Stereoselective and efficient total synthesis of optically active tetrodotoxin from D-glucose

Article abstract of DOI:10.1021/jo701655v

(Chemical Equation Presented) A stereoselective and efficient total synthesis of optically active tetrodotoxin (TTX) is described. A polyfunctionalized key cyclitol compound containing branched-chains for the synthesis of TTX was prepared from D-glucose e

Full text of DOI:10.1021/jo701655v

Stereoselective and Efficient Total Synthesis of Optically Active
Tetrodotoxin from D-Glucose
Ken-ichi Sato,* Shoji Akai, Hirotsugu Shoji, Naoki Sugita, Shiho Yoshida, Yoshinao Nagai,
Katsuhiko Suzuki, Yutaka Nakamura, Yasuhiro Kajihara, Masuo Funabashi,† and
Juji Yoshimura‡
Department of Applied Chemistry, Faculty of Engineering, Kanagawa UniVersity,
Yokohama, 221-8686, Japan, Department of Chemistry, Faculty of Sciences, Chiba UniVersity,
Chiba, 263-8522, Japan, and Department of Basic Science, College of Science and Engineering,
Iwaki Meisei UniVersity, Iwaki, 970-8551, Japan
satouk01@kanagawa-u.ac.jp
ReceiVed August 29, 2007
A stereoselective and efficient total synthesis of optically active tetrodotoxin (TTX) is described. A
polyfunctionalized key cyclitol compound containing branched-chains for the synthesis of TTX was
prepared from D-glucose employing the Henry reaction (Nitro aldol reaction) as the key transformation.
Stereoselective construction of the R-azido-aldehyde branched-chain was achieved via the key spiro
R-chloroepoxide intermediate.
Introduction
found and isolated not only from the puffer fish, but also from
newts, frogs, octopi, crabs, shellfish, and numerous other
animals. Furthermore, it is clear that the animals themselves
do not produce TTX, but rather, it is produced by bacteria such
as Alteromonas sp., Vibrio sp., and Shewanella, etc.8 Yasumoto
proposed the biosynthetic pathway of TTX based on the
structure of TTX and its analogues.9,10 TTX and its analogues
are expected to provide much important information toward
progress in areas such as pharmaceutical studies, elucidation
of structure-activity relationships, and biological roles.11
Therefore, a facile and large-scale synthesis of TTX and its
Tetrodotoxin (TTX, 1), one of the best-known marine toxins,
was originally isolated from the puffer fish.1 At the 30th
International Natural Product Chemistry Conference in 1964,
the structural determination of TTX was reported by four
research groups: Tsuda et al.,2 Hirata et al.,3 Woodward et al.,4
and Mosher et al.5 (the original name was “taricatoxin”) (Figure
1). TTX is known to selectively interact with elements of the
sodium channel, thus inhibiting its activity in the cell mem-
brane.6 Therefore, TTX is utilized as a tool to analyze various
vital events that occur via the sodium channel.7 TTX has been
(6) Narahashi, T.; Moore, J. W.; Scott, W. R. J. Gen. Physiol. 1964, 47,
965-974.
* Address correspondence to this author at Kanagawa University.
† Chiba University.
(7) (a) Narahashi, T. Physiol. ReV. 1974, 54, 813-889. (b) Hucho, F.
Angew. Chem., Int. Ed. Engl. 1995, 34, 39-50. (c) Balerna, M.; Lombet,
A.; Chicheportiche, R.; Romey, G.; Lazdunski, M. Biochem. Biophys. Acta
1981, 644, 219-225. (d) Bontemps, J.; Cantineau, R.; Grandfils, C.; Lprince,
P.; Dandrifosse, G.; Schoffeniels, E. Anal. Biochem. 1984, 139, 149-157.
(e) Wu, B. Q.; Yang, L.; Kao, C. Y.; Levinson, S. R.; Yotsu-Yamashita,
M.; Yasumoto, T. Toxicon 1996, 34, 407-416.
‡ Iwaki Meisei University.
(1) Tahara, Y. Biochem. Z. 1911, 30, 255-275.
(2) Tsuda, K.; Ikuma, S.; Kawamura, M.; Tachikawa, K.; Sakai, K.;
Tamura, C.; Amakasu, O. Chem. Pharm. Bull. 1964, 12, 1357-1374.
(3) Goto, T.; Kishi, Y.; Takahashi, S.; Hirata, Y. Tetrahedron 1965, 21,
2059-2088.
(4) (a) Woodward, R. B. Pure Appl. Chem. 1964, 9, 49-74. (b)
Woodward, R. B.; Gougoutas, J. Z. J. Am. Chem. Soc. 1964, 86, 5030.
(5) Mosher, H. S.; Fuhrman, F. A.; Buchwald. H. D.; Fischer, H. G.
Science 1964, 144, 1100-1110.
(8) (a) Yasumoto, T.; Yasumura, D.; Yotsu, M.; Michishita, T.; Endo,
A.; Kotaki, Y. Agric. Biol. Chem. 1986, 50, 793-795. (b) Noguchi, T.;
Jeon, J.-K.; Arakawa, O.; Sugita, H.; Deguchi, Y.; Shida, Y.; Hashimoto,
K. J. Biochem. 1986, 99, 311-314.
10.1021/jo701655v CCC: $40.75 © 2008 American Chemical Society
Published on Web 01/19/2008
1234
J. Org. Chem. 2008, 73, 1234-1242

Total Synthesis of Optically ActiVe Tetrodotoxin
SCHEME 1. Retrosynthetic Analysis of (-)-TTX from
D-Glucose
FIGURE 1. Tetrodotoxin (1) and its analogues (1a-k).
analogues is of great importance. However, it is difficult to
prepare modified TTX derivatives from the naturally occurring
compound due to its unique structural and chemical properties.12
The total synthesis of TTX and its analogues remains a
fascinating and extremely difficult challenge to synthetic
chemists. Despite the attempts of numerous research groups to
synthesize TTX,13 a more efficient synthesis of optically active
TTX has not been reported during the 30 years following Kishi
and co-workers first total synthesis of (()-TTX.14 Recently, the
Isobe and Du Bois research groups have succeeded in the
synthesis of (-)-TTX.15
(9) For examples of TTX analogues, 5,6,11-trideoxyTTX: (a) Yotsu-
Yamashita, M.; Yamagishi, Y.; Yasumoto, T. Tetrahedron Lett. 1995, 36,
9329-9332. (b) Nakagawa, T.; Jang, J.; Yotsu-Yamashita, M. Anal.
Biochem. 2006, 352, 142-144. (c) Umezawa, T.; Hayashi, T.; Sakai, H.;
Teramoto, H.; Yoshikawa, T.; Izumida, M.; Tamatani, Y.; Hirose, T.;
Ohfune, Y.; Shinada, T. Org. Lett. 2006, 8, 4971-4974. 1-Hydroxy-5,11-
dideoxyTTX: (d) Kotaki, Y.; Shimizu, Y. J. Am. Chem. Soc. 1993, 115,
827-830. 4-epiTTX: (e) Yasumoto, T.; Michishita, T. Agric. Biol. Chem.
1985, 49, 3077-3088. 6-epiTTX, 11-deoxyTTX: (f) Yasumoto, T.; Yotsu,
M.; Murata, M.; Naoki, H. J. Am. Chem. Soc. 1988, 110, 2344-2345.
8,11-dideoxyTTX: (g) Nishikawa, T.; Urabe, D.; Yoshida, K.; Iwabuchi,
T.; Asai, M.; Isobe, M. Chem. Eur. J. 2004, 10, 452-462. (h) Nishikawa,
T.; Urabe, D.; Yoshida, K.; Iwabuchi, T.; Asai, M.; Isobe, M. Org. Lett.
2002, 4, 2679-2682. 11-oxoTTX: (i) Khora, S. S.; Yasumoto, T.
Tetrahedron Lett. 1989, 30, 4393-4394. 11-norTTX-6(R)-ol: (j) Endo, A.;
Khora, S. S.; Murata, M.; Yasumoto, T. Tetrahedron Lett. 1988, 29, 4127-
4128. 11-norTTX-6(S)-ol: (k) Yotsu, M.; Hayashi, Y.; Khora, S. S.; Sato,
S.; Yasumoto, T. Biosci. Biotechnol. Biochem. 1992, 56, 370-371. 5,11-
dideoxyTTX: (l) Asai, M.; Nishikawa, T.; Ohyabu, N.; Yamamoto, N.;
Isobe, M. Tetrahedron 2001, 57, 4543-4558. Several TTX analogues: (m)
Yotsu-Yamashita, M. J. Toxicol. Toxin ReV. 2001, 20, 50-66. (n) Yotsu-
Yamashita, M.; Goto, A.; Nakagawa, T. Chem. Res. Toxicol. 2005, 18, 865-
871.
(10) (a) Yasumoto, T. Kagaku to seibutsu 1989, 27, 401-406 (in
Japanese); Chem. Abstr. 1989, 111, 72582z. (b) Yotsu-Yamashita, M.;
Yamagishi, Y.; Yasumoto, T. Tetrahedron Lett. 1995, 36, 9329-9332. (c)
Shimizu, Y.; Kobayashi, M. Chem. Pharm. Bull. 1983, 31, 3625-3631.
(d) Shimizu, Y. Ann. N.Y. Acad. Sci. 1986, 479, 24-31.
(11) (a) Kodama, M.; Ogata, T.; Sato, S. Mar. Biol. 1985, 87, 199-
202. (b) Matsumura, K. Nature 1995, 378, 563-564. (c) Saito, T.; Noguchi,
T.; Harada, T.; Murata, O.; Hashimoto, K. Nippon Suisan Gakkaishi 1985,
51, 1175-1180 (in Japanese); Chem. Abstr. 1985, 103, 120354k.
(12) (a) Kao, C. Y.; Lovinson, S. Ann. N.Y., Acad. Sci. 1986, 479, 52-
67. (b) Kobayashi, J.; Ishibashi M. ComprehensiVe Natural Products
Chemistry; Paragamon: Oxford, UK, 1999; pp 415-649.
a The actual conformation of B is different: see compound 24.
We have been engaged in the total syntheses of naturally
occurring branched-chain cyclitol compounds such as cyclo-
phellitol,16 mytillitol, laminitol,17 and (-)-TTX18 starting from
(13) (a) Noya, B.; Paredes, M. D.; Ozores, L.; Alonso, R. J. Org. Chem.
2000, 65, 5960-5968. (b) Burgey, C. S.; Vollerthun, R.; Fraser-Reid, B. J.
Org. Chem. 1996, 61, 1609-1618. (c) Nachman, R. J.; Honel, M.; Williams,
T. M.; Halaska, R. C.; Mosher, H. S. J. Org. Chem. 1986, 51, 4802-4806.
(d) Keana, J. F. W.; Bland, J. S.; Boyle, P. J.; Erion, M.; Hartling, R.;
Husman, J. R.; Roman, R. B. J. Org. Chem. 1983, 48, 3621-3626. (e)
Keana, J. F. W.; Bland, J. S.; Boyle, P. J.; Erion, M.; Hartling, R.; Husman,
J. R.; Roman, R. B. J. Org. Chem. 1983, 48, 3627-3631. (f) Itoh, T.;
Watanabe, M.; Fukuyama, T. Synlett 2002, 1323-1325. (g) Ohtani, Y.;
Shinada, T.; Ohfune, Y. Synlett 2003, 619-622. (h) Fernandez-Gonzalez,
M.; Alonso, R. J. Org. Chem. 2006, 71, 6767-6775. (i) Taber, D. F.; Storck,
P. H. J. Org. Chem. 2003, 68, 7768-7771.
(14) (a) Kishi, Y.; Aratani, M.; Fukuyama, M.; Nakatsubo, F.; Goto, T.;
Inoue, S.; Tanino, H.; Sugiura, S.; Kakoi, H. J. Am. Chem. Soc. 1972, 94,
9217-9219. (b) Kishi, Y.; Fukuyama, T.; Aratani, M.; Nakatsubo, F.; Goto,
T.; Inoue, S.; Tanino, H.; Sugiura, S.; Kakoi, H. J. Am. Chem. Soc. 1972,
94, 9219-9221.
J. Org. Chem, Vol. 73, No. 4, 2008 1235

Sato et al.
SCHEME 2. Synthesis of the Nitro Cyclitol 12 (E) Employing the Henry Reaction
D-glucose. On the basis of these investigations, we have recently
accomplished a novel and stereoselective synthesis of (()-TTX
from myo-inositol.19 Herein, we describe the total synthesis of
optically active TTX from D-glucose employing the Henry
reaction (Nitro aldol reaction)20 as the key transformation.
Scheme 1 shows the retrosynthetic plan for the synthesis of
(-)-TTX from D-glucose, which focuses on the preparation of
the key intermediate, ketone D. This intermediate has previously
been successfully converted to TTX in our laboratory.19 In a
previous work, we synthesized (()-TTX via compounds A, B,
C, and D. Therefore, synthesis of optically active compound
D from D-glucose was a promising route to the synthesis of
(-)-TTX. Compound D can be synthesized from compound E
by employing the Henry reaction, as previously described.18c
The key intermediate, E, was synthesized using standard
reactions from D-glucose, as described below.
(15) (a) Ohyabu, N.; Nishikawa, T.; Isobe, M. J. Am. Chem. Soc. 2003,
125, 8798-8805. (b) Nishikawa, T.; Urabe, D.; Isobe, M. Angew. Chem.,
Int. Ed. 2004, 43, 4782-4785. (c) Urabe, D.; Nishikawa, T.; Isobe, M.
Chem. Asian J. 2006, 1-2, 125-135. (d) Hinmam, A.; Du Bois, J. J. Am.
Chem. Soc. 2003, 125, 11510-11511. (e) Isobe, M.; Ohyabu, N.; Nishikawa,
T. J. Synth. Org. Chem. Jpn. (Yuki Gosei Kagaku Kyokaishi) 2007, 65,
492-501.
(16) Sato, K.; Bokura, M.; Moriyama, H.; Igarashi, T. Chem. Lett. 1994,
37-40.
(17) Sato, K.; Bokura, M.; Taniguchi, M. Bull. Chem. Soc. Jpn. 1994,
67, 1633-1640.
(18) (a) Akai, S.; Nakamura, Y.; Kajihara, Y.; Yoshimura, J.; Sato, K.
Anal. Sci. 1999, 15, 503-504. (b) Sato, K.; Kajihara, Y.; Nakamura, Y.;
Yoshimura, J. Chem. Lett. 1991, 1559-1562. (c) Funabashi, M.; Wakai,
H.; Sato, K.; Yoshimura, J. J. Chem. Soc., Perkin Trans. 1 1980, 1, 14-
19.
(19) (a) Akai, S.; Nakamura, Y.; Kajihara, Y.; Yoshimura, J.; Sato, K.
Anal. Sci. 1999, 15, 501-502. (b) Sato, K.; Akai, S.; Sugita, N.; Ohsawa,
T.; Kogure, T.; Hirotsugu, S.; Yoshimura, J. J. Org. Chem. 2005, 70, 7496-
7504.
Results and Discussion
3-C-Hydroxymethyl-1,2:5,6-di-O-isopropylidene-R-D-gluco-
hexofuranose (4)21 was prepared by stereoselective m-chloro-
perbenzoic acid (m-CPBA) oxidation of 3-deoxy-1,2:5,6-di-O-
isopropylidene-3-C-methylene-R-D-ribo-hexofuranose (2)22 de-
rived from D-glucose, followed by hydrolysis with 1 M aq
NaOH. The two hydroxyl groups of 4 were protected with a
(20) For review of the Henry reaction see: Luzzio, F. A. Tetrahedron
2001, 57, 915-945.
(21) Yoshimura, J.; Kobayashi, K.; Sato, K.; Funabashi, M. Bull. Chem.
Soc. Jpn. 1972, 45, 1806-1812.
1236 J. Org. Chem., Vol. 73, No. 4, 2008

Total Synthesis of Optically ActiVe Tetrodotoxin
SCHEME 3. Synthesis of Key Intermediate 19 (D)
benzyl (Bn) group to give 3,3′-di-O-benzyl derivative 5 in 80%
yield. Compound 5 was then selectively hydrolyzed using 70%
aq acetic acid at room temperature to give the 5,6-diol 6 in
quantitative yield. Oxidative degradation of 6 with sodium meta-
periodate in aqueous methanol gave the corresponding aldehyde
7, which was then treated with nitromethane in methanol in the
presence of sodium methoxide to give nitro alcohol 8 (diaste-
reomer ratio ) ca. 10:1) in 75% yield (2 steps). The diastere-
omeric mixture of nitro alcohol 8 was treated with methane-
sulfonyl chloride in the presence of triethylamine to give the
corresponding single nitro-olefin 9 (G in Scheme 1) in 85%
yield. Reaction of 9 with lithium diisopropylamide (LDA) and
bis(phenylthio)methane gave the branched bis(phenyl)dithio-
acetal derivative 10a and 10b. The ratio of 10a:10b (ca. 10:1)
1
was determined by H NMR (comparison of the intensities of
H-5) of the crude mixture. The addition of dithioacetal anion
proceeded with higher stereoselectivity (ca. 10:1) than that of
our previous report18c using 1,3-dithiane (ca. 5:4). The higher
stereoselectivity might be induced by the bulkiness of the
reagent, bis(phenylthio)methane. The desired compound 10a was
isolated by fractional crystallization in 80% yield. The config-
uration at C-5 of 10a was determined by derivation into the
corresponding cyclitol compound 12′, as described below.
The 1,2-O-isopropylidene group of 10a was hydrolyzed upon
treatment with 85% aq acetic acid under reflux. The resultant
nitro-sugar 11 (F in Scheme 1) was treated with 1.5 mol equiv
of sodium hydrogencarbonate in aqueous methanol to give a
crystalline muco-inositol derivative (12)23 (E in Scheme 1) in
84% yield (2 steps). Acetylation of 12 under standard conditions
gave tri-O-acetate 12′ quantitatively. The coupling constant for
12′ (J1,2 ) 2.5 Hz, J4,5 ) 3.5 Hz, J1,6 ) J5,6 ) 11.0 Hz) sug-
gested the shown configuration for C-5 (C-8 in TTX number-
ing). In the above reaction (Henry reaction), the formation of
four stereoisomers including 12 is possible, but the undesired
three stereoisomers were not isolated at all. This stereoselectivity
might be rationalized by the thermodynamic stability of 12.
Reaction of the Vicinal-diol of 12 with 2,2-dimethoxypropane
and a catalytic amount of p-toluenesulfonic acid (p-TsOH) gave
the corresponding acetonide 13 in 86% yield. Acetonide 13 was
then treated with dimethoxymethane and diphosphorous pen-
toxide to give the fully protected cyclitol 14 in 93% yield.
Treatment of 14 with N-bromosuccinimide (NBS) in aqueous
acetonitrile gave the unstable aldehyde 15, which was im-
mediately reduced with sodium borohydride to give the hy-
droxymethyl derivative 16 in 82% yield (2 steps). Silylation of
16 with tert-butyldiphenylsilyl chloride (TBDPS-Cl) and imi-
dazole gave the fully protected nitro cyclitol 17 in 95% yield
(Scheme 3).
subsequently decomposition under basic conditions) had been
proceeding in the oxidation of the nitronate intermediate.
Therefore, McMurry’s transformation24b from the nitronate to
the carbonyl was applied as follows. Compound 17 was treated
with t-BuOK, and the resulting nitronate was subjected to
ozonolysis (O3) in toluene at -78 °C to give the required ketone
18 in moderate yield (79%). The transformation of 18 into
compound 19 (D in Scheme 1) was achieved by catalytic
reduction, and subsequent acetonide protection of the resulting
diol in 79% yield (2 steps) (Scheme 3).
The further conversion of ketone 19 into (-)-TTX was carried
out to established our route for (()-TTX synthesis including
successive spiro R-chloroepoxide formation and its ring-opening
with azide anion25 as a crucial key step.
To obtain compound 22, ketone 19 was treated with lithium
diisopropylamide (LDA) and dichloromethane at -78 °C to give
the expected dichloroethanol derivative 20 as a single isomer
in 79% yield. The dichloroethanol derivative 20 was treated
with NaN3 and 15-crown-5 ether in DMSO (Me2SO) at 75 °C
to give the R-azido-aldehyde 22 (C in Scheme 1) via spiro
R-chloroepoxide derivative 21 in 64% yield, with complete
stereo- and regioselectivities. The structure of 22 including the
stereochemistry at C-6 (C-8a in TTX numbering) was deter-
mined by X-ray structure analysis. The reaction of R-azido-
aldehyde 22 and TMS-CN/Et3N in MeOH gave the corre-
sponding cyanohydrin 23 and its epimer 23a in 56% and 17%
yields, respectively. The stereochemistry at C-6′ (C-9 in TTX
numbering) of 23 was the same as that observed in the total
The transformations of the nitro derivative into the carbonyl
derivative were subsequently examined. Initially, compound 17
was treated with potassium tert-butoxide (t-BuOK) and m-CPBA
in benzene24a to give a polar decomposed compound(s) and a
very slight amount of the desired product 18 (ca. 5% yield). It
seems that some side reactions (mainly retro-aldol reaction and
(22) (a) Szarek, W. A.; Jewell, J. S.; Szczerek, I.; Jones, J. K. N. Can.
J. Chem. 1969, 47, 4473-4476. (b) Rosenthal, A.; Sprinzl, M. Can. J. Chem.
1969, 47, 4477-4481. (c) Kartha, K. P. R. Tetrahedron Lett. 1986, 27,
3415-3416. (d) Yoshimura, J.; Sato, K.; Hashimoto, H. Chem. Lett. 1977,
1327-1330. (e) Kinoshita, M.; Taniguchi, M.; Morioka, M.; Takami, H.;
Mizusawa, Y. Bull. Chem. Soc. Jpn. 1988, 61, 2147-2156.
(23) The IUPAC name of compound 11 is 1-L-(1,2,3′,4,5/3,6)-3-
hydroxymethyl-3,3′-di-O-benzyl-6-nitro-2,3,4,5-tetrahydroxy cyclohexane-
carbaldehyde diphenyldithioacetal.
(24) (a) Review of the Nef reaction: Ballini, R.; Petrini, M. Tetrahedron
2004, 60, 1017-1047. (b) McMurry, J. E.; Melton, J.; Padgett, H. J. Org.
Chem. 1974, 39, 259-260.
(25) (a) Sato, K.; Kajihara, Y.; Nakamura, Y.; Yoshimura, J. Chem. Lett.
1991, 1559-1562. (b) Sato, K.; Suzuki, K.; Ueda, M.; Kajihara, Y.; Hori,
H. Bull. Chem. Soc. Jpn. 1997, 70, 225-230. (c) Sato, K.; Sekiguchi, T.;
Hozumi, T.; Yamazaki, T.; Akai, S. Tetrahedron Lett. 2002, 43, 3087-
3090.
J. Org. Chem, Vol. 73, No. 4, 2008 1237

Sato et al.
SCHEME 4. The Further Conversion of Ketone 19 (D) into (-)-TTX (1)
synthesis of (()-TTX.19 The undesired isomer 23a could be
isomerized into the desired isomer 23 under the same reaction
conditions. After two cycles of this operation, the total yield of
23 was 68%. To introduce amino and orthoester moieties, the
hydroxyl group of 23 was protected with the methoxymethyl
(MOM) group, and subsequently treated with diisobutylalu-
minium hydride (DIBAL-H) to give the corresponding aldehyde
25 in 82% yield. Selective deprotection of the MOM group at
O-4 (O-5 in TTX numbering) of 25 and subsequent treatment
with Jones’ reagent gave the δ-lactone 26 in 90% yield as a
single product. The monitoring of the reactions of aldehyde 24
by TLC (hexane/ethyl acetate 4:1) suggested that the deprotec-
tion of the MOM group was first undertaken to form the
hemiacetal intermediate 25′, then it was immediately oxidized
into δ-lactone 26. To introduce the guanidine moiety, the azido
group of 26 was first reduced with 10% Pd-C and H2 to give
the amine 27 in quantitative yield. Subsequent deprotection of
the TBDPS group using tetra-n-butylammononium fluoride
(TBAF) gave alcohol 28. Guanidinylation26 of 28 provided the
precursor 29 (A in Scheme 1), which was converted to 4,9-
anhydro-4-epi-TTX (anhydroTTX, 1a) by oxidation with py-
ridinium chlorochromate (PCC) and subsequent treatment with
4M HCl-dioxane/MeOH,15a,b and followed by 30% aq
CF3COOH solution in 50% yield. Isomerization of 1a by
treatment with 4% aq acetic acid solution at 60 °C for 2 days
yielded a 1:4 mixture of 1a and 1. The mixture was purified by
HPLC15a to give 1 in 56% yield (Scheme 4). The spectral data
(1H, MS) for synthetic 1 were in good agreement with those of
the natural TTX9d,15a,b,27 (Scheme 4 and Table 1). Moreover,
the specific rotation of the synthetic 1a and 1 was [R]2D8 +1.2
(c 0.18, 3% AcOH aq) and [R]2D8 -3.75 (c 0.13, 3% AcOH aq),
respectively. Both rotation values were in good agreement with
that reported by Isobe’s group.15a-c,e Full experimental details
for conversion of 19 into (-)-TTX are available in the
Supporting Information.
In conclusion, we have accomplished the total synthesis of
optically active (-)-TTX from D-glucose employing the Henry
reaction as a key framework with a highly stereoselective
(26) (a) Kim, K. S.; Qian, L. Tetrahedron Lett. 1993, 34, 7195-7196.
(b) Bergeron, R. J.; McManis, J. S. J. Org. Chem. 1987, 52, 1700-1703.
(27) A sample of natural (-)-tetrodotoxin was obtained from Sankyo
Co. Ltd. (Tokyo, Japan).
1238 J. Org. Chem., Vol. 73, No. 4, 2008

Total Synthesis of Optically ActiVe Tetrodotoxin
1
TABLE 1. Comparative H NMR Data of Tetrodotoxin
position
synthetic TTXa
natural TTXb
synthetic anhydroTTX
4
4a
5
7
8
5.50 (d, J ) 8.9 Hz)
2.35 (d, J ) 9.6 Hz)
4.25 (br s)
4.09 (t, J ) 2.1 Hz)
4.30 (d, J ) 2.1 Hz)
3.96 (s)
5.50 (d, J ) 9.4 Hz)
2.35 (d, J ) 9.5 Hz)
4.25 (br s)
4.08 (t, J ) 1.8 Hz)
4.30 (d, J ) 1.5 Hz)
3.96 (s)
5.53 (s)
2.94 (d, J ) 2.6 Hz)
4.36 (dd, J ) 2.2, 2.6 Hz)
4.17 (t, J ) 2.2, 2.6 Hz)
4.63 (d, J ) 2.2 Hz)
4.58 (s)
9
11
4.01 (d, J ) 12.4 Hz)
4.06 (d, J ) 12.4 Hz)
4.02 (d, J ) 12.6 Hz)
4.04 (d, J ) 12.6 Hz)
4.00 (d, J ) 12.2 Hz)
3.96 (d, J ) 12.2 Hz)
a 600 MHz, in 3% CD3COOD/D2O, referenced to CHD2COOD (2.06 ppm). b Reference 9d.
1.2 Hz, CHO), 7.36-7.21 (10H, m, PhH), 6.06 (1H, d, J1,2 ) 3.5
Hz, H-1), 4.67 (1H, d, H-2), 4.65, 4.63 (2H, 2 × d, JA,B ) 11.6
Hz, CH2Ph), 4.62, 4.56 (2H, 2 × d, JA,B ) 11.9 Hz, CH2Ph), 4.47
(1H, d, H-4), 4.04, 3.95 (2H, 2 × d, Ja,b ) 11.0 Hz, H-3′), 1.57,
1.34 (6H, 2 × s, C(CH3)2). ESI-TOF-MS calcd for C23H27O6 m/z
[M + H]+ 399.1808, found 399.1808.
manner in 34 steps from D-glucose (0.38% overall yield). This
synthetic methodology will be applicable to the synthesis of
not only TTX and its analogues, but also highly complex natural
cyclitols bearing branched-chain structures.
Experimental Section
3,3′-Di-O-benzyl-6-deoxy-3-C-hydroxymethyl-1,2-O-isopro-
pylidene-6-nitro-r-D-glucofuranose (8R) and 3,3′-Di-O-benzyl-
6-deoxy-3-C-hydroxymethyl-1,2-O-isopropylidene-6-nitro-â-L-
idofuranose (8S). To a solution of aldehyde 7 (6.3 g, 18.7 mmol)
in MeOH (15 mL) was added a mixture of CH3NO2 (8 mL, 148
mmol) and NaOMe (1.0 M solution in methanol, 15 mL) with
continued stirring at rt. After 30 min, the reaction mixture was
neutralized with acetic acid, poured into brine, extracted with
CHCl3, washed with brine and water, dried over anhyd MgSO4,
and evaporated to give 8 (diastereomer ratio ) ca. 10:1-5:1) (6.4
g, 75% yield from 6); IR (KBr, neat) ν 3350 (OH), 1556 cm-1
3,3′-Di-O-benzyl-3-C-hydroxymethyl-1,2:5,6-di-O-isopropyli-
dene-r-D-glucofuranose (5). To a solution of 3-C-hydroxymethyl-
1,2:5,6-di-O-isopropylidene-R-D-gluco-hexofuranose (4)21 (7.9 g,
27.2 mmol) in dry DMF (60 mL) was added sodium hydride (60%
dispersion in mineral oil, 4.4 g, 108.8 mmol), and the solution was
stirred at rt. After 30 min, benzyl bromide (9.8 mL, 81.6 mmol)
was added dropwise to the reaction mixture, with continued stirring
at rt for 1 h. After the disappearance of 4 on TLC with 1:1 hexane-
EtOAc, 1 M MeONa-MeOH (15 mL) was added, stirring was
continued for 1 h, then the solution was evaporated to give a residue.
The remaining residue was poured into aq NH4Cl solution, extracted
with EtOAc, washed with brine and water, dried over anhyd
MgSO4, and evaporated to give 5 (12.1 g, 95% yield), which was
purified on a column of silica gel with 30:1-8:1 toluene-acetone;
colorless syrup; [R]2D5 +17.6 (c 1.22, CHCl3); 1H NMR (600 MHz)
δ 7.32-7.19 (10H, m, PhH), 5.79 (1H, d, J1,2 ) 3.6 Hz, H-1),
4.77, 4.72 (2H, 2 × d, JA,B ) 11.9 Hz, CH2Ph), 4.64 (1H, d, H-2),
4.55, 4.51 (2H, 2 × d, JA,B ) 12.0 Hz, CH2Ph), 4.38 (1H, ddd, J5,4
) 6.5 Hz, J5,6 ) 6.5 Hz, J5,6′ ) 6.5 Hz, H-5), 3.99 (1H, d, H-4),
3.96 (1H, dd, J6,6′ ) 8.6 Hz, H-6), 3.94 (1H, dd, H-6′), 3.93, 3.80
(2H, 2 × d, Ja,b ) 11.0 Hz, H-3′), 1.46, 1.34, 1.28, 1.27 (12H, 4 ×
s, 2 × C(CH3)2). Anal. Calcd for C27H34O7 (470.54): C, 68.92; H,
7.28. Found: C, 68.70; H, 7.37.
1
(NO2); H NMR (600 MHz) δ 7.37-7.25 (10H, m, PhH), 5.95
(miner) and 5.82 (major) (1H, d, J1,2 ) 3.7 Hz, H-1), 4.72 (1H, m,
H-5), 4.67 (2H, m, H-6,6′), 4.69, 4.51 (2H, 2 × d, JA,B ) 10.7 Hz,
CH2Ph), 4.61, 4.52 (2H, 2 × d, JA,B ) 11.7 Hz, CH2Ph), 4.57 (1H,
d, H-2), 4.52 (1H, d, J5,OH ) 11.0 Hz, OH), 4.11 (1H, d, J4,5 ) 8.2
Hz, H-4), 4.10, 3.75 and 4.08, 3.74 (2H, 2 × d, Ja,b ) 11.3 Hz,
H-3′), 1.50 (major), 1.29 (major) and 1.48 (miner), 1.30 (miner)
1
(6H, 2 × s, C(CH3)2); H NMR (600 MHz in C6D6) (major) δ
7.23-7.08 (10H, m, PhH), 5.64 (1H, d, J1,2 ) 3.5 Hz, H-1), 4.84
(1H, dddd, H-5), 4.46 (1H, dd, J6,5 ) 3.2 Hz, J6,6′ ) 12.4 Hz, H-6),
4.44 (1H, d, J5,OH ) 3.0 Hz, OH), 4.40, 4.14 (2H, 2 × d, JA,B
)
11.4 Hz, CH2Ph), 4.16, 4.00 (2H, 2 × d, JA,B ) 11.8 Hz, CH2Ph),
4.34 (1H, dd, J6′,5 ) 7.6 Hz, H-6′), 4.23 (1H, d, H-2), 4.22 (1H, d,
J4,5 ) 8.9 Hz, H-4), 3.76, 3.64 (2H, 2 × d, Ja,b ) 11.4 Hz, H-3′),
1.40, 1.10 (6H, 2 × s, C(CH3)2). Anal. Calcd for C24H29NO8
(459.49): C, 62.73; H, 6.36; N, 3.05. Found: C, 62.74; H, 6.41;
N, 2.99.
3,3′-Di-O-benzyl-3-C-hydroxymethyl-1,2-O-isopropylidene-r-
D-glucofuranose (6). Di-O-benzyl derivative 5 (9.0 g, 19.2 mmol)
was dissolved in 70% aq acetic acid solution, and the solution was
stirred for 12 h. After the disappearance of 5 on TLC with 2:1
hexane-EtOAc, the reaction mixture was evaporated to give 6 (8.23
g, quantitatively): mp 63.0-64.5 °C (colorless prisms, ether-
hexane); [R]2D5 +29.1 (c 1.10, CHCl3); IR (KBr, disk) ν 3500 cm-1
(OH); 1H NMR (600 MHz) δ 7.36-7.25 (10H, m, PhH), 5.83 (1H,
d, J1,2 ) 3.8 Hz, H-1), 4.67, 4.53 (2H, 2 × d, JA,B ) 11.7 Hz,
CH2Ph), 4.66, 4.56 (2H, 2 × d, JA,B ) 11.4 Hz, CH2Ph), 4.58 (1H,
3,3′-Di-O-benzyl-5,6-dideoxy-3-C-hydroxymethyl-1,2-O-iso-
propylidene-6-nitro-r-D-xylo-hex-5-enofuranose (9, G). To a
stirred solution of nitro alcohol 8 (1.48 g, 3.22 mmol) in CH2Cl2
(15 mL) was added methanesulfonyl chloride (0.75 mL, 9.66 mmol)
at 0 °C, then triethylamine (1.80 mL, 12.9 mmol) was added
dropwise. After the disappearance of starting compound on TLC
with 2:1 hexane-EtOAc, the reaction mixture was diluted with
CH2Cl2 (20 mL), washed with aq NaHCO3 solution, brine, and
water, dried over anhyd MgSO4, and evaporated to give a residue.
The remaining residue was purified on a column of silica gel with
5:1 to 3:1 hexane-EtOAc to give 9 (G) (1.21 g, 85% yield): mp
90.0-91.0 °C (colorless prisms, ether-hexane); [R]D28
d, H-2), 4.42 (1H, br d, JOH,5 ) 1.3 Hz, 5-OH), 4.12 (1H, d, J4,5
)
8.8 Hz, H-4), 4.10, 3.81 (2H, 2 × d, Ja,b ) 11.3 Hz, H-3′), 4.05
(1H, dddd, J5,6 ) 3.4 Hz, J5,6′ ) 4.8 Hz, H-5), 3.83 (1H, dd, J6,6′
) 1.5 Hz, H-6), 3.73 (1H, dd, H-6′), 2.35 (1H, br s, 6-OH), 1.50,
1.29 (2 × s, 6H, C(CH3)2). Anal. Calcd for C24H30O7 (430.48): C,
66.96; H, 7.02. Found: C, 66.63; H, 7.00.
+10.1 (c
1.04, CHCl3); IR (KBr, disk) ν 1670 (CdC), 1540 cm-1 (NO2);
1H NMR (600 MHz) δ 7.54 (1H, dd, J4,6 ) 3.6 Hz, J5,6 ) 13.2 Hz,
H-6), 7.38-7.20 (11H, m, PhH, H-5), 5.94 (1H, d, J1,2 ) 3.6 Hz,
H-1), 4.89 (1H, dd, J4,5 ) 2.1 Hz, H-4), 4.62, 4.57 (2H, 2 × d,
JA,B ) 11.9 Hz, CH2Ph), 4.60, 4.54 (2H, 2 × d, JA,B ) 12.2 Hz,
CH2Ph), 4.53 (1H, d, H-2), 4.02, 3.84 (2H, 2 × d, Ja,b ) 11.2 Hz,
H-3′), 1.49, 1.31 (6H, 2 × s, C(CH3)2); 13C NMR (150 MHz) δ
140.5, 138.0, 137.7, 137.2, 128.5, 128.4, 128.0, 127.7, 127.6, 126.6,
113.0, 105.1, 87.3, 82.2, 80.9, 73.7, 67.4, 66.3, 27.1, 26.4. Anal.
3,3′-Di-O-benzyl-3-C-hydroxymethyl-1,2-O-isopropylidene-r-
D-xylo-pentoaldofranose (7). To a solution of diol 6 (8.0 g, 18.6
mmol) in 3:1 MeOH-H2O was added a solution of NaIO4 (4.75 g,
22.3 mmol) in water (45 mL), and the mixture was stirred at 0 °C
for 30 min, then at rt for 30 min. After the disappearance of 6 on
TLC with 8:1 toluene-acetone, the reaction mixture was poured
into brine, extracted with CHCl3, washed with brine and water,
and evaporated to give 7 (7.4 g): colorless syrup; IR (KBr, neat)
ν 1750 cm-1 (C)O); 1H NMR (500 MHz) δ 9.74 (1H, d, JCHO,4
)
J. Org. Chem, Vol. 73, No. 4, 2008 1239

Sato et al.
Calcd for C24H27O7N (441.47): C, 65.29; H, 6.16; N, 3.17.
Found: C, 64.92; H, 6.16; N, 3.11.
d, J1′,1 ) 4.6 Hz, H-1′), 3.67, 3.42 (1H, 2 × d, Ja,b ) 9.8 Hz, H-3′),
3.34 (1H, ddd, H-1), 2.15, 1.97, 1.95 (9H, 3 × s, 3 × OCOCH3).
Anal. Calcd for C40H41O7NS2 (759.89): C, 63.22; H, 5.44; N, 1.84.
Found: C, 63.62; H, 5.32; N, 1.93.
5-C-Bis(phenylthio)methyl-3,3′-di-O-benzyl-5,6-dideoxy-3-C-
hydroxymethyl-1,2-O-isopropylidene-6-nitro-r-D-gulucofra-
nose (10a). To a stirred solution of bis(phenyl)thiomethane (616
mg, 2.65 mmol) in THF (6 mL) was added butyllithium (1.6 M
solution in hexane, 2.3 mL, 3.68 mmol) at -78 °C under argon.
After 15 min, a solution of nitro-olefin 9 (730 mg, 1.66 mmol) in
THF (3 mL) was added to the above mixture, then the solution
was stirred for 30 min. After the disappearance of 9 on TLC with
3:1 hexane-EtOAc, acetic acid (5 mL) and subsequently methanol
(50 mL) were added then evaporated to give a residue. The residue
was diluted with CHCl3, washed with aq NaHCO3 solution, brine,
and water, dried over anhyd MgSO4, and evaporated to give a
residue. The remaining residue was purified on a column of silica
gel with 6:1 to 3:1 hexane-EtOAc to give 10a (900 mg, 80%
yield): mp 120-121 °C (colorless prisms, ether-hexane); [R]D25
1L-(1,2,4,5/3(OH),6)-3,3′-Di-O-benzyl-1-C-bis(phenylthio)-
methyl-3-C-hydroxymethyl-4,5-O-isopropylidene-6-nitro-2,3,4,5-
cyclohexanetetrol (13). To a solution of nitro cyclitol derivative
12 (36 mg, 60.2 µmol) in dry dichloromethane (1 mL) were added
2,2-dimethoxypropane (75 µL, 602 µmol) and p-toluenesulfonic
acid monohydrate (1 mg, 6.02 µmol) with continued stirring for 1
h. After the disappearance of 12 on TLC with 2:1 hexane-EtOAc,
the reaction mixture was poured into saturated aq NaHCO3 solution,
extracted with CHCl3, washed with brine and water, dried over
anhyd MgSO4, and evaporated to give 13 (35 mg, 86% yield), which
was purified on a column of silica gel with 3:1 hexane-EtOAc:
colorless oil; [R]2D6 -99.2 (c 0.83, CHCl3); IR (KBr, neat) ν 3507
(OH), 1552 cm-1 (NO2); 1H NMR (600 MHz) δ 7.58-6.93 (20H,
m, PhH), 5.42 (1H, dd, J6,1 ) 12.2 Hz, J6,5 ) 8.3 Hz, H-6), 5.14
(1H, br ddd, J2,1 ) 2.0 Hz, J2,4 ) 1.3 Hz, J2,OH ) 8.9 Hz, H-2),
4.69, 4.61 (2H, 2 × d, JA,B ) 12.0 Hz, CH2Ph), 4.63 (1H, dd, J5,4
) 4.9 Hz, H-5), 4.58, 4.31 (2H, 2 × d, JA,B ) 10.7 Hz, CH2Ph),
4.35 (1H, d, J1′,1 ) 3.9 Hz, H-1′), 4.41 (1H, dd, H-4), 4.10, 3.99
(2H, 2 × d, Ja,b ) 11.3 Hz, H-3′), 3.09 (1H, ddd, H-1), 2.75 (1H,
d, H-1), 1.66, 1.36 (6H, 2 × s, C(CH3)2); 13C NMR (150 MHz) δ
137.7, 137.5, 135.0, 133.5, 130.4, 129.2, 129.1, 128.5, 128.3, 127.9,
127.8, 127.5, 127.4, 127.3, 111.0, 88.4, 77.4, 76.9, 76.6, 73.8,
68.3, 68.0, 65.3, 59.4, 41.61, 28.34, 25.80. Anal. Calcd for
C37H39O7NS2 (673.84): C, 65.95; H, 5.83; N, 2.08. Found: C,
65.98; H, 6.00; N, 2.20.
1L-(1,2,4,5/3(OH),6)-3,3′-Di-O-benzyl-1-C-bis(phenylthio)-
methyl-3-C-hydroxymethyl-4,5-O-isopropylidene-2-O-methoxy-
methyl-6-nitro-2,3,4,5-cyclohexanetetrol (14). To a solution of
isopropylidene derivative 13 (5.72 g, 8.49 mmol) in dry dichlo-
romethane (175 mL) were added dimethoxymethane (7.51 mL, 84.9
mmol) and P2O5 (300 mg) with continued stirring for 2 h at rt.
After the disappearance of 13 on TLC with 3:1 hexane-EtOAc,
the reaction mixture was poured into aq NaHCO3 solution, extracted
with CHCl3, washed with brine and water, dried over anhyd MgSO4,
and evaporated to give 14 (5.70 g, 93% yield), which was purified
on a column of silica gel with 4:1 hexane-EtOAc: colorless syrup;
[R]2D6 -100.3 (c 0.98, CHCl3); IR (KBr, neat) ν 1551 cm-1 (NO2);
1H NMR (600 MHz) δ 7.55-6.93 (20H, m, PhH), 5.46 (1H, dd,
1
-64.7 (c 0.98, CHCl3); IR (KBr, disk) ν 1560 cm-1 (NO2); H
NMR (600 MHz) δ 7.48-7.14 (20H, m, PhH), 5.83 (1H, d, J1,2
)
3.6 Hz, H-1), 5.06 (1H, dd, J5,6 ) 3.4 Hz, J6,6′ ) 14.7 Hz, H-6),
4.90 (1H, dd, J5,6′ ) 9.0 Hz, H-6′), 4.77 (1H, d, J4,5 ) 1.5 Hz,
H-4), 4.69 (1H, d, J5,5′ ) 3.6 Hz, H-5′), 4.61, 4.54 (2H, 2 × d, JA,B
) 11.5 Hz, CH2Ph), 4.59 (1H, d, H-2), 4.37, 4.29 (2H, 2 × d, JA,B
) 12.4 Hz, CH2Ph), 3.92, 3.50 (2H, 2 × d, Ja,b ) 10.8 Hz, H-3′),
3.64 (1H, dddd, H-5), 1.60, 1.34 (6H, 2 × s, C(CH3)2); 13C NMR
(150 MHz) δ 137.8, 137.2, 134.1, 133.5, 132.4, 130.2, 128.8, 128.7,
128.7, 128.1 × 2, 127.7, 127.4, 127.3, 127.2, 127.0 × 2, 112.5,
104.5, 87.0, 80.6, 79.9, 74.3, 73.1, 68.3, 66.2, 60.1, 40.5, 27.0, 26.4.
Anal. Calcd for C37H39O7NS2 (673.84): C, 65.95; H, 5.83; N, 2.08.
Found: C, 65.79; H, 5.85; N, 2.11.
1L-(1,2,3′,4,5/3,6)-3,3′-Di-O-benzyl-3-C-hydroxymethyl-6-ni-
tro-2,3,4,5,6-tetrahydroxycyclohexancarbaldehyde Bis(phen-
yldithio)acetal (12, E). A mixture of 10a (820 mg, 1.19 mmol) in
aq 85% acetic acid solution (30 mL) was stirred under reflux
conditions for 6 h. After the disappearance of starting compound
10a on TLC with 2:1 hexane-EtOAc, the reaction mixture was
evaporated to give crude 11. 11 was diluted with MeOH (15 mL),
and then NaHCO3 (200 mg) and water (5 mL) were added and the
solution was stirred at rt. After 8 h, the above reaction mixture
was neutralized with ion-exchange resin (Amberlite IR-120B (H+
form)), filtered off, and evaporated to give 12 (650 mg, 84% yield
from 10a), which was purified on a column of silica gel with 8:1
toluene-acetone: mp 113.0-114.5 °C (colorless prisms, ether-
hexane); [R]2D8 -74.7 (c 1.25, EtOH); IR (KBr, neat) ν 3417 (OH),
J6,1 ) 11.9 Hz, J6,5 ) 8.7 Hz, H-6), 5.01, 4.93 (2H, 2 × d, JA,B
)
6.3 Hz, CH2OCH3), 4.94 (1H, br d, J2,1 ) 1.7 Hz, H-2), 4.75, 4.54
(2H, 2 × d, JA,B ) 11.9 Hz, CH2Ph), 4.61, 4.39 (2H, 2 × d, JA,B
) 10.7 Hz, CH2Ph), 4.55 (1H, dd, J2,1 ) 5.3 Hz, H-5), 4.34
(1H, br d, J1′,1 ) 4.4 Hz, H-1′), 4.33 (1H, br d, H-4), 4.15, 3.93
(2H, 2 × d, Ja,b ) 11.0 Hz, H-3′), 3.41 (3H, s, OCH3), 3.13 (1H,
ddd, H-1), 1.62, 1.25 (6H, 2 × s, C(CH3)2). Anal. Calcd for
C37H39O7NS2 (673.84): C, 65.25; H, 6.04; N, 1.95. Found: C,
65.20; H, 5.98; N, 1.99.
1
1560 cm-1 (NO2); H NMR (600 MHz) δ 7.59-6.96 (20H, m,
PhH), 5.39 (1H, dd, J6,1 ) 11.7 Hz, J6,5 ) 10.3 Hz, H-6), 5.13
(1H, ddd, J2,1 ) 2.4 Hz, J2,4 ) 1.4 Hz, J2,OH ) 7.9 Hz, H-2), 4.63,
4.61 (2H, 2 × d, JA,B ) 12.0 Hz, CH2Ph), 4.45, 4.26 (2H, 2 × d,
JA,B ) 11.0 Hz, CH2Ph), 4.40 (1H, dd, J5,4 ) 3.4 Hz, J5,OH ) 10.0
Hz, H-5), 4.35 (1H, d, J1,1′ ) 4.1 Hz, H-1′), 4.17 (1H, ddd, J4,OH
)
7.4 Hz, H-4), 4.08, 4.04 (2H, 2 × d, Ja,b ) 11.5 Hz, H-3′), 3.45
(1H, d, 4-OH), 3.22 (1H, d, 2-OH), 3.13 (1H, ddd, H-1), 2.83 (1H,
d, 5-OH). Anal. Calcd for C34H35O7NS2 (633.78): C, 64.44; H,
5.57; N, 2.21. Found: C, 64.81; H, 5.87; N, 2.18.
1L-(1,2,4,5/3(OH),6)-3,3′-Di-O-benzyl-3-C-hydroxymethyl-4,5-
O-isopropylidene-2-O-methoxymethyl-6-nitro-2,3,4,5-tetrahy-
droxycyclohexanecarbaldehyde (15). To a solution of methoxy-
methyl ether derivative 14 (1.70 g, 2.37 mmol) in 70% CH3CN
aqueous solution (50 mL) was added N-bromosuccineimide (2.53
g, 14.2 mmol) with continued stirring for 10 min at rt. After the
disappearance of 14 on TLC with 2:1 hexane-EtOAc, the reaction
mixture was poured into aq sodium thiosulfate solution, extracted
with CHCl3, washed with brine and water, dried over anhyd MgSO4,
and evaporated to give 15 (1.105 g, 85% yield), which was purified
on a column of silica gel with 4:1 hexane-EtOAc: colorless syrup;
[R]2D5 -43.7 (c 0.64, CHCl3); IR (KBr, disc) ν 1726 (CdO), 1554
1L-(1,2,3′,4,5/3,6)-2,4,5,-Tri-O-acetyl-3,3′-di-O-benzyl-3-C-hy-
droxymethyl-6-nitro-2,3,4,5,-tetrahydroxycyclohexancarbal-
dehyde Bis(phenylthio)acetal (12′). To a solution of 12 (100 mg,
0.15 mmol) in Py (2 mL) were added acetic anhydrous (1 mL) and
a catalytic amount of DMAP then the solution was stirred at rt.
After 24 h, the reaction mixture was evaporated to give a residue.
The remaining residue was purified on a column of silica gel with
2:1 hexane-EtOAc to quantitatively give 12′ (115 mg): mp 63.0-
66.0 °C (colorless prisms, ether-hexane); [R]2D8 -49.8 (c 1.46,
EtOH); IR (KBr neat) ν 1758 (CdO), 1560 cm-1 (NO2); 1H NMR
(200 MHz) δ 7.60-6.89 (20H, m, PhH), 6.18 (1H, d, J2,1 ) 1.5
Hz, H-2), 5.94 (1H, d, J4,5 ) 1.7 Hz, H-4), 5.62 (2H, m, J5,6 ) J6,1
) 11.0 Hz, H-5, H-6), 4.71, 4.59 (2 H, 2 × d, JA,B ) 11.0 Hz,
CH2Ph), 4.51, 4.30 (2H, 2 × d, JA,B ) 11.7 Hz, CH2Ph), 4.13 (1H,
1
cm-1 (NO2); H NMR (600 MHz) δ 9.57 (1H, s, CHO), 7.39-
7.25 (10H, m, PhH), 5.00 (1H, dd, J6,1 ) 11.9 Hz, J6,5 ) 8.8 Hz,
H-6), 4.78, 4.50 (2H, 2 × d, JA,B ) 6.9 Hz, CH2OCH3), 4.70 (2H,
s, CH2Ph), 4.69 (1H, dd, J2,1 ) 2.1 Hz, J2,4 ) 1.5 Hz, H-2), 4.64,
4.53 (2H, 2 × d, JA,B ) 11.7 Hz, CH2Ph), 4.44 (1H, dd, J5,4 ) 5.2
1240 J. Org. Chem., Vol. 73, No. 4, 2008

Total Synthesis of Optically ActiVe Tetrodotoxin
Hz, H-5), 4.26 (1H, dd, H-4), 4.03, 3.88 (2H, 2 × d, Ja,b ) 11.2
Hz, H-3′), 3.62 (1H, dd, H-1), 3.20 (3H, s, OCH3), 1.58, 1.33 (6H,
2 × s, C(CH3)2). Anal. Calcd for C27H33O9N (515.55): C, 62.90;
H, 6.45; N, 2.72. Found: C, 62.67; H, 6.40; N, 2.53.
4.63, 4.59 (2H, 2 × d, JA,B ) 6.4 Hz, CH2OCH3), 4.61 (1H, dd,
J3,2 ) 6.2 Hz, H-3), 4.42 (1H, d, H-2), 4.14, 4.01 (2H, 2 × d, JA,B
) 10.9 Hz, H-4′), 4.02 (1H, dd, J6′a,6 ) 5.0 Hz, J6′a,6′b ) 10.6 Hz,
H-6′a), 3.95 (1H, dd, J6b′,6 ) 10.0 Hz, H-6′b), 3.34 (1H, ddd, H-6),
3.22 (3H, s, OCH3), 1.37, 1.36 (6H, 2 × s, C(CH3)2), 1.04 (9H, s,
C(CH3)3). Anal. Calcd for C43H52O8Si (724.95): C, 71.24; H, 7.23.
Found. C, 71.25; H, 7.13.
1D-(1,2,4,5/3(OH),6)-3,3′-Di-O-benzyl-3,5-di-C-hydroxymethyl-
1,2-O-isopropylidene-4-O-methoxymethyl-6-nitro-1,2,3,4-cyclo-
hexanetetrol (16). To a solution of aldehyde 15 (1.105 mg, 2.14
mmol) in methanol (50 mL) was added NaBH4 (269 mg, 7.10
mmol) with continued stirring at rt for 1 h. After the disappearance
of 15 on TLC with 2:1 hexane-EtOAc, the reaction mixture was
poured into aq NaHCO3 solution, extracted with EtOAc, washed
with brine and water, dried over anhyd MgSO4, and evaporated to
give 16 (1.076 g, 97% yield), which was purified on a column of
silica gel with 4:1 hexane-EtOAc: colorless syrup; [R]2D8 +3.29
(c 1.03, CHCl3); IR (KBr, neat) ν 3444 (OH), 1552 cm-1 (NO2);
1H NMR (600 MHz) δ 7.39-7.26 (10H, m, PhH), 4.83, 4.66 (2H,
2 × d, JA,B ) 6.3 Hz, CH2OCH3), 4.71 (1H, dd, J6,5 ) 11.2 Hz,
J6,1 ) 10.0 Hz, H-6), 4.72, 4.62 (2H, 2 × d, JA,B ) 11.2 Hz,
CH2Ph), 4.66 (1H, dd, J1,2 ) 4.9 Hz, H-1), 4.62, 4.54 (2H, 2 × d,
JA,B ) 11.7 Hz, CH2Ph), 4.37 (1H, dd, J4,5 ) 2.3 Hz, J4,2 0.9 Hz,
H-4), 4.27 (1H, dd, H-2), 4.02, 3.85 (2H, 2 × d, Ja,b ) 10.9 Hz,
H-3′), 3.67 (1H, ddd, J5,5′a ) 9.7 Hz, J5′a,5′b ) 11.7 Hz, H-5′a),
3.43 (3H, s, OCH3), 3.52 (1H, ddd, J5,5′b ) 4.9 Hz, H-5′b), 3.02
(1H, dd, JOH,5′a ) 6.6 Hz, J5,5′b ) 7.4 Hz, OH), 2.70 (1H, dddd,
H-5), 1.52, 1.32 (6H, 2 × s, C(CH3)2). Anal. Calcd for C27H35O9N
(517.57): C, 62.66; H, 6.82; N, 2.71. Found: C, 62.37; H, 7.06;
N, 2.63.
1D-(1,2,4,5/3(OH),6)-3,3′-Di-O-benzyl-5′-O-tert-butyldiphenyl-
silyl-3,5-di-C-hydroxymethyl-1,2-O-isopropylidene-4-O-meth-
oxymethyl-6-nitro-1,2,3,4-cyclohexanetetrol (17). To a solution
of hydroxymethyl derivative 16 (906 mg, 1.80 mmol) in dichlo-
romethane (30 mL) were added tert-butyldiphenylsilyl chloride (554
µL, 2.16 mmol) and imidazole (220 mg, 3.24 mmol) with continued
stirring for 2 h at rt. After the disappearance of 16 on TLC with
2:1 hexane-EtOAc, the reaction mixture was poured into aq
NaHCO3 solution, extracted with CHCl3, washed with brine and
water, dried over anhyd MgSO4, and evaporated to give 17 (1.26
g, 95% yield), which was purified on a column of silica gel with
5:1 hexane-EtOAc: colorless syrup; [R]2D5 -41.7 (c 0.1, CHCl3);
IR (KBr, neat) ν 1556 cm-1 (NO2); 1H NMR (600 MHz) δ 7.59-
7.24 (20H, m, PhH), 4.77, 4.60 (2H, 2 × d, JA,B )11.0 Hz,
CH2Ph), 4.77-4.60 (4H, m, CH2OCH3, H-1, H-6), 4.66, 4.56 (2H,
2 × d, JA,B ) 12.0 Hz, CH2Ph), 4.50 (1H, br d, J4,5 ) 1.7 Hz,
H-4), 4.37 (1H, dd, J2,1 ) 3.8 Hz, H-2), 4.07, 3.93 (2H, 2 × d, Ja,b
) 10.8 Hz, H-3′), 3.74 (1H, dd, J5′a,5 ) 10.0 Hz, J5′a,5′b ) 10.3 Hz,
H-5′a), 3.49 (1H, dd, J5′b,5 ) 5.2 Hz, H-5′b), 3.27 (3H, s, OCH3),
2.76 (1H, dddd, J5,6 ) 11.5 Hz, H-1), 1.48, 1.33 (6H, 2 × s,
C(CH3)2), 1.01 (9H, s, C(CH3)3). Anal. Calcd for C43H53NO9Si
(755.97): C, 68.32; H, 7.07; N, 1.85. Found. C, 68.39; H, 6.78; N,
2.15.
2D-(2,3,5,6/4(OH))-6′-O-tert-butyldiphenylsilyl-4,6-di-C-hy-
droxymethyl-2,3:4,4′-di-O-isopropylidene-5-O-methoxymethyl-
2,3,4,5-tetrahydroxycyclohexane (19). A solution of carbonyl
derivative 17 (1.04 g, 1.47 mmol) (120 mg, 0.21 mmol) in THF
(41 mL) was hydrogenated in the presence of a catalytic amount
of 20% Pd(OH)2-C (ca. 500 mg) under hydrogen at 50 °C for 2
h. After the disappearance of starting compound 18 on TLC with
2:1 hexane-EtOAc, catalyst was filtered off, and the solution was
evaporated to give a colorless syrup. Subsequently this syrup was
dissolved in dichloromethane (5 mL), and next, 2,2-dimethoxypro-
pane (75 µL, 0.602 mmol) and p-toluenesulfonic acid monohydrate
(1 mg, 6.02 µmol) were added with stirring for 1 h at rt. After the
disappearance of starting compound on TLC with 2:1 hexane-
EtOAc, the reaction mixture was diluted with CHCl3, washed with
aq NaHCO3 solution, and brine wand water, dried over anhyd
MgSO4, and evaporated to give corresponding acetonide 19 (620
mg, 79% yield), which was purified on a column of silica gel with
3:1 hexane-EtOAc: colorless syrup; [R]2D6 +17.0 (c 0.83, CHCl3);
IR (KBr, neat) ν 1732 cm-1 (CdO); 1H NMR (600 MHz) δ
7.65-7.34 (10H, m, PhH), 4.62, 4.54 (2H, 2 × d, JA,B ) 6.7 Hz,
CH2OCH3), 4.44 (1H, dd, J3,2 ) 6.0 Hz, J3,5 ) 1.9 Hz, H-3), 4.43,
4.35 (2H, 2 × d, Ja,b ) 9.6 Hz, H-4′), 4.40 (1H, d, H-2), 4.37 (1H,
dd, J5,6 ) 2.1 Hz, H-5), 4.01 (1H, dd, J6′a,6 ) 4.8 Hz, J6′a,6′b ) 11.0
Hz, H-6′a), 3.93 (1H, dd, J6b′,6 ) 10.3 Hz, H-6′b), 3.30 (3H, s,
OCH3), 3.28 (1H, ddd, H-6), 1.51, 1.50, 1.36, 1.34 (12H, 4 × s,
C(CH3)2), 1.04 (9H, s, C(CH3)3). Anal. Calcd for C32H44O8Si
(584.77): C, 65.73; H, 7.58. Found. C, 65.79; H, 7.33.
1D-(1,2,3,5,6/4(OH))-6′-O-tert-butyldiphenylsilyl-1′-C-dichlo-
romethyl-4,6-di-C-hydroxymethyl-2,3:4,4′-di-O-isopropylidene-
5-O-methoxymethyl-1,2,3,4,5-cyclohexanepentol (20). [R]D26
-24.8 (c 0.91, CHCl3).
1D-(1,2,3,5,6/4(OH))-1′-Azido-6′-O-tert-butyldiphenylsilyl-4,6-
di-C-hydroxymethyl-2,3:4,4′-di-O-isopropylidene-5-O-methoxy-
methyl-2,3,4,5-tetrahydroxycyclohexanecarbaldehyde
(22).
[R]2D6 -62.7 (c 1.07, CHCl3).
1D-(1,2,3,4,5/3(OH),6)-6-Azido-5′-O-tert-butyldiphenylsilyl-6′-
C-[2(S)-hydroxycyanomethyl]-3,5-di-C-hydroxymethyl-1,2:3,3′-
di-O-isopropylidene-4-O-methoxymethyl-1,2,3,4-cyclohexane-
tetrol (23). [R]2D6 -0.60 (c 1.01, CHCl3).
1D-(1,2,3,4,5/3(OH),6)-6-Azido-5′-O-tert-butyldiphenylsilyl-6′-
C-[2(R)-hydroxycyanomethyl]-3,5-di-C-hydroxymethyl-1,2:3,3′-
di-O-isopropylidene-4-O-methoxymethyl-1,2,3,4-cyclohexane-
tetrol (23a). [R]2D6 +29.4 (c 1.01, CHCl3).
1D-(1,2,3,4,5/3(OH),6)-6-azido-5′-O-tert-butyldiphenylsilyl-6′-
C-[2(S)-hydroxycyanomethyl]-3,5-di-C-hydroxymethyl-1,2:3,3′-
di-O-isopropylidene-4,6′-di-O-methoxymethyl-1,2,3,4-cyclohex-
anetetrol (24). [R]2D6 -3.61 (c 0.95, CHCl3).
1D-(1,2,4,5/3(OH),6(N3))-6-Azido-5′-O-tert-butyldiphenylsilyl-
1,2:3,3′-di-O-isopropylidene-4-O-methoxymethyl-6-C-(S)-(6′-
formyl-6′-methoxymethoxymethyl)-3,5-di-C-hydroxymethylcy-
clohexane-1,2,3,4-tetrol (25). [R]2D6 +49.3 (c 1.21, CHCl3).
1D-(1,2,4,5/3(OH),6(N3))-6-Azido-5′-O-tert-butyldiphenylsilyl-
1,2:3,3′-di-O-isopropylidene-6-C-(S)-(6′-formyl-6′-meth-
oxymethoxymethyl)-3,5-di-C-hydroxymethylcyclohexane-1,2,3,4-
tetrol 6′′,4-Lactone (26). [R]2D6 -57.9 (c 0.33, CHCl3).
1D-(1,2,4,5/3(OH),6(N3))-6-Amino-5′-O-tert-butyldiphenylsilyl-
1,2:3,3′-di-O-isopropylidene-6-C-(S)-(6′-formyl-6′-meth-
oxymethoxymethyl)-3,5-di-C-hydroxymethylcyclohexane-1,2,3,4-
tetrol 6′′,4-Lactone (27). [R]2D6 -53.5 (c 0.73, CHCl3).
1D-(1,2,4,5/3(OH),6(NH2))-6-Amino-1,2:3,3′-di-O-isopro-
pylidene-6-C-(S)-6′-methoxymethoxymethyl-3,5-di-C-hydroxy-
2D-(2,3,5,6/4(OH))-4,4′-Di-O-benzyl-6′-O-tert-butyldiphenyl-
silyl-4,6-di-C-hydroxymethyl-2,3-O-isopropylidene-5-O-meth-
oxymethyl-2,3,4,5-tetrahydroxycyclohexanone (18). To a solution
of silylether derivative 17 (1.10 g, 1.46 mmol) in dry toluene (30
mL) was added potassium tert-butoxide (327 mg, 2.92 mmol) with
continued stirring at rt. After 30 min, O3 gas was babbled into the
reaction mixture for 10 min at -78 °C. After the disappearance of
17 on TLC with hexane-EtOAc (3:1 v/v), acetic acid (550 µL)
and zinc powder (550 mg) were added to the above mixture, which
was then warmed to rt. The above reaction mixture was poured
into aq NaHCO3 solution, extracted with EtOAc, washed with brine
and water, dried over anhyd MgSO4, and evaporated to give
carbonyl compound 18 (817 mg, 79% yield), which was purified
on a column of silica gel with 5:1 hexane-EtOAc: colorless syrup;
[R]2D5 +1.38 (c 0.32, CHCl3); IR (KBr, neat) ν 1732 cm-1 (CdO);
1H NMR (500 MHz) δ 7.65-7.24 (20H, m, PhH), 4.88, 4.73 (2H,
2 × d, JA,B ) 10.7 Hz, CH2Ph), 4.71 (1H, dd, J5,6 ) 2.4 Hz, J5,3
) 10.7 Hz, H-5), 4.69, 4.58 (2H, 2 × d, JA,B ) 11.9 Hz, CH2Ph),
J. Org. Chem, Vol. 73, No. 4, 2008 1241

Sato et al.
methylcyclohexane-1,2,3,4-tetrol 6′′,4-Lactone (28). [R]2D6 +25.0
(c 0.3, CHCl3).
Hashimoto, Professor Emeritus of Tokyo Institute of Technol-
ogy, for helpful discussions. This work was partially supported
by a “Science Frontier Project of Kanagawa University” and
Grants-in-Aid for Scientific Research (No. 19750147) from the
Ministry of Education, Science, Sports and Culture, Japan.
1D-(1,2,4,5/3(OH),6(NH))-6-N-[N,N′-bis-(tert-buthoxycarbon-
yl)guanidino]-1,2:3,3′-di-O-isopropylidene-6-C-(S)-(6′-meth-
oxymethoxymethyl)-3,5-di-C-hydroxymethylcyclohexane-1,2,3,4-
tetrol 6′′,4-Lactone (29). [R]2D5 +1.54 (c 0.86, CDCl3).
(-)-4,9-Anhydro-epi-TTX (1a). [R]2D8 +1.2 (c 0.18, 3% AcOH).
(-)-Tetrodotoxin (1). [R]2D8 -3.75 (c 0.13, 3% AcOH);
Supporting Information Available: Experimental details and
analytical and spectral characterization data, sa well as copies of
1H and 13C NMR. This material is available free of charge via the
Internet at http://pubs.acs.org.
Acknowledgment. The authors thank Dr. T. Nakagawa,
Professor Emeritus of Yokohama City University, and Dr. H.
JO701655V
1242 J. Org. Chem., Vol. 73, No. 4, 2008