Stereochemistry of enacyloxins. Part 3: (12′S, 17′r,18′s,19′r)- absolute configuration of enacyloxins, a series of antibiotics from Frateuria sp. W-315

Article abstract of DOI:10.1039/b104341m

The absolute configuration of the 12′,17′,18′,19′-positions of enacyloxins (ENXs), a series of polyhydroxy-polyenic antibiotics from Frateuria sp. W-315, was determined. As degradation of decarbamoyl (dec) ENX IIa gave (5R,6S,1′E)-6-(but-1′-enyl)-5-chloro

Full text of DOI:10.1039/b104341m

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Stereochemistry of enacyloxins. Part 3.1 (12ЈS,17ЈR,18ЈS,19ЈR)-
Absolute configuration of enacyloxins, a series of antibiotics from
Frateuria sp. W-315
1
Ryo Takeuchi,a Hiromasa Kiyota,*a Manabu Yaosaka,a Toshihiko Watanabe,b Keijiro Enari,b
Takeyoshi Sugiyamaa and Takayuki Oritania
a Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiya,
Aoba-ku, Sendai 981-8555, Japan
b Faculty of Engineering, Tohoku Institute of Technology, 35-1, Yagiyama-kasumicho,
Taihaku-ku, Sendai 982-8577, Japan
Received (in Cambridge, UK) 17th May 2001, Accepted 17th August 2001
First published as an Advance Article on the web 1st October 2001
The absolute configuration of the 12Ј,17Ј,18Ј,19Ј-positions of enacyloxins (ENXs), a series of polyhydroxy-polyenic
antibiotics from Frateuria sp. W-315, was determined. As degradation of decarbamoyl (dec) ENX IIa gave
(5R,6S,1ЈE)-6-(but-1Ј-enyl)-5-chloro-5,6-dihydro-2H-pyran-2-one, which corresponded to the 15Ј–23Ј skeleton
of dec ENX IIa, its enantiomers were synthesized from tri-O-acetyl--glucal. Comparison of the HPLC retention
time of these naturally derived and synthetic compounds revealed the 17ЈR,18ЈS,19ЈR-configuration of ENXs.
Hydrogenation and oxidation of ENX IIa gave methyl 13-hydroxy-6,12-dimethyltridecanoate, which was
converted to the 13-MTPA ester. Comparison of the 1H NMR chemical shifts and the coupling constants
with the model compounds revealed the 12ЈS-configuration. This absolute stereochemistry is necessarily
applicable to other enacyloxins.
at 0 ЊC. As 7 could be dehydrated to give the simpler lactone 8
Introduction
under neutral conditions (DCC, CuCl),7 we aimed to synthesize
both enantiomers of 8 to determine the absolute configuration
(Scheme 2).
Enacyloxins (ENXs) are polyhydroxy-polyenic and yellow-
colored antibiotics produced by Frateuria sp. W-315 in a
Czapek-Dox medium spent by Neurospora crassa.2 ENX IIa 1 is
the main product and has antibiotic activity against Gram-
positive and Gram-negative bacteria.3 Its mode of action was
considered to be the inhibition of peptide biosynthesis,4 and
its inhibition mechanism on ribosomes was recently reported.5
Furthermore, ENXs have attracted considerable attention
because they show antibiotic inhibitory activity toward organ-
elle protein synthesis in Plasmodium falciparum.6 ENX IIa 1
is an enzymatic oxidation product of ENX IVa 23d and both
are also converted enzymatically to their decarbamoylated
products, dec ENX IIa (cyclic form 3 and linear form 3Ј) and
dec ENX IVa 4, respectively (Scheme 1).1,3d As shown in
Scheme 1, the relative 17ЈS*,18ЈR*,19ЈS*-configuration of 1
was elucidated from the 6-membered hemiacetal form of 3. To
determine the absolute configuration of this fragment of 1, a
degradation study was performed. In this paper we describe the
determination of the absolute configuration of this fragment.
Synthesis of both enantiomers of the lactone 8Ј. As shown in
Scheme 3, our synthesis started from tri-O-acetyl--glucal 9,
which was converted to the methoxyphenyl (MP) ether 10 by
our reported procedure.8 The hydroxy group was oxidized
under Swern conditions followed by a Wittig–Horner reaction
to give ester 11. The ethoxycarbonyl group of 11 was reduced to
give 12 and the resulting hydroxy group was acetylated to afford
13. Copper catalyzed Grignard substitution of this allylic
acetate gave 14. The methoxyphenyl group was removed using
silver dipicolinate [Ag(DPAH)2]9 and the resulting hemiacetal
was oxidized to give lactone 15. Deprotection of the THP
group gave alcohol 16, and Mitsunobu conditions using
p-nitrobenzoic acid successfully inverted the 5-position to give
17. However, isomerization to the more stable γ-lactone 18
occurred during removal of the PNB group. To prevent this
isomerization, we chose acetic acid as the Mitsunobu donor.
The acetyl group of 19 was successfully removed by enzymatic
hydrolysis without isomerization to give (Ϫ)-20. Finally, the
hydroxy group of (Ϫ)-20 was converted to the chloride with
inversion of configuration to afford the desired (ϩ)-8Ј. Next
we prepared the enantiomer. Alkaline treatment of alcohol 15
gave the corresponding hydroxy acid, which was submitted to
Mitsunobu conditions to give lactone 21. Compound 21 was
converted to (Ϫ)-8Ј via (ϩ)-20 as described above.
Results and discussion
1. Determination of the absolute configuration of the
17Ј,18Ј,19Ј-positions
Degradation study. Treatment of dec ENX IIa 3 with NaIO4
in MeOH gave hemiacetal 5 (excess NaIO4) or ester 6 (1–2 eq.
NaIO4), while lactone 7 was formed using Pb(OAc)4 in MeCN
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This journal is © The Royal Society of Chemistry 2001
DOI: 10.1039/b104341m

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Determination of the absolute configuration. Chiral HPLC
analysis of the naturally derived and the synthetic 8Ј was per-
formed (Column, Shiseido Ceramosphere Chiral RU-2, 4.6 ×
150 mm; MeOH–H2O = 1 : 1 at 1.0 ml minϪ1; 245 nm). The
retention time of the naturally derived 8 coincided with that
of (ϩ)-8Ј (4.8 min), whilst that of (Ϫ)-8Ј was 2.9 min, so the
absolute configuration of naturally derived 8 was confirmed to
be 5S,6R. Consequently, the absolute configuration of ENX IIa
1 was determined to be 17ЈR,18ЈS,19ЈR.
2. Determination of the absolute configuration of the
12Ј-position
Fig. 1 Parts of the 1H NMR spectra of the natural and the model
compounds.
Degradation study. We adopted the MTPA ester method
which is used in the determination of the absolute configuration
of α-methyl fatty acids.10 The polyene fragment of ENX IIa
methyl ester 22 was hydrogenated over PtO2 to give 23
(Scheme 4). The 13Ј,14Ј-vicinal diol was cleaved with NaIO4–
NaBH4 to afford a mixture of ester 24 and free acid 25, which
were treated with CH2N2 followed by alkaline methanol to give
alcohol 26. This compound was converted to the corresponding
(S)-MTPA ester 27.
absolute configuration of the 12Ј-position was determined to
be S.
Conclusion
The 12ЈS,17ЈR,18ЈS,19ЈR-absolute configuration of ENX IIa, a
polyhydroxy-polyenic antibiotic from Frateuria sp. W-315, was
determined by comparison of degradation products of the
natural compounds and the synthetic model compounds. This
absolute stereochemistry is necessarily applicable to all ENXs.
The model compound, (S)-2-methyltetradecanol 30, was
synthesized from methyl (S)-3-hydroxy-2-methylbutanoate 28
via the known iodide 29.11 The alcohol 30 was then converted
to its (S)-MTPA ester 31.10a The corresponding 2RS com-
1
pound 32 was also prepared.12 The H NMR spectrum of 27
Experimental
General
was compared with those of the model compounds 31 and
32.10b As shown in Fig. 1, the chemical shifts and the splitting
pattern of 27 closely match those of 31. Consequently, the
NMR spectra were obtained on Varian Unity Inova 500
Scheme 1 Enacyloxins and decarbamoyl enacyloxins.
Scheme 2 Degradation of dec ENX IIa 3.
J. Chem. Soc., Perkin Trans. 1, 2001, 2676–2681
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(500 MHz for 1H) and GEMINI 3000 (300 MHz for 1H
and 75 MHz for 13C) spectrometers in CDCl3 using Me4Si
as an internal standard, mass spectra were recorded on a
JEOL DX-303 HF, and IR spectra were measured on a JASCO
IR-810. HPLC were measured on a Shimadzu LC-10. Optical
brine, dried (MgSO4) and concentrated in vacuo. The residue
was chromatographed on silica gel (hexane–EtOAc = 2 : 1) to
give 7 (0.20 µg, 54%); δH (500 MHz) 1.04 (3 H, t, J 7.4 Hz,
4Ј-H), 1.56 (2 H, dq, J 6.4, 7.4 Hz, 3Ј-H), 2.60 (1 H, d, J 2.9 Hz,
OH), 2.65 (1 H, dd, J 9.5, 17.6 Hz, 3-H), 3.14 (1 H, dd, J 6.2,
17.6 Hz, 3-H), 3.75 (1 H, dd, J 10.5, 9.4 Hz, 5-H), 4.15 (1 H,
dddd, J 2.9, 6.2, 9.4, 9.5 Hz, 4-H), 4.60 (1 H, dd, J 7.8, 10.5 Hz,
6-H), 5.50 (1 H, dd, J 7.8, 15.4 Hz, 1Ј-H), 6.00 (1 H, dt, J 6.4,
15.4 Hz, 2Ј-H); m/z (EI) 204 (Mϩ). This compound was used in
the next step without further purification.
rotations are given in 10Ϫ1 deg cm2 gϪ1
.
Determination of the 17,18,19-positions
Natural (4R,5S,6R,1ЈE )-6-(but-1Ј-enyl)-5-chloro-2-formyl-
3,4,5,6-tetrahydro-2H-pyran-2,4-diol
5 and methyl (3R,4S,
5R,6E )-4-chloro-3,5-dihydroxynon-6-enoate 6. To a solution of
dec ENX IIa (1.0 mg, 1.5 µmol) in MeOH (1 cm3) was added a
solution of NaIO4 (1 mg, 5 mmol) in H2O (1 cm3) and the
mixture was stirred for 1 h at 20 ЊC. Then the mixture was
diluted with EtOAc, washed with aq. Na2S2O3, H2O and brine,
dried (MgSO4) and concentrated in vacuo. The residue was
chromatographed on silica gel (hexane–EtOAc = 3 : 1) to give 5
and 6 in trace amounts. 5; δH (500 MHz) 1.16 (3 H, t, J 7.4 Hz,
4Ј-H), 1.82 (2 H, pseudo dd, J 12.0, 3.8 Hz, 3-H), 2.12 (2 H, m,
3Ј-H), 2.34 (1 H, ddd, J 12.0, 4.9, 0.8 Hz, 3-H), 2.65 (1 H, m,
4Ј-H), 3.36 (1 H, dt, J 10.2, 11.8 Hz, 5-H), 4.49 (1 H, dd, J 7.4,
10.2 Hz, 6-H), 5.50 (1 H, ddt, J 15.4, 9.1, 1.6 Hz, 1Ј-H), 5.94
(1 H, dd, J 7.4, 10.2 Hz, 2Ј-H), 8.11 (1 H, s, CHO); m/z (EI) 234
(Mϩ). 6; δH (500 MHz) 1.04 (3 H, t, J 7.4 Hz, 9-H), 2.12 (2 H, m,
8-H), 2.58 (1 H, pseudo d, J 16.2 Hz, 2-H), 2.78 (1 H, dd, J 16.2,
8.6 Hz, 2-H), 3.90 (1 H, dt, J 1.9, 5.8 Hz), 4.44 (1 H, m), 4.63
(1 H, m, 5-H), 5.57 (1 H, dd, J 15.1, 6.3 Hz, 6-H), 5.91 (1 H, dt,
J 15.4, 6.3, 7-H).
Natural (5S,6R,1ЈE )-6-(but-1Ј-enyl)-5-chloro-5,6-dihydro-2H-
pyran-2-one (5S,6R)-8. A solution of 7 (0.20 µg, 0.98 µmol),
dicyclohexylcarbodiimide (DCC, 1 mg, 5 µmol) and CuCl (cat.)
in ether (5 cm3) was stirred at reflux for 1 h under Ar. After
being cooled to 20 ЊC, the mixture was concentrated in vacuo
and the residue was purified by HPLC (hexane–PriOH = 20 : 1,
ERC-Si-1811, 20 ЊC, 1.0 cm3 minϪ1, 222 nm, tR = 7.5 min) to
give (5S,6R)-8 (0.10 µg, 55%) as a colourless oil. The spectral
data were identical with those of synthetic (5S,6R)-8.
(2R,5S,6R,1ЈE,2ЉRS)-5,6-Dihydro-6-(2Ј-ethoxycarbonyleth-
1Ј-enyl)-2-( p-methoxyphenoxy)-5-(tetrahydro-2ЉH-pyran-2Љ-
yloxy)-2H-pyran 11. To a solution of oxalyl chloride (1.2 cm3,
14 mmol) in THF (60 cm3) was added DMSO (2.5 cm3,
32 mmol) at Ϫ78 ЊC under Ar and the mixture was stirred for
0.5 h. A solution of 10 (4.00 g, 11.1 mmol) in THF (20 cm3) was
added dropwise and the mixture was stirred as the temperature
gradually rose. At Ϫ30 ЊC, to this was added Et3N (4.0 cm3,
28 mmol) and the resulting mixture was stirred for 3 h until the
temperature increased to 0 ЊC. The mixture was poured into
H2O and extracted with ether. The extract was washed with
brine, dried (MgSO4) and concentrated in vacuo. This crude
aldehyde was used in the next step without further purification.
To a suspension of NaH (ca. 60% oil dispersion, 0.50 g, ca.
13 mmol) in dry THF (60 cm3) was added triethyl phosphono-
Natural
(4R,5S,6R,1ЈE )-6-(but-1Ј-enyl)-5-chloro-3,4,5,6-
tetrahydro-4-hydroxy-2H-pyran-2-one 7. To a solution of dec
ENX IIa (1.2 mg, 1.8 µmol) in MeCN (0.6 cm3) was added
slowly a suspension of Pb(OAc)4 (10 mg) in MeCN (1 cm3)
at 0 ЊC. After the mixture was stirred for 30 min, ethylene
glycol (0.5 cm3) was added. The mixture was stirred for a fur-
ther 10 min, diluted with EtOAc, washed with aq. NaHCO3 and
Scheme 3 Synthesis of both enantiomers of the lactone 8Ј.
2678
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acetate (2.5 cm3, 13 mmol) at 0 ЊC. After the mixture was cooled
to Ϫ20 ЊC, a solution of the above mentioned oil in dry THF
(20 cm3) was added. The resulting mixture was stirred until the
temperature reached 0 ЊC. The reaction mixture was quenched
with aq. NH4Cl and extracted with EtOAc. The extract was
washed with brine, dried (MgSO4) and concentrated in vacuo.
The residue was chromatographed on silica gel (hexane–EtOAc =
3 : 1) to give 11 (4.50 g, 80.7%) as a colourless oil; νmax(film)/
cmϪ1 1720, 1650 and 1500; δH (300 MHz) 1.28 and 1.29 (total
3 H, each t, J 7.1 Hz, CH3CH2), 1.55–2.01 [6 H, m, (CH2)3], 3.53
(1 H, m, THP), 3.78 (3 H, s, MeO), 3.97 (1 H, m, 6-H), 4.01 and
4.02 (total 1 H, dd, J 1.6, 9.6 Hz, 2Љ-H), 4.20 (total 2 H, each d,
J 7.1 Hz, CH3CH2), 4.57 (0.5 H, dd, J 1.4, 1.8 Hz, THP), 4.59
(0.5 H, dd, J 1.8, 9.6 Hz, THP), 4.68 (0.5 H, dd, J 2.7, 4.4 Hz,
6-H), 4.91 (0.5 H, dd, J 2.7, 3.0 Hz, 6-H), 5.57 and 5.59 (total
1 H, pseudo d, J 2.5 Hz, 5-H), 5.90 (0.5 H, ddd, J 2.2, 2.7,
10.4 Hz, 4-H), 5.96 (0.5 H, ddd, J 1.9, 2.7, 10.4 Hz, 4-H), 6.14
and 6.17 (total 1 H, dd, J 1.9, 15.7 Hz, 2Ј-H), 6.18 (0.5 H, m,
3-H), 6.23 (0.5 H, pseudo d, J 10.2 Hz, 3-H), 6.8–5.05 (4 H, m,
Ar), 7.04 (0.5 H, dd, J 4.4, 15.7 Hz, 1Ј-H), 7.23 (0.5 H, dd, J 4.1,
15.7 Hz, 1Ј-H). δC 14.3, 19.0, 19.6, 25.4, 30.8, 55.8, 60.5, 62.3,
63.0, 69.1, 69.5, 74.6, 94.2, 95.2, 101.4, 116,7, 121.9, 126.0,
132.5, 144.6, 153.5, 166.7; m/z (EI) 404.1835 (Mϩ. C22H28O7
requires 404.1833).
(2R,5S,6R,1ЈE )-6-(3Ј-Hydroxyprop-1Ј-enyl)-5,6-dihydro-2-
( p-methoxyphenoxy)-5-(tetrahydro-2ЉH-pyran-2Љ-yloxy)-2H-
pyran 12. To a solution of 11 (3.7 g, 9.5 mmol) in dry Et2O (100
cm3) was added DIBAL-H (1 M in hexane, 21.0 cm3, 21 mmol)
at Ϫ78 ЊC under Ar and the mixture was stirred for 1 h at this
temperature. To this was added MeOH, and the mixture was
stirred until the whole solution became a gel. The resulting gel
was filtered through a Celite pad and the filtrate was concen-
trated in vacuo. The residue was chromatographed on silica gel
(elution with hexane–EtOAc = 1 : 1) to give 12 (2.9 g, 84%) as a
colourless oil (Found: C, 66.04; H, 7.31. C20H26O6 requires C,
66.28; H, 7.23%); νmax(film)/cmϪ1 3430 and 1500; δH (300 MHz)
1.5–1.9 [6 H, m, (CH2)3], 3.4–3.6 (1.5 H, m), 3.76 (3 H, s, OMe),
3.8–4.1 (2.5 H, m), 4.16 (2 H, m), 4.41 (1 H, m), 4.69 (0.5 H,
dd, J 2.7, 4.4 Hz, 5-H), 4.86 (0.5 H, dd, J 3.0, 3.3 Hz, 5-H),
5.54 (1 H, m, 2-H), 5.7–6.1 (3 H, m), 6.15 (0.5 H, pseudo d,
J 10.2 Hz, 3-H), 6.21 (0.5 H, pseudo d, J 10.2 Hz, 3-H), 6.75–
6.85 (2 H, m, Ar), 6.95–7.1 (2 H, m, Ar). δC 19.3, 19.5, 25.5,
30.9, 55.8, 62.7, 63.2, 63.3, 70.1, 70.6, 74.6, 94.3, 95.6, 101.1,
116.8, 126.1, 128.0, 131.5, 133.5, 152.7.
(2R,5S,6R,1ЈE )-6-(3Ј-Acetoxyprop-1Ј-enyl)-5,6-dihydro-2-
( p-methoxyphenoxy)-5-(tetrahydro-2ЉH-pyran-2Љ-yloxy)-2H-
pyran 13. A solution of 12 (5.00 g, 13.8 mmol) and acetic
Scheme 4 Degradation of ENX IIa methyl ester 22.
J. Chem. Soc., Perkin Trans. 1, 2001, 2676–2681
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anhydride (10 cm3) in pyridine (25 cm3) was stirred for 1 h at
20 ЊC. The reaction mixture was diluted with EtOAc, succes-
sively washed with 1 M HCl aq. and aq. NaHCO3, dried
(MgSO4) and concentrated in vacuo. The residue was chrom-
atographed on silica gel. Elution with hexane–EtOAc (3 : 1)
gave 13 (5.57 g, quant) as a colourless oil; νmax(film)/cmϪ1 1735
and 1500; δH (300 MHz) 1.5–1.8 [6 H, m, (CH2)3], 2.06 (3 H, s,
Ac), 3.50 (1 H, m), 3.76 (3 H, s, OMe), 3.9 (1 H, m), 3.98 and
4.14 (total 1 H, each dd, J 1.5, 9.5 Hz, 6-H), 4.41 (1 H, m), 4.58
(2 H, dd, J 4.1, 8.5 Hz, 3Ј-H), 4.66 and 4.92 (total 1 H, each m,
5-H), 5.54 (1 H, m, 2-H), 5.8–6.0 (3 H, m), 6.20 (1 H, dd, J 1.4,
10.2 Hz, 3-H), 6.8–7.3 (4 H, m, Ar). δC 18.7, 19.4, 20.8, 25.3,
30.6, 55.6, 61.8, 62.7, 64.3, 69.6, 70.3, 74.3, 94.2, 94.7, 100.9,
116.5, 125.8, 126.7, 131.2, 132.8, 153.3, 170.8; m/z (EI) 404.1832
(Mϩ. C22H28O7 requires 404.1833).
(c 0.080, CHCl3); νmax(film)/cmϪ1 3400 and 1720; δH (300 MHz)
1.04 (3 H, t, J 7.4 Hz, 4Ј-H), 2.14 (2 H, m, 3Ј-H), 2.20 (1 H, m,
OH), 4.33 (1 H, pseudo d, J 2.5 Hz, 5-H), 4.66 (1 H, ddd, J 8.5,
8.0, 0.8 Hz, 6-H), 5.53 (1 H, ddt, J 15.7, 8.0, 1.5 Hz, 1Ј-H), 6.20
(1 H, ddt, J 15.7, 6.0, 0.8 Hz, 2Ј-H), 6.00 (1 H, dd, J 9.9, 1.9 Hz,
3-H), 6.87 (1 H, dd, J 2.5, 9.9 Hz, 4-H). δC 13.0, 25.4, 66.3, 83.7,
121.1, 123.6, 141.0, 148.0, 163.1; m/z (EI) 169.0871 (Mϩ ϩ H.
C9H13O3 requires 169.0864).
(5R,6R,1ЈE )-6-(But-1Ј-enyl)-5,6-dihydro-5-( p-nitrobenzoyl-
oxy)-2H-pyran-2-one 17. To a solution of 16 (0.40 g, 2.4 mmol),
p-nitrobenzoic acid (0.44 g, 2.6 mmol) and Ph3P (0.70 g,
2.6 mmol) in dry THF (10 ml) was added DEAD (0.4 cm3,
2.5 mmol) at 0 ЊC and the mixture was stirred for 2 h at 20 ЊC.
Then the solution was concentrated in vacuo, and the residue
was chromatographed on silica gel (hexane–EtOAc = 3 : 1) to
give 17 (0.50 g, 1.7 mmol, 72.1%) as yellow plates, mp 152 ЊC;
νmax(KBr)/cmϪ1 3100, 3060, 1730, 1720 and 1600; δH (300 MHz)
0.95 (3 H, t, J 7.4 Hz, 4Ј-H), 2.02 (2 H, qd, J 6.3, 7.4 Hz, 3Ј-H),
5.10 (1 H, pseudo ddd, J 0.8, 2.7, 6.9 Hz, 6-H), 5.52 (1 H, dd,
J 2.7, 5.5 Hz, 5-H), 5.62 (1 H, ddt, J 15.7, 6.9, 1.6 Hz, 1Ј-H),
6.06 (1 H, ddt, J 15.7, 6.3, 1.1 Hz, 2Ј-H), 6.32 (1 H, d, J 9.6 Hz,
3-H), 7.10 (1 H, dd, J 5.5, 9.6 Hz, 4-H), 8.13–8.34 (4 H, m, Ar).
(2R,5S,6R,1ЈE )-6-(But-1Ј-enyl)-5,6-dihydro-2-( p-methoxy-
phenoxy)-5-(tetrahydro-2ЉH-pyran-2Љ-yloxy)-2H-pyran 14. To a
solution of 13 (5.50 g, 13.0 mmol) and Li2CuCl4 (0.1 M in THF,
1.3 cm3, 0.13 mmol) in THF (40 cm3) was added MeMgCl (3 M
in THF, 6.0 cm3, 18 mmol) in THF (30 cm3) at Ϫ8 ЊC and the
mixture was stirred for 1 h at Ϫ8 ЊC. The reaction mixture was
poured into water, extracted with ether, washed with water and
brine, dried (MgSO4) and concentrated in vacuo. The residue
was chromatographed on silica gel. Elution with hexane–
EtOAc (8 : 1) gave 14 (4.00 g, 85.4%) as a colourless oil;
νmax(film)/cmϪ1 1500; δH (300 MHz) 0.99 and 1.00 (total 3 H,
each t, J 7.7 Hz, 4Ј-H), 1.5–1.8 [6 H, m, (CH2)3], 2.08 (2 H, m,
3Ј-H), 3.52 (1 H, m), 3.77 (3 H, s, OMe), 3.90 (1 H, m), 4.02 and
4.15 (total 1 H, each m, 5-H), 4.35 (1 H, m), 4.70 and 4.95 (total
1 H, each m, 6-H), 5.48 and 5.59 (total 1 H, each, ddt, J 15.5,
6.8, 1.5 Hz, 1Ј-H), 5.51 (1 H, m, 2-H), 5.85 (1 H, m, 2Ј-H), 5.87
and 5.92 (total 1 H, ddd, J 0.8, 1.9, 10.2 Hz, 3-H), 6.15 and 6.18
(total 1 H, ddd, J 1.1, 1.6, 10.2 Hz, 4-H), 6.8–7.1 (4 H, m, Ar).
δC 13.1, 18.4, 19.3, 25.4, 30.5, 55.6, 61.3, 62.5, 69.6, 71.0, 71.7,
74.0, 94.3, 94.5, 100.5, 112.6, 125.8, 126.5, 126.7, 136.7, 153.4;
m/z (EI) 360.1943 (Mϩ. C21H28O5 requires 360.1935).
(2R,1ЈR,2ЈE )-2,5-Dihydro-2-(1Ј-hydroxypent-2Ј-enyl)furan-
5-one 18. A solution of 17 (0.10 g, 0.34 mmol) and K2CO3
(5 mg) in MeOH–H2O (3 : 1, 4 cm3) was stirred at 20 ЊC for
30 min. The reaction gave a complex mixture monitored by
TLC. The mixture was diluted with EtOAc and washed with
water and brine. The organic layer was dried with MgSO4 and
concentrated in vacuo. The residue was chromatographed on
silica gel (hexane–EtOAc = 2 : 1) to give 18 as the main product;
νmax(film)/cmϪ1 3450, 3010, 1770 and 760.
(5S,6R,1ЈE )-5-Acetoxy-6-(but-1Ј-enyl)-5,6-dihydro-2H-
pyran-2-one 19. To a solution of 16 (0.210 g, 1.25 mmol), Ph3P
(1.36 g, 5.20 mmol) and acetic acid (0.36 cm3, 4.8 mmol) in
dry THF (10 cm3) was added a solution of DEAD (0.80 cm3,
5.0 mmol) in THF (3 cm3) at Ϫ45 ЊC under N2. After being
stirred at 20 ЊC for 12 h, the mixture was poured into water and
extracted with EtOAc. The extract was washed with 1 M HCl,
aq. NaHCO3 and brine, dried (MgSO4) and concentrated
in vacuo. The residue was chromatographed on silica gel (elution
with hexane–EtOAc = 2 : 1) to give 19 (184 mg, 69.9%) as
colourless needles, mp 48.5–49.5 ЊC, [α]2D5 Ϫ65 (c 0.013, CHCl3);
νmax(film)/cmϪ1 1740 and 1720; δH (300 MHz) 1.04 (3 H, t,
J 7.4 Hz, 4Ј-H), 2.10 (3 H, s, Ac), 2.11 (2 H, m, 3Ј-H), 4.96 (1 H,
ddd, J 0.8, 3.0, 7.1 Hz, 6-H), 5.25 (1 H, dd, J 3.0, 5.5 Hz, 5-H),
5.57 (1 H, ddt, J 15.6, 7.1, 1.6 Hz, 1Ј-H), 5.99 (1 H, ddt, J 15.6,
6.3, 0.8 Hz, 2Ј-H), 6.12 (1 H, d, J 9.6 Hz, 3-H), 6.96 (1 H, dd,
J 5.5, 9.6 Hz, 4-H). δC 13.0, 20.5, 25.3, 64.1, 79.5, 121.4, 125.0,
139.7, 140.8, 162.8, 170.2; m/z (EI) 211.0973 (Mϩ ϩ H.
C11H15O4 requires 211.0969).
(5S,6R,1ЈE )-6-(But-1Ј-enyl)-5,6-dihydro-5-(tetrahydro-2ЉH-
pyran-2Љ-yloxy)-2H-pyran-2-one 15. A solution of 14 (0.900 g,
2.48 mmol), silver dipicolinate [Ag(DPAH)2, 2.3 g, 5.0 mmol]
in MeCN–H2O (4 : 1, 10 cm3) was stirred at 20 ЊC for 1 h. The
mixture was filtered, the filtrate was poured into aq. Na2S2O3
and extracted with ether. The extract was washed with brine,
dried (MgSO4) and concentrated in vacuo. The residue was
chromatographed on silica gel (elution with hexane–EtOAc =
2 : 1) to give a colourless oil, which was used in the next step
without further purification.
A suspension of the above mentioned oil and active MnO2
(3.0 g) in toluene (10 cm3) was shaken at 20 ЊC for 2 h. The
mixture was filtered through a Celite pad and concentrated in
vacuo. The residue was chromatographed on silica gel (elution
with hexane–EtOAc = 4 : 1) to 15 (0.500 g, 79.9%) as a colour-
less oil; νmax(film)/cmϪ1 1725 and 1670; δH (300 MHz) 1.00 (3 H,
t, J 7.4 Hz, 4Ј-H), 1.5–1.9 [6 H, m, (CH2)3], 2.10 (2 H, dq, J 0.8,
7.4 Hz, 3Ј-H), 3.54 and 3.88 (total 1 H, each m, OCH2 of THP),
4.26 (1 H, ddd, J 1.9, 3.0, 7.9 Hz, 5-H), 4.70 (1 H, m, OCHO of
THP), 4.76 (1 H, dd, J 7.9, 0.8 Hz, 6-H), 5.50 (1 H, ddt, J 15.4,
7.4, 1.6 Hz, 2Ј-H), 5.94 (1 H, ddt, J 15.4, 0.8, 6.4 Hz, 1Ј-H), 5.99
(1 H, dd, J 1.9, 10.2 Hz, 3-H), 6.91 (1 H, dd, J 2.7, 10.2 Hz,
4-H). δC 13.1, 19.4, 25.3, 25.4, 30.4, 63.0, 71.6, 81.9, 100.5,
121.0, 124.0, 139.2, 147.8, 163.1; m/z (EI) 252.1345 (Mϩ.
C14H20O4 requires 252.1360).
(5R,6R,1ЈE )-6-(But-1Ј-enyl)-5,6-dihydro-5-hydroxy-2H-
pyran-2-one (؊)-20. A solution of 19 (46.3 mg, 0.220 mmol)
and lipase P (Amano) in Pri2O (4 cm3) and phosphate buffer
(pH 7.0, 0.1 M, 2 cm3) was stirred at 20 ЊC for 2 d. The mixture
was diluted with EtOAc, washed with aq. NaHCO3 and brine,
dried (MgSO4) and concentrated in vacuo. The residue was
purified by PTLC (hexane–EtOAc = 1 : 1) to give (Ϫ)-20
(42.5 mg, 96.2%) as a colourless oil, [α]2D6 Ϫ250 (c 0.060, CHCl3);
νmax(film)/cmϪ1 3400 and 1720; δH (300 MHz) 1.05 (3 H, t,
J 7.4 Hz, 4Ј-H), 2.17 (2 H, dq, J 7.4, 6.3 Hz, 3Ј-H), 2.10 (1 H, br,
OH), 4.20 (1 H, m, 5-H), 4.84 (1 H, m), 5.70 (1 H, ddt, J 15.5,
7.0, 1.5 Hz, 1Ј-H), 6.05 (1 H, ddt, J 15.5, 6.3, 0.8 Hz, 2Ј-H), 6.13
(1 H, d, J 9.6 Hz, 3-H), 6.99 (1 H, dd, J 5.5, 9.6 Hz, 4-H). δC
13.0, 25.5, 63.2, 81.3, 121.7, 123.0, 139.9, 144.8, 163.5; m/z (EI)
169.0867 (Mϩ ϩ H. C9H13O3 requires 169.0864).
(5S,6R,1ЈE )-6-(But-1Ј-enyl)-5,6-dihydro-5-hydroxy-2H-
pyran-2-one 16. A suspension of 15 (0.329 g, 1.30 mmol) and
Amberlyst H-15 in MeOH (2 cm3) was stirred at 20 ЊC for 3 h.
The mixture was filtered and the filtrate was concentrated
in vacuo. The residue was purified by PTLC (hexane–EtOAc =
3 : 2) to give 16 (0.210 g, 96.2%) as a colourless oil, [α]2D5 Ϫ310
2680
J. Chem. Soc., Perkin Trans. 1, 2001, 2676–2681

View Article Online
(5S,6R,1ЈE )-6-(But-1Ј-enyl)-5-chloro-5,6-dihydro-2H-pyran-
2-one (؉)-8Ј. To a solution of (Ϫ)-20 (19 mg, 0.11 mmol) in
THF (0.5 cm3) was added successively pyridine (0.2 cm3) and
MsCl (0.05 cm3) at 0 ЊC and the mixture was stirred for 1 h.
Then to this was added a solution of tetrabutylammonium
chloride (0.34 g, 6.0 mmol) in THF (2 cm3) and the mixture was
stirred at 20 ЊC for 1 d. The reaction mixture was diluted with
EtOAc, washed with 1 M HCl, aq. NaHCO3 and brine, dried
(MgSO4) and concentrated in vacuo. The residue was purified
by PTLC (hexane–EtOAc = 3 : 1) to give (ϩ)-8Ј (14 mg, 71%) as
a colourless oil, [α]2D5 ϩ220 (c 0.030, CDCl3); νmax(film)/cmϪ1
1730; δH (300 MHz) 1.02 (3 H, t, J 7.4 Hz, 4Ј-H), 2.12 (2 H, dq,
J 7.4, 6.3 Hz, 3Ј-H), 4.50 (1 H, ddd, J 1.5, 3.3, 6.9 Hz, 5-H), 4.93
(1 H, dd, J 7.1, 6.9 Hz, 6-H), 5.52 (1 H, ddt, J 15.4, 7.1, 1.6 Hz,
1Ј-H), 6.01 (1 H, ddt, J 15.4, 6.3, 1.1 Hz, 2Ј-H), 6.09 (1 H, dd,
J 9.9, 1.5 Hz, 3-H), 6.48 (1 H, dd, J 3.6, 9.9 Hz, 4-H); m/z (EI)
186.0433 (Mϩ. C9H11O235Cl requires 186.0447).
and PtO2 (cat.) in MeOH (1 cm3) was stirred under H2 for 2 h.
The mixture was filtered through a silica gel pad and concen-
trated in vacuo to give crude compound 23. This residue
(14.9 mg) and NaIO4 (18.0 mg, 84.0 µmol) in MeOH (1 cm3)
was stirred at 20 ЊC for 1.5 h. The mixture was diluted with
EtOAc, washed with aq. Na2S2O3 and brine, dried (MgSO4) and
concentrated in vacuo. A solution of the residue and NaBH4
(10.0 mg, 30.0 µmol) was stirred at 20 ЊC for 12 h. The reaction
was quenched with 1 M HCl, diluted with EtOAc, washed with
aq. NaHCO3 and brine, dried (MgSO4) and concentrated in
vacuo to give a mixture of 24 and 25. This mixture was treated
with CH2N2 in ether to give a pale yellow oil. This oil was
stirred with K2CO3 (1.0 mg) in MeOH (1 cm3) for 12 h. The
mixture was diluted with EtOAc, washed with H2O and brine,
dried (MgSO4) and concentrated in vacuo. The residue was
chromatographed on silica gel (hexane–EtOAc = 4 : 1) to give
26 (2.0 mg, 6.5 µmol, 39%) as a colourless oil; δH 0.84 (3 H, d,
J 6.3 Hz, Me), 0.92 (3 H d, J 6.3 Hz, Me), 1.0–1.5 (16 H, m,
CH2), 1.5–1.7 (2 H, m, CH), 2.31 (2 H, dd, J 7.4, 7.7 Hz, 2-H),
3.4–3.53 (2 H, m, 13-H), 3.67 (3 H, s, OMe); m/z (FAB)
273.2422 (Mϩ ϩ H. C16H33O3 requires 273.2428).
(5S,6S,1ЈE )-6-(But-1Ј-enyl)-5,6-dihydro-5-(tetrahydro-2ЉH-
pyran-2Љ-yloxy)-2H-pyran-2-one 21. To a solution of 16 (0.24 g,
0.94 mmol) in 1,4-dioxane–H2O (1 : 1, 3 cm3) was added 1 
NaOH (1.5 cm3) at 0 ЊC and the mixture was stirred at 0 ЊC for
0.5 h. The solution was acidified with 1 M HCl and extracted
with EtOAc. The extract was washed with brine, dried (MgSO4)
and concentrated in vacuo. The residual oil was used in the
following step without further purification.
Methyl (6RS,12R)-13-[(S)-ꢀ-methoxy-ꢀ-trifluoromethylphen-
ylacetoxy]-6,12-dimethyltridecanonate 27. To a solution of 26
(0.90 mg, 2.9 µmol) in pyridine (0.4 cm3) was added (ϩ)-(R)-
MTPACl (13 mg, 53 µmol) and the mixture was stirred at 20 ЊC
for 12 h. The reaction mixture was diluted with water and
EtOAc, washed with 1 M HCl, aq. NaHCO3 and brine, dried
(MgSO4) and concentrated in vacuo. The residue was chrom-
atographed on silica gel (hexane–EtOAc = 10 : 1) to give 27
(1.0 mg, 1.8 µmol, 62%) as a colourless oil. δH 0.83 (3 H, d,
J 6.3 Hz, Me), 0.92 (3 H, d, J 6.3 Hz, Me), 1.0–2.0 (18 H, m,
CH2), 2.31 (2 H, t, J 7.7 Hz, 2-H), 3.67 (3 H, s, OMe), 4.15 (1 H,
m, 13-H), 4.17 (1 H, m, 13-H), 7.4–7.55 (5 H, m, Ar).
To a solution of PPh3 (0.25 g, 0.95 mmol) in THF (20 cm3)
was added DEAD (0.16 cm3, 0.10 mmol) and the above men-
tioned oil in THF (10 cm3) at Ϫ40 ЊC and the mixture was
stirred for 12 h as the temperature of this gradually rose to
20 ЊC. The reaction mixture was concentrated in vacuo and
the residue was chromatographed on silica gel (elution with
hexane–EtOAc = 3 : 1) to give 21 (62 mg, 26%) as a colourless
oil; νmax(film)/cmϪ1 1725 and 1670; δH (300 MHz) 1.02 (3 H, t,
J 7.4 Hz, 4Ј-H), 1.4–1.8 [6 H, m, (CH2)3], 2.10 (2 H, dq, J 0.8,
7.4 Hz, 3Ј-H), 3.54 and 3.88 (total 1 H, each m, OCH2 of THP),
4.26 (1 H, ddd, J 1.9, 3.0, 7.9 Hz, 5-H), 4.70 (1 H, m, OCHO of
THP), 4.76 (1 H, dd, J 7.9, 0.8 Hz, 6-H), 5.50 (1 H, ddt, J 15.4,
7.4, 1.6 Hz, 2Ј-H), 5.94 (1 H, ddt, J 15.4, 0.8, 6.4 Hz, 1Ј-H), 5.99
(1 H, dd, J 1.9, 10.2 Hz, 3-H), 6.91 (1 H, dd, J 2.7, 10.2 Hz,
4-H). δC 13.1, 19.4, 25.3, 25.4, 30.4, 63.0, 71.6, 81.9, 100.5,
121.0, 124.0, 139.2, 147.8, 163.1; m/z (EI) 252.1345 (Mϩ.
C14H20O4 requires 252.1360).
References
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(5S,6S,1ЈE )-6-(But-1Ј-enyl)-5,6-dihydro-5-hydroxy-2H-
pyran-2-one (؉)-20. In a similar manner as described for 16, 21
(56 mg, 0.22 mmol) gave (ϩ)-20 (35 mg, 0.21 mmol, 90%).
(5R,6S,1ЈE )-6-(But-1Ј-enyl)-5-chloro-5,6-dihydro-2H-pyran-
2-one (؊)-8Ј. In a similar manner as described for (ϩ)-8Ј, (ϩ)-
20 (35 mg, 0.21 mmol) gave (Ϫ)-8Ј (20 mg, 0.11 mmol, 55%);
m/z (FAB) 187.0535 (M ϩ Hϩ. C9H12O2 35Cl requires 187.0525).
4 R. Cetin, I. M. Krab, P. H. Anborgh, R. H. Cool, T. Watanabe,
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Tohoku University, 1989.
HPLC analysis of the natural derived 8 and the synthetic 8Ј.
Column, Shiseido Ceramosphere Chiral RU-2, 4.6 × 150 mm;
temperature, 20 ЊC; eluent, MeOH–H2O = 1 : 1 at 1.0 ml minϪ1
;
tR, 2.9 min [(Ϫ)-8Ј] and 4.8 min [(ϩ)-8Ј and 8]; detection at
245 nm.
11 K. Mori, H. Harada, P. Zagatti, A. Cork and D. R. Hall, Liebigs
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Determination of the 12Ј-position
Methyl (6RS,12R)-13-hydroxy-6,12-dimethyltridecanoate 26.
A suspension of ENX IIa methyl ester (22, 11.7 mg, 16.7 µmol)
J. Chem. Soc., Perkin Trans. 1, 2001, 2676–2681
2681