. Synthesis of ethyl shikimate (1) from (ꢁ)-13.
endo); 13C NMR (CDCl3)
d 174.3, 172.7, 137.7, 135.3 (2C), 133.1, 81.5,
Attempts for the simultaneous inversion of the stereochemistry
at C-3 and C-4 of 18 via the corresponding dimesylate, bischlor-
omethylsulfonate, and ditriflate, resulted in the complex mixture of
structurally undefined products. Thus, a stepwise and successive
route was employed. At first, diol at C-3 and C-4 was activated as
cyclic sulfite 19. Acetate was introduced to C-3 allylic position by
the treatment of cesium acetate to give inverted acetate 20. Since
the acidity of H-3 was high because of allylic position and electron-
withdrawing acetyl group, allylic acetate 20 easily decomposed.
Thus, diacetate 20 was transformed to ethyl shikimate (1) as soon
as possible without purification. The hydroxy group at C-4 position
was triflated, and the resulting triflate 21 was immediately treated
with KNO2 in DMF to provide 22. Since deprotection of diacetate 22
by C. antarctica lipase (Novozym 435) required long reaction time to
cause decomposition, final removal of the two acetyl groups was
performed under acidic condition to furnish ethyl shikimate [(ꢁ)-1]
in 7% yield over five steps.
79.6, 79.4, 78.6, 61.5, 61.4, 43.5, 43.4, 29.6, 29.1, 14.8 (2C).
4.3. Ethyl (1R*,2R*,3S*,4R*,5S*)-2,5-epoxy-3,4-
dihydroxycyclohexanecarboxylate (8, endo isomer) and
(1R*,2S*,3R*,4S*,5R*)-2,5-epoxy-3,4-
dihydroxycyclohexanecarboxylate (9, exo isomer)
To a solution of the mixture of (ꢀ)-6 and (ꢀ)-7 as above (14.2 g,
84 mmol) in acetone (200 mL) and water (100 mL) were added N-
methylmorpholine N-oxide (50% in water, 23.3 mL, 120 mmol) and
K2OsO2(OH)4 (255 mg, 0.84 mmol), and the mixture was stirred for
8 h at room temperature. The reaction was quenched with satu-
rated Na2S2O3 aq solution and organic materials were extracted
with EtOAc three times. The combined extract was washed with
brine, dried over Na2SO4, and concentrated in vacuo. The residue
was purified by silica gel column chromatography (150 g). Elution
with hexaneeEtOAc (1:1) afforded a mixture of (ꢀ)-8 (endo) and
(ꢀ)-9 (exo) as a yellow solid (16.9 g, 99%, endo:exo¼1:1.4). A small
portion was separated by preparative TLC [developed with hex-
aneeEtOAc (1:2)] to afford analytically pure samples of (ꢀ)-8 and
(ꢀ)-9 as colorless solids, respectively. (ꢀ)-8: IR 3371, 3305, 2989,
3. Conclusion
A ‘diastereomeric substrate’ (ꢀ)-12 for lipase-catalyzed kinetic
resolution was prepared and reliable (E >500, conv.¼50%) resolu-
tion condition was elaborated with the use of B. cepacia lipase
(Amano PS-IM). Both of the resolved enantiomers were converted
to natural form of ethyl shikimate [(ꢁ)-1] with high enantiomeric
excess by way of regioselective inversion of the stereochemistry.
2958, 1720, 1450, 1187, 1068, 995, 910 cmꢁ1; 1H NMR (CDCl3)
d 4.46
(d, J¼5.9 Hz, 1H), 4.36 (d, J¼5.7 Hz, 1H), 4.13 (q, J¼7.1 Hz, 2H), 3.92
(d, J¼6.0 Hz, 1H), 3.89 (d, J¼6.0 Hz, 1H), 3.33 (br s, 2H), 2.92
(dt, J¼11.4, 5.9 Hz, 1H), 1.88 (ddd, J¼12.7, 11.4, 5.7 Hz, 1H), 1.75 (dd,
J¼12.7, 5.9 Hz, 1H), 1.24 (t, J¼7.1 Hz, 3H); 13C NMR (CDCl3)
d 171.7,

6530
Y. Yamashita et al. / Tetrahedron 69 (2013) 6527e6532
83.4, 82.80, 74.8, 72.0, 61.3, 44.0, 28.4, 14.3; mp 83.5e84.0 ꢂC. Anal.
Calcd for C9H14O5: C, 53.46; H, 6.98; found: C, 53.36; H, 6.95. (ꢀ)-9:
IR 3386, 3317, 2981, 2950,1720,1446,1045,1002, 898, 771, cmꢁ1; 1H
4.6. Lipase-catalyzed acetylation of ( )-12 and ( )-15
To a mixture of alcohol (ꢀ)-12 (15 g, 62 mmol) in vinyl acetate
(100 mL) was added B. cepacia lipase (Amano PS-IM, 5 g) and the
mixture was stirred for 8 h at room temperature. The lipase was
filtered off and the filtrate was concentrated in vacuo. The residue
was purified by silica gel column chromatography (200 g).
Elution with hexaneeEtOAc (2:1) firstly afforded acetate (ꢁ)-13 as
a colorless solid (8.3 g, 48.5%), and secondly, alcohol (þ)-12 (7.4 g,
49.3%). (ꢁ)-13: HPLC analysis [column, Daicel Chiralcel AY-3,
0.46 cmꢃ25 cm; hexaneeisopropyl alcohol (30:1); flow rate
0.5 mL minꢁ1; detected at 210 nm]: tR (min)¼21.8 [(ꢁ)-13, 99.9%],
23.9 [(þ)-13, 0.1%]; IR 2987, 1733, 1702, 1373, 1214, 1064, 1039, 950,
NMR (CDCl3)
d
4.57 (s, 1H), 4.40 (d, J¼5.7 Hz, 1H), 4.12 (q, J¼7.1 Hz,
2H), 3.86 (d, J¼5.9 Hz, 1H), 3.82 (d, J¼5.9 Hz, 1H), 3.50 (br s, 2H),
2.47 (dd, J¼9.2, 4.9 Hz, 1H), 2.04 (ddd, J¼12.9, 5.7, 4.9 Hz, 1H), 1.58
(dd, J¼12.9, 9.2 Hz, 1H), 1.23 (t, J¼7.1 Hz, 3H); 13C NMR (CDCl3)
d
172.9, 84.5, 82.0, 74.4, 74.3, 61.4, 43.1, 29.0, 14.3; mp 86.5e87.1 ꢂC;
Anal. Calcd for C9H14O5: C, 53.46; H, 6.98; found: C, 53.50; H, 6.98.
4.4. Ethyl (1R*,2R*,3S*,4R*,5S*)-2,5-epoxy-3,4-
isopropylidenedioxycyclohexanecarboxylate (10, endo isomer)
and (1R*,2S*,3R*,4S*,5R*)-2,5-epoxy-3,4-
isopropylidenedioxycyclohexanecarboxylate (11, exo isomer)
862 cmꢁ1
;
1H NMR (CDCl3)
d
6.76 (s, 1H), 5.06 (ddd, J¼7.6, 5.5,
2.1 Hz, 1H), 4.75 (d, J¼4.9 Hz, 1H), 4.41 (dd, J¼5.5, 2.1 Hz, 1H), 4.19
(q, J¼7.1, 2H), 2.67 (dd, J¼16.4, 5.5 Hz, 1H), 2.49 (dd, J¼16.4, 7.6 Hz,
1H), 2.11 (s, 3H), 1.38 (s, 3H), 1.35 (s, 3H), 1.27 (t, J¼7.1 Hz, 3H); 13C
To a solution of the mixture of (ꢀ)-8 and (ꢀ)-9 as above (16.9 g,
84 mmol) in acetone (200 mL) were added 2,2-dimethoxypropane
(36 mL, 256 mmol) and pyridinium p-toluenesulfonate (4.0 g,
15 mmol) and the mixture was stirred for 36 h at room temperature.
The reaction was quenched with saturated NaHCO3 aq solution and
organic materials were extracted with EtOAc. The combined extract
was washed with brine, dried over Na2SO4, and concentrated in
vacuo. The residue was purified by silica gel column chromatogra-
phy (200 g). Elution with hexaneeEtOAc (3:1) afforded a mixture of
(ꢀ)-10 (endo) and (ꢀ)-11 (exo) as a yellow solid (19.5 g, 96%,
endo:exo¼1:1.4). A small portion was separated by preparative TLC
[developed with hexaneeEtOAc (2:1)] to afford analytical pure
samples of (ꢀ)-10 and (ꢀ)-11 as colorless solids, respectively.
NMR (CDCl3)
28.4, 27.3, 24.9, 21.9, 14.9; [
d 171.2, 166.7, 135.6, 129.7, 111.4, 74.4, 74.3, 69.8, 61.8,
26
a]
ꢁ37.0 (c 1.00, MeOH); mp
D
71.1e71.5 ꢂC; Anal. Calcd for C14H20O6: C, 59.14; H, 7.06; found: C,
59.20; H, 7.07. (þ)-12: HPLC analysis [column, Daicel Chiralcel AY-3,
0.46 cmꢃ25 cm; hexaneeisopropyl alcohol (30:1); flow rate
0.5 mL minꢁ1; detected at 210 nm]: tR (min)¼79.6 [(ꢁ)-12, 1.0%],
26
81.3 [(þ)-12, 99.0%]; [
a]
þ61.4 (c 0.60, MeOH). Its 1H NMR spec-
D
trum was in good accordance with that of racemic sample.
To a mixture of alcohol (ꢀ)-12 (10 mg, 0.041 mmol) in vinyl
acetate (1 mL) was added C. rugosa lipase (Meito OF, 10 mg) and the
mixture was stirred for 4 h at room temperature. In the similar
workup and separation as describe for B. cepacia lipase-catalyzed
resolution, (ꢁ)-13 (5.4 mg, 49.4%) and (þ)-12 (4.9 mg, 49.0%)
were obtained. (þ)-12: under the same conditions as above: tR
(min)¼79.6 [(ꢁ)-12, 0.1%], 81.3 [(þ)-12, 99.9%]. (ꢁ)-13: HPLC under
the same conditions as above: tR (min)¼21.8 [(ꢁ)-13, 99.5%], 23.9
[(þ)-13, 0.5%].
(ꢀ)-10: IR 2981, 2939, 1720, 1373, 1195, 1160, 1049, 1002, 867 cmꢁ1
;
1H NMR (CDCl3)
d
4.53 (d, J¼5.8 Hz, 1H), 4.42 (d, J¼6.0 Hz, 1H), 4.26
(s, 2H), 4.15 (q, J¼7.2 Hz, 2H), 2.94 (dt, J¼11.2, 5.8 Hz, 1H), 1.89 (ddd,
J¼12.9,11.2, 6.0 Hz,1H),1.70 (dd, J¼12.9, 5.8 Hz,1H),1.45 (s, 3H),1.27
(t, J¼7.2 Hz, 3H),1.25 (s, 3H); 13C NMR (CDCl3)
d 171.7,111.1, 82.2, 80.2,
79.7, 79.5, 61.3, 43.3, 27.2, 25.9, 25.0, 14.3; mp 46.1e46.7 ꢂC; HRMS
(FAB-MS): calcd for C12H19O5: [MþH]þ: 243.1232; found:
m/z¼243.1237. (ꢀ)-11: IR 2981, 2962, 1727, 1268, 1203, 1153, 1072,
The reaction (38 h), workup, and purification with C. antarctica
lipase B (Novozym 435) was carried out in a similar manner. From
(ꢀ)-12 (10 mg, 0.041 mmol), (þ)-13 (5.1 mg, 47.2%), and (ꢁ)-12
(4.9 mg, 49.0%) were obtained. (ꢁ)-12: HPLC under the same con-
ditions: tR (min)¼79.6 [(ꢁ)-12, 85.8%], 81.3 [(þ)-12, 14.2%]. (þ)-13:
HPLC under the same conditions: tR (min)¼21.8 [(ꢁ)-13, 7.5%], 23.9
[(þ)-13, 92.5%].
1033, 1002, 856 cmꢁ1 1H NMR (CDCl3)
; d 4.65 (s, 1H), 4.46 (d,
J¼5.8 Hz, 1H), 4.22 (q, J¼7.0 Hz, 2H), 4.15 (d, J¼5.7 Hz, 1H), 4.13 (d,
J¼5.7 Hz, 1H), 2.37 (dd, J¼9.2, 4.9 Hz, 1H), 2.11 (ddd, J¼12.9, 5.8,
4.9 Hz,1H),1.52 (s, 3H),1.48 (dd, J¼12.9, 9.0 Hz,1H),1.45 (s, 3H),1.24
(t, J¼7.0 Hz, 3H); 13C NMR (CDCl3)
d 172.5,111.8, 82.3, 82.1, 82.0, 78.7,
61.2, 42.1, 27.7, 25.9, 25.2, 14.2; mp 48.5e49.2 ꢂC; Anal. Calcd for
To a mixture of alcohol (ꢀ)-15 (10 mg, 0.037 mmol) in vinyl
acetate (1 mL) was added C. rugosa lipase (Meito OF, 10 mg) and the
mixture was stirred for 16 h at room temperature. In the similar
workup and separation as describe above, the corresponding
(ꢁ)-acetate (5.1 mg, 41.8%) and (þ)-15 (4.4 mg, 44.0%) were ob-
tained. (þ)-15: HPLC analysis [column, Daicel Chiralcel OD-H,
0.46 cmꢃ25 cm; hexaneeisopropyl alcohol (30:1); flow rate
0.5 mL minꢁ1; detected at 210 nm]: tR (min)¼32.7 [(þ)-15, 88.9%],
37.1 [(ꢁ)-15, 11.1%]. The stereochemical assignment on the prefer-
ential enantiomer for 15 is based on the retention times on HPLC
analysis. In the case of 12, (þ)-12 showed shorter retention time
than that of (ꢁ)-12 in the use of Chiralcel OD-H, while (þ)-12
showed longer retention time than that of (ꢁ)-12 on Chiralcel AY-3.
Unfortunately, no good separation was observed between the en-
antiomers of 15 on Chiralcel AY-3. In the case of 15, the conversion
(44.7%) was determined by the comparison of peak area in 1H NMR
C12H18O5: C, 59.49; H, 7.49; found: C, 59.50; H, 7.43.
4.5. Ethyl (3R*,4S*,5S*)-5-hydroxy-3,4-
isopropylidenedioxycyclohex-1-enecarboxylate (12)
To a solution of hexamethyldisilazane (25 mL, 96 mmol) in THF
(400 mL) was added n-BuLi solution (1.57 M in hexane, 72 mL,
104 mmol) dropwise at 0 ꢂC and the mixture was stirred for 10 min
at that temperature. To the mixture was added a solution of the
mixture of (ꢀ)-10 and (ꢀ)-11 as above (19.5 g, 80 mmol) in THF
(80 mL) dropwise at ꢁ50 ꢂC and the mixture was stirred for 30 min
at that temperature. The reaction was quenched with saturated
NH4Cl aq solution and organic materials were extracted with EtOAc.
The combined extract was washed with brine, dried over Na2SO4,
and concentrated in vacuo. The residue was purified by silica gel
column chromatography (200 g). Elution with hexaneeEtOAc (2:1)
afforded (ꢀ)-12 as a colorless solid (18.1 g, 93%). IR 3440, 2985,
spectrum of crude reaction mixture:
(s, 1H, H-2 for the acetate).
d 6.75 (s, 1H, H-2 for 15), 6.71
2935, 2912, 1708, 1365, 1226, 1095, 1049, 909, 852, 732 cmꢁ1
NMR (CDCl3)
;
1H
d
6.77 (s, 1H), 4.70 (m, 1H), 4.39 (dd, J¼5.9, 2.7 Hz, 1H),
4.7. Ethyl (3R,4S,5R)-5-hydroxy-3,4-
isopropylidenedioxycyclohex-1-enecarboxylate (17)
4.19 (q, J¼7.0 Hz, 2H), 3.93 (ddd, J¼8.2, 4.5, 2.7 Hz, 1H), 2.62 (dd,
J¼16.6, 4.9 Hz, 1H), 2.49 (dd, J¼16.7, 8.2 Hz, 1H), 1.39 (s, 3H), 1.37 (s,
3H), 1.28 (t, J¼7.0 Hz, 3H); 13C NMR (CDCl3)
d
166.8, 135.0, 130.0,
To a solution of (þ)-12 (1.4 g, 5.8 mmol) in CH2Cl2 (30 mL) were
added pyridine (2.1 mL, 17.3 mmol), Tf2O (3.1 mL, 11.5 mmol), and
DMAP (170 mg, 1.20 mmol), and the mixture was stirred for 30 min
110.5, 76.0, 73.4, 67.5, 61.5, 28.2, 27.9, 26.5, 14.6; mp 46.1e47.1 ꢂC;
Anal. Calcd for C12H18O5: C, 59.49; H, 7.49; found: C, 59.48; H, 7.43.

Y. Yamashita et al. / Tetrahedron 69 (2013) 6527e6532
6531
at 0 ꢂC. The reaction was quenched with saturated NaHCO3
aq solution and organic materials were extracted with EtOAc. The
combined extract was washed with brine, dried over Na2SO4, and
concentrated in vacuo to afford 16 as a colorless solid; yield: 2.2 g.
This was employed for the next step without further purification.
To a solution of 16 (2.2 g, 5.87 mmol) in DMF (25 mL) was added
KNO2 (1.0 g, 11.8 mmol), and the mixture was stirred for 8 h at room
temperature. The reaction was quenched with saturated 0.1 M
phosphate buffer solution (pH 7.0) and organic materials were
extracted with EtOAc. The combined extract was washed with
brine, dried over Na2SO4, and concentrated in vacuo. The residue
was purified by silica gel column chromatography (20 g). Elution
with hexaneeEtOAc (2:1) afforded (ꢁ)-17 as a colorless oil (1.1 g,
To a solution of the above-mentioned 19 (151 mg, 0.52 mmol) in
DMF (5 mL) was added CsOAc (200 mg, 1.04 mmol) and the mixture
was stirred for 12 h at 40 ꢂC. The reaction was quenched with
saturated NH4Cl aq solution and organic materials were extracted
with EtOAc. The combined extract was washed with brine, dried
over Na2SO4, and concentrated in vacuo and afforded 20 as a yellow
oil (89 mg). This was employed for the next step without further
purification. 1H NMR (CDCl3)
d
6.70 (d, J¼2.5 Hz, 1H), 5.55 (dd,
J¼5.9, 2.5 Hz, 1H), 5.28 (dd, J¼6.9, 4.5 Hz, 1H), 4.19 (q, J¼7.2 Hz, 2H),
3.94 (d, J¼5.9 Hz, 1H), 2.67 (dd, J¼16.2, 6.9 Hz, 1H), 2.66 (dd, J¼16.2,
4.5 Hz, 1H), 2.09 (s, 3H), 2.07 (s, 3H), 1.27 (t, J¼7.2 Hz, 3H).
To a solution of 20 (89 mg, 0.31 mmol) in CH2Cl2 (3 mL) were
added pyridine (38 mL, 0.47 mmol), Tf2O (76 mL, 0.47 mmol), and
75% over two steps). 1H NMR (CDCl3)
d
6.92 (s, 1H), 4.73 (m, 1H),
DMAP (3.6 mg, 0.03 mmol) and the mixture was stirred for 30 min
at 0 ꢂC. The reaction was quenched with saturated NaHCO3
aq solution and organic materials were extracted with EtOAc. The
combined extract was washed with brine, dried over Na2SO4, and
concentrated in vacuo to afford 21 as a yellow oil (130 mg). This was
employed for the next step without further purification.
4.20 (q, J¼7.0 Hz, 2H), 4.06 (dd, J¼7.1, 6.9 Hz, 1H), 3.87 (ddd, J¼12.9,
8.6, 4.7 Hz, 1H), 2.79 (dd, J¼17.4, 4.7 Hz, 1H), 2.21 (dd, J¼17.4, 8.6 Hz,
26
1H), 1.43 (s, 3H), 1.38 (s, 3H), 1.27 (t, J¼7.0 Hz, 3H); [
a
]
ꢁ33.0 (c
D
0.50, EtOAc) [lit.10
[
a]
25 ꢁ31.0 (c 3.0, EtOAc)]. Its IR and NMR spectra
D
were identical with those reported previously.10
To a solution of the above-mentioned 21 (130 mg, 0.31 mmol) in
DMF (3 mL) was added KNO2 (53 mg, 0.62 mmol) and the mixture
was stirred for 3 h at room temperature. The reaction was quenched
with 0.1 M phosphate buffer solution (pH 7.0) and organic materials
were extracted with EtOAc. The combined extract was washed with
brine, dried over Na2SO4, and concentrated in vacuo to afford 22 as
4.8. Ethyl shikimate (1)
To a solution of the above-mentioned (ꢁ)-17 (1.1 g, 4.3 mmol) in
EtOH (20 mL) was added Dowex 50W-X8 acidic ion-exchange resin
(2.0 g) and the mixture was stirred for 48 h at room temperature.
The resin was filtered off, and the filtrate was concentrated in
vacuo. The residue was purified by silica gel column chromatog-
raphy (20 g). Elution with hexaneeEtOAc (1:3) afforded (ꢁ)-1 as
a colorless solid (40 mg). 1H NMR (CDCl3)
d 6.59 (s, 1H), 5.58 (d,
J¼8.6 Hz, 1H), 5.07 (dd, J¼9.4, 8.3 Hz, 1H), 4.20 (q, J¼7.2 Hz, 2H),
3.95 (m, 1H), 2.96 (dd, J¼17.6, 8.3 Hz, 1H), 2.37 (dd, J¼17.6, 9.4 Hz,
1H), 2.10 (s, 3H), 2.08 (s, 3H), 1.28 (t, J¼7.2 Hz, 3H). This was
employed for the next step without further purification.
To a solution of diacetate 22 (40 mg, 0.14 mmol) in EtOH (1 mL)
was added H2SO4 (7.5 mL, 0.14 mmol) and the mixture was stirred
for 14 h at room temperature. The reaction was quenched with
saturated NaHCO3 aq solution and organic materials were extracted
with EtOAc 10 times. The combined extract was washed with brine,
dried over Na2SO4, and concentrated in vacuo. The residue was
purified by preparative TLC [developed with hexaneeEtOAc (1:3)]
to afford ethyl shikimate (1) as a colorless solid (8.0 mg, 7% over five
steps). Its physical properties and spectral data were in good ac-
cordance with those of (ꢁ)-1 derived from (þ)-12.
a colorless solid (820 mg, 78%). 1H NMR (CDCl3)
d 6.88 (s, 1H), 4.46
(m, 1H), 4.20 (q, J¼7.2 Hz, 2H), 3.96 (dd, J¼8.8, 4.0 Hz, 1H), 3.61 (dd,
J¼9.0, 4.0 Hz, 1H), 2.94 (dd, J¼17.4, 6.0 Hz, 1H), 2.20 (dd, J¼17.4,
8.8 Hz, 1H), 1.67 (br s, 2H), 1.27 (t, J¼7.2 Hz, 3H); [
a]
23 ꢁ97.6 (c 1.00,
D
MeOH). Its 1H NMR spectra was in good accordance with that of
ethyl shikimate.13
4.9. Ethyl (3S,4S,5R)-5-acetoxy-3,4-dihydroxycyclohex-1-ene-
carboxylate (18)
To a solution of acetate (ꢁ)-13 (6.7 g, 23 mmol) in CH2Cl2
(200 mL) was added FeCl3$6H2O (18 g, 69 mmol) and the mixture
was stirred for 6 h at room temperature. The reaction was quenched
with saturated NaHCO3 aq solution and organic materials were
extracted with EtOAc three times. The combined extract was
washed with brine, dried over Na2SO4, and concentrated in vacuo.
The residue was purified by silica gel column chromatography
(100 g). Elution with hexaneeEtOAc (1:1) afforded 18 as a colorless
solid (5.0 g, 87%). IR 3432, 2983, 1724, 1641, 1382, 1261, 1240, 1153,
Acknowledgements
This work was supported by MEXT-Supported Program for the
Strategic Research Foundation at Private Universities, 2011e2015.
We acknowledge the generous gift of lipases, from Amano Enzyme
Inc. for PS-IM, Novozymes Japan for Novozym 435, and Meito
Sangyo Co. Ltd. for Meito OF.
1105 cmꢁ1
;
1H NMR (CDCl3)
d
6.77 (s, 1H), 5.03 (dt, J¼5.9, 2.3 Hz,
1H), 4.39 (s, 1H), 4.19 (q, J¼7.1 Hz, 2H), 4.08 (d, J¼2.3 Hz, 1H), 2.64
Supplementary data
(dd, J¼7.4, 5.9 Hz, 1H), 2.54 (dd, J¼7.4, 5.9 Hz, 1H), 2.09 (s, 3H), 1.28
(t, J¼7.1 Hz, 3H); 13C NMR (CDCl3)
d
171.5, 167.0, 138.4, 130.0, 72.0,
þ26.2 (c 0.50, MeOH); mp
27
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2013.05.004.
69.7, 68.7, 62.2, 27.0, 22.2, 15.2; [
a
]
D
79.5e80.1 ꢂC; Anal. Calcd for C11H16O6: C, 54.09; H, 6.60; found: C,
53.88; H, 6.56.
References and notes
4.10. Ethyl shikimate (1) from 18
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without further purification.

6532
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