The diastereoselective asymmetric total synthesis of NG-391, a neuronal cell-protecting molecule

Article abstract of DOI:10.1016/S0040-4020(02)01290-5

The stereocontrolled total synthesis of (+)-NG-391, a neuronal cell-protecting molecule, is described along with the determination of its absolute stereochemistry. The following reactions in this synthesis are particularly noteworthy: (1) The stereoselect

Full text of DOI:10.1016/S0040-4020(02)01290-5

Tetrahedron 58 (2002) 9839–9846
The diastereoselective asymmetric total synthesis of NG-391,
a neuronal cell-protecting molecule
*
Yujiro Hayashi, Junichiro Yamaguchi and Mitsuru Shoji
Department of Industrial Chemistry, Faculty of Engineering, Tokyo University of Science, Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
Received 19 August 2002; accepted 3 October 2002
Abstract—The stereocontrolled total synthesis of (þ)-NG-391, a neuronal cell-protecting molecule, is described along with the
determination of its absolute stereochemistry. The following reactions in this synthesis are particularly noteworthy: (1) The stereoselective
construction of the conjugated (E,E,E,E,E)-pentaene from an (E,E,E)-alcohol using an IBX oxidation followed by stereoselective Horner–
Emmons reaction. (2) The (E)-selective Knoevenagel condensation of a b-ketonitrile with a chiral 2-alkoxyaldehyde prepared from (S)-malic
acid. (3) A diastereoselective epoxidation. q 2002 Elsevier Science Ltd. All rights reserved.
NG-391 (1), which was isolated from a Fusarium sp. TF-
0452 by a group at Taisho corporation, shows neurotrophic
activity and an effect on neurite outgrowth.1 Recently
Kakeya and Osada et al., reisolated NG-391 from a
Fusarium sp. RK 97-94 together with lucilactaene, a cell
cycle inhibitor in p53-transfected cancer cells.2 NG-391
may have potential for development as a new drug for
various neurodegenerative diseases such as dementia.
Structurally, it contains the 3-alkenoyl-3,4-epoxy-2-pyrro-
lidinone moiety and a labile, substituted pentaene, and its
absolute stereochemistry is not known.
In 1998 we succeeded in the first total synthesis of
epolactaene,3 a neurotrophic reagent isolated by Kakeya
and Osada et al.4 Not only do NG-391 and epolactaene have
similar biological properties, but they also have a very close
As initially we thought that construction of the unstable
structural similarity, both containing an epoxy-lactam and
pentaene should be left to the last stages of the total
an unsaturated, hydrophobic side-chain. In order to
synthesis, the following retrosynthetic scheme was designed
elucidate the mechanism of action of these drugs, the
(Scheme 1). Mild oxidation of selenium derivative 2 would
afford NG-391, and the epoxy lactam moiety of 2 could be
constructed from b-ketonitrile 3 using a Knoevenagel
examination of structure–reactivity relationships of NG-
391, epolactaene and their derivatives is highly desirable,
and to this end a flexible total synthesis of NG-391 is
required. From the synthetic point of view, the synthesis of
NG-391 is more challenging, and expected to be much more
difficult than that of epolactaene, owing to the substituted,
reaction5 and epoxidation as key steps. b-Ketonitrile 3
was to be synthesized from the triene derivative 4 used in
the synthesis of epolacatene.3a
conjugated pentaene, labile to acid, base, light, and
oxidative conditions. In this paper we will describe the
diastereoselective first synthesis of the naturally-occuring
enantiomer of NG-391, thus determining its absolute
stereochemistry.
The triene derivative 4 was synthesized stereoselectively
from tetrahydropyran-2-ol by our reported method.3a
Oxidation of alcohol 4 with SO3·pyridine6 afforded
aldehyde 5 quantitatively (Scheme 2). a-Phenylselenation
of aldehyde 5 was achieved using N,N-diethylbenzene-
selenamide,7 and the subsequent Horner–Emmons reaction
of 6 proceeded stereoselectively, affording g-phenylseleno-
E-a,b-unsaturated ester 7 in 48% yield over 2 steps, along
with the deselenated side product. The methyl ester 7
Keywords: NG-391; natural product; IBX oxidation; Knoevenagel reaction.
*
Corresponding author. Tel.: þ81-3-5228-8318; fax: þ81-3-5261-4631;
e-mail: hayashi@ci.kagu.tus.ac.jp
0040–4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020(02)01290-5

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Y. Hayashi et al. / Tetrahedron 58 (2002) 9839–9846
Scheme 1. The retrosynthesis of NG-391.
reacted with LiCH2CN to afford b-ketonitrile 8 in 55%
yield. The transformation of t-butyl ester 8 to methyl ester 9
by treatment with CF3CO2H, and the subsequent reaction
with CH2N2 is not efficient, affording methyl ester 9 in low
yield (36% for 2 steps). The low yield of the last 5 steps
from 5 due to the phenylseleno substituent prompted us to
modify the synthetic route.
acid and base as long as there are two electron-withdrawing
carbonyl groups attached at each end of the pentaene, but
that it isomerizes gradually under illumination.
With these results in hands, we decided that it should be
possible to prepare NG-391 by constructing the epoxy-
lactam moiety during the last stages of the total synthesis
after the formation of the pentaene portion, provided that the
reactions employed in making the epoxy-lactam moiety
were performed under mild conditions.
During the course of these synthetic studies, the synthesis of
the pentaene moiety was examined in order to check its
stability (Scheme 3). When g-seleno-a,b-unsaturated ester
7 was treated with MCPBA at low temperature, a-hydroxy-
E-b,g-unsaturated ester 10 was formed via [2,3]sigmatropic
rearrangement8 instead of the expected pentaene 12.
Though the one step conversion of g-seleno-a,b-unsatu-
rated ester 7 to pentaene 12 had not been achieved, a 2 step
transformation of a-hydroxy-b,g-unsaturated ester 10 to
pentaene 12 was developed: when the a-hydroxy-b,g-
unsaturated ester 10 was treated with SOCl2 in pyridine, a
[3,3]sigmatropic rearrangement proceeded, affording
g-chloro-E-a,b-unsaturated ester 11 in 75% yield. Elimin-
ation of HCl occurred on treatment of 11 with DBU in
CH2Cl2 at rt, affording pentaene 12 in 78% yield as an
inseparable E/Z mixture (E/Z¼3:1). Although the E/Z
selectivity could not be improved by altering the base or
temperature, the stability of the pentaene moiety could be
examined. It was found to be tolerant of exposure to weak
We next focused in detail on the stereoselective synthesis of
pentaene 12 (Scheme 4). After some experimentation, we
found that (E,E,E)-alcohol 4 was effectively oxidized with
IBX (o-iodoxybenzoic acid, 5 equiv.) in the presence of
TsOH at 608C for 3 h under Nicolaou’s conditions,9 to
afford (E,E,E,E)-tetraene 13 selectively in 60% yield.
Subsequent Horner–Emmons reaction with methyl diethyl-
phosphonopropionate under Heathcock’s conditions10
afforded (E,E,E,E,E)-pentaene 12 stereoselectively. As the
pentaene 12 had been synthesized in only 2 steps from
alcohol 4 with very high stereoselectivity, the remaining
steps towards total synthesis were examined further. The
reaction of methyl ester 12 with LiCH2CN (2 equiv.)
proceeded at 2908C after 20 min to afford b-ketonitrile
14 in good yield (98%) without affecting the t-butyl group.
After brief treatment of t-butyl ester 14 with CF3CO2H in
Scheme 2. The first attempt for the synthesis of pentaene moiety.

Y. Hayashi et al. / Tetrahedron 58 (2002) 9839–9846
9841
Scheme 3. The second attempt for the synthesis of pentaene (12).
CH2Cl2 at 08C for 1 h, the resulting carboxylic acid was
treated with diazomethane at 2788C,11 affording methyl
ester 15 in 96% yield. Knoevenagel condensation of
b-ketonitrile 15 with (S)-4-(t-butyldiphenylsiloxy)-2-
triethylsiloxybutanal (16),12 prepared from (S)-malic acid,
proceeded efficiently in the presence of a catalytic amount
of ethylenediammonium diacetate in benzene at rt for 3 h,
affording E-Knoevenagel adduct 17 stereoselectively. The
TES protecting group of 17 is essential for high yield in the
Knoevenagel reaction, as reaction with the corresponding
aldehyde having the more bulky TBS protecting-group
proceeded slowly, affording the condensation product in
low yield. Epoxidation with tritylperoxide in the presence of
BuLi proceeded stereoselectively at low temperature from
the side opposite the TES group, to give epoxynitrile 18
without affecting the conjugated pentaene. As epoxynitrile
18 and the following several compounds are labile, the next
reactions were conducted without purification. Treatment of
epoxynitrile 18 with TsOH at rt for 50 min removed the TES
protecting group, affording hydroxynitrile 19. The hydroly-
sis of the nitrile to an amide occurred under very mild
reaction conditions during TLC (thin layer chromatography)
on silica gel via intramolecular hydroxyl group assistance,
and without damaging the labile pentaene to afford lactone
20 in 80% yield over 3 steps from the Knoevenagel
condensation product 17. Treatment of lactone 20 with
ammonia in MeOH at 08C for 10 min gave hydroxyamide
21 in 78% yield. Oxidation with the Dess–Martin periodi-
nane3b,c,13 in CH2Cl2 for 10 min gave the epoxy lactam in
60% yield, and the final of the t-butyldiphenylsilyl group
was effectively achieved with tetra-n-butylammonium
fluoride in THF for 10 min at 08C, affording NG-391 (1)
Scheme 4. Total synthesis of NG-391 (1).

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Y. Hayashi et al. / Tetrahedron 58 (2002) 9839–9846
Scheme 5. Determination of the stereochemistry of the model epoxide.
quantitatively as an appropriately 5:1 diastereomeric
mixture at the acetal position of g-lactam moiety.
1.1.1. (3E,5E,7E)-2-[(E)-Ethylidene]-4-methyl-9-oxo-
nona-3,5,7-trienoic acid tert-butyl ester (13). To a toluene
and DMSO mixed solution (1:1, 0.27 mL) of alcohol 43a
(20.7 mg, 0.078 mmol) was added IBX (109 mg,
0.389 mmol) and TsOH·H2O (3.0 mg, 0.016 mmol) at rt
and the reaction mixture was stirred for 10 min at rt then for
3 h at 608C. The reaction was quenched by the addition of
saturated NaHCO3 solution, and the organic materials were
extracted with ethyl acetate four times, then the combined
organic extracts were washed with NaHCO3 solution and
brine, dried over anhydrous Na2SO4, and concentrated in
vacuo after filtration. Purification by flash column chroma-
tography (ethyl acetate/hexane¼1/20) gave 12.1 mg (60%)
of aldehyde 13.
We determined the stereochemistry of 18 as (12R,13S),
based on the following model study which was conducted in
the total synthesis of epolactaene (Scheme 5).14
The epoxidation was performed by the model alkene 22,
giving one diastereomer 23 stereoselectively. The epoxide
23 was transferred to the previously synthesized lactone 25,
the srereochemistry of which was already determined by the
difference NOE experiment.3a
Synthetic NG-391 exhibited identical properties to those
reported for the natural substance1 (1H, 13C NMR and IR).
Comparison of the optical rotation (synthetic NG-391:
[a]2D5¼þ41.7 (c¼0.37, MeOH), natural NG-391:1
[a]¼þ39.3 (c¼0.5, MeOH)), determines the absolute
stereochemistry to be as shown in 1.
1H NMR (CDCl3) d¼1.46 (9H, s), 1.67 (3H, d, J¼7.9 Hz),
1.69 (3H, s), 6.17 (1H, dd, J¼13.7, 7.9 Hz), 6.29 (1H, s),
6.45 (1H, dd, J¼15.2, 11.0 Hz), 6.78 (1H, d, J¼15.2 Hz),
6.85 (1H, q, J¼7.0 Hz), 7.17 (1H, dd, J¼15.2, 11.0 Hz),
9.55 (1H, d, J¼7.9 Hz); 13C NMR (CDCl3) d 14.3, 15.7,
28.0, 80.8, 125.9, 131.1, 131.3, 131.8, 137.1, 139.4, 146.6,
152.3, 165.8, 193.5; IR (neat) 2978, 1707, 1678, 1280, 1255,
1132, 1012, 850, 572 cm21; HRMS (EI): calcd for
C16H22O3: 262.1569, found: 262.1581.
In summary, the first total synthesis of NG-391 has been
accomplished in an enantio- and highly diastereoselective
manner, enabling determination of the absolute stereo-
chemistry. The synthesis has several noteworthy features. In
particular the conjugated, substituted pentaene moiety was
stereoselectively synthesized from our previously reported
triene 4 in a short sequence using the IBX oxidation and
Horner–Emmons reactions.
1.1.2. (2E,4E,6E,8E)-10-[(E)-Ethylidene]-2,8-dimethyl-
undeca-2,4,6,8-tetraenedioic acid 11-tert-butyl ester
1-methyl ester (12). To a DME (0.5 mL) solution of
methyl
2-(diethylphosphono)propanate
(115 mg,
0.51 mmol) was added a hexane solution of BuLi (1.45 M,
0.30 mL, 0.43 mmol) at 08C. The reaction mixture was
stirred for 10 min at this temperature, then a DME (0.6 mL)
solution of aldehyde 13 (45.0 mg, 0.17 mmol) was added at
rt. After a further 1 h of stirring, a buffer solution was added
and the organic materials were extracted with ethyl acetate,
then the combined organic phases were dried over
anhydrous Na2SO4, and concentrated in vacuo after
filtration. Purification by flash column chromatography
(ethyl acetate/hexane¼1/5) gave 52.6 mg (92%) of ester 12.
1H NMR (CDCl3) d 1.49 (9H, s), 1.61 (3H, s), 1.63 (3H, d,
J¼7.0 Hz), 3.74 (3H, s), 6.12 (1H, s), 6.36 (1H, dd, J¼15.1,
10.0 Hz), 6.81 (1H, q, J¼7.0 Hz), 6.51 (1H, dd, J¼14.6,
10.8 Hz), 6.52 (1H, d, J¼15.1 Hz), 6.58 (1H, dd, J¼14.6,
10.0 Hz), 7.21 (1H, d, J¼10.8 Hz); 13C NMR (CDCl3) d
12.7, 14.4, 15.7, 28.1, 51.7, 80.5, 126.4, 127.4, 127.6, 128.1,
1. Experimental
1.1. General procedures
All reactions were carried out under argon and monitored by
thin-layer chromatography using Merck 60 F254 precoated
silica gel plates (0.25 mm thickness). Specific optical
rotations were measured using a JASCO P-1020 polari-
meter. FTIR spectra were recorded on an Horiba FT-720
spectrometer. 1H and 13C NMR spectra were recorded on a
Brucker AM400 instrument. High-resolution mass spectral
analyses (HRMS) were carried out using JEOL JMS-SX
102A. Preparative thin-layer chromatography was per-
formed using Wakogel B-5F purchased from Wako Pure
Chemical Industries, Tokyo, Japan. Flash column chroma-
tography was performed using silica gel Merck Art 7734.

Y. Hayashi et al. / Tetrahedron 58 (2002) 9839–9846
9843
132.2, 137.5, 138.5, 138.6, 139.8, 140.3, 166.3, 168.8; IR
(neat) 2977, 1708, 1590, 1367, 1153, 991, 750 cm21
HRMS (FAB): calcd for C20H28O4: 332.1988, found:
332.1978.
6.61 (1H, d, J¼14.6 Hz), 6.72 (1H, dd, J¼14.6, 10.7 Hz),
6.95 (1H, q, J¼7.1 Hz), 7.02 (1H, d, J¼11.0 Hz); 13C NMR
(CDCl3) d 11.7, 14.2, 15.9, 28.2, 51.9, 114.3, 127.4, 128.1,
128.3, 130.4, 133.4, 137.9, 141.1, 142.2, 142.8, 142.9,
167.4, 187.6; IR (neat) 2951, 2256, 1712, 1666, 1585, 1434,
1253, 993, 732 cm21; HRMS (FAB): calcd for C18H21NO3:
299.1521, found: 299.1467.
;
1.1.3. (3E,5E,7E,9E)-12-Cyano-2-[(E)-ethylidene]-4,10-
dimethyl-11-oxododeca-3,5,7,9-tetraenoic acid tert-
butyl ester (14). To a THF (1.2 mL) solution of CH3CN
(0.019 mL, 0.361 mmol) was added BuLi (1.45 M,
0.11 mL, 0.153 mmol) at 2788C and the reaction mixture
was stirred for 1 h at this temperature. To the reaction
mixture was added a THF (2 mL) solution of ester 12
(30.0 mg, 0.090 mmol) at 2908C. The reaction was stirred
for 10 min, then was quenched by the addition of a buffer
solution. The organic materials were extracted with ethyl
acetate, and the combined organic phases were dried over
anhydrous Na2SO4, and concentrated in vacuo after
filtration. Purification by flash column chromatography
(ethyl acetate/hexane¼1/5) gave 30.1 mg (98%) of keto-
nitrile 14.
1.1.6. (14S)-(3E,5E,7E,9E,12E)-16-(tert-Butyldiphenyl-
siloxy)-12-cyano-2-[(E)-ethylidene]-4,10-dimethyl-11-
oxo-14-triethylsiloxyhexadeca-3,5,7,9,12-pentaenoic
acid methyl ester (17). To a benzene (0.4 mL) solution of
ketonitrile 15 (45.0 mg, 0.150 mmol) was added (S)-
aldehyde 16 (214 mg, 0.469 mmol) and ethylenediammo-
nium diacetate (8.0 mg, 0.045 mmol), and the reaction
mixture was stirred for 3 h at rt. After the solvent was
removed in vacuo, rapid flash column chromatography on
florisil gel (ethyl acetate/hexane¼1/10) gave the crude
olefin 17 (81.8 mg). Purification on silica gel caused
substantial decomposition of the product.
1H NMR (CDCl3) d 1.46 (9H, s), 1.67 (3H, s), 1.68 (3H, d,
J¼6.9 Hz), 1.93 (3H, s), 3.77 (2H, s), 6.19 (1H, s), 6.41 (1H,
dd, J¼15.0, 10.7 Hz), 6.59 (1H, dd, J¼15.1, 11.1 Hz), 6.61
(1H, d, J¼14.6 Hz), 6.72 (1H, dd, J¼14.6, 10.7 Hz), 6.83
(1H, q, J¼6.9 Hz), 7.1 (1H, d, J¼11.1 Hz); 13C NMR
(CDCl3) d 11.7, 14.3, 15.7, 28.1, 28.2, 80.7, 114.4, 127.1,
127.7, 128.9, 132.0, 133.2, 137.4, 138.9, 141.5, 142.6,
142.9, 166.1, 187.7; IR (neat) 2979, 2256, 1704, 1666, 1585,
1367, 1282, 993, 850, 732 cm21; HRMS (FAB): calcd for
[C17H19NO3–tertBu]: 285.1365, found: 285.1348.
1H NMR (CDCl3) d 0.61–0.67 (6H, m), 0.93–0.97 (9H, m),
1.04 (9H, s), 1.70 (3H, s), 1.74 (3H, d, J¼7.3 Hz), 3.36 (3H,
s), 3.75–3.85 (2H, m), 4.98 (1H, q, J¼6.7 Hz), 6.21 (1H, s),
6.38–6.48 (1H, m), 6.58–6.62 (2H, m), 6.98 (1H, q,
J¼7.3 Hz), 7.03–7.10 (2H, m 7.35–7.40 (6H, m), 7.63–
7.68 (4H, m); 13C NMR (CDCl3) d 4.7, 4.9, 6.7, 12.5, 14.2,
15.9, 19.1, 26.8, 40.1, 59.9, 68.4, 113.7, 127.4, 127.7, 127.8,
128.2, 129.7, 130.4, 133.4, 133.5, 135.5, 135.6, 138.0,
140.4, 141.8, 142.2, 142.6, 161.2, 167.4, 188.2; IR (neat)
2954, 1718, 1585, 1245, 1112, 1085, 731, 701, 615 cm21
;
HRMS (FAB): calcd for [C44H60O5NSi2þH]þ: 738.4010,
1.1.4. (3E,5E,7E,9E)-12-Cyano-2-[(E)-ethylidene]-4,10-
dimethyl-11-oxododeca-3,5,7,9-tetraenoic acid. To
found: 738.4058; [a]2D4¼þ7.0 (c¼0.55, MeOH).
a
CH2Cl2 (0.6 mL) solution of ketonitrile 14 (28.0 mg,
0.082 mmol) was added CF3COOH (0.6 mL) at 08C and
the reaction mixture was stirred for 1 h at 08C. The solvent
and CF3COOH were removed in vacuo, affording the
carboxylic acid, which was used directly in the next
reaction.
1.1.7. (12R,13S,14S)(3E,5E,7E,9E)-16-(tert-Butyldiphenyl-
siloxy)-12-cyano-2-[(E)-ethylidene]-4,10-dimethyl-11-
oxo-14-triethylsiloxy-12,13-epoxyhexadeca-3,5,7,9-pen-
taenoic acid methyl ester (18). To a THF solution (2 mL)
of tritylperoxide (122 mg, 0.325 mmol) was added a hexane
solution of BuLi (0.187 mL, 1.45 M, 0.27 mmol) at 2788C,
and the reaction mixture was stirred at this temperature for
1 h. To this reaction mixture was added a THF (3 mL)
solution of crude olefin 17, and the mixture was stirred for
1 h at 2788C. The reaction was quenched with a buffer
solution and the organic materials were extracted with ethyl
acetate, and combined organic phases were dried over
anhydrous Na2SO4, and concentrated in vacuo after
filtration. The crude epoxide was used directly in the next
reaction.
1H NMR (CDCl3) d 1.72 (3H, s), 1.77 (3H, d, J¼7.1 Hz),
1.94 (3H, s), 3.79 (2H, s), 6.23 (1H, s), 6.45 (1H, dd,
J¼15.1, 10.6 Hz), 6.62 (1H, dd, J¼15.1, 10.9 Hz), 6.63 (1H,
d, J¼14.4 Hz), 6.73 (1H, dd, J¼14.4, 10.6 Hz), 7.02 (1H, d,
J¼10.9 Hz), 7.11 (1H, q, J¼7.1 Hz); 13C NMR (CDCl3)
d 11.8, 14.3, 16.2, 77.2, 127.4, 127.6, 128.4, 133.4,
138.6, 142.0, 142.7, 142.9, 170.0, 187.6; IR (neat) 2923,
2260, 1666, 1616, 1585, 1234, 995, 755 cm21
;
HRMS (FAB): calcd for C17H19O3: 285.1365, found:
285.1363.
1.1.8. (3E,5E,7E,9E)-11-{(1R,4S,5S)-4-[(2-tert-Butyl-
diphenylsiloxy)ethyl]-2-oxo-3,6-dioxabicyclo[3.1.0]hex-
1-yl}-2-[(E)-ethylidene]-4,10-dimethyl-11-oxoundeca-
3,5,7,9-tetraenoic acid methyl ester (20). To the crude
epoxide 18 was added THF (1.2 mL), H2O(70 mL), and
TsOH·H2O (20 mg) at 08C and the reaction mixture was
stirred for 1 h at rt. After addition of a saturated NaHCO3
solution, the organic materials were extracted with ethyl
acetate, and the organic phases were dried over anhydrous
Na2SO4, and concentrated in vacuo after filtration. Purifi-
cation by rapid flash column chromatography (ethyl
acetate/hexane¼1/5) gave crude hydroxynitrile 19. The
crude hydroxynitrile 19 was charged on to a thin-layer
1.1.5. (3E,5E,7E,9E)-12-Cyano-2-[(E)-ethylidene]-4,10-
dimethyl-11-oxododeca-3,5,7,9-tetraenoic acid methyl
ester (15). To an ether (4 mL) solution of the crude
carboxylic acid was added an ether solution of CH2N2 at
2788C. The solvent was removed in vacuo. Purification by
flash column chromatography (ethyl acetate/hexane¼1/5)
gave 23.5 mg (96% for 2 steps) of ketonitrile 15.
1H NMR (CDCl3) d 1.68 (3H, s), 1.72 (3H, d, J¼7.1 Hz),
1.93 (3H, s), 3.70 (3H, s), 3.78 (2H, s), 6.20 (1H, s), 6.42
(1H, dd, J¼15.2, 10.7 Hz), 6.59 (1H, dd, J¼15.2, 11.0 Hz),

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Y. Hayashi et al. / Tetrahedron 58 (2002) 9839–9846
chromatography plate and developed by ethyl acetate/
hexane mixed solvent (1/1). 51.0 mg of lactone 20 was
obtained in 80% over 3 steps.
2.02 (3H, d, J¼1.2 Hz), 2.01–2.12 (2H, m), 3.84–3.91 (1H,
m), 3.72 (3H, s), 3.96 (1H, d, J¼7.2 Hz), 4.01–4.09 (1H, m),
4.91 (1H, bs), 6.19 (1H, s), 6.45 (1H, dd, J¼15.2, 10.4 Hz),
6.58 (1H, d, J¼15.2 Hz), 6.66 (1H, dd, J¼14.6, 10.8 Hz), 6.73
(1H, dd, J¼14.6, 10.4 Hz), 6.95 (1H, q, J¼7.2 Hz), 7.13–7.47
(7H, m), 7.59–7.67 (4H, m); 13C NMR (CDCl3) d 11.4, 14.2,
15.9, 19.0, 35.9, 52.2, 60.4, 61.7, 63.7, 77.3, 85.5, 127.8,128.0,
128.1, 128.5, 130.3, 130.4, 132.1, 133.9, 135.5, 138.1, 140.4,
141.9, 143.0, 144.4, 167.4, 169.2, 189.3; IR (neat) 3401, 2929,
1722, 1581, 1428, 1265, 1112, 991, 734, 703 cm21; HRMS
(FAB): calcd for C38H43NO7 Si: 655.2965, found: 655.2957;
[a]2D4¼þ33.5 (c¼0.57, MeOH).
1.1.11. NG-391 (1).1 To a THF (0.1 mL) solution of lactam
(6.5 mg, 0.001 mmol) was added a THF solution of tetra-n-
butylammonium fluoride (1.0 M, 0.02 mL, 0.02 mmol) at
08C, and the reaction mixture was stirred for 10 min at 08C.
The reaction was quenched with a saturated NH4Cl solution,
and the organic materials were extracted with ethyl acetate.
The combined organic extracts were washed with brine,
dried over anhydrous Na2SO4, and concentrated in vacuo
after filtration. Purification by preparative thin layer
chromatography (ethyl acetate/hexane¼3/1) gave 4.5 mg
of NG-391 (1) quantitatively.
1H NMR (CDCl3) d 1.05 (9H, s), 1.71 (3H, s), 1.73 (3H, d,
J¼7.3 Hz), 1.87 (3H, s), 3.74 (3H, s), 3.81–3.92 (2H, m),
4.23 (1H, s), 4.80–4.87 (1H, m), 6.22 (1H, s), 6.45 (1H, dd,
J¼15.2, 10.5 Hz), 6.70 (1H, q, J¼7.3 Hz), 6.98 (1H, q,
J¼7.3 Hz), 7.35–7.48 (6H, m), 7.61–7.68 (4H, m); 13C
NMR (CDCl3) d 11.4, 14.2, 15.9, 19.2, 26.9, 35.2, 51.2,
51.9, 59.1, 60.4, 63.4, 127.8, 127.9, 128.1, 128.3, 129.9, 130.4,
133.1, 133.5, 135.5, 138.0, 140.5, 142.4, 143.5, 145.1, 167.4,
168.5, 187.8; IR (neat) 2929, 1787, 1680, 1635, 1112, 991,
735 cm21; HRMS (FAB): calcd for C38H44O7Si: 640.2856,
found: 640.2855; [a]2D5¼220.3 (c¼0.953, MeOH).
1.1.9. (14R,15S,16S)(3E,5E,7E,9E)-16-(tert-Butyldiphe-
nylsiloxy)-12-carbamoyl-4,10-dimethyl-2-[(E)-ethyl-
idene]-12,13-epoxy-14-hydroxy-11-oxohexadeca-3,5,7,9-
tetraenoic acid methyl ester (21). To a MeOH (2 mL)
solution of lactone 20 (51.1 mg, 0.080 mmol) was added
NH4OH solution (30%, 1.0 mL) at 08C, and the reaction
mixture was stirred for 20 min at this temperature. The
reaction was quenched with a buffer solution and the
organic materials were extracted with CHCl3 four times,
then the combined organic phases were dried over
anhydrous Na2SO4, and concentrated in vacuo after
filtration. Purification by preparative thin layer chromato-
graphy (ethyl acetate/hexane¼2/1) gave 40.0 mg (78%) of
hydroxyamide 21.
1H NMR (CDCl3) d 1.68 (3H, s), 1.73 (3H, d, J¼7.0 Hz),
1.86 (3H, s), 2.02 (1H, s), 2.04–2.13 (2H, m), 3.72 (3H, s),
3.87–3.97 (1H, m), 4.00 (1H, s), 4.02–4.12 (2H, m),
6.20 (1H, s), 6.38–6.53 (2H, m), 6.57–6.69 (2H, m),
6.75 (1H, dd, J¼14.6, 10.7 Hz), 6.92–7.02 (2H, m),
7.45 (1H, d, J¼11.4 Hz); 13C NMR (CDCl3) d 11.3, 14.2,
15.9, 35.8, 51.9, 58.3, 61.7, 63.6, 85.3, 127.9, 128.4, 130.3,
133.8, 138.0, 140.5, 142.2, 143.5, 145.3, 167.4, 169.8,
190.0; IR (neat) 3404, 2929, 1722, 1581, 1428, 1265,
991 cm21; HRMS (FAB): calcd for [C22H27NO7þH]þ:
418.1866, found: 418.1839; [a]2D5¼þ41.7 (c¼0.37,
MeOH).
1H NMR (CDCl3) d 1.04 (9H, s), 1.69 (3H, s), 1.72 (3H, d,
J¼7.4 Hz), 1.92 (3H, s), 3.23 (1H, d, J¼8.0 Hz), 3.73 (3H,
s), 3.82–3.89 (1H, m), 3.89–3.97 (1H, m), 5.74 (1H, bs),
6.18 (1H, s), 6.43 (1H, dd, J¼15.1, 10.6 Hz), 6.53 (1H, bs),
6.57 (1H, d, J¼15.7 Hz), 6.65 (1H, dd, J¼14.6, 11.2 Hz),
6.75 (1H, dd, J¼14.6, 10.6 Hz), 6.96 (1H, q, J¼7.4 Hz),
7.27–7.47 (7H, m), 7.58–7.70 (4H, m); 13C NMR (CDCl3)
d 11.4, 14.2, 15.9, 19.1, 26.8, 36.0, 51.9, 61.9, 64.2, 65.9, 68.8,
71.6, 127.8, 127.9, 128.0, 128.4, 129.9, 132.6, 132.9, 135.5,
138.0, 140.4, 142.0, 143.3, 146.0, 168.9, 167.5, 192.9; IR
(neat) 3454, 2929, 1714, 1693, 1652, 1581, 1428, 1249, 1111,
991, 734, 703, 505 cm21; HRMS (FAB): calcd for
C38H47NO7Si: 657.3122, found: 657.3124; [a]2D3¼249.7
(c¼0.65, CHCl3).
1.2. Synthesis of chiral aldehyde 16
Aldehyde 16 was prepared from (S)-malic acid according to
the following scheme via the known ester 28 by a
modification of the procedure of Gong and Lynn.15 (S)-
Malic acid was treated with trifluoroacetic anhydride, then
with MeOH, affording hydroxy carboxylic acid 27 in 87%
yield. Reduction of the carboxylic acid was effectively
carried out with BH3·SMe2, affording dihydroxy ester 28.
As the hydroxy-ester easily cyclized to a lactone, 28 was
treated with tert-butyldimethylsilylchloride and triethyl-
silylchloride successively to give ester 29 in moderate yield.
Reduction of ester 29 and oxidation of the resulting alcohol
afford chiral aldehyde 16 in 66% yield over 2 steps
(Scheme 6).
1.1.10. (3E,5E,7E,9E)-11-{(1R,5S)-4-[2-(tert-Butyldiphe-
nylsiloxy)ethyl]-4-hydroxy-2-oxo-3-aza-6-oxabicyclo-
[3.1.0]hex-1-yl}-2-[(E)-ethylidene]-4,10-dimethyl-11-
oxoundeca-3,5,7,9-tetraenoic acid methyl ester. To a
CH2Cl2 (0.2 mL) solution of hydroxyamide 21 (13.0 mg,
0.0197 mmol) was added Dess–Martin periodinane
(16.8 mg, 0.0395 mmol) at 08C, and the reaction mixture
was stirred for 2 h at rt. The reaction was quenched with a
saturated NaHCO3 solution. The organic materials were
extracted with ethyl acetate, and the combined organic
extracts were washed with a saturated NaHCO3 solution,
dried over anhydrous Na2SO4, and concentrated in vacuo
after filtration. Purification by preparative thin layer
chromatography (ethyl acetate/hexane¼3/2) gave 7.7 mg
(60%) of lactam.
1.2.1. (S)-2-Hydroxysuccinic acid 1-methyl ester (27). To
(S)-malic acid (3.54 g, 26.3 mol) was added trifluoroacetic
anhydride (14.8 mL), and the reaction mixture was stirred
for 40 min. After removal of the remaining trifluoroacetic
anhydride in vacuo, MeOH (15 mL) was added to the
remaining solid, which was stirred for 1.5 h at rt. Volatile
materials were removed in vacuo and the residue was
crystallized from ether/hexane to give 3.38 g (87%) of
esther 27.
1H NMR (CDCl3) d 1.07 (9H, s), 1.69 (3H, s), 1.97 (3H, s),

Y. Hayashi et al. / Tetrahedron 58 (2002) 9839–9846
9845
Scheme 6. Synthesis of chiral aldehyde 16.
1H NMR (CDCl3) d 2.82 (1H, dd, J¼16.7, 6.1 Hz), 2.89
(1H, dd, J¼16.7, 4.2 Hz), 3.80 (3H, s), 4.32 (1H, dd, J¼6.1,
4.2 Hz); 13C NMR (CDCl3) d 35.9, 52.4, 59.2, 68.9, 175.3;
mp 70.0–71.08C; [a]2D3¼215.6 (c¼1.33, MeOH).
1.2.4. (S)-4-(tert-Butyldiphenylsiloxy)-2-triethylsiloxy-
butan-1-ol. To a CH2Cl2 (14 mL) solution of ester 29
(3.81 g, 7.83 mmol) was added a hexane solution of DIBAL
(0.95 M, 28.8 mL, 27.4 mmol) at 2508C, and the reaction
mixture was stirred for 1 h at 2108C. To the reaction
mixture were added MeOH (1.44 mL, 32.9 mmol) and
Na2SO4·10H2O(13.2 g, 43.9 mmol), and stirring was con-
tinued for 40 min. After filtration of the inorganic materials,
the solvent was removed in vacuo to give 2.36 g (66%) of
the alcohol, which was used in the next reaction without
purification.
1.2.2. (S)-2,4-Dihydroxybutyric acid methyl ester (28).
To a THF (15 mL) solution of ester 27 (1.42 g, 9.59 mmol)
was added BH3·SMe2 (3.7 mL) at 08C. After stirring the
reaction for 2 h at rt, it was quenched with MeOH. The
solvent was removed in vacuo, and the remaining oil was
evaporated from MeOH several times to remove the
methylborate, giving 1.28 g of diol 28 quantitatively,
which was used in next reaction without further purification
owing to its easy lactonization.
1H NMR (CDCl3) d 0.59 (6H, q, J¼7.8 Hz), 0.93 (9H, t,
J¼7.8 Hz), 1.04 (9H, s), 1.70–1.82 (2H, m), 2.18 (1H, t,
J¼6.6 Hz), 3.43–3.51 (1H, m), 3.55–3.62 (1H, m), 3.71
(2H, t, J¼5.9 Hz), 3.95–4.02 (1H, m), 7.33–7.43 (6H, m),
7.62–7.68 (4H, m); IR (neat) 3436, 2933, 2877, 1471, 1427,
1112, 1006, 738, 721 cm21; HRMS (FAB): calcd for
[C26H43O3Si2þH]þ: 459.2751, found: 459.2805;
[a]2D5¼þ12.2 (c¼0.95, CHCl3).
1H NMR (CDCl3) d 1.85–1.96 (2H, m), 2.02–2.12 (2H, m),
2.41–2.79 (2H, br), 3.80 (3H, s), 3.76–3.98 (2H, m); 13C
NMR (CDCl3) d 19.1, 26.8, 36.3, 52.3, 60.5, 68.6, 127.6,
129.7, 133.2, 135.5, 175.3; IR (neat) 3501, 2931, 1735,
1427, 1220, 1112, 823, 701, 613, 505 cm21
.
1.2.3. (S)-4-(tert-Butyldiphenylsiloxy)-2-triethylsiloxy-
butyric acid methyl ester (29). To a CH2Cl2 (6 mL)
solution of ester 28 (1.57 g, 11.7 mmol), triethylamine
(1.96 mL, 14.1 mmol) and DMAP (143 mg, 1.17 mmol)
1.2.5. (S)-4-(tert-Butyldiphenylsiloxy)-2-triethylsiloxy-
butanal (16). To a CH2Cl2 (0.68 mL) solution of alcohol
(315.0 mg, 0.687 mmol) was added triethylamine
(0.48 mL), DMSO (0.68 mL) and SO3·pyridine (328 mg,
2.06 mmol) at 08C, and the reaction mixture was stirred for
1.5 h. After a buffer solution had been added, the organic
materials were extracted with ethyl acetate three times, and
the combined organic extracts were washed with brine,
dried over anhydrous Na2SO4, concentrated in vacuo after
filtration to give 313 mg of aldehyde 16 in quantitative
yield.
was
added
tert-butyldiphenylsilylchloride
(3.55 g,
12.9 mmol) at 08C, and the reaction mixture was stirred
for 13 h at rt. After a buffer solution had been added, the
organic materials were extracted with ethyl acetate, and the
combined organic extracts were washed with brine, dried
over anhydrous MgSO4, and concentrated in vacuo after
filtration. The crude hydroxyester was used directly in the
next step. To a DMF (12 mL) solution of the crude
hydroxyester (4.37 g, 11.7 mmol) was added imidazole
(1.43 g, 21.1 mmol) and triethylsilylchloride (2.65 g,
17.6 mmol) at 08C, and the reaction mixture was stirred
for 2 h at rt. After a buffer solution had been added, the
organic materials were extracted with ethyl acetate, and the
combined organic extracts were washed with brine, dried
over anhydrous MgSO4, and concentrated in vacuo after
filtration. Purification by flash column chromatography
(ethyl acetate/hexane¼1/10) gave 3.81 g (67%) of ester 29.
1H NMR (CDCl3) d 0.64 (6H, q, J¼7.9 Hz), 0.97 (9H, t,
J¼7.9 Hz), 1.04 (9H, s), 1.83–1.99 (2H, m), 3.67–3.73
(1H, m), 3.83–3.90 (1H, m), 4.24 (1H, t, J¼5.3 Hz), 7.36–
7.44 (6H, m), 7.65–7.70 (4H, m), 9.72 (1H, s); 13C NMR
(CDCl3) d 4.8, 5.0, 6.7, 19.0, 26.8, 36.4, 58.8, 74.7, 127.7,
129.6, 133.5, 135.6, 204.2; IR (neat) 2956, 2859, 1738,
1427, 1113, 1009, 702, 505.
Acknowledgements
1H NMR (CDCl3) d 0.60 (6H, q, J¼7.8 Hz), 0.94 (9H, s),
1.04 (9H, t, J¼7.8 Hz), 1.82–1.90 (1H, m), 1.93–2.22 (1H,
m), 3.67 (3H, s), 3.67–3.82 (2H, m), 4.45 (1H, d,
J¼4.6 Hz); 13C NMR (CDCl3) d 4.6, 6.7, 19.2, 26.8, 38.1,
51.7, 59.7, 68.8, 127.6, 129.6, 133.8, 135.5, 178.3; IR (neat)
2954, 2933, 2877, 1758, 1428, 1139, 1112, 823,
701, 505 cm21; [a]D25¼243.4 (c¼1.10, CHCl3); HRMS
(FAB): calcd for [C27H43O4Si2þH]þ: 487.2700, found:
487.2690.
This work was supported by the Sumitomo Foundation and
Grants-in-Aid for Scientific Research from the Ministry of
Education, Culture, Sports, Science and Technology of
Japan. The authors thank Drs H. Osada and H. Kakeya, of
RIKEN, for sending us NMR data for NG-391 and for
helpful discussion throughout the course of this research.
The authors are grateful to Shinetsu-Kagaku Corporation for
the gift of TBSCl.

9846
Y. Hayashi et al. / Tetrahedron 58 (2002) 9839–9846
7. Jefson, M.; Meinwald, J. Tetrahedron Lett. 1981, 22, 3561.
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