The first synthesis of herbicidin B. stereoselective construction of the tricyclic undecose moiety by a conformational restriction strategy using steric repulsion between adjacent bulky silyl protecting groups on a pyranose ring

Article abstract of DOI:10.1021/ja992608h

The first total synthesis of the nucleoside antibiotic herbicidin B (1b) was achieved, where a novel aldol-type C-glycosidation reaction promoted by samarium diiodide (SmI₂) was used as a key step. Treatment of methyl 3,4-O-(1,1,3,3-tetraisopro

Full text of DOI:10.1021/ja992608h

10270
J. Am. Chem. Soc. 1999, 121, 10270-10280
The First Synthesis of Herbicidin B. Stereoselective Construction of
the Tricyclic Undecose Moiety by a Conformational Restriction
Strategy Using Steric Repulsion between Adjacent Bulky Silyl
Protecting Groups on a Pyranose Ring†
Satoshi Ichikawa, Satoshi Shuto, and Akira Matsuda*
Contribution from the Graduate School of Pharmaceutical Sciences, Hokkaido UniVersity, Kita-12, Nishi-6,
Kita-ku, Sapporo 060-0812, Japan
ReceiVed July 22, 1999
Abstract: The first total synthesis of the nucleoside antibiotic herbicidin B (1b) was achieved, where a novel
aldol-type C-glycosidation reaction promoted by samarium diiodide (SmI2) was used as a key step. Treatment
of methyl 3,4-O-(1,1,3,3-tetraisopropyl-1,3-disiloxanediyl)-1-phenylthio-2-ulos-â-D-glucuronate (13) with SmI2
in THF regioselectively gave the corresponding 1-enolate, which was readily trapped with 1-â-D-xylosyladenine
5′-aldehyde derivative 7 to afford the product 19a,b as an anomeric mixture. Dehydration of the 5′-hydroxyl
in 19a,b with using Burgess’s inner salt gave the enone 20, which was subsequently hydrogenated to give
undeculofuranuronyl adenine derivative 21. Deprotection of 21 gave a tricyclic sugar nucleoside, 23. However,
it was an epimer of herbicidin B at the 6′-position. Construction of the desired 6′-R-configuration was achieved
by using a conformational restriction strategy based on repulsion between adjacent bulky protecting groups on
the pyranose ring. Thus, when methyl 3-O-tert-butyldimethylsilyl-4-O-tert-butyldiphenylsilyl-1-phenylthio-
1
2-ulos-D-glucuronate (29c), the conformation of which was restricted in an unusual C4-like conformation,
was used as a precursor for ulose 1-enolate in the SmI2-promoted aldol reaction with 7, the desired 6′-R-aldol
product 30c was predominantly obtained. Compound 30c was dehydrated, followed by hydrogenation of the
alkenyl bond and then deprotection to form an internal ketal linkage between the 3′- and 7′-positions, which
spontaneously gave herbicidin B.
Introduction
Nucleoside antibiotics are fascinating compounds that show
a variety of biological activities.1 They are not only used as
medicines, lead compounds for the development of drugs, and
biological tools but are also important as total synthetic targets.2
Herbicidins (1a-f),3 aureonucleomycin (2),4 and S12245 (3),5
a series of adenine nucleoside antibiotics that have the same
backbone structure (Figure 1), have been isolated from strains
of Streptomyces. Herbicidin A (1a) and B (1b), as well as
aureonuclemycin (2), efficiently inhibit the growth of Xan-
thomonas oryzae, which causes rice leaf blight, and are also
selectively toxic toward dicotyledon. These compounds have
some interesting structural features: (1) adenine is glycosylated
* To whom correspondence and reprint requests should be addressed.
Phone: +81-11-706-3228. Fax: +81-11-706-4980. E-mail: matuda@
pharm.hokudai.ac.jp.
Figure 1. Structures of herbicidins.
† This paper constitutes Part 190 of Nucleosides and Nucleotides. For
part 189 in the series, see: Naka, T.; Nishizono, N.; Minakawa, N.; Matsuda,
A. Tetrahedron Lett. 1999, 40, 6297-6300.
at the 1â-position of an unusual sugar, undecose, which has a
tricyclic furano-pyrano-pyran structure; (2) there is an internal
hemiketal linkage between the C-3′- and -7′-positions which
forms a trans junction for a pyrano-pyran ring; and (3) all of
the substituents at the C-7′-, -8′-, -9′-, and -10′-positions on the
second pyranose are fixed in axial positions due to the tricyclic
structure of the undecose. Although considerable effort has been
devoted to the total synthesis of herbicidins because of their
unique and complex structures,6,7 none of these attempts has
yet been successful.
(1) (a) Isono, K. J. Antibiot. 1988, 41, 1711-1739. (b) Isono, K.
Pharmacol. Ther. 1991, 52, 296-286.
(2) Knapp, S. Chem. ReV. 1995, 95, 1859-1876.
(3) (a) Arai, M.; Haneishi, T.; Kitahara, N.; Enokita, R.; Kawakubo, K.;
Kondo, Y. J. Antibiot. 1976, 29, 863-869. (b) Haneishi, T.; Terahara, A.;
Kayamori, H.; Yabe, J.; Arai, M. J. Antibiot. 1976, 29, 870-875. (c)
Taguchi, Y.; Yoshikawa, H.; Terahara, A.; Torikata, A.; Terao, M. J.
Antibiot. 1979, 32, 857-861. (d) Takiguchi, Y.; Yoshikawa, H.; Terahara,
A. J. Antibiot. 1979, 32, 862-867. (e) Terahara, A.; Haneishi, T.; Arai, M.
J. Antibiot. 1982, 35, 1711-1714.
(4) Dai, X.; Li, G.; Wu, Z.; Lu, D.; Wang, H.; Li, Z.; Zhou, L.; Chen,
X.; Chen, W. Chem. Abstr. 1989, 111, 230661f.
In this paper, we describe the synthesis of herbicidin B (1b),
(5) Tsuzuki, M.; Suzuki, G. Chem. Abstr. 1988, 109, 53206x.
in which a novel samarium diiodide (SmI2)-promoted aldol-
10.1021/ja992608h CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/16/1999

Total Synthesis of Herbicidin B
J. Am. Chem. Soc., Vol. 121, No. 44, 1999 10271
Scheme 1
Scheme 2
type C-glycosidation reaction with 1-phenylthio-2-ulose deriva-
tives, as a precursor for generating ulose-1-enolate,8 is ef-
fectively used as a key step. This is the first total synthesis of
a herbicidin congener.
Results and Discussion
derivative is possible by SmI2-promoted reductive cleavage of
a C-S bond at the anomeric position,9 (3) substrates such as
nucleoside 5′-aldehydes, which are unstable under basic and/or
acidic conditions,10 can be used, since the reaction proceeds
under neutral conditions at -78 °C, and (4) the reaction gives
the corresponding R-C-glycosides as a major product in high
yields. Based on these findings, we expected that the 6′-R-aldol
product 5 could be obtained by the SmI2-promoted condensation
reaction between 6 and 7.
Retrosynthetic Analysis and Strategy. Our retrosynthetic
analysis and synthetic strategy for herbicidin B (1b) are shown
in Scheme 1. Herbicidin B can be considered the equivalent of
a ring-opened 7′-keto compound, 4, and appropriate protection
of the hydroxyl groups and the introduction of a hydroxyl group
at the C-5′ of 4 leads to aldol product 5. This aldol product 5
is then retrosynthetically disassembled by an aldol-type reaction
to the phenylthioulose 6 as a precursor of enolate and 1-â-D-
xylosyladenine 5′-aldehyde derivative 7 as an acceptor. Com-
pounds 6 and 7 can be synthesized from D-glucose and
adenosine, respectively.
In this retrosynthetic analysis and synthetic strategy, the
following two steps are considered key steps: (a) formation of
the tricyclic structure with the desired stereochemistry, namely
6′-R-(6′,7′-trans)-configuration, in the second pyranose ring in
which the substituents at the C-8′-, -9′-, and -10′-positions are
all in axial positions, and (b) a stereoselective C-glycosidation
which gives the 6′-R-configuration by an aldol-type reaction
between a ulose derivative and an adenine nucleoside 5′-
aldehyde. In the former step, we expected that spontaneous
cyclization by the formation of a ketal linkage between the 3′-
and 7′-positions would be achieved in a stereoselective manner
to give the desired herbicidin B when the protecting groups of
the hydroxyls are removed. In the latter step, we planned to
use a SmI2-promoted aldol-type C-glycosidation reaction, which
we recently developed (Scheme 2).8 This reaction is very useful
because (1) phenylthio-2-ulose derivatives, the precursor for
generating enolates, are stable and easy to prepare, (2) regi-
oselective enolization at the anomeric position of the ulose
Preparation of the 1-Phenylthio-2-ulose Unit. We first
selected 13 as a precursor for ulose 1-enolate, in which the 3,4-
trans hydroxyls were protected by a 1,1,3,3-tetraisopropyldisi-
loxane (TIPDS) group. Scheme 3 shows its preparation.
Protection of the 4- and 6-hydroxyls of phenyl 1-thio-â-D-
glucoside (8) by a TIPDS group, followed by acid-catalyzed
(9) Gallagher et al. reported that the generation of the 1-enolate was
successful when 3,6-anhydro-ulose A was used as a substrate. Compound
B was further glycosylated with adenine to give nucleoside derivative D.
However, hydrolysis of the 8′,11′-ether linkage on D was unsuccessful;
see ref 7c.
(6) (a) Beader, J. R.; Dewis, M. L.; Whiting, D. A. J. Chem. Soc., Perkin
Trans. 1 1995, 227-233. (b) Fairbanks, A. J.; Perrin, E.; Sinay, P. Synlett
1996, 679-681. (c) Emery, F.; Vogel, P. J. Org. Chem. 1995, 60, 5843-
5854. (d) Emery, F.; Vogel, P. Tetrahedron Lett. 1994, 34, 4209-4212.
(7) (a) Binch, H. M.; Griffin, A. M.; Gallagher, T. Pure Appl. Chem.
1996, 68, 589-592. (b) Newcombe, N. J.; Mahon, M. F.; Molloy, K. C.;
Alker, D.; Gallagher, T. J. Am. Chem. Soc. 1993, 115, 6430-6431. (c)
Binch, H. M.; Gallagher, T. J. Chem. Soc., Perkin Trans. 1 1996, 401-
402.
(8) Ichikawa, S.; Shuto, S.; Matsuda, A. Tetrahedreon Lett. 1998, 39,
4525-4528. SmI2-promoted C-glycosidation reaction with mannosyl py-
ridylsulfones as substrates were also reported: Jarreton, O.; Skrydstrup,
T.; Beau J.-M. Tetrahedron Lett. 1997, 38, 1767-1770.
(10) Gallagher et al. tried to prepare an aldol condensation product
between A (footnote 9) and adenosine 5′-aldehyde derivative which was
almost the same as 7, but this was unsuccessful due to the instability of
adenosine 5′-aldehyde under the basic conditions used. Therefore, reductive
coupling using ulosyl bromides as enolates was developed. However, ulosyl
bromides are not very stable, and the substrates that can be synthesized are
limited: Binch, H. M.; Griffin, A. M.; Schwidetzky, S.; Ramsay, M. V. J.;
Gallagher, T.; Lichtenthaler, F. W. J. Chem. Soc., Chem. Commun. 1995,
967-968.

10272 J. Am. Chem. Soc., Vol. 121, No. 44, 1999
Ichikawa et al.
Scheme 3a
Scheme 4a
a Reagents: (a) TIPDSCl2, pyridine; (b) p-TsOH, DMF; (c) TrCl,
pyridine; (d) Cl3COCl; (e) TFA, CH2Cl2; (f) DCC, TFA, DMSO; (g)
PDC, MeOH, DMF; (h) K2CO3, MeOH; (i) (COCl)2, DMSO, Et3N,
CH2Cl2.
isomerization,11 gave 9 in 59% yield in two steps. After
protection of the 2-hydroxyl of 9 by a trichloroacetyl group, it
was successively treated by Moffatt oxidation conditions and
PDC in the presence of MeOH12 to give methyl ester derivative
11 in 61% yield. Removal of the trichloroacetyl group at the
2-position of 11 with K2CO3/MeOH, followed by Swern
oxidation of the resulting secondary alcohol, gave 1-phenylthio-
2-ulose derivative 13 in excellent yield. The compound 13 was
sufficiently stable to be purified by silica gel column chroma-
tography.
a Reagents: (a) TrCl, pyridine; (b) CrO3, pyridine, Ac2O, 4-Å
molecular sieves, CH2Cl2; (c) NaBH4, AcOH; (d) TBSCl, imidazole;
(e) BzCl, pyridine; (f) TFA, CH2Cl2; (g) Dess-Martin periodinane,
CH2Cl2.
Scheme 5
Preparation of the 1-â-D-Xylosyladenine 5′-Aldehyde Unit.
1-â-D-Xylosyladenine 5′-aldehyde derivative 7 was prepared as
shown in Scheme 4. After the 5′-primary hydroxyl of 2′-O-
methyladenosine 14 (prepared by a known method13) was
protected by a triphenylmethyl (Tr) group, the 3′-hydroxyl was
inverted by a successive oxidation-reduction procedure with
CrO3/Ac2O/pyridine and NaBH4/AcOH systems14 to give xy-
lonucleoside 16 in 78% yield. Protection of the resulting 3′-
hydroxyl and 6-amino groups of 16 with tert-butyldimethysilyl
(TBS) and benzoyl groups, respectively, by usual procedures
gave 17 in 83% yield. Removal of the Tr group of 17 under
acidic conditions, followed by oxidation with Dess-Martin
periodinane, gave 7, an acceptor of the aldol reaction. The
aldehyde 7 was used for the next reaction without further
purification because of its instability.
Synthesis of 6′-epi-Herbicidin B Using a SmI2-Promoted
Aldol-Type C-Glycosidation Reaction as a Key Step. We
examined the SmI2-promoted aldol-type C-glycosidation reaction
with 13 and 7 (Scheme 5). When a solution of 13 in THF was
added dropwise to a stirring solution of SmI2 (2.0 equiv) in
THF at -78 °C, the corresponding samarium 1-enolate was
successfully generated, to which a solution of 7 (1.0 equiv) in
THF was added to give the desired aldol products in 75% yield
as an anomeric mixture (19a/19b ) 79/21). NOE experiments
of the mixture revealed their 6′-stereochemistries; correlation
between H-6′ and H-9′ for the R-anomer 19a and correlations
between H-6′ and H-8′, and between H-6′ and H-10′, for the
â-anomer 19b were observed (Figure 2).15
Radical deoxygenation of the 5′-hydroxyl group of the
anomeric mixture 19a,b via the corresponding 5′-O-methyl
oxalate16 or 5′-thiocarbonylimidazolidate17 was tried but was
(15) The 5′-configurations of 19a and 19b were suggested to be 5′R and
5′S, respectively, on the basis of the possible six-membered-ring chelation
transition state in the SmI2-mediated aldol reaction. In fact, the 5′R-
configuration of 19a was confirmed as shown below. During the treatment
of 19a with SmI2 in MeOH, an isomerization of the configuration at the
6′-position was observed.
(16) (a) Matsuda, A.; Takenuki, K.; Itoh, H.; Sasaki, T.; Ueda, T. Chem.
Pharm. Bull. 1987, 35, 3967-3970. (b) Matsuda, A.; Takenuki, K.; Sasaki,
T.; Ueda, T. J. Med. Chem. 1991, 34, 235-239. (c) Dolan, S. C.; MacMillan,
J. J. Chem. Soc., Chem. Commun. 1985, 1588-1589.
(11) van Boeckel, C. A. A.; van Boom, J. H. Tetrahedron 1985, 41,
4545-4555.
(12) Garegg, P. J.; Olsson, L.; Oscarson, S. J. Org. Chem. 1995, 60,
2200-2204.
(13) Yano, J.; Kan, L. S.; Ts’o, P. O. P. Biochim. Biophys. Acta 1980,
629, 178-183.
(14) Robins, M. J.; Samano, V.; Johnson, M. D. J. Org. Chem. 1990,
55, 410-412.

Total Synthesis of Herbicidin B
J. Am. Chem. Soc., Vol. 121, No. 44, 1999 10273
Figure 3. Structure determination of 6′-epi-herbicidin B (23) by NOE
experiments.
enone 20 in 49% yield as a mixture of inseparable isomers due
to a cis/trans geometry at the 5′-position. The enone 20 was
hydrogenated with H2 in the presence of palladium-on-carbon
in EtOAc to give 21 quantitatively, the anomeric configuration
of which was determined to be the undesired â by NOE
experiments; correlations between H-6′ and H-8′, and between
H-6′ and H-10′, were observed.20 However, we expected that
isomerization at the 6′-position, which was adjacent to the 7′-
carbonyl, into the desired R-configuration might occur in the
following stages.
Figure 2. Determination of stereochemistry at the 6′-position of 19a
and 19b by NOE experiments.
Scheme 6a
Therefore, removal of the protecting groups was examined
next. When 21 was treated with NaOMe or K2CO3 in MeOH
to remove the benzoyl group at the N6-position, it decomposed
and did not give any of the debenzoylated 22. However,
exposure of 21 to samarium and I2 in MeOH21 successfully gave
the debenzoylated product 22. When 22 was treated with
tetrabutylammonium fluoride (TBAF) in THF, all of the silyl
protecting groups were removed simultaneously to give a
tricyclic sugar product by spontaneously forming an internal
ketal linkage between the 3′- and 7′-positions, as expected.
However, the product was not herbicidin B, but rather 6′-epi-
herbicidin B (23), an epimer of herbicidin B at the 6′-position.
The structure of 23 was confirmed by 1H NMR and NOE
experiments. As shown in Figure 3, the coupling constants, J8′,9′
9′
) J9′,10′ ) 9.5 Hz, suggested its C6′-structure, and NOE
correlations between H-6′ and H-8′, H-8′ and H-10′, and H-9′
and H-8 at the adenine moiety suggested a â-configuration at
the 6′-position. Although isomerization of 23 into herbicidin B
was investigated by treating it under acidic and basic conditions,
such isomerization was not observed.22
Conformation-Flip Strategy. Based on the above results,
we recognized that it would be essential to provide the 6′-R-
C-glycosidic structure before forming the 3′,7′-ketal linkage to
construct the desired tricyclic structure of the sugar moiety of
herbicidin B. Therefore, stereoselective hydrogenation from the
R-face of the 5′,6′-alkenyl bond in the enone system was
required. The 1H NMR spectrum of 20 showed that the
substituents at 8′, 9′, and 10′ were in equatorial positions; both
a Reagents: (a) MeO2CNSO2NEt3, toluene; (b) H2, Pd/C, EtOAc;
(c) Sm, I2, MeOH; (d) TBAF, THF.
unsuccessful.18 We next sought to dehydrate it by elimination
of the 5′-hydroxy of 19a,b, followed by hydrogenation of the
resulting alkenyl bond. Thus, 19a,b was converted to the
corresponding 5′-O-mesylate and -triflate. However, treatment
of these 5′-O-sulfonates with a base led only to their decom-
position, and the desired elimination product 20 was not
obtained. On the other hand, as shown in Scheme 6, when 19a,b
was treated with MeO2CNSO2NEt3 (Burgess’s inner salt)19 in
toluene, the desired elimination reaction proceeded to give the
(19) Burgess, E. M.; Penton, H. R.; Taylar, E. A. J. Org. Chem. 1973,
38, 26-31.
(20) 1H NMR analysis of the reaction mixture suggested that the
hydrogenation product was a mixture of anomers, and the R-anomer readily
isomerized during the workup to give the â-anomer as the sole product.
(21) Yanada, R.; Negoro, N.; Bessho, K.; Yanada, K. Synlett 1995,
1261-1263.
(22) Molecular modeling of both herbicidin B (1b) and its 6′-epimer 23
was carried out using Macromodel (version 4.5) software. Preferred
conformations were determined from the results of Monte Carlo conformer
searches starting from previously minimized structures of the two com-
pounds. Minimization employed the MM2* force field. Sets of conformers
close to minimum were found for 1b and 23, respectively. The minimum-
energy conformation for 23 was consistent with that suggested from the
coupling constants and NOE relationships of 23. The minimum-energy
conformer of 6′-epi-herbicidin B (23) was approximately 3.0 kcal/mol more
stable than that of herbicidin B.
(17) Pankiewicz, K.; Matsuda, A.; Watanabe, K. A. J. Org. Chem. 1982,
47, 485-488.
(18) It has been reported that deoxygenation of the 5-hydroxyl group in
undecose derivatives was very difficult, possibly because of the instability
of the aldol products and significant steric hindrance around the hydroxyl:
Cox, P. J.; Griffin, A. M.; Newcombe, N. J.; Lister, S.; Ramsay, M. V. J.;
Alker, D.; Gallgher, Y. J. Chem. Soc., Perkin Trans. 1 1994, 1443-1447.

10274 J. Am. Chem. Soc., Vol. 121, No. 44, 1999
Ichikawa et al.
Figure 4.
Scheme 7a
Figure 5.
a Reagents: (a) K2CO3, MeOH; (b) TBSCl, TIPSCl, or TBDPSCl,
imidazole, DMF; (c) dimethyldioxirane, acetone; (d) PhSH, BF3Et2O,
CH2Cl2; (e) Dess-Martin periodinane, CH2Cl2.
Recently, it was reported that introducing significantly bulky
protecting groups at vicinal hydroxyl groups on pyranoses
caused a flip of their conformation from the usual 4C1-form into
an unusual 1C4-form, where the substituents were in axial
orientations due to steric repulsion between the bulky protecting
groups (Figure 5).23 We expected that enone 20′, which has
bulky protecting groups at both the 8′- and 9′-hydroxyls, would
6′
adopt a C9′-like conformation, as shown in Figure 6, due to
steric repulsion between the bulky protecting groups. If so,
hydrogenation of 20′ would selectively occur from the â-face
to give the desired R-product 21′, due to a significant steric
repulsion for the 9′-axial protecting group when the catalyst
accesses the alkenyl bond from the R-face. In addition, the
desired R-glycoside 21′ would be more thermodynamically
stable than the corresponding â-C-glycoside, since the substitu-
ent at the 6′-position of 21′ is in an equatorial position. Thus,
isomerization from a â- to an R-configuration at the 6′-position
would occur if the hydrogenation does not proceed selectively
from the â-face. Based on these considerations, we designed
phenylthiouloses 29a-c (Scheme 7), which had bulky silyl
protecting groups at both the 8′- and 9′-positions, as alternative
substrates for the aldol reaction.
Figure 6.
J8′,9′ and J9′,10′ were ca. 9-10 Hz. Accordingly, 20 preferentially
adopts a half-chair conformation, as shown in Figure 4. Since
hydrogenation from the â-face of the alkenyl bond of 20 would
be disfavored probably due to steric repulsion for the 9′-axial
proton, R-face attack proceeded to give the undesired 6′-â-C-
glycosidic product 21 as the major product. It is also possible
that isomerization at the anomeric 6′-position into the undesired
â-configuration might occur if the hydrogenation product was
the desired R-C-glycoside. 1H NMR analysis of 6′-â-C-glycoside
9′
21 suggested that it adopts a C6′-like conformation in which
all of the substituents on the ulose moiety are in equatorial
positions. 6′-â-C-Glycoside 21 would be more thermodynami-
cally stable than the corresponding R-C-glycoside, which has a
very bulky 6′-substituent in an axial position, and therefore the
undesired isomerization might occur.
(23) (a) Walford, C.; Jackson, R. F. W.; Rees, N. H.; Clegg, W.; Heath,
S. L. Chem. Commun. 1997, 1855-1856. As for reactions: (b) Hosoya,
T.; Ohashi, Y.; Matsumoto, T.; Suzuki, K. Tetrahedron Lett. 1996, 37, 663-
666. (c) Roush, W. R.; Sebesta, S. P.; Bennett, C. E. Tetrahedron 1997,
53, 8825-8836. (d) Roush, W. R.; Sebesta, D. P.; James, R. A. Tetrahedron
1997, 53, 8837-8852.

Total Synthesis of Herbicidin B
J. Am. Chem. Soc., Vol. 121, No. 44, 1999 10275
Scheme 8a
Figure 7. Conformation of the pyranose ring on the enones.
the basis of their coupling constants between H-3 and H-4, and
between H-4 and H-5 (J3,4, J4,5 ) 0-4.3 Hz).
Synthesis of Herbicidin B. The total synthesis of herbicidin
B was achieved as shown in Scheme 8. SmI2-promoted aldol
reactions8 with phenylthioulose 29a-c and aldehyde 7 were
examined. When 29a was treated with SmI2 at -78 °C, the
samarium enolate was not generated efficiently,28 and the yield
of the coupling product was low. However, the condensation
reaction proceeded effectively at -40 °C, and the desired
coupling product 30a was obtained in 65% yield as a mixture
of two diastereoisomers.29 By similar condensation reactions,
the aldol products 30b and 30c were obtained from 29b and
29c, respectively. Treatment of 30a-c with Burgess’s inner salt
gave the corresponding enones 31a-c in 66-79% yields as a
single isomer, respectively, while the alkene geometry was
unknown.
The conformations of enones 31a-c were investigated by
1
a Reagents: (a) SmI2, THF, then 7; (b) MeO2CNSO2NEt3, toluene;
their H NMR spectra. Small coupling constants between the
(c) Pd/C, HCO2NH4, MeOH; (d) Sm, I2, MeOH; (e) TBAF, THF.
protons on the pyranose ring, J8′,9′ ) 0-2 Hz and J9′,10′ ) 3-4
Hz, suggested that they had flipped conformations where the
8′- and 9′-O-silyl substituents were in axial positions (Figure
7). Reduction of the enones under a variety of conditions was
investigated next. Enone 31b, which has a pair of significantly
bulky TIPS groups at the 8′- and 9′-hydroxyls, was resistant to
all of the reduction conditions examined.30 However, when
enone 31a, which has less bulky TBS groups instead of TIPS
groups, was treated with HCO2NH4 as a hydrogen donor in the
presence of Pd-C in MeOH,31 the desired reduced product 32a
was obtained.32,33 Compound 32a was then successively treated
with SmI2/MeOH and TBAF/TFH to form an internal ketal
linkage between the 3′- and 7′-positions, to spontaneously give
Preparation of Conformation-Flipped 1-Phenylthio-2-
ulose Units. The preparation of 1-phenylthio-2-uloses 29a-c
is summarized in Scheme 7. Glycal 24, derived from D-glucu-
rono-3,6-lactone, was treated with NaOMe in MeOH to give
25.24 The 3,4-diol of 25 was silylated by usual methods to afford
26a and 26b, which have TBS or TIPS groups at both the 3-
and 4-hydroxyls, respectively. Glycal 26c was prepared by
successive treatment of 25 with TBSCl and TBDPSCl in the
presence of imidazole in DMF. Epoxidation of 26a with
dimethyldioxirane25 gave the gluco-type epoxide 27a selectively
in quantitative yield.26 Next, ring-opening of the epoxide was
examined. When 27a was treated with PhSH and Et3N, only a
trace of the desired phenylthioglycoside 28a was obtained.
Treatment with 10 equiv of PhSH in the presence of a catalytic
amount of BF3‚OEt2 gave 28a in good yield as an anomeric
mixture. Oxidation of 28a with Dess-Martin periodinane27 gave
an anomeric mixture of 1-phenylthio-2-ulose (29a) in 80% yield.
Similarly, other aldol substrates 29b and 29c were prepared from
26b and 26c, respectively. The conformations of these phe-
nylthiouloses 29a-c were investigated by their 1H NMR spectra.
The large coupling constants (J3,4 ) 5.8, J4,5 ) 12.8 Hz) of
29a showed that it adopted an undesired 4C1-like conformation,
similar to that of 3,4-O-TIPDS-phenylthioulose 13. This result
suggested that a TBS group would be not bulky enough to flip
the conformation. On the other hand, a preference for the desired
1C4 conformations in 29b and 29c, where the substituents at
the 3- and 4-positions are in axial positions, was suggested on
1
a tricyclic sugar compound, the H NMR spectrum of which
was consistent with that of herbicidin B (1b), while the yield
was low (5% from 31a).
The yield was improved when 31c, which had a TBS group
and a TBDPS group at the 8′- and 9′-hydroxyls, respectively,
was used as a substrate. Thus, treatments of 31c with HCO2-
NH4/Pd-C/MeOH,33 SmI2/MeOH, and TBAF/THF gave her-
bicidin B (1b) in 31% yield after preparative silica gel TLC
purification. In this reaction, production of 6′-epi-herbicidin B
(23) was not observed at all. This completes the first synthesis
of herbicidin B. Its spectroscopic and analytical data are in full
agreement with those of the authentic sample.
(28) Remaining starting material 29a was observed on TLC.
(29) The stereochemistries of the two diastereomers were not confirmed.
(30) For example, catalytic hydrogenations with Pd-C, PtO, Raney-Ni,
or Pd-black and hydride reductions with DIBAL/HMPA, NaBH4/NiCl2, or
Bu3SnH were tried.
(24) Nishimura, S.; Nomura, S.; Yamada, K. Chem. Commun. 1998,
617-618.
(25) Adam, W.; Chan, Y. Y.; Cremer, D.; Gauss, J.; Scheutzow, D.;
Schindler, M. J. Org. Chem. 1987, 52, 2800-2803.
(26) Friesen, R.; Danishefsky, S. J. J. Am. Chem. Soc. 1989, 111, 6656-
6660.
(31) Bieg, T.; Szeja, W. Synthesis 1985, 76-77.
(32) The 1H NMR spectrum of the crude reduction product suggested
that it was an anomeric mixture (R/â ) 3/1).
(33) A byproduct, the structure of which has not been determined, was
also obtained in the hydrogenation of 31a, and it made the yield of 32a
low. On the other hand, production of such a byproduct was not observed
in the hydrogenation of 31c.
(27) Dess, D. B.; Martin, J. C. J. Am. Chem. Soc. 191, 113, 7277-7279.

10276 J. Am. Chem. Soc., Vol. 121, No. 44, 1999
Ichikawa et al.
9H), 6.86 (d, 1H, J ) 10.6 Hz), 5.80 (br s, 2H, exchanged with D2O),
5.77 (d, 1H, J ) 1.5 Hz), 4.27 (dd, 1H, J ) 5.6, 8.7 Hz), 4.21 (dd, 1H,
J ) 3.0, 10.5 Hz), 4.18 (d, 1H, J ) 1.5 Hz), 3.45 (s, 3H); 13C NMR
(CDCl3, 125 MHz) δ 152.6, 144.0, 140.9, 128.9, 127.9, 127.2, 127.1,
126.7, 91.9, 90.9, 87.3, 82.9, 73.9, 62.4, 58.3; MS (EI) m/z 523 (M+).
Anal. Calcd for C30H29N5O4: C, 68.82; H, 5.58; N, 13.38. Found: C,
68.61; H, 5.74; N, 13.19.
Conclusions
Using a novel aldol-type C-glycosidation reaction promoted
by SmI2 as a key step and a strategy involving the axial
orientation of vicinal substituents, we completed the first total
synthesis of the nucleoside antibiotic herbicidin B (1b). This
aldol-type C-glycosidation reaction promoted by SmI2 was very
effective for constructing the undecose nucleoside 19 and 30
using 1-â-D-xylosyladenine 5′-aldehyde derivative as an accep-
tor, which was very unstable under either acidic or basic
conditions. The fact that the reactions promoted by SmI2
proceeded under mild and neutral conditions made this result
possible, and since phenylthiouloses as the enolate source are
readily synthesized and stable, this approach can be applied to
a variety of compounds. Thus, the aldol-type C-glycosidation
reaction promoted by SmI2 may be a powerful tool for
synthesizing other higher carbon sugar nucleosides. Reduction
followed by the deprotection of 20, in which the conformation
of the pyranose ring was 9′C6′, gave selectively 6′-epi-herbicidin
B, which is an analogue of herbicidin B. On the other hand,
similar conversion of enones 31, which adopted a O,8′B-type
conformation on the pyranose ring, by the introduction of bulky
protecting groups gave herbicidin B (1b). This work is the first
total synthesis of herbicidin congeners, and our methods should
be applicable to the synthesis of other herbicidin congeners and
their analogues.
N6-Benzoyl-9-(3-O-tert-butyldimethylsily-2-O-methyl-5-O-trityl-
â-D-xylofuranosyl)adenine (17). A mixture of 16 (1.48 g, 2.82 mmol),
TBSCl (852 mg, 5.62 mmol), and imidazole (767 mg, 11.3 mmol) in
DMF (30 mL) was stirred for 15 h at room temperature. After MeOH
(5 mL) was added, the mixture was stirred for an additional 12 h and
evaporated under reduced pressure. The residue was partitioned between
EtOAc (200 mL) and H2O (100 mL), and the organic layer was washed
with brine (50 mL), dried (Na2SO4), and evaporated under reduced
pressure. A mixture of the residue and BzCl (0.72 mL, 6.2 mmol) in
pyridine (30 mL) was stirred for 3 h at room temperature. After NH4-
OH (28%, 10 mL) was added to the mixture, the resulting mixture
was stirred for a further 20 min and evaporated under reduced pressure.
The residue was partitioned between EtOAc (200 mL) and H2O (100
mL), and the organic layer was washed with brine (50 mL), dried (Na2-
SO4), and evaporated under reduced pressure. The residue was purified
by column chromatography (SiO2, 33% EtOAc/hexane) to give 17 (1.73
g, 83% as a white foam): [R]D -27.3° (c 1.10, CHCl3); 1H NMR
(CDCl3, 500 MHz) δ 9.23 (br s, 1H, exchanged with D2O), 9.00 (s,
1H), 8.30 (s, 1H), 8.19 (d, 2H, J ) 7.5 Hz), 7.98 (d, 1H, J ) 7.5 Hz),
7.66-7.40 (m, 17H), 6.50 (s, 1H), 4.81 (dd, 1H, J ) 3.3, 3.7 Hz),
4.36 (s, 1H), 4.09 (s, 1H), 3.81 (dd, 1H, J ) 3.7, 10.5 Hz), 3.80 (s,
3H), 3.43 (dd, 1H, J ) 3.3, 10.3 Hz), 0.73 (s, 9H), -0.76 (s, 3H),
-0.89 (s, 3H); 13C NMR (CDCl3, 125 MHz) δ 152.9, 144.0, 141.9,
132.9, 132.2, 129.1, 128.9, 128.8, 128.1, 128.0, 127.6, 127.4, 90.8,
88.9, 87.4, 84.3, 63.5, 58.6, 25.6, 18.0, -4.9, -5.3; MS (EI) m/z 498
(M+ - Tr). Anal. Calcd for C43H47N5O5Si‚0.5H2O: C, 68.77; H, 6.44;
N, 9.33. Found: C, 69.06; H, 6.43; N, 9.37.
Experimental Section
9-(2-O-Methyl-5-O-trityl-â-D-ribofuranosyl)adenine (15). A mix-
ture of 14 (12.9 g, 40 mmol) and TrCl (11.2 g, 44 mmol) in pyridine
(100 mL) was stirred for 12 h at 60 °C. After MeOH (10 mL) was
added, the solution was evaporated under reduced pressure, and the
residue was partitioned between CHCl3 (500 mL) and H2O (200 mL).
The organic layer was washed with brine (200 mL), dried (Na2SO4),
and evaporated under reduced pressure. The residue was purified by
column chromatography (SiO2, 6% MeOH/CHCl3) to give 15 (19.2 g,
92% as a white foam): [R]D +0.29° (c 1.14, CHCl3); 1H NMR (CDCl3,
500 MHz) δ 8.30 (s, 1H), 8.02 (s, 1H), 7.45-7.23 (m, 15H), 6.14 (d,
1H, J ) 3.7 Hz), 5.59 (br s, 2H, exchanged with D2O), 4.50 (dd, 1H,
J ) 5.5, 11.1 Hz), 4.42 (dd, 1H, J ) 3.8, 5.3 Hz), 4.20 (ddd, 1H, J )
3.3, 4.5, 11.1 Hz), 3.57 (s, 3H), 3.52 (dd, 1H, J ) 3.3, 10.7 Hz), 3.43
(dd, 1H, J ) 4.5, 10.7 Hz), 2.74 (d, 1H, J ) 6.3 Hz, exchanged with
D2O); 13C NMR (CDCl3, 125 MHz) δ 155.8, 153.4, 149.8, 143.8, 139.2,
128.9, 128.8, 128.8, 128.2, 127.5, 120.3, 87.4, 86.9, 84.0, 83.6, 77.5,
77.3, 77.0, 70.0, 63.5, 59.0, 58.5; MS (EI) m/z 523 (M+). Anal. Calcd
for C30H29N5O4‚1.2H2O: C, 66.09; H, 5.80; N, 12.85. Found: C, 66.03;
H, 5.56; N, 12.64.
9-(2-O-Methyl-5-O-trityl-â-D-xylofuranosyl)adenine (16). To a
mixture of CrO3 (11.2 g, 112 mmol) and 4-Å molecular sieves (28 g)
in CH2Cl2 (250 mL) was added pyridine (18.0 mL, 224 mmol) at 0
°C. The mixture was stirred for 30 min at 0 °C, and then Ac2O (10.6
mL, 112 mmol) was added at the same temperature, and the whole
was stirred for additional 15 min. To the resulting mixture was added
15 (14.6 g, 27.9 mmol) in CH2Cl2 (100 mL), and the mixture was stirred
for 30 min at room temperature. The solution was diluted with EtOAc
(1 L) and filtered through a Celite pad, and the filtrate was concentrated
to about 500 mL under reduced pressure. The solution was washed
with H2O (3 × 200 mL) and brine (200 mL), dried (Na2SO4), and
evaporated under reduced pressure. A mixture of the residue and NaBH4
(6.87 g, 181 mmol) in AcOH (300 mL) was stirred for 12 h at 4 °C.
The mixture was evaporated under reduced pressure, and the residue
was coevaporated with EtOH (3 × 30 mL). The residue was partitioned
between CHCl3 (500 mL) and H2O (2 × 200 mL), and the organic
layer was washed with saturated NaHCO3 (200 mL) and brine (200
mL), dried (Na2SO4), and evaporated under reduced pressure. The
residue was crystallized from EtOAc to give 16 (11.3 g, 78%): mp
205-206 °C; [R]D -38.8° (c 0.82, CHCl3); 1H NMR (CDCl3, 500 MHz)
δ 8.23 (s, 1H), 7.92 (s, 1H), 7.44 (d, 6H, J ) 7.4 Hz), 7.26-7.18 (m,
N6-Benzoyl-9-(3-O-tert-butyldimethylsily-2-O-methyl-â-D-xylo-
furanosyl)adenine (18). A mixture of 17 (7.31 g, 9.86 mmol) and 80%
aqueous TFA (5 mL) in CHCl3 (100 mL) was stirred for 1 h at room
temperature. The mixture was washed with H2O (2 × 50 mL), saturated
NaHCO3 (50 mL), and brine (30 mL), dried (Na2SO4), and evaporated
under reduced pressure. The residue was purified by column chroma-
tography (SiO2, 75% EtOAc/hexane) to give 18 (3.99 g, 81% as a white
1
foam): [R]D -42.3° (c 1.28, CHCl3); H NMR (CDCl3, 500 MHz) δ
9.09 (br s, 1H, exchanged with D2O), 8.83 (s, 1H), 8.39 (s, 1H), 8.03
(d, 2H, J ) 7.5 Hz), 7.61 (t, 1H, J ) 7.5 Hz), 7.53 (t, 2H, J ) 7.4 Hz),
6.20 (d, 1H, J ) 1.9 Hz), 4.39-4.37 (m, 2H), 4.15 (d, 1H, J ) 1.9
Hz), 4.06 (dd, 1H, J ) 4.6, 11.3 Hz), 3.99 (dd, 1H, J ) 3.2, 11.3 Hz),
3.55 (s, 3H), 2.75 (br s, 1H, exchanged with D2O), 0.81 (s, 9H), 0.11
(s, 3H), -0.03 (s, 3H); 13C NMR (CDCl3, 125 MHz) δ 152.9, 149.7,
142.0, 134.0, 132.9, 129.0, 128.1, 127.6, 90.5. 88.3, 61.6, 58.8, 25.8,
18.2, -4.7, -5.0; MS (EI) m/z 499 (M+). Anal. Calcd for C24H33N5O5-
Si: C, 57.69; H, 6.66; N, 14.02. Found: C, 57.73; H, 6.56; N, 14.05.
N6-Benzoyl-9-(3-O-tert-butyldimethylsily-2-O-methyl-â-D-xylo-
furanos-5-urosyl)adenine (7). Trifluoroacetic acid (1.09 mL, 4.5 mmol)
was added to a solution of 18 (4.51 g, 9.05 mmol), DCC (5.63 g, 27.2
mmol), and pyridine (0.91 mL, 9.1 mmol) in DMSO (50 mL) at room
temperature, and the mixture was stirred for 2 h. The mixture was
filtered to remove dicyclohexylurea, and the filtrate was washed with
hexane (3 × 50 mL) and partitioned with EtOAc (200 mL) and H2O
(200 mL). The organic layer was washed with brine (20 mL), dried
(Na2SO4), and evaporated under reduced pressure. The residue was
coevaporated with toluene (3 × 50 mL) under reduced pressure to give
crude 7 (4.77 g as a syrup, quantitative). This compound was used in
the next reaction without further purification, because it was too unstable
to be isolated: 1H NMR (CDCl3, 500 MHz) δ 9.78 (s, 1H), 9.16 (br s,
1H, exchanged with D2O), 8.81 (s, 1H), 8.50 (s, 1H), 8.01 (d, 2H, J )
7.5 Hz), 7.59 (t, 1H, J ) 7.5 Hz), 7.51 (t, 2H, J ) 7.4 Hz), 6.39 (s,
1H), 4.79 (d, 1H, J ) 3.7 Hz), 4.68 (d, 1H, J ) 3.8 Hz), 4.13 (s, 1H),
3.62 (s, 3H), 0.68 (s, 9H), 0.04 (s, 3H), -0.15 (s, 3H).
Methyl Glucuronate-D-glycal (25). A mixture of 24 (258 mg, 1.00
mmol) in MeOH (10 mL) containing NaOMe (28% in MeOH, 10 µL)
was stirred for 1 h at room temperature. The mixture was neutralized

Total Synthesis of Herbicidin B
J. Am. Chem. Soc., Vol. 121, No. 44, 1999 10277
with AcOH and evaporated under reduced pressure. The resulting syrup
was partitioned between EtOAc (50 mL) and H2O (50 mL), and the
organic layer was washed with H2O (50 mL) and brine (20 mL). The
organic layer was dried (Na2SO4) and evaporated under reduced
pressure. The residue was purified by silica gel column chromatography
(SiO2, 4% MeOH/CHCl3) to give 25 (150 mg, 86% as a white solid),
which was crystallized from MeOH/CHCl3: mp 148-151 °C; [R]D
give 27a (210 mg, quantitative): [R]D -34.1° (c 1.00, CHCl3); 1H NMR
(CDCl3, 500 MHz) δ 5.07 (d, 1H, J ) 2.4 Hz), 4.18 (d, 1H, J ) 4.5
Hz), 4.09 (dd, 1H, J ) 2.7, 8.9 Hz), 3.97 (t, 1H, J ) 2.4 Hz), 3.74 (s,
3H), 2.92 (t, 1H, J ) 2.4 Hz), 0.91 (s, 9H), 0.90 (s, 9H), 0.15 (s, 3H),
0.14 (s, 3H), 0.11 (s, 3H), 0.07 (s, 3H); 13C NMR (CDCl3, 125 MHz)
δ 170.8, 76.6, 74.5, 72.8, 69.6, 54.1, 52.5, 25.9, -1.1, -4.6, -4.7,
-4.9; MS (FAB) m/z 419 (MH+). Anal. Calcd for C19H38O6Si2: C,
54.51; H, 9.15. Found: C, 54.28; H, 9.02.
1
-13.5° (c 1.00, MeOH); H NMR (DMSO-d6, 500 MHz) δ 6.37 (d,
1H, J ) 6.2 Hz), 5.43 (d, 1H, J ) 5.0 Hz, exchanged with D2O), 4.98
(d, 1H, J ) 4.0 Hz, exchanged with D2O), 4.72 (t, 1H, J ) 5.0, 6.2
Hz), 4.40 (d, 1H, J ) 5.1 Hz), 3.82 (ddd, 1H, J ) 5.1, 4.6, 4.0 Hz),
3.74 (ddd, 1H, J ) 5.0, 4.6, 5.0 Hz), 3.61 (s, 3H).
Methyl (3,4-Di-O-triisopropylsilyl-2,3-anhydro)-D-glucuronate
(27b). In a manner similar to that described for 27a, the reaction of
26b (1.94 g, 4.00 mmol) with an acetone solution of dimethyldioxirane
(ca. 0.05 M, 100 mL, 5.00 mmol) gave 27b (2.03 g, quantitative as a
foam): 1H NMR (CDCl3, 500 MHz) δ 5.30 (s, 1H), 4.33 (s, 1H), 4.31
(br s, 2H), 3.72 (s, 3H), 3.09 (br s, 1H), 1.18-1.04 (m, 42H); 13C NMR
(CDCl3, 125 MHz) δ 169.8, 132.5, 130.8, 129.0, 128.8, 125.3, 75.5,
73.1, 67.4, 53.2, 52.0, 18.8, 18.7, 18.6, 18.3, 17.9, 14.0, 12.8, 12.7,
12.4, 12.3, 12.1; MS (FAB) m/z 503 (MH+).
Methyl (3-O-tert-Butyldimethylsilyl-4-O-tert-butyldiphenylsilyl-
2,3-anhydro)-D-glucuronate (27c). In a manner similar to that
described for 27a, the reaction of 26c (2.10 g, 4.00 mmol) with an
acetone solution of dimethyldioxirane (ca. 0.05 M, 100 mL, 5.00 mmol)
gave 27c (2.21 g, quantitative): 1H NMR (CDCl3, 500 MHz) δ 7.74-
7.36 (m, 10H), 5.12 (d, 1H, J ) 2.4 Hz), 4.18 (br s, 2H), 4.07 (dd, 1H,
J ) 1.9, 3.8 Hz), 3.57 (s, 3H), 3.01 (d, 1H, J ) 1.4 Hz), 1.09 (s, 9H),
0.74 (s, 9H), -0.09 (s, 3H), -0.14 (s, 3H); 13C NMR (CDCl3, 125
MHz) δ 169.8, 132.5, 130.8, 129.0, 128.8, 125.3, 75.5, 73.1, 67.4, 53.2,
52.0, 18.8, 18.7, 18.6, 18.3, 17.9, 14.0, 12.8, 12.7, 12.4, 12.3, 12.1;
MS (FAB) m/z 543 (MH+). Anal. Calcd for C29H42O6Si2: C, 64.17;
H, 7.80. Found: C, 64.68; H, 7.76.
Methyl 3,4-Di-O-tert-butyldimethylsilyl-1-phenylthio-D-glucur-
onate (28a). Boron trifluoride diethyl ether complex (49 µL, 0.4 mmol)
was added dropwise to a mixture of 27a (1.67 g, 4.00 mmol) and PhSH
(4.11 mL, 40.0 mmol) in CH2Cl2 (40 mL), and the mixture was stirred
for 30 min at -40 °C. The mixture was washed with saturated aqueous
NaHCO3 (40 mL), H2O (50 mL), and brine (50 mL), dried (Na2SO4),
and evaporated under reduced pressure. The residue was purified by
column chromatography (SiO2, 75% benzene/hexane) to give 28a as
an inseparable anomeric mixture (1.44 g, 80% as a colorless syrup,
the ratio of R/â ) 39/61): MS (FAB) m/z 528 (M+). Anal. Calcd for
C25H44O6SSi2: C, 56.78; H, 8.39. Found: C, 56.93; H, 8.09. For
â-anomer: 1H NMR (CDCl3, 500 MHz) δ 7.57 (d, 2H, J ) 7.5 Hz),
7.33-7.18 (t, 3H), 5.16 (d, 1H, J ) 5.8 Hz), 4.30 (t, 1H, J ) 3.8 Hz),
4.27 (d, 1H, J ) 3.1 Hz), 3.85 (t, 1H, J ) 4.3 Hz), 3.67 (s, 3H), 3.22
(d, 1H, J ) 7.7 Hz, exchanged with D2O), 0.89 (s, 9H), 0.88 (s, 9H),
0.18 (s, 3H), 0.17 (s, 3H), 0.15 (s, 3H), 0.11 (s, 3H); 13C NMR (CDCl3,
125 MHz) δ 169.9, 135.5, 133.1, 129.4, 129.0, 87.1, 72.8, 71.8, 70.7,
64.4, 52.1, 26.2, 25.9, 18.6, 18.1, -4.1, -4.2, -4.8, -4.9. For
R-anomer: 1H NMR (CDCl3, 500 MHz) δ 7.71 (d, 2H, J ) 7.7 Hz),
7.33-7.18 (t, 3H), 5.94 (s, 1H), 4.48 (s, 1H), 4.20 (t, 1H, J ) 1.4 Hz),
3.98 (t, 1H, J ) 3.4 Hz), 3.95 (s, 1H), 3.73 (m, 2H), 3.72 (s, 3H), 0.94
(s, 9H), 0.85 (s, 9H), 0.18 (s, 3H), 0.17 (s, 3H), 0.07 (s, 3H), 0.06 (s,
3H); 13C NMR (CDCl3, 125 MHz) δ 169.7, 143.7, 133.1, 127.3, 126.4,
81.7, 77.8, 75.6, 73.1, 72.2, 69.9, 26.0, 25.8, 18.2, 11.7, -4.3, -4.5,
-4.5, -4.6.
Methyl 3,4-Di-O-triisopropylsilyl-1-phenylthio-D-glucuronate (28b).
In a manner similar to that described for 28a, reaction of 27b (2.03 g,
4.00 mmol) with BF3‚OEt2 (49 µL, 0.4 mmol) and PhSH (4.11 mL,
40.0 mmol) in CH2Cl2 (40 mL) and purification by column chroma-
tography (SiO2, 75% benzene/hexane) gave 28b as an inseparable
anomeric mixture (1.53 g, 63% as a colorless syrup, the ratio of R/â )
60/40): MS (FAB) m/z 613 (M+). Anal. Calcd for C31H56O6SSi2: C,
60.74; H, 9.21. Found: C, 60.42; H, 9.53. For R-anomer: 1H NMR
(CDCl3, 500 MHz) δ 7.59 (d, 2H, J ) 7.3 Hz), 7.32-7.19 (m, 3H),
5.35 (d, 1H, J ) 5.8 Hz), 4.68 (d, 1H, J ) 2.3 Hz), 4.54 (s, 1H), 4.12
(d, 1H, J ) 6.5 Hz), 3.82 (m, 1H), 3.66 (s, 3H), 3.20 (d, 1H, J ) 8.8
Hz, exchanged with D2O), 1.12-1.04 (m, 42H); 13C NMR (CDCl3,
125 MHz) δ 171.1, 136.6, 132.4, 130.0, 127.4, 87.0, 74.6, 73.6, 72.3,
71.2, 53.1, 19.5, 19.3, 19.2, 19.1, 13.6, 13.4. For â-anomer: 1H NMR
(CDCl3, 500 MHz) δ 7.70 (d, 2H, J ) 7.0 Hz), 7.31-7.22 (m, 3H),
5.99 (s, 1H), 4.58 (s, 1H), 4.43 (m, 1H), 4.20 (t, 1H, J ) 3.3 Hz), 4.05
(d, 1H, J ) 10.1 Hz, exchanged with D2O), 3.82 (m, 1H), 3.69 (s,
Methyl (3,4-Di-O-tert-butyldimethylsilyl-D-glucuronate)glycal (26a).
A mixture of 25 (1.74 g, 10.0 mmol), TBSCl (4.51 g, 30.0 mmol), and
imidazole (4.08 g, 60.0 mmol) in DMF (50 mL) was stirred for 4 h at
100 °C. After being cooled to room temperature, MeOH (10 mL) was
added. The reaction mixture was partitioned between EtOAc (200 mL)
and H2O (200 mL), and the organic layer was washed with H2O (200
mL) and brine (50 mL), dried (Na2SO4), and evaporated under reduced
pressure. The residue was purified by column chromatography (SiO2,
10% EtOAc/hexane) to give 26a (3.97 g, 99% as a colorless syrup):
1
[R]D -27.2° (c 1.05, CHCl3); H NMR (CDCl3, 500 MHz) δ 6.50 (d,
1H, J ) 6.6 Hz), 4.81 (m, 1H), 4.53 (br s, 1H), 4.23 (dd, 1H, J ) 2.0,
4.0 Hz), 3.77 (m, 1H), 3.71 (s, 3H), 0.90 (s, 9H),0.83 (s, 9H), 0.13 (s,
3H), 0.12 (s, 3H), 0.06 (s, 3H), 0.05 (s, 3H); 13C NMR (CDCl3,125
MHz) δ 169.7, 144.3, 101.6, 75.8, 64.5, 52.2, 25.9, 25.8, -4.4, -4.7,
-4.8, -4.9; MS (FAB) m/z 402 (MH+). Anal. Calcd for C19H38O5Si2:
C, 56.67; H, 9.51. Found: C, 56.55; H, 9.67.
Methyl (3,4-Di-O-triisopropylsilyl-D-glucuronate)glycal (26b). In
a manner similar to that described for 26a, reaction of 25 (2.00 g, 11.4
mmol) with TIPSCl (7.38 mL, 34.2 mmol) and imidazole (4.66 g, 68.4
mmol) in DMF (50 mL) and purification by column chromatography
(SiO2, 10% EtOAc/hexane) gave 26b (5.24 g, 95% as a colorless
1
syrup): [R]D -24.8° (c 1.12, CHCl3); H NMR (CDCl3, 500 MHz) δ
6.52 (d, 1H, J ) 6.4 Hz), 4.90 (m, 1H), 4.64 (br s, 1H), 4.47 (dd, 1H,
J ) 2.0, 4.0 Hz), 3.95 (ddd, 1H, J ) 1.2, 2.0, 4.0 Hz), 3.70 (s, 3H),
1.87-1.04 (m, 42H); 13C NMR (CDCl3, 125 MHz) δ 168.8, 143.5,
101.1, 75.5, 70.7, 64.2, 52.2, 18.3, 18.2, 18.2, 18.1, 18.1, 17.9, 12.8,
12.7, 12.6, 12.6, 12.4, 12.3, 12.1; MS (FAB) m/z 443 (MH+ - i-Pr).
Anal. Calcd for C25H50O5Si2: C, 61.68; H, 10.35. Found: C, 61.31;
H, 10.11.
Methyl (3-O-tert-Butyldimethylsilyl-4-O-tert-butyldiphenylsilyl-
D-glucuronate)glycal (26c). A mixture of 25 (107 mg, 0.61 mmol),
TBSCl (110 mg, 0.73 mmol), and imidazole (99.7 mg, 1.46 mmol) in
DMF (5 mL) was stirred for 2 h at room temperature. After MeOH (2
mL) was added, the mixture was partitioned between EtOAc (50 mL)
and H2O (50 mL), and the organic layer was washed with H2O (20
mL) and brine (20 mL), dried (Na2SO4), and evaporated under reduced
pressure. A mixture of the above residue, TBDPSCl (238 µL, 0.92
mmol), and imidazole (125 mg, 1.80 mmol) in DMF (5 mL) was stirred
for 4 h at 100 °C. After MeOH (2 mL) was added, the reaction mixture
was partitioned between EtOAc (50 mL) and H2O (50 mL), and the
separated organic layer was washed with H2O (20 mL) and brine (20
mL), dried (Na2SO4), and evaporated under reduced pressure. The
residue was purified by column chromatography (SiO2, 10% EtOAc/
hexane) to give 26c (298 mg, 93% as a colorless syrup): [R]D -8.15°
(c 1.34, CHCl3); 1H NMR (CDCl3, 500 MHz) δ 7.72-7.38 (m, 10H),
6.51 (d, 1H, J ) 6.3 Hz), 4.85 (m, 1H), 4.52 (br s, 1H), 4.32 (dd, 1H,
J ) 1.2, 5.6 Hz), 3.77 (m, 1H), 3.56 (s, 3H), 1.05 (s, 9H), 0.72 (s, 9H),
-0.14 (s, 3H), -0.17 (s, 3H); 13C NMR (CDCl3, 125 MHz) δ 168.6,
143.8, 136.0, 135.9, 133.7, 133.5, 130.2, 128.1, 128.0, 101.2, 74.9,
71.0, 63.6, 52.0, 27.1, 25.9, -4.5, -4.9; MS (FAB) m/z 469 (MH+
-
t-Bu). Anal. Calcd for C29H42O5Si2: C, 66.12; H, 8.04. Found: C, 66.32;
H, 7.97.
Methyl (3,4-Di-O-tert-butyldimethylsilyl-2,3-anhydro)-D-glucur-
onate (27a). A solution of 26a (200 mg, 0.40 mmol) in CH2Cl2 (4
mL) was added dropwise to an acetone solution of dimethyldioxirane
(ca. 0.05 M, 10 mL, 0.50 mmol), and the mixture was stirred for 2 h
at room temperature. After most of the acetone was removed under
reduced pressure, the residue was dissolved in CH2Cl2, dried (Na2SO4),
and filtered, and the filtrate was evaporated under reduced pressure to

10278 J. Am. Chem. Soc., Vol. 121, No. 44, 1999
Ichikawa et al.
3H), 1.12-1.00 (m, 42H); 13C NMR (CDCl3, 125 MHz) δ 170.7, 144.6,
136.9, 130.6, 130.0, 128.2, 102.2, 82.9, 76.6, 73.5, 71.8, 65.2, 19.3,
19.2, 19.1, 18.9, 13.7, 13.5.
50% benzene/hexane) gave an inseparable anomeric mixture of 29c
(1.75 g, 99% as a colorless syrup, the ratio of R/â ) 74/26): MS (FAB)
m/z 651 (MH+). Anal. Calcd for C35H46O6SSi2‚1/6benzene: C, 65.12;
H, 7.13. Found: C, 65.22; H, 7.26. For R-anomer: 1H NMR (CDCl3,
500 MHz) δ 7.73-7.26 (m, 15H), 5.74 (s, 1H), 4.70 (d, 1H, J ) 4.0
Hz), 4.56 (s, 1H), 3.87 (d, 1H, J ) 4.0 Hz), 3.65 (s, 3H), 0.95 (s, 9H),
0.89 (s, 9H), -0.18 (s, 3H), -0.19 (s, 3H); 13C NMR (CDCl3, 125
MHz) δ 199.0, 168.6, 136.1, 135.9, 135.7, 132.2, 130.1, 129.0, 127.8,
127.7, 86.4, 77.9, 74.1, 73.3, 52.1, 26.8, 26.7. For â-anomer: 1H NMR
(CDCl3, 500 MHz) δ 7.73-7.26 (m, 15H), 6.41 (s, 1H), 4.66 (s, 1H),
4.58 (d, 1H, J ) 4.0 Hz), 3.89 (d, 1H, J ) 4.0 Hz), 3.62 (s, 3H), 0.93
(s, 9H), 0.91 (s, 9H), -0.14 (s, 3H), -0.21 (s, 3H); 13C NMR (CDCl3,
125 MHz) δ 193.4, 164.7, 135.8, 135.7, 135.6, 133.9, 132.2, 131.9,
129.8, 127.6, 127.5, 86.3, 76.2, 76.6, 76.1, 50.9, 26.7, 26.5.
Methyl 3-O-tert-Butyldimethylsilyl-4-O-tert-butyldiphenylsilyl-1-
phenylthio-D-glucuronate (28c). In a manner similar to that described
for 28a, reaction of 27c (2.71 g, 4.00 mmol) with BF3‚OEt2 (49 µL,
0.4 mmol) and PhSH (4.11 mL, 40.0 mmol) in CH2Cl2 (40 mL) and
purification by column chromatography (SiO2, 75% benzene/hexane)
gave 28c as an inseparable anomeric mixture (1.96 g, 75% as a colorless
syrup, the ratio of R/â ) 72/28): MS (FAB) m/z 652 (M+). Anal. Calcd
for C35H48O6SSi2‚0.5benzene: C, 65.95; H, 7.42. Found: C, 65.98; H,
7.41. For R-anomer: 1H NMR (CDCl3, 500 MHz) δ 7.89-7.46 (m,
15H), 5.67 (d, 1H, J ) 5.0 Hz), 4.64 (d, 1H, J ) 1.7 Hz), 4.55 (s, 1H),
4.17 (t, 1H, J ) 3.0 Hz), 3.99 (m, 1H), 3.72 (d, 1H, J ) 7.8 Hz,
exchanged with D2O), 3.64 (s, 3H), 1.23 (s, 9H), 0.94 (s, 9H), 0.40 (s,
3H), 0.00 (s, 3H); 13C NMR (CDCl3,125 MHz) δ 169.7, 1362-126.3,
86.5, 73.1, 72.4, 71.4, 51.8, 27.2, 27.2, 25.9, 19.3, 19.2, 18.3, -5.0,
-5.1. For â-anomer: 1H NMR (CDCl3, 500 MHz) δ 7.89-7.46 (m,
15H), 6.10 (s, 1H), 4.57 (s, 1H), 4.37 (t, 1H, J ) 1.6 Hz), 4.24 (d, 1H,
J ) 11.9 Hz, exchanged with D2O), 4.20 (t, 1H, J ) 3.4 Hz), 3.99 (m,
1H), 3.68 (s, 3H), 1.30 (s, 9H), 0.89 (s, 9H), 0.05 (s, 3H), -0.03 (s,
3H); 13C NMR (CDCl3, 125 MHz) δ 169.4, 1362-126.3, 81.6, 76.1,
72.2, 71.2, 70.0, 26.8, 25.8, 19.3, 18.1, -5.0, -5.2.
Methyl 3,4-Di-O-tert-butyldimethylsilyl-1-phenylthio-2-ulos-D-
glucuronate (29a). A mixture of 28a (1.31 g, 2.48 mmol, the ratio of
R/â ) 39/61) and Dess-Martin periodinane (1.26 g, 2.98 mmol) in
CH2Cl2 (25 mL) was stirred for 3 h at room temperature. After a mixture
of saturated aqueous NaHCO3 and saturated aqueous Na2S2O3 (5:1)
was added, the mixture was vigorously stirred until the organic layer
turned clear. The separated organic layer was washed with H2O (50
mL) and brine (50 mL), dried (Na2SO4), and evaporated under reduced
pressure. The residue was purified by column chromatography (SiO2,
50% benzene/hexane) to give 29a as an inseparable anomeric mixture
(1.23 g, 94% as a colorless syrup, the ratio of R/â ) 39/61): MS (FAB)
m/z 527 (MH+). Anal. Calcd for C25H42O6SSi2: C, 57.00; H, 8.04.
Found: C, 56.81; H, 7.80. For â-anomer: 1H NMR (CDCl3, 500 MHz)
δ 7.50 (d, 2H, J ) 7.0 Hz), 7.23-7.15 (m, 3H), 5.47 (s, 1H), 4.45 (dd,
1H, J ) 3.3, 5.4 Hz), 4.33 (d, 1H, J ) 3.3 Hz), 3.96 (d, 1H, J ) 5.4
Hz), 3.69 (s, 3H), 0.79 (s, 9H), 0.76 (s, 9H), 0.01 (s, 3H), 0.00 (s, 3H),
-0.01 (s, 3H), -0.08 (s, 3H); 13C NMR (CDCl3, 125 MHz) δ 199.2,
169.1, 133.4, 132.2, 128.9, 128.1, 127.7, 86.9, 78.9, 76.3, 74.0, 52.5,
26.0, 25.8, -4.8, -4.9, -5.1. For R-anomer: 1H NMR (CDCl3, 500
MHz) δ 7.45 (d, 2H, J ) 7.0 Hz), 7.23-7.15 (m, 3H), 5.75 (s, 1H),
4.68 (d, 1H, J ) 5.8 Hz), 4.17 (dd, 1H, J ) 5.8, 12.8 Hz), 4.17 (d, 1H,
J ) 12.8 Hz), 3.70 (s, 3H), 0.84 (s, 9H), 0.80 (s, 9H), 0.03 (s, 3H),
-0.04 (s, 3H), -0.05 (s, 3H), -0.09 (s, 3H); 13C NMR (CDCl3, 125
MHz) δ 198.1, 169.1, 132.8, 132.1, 129.2, 128.3, 88.2, 78.1, 75.5, 75.4,
52.4, 25.8, 25.7, -3.8, -4.1, -4.5.
N6-Benzoyl-9-[methyl 6,10-Anhydro-3,8,9-tri-O-(tert-butyldime-
thylsilyl)-2-O-methyl-r-D-arabino-L-ido-7-undeculofuranuronyl]ad-
enine (30a-r) and N6-Benzoyl-9-[methyl 6,10-Anhydro-3,8,9-tri-O-
(tert-butyldimethylsilyl)-2-O-methyl-â-D-arabino-D-gluco-7-unde-
culofuranuronate]adenine (30a-â). A THF solution of SmI2 (0.1 M,
7.0 mL, 0.70 mmol) was cooled to -40 °C, and then 29a (168 mg,
0.32 mmol) in THF (3 mL) was added dropwise to the mixture. After
the TLC analysis indicated the disappearance of 29a, oxygen gas was
passed through the mixture. Then, 7 (160 mg, 0.32 mmol) in THF (3
mL) was added dropwise to the above mixture, and the whole was
stirred for 15 min at the same temperature. After the mixture was
allowed to warm to room temperature, saturated aqueous NH4Cl was
added. The mixture was filtrated through a Celite pad, the filtrate was
partitioned between EtOAc (50 mL) and H2O (50 mL), and the
separated organic layer was washed with saturated aqueous NaHCO3
(50 mL) and brine (30 mL), dried (Na2SO4), and evaporated under
reduced pressure. The residue was purified by flash column chroma-
tography (SiO2, 40% EtOAc/hexane) to give 30a-r (22.8 mg, 16% as
a white foam) and 30a-â (123 mg, 42% as a white foam). For
R-anomer: [R]D -45.0° (c 1.10, CHCl3); 1H NMR (CDCl3, 500 MHz)
δ 9.02 (br s, 1H, exchanged with D2O), 8.83 (s, 1H), 8.40 (s, 1H),
8.03 (d, 2H, J ) 7.6 Hz), 7.61 (t, 1H, J ) 7.4 Hz), 7.53 (t, 2H, J ) 7.6
Hz), 6.23 (s, 1H), 4.56 (m, 2H), 4.52 (m, 3H), 3.99 (br s, 1H), 3.86 (d,
1H, J ) 2.8 Hz), 3.80 (s, 3H), 3.71 (d, 1H, J ) 5.1 Hz), 3.61 (s, 3H),
0.89 (s, 9H), 0.85 (s, 9H), 0.74 (s, 9H), 0.13 (s, 3H), 0.11 (s, 3H), 0.10
(s, 3H), 0.07 (s, 3H), 0.02 (s, 3H), -0.08 (s, 3H); 13C NMR (CDCl3,
125 MHz) δ 203.0, 170.1, 152.4, 150.7, 149.1, 141.9, 133.8, 132.6,
132.5, 128.7, 127.8, 122.8, 90.6, 88.5, 82.1, 80.7, 77.9, 75.7, 75.1, 73.4,
69.9, 58.2, 52.4, 25.7, 25.6, 25.5, 18.3, 18.0, -4.7, -4.8, -4.9, -5.1;
MS (FAB) m/z 917 (MH+); exact MS (FAB) calcd for C43H70N5O11Si3
916.4379, found 916.4398. Anal. Calcd for C43H69N5O11Si3: C, 56.36;
H, 7.59; N, 7.64. Found: C, 55.90; H, 7.47; N, 7.69. For â-anomer:
[R]D +5.08° (c 1.15, CHCl3); 1H NMR (CDCl3, 500 MHz) δ 9.00 (br
s, 1H, exchanged with D2O), 8.82 (s, 1H), 8.65 (s, 1H), 7.92 (d, 2H, J
) 7.5 Hz), 7.61 (t, 1H, J ) 7.2 Hz), 7.53 (t, 2H, J ) 7.3 Hz), 6.23 (s,
1H, J ) 3.6 Hz), 4.97 (d, 1H, J ) 7.1 Hz), 4.47 (d, 1H, J ) 7.1 Hz),
4.56 (dd, 2H, J ) 3.2, 6.6 Hz), 4.37 (m, 2H), 4.26 (d, 1H, J ) 4.5 Hz),
3.72 (s, 3H), 3.64 (d, 1H, J ) 4.4 Hz), 3.44 (s, 3H), 0.89 (s, 9H), 0.85
(s, 9H), 0.84 (s, 9H), 0.13 (s, 3H), 0.12 (s, 3H), 0.11 (s, 3H), 0.07 (s,
3H), 0.04 (s, 3H), 0.02 (s, 3H); 13C NMR (CDCl3, 125 MHz) δ 205.6,
169.0, 152.2, 151.0, 149.1, 142.0, 133.5, 132.3, 128.5, 127.7, 122.7,
89.2, 86.7, 80.3, 77.3, 77.2, 77.0, 76.7, 76.5, 76.1, 75.8, 75.3, 74.2,
68.0, 58.4, 52.0, 25.6, 25.5, 25.4, 18.1, 17.8, 17.7, -4.8, -4.8, -5.0,
-5.0, -5.1, -5.2; MS (FAB) m/z 917 (MH+); exact MS (FAB) calcd
for C43H70N5O11Si3 916.4379, found 916.4352. Anal. Calcd for
C43H69N5O11Si3: C, 56.36; H, 7.59; N, 7.64. Found: C, 56.36; H, 7.50;
N, 7.61.
Methyl 3,4-Di-O-triisopropylsilyl-1-phenylthio-2-ulos-D-glucur-
onate (29b). In a manner similar to that described for 29a, the reaction
of 28b (1.39 g, 2.28 mmol, the ratio of R/â ) 60/40) with Dess-
Martin periodinane (1.16 g, 2.74 mmol) in CH2Cl2 (25 mL) and
purification by column chromatography (SiO2, 50% benzene/hexane)
gave 29b as an inseparable anomeric mixture (1.12 g, 81% as a colorless
syrup, the ratio of R/â ) 60/40): MS (FAB) m/z 611 (M+). Anal. Calcd
for C31H54O6SSi2: C, 60.94; H, 8.91. Found: C, 60.83; H, 8.83. For
R-anomer: 1H NMR (CDCl3, 500 MHz) δ 7.62 (d, 2H, J ) 7.0 Hz),
7.31-7.22 (m, 3H), 5.65 (s, 1H), 4.92 (d, 1H, J ) 4.3 Hz), 4.6 (s,
1H), 4.15 (d, 1H, J ) 4.3 Hz), 3.79 (s, 3H), 1.12-1.00 (m, 42H); 13
C
NMR (CDCl3,125 MHz) δ 199.2, 169.1, 133.4, 132.2, 129.2, 128.3,
127.7, 86.9, 78.9, 76.3, 74.0, 52.5, 25.9, 25.8. For â-anomer: 1H NMR
(CDCl3, 500 MHz) δ 7.64 (d, 2H, J ) 7.0 Hz), 7.31-7.22 (m, 3H),
6.42 (s, 1H), 4.85 (d, 1H, J ) 4.1 Hz), 4.70 (s, 1H), 4.19 (d, 1H, J )
4.1 Hz), 3.78 (s, 3H), 1.12-1.00 (m, 42H); 13C NMR (CDCl3, 125
MHz) δ 198.0, 169.0, 132.8, 132.1129.2, 128.3, 128.1, 88.2, 78.1, 75.5,
75.4, 52.4, 25.8, 25.7.
Methyl 3-O-tert-Butyldimethylsilyl-4-O-tert-butyldiphenylsilyl-1-
phenylthio-2-ulos-D-glucuronate (29c). In a manner similar to that
described for 28a, the reaction of 28c (1.78 g, 2.74 mmol, the ratio of
R/â ) 72/28) with Dess-Martin periodinane (1.39 g, 3.29 mmol) in
CH2Cl2 (30 mL) and purification by column chromatography (SiO2,
N6-Benzoyl-9-[methyl 6,10-Anhydro-3-O-(tert-butyldimethylsilyl)-
2-O-methyl-8,9-di-O-(triisopropylsilyl)-r-D-arabino-L-ido-7-undecu-
lofuranuronyl]adenine (30b-r) and N6-Benzoyl-9-[methyl 6,10-
Anhydro-3-O-(tert-butyldimethylsilyl)-2-O-methyl-8,9-di-O-(triiso-
propylsilyl)-â-D-arabino-D-gluco-7-undeculofuranuronate]adenine
(30b-â). In a manner similar to that described for 30a, from 29b (196
mg, 0.32 mmol), 30b-r (122 mg, 38% as a white foam) and 30b-â
(103 mg, 33% as a white foam) were obtained after purification by
flash column chromatography (SiO2, 40% EtOAc/hexane). For R-ano-
1
mer: [R]D -32.7° (c 1.06, CHCl3); H NMR (CDCl3, 500 MHz) δ

Total Synthesis of Herbicidin B
J. Am. Chem. Soc., Vol. 121, No. 44, 1999 10279
9.08 (br s, 1H, exchanged with D2O), 8.83 (s, 1H), 8.39 (s, 1H), 8.03
(d, 2H, J ) 7.5 Hz), 7.61 (t, 1H, J ) 7.4 Hz), 7.53 (t, 2H, J ) 7.8 Hz),
6.22 (s, 1H), 4.84 (d, 1H, J ) 4.3 Hz), 4.61 (s, 1H), 4.58 (br s, 3H),
4.54 (s, 1H), 4.03 (d, 1H, J ) 4.3 z), 3.93 (br s, 1H), 3.79 (s, 3H), 3.61
(s, 3H), 3.57 (br s, 1H, exchanged with D2O), 1.05-1.01 (m, 42H),
0.73 (s, 9H), 0.13 (s, 3H), -0.96 (s, 3H); 13C NMR (CDCl3, 125 MHz)
δ 203.4, 169.9, 164.5, 152.5, 149.0, 141.9, 133.8, 132.5, 128.7, 127.7,
90.5, 88.6, 82.1, 80.3, 77.9, 77.2, 75.1, 74.1, 69.8, 58.2, 52.3, 25.5,
17.9, 17.7, 12.1, -5.1, -5.2; MS (FAB) m/z 1001 (MH+); exact MS
(FAB) calcd for C49H82N5O11Si3 1000.5318, found 1000.5320. Anal.
Calcd for C49H81N5O11Si3: C, 58.83; H, 8.16; N, 7.00. Found: C, 58.62;
reduced pressure. The residue was purified by flash column chroma-
tography (SiO2, 40% EtOAc/hexane) to give 31a (28 mg, 66% as a
1
pale yellow foam): [R]D -7.55° (c 1.02, CHCl3); H NMR (CDCl3,
500 MHz) δ 9.04 (br s, 1H, exchanged with D2O), 8.84 (s, 1H), 8.41
(s, 1H), 8.03 (d, 2H, J ) 7.5 Hz), 7.61 (t, 1H, J ) 7.5 Hz), 7.54 (t, 2H,
J ) 7.5 Hz), 6.32 (s, 1H), 6.08 (d, 1H, J ) 8.1 Hz), 5.36 (dd, 1H, J )
2.9, 8.1 Hz), 4.65 (d, 1H, J ) 1.7 Hz), 4.56 (dd, 1H, J ) 1.7, 3.8 Hz),
4.28 (d, 1H, J ) 2.8 Hz), 4.12 (d, 1H, J ) 1.7 Hz), 3.99 (d, 1H, J )
3.9 Hz), 3.77 (s, 3H), 3.61 (s, 3H), 0.89 (s, 9H), 0.86 (s, 9H), 0.76 (s,
9H), 0.15 (s, 3H), 0.13 (s, 3H), 0.10 (s, 3H), 0.07 (s, 3H), 0.02 (s, 3H),
-0.09 (s, 3H); 13C NMR (CDCl3, 125 MHz) δ 189.2, 168.5, 152.5,
150.8, 149.2, 147.5, 141.9, 133.8, 132.6, 128.7, 127.8, 122.6, 111.3,
91.4, 88.1, 79.6, 76.5, 76.4, 72.8, 72.5, 58.4, 52.4, 25.6, 25.6, 25.5,
18.4, 18.0, -4.8, -4.9, -5.0, -5.0, -5.1, -5.2; MS (FAB) m/z 899
(MH+); exact MS (FAB) calcd for C43H68N5O10Si3 898.4273, found
898.4302. Anal. Calcd for C43H67N5O10Si3‚H2O: C, 56.36; H, 7.59;
N, 7.64. Found: C, 56.16; H, 7.39; N, 7.68.
1
H, 8.09; N, 6.75. For â-anomer: [R]D 1 + 12.1° (c 0.94, CHCl3); H
NMR (CDCl3, 500 MHz) δ 9.01 (br s, 1H, exchanged with D2O), 8.82
(s, 1H), 8.72 (s, 1H), 8.02 (d, 2H, J ) 7.1 Hz), 7.61 (t, 1H, J ) 7.4
Hz), 7.53 (t, 2H, J ) 7.4 Hz), 6.24 (s, 1H, J ) 4.9 Hz), 5.16 (d, 1H,
J ) 7.9 Hz), 4.82 (dd, 1H, J ) 1.7, 4.0 Hz), 4.62 (dd, 1H, J ) 1.4, 6.8
Hz), 4.54 (d, 1H, J ) 6.2 Hz), 4.39 (br s, 1H), 4.32 (m, 2H), 4.10 (d,
1H, J ) 4.0 z), 3.70 (s, 3H), 3.37 (s, 3H), 3.29 (br s, 1H, exchanged
with D2O), 1.06-1.00 (m, 42H), 0.87 (s, 9H), 0.11 (s, 3H), 0.06 (s,
3H); 13C NMR (CDCl3, 125 MHz) δ 206.0, 168.9, 164.4, 152.5, 151.3,
149.1, 142.3, 133.8, 132.5, 128.7, 127.7, 122.7, 88.8, 86.4, 78.9, 76.5,
76.2, 75.6, 75.5, 72.1, 67.6, 58.7, 52.0, 25.6, 17.9, 17.8, 17.7, 17.6,
12.2, 12.0, -4.8, -5.0; MS (FAB) m/z 1001 (MH+); exact MS (FAB)
calcd for C49H82N5O11Si3 1000.5318, found 1000.5390. Anal. Calcd
for C49H81N5O11Si3: C, 58.83; H, 8.16; N, 7.00. Found: C, 58.74; H,
8.02; N, 6.99.
N6-Benzoyl-9-[methyl 6,10-Anhydro-3-O-(tert-butyldimethylsilyl)-
6-dehydro-5-deoxy-8,9-di-O-(triisopropylsilyl)-2-O-methyl-r-D-ara-
bino-L-ido-7-undeculofuranuronyl]adenine (31b). In a manner similar
to that described for 31a, the reaction of 30b (60 mg, 60 µmol) with
Burgess’s inner salt (87 mg, 360 µmol) in toluene (5 mL) and
purification by flash silica gel column chromatography (SiO2, 40%
EtOAc/hexane) gave 31b (41 mg, 70% as a pale yellow foam): [R]D
1
-13.6° (c 1.02, CHCl3); H NMR (CDCl3, 500 MHz) δ 9.04 (br s,
1H, exchanged with D2O), 8.84 (s, 1H), 8.40 (s, 1H), 8.03 (d, 2H, J )
7.6 Hz), 7.61 (t, 1H, J ) 7.5 Hz), 7.53 (t, 2H, J ) 7.6 Hz), 6.31 (s,
1H), 6.04 (d, 1H, J ) 8.2 Hz), 5.39 (dd, 1H, J ) 2.9, 8.2 Hz), 4.83
(dd, 1H, J ) 1.7, 3.6 Hz), 4.75 (s, 1H), 4.26 (d, 1H, J ) 2.9 Hz), 4.13
(d, 1H, J ) 3.9 Hz), 3.99 (s, 1H), 3.76 (s, 3H), 3.63 (s, 3H), 1.14-
1.02 (m, 42H), 0.76 (s, 9H), 0.04 (s, 3H), -0.10 (s, 3H); 13C NMR
(CDCl3, 125 MHz) δ 189.2, 168.5, 152.5, 150.8, 149.2, 147.5, 141.9,
133.8, 132.6, 128.7, 127.8, 122.6, 111.3, 91.4, 88.1, 79.6, 76.5, 76.4,
72.8, 72.5, 58.4, 52.4, 25.6, 25.6, 25.5, 18.4, 18.0, -4.8, -4.9, -5.0,
-5.0, -5.1, -5.2; MS (FAB) m/z 983 (MH+); exact MS (FAB) calcd
for C49H80N5O10Si3 982.5212, found 982.5192. Anal. Calcd for
C49H79N5O10Si3‚0.5EtOAc: C, 59.67; H, 8.15; N, 6.82. Found: C,
59.26; H, 7.76; N, 7.16.
N6-Benzoyl-9-[methyl 6,10-Anhydro-3,8-O-(tert-butyldimethyl-
silyl)-2-O-methyl-9-O-(tert-butyldiphenylsilyl)-r-D-arabino-L-ido-7-
undeculofuranuronyl]adenine (30c-r) and N6-Benzoyl-9-[methyl
6,10-Anhydro-3,8-O-(tert-butyldimethylsilyl)-2-O-methyl-9-O-(tert-
butyldiphenylsilyl)-â-D-arabino-D-gluco-7-undeculofuranuronate]ad-
enine (30c-â). In a manner similar to that described for 30a, from 29c
(300 mg, 0.46 mmol), 30c-r (198 mg, 41% as a white foam) and 30c-â
(135 mg, 29% as a white foam) were obtained after purification by
flash column chromatography (SiO2, 40% EtOAc/hexane). For R-ano-
1
mer: [R]D -36.3° (c 1.15, CHCl3); H NMR (CDCl3, 500 MHz) δ
9.06 (br s, 1H, exchanged with D2O), 8.84 (s, 1H), 8.43 (s, 1H), 8.03
(d, 2H, J ) 7.3 Hz), 7.65-7.39 (m, 13H), 6.26 (s, 1H), 4.74 (d, 1H, J
) 2.1 Hz), 4.57 (m, 5H), 3.98 (br s, 2H), 3.68 (d, 1H, J ) 4.2 z), 3.64
(s, 3H), 3.60 (s, 3H), 1.02 (s, 9H), 0.74 (s, 9H), 0.68 (s, 9H), 0.14 (s,
3H), -0.08 (s, 3H),- 0.17 (s, 3H), -0.23 (s, 3H); 13C NMR (CDCl3,
125 MHz) δ 203.3, 170.2, 152.5, 150.7, 149.1, 141.9, 135.7, 133.8,
132.5, 132.1, 132.0, 130.3, 130.1, 128.7, 127.9, 127.8, 127.7, 122.8,
90.7, 88.5, 82.1, 80.8, 77.2, 75.0, 73.3, 73.1, 70.2, 58.2, 52.2, 26.8,
25.6, 25.4, 19.1, 18.1, 18.0, -5.1, -5.2, -5.6; MS (FAB) m/z 1041
(MH+); exact MS (FAB) calcd for C53H74N5O11Si3 1040.4692, found
1040.4700. Anal. Calcd for C53H73N5O11Si3‚EtOAc: C, 60.66; H, 7.23;
N, 6.21. Found: C, 60.35; H, 7.05; N, 6.25. For â-anomer: [R]D +11.4°
(c 1.06, CHCl3); 1H NMR (CDCl3, 500 MHz) δ 9.03 (br s, 1H,
exchanged with D2O), 8.82 (s, 1H), 8.72 (s, 1H), 8.02 (d, 2H, J ) 7.3
Hz), 7.60-7.38 (m, 13H), 6.25 (d, 1H, J ) 4.4 Hz), 5.06 (d, 1H, J )
7.9 Hz), 4.69 (d, 1H, J ) 6.5 Hz), 4.55 (m, 3H), 4.41 (d, 1H, J ) 6.7
Hz), 4.32 (br s, 2H), 3.84 (d, 1H, J ) 4.0 Hz), 3.57 (s, 3H), 3.39 (s,
3H), 1.06 (s, 9H), 0.88 (s, 9H), 0.69 (s, 9H), 0.15 (s, 3H), 0.07 (s, 3H),
- 0.16 (s, 3H), -0.17 (s, 3H); 13C NMR (CDCl3, 125 MHz) δ 206.1,
168.8, 152.5, 151.4, 149.2, 142.3, 135.6, 135.5, 133.8, 132.5, 132.2,
130.2, 130.1, 128.7, 127.9, 127.8, 127.7, 122.6, 89.0, 86.6, 79.3, 76.7,
75.7, 75.5, 75.0, 67.8, 58.7, 51.9, 89.0, 86.6, 79.3, 77.3, 77.0, 76.7,
75.7, 75.5, 75.0, 72.5, 67.8, 58.7, 51.9, 26.8, 25.7, 25.4, 19.2, 18.0,
17.9, -4.7, -4.8, -5.2, -5.3; MS (FAB) m/z 1041 (MH+); exact MS
(FAB) calcd for C53H74N5O11Si3 1040.4692, found 1040.4680. Anal.
Calcd for C53H73N5O11Si3‚EtOAc: C, 60.66; H, 7.23; N, 6.21. Found:
C, 60.47; H, 6.97; N, 6.50.
N6-Benzoyl-9-[methyl 6,10-Anhydro-3,8-di-O-(tert-butyldimeth-
ylsilyl)-6-dehydro-5-deoxy-9-O-(tert-butyldiphenylsilyl)-2-O-methyl-
r-D-arabino-L-ido-7-undeculofuranuronyl]adenine (31c). In a manner
similar to that described for 31a, the reaction of 30c (60 mg, 66 µmol)
with Burgess’s inner salt (96 mg, 396 µmol) in toluene (5 mL) and
purification by flash silica gel column chromatography (SiO2, 40%
EtOAc/hexane) gave 31c (28 mg, 79% as a pale yellow foam): [R]D
1
-22.0° (c 0.68, CHCl3); H NMR (CDCl3, 500 MHz) δ 9.12 (br s,
1H, exchanged with D2O), 8.84 (s, 1H), 8.43 (s, 1H), 8.03 (d, 2H, J )
7.5 Hz), 7.61 (t, 1H, J ) 7.5 Hz), 7.54 (t, 2H, J ) 7.5 Hz), 7.49-7.40
(m, 10H), 6.33 (s, 1H), 6.11 (d, 1H, J ) 8.3 Hz), 5.42 (dd, 1H, J )
2.9, 8.3 Hz), 4.68 (d, 1H, J ) 1.4 Hz), 4.55 (dd, 1H, J ) 2.0, 3.6 Hz),
4.32 (d, 1H, J ) 2.9 Hz), 4.01 (s, 1H), 3.83 (d, 1H, J ) 3.6 Hz), 3.65
(s, 3H), 3.64 (s, 3H), 1.06 (s, 9H), 0.78 (s, 9H), 0.69 (s, 9H), 0.09 (s,
3H), 0.07 (s, 3H), -0.14 (s, 3H), -0.15 (s, 3H); 13C NMR (CDCl3,
125 MHz) δ 181.3, 169.6, 169.3, 163.0, 139.7, 134.6, 132.0, 129.3,
128.1, 111.4, 102.4, 101.7, 100.1, 88.6, 87.2, 84.9, 76.4, 76.2, 75.9,
71.9, 69.5, 68.4, 63.8, 36.0, 30.3, 27.9, 26.0, 21.4, 20.9, -4.0, -4.2,
-4.5, -4.8; MS (FAB) m/z 1023 (MH+); exact MS (FAB) calcd for
C53H72N5O10Si3 1022.4586, found 1022.4579. Anal. Calcd for C53H71-
N5O10Si3: C, 62.26; H, 7.00; N, 6.85. Found: C, 62.54; H, 6.77; N,
6.32.
Herbicidin B (1b). A mixture of 31c (50 mg, 55 µmol), HCO2NH4
(173 mg, 5.5 mmol), and Pd-on-carbon (20%, 15 mg) in MeOH (5
mL) was stirred for 24 h at room temperature. The mixture was filtrated
through a Celite pad, and the filtrate was evaporated under reduced
pressure. The residue was partitioned between EtOAc (5 mL) and H2O
(2 mL), and the separated organic layer was washed with H2O (3 mL)
and brine (3 mL). The organic layer was dried (Na2SO4) and evaporated
under reduced pressure. A mixture of the residue in MeOH (5 mL)
containing Sm (9.2 mg, 59 µmol) and I2 (15 mg, 59 µmol) was stirred
for 15 min at room temperature. The mixture was evaporated under
reduced pressure, and the residue was partitioned between EtOAc (5
N6-Benzoyl-9-[methyl 6,10-Anhydro-3,8,9-tri-O-(tert-butyldime-
thylsilyl)-6-dehydro-5-deoxy-2-O-methyl-r-D-arabino-L-ido-7-unde-
culofuranuronyl]adenine (31a). A mixture of 30a (60 mg, 66 µmol)
and Burgess’s inner salt (96 mg, 396 µmol) in toluene (5 mL) was
heated under reflux for 1 h. After being cooled to room temperature,
the mixture was evaporated under reduced pressure. The residue in
EtOAc (30 mL) was washed with H2O (3 × 20 mL) and brine (10
mL). The organic layer was dried (Na2SO4) and evaporated under

10280 J. Am. Chem. Soc., Vol. 121, No. 44, 1999
Ichikawa et al.
mL) and H2O (2 mL). The organic layer was washed with H2O (3 mL)
and brine (3 mL), dried (Na2SO4), and evaporated under reduced
pressure. A solution of the residue in THF (5 mL) containing TBAF
(1 M THF solution, 50 µL, 50 µmol) was stirred for 30 min at 0 °C.
The mixture was evaporated under reduced pressure, and the residue
was purified by preparative TLC (17% MeOH/CHCl3) to give herbicidin
B (7.3 mg, 31%): [R]D +55.1° (c 0.61, MeOH), lit.3b [R]D +63° (c 1,
Found: C, 47.89; H, 5.09; N, 14.78.
Acknowledgment. We thank the Japan Society for Promo-
tion of Sciences (S.I.) for support of this research. Herbicidin
B was generously given by Sankyo Co., Tokyo, Japan.
Supporting Information Available: General experimental
methods, experimental details for the synthesis of 9-13, 19a,b,
and 20-23, and complete 1H NMR spectral information for 22,
23, 25, 27b, and synthetic and natural herbicidin B (PDF). This
material is available free of charge via the Internet at
http://pubs.acs.org.
1
MeOH); H NMR (CD3OD, 500 MHz) δ 8.59 (s, 1H), 8.11 (s, 1H),
6.08 (s, 1H), 4.58 (t, 1H, J ) 8.6 Hz), 4.35 (s, 1H), 4.33 (d, 1H, J )
2.3 Hz), 4.27 (s, 1H), 4.25 (d, 1H, J ) 3.3 Hz), 3.90 (s, 1H), 3.62 (s,
3H), 3.37 (t, 1H, J ) 9.5 Hz), 3.44 (s, 3H), 2.14 (br s, 1H), 2.12 (s,
1H); 13C NMR (CD3OD, 125 MHz) δ 171.8, 154.0, 142.4, 94.6, 92.2,
89.1, 79.7, 78.0, 74.4, 73.8, 71.3, 65.5, 58.4, 26.4; MS (FAB) m/z 454
(MH+). Anal. Calcd for C18H23N5O9: C, 47.68; H, 5.11; N, 15.45.
JA992608H