Synthesis of the hexasaccharide fragment of landomycin A: Application of glycosyl tetrazoles and phosphites in the synthesis of a deoxyoligosaccharide

Article abstract of DOI:10.1021/ja973348b

The synthesis of the hexasaccharide fragment of the antitumor antibiotic landomycin A (1) (aka. NSC 639187) is described. The stereocontrolled introduction of key glycoside linkages relies on the combined application of glycosyl tetrazoles and phosphites

Full text of DOI:10.1021/ja973348b

1392
J. Am. Chem. Soc. 1998, 120, 1392-1397
Synthesis of the Hexasaccharide Fragment of Landomycin A:
Application of Glycosyl Tetrazoles and Phosphites in the Synthesis of
a Deoxyoligosaccharide
Yu Guo and Gary A. Sulikowski*
Contribution from the Department of Chemistry, Texas A&M UniVersity, College Station, Texas 77843
ReceiVed September 24, 1997
Abstract: The synthesis of the hexasaccharide fragment of the antitumor antibiotic landomycin A (1) (aka.
NSC 639187) is described. The stereocontrolled introduction of key glycoside linkages relies on the combined
application of glycosyl tetrazoles and phosphites to establish R and â glycosidic linkages, respectively. Spectral
comparison of landomycin A octaacetate (2) and hexasaccharide pentaacetate (3) serves to corroborate the
assigned structure of 1 within the oligosaccharide domain.
Deoxygenated oligosaccharides are ubiquitous among sec-
not known but recent work has indicated 1 inhibits the uptake
of tritium labeled thymidine in cell culture, suggesting interfer-
ence with DNA synthesis to be operative.6,7 In an effort to more
fully elucidate the mode of action of landomycin A as well as
to define the relationship between the oligosaccharide structure
and antitumor activity we initiated a program directed toward
the total synthesis of landomycin A. As a first step, we describe
the assembly of hexasaccharide 3. Further, spectral comparison
of 3 to 2 serves to confirm the assigned structure of 1 within
the oligosaccharide domain.
From the strategic perspective, bond disconnection about the
C1′′′-C4′′ glycoside linkage reduces the synthesis of 3 to the
preparation of trisaccharides 4 and 5, which possess identical
stereochemical as well as constitutional features, and can be
assembled in parallel with minor adjustments in the protecting
group scheme. In the final merger of 4 and 5, an activated
derivative of trisaccharide 4 would serve as a glycosyl donor,
while 5 would serve as the corresponding acceptor. Implicit
within this plan was the formidable challenge of merging
deoxysugar units to produce 2-deoxy glycosides in the desired
stereochemical arrangement. Of the many methods available
for the introduction of 2-deoxy-R-glycoside linkages, we chose
to take advantage of glycosyl tetrazoles as donors, since these
are hydrolytically stable even within 2,3,6-trideoxy sugars.8,9
On the other hand, the choice of glycosyl donor for the
stereocontrolled introduction of the four 2-deoxy-â-glycoside
linkages within 3 was less clear. With few exceptions, most â
selective glycosylation methods rely on participation of an
equatorially disposed C(2) heteroatom within the glycosyl donor,
which is subsequently removed following the coupling reac-
tion.10,11 One notable exception is the use of glycosyl phosphites
as donors, which have been reported to afford 2-deoxy-â-
ondary metabolites, particularly within the genus streptomyces.1
Recently, the importance of the oligosaccharide component of
these substances in relation to bioactivity has become apparent,
particularly evident among the aureolic acid2 and enediyne
antitumor antibiotics.3 Landomycin A (1), a member of the
angucycline group of antibiotics, was discovered during the
course of screening Streptomyces for new antitumor agents and
has been characterized as the octaacetate derivative 2.4
A
particularly striking feature of 1 is the deoxygenated hexasac-
charide unit comprising two repeating trisaccharides, each
consisting of the sequence R-L-rhodinose-(1f3)-â-D-olivose-
(1f4)-â-D-olivose. In vitro evaluation of landomycin A (1) at
the National Cancer Institute under the synonym NSC 639187
revealed a broad spectrum of antitumor activity.5 However,
subsequent in vivo evaluation demonstrated 1 to be overtly
cytotoxic, which precluded any further development as a drug
candidate. The specific mode of action of landomycin A (1) is
(1) (a) Kennedy, J. F.; White, C. A. BioactiVe Carbohydrates in
Chemistry, Biochemistry and Biology; Ellis Horwood: Chichester, 1983.
(b) Kirschning, A.; Bechthold, A.; Rohr, J. Top. Curr. Chem. 1997, 188, 1.
(2) Aureolic acids: (a) Remers, W. A. In The Chemistry of Antitumor
Antibiotics; Wiley-Interscience: New York, 1979; Vol. 1, Chapter 3, p 133.
(b) Gao, X.; Patel, D. J. Biochemistry 1989, 28, 751. (c) Banville, D. L.;
Keniry, M. A.; Kam, M.; Shafer, R. H. Biochemistry 1990, 29, 6521. (d)
Banville, D. L.; Keniry, M. A.; Shafer R. H. Biochemistry 1990, 29, 9294.
(e) Snyder, R. C.; Ray, R.; Blume, S.; Miller, D. M. Biochemistry 1991,
30, 4290. (f) Sastry, M.; Patel, D. J. Biochemistry 1993, 32, 6588. (g) Silva,
D. J.; Kahne, D. J. Am. Chem. Soc. 1993, 115, 7962. (h) Silva, D. J.; Kahne,
D. J. Am. Chem. Soc. 1994, 116, 2641.
(3) Enediyne antibiotics: (a) Zein, N.; Sinha, A. M.; McGahren, W. J.;
Ellestad, G. A. Science 1988, 240, 1198. (b) Zein, N.; Poncin, M.;
Nilakantan, R.; Ellestad, G. A. Science 1989, 244, 697. (c) Drak, J.; Iwasawa,
N.; Danishefsky, S.; Crothers, D. M. Proc. Natl. Acad. Sci. U.S.A. 1991,
88, 7464. (d) Walker, S.; Landovitz, R.; Ding, W.-D.; Ellestad, G. A.; Kahne,
D. Proc. Natl. Acad. Sci. U.S.A. 1992, 89, 4608. (e) Aiyar, J.; Danishefsky,
S. J.; Crothers, D. M. J. Am. Chem. Soc. 1992, 114, 7552. (f) Nicolaou, K.
C.; Tsay, S.-C.; Suzuki, T.; Joyce, G. F. J. Am. Chem. Soc. 1992, 114,
7555. (g) Paloma, L. G.; Smith, J. A.; Chazin, W. J.; Nicolaou, K. C. J.
Am. Chem. Soc. 1994, 116, 6, 3697. (h) Li, T.; Zeng, Z.; Estevez, V. A.;
Baldenium, K. U.; Nicolaou, K. C.; Joyce, G. F. J. Am. Chem. Soc. 1994,
116, 3709. (i) Nicolaou, K. C.; Smith, B. M.; Pastor, J.; Watanabe, Y.;
Weinstein, D. S. Synlett 1997, 401.
(6) Unpublished results of Professor Kenneth Ramos and Dr. Robert
Crow, Texas A&M Univeristy, Departments of Chemistry and Veterinary
Physiology and Pharmacology.
(7) The cytostatic activity of landomycins A-E is reported to be
dependent on the length of the oligosaccharide side-chain. See: Rohr, J.;
Wohlert, S.-E.; Oelkers, C.; Kirschning, A.; Ries, M. J. Chem. Soc., Chem.
Commun. 1997, 973.
(8) For a review of O-glycosylation methods, see: Toshima, K.; Tatsuta,
K. Chem. ReV. 1993, 93, 1503.
(9) (a) Falahatpisheh, N.; Sulikowski, G. A. Synlett 1994, 672. (b) Sobti,
K.; Kim, K.; Sulikowski, G. A. J. Org. Chem. 1996, 61, 6.
(4) (a) Henkel, T.; Rohr, J.; Beale, J.; Schwenen, L. J. Antibiot. 1990,
43, 492. (b) Structure Revision: Weber, S.; Zolke, C.; Rohr, J.; Beale, J.
J. Org. Chem. 1994, 59, 4211.
(5) Personal communication. Dr. Anthony B. Mauger, Drug Synthesis
and Chemistry Branch, National Cancer Institute, Bethesda, MD.
S0002-7863(97)03348-9 CCC: $15.00 © 1998 American Chemical Society
Published on Web 02/06/1998

Synthesis of the Hexasaccharide Fragment of Landomycin A
J. Am. Chem. Soc., Vol. 120, No. 7, 1998 1393
Scheme 1a
glycosides as the major isomer.12 Herein we illustrate through
the described synthesis of 3 the combined utility of glycosyl
tetrazoles and phosphites in the stereocontrolled assembly of
deoxygenated oligosaccharides.
Glycosyl tetrazole 7 was obtained by the Mitsunobu reaction
of L-rhodinose derivative 6 and 1H-tetrazole (Scheme 1).13,14
Next, glycosyl tetrazole 7 was coupled with D-rhamnal using
Me3OBF4 as an activating agent and propionitrile as the solvent.
Under these conditions a single disaccharide 8 was obtained in
75% yield. Notably, in this coupling reaction no O(4) glycos-
ylation was observed.15 Acetylation of 8 afforded glycal 9
which was converted to the phenylselenyl acetates 10a and 10b.
Following a series of failed attempts to engage 10a (and other
derivatives) in a â selective glycosylation we turned our attention
to the use of the corresponding 2-deoxy glycosyl phosphite as
a â selective glycosyl donor.12a To implement this strategy,
we initially planned a two-step sequence to remove the
phenylselenyl group and anomeric acetate separately. However,
when 10a (or 10b) was subjected to an excess of tributyltin
hydride (with catalytic AIBN), we found the phenylselenyl
group and anomeric acetate had been removed as well as the
choroacetate reduced. Though the mechanism of the process
a (a) THF, 0-20 °C, 70%. (b) C2H5CN, 4 Å molecular sieves, -78
to 20 °C, 75%. (c) DMAP, CH2Cl2, 20 °C, 91%. (d) PhCH3, 0-20 °C,
83%. (e) PhCH3, reflux, 80%. (f) CH2Cl2, -78 °C, 76%. (g) PhCH3,
-94 °C, 5 min, 69%. (h) THF, 0 °C, 92%. (i) DMAP, CH2Cl2, 20 °C,
93%. (j) MeOH, 20 °C, 78%.
leading to the loss of the anomeric acetate requires further
investigation, we were pleased to discover a direct preparation
of lactol 11 without the loss of other acetate protecting groups.16
Disaccharide 11 was converted to glycosyl phosphite 12 in 76%
yield.17 The stage was now set for the crucial coupling between
12 and 13. In the event, coupling of 12 with acceptor 13 at
-94 °C in toluene (cat. TMSOTf) furnished trisaccharide 14
in 69% yield with good â selectivity (R:â 24:76). Following
exchange of the C3 silyl ether for an acetate group, the anomeric
acetate of trisaccharide 16 was removed by hydrazinolysis to
afford 4 in 78% yield.18
(10) (a) Roush, W. R.; Sebesta, D. P.; Bennett, C. E. Tetrahedron 1997,
53, 8825 and references cited within. (b) Roush, W. R.; Sebesta, D. P.;
James, R. A. Tetrahedron 1997, 53, 8837 and references cited within. (c)
Ramesh, S.; Kaila, N.; Gewal, G.; Franck, R. W. J. Org. Chem. 1990, 55,
5 and references cited within.
(11) (a) Garegg, P. J.; Ossowski, P. Acta Chem. Scand., Ser. B 1983, B
37, 249. (b) Garegg, P. J.; Kopper, S.; Ossowski, P.; Thiem, J. J. Carbohydr.
Chem. 1986, 5, 59. (c) Wiesner, K.; Tsai, T. Y. R.; Jin, H. HelV. Chim.
Acta 1985, 68, 300. (d) Crich, D.; Ritchie, T. J. Chem. Soc., Chem. Commun.
1988, 1461. (e) Kahne, D.; Yang, D.; Lim, J. J.; Miller, R.; Paguaga, E. J.
Am. Chem. Soc. 1988, 110, 8716. (f) Binkley, R.; Sivik, M. R. J. Carbohydr.
Chem. 1991, 10, 399. (g) Marzabadi, C. H.; Franck, R. W. J. Chem. Soc.,
Chem. Commun. 1996, 2651.
Having completed the assembly of donor trisaccharide 4, we
next turned our attention to the assembly of acceptor trisaccha-
ride 5. Roush has illustrated the utility of an equatorially
disposed C(2) phenylselenide for the stereocontrolled introduc-
tion of a â-arylglycoside using the Mitsunobu protocol.19 With
this in mind we prepared selenide 19, which was coupled with
(12) (a) Hashimoto, S.; Sano, A.; Sakamoto, H.; Nakajima, M.; Yanagiya,
Y. Ikegabi. S. Synlett 1995, 1271. (b) Peterson, I.; Mcleod, M. Tetrahedron
Lett. 1995, 36, 9065.
(13) (a) Mitsunobu, O. Synthesis 1981, 1. (b) Hughes, D. L. Organic
Prepr. and Proced. 1996, 28, 127.
(14) The corresponding N1 isomer of 7 was produced as a minor
component contaminated with triphenylphosphine oxide. This material was
not utilized in the subsequent coupling reaction.
(15) Danishefsky, S. J.; Koseki, K.; Griffith, D. A.; Gervay, J.; Peterson,
J. M.; McDonald, F. E.; Oriyama, T. J. Am. Chem. Soc. 1992, 114, 8331.
(16) The reduction of the anomeric acetate proceeds at a slower rate
relative to reduction of the C(4′) chloroacetate and C(2) phenylselenide.
Also, additional AIBN is required for removal of the anomeric acetate.
(17) The ratio of anomeric phosphites was determined by 121.4 MHz
31P NMR using 85% H3PO4 as an internal standard. 12: 66:34 (R/â) δ )
110.2 and δ ) 109.0; 22: 57:43 (R/â) δ ) 140.0 and δ ) 138.9; 27: 58:
42 (R/â) δ ) 147.5 and δ ) 146.0.
(18) Exoffier, G.; Gagnaire, D.; Utille, J.-P. Carbohydr. Res. 1975, 39,
368.

1394 J. Am. Chem. Soc., Vol. 120, No. 7, 1998
Guo and Sulikowski
Scheme 2a
a (a) PhCH3, 0-20 °C, 85%. (b) MeOH, 20 °C, 74%. (c) PhCH3, 4
Å molecular sieves, 0 °C, 77%. (d) PhH, reflux, 77%. (e) PhCH3, -94
°C, 5 min, 72%. (f) THF, 0 °C, 85%. (g) DMAP, CH2Cl2, 20 °C, 90%.
(h) MeOH, 20 °C, 72%.
p-methoxyphenol using Mitsunobu reaction conditions to pro-
vide 20 with very good â selectivity (R:â 1:10). Reductive
removal of the C(2) phenylselenide afforded 21, which was
coupled with glycosyl phosphite 2217,20 (prepared starting from
the C(4) phenoxyacetate derivative of L-rhodinose). The
coupling of 21 and 22 proceeded in 72% yield and with â
selectivity (R:â 26:74). Following exchange of the O(3)
triethylsilyl group for an acetyl, removal of the O(4′′) phenoxy-
acetyl group afforded trisaccharide 5.21
Figure 1. Partial 13C NMR (75 MHz, CDCl3) spectra for landomycin
A octaacetate (2), hexasaccharide pentaacetate 3, and hexasaccharide
pentaacetate R-3 in the anomeric carbon region: (A) landomycin A
octaacetate (2), (B) hexasaccharide pentaacetate 3, and (C) hexasac-
charide pentaacetate R-3.
pertinent respects with landomycin A octaacetate (2).22 Par-
ticularly supportiVe of the assigned structures were the es-
sentially superimposable signals corresponding to the anomeric
carbons within the 13C NMR spectrum of hexasaccharide 3 and
landomycin A octaacetate (2) (Figure 1).
In conclusion, we have described the synthesis of the
hexasaccharide fragment of landomycin A (3) using a combina-
tion of the glycosyl tetrazole and glycosyl phosphite glycosy-
lation protocols. Currently, we are comparing the biological
activity hexasaccharide 3 to landomcyin A as well as continuing
the total synthesis of landomcyin A itself.
In our synthetic scheme, the â selective coupling of trisac-
charides 4 and 5 depended on derivatization of the former as a
glycosyl phosphite. Attempts to prepare the corresponding
diethyl phosphite (26) proved unworkable presumably due to
its hydrolytic instability. However, the corresponding pinacol
phosphite 27 was isolable (67% yield) and was observable by
31P NMR.17 The utility of 27 was demonstrated in the
glycosylation of the C(4′′) hydroxyl group of acceptor 5 to afford
hexasaccharide 3 along with the corresponding R isomer (R:â
52:48, 42% yield). Importantly, the derived spectroscopic data
of 3 (1H and 13C NMR) were found to correlate well in all
Experimental Section
General Methods. All reactions were carried out under a nitrogen
or argon atmosphere using dry glassware which had been flame-dried
under a stream of nitrogen, unless otherwise noted. All necessary
solvents were purified prior to use. Tetrahydrofuran and ethyl ether
were distilled from sodium/benzophenone; dichloromethane and ben-
zene were distilled from calcium hydride. Pyridine and triethylamine
were distilled from calcium hydride and stored over sodium hydroxide.
Toluene was distilled from calcium hydride. Reactions were monitored
by thin-layer chromatography (TLC) using 0.25-mm E. Merck precoated
silica gel plates. Visualization was accomplished with UV light and
aqueous ceric ammonium molybdate solution or anisaldehyde stain
followed by charring on a hot-plate. Flash chromatography was
performed with the indicated solvents using silica gel 60 (particle size
0.040-0.063 mm). Yields refer to chromatographically and spectro-
(19) (a) Roush, R.; Lin, X.-F. Tetrahedron Lett. 1993, 34, 6829. (b)
Roush, W. R.; Lin, X.-F. J. Am. Chem. Soc. 1995, 117, 2236 and references
cited within.
(20) In contrast to the reduction of chloroacetate 10 to acetate 11, the
phenoxyacetate was unaffected upon exposure to an excess of tributyltin-
hydride (cat AIBN, refluxing toluene).
(22) We thank Professor Jurgen Rohr (Universitat Gottingen) for kindly
providing a sample of landomycin A octaacetate.
(21) Kocienski, P. Protecting Groups; Thieme, New York, 1994; p 24.

Synthesis of the Hexasaccharide Fragment of Landomycin A
J. Am. Chem. Soc., Vol. 120, No. 7, 1998 1395
scopically pure compounds unless otherwise stated. Melting points
are uncorrected unless otherwise noted. 1H and 13C NMR spectra were
recorded on a Varian-200, -300, and -400 spectrometers at ambient
temperature. 1H and 13C NMR data are reported as δ values relative
to tetramethylsilane. Infrared spectra were recorded on Mattson Galaxy
Series FT-IR 5000 or FT-IR 6021 spectrometers. Optical rotations were
measured on a Jasco DIP-181 digital polarimeter at ambient temper-
ature. High-performance liquid chromatography (HPLC) was per-
formed with a Rainin sytem. The HPLC system was equipped with a
Dynamax method manager, Rainin HPXL solvent delivery system, a
Rheodyne injector, and a Dynamax model UV-1 variable-wavelength
UV detector. The column measured 21.4 mm × 25 cm with 8-mm,
60 Å normal-phase packing. High-resolution mass spectra were
obtained at Texas A&M University Mass Spectrometry Service Center
on a VG Analytical 70S high resolution, double focusing, sectored (EB)
mass spectrometer.
mg, 0.45 mmol). After stirring at 0 °C for 30 min, silver carbonate
(100 mg, 0.60 mmol) was added. The resulting mixture was stirred
for 3.5 h and allowed to warm to room temperature. The mixture was
filtered through a plug of Celite and concentrated. The residue was
purified by flash chromatography (gradient elution: 6:1 to 3:1 hexanes-
ethyl acetate) to furnish 106 mg (61%) of 10a and 35 mg (20%) of
10b, both amorphous solids. Selenide 10a exhibited the following
characteristics: 1H NMR (300 MHz, CDCl3) δ 7.55 (m, 2H, arom),
7.26 (m, 3H, arom), 5.69 (d, J ) 9.6 Hz, 1H), 5.15 (br s, 1H), 4.84 (br
s, 1H), 4.80 (dd, J ) 9.0, 9.0 Hz, 1H), 4.10 (s superimposed m, 3H),
3.65 (dd, J ) 10.8, 8.7 Hz, 1H), 3.60 (dq, J ) 9.6, 6.3 Hz, 1H), 3.25
(dd, J ) 10.8, 9.9 Hz, 1H), 2.07 (s, 3H), 1.89 (s, 3H), 2.05-1.69 (m,
4H), 1.15 (d, J ) 6.0 Hz, 3H), 1.06 (d, J ) 6.6 Hz, 3H); HRMS(FAB)
m/z 601.0707 [(M + Na)+, calcd for C24H31O9NaSeCl 601.0719].
Lactol 11. To a solution of selenide 10a (550 mg, 0.99 mmol) in
15 mL of toluene was added tributyltin hydride (1.60 mL, 5.94 mmol)
followed by a catalytic amount of AIBN (ca. 5 mg). The mixture was
refluxed for 12 h with additional AIBN (ca. 5 mg) added every 3 h.
After cooling to room temperature, the reaction mixture was concen-
trated, and the residue purified by flash chromatography (1:1 hexanes-
ethyl acetate) to afford 277 mg (81%) of lactol 11 as an amorphous
solid: IR (CHCl3) 3427, 1738, 1442, 1376, 1050 cm-1; 1H NMR (300
MHz, CDCl3) δ 5.30 (br s), 4.92 (br s), 4.89 (br s), 4.72 (br s), 4.67
(m), 4.19-4.61 (m), 3.43 (superimposed m), 2.18 (m), 2.11 (m), 2.07
(s), 2.06 (s), 2.01 (s), 2.00 (s) 1.16 (d, J ) 6.0 Hz), 1.11 (d, J ) 6.3
Hz), 1.05 (d, J ) 6.6 Hz); 13C NMR (75 MHz, CDCl3) δ 170.9, 170.8,
170.0, 169.8, 93.7, 92.9, 92.5, 91.5, 77.2, 75.7, 74.9, 71.1, 70.2, 69.3,
69.2, 69.1, 65.8, 65.0; HRMS(FAB) m/z 369.1548 [(M + Na)+, calcd
for C16H26NaO8 369.1525].
Disaccharide 8. Diisopropyl azodicarboxylate (1.44 mL, 7.35
mmol) was added dropwise to a solution of lactol 6 (930 mg, 4.45
mmol), triphenylphosphine (1.93 g, 7.35 mmol), and 1H-tetrazole (421
mg, 6.02 mmol) in 20 mL of THF at 0 °C. The resulting mixture was
stirred for 75 min at 0 °C and concentrated. Flash chromatography
(gradient: 6:1 to 3:1 hexanes-ethyl acetate) of the residue furnished
2.05 g (∼65%) of glycosyl tetrazole 7 contaminated with diethyl
hydrazinedicarboxylate. This mixture was used in the next reaction
without further purification. A sample of R-7 exhibited the following
characteristics: [R]25D -25.5° (c 1.9, CHCl3); IR (CHCl3) 1730, 1450,
1
1369, 1284, 1130 cm-1; H NMR (300 MHz, CDCl3) δ 8.59 (s, 1H),
6.43 (d, J ) 4.2 Hz, 1H), 5.05 (br s, 1H), 4.19 (s, 2H), 3.92 (dq, J )
1.5, 6.3 Hz, 1H), 2.70-2.05 (complex m, 4H), 1.16 (d, J ) 6.6 Hz,
3H); 13C NMR (50 MHz, CDCl3) δ 166.9, 152.6, 85.7, 70.3, 68.5, 40.8,
23.0, 21.6, 16.9.
Trisaccharide 14. Glycosyl phosphite 12 (220 mg, 0.49 mmol)
and glycosyl acceptor 13 (164 mg, 0.54 mmol) were concentrated from
benzene (3 × 5 mL). Anhydrous toluene (5 mL) was introduced, and
the resultant solution cooled to -94 °C. TMSOTf (10 µL of 0.5 M
solution in dichloromethane, 0.005 mmol) was added to the solution,
and the mixture was stirred for 5 min and quenched with triethylamine
(0.5 mL). The resulting mixture was allowed to warm to 0 °C and
poured into a mixture of ethyl acetate and saturated aqueous NaHCO3
(4:1, 50 mL). The aqueous layer was extracted with ethyl acetate (3
× 40 mL), and the combined organic extracts were dried (MgSO4)
and concentrated. The residue was purified by flash chromatography
(gradient elution, 6:1 to 4:1 hexane/ethyl acetate) to afford 161 mg
(51%) of trisaccharide 14 and 55 mg (18%) of the corresponding R
isomer, both amorphous solids. Trisaccharide 14 exhibited the fol-
lowing characteristics: [R]25D -12.9° (c 0.92, CHCl3); IR(CHCl3) 3019,
To a solution of tetrazole 7 (∼2.90 mmol) and D-rhamnal (390 mg,
3.00 mmol) in 25 mL of propionitrile were added powered 4 Å mol
sieves (ca. 500 mg) and 2,6-di-tert-4-methylpyridine (615 mg, 3.00
mmol). The mixture was stirred at room temperature for 30 min and
cooled to -78 °C, and trimethyloxomium tetrafluroborate (799 mg,
5.40 mmol) was added. The reaction mixture was allowed to gradually
warm to 15 °C (6 h), quenched with solid sodium bicarbonate (ca. 1
g), and filtered through a plug of Celite. The filtrate was concentrated,
and the residue purified by flash chromatography (6:1 hexanes-ethyl
acetate) to afford 622 mg (67%) of 8 as a white solid: mp 104-105
°C; [R]25D -91.6° (c 0.97, CHCl3); IR (CHCl3) 3418, 1741, 1655, 1160
1
cm-1; H NMR (200 MHz, CDCl3) δ 6.37 (dd, J ) 7.0, 1.6 Hz, 1H),
5.05 (d, J ) 2.2 Hz, 1H), 4.95 (d, J ) 1.2 Hz, 1H), 4.66 (dd, J ) 6.1,
2.1 Hz, 1H), 4.50 (d, J ) 2.0 Hz, 1H), 4.29 (dq, J ) 1.3, 6.4 Hz, 1H),
4.15 (s, 2H), 4.10 (dt, J ) 6.9, 1.6 Hz, 1H), 3.86 (dq, J ) 9.9, 6.4 Hz,
1H), 3.41 (ddd, J ) 9.9, 6.9, 1.9 Hz, 1H), 2.25-1.55 (complex m,
4H), 1.42 (d, J ) 6.3 Hz, 3H), 1.20 (d, J ) 6.6 Hz, 3H); 13C NMR (50
MHz, CDCl3) δ 167.0, 145.2, 100.9, 98.1, 80.9 74.4, 73.1, 71.4, 66.2,
40.9, 24.5, 22.6, 17.4, 17.0; HRMS(FAB) m/z 343.0914 [(M + Na)+,
calcd for C14H21O6NaCl 343.0924].
Acetate 9. To a solution of disaccharide 8 (336 mg, 1.05 mmol) in
5 mL of dichloromethane and 1.2 mL of pyridine cooled to 0 °C was
added acetic anhydride (0.4 mL, 4.19 mmol) followed by a catalytic
amount (ca. 5 mg) of 4-(dimethylamino)pyridine. The resulting mixture
was stirred at room temperature for 5 h, diluted with dichloromethane
(25 mL), and sequentially washed with 20% aqueous CuSO4 solution
(2 × 15 mL), water (10 mL) and brine (10 mL). The organic layer
was dried (MgSO4) and concentrated. The residue was purified by
flash chromatography (5:1 hexanes-ethyl acetate) to afford 345 mg
(91%) of 9 as a white solid: [R]25D -91.6° (c 0.93, CHCl3); IR (CHCl3)
3025, 2928, 1737, 1644, 1232, 1124 cm-1; 1H NMR (300 MHz, CDCl3)
δ 6.33 (d, J ) 6.2 Hz, 1H), 4.97 (br s, 1H), 4.94 (m, 1H), 4.80 (m,
overlapping signals, 2H), 4.18 (m, 1H), 4.07 (s, 2H), 4.00 (m, 2H),
2.03 (s, 3H), 2.00-1.41 (complex m, 4H), 1.24 (d, J ) 6.5 Hz, 3H),
1.05 (d, J ) 6.6 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 169.7, 167.0,
144.7, 94.4, 93.7, 72.7, 72.4, 71.6, 68.7, 65.0, 40.9, 24.0, 22.5, 10.9,
16.9, 16.5; HRMS(FAB) m/z 385.1040 [(M + Na)+, calcd for C16H23O7-
NaCl 385.1030].
1
2960, 1741, 1375, 1217, 1041; H NMR (300 MHz, CDCl3) δ 5.65
(dd, J ) 9.6, 2.1 Hz, 1H), 4.95 (br s, 1H), 4.77 (br s, 1H), 4.66 (app
t, J ) 9.6 Hz, 1H), 4.63 (dd, J ) 9.6, 1.5 Hz, 1H), 3.92 (dq, J ) 0.9,
6.6 Hz, 1H), 3.74 (m, 2H), 3.37 (m, 2H), 3.15 (app t, J ) 8.7 Hz, 1H),
2.35 (m, 1H), 2.10 (s, 3H), 2.08 (s, 3H), 2.04 (s, 3H), 1.92-1.41
(complex m, 7H), 1.27 (d, J ) 6.3 Hz, 3H), 1.19 (d, J ) 6.6 Hz, 3H),
1.09 (d, J ) 6.6 Hz, 3H), 0.94 (t, J ) 7.8 Hz, 9H), 0.60 (q, J ) 7.8
Hz, 6H); 13C NMR (75 MHz, CDCl3) δ 170.6, 169.7, 169.1, 99.4, 92.5,
91.4, 82.1, 75.0, 72.1, 71.1, 70.2, 70.1, 69.1, 65.0, 39.0, 35.5, 23.9,
22.7, 22.6, 21.0, 20.9, 18.3, 17.7, 17.0, 6.7, 4.8; HRMS (FAB) m/z
655.3133 [(M + Na)+, calcd for C30H52O12NaSi: 655.3126].
Characterization data for trisaccharide r-14: 1H NMR (300 MHz,
CDCl3) δ 5.63 (dd, J ) 9.9, 1.8 Hz, 1H), 5.42 (d, J ) 3.0 Hz, 1H),
4.89 (br s, 1H), 4.75 (br s, 1H), 4.68 (t, J ) 9.3 Hz, 1H), 3.95 (m,
overlapping signals, 2H), 3.83 (m, overlapping signals, 2H), 3.40 (dd,
J ) 9.0 Hz, 6.0 Hz, 1H), 3.15 (app t, J ) 8.4 Hz, 1H), 2.22 (m, 1H),
2.09 (s, 3H), 2.07 (s, 3H), 2.03 (s, 3H), 1.99-1.58 (complex m, 7H),
1.30 (d, J ) 6.0 Hz, 3H), 1.12 (d, J ) 6.0 Hz, 3H), 1.08 (d, J ) 6.6
Hz, 3H), 0.93 (t, J ) 7.8 Hz, 9H), 0.57 (q, J ) 7.8 Hz, 6H); 13C NMR
(75 MHz, CDCl3) δ 170.7, 169.9, 169.2, 98.0, 93.2, 91.3, 81.3, 75.5,
73.0, 71.5, 69.6, 69.3, 66.4, 65.0, 39.2, 34.5, 24.3, 22.7, 21.1, 21.0,
20.9, 18.5, 17.4, 17.0, 6.8, 5.1; HRMS (FAB) m/z 655.3123 [(M +
Na)+, calcd for C30H52O12NaSi: 655.3126].
Alcohol 15. To a solution of trisaccharide 14 (266 mg, 0.42 mmol)
in 4 mL of THF at 0 °C was added TBAF (0.84 mL of 1 M solution
in THF, 0.84 mmol). After 5 min, the reaction was quenched with
saturated aqueous NH4Cl solution. The mixture was extracted with
Selenide 10. To a solution of disaccharide 9 (109 mg, 0.30 mmol)
in 3 mL of toluene at 0 °C was added phenylselenenyl chloride (86

1396 J. Am. Chem. Soc., Vol. 120, No. 7, 1998
Guo and Sulikowski
ethyl acetate (3 × 30 mL). The combined organic extracts were dried
(Na2SO4) and concentrated. The residue was purified by flash
chromatography (1.5:1 hexanes-ethyl acetate) to furnish 196 mg (91%)
of trisaccharide 23 and 27 mg (18%) of the corresponding R isomer,
both amorphous solids. Trisaccharide 23 exhibited the following
characteristics: [R]25D -53.2° (c 0.99, CHCl3); IR (CHCl3) 3016, 2872,
1
of 15 as an amorphous solid: [R]25 -70.9° (c 0.96, CHCl3); IR
1745, 1600, 1508 cm-1; H NMR (300 MHz, CDCl3) δ 7.29 (t, J )
D
1
(CHCl3) 3457, 2938, 1737, 1371, 1244, 1041 cm-1; H NMR (300
7.5 Hz, 2H, arom), 7.01-6.90 (m, 5H, arom), 6.80 (d, J ) 9.3 Hz, 2H,
arom), 4.95 (overlapping signals, 3H), 4.70 (overlapping signals, 4H),
3.98 (q, J ) 6.3 Hz, 1H), 3.79 (s superimposed m, 5H), 3.40 (m, 2H),
3.22 (app t, J ) 8.7 Hz, 1H), 2.27 (m, 2H), 2.06 (s, 3H), 1.99-1.41
(m, 6H), 1.34 (d, J ) 6.0 Hz, 3H), 1.23 (d, J ) 6.0 Hz, 3H), 1.10 (d,
J ) 6.6 Hz, 3H), 0.99 (t, J ) 7.8 Hz, 9H), 0.66 (q, J ) 7.8 Hz, 6H);
13C NMR (75 MHz, CDCl3) δ 169.7, 168.6, 157.6, 154.8, 151.1, 129.4,
121.6, 117.6, 114.5, 114.3, 99.4, 98.0, 92.5, 82.4, 75.0, 71.3, 71.2, 70.7,
70.4, 70.3, 65.1, 64.8, 55.5, 40.4, 35.6, 23.8, 22.6, 18.4, 17.6, 16.9,
6.8, 4.8; HRMS (FAB) m/z 811.3729 [(M + Na)+, calcd for C41H60-
NaO13Si: 811.3701].
Characterization data for trisaccharide r-23: 1H NMR (300 MHz,
CDCl3) δ 7.29 (t, J ) 7.5 Hz, 2H, arom), 7.03-6.80 (m, 7H, arom),
5.51 (d, J ) 1.8 Hz, 1H), 4.99 (d, 9.6 Hz, 1H), 4.94(br s, 2H), 4.74
(overlapping signals, 4H), 4.05 (overlapping signals, 3H), 3.80 (s 3H),
3.38 (m, 2H), 2.27 (m, 2H), 2.10 (s, 3H), 1.99-1.41 (m, 6H), 1.39 (d,
J ) 6.0 Hz, 3H), 1.09 (d, J ) 6.0 Hz, 3H), 1.06 (d, J ) 6.6 Hz, 3H),
0.99 (t, J ) 7.5 Hz, 9H), 0.66 (q, J ) 7.5 Hz, 6H).
MHz, CDCl3) δ 5.63 (dd, J ) 10.2, 2.1 Hz, 1H), 4.90 (br s, 1H), 4.70
(br s, 1H), 4.66 (app t, J ) 9.6 Hz, 1H), 4.46 (dd, J ) 9.9, 2.1 Hz,
1H), 4.40 (s, 1H, -OH), 3.87 (dq, J ) 1.2, 6.6 Hz, 1H), 3.76 (m, 1H),
3.60 (m, 1H), 3.46 (dq, J ) 9.9, 6.6 Hz, 1H), 3.38 (dq, J ) 9.0, 6.0
Hz, 1H), 2.93 (app t, J ) 8.7 Hz, 1H), 2.35 (m, 1H), 2.15 (m, 1H),
2.03 (s, 3H), 2.02 (s, 3H), 1.98 (s, 3H), 1.90-1.38 (complex m, 6H),
1.20 (d, J ) 6.3 Hz, 3H), 1.16 (d, J ) 6.3 Hz, 3H), 1.02 (d, J ) 6.6
Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 170.5, 169.5, 169.0, 100.6,
92.5, 91.4, 87.9, 74.2, 71.0, 70.6, 70.4, 69.0, 65.0, 36.6, 35.4, 23.8,
22.5, 20.9, 20.9, 20.8, 17.5, 17.3, 16.9; HRMS (FAB) m/z 541.2266
[(M + Na)+, calcd for C24H38NaO12 541.2261].
Tetraacetate 16. To a solution of trisaccharide 15 (215 mg, 0.41
mmol) in 4 mL of dichloromethane and 1.2 mL of pyridine was added
acetic anhydride (150 µL, 1.60 mmol) followed by a catalytic amount
(ca. 5 mg) of 4-(dimethylamino)pyridine. The resulting mixture was
stirred at room temperature for 5 h, diluted with dichloromethane (50
mL), and sequentially washed with 20% aqueous CuSO4 solution (2
× 15 mL), water (10 mL), and brine (10 mL). The organic layer was
dried (MgSO4) and concentrated. The residue was purified by flash
chromatography (4:1 hexanes-ethyl acetate) to afford 214 mg (92%)
of tetraacetate 16 as an amorphous solid: [R]25D -46.9° (c 1.12, CHCl3)
IR (CHCl3) 3019, 2936, 1734, 1373, 1748, 1052 cm-1; 1H NMR (300
MHz, CDCl3) δ 5.64 (dd, J ) 9.9, 2.1 Hz, 1H), 4.98 (m, 1H), 4.86 (br
s, 1H), 4.70 (br s, 1H), 4.59 (app t, J ) 9.6 Hz, 1H), 4.43 (dd, J ) 9.6,
1.8 Hz, 1H), 3.86 (q, J ) 6.6 Hz, 1H), 3.57 (m, 1H), 3.47 (m, 1H),
3.34-3.22 (overlapping signals, 2H), 2.20 (m, 2H), 2.04 (s, 3H), 2.02
(s, 3H), 1.98 (s, 3H), 1.97 (s, 3H) 1.32-1.18 (complex m, 6H), 1.23
(d, J ) 6.3 Hz, 3H), 1.13 (d, J ) 6.3 Hz, 3H), 1.02 (d, J ) 6.6 Hz,
3H); 13C NMR (75 MHz, CDCl3) δ 170.6, 169.8, 169.7, 168.8, 99.7,
92.5, 91.0, 81.1, 74.8, 71.9, 70.9, 69.8, 69.0, 64.9, 35.6, 35.1, 23.8,
22.5, 21.1, 20.9, 20.8, 20.8, 17.8, 17.7, 16.9; HRMS (FAB) m/z
583.2397 [(M + Na)+, calcd for C26H40NaO13 583.2367].
Alcohol 24. To a solution of trisaccharide 23 (260.0 mg, 0.33 mmol)
in 4 mL of THF at 0 °C was added TBAF (0.7 mL of 1 M solution in
THF, 0.70 mmol). After 5 min, the reaction was quenched with
saturated aqueous NH4Cl solution. The mixture was extracted with
ethyl acetate (3 × 30 mL). The combined extracts were dried (Na2-
SO4) and concentrated. The residue was purified by flash chromatog-
raphy (1.5:1 hexanes-ethyl acetate) to furnish 193 mg (86%) of 24 as
an amorphous solid: [R]25D -72.4° (c 0.89, CHCl3); IR (CHCl3) 2976,
1737, 1378, 1240, 1046 cm-1; 1H NMR (300 MHz, CDCl3) δ 7.25 (m,
2H, arom), 6.96-6.91 (overlapping signals, 7H, arom), 5.02 (dd, J )
9.6, 1.5 Hz, 1H), 4.96 (br s, 1H), 4.91 (br s, 1H), 4.75 (app t, J ) 9.3
Hz, 1H), 4.71 (s, 2H), 4.54 (d, J ) 10.5 Hz, 1H), 4.52 (br s, 1H), 3.97
(q, J ) 6.9 Hz, 1H), 3.84 (m, 1H), 3.76 (s, 3H), 3.70 (m, 1H), 3.55
(dq, J ) 9.6, 6.0 Hz, 1H), 3.45 (dq, J ) 9.3, 6.3 Hz, 1H), 3.06 (app t,
J ) 8.7 Hz, 1H), 2.22 (m, 2H), 2.07 (s, 3H), 2.00-1.42 (m, 6H), 1.32
(d, J ) 6.0 Hz, 3H), 1.26 (d, J ) 6.0 Hz, 3H), 1.10 (d, J ) 6.6 Hz,
3H); 13C NMR (75 MHz, CDCl3) δ 169.9, 168.6, 157.5, 154.8, 150.9,
129.4, 121.6, 117.7, 114.4, 114.3, 100.6, 98.2, 92.5, 88.3, 74.2, 70.7,
70.4, 70.3, 69.2, 65.0, 64.8, 55.4, 37.9, 35.5, 23.7, 22.6, 20.8, 17.7,
17.3, 16.8; HRMS (FAB) m/z 697.2841 [(M + Na)+, calcd for C35H46-
Trisaccharide 4. To a solution of trisaccharide 16 (76 mg, 0.14
mmol) in 1.2 mL of methanol at 0 °C was added anhydrous hydrazine
(1.2 mL of a 0.19 M solution in methanol, 0.23 mmol). The reaction
mixture was stirred at 0 °C for 3.5 h and quenched with 20% CuSO4
(10 mL). The aqueous layer was extracted with ethyl acetate (3 × 20
mL). The combined organic extracts were washed sequentially with
water (10 mL) and brine (10 mL). The organic layer was dried
(MgSO4) and concentrated. The residue was purified by flash chro-
matography (gradient elution: 2:1 to 1:1 hexanes-ethyl acetate) to
afford 50 mg (69%) of lactol 4 as an amorphous solid plus recovered
starting material (9 mg, 12%). Trisaccharide 4 exhibited the following
characteristics: [R]25D -20.4° (c 0.37, CHCl3); IR (CHCl3) 1738, 1216
NaO13 697.2836]. [R]25 -53.5° (c 0.74, CHCl3); IR (CHCl3) 2931,
D
1
1741, 1509, 1219, 1046; H NMR (300 MHz, CDCl3) δ 7.38-7.22
(m, 2H, arom), 7.05-6.84 (complex m, 7H, arom), 5.06 (m, 1H), 5.02
(dd, J ) 9.3, 1.8 Hz, 1H), 4.94 (br s, 1H), 4.93 (br s, 1H), 4.71 (s,
2H), 4.68 (app t, J ) 9.3 Hz, 1H), 4.52 (dd, J ) 9.9, 1.5 Hz, 1H), 3.97
(q, J ) 6.6 Hz, 1H), 3.79 (m, 1H), 3.77 (s, 3H), 3.49 (m, 1H), 3.39
(overlapping signals, 2H), 2.45-2.25 (m, 2H), 2.07 (s, 3H), 2.06 (s,
3H), 2.00-1.40 (complex m, 6H), 1.34 (d, J ) 6.3 Hz, 3H), 1.22 (d,
J ) 6.3 Hz, 3H), 1.09 (d, J ) 6.6 Hz, 3H); 13C NMR (75 MHz, CDCl3)
δ 170.1, 169.8, 168.7, 157.7, 155.1, 150.9, 129.5, 121.8, 118.1, 114.5,
114.4, 99.9, 98.1, 92.5, 81.5, 74.9, 71.2, 71.1, 70.4, 70.3, 70.1, 65.1,
64.9, 55.6, 36.5, 35.8, 23.8, 22.7, 21.3, 21.0, 18.1, 17.8, 17.0; HRMS
(FAB) m/z 697.2841 [(M + Na)+, calcd for C37H48NaO14 697.2836].
Diacetate 25. To a solution of trisaccharide 24 (215 mg, 0.41 mmol)
in 2.8 mL of dichloromethane and 0.7 mL of pyridine was added acetic
anhydride (150 µL, 1.60 mmol) followed by a catalytic amount (ca. 5
mg) of 4-(dimethylamino)pyridine. The resulting mixture was stirred
at room temperature for 5 h, diluted with dichloromethane (50 mL),
and sequentially washed with 20% aqueous CuSO4 solution (2 × 15
mL), water (10 mL) and brine (10 mL). The organic layer was dried
(MgSO4) and concentrated. The residue was purified by flash chro-
matography (4:1 hexanes-ethyl acetate) to afford 214 mg (92%) of
25 as an amorphous solid: [R]25D -53.5° (c 0.74, CHCl3); IR (CHCl3)
1
cm-1; H NMR (300 MHz, CDCl3) δ 5.34 (m), 5.30 (br s), 4.99 (m),
4.96 (br s) 4.79 (br s) 4.68 (app t, J ) 9.6 Hz), 4.51 (d, J ) 9.9 Hz),
4.06-3.92 (m), 3.83-3.74 (m), 3.47-3.27 (m), 3.09 (br s -OH), 2.35-
1.45 (m), 2.12 (s), 2.06 (s), 2.05 (s), 2.04 (s), 1.30 (d, J ) 6.0 Hz),
1.25 (d, J ) 7.5 Hz), 1.21 (d, J ) 6.3 Hz), 1.11 (d, J ) 6.6 Hz); 13C
NMR (75 MHz, CDCl3) δ 170.8, 170.1, 169.8, 99.9, 93.5, 92.5, 91.3,
82.4, 81.5, 75.0 74.9, 71.2, 71.1, 71.0, 70.3, 70.0, 69.2, 68.5, 68.8,
65.0, 37.9, 35.7, 35.5, 23.9, 22.7, 21.4, 21.3, 21.0, 20.9, 18.0, 17.8,
17.0; HRMS(FAB) m/z 541.2274 [(M + Na)+, calcd for C24H38NaO12
541.2261].
Trisaccharide 23. Glycosyl phosphite 22 (108 mg, 0.19 mmol)
and glycosyl acceptor 21 (78 mg, 0.21 mmol) were concentrated from
benzene (3 × 5 mL). Anhydrous toluene (1.5 mL) was introduced,
and the resultant solution cooled to -94 °C. TMSOTf (8 µL of 0.5 M
solution in dichloromethane, 0.004 mmol) was added to the solution,
and the mixture was stirred for 5 min and quenched with triethylamine
(0.5 mL). The resulting mixture was allowed to warm to 0 °C and
poured into a mixture of ethyl acetate and saturated aqueous NaHCO3
(4:1, 10 mL). The aqueous layer was extracted with ethyl acetate (3
× 20 mL), and the combined extracts were dried (Na2SO4) and
concentrated. The residue was purified by flash chromatography
(gradient elution, 8:1 to 5:1 hexane/ethyl acetate) to afford 82 mg (54%)
1
2931, 1741, 1509, 1219, 1046; H NMR (300 MHz, CDCl3) δ 7.38-
7.22 (m, 2H, arom), 7.05-6.84 (complex m, 7H, arom), 5.06 (m, 1H),
5.02 (dd, J ) 9.3, 1.8 Hz, 1H), 4.94 (br s, 1H), 4.93 (br s, 1H), 4.71
(s, 2H), 4.68 (app t, J ) 9.3 Hz, 1H), 4.52 (dd, J ) 9.9, 1.5 Hz, 1H),
3.97 (q, J ) 6.6 Hz, 1H), 3.79 (m, 1H), 3.77 (s, 3H), 3.49 (m, 1H),
3.39 (overlapping signals, 2H), 2.45-2.25 (m, 2H), 2.07 (s, 3H), 2.06

Synthesis of the Hexasaccharide Fragment of Landomycin A
J. Am. Chem. Soc., Vol. 120, No. 7, 1998 1397
(s, 3H), 2.00-1.40 (complex m, 6H), 1.34 (d, J ) 6.3 Hz, 3H), 1.22
(d, J ) 6.3 Hz, 3H), 1.09 (d, J ) 6.6 Hz, 3H); 13C NMR (75 MHz,
CDCl3) δ 170.1, 169.8, 168.7, 157.7, 155.1, 150.9, 129.5, 121.8, 118.1,
114.5, 114.4, 99.9, 98.1, 92.5, 81.5, 74.9, 71.2, 71.1, 70.4, 70.3, 70.1,
65.1, 64.9, 55.6, 36.5, 35.8, 23.8, 22.7, 21.3, 21.0, 18.1, 17.8, 17.0;
HRMS (FAB) m/z 739.2956 [(M + Na)+, calcd for C37H48NaO14
739.2942].
(s, 3H, -OAc), 2.05 (s, 3H, -OAc), 1.95-1.42 (complex m, 13H),
1.33 (d, J ) 6.0 Hz, 3H, -Me), 1.27 (d, J ) 7.2 Hz, 3H, -Me), 1.21
(d, J ) 6.4 Hz, 3H, -Me), 1.20 (d, J ) 6.4 Hz, 3H, -Me), 1.13 (d, J
) 6.4 Hz, 3H, -Me), 1.11 (d, J ) 6.4 Hz, 3H, -Me); 13C NMR (75
MHz, CDCl3) δ 170.8, 170.3, 170.1, 170.0, 169.8, 155.1, 150.9, 118.1,
114.5, 101.1, 100.0, 98.2, 92.9, 92.6, 81.7, 81.5, 78.4, 77.2, 75.1, 75.0,
71.3, 71.0, 70.7, 70.4, 70.1, 69.2, 66.1, 65.1, 60.4, 55.6, 36.7, 36.5,
35.8, 29.7, 24.5, 24.1, 24.0, 22.7, 21.3, 21.1, 21.0, 20.9, 18.1, 18.0,
17.8, 17.1, 17.0; HRMS(FAB) m/z 1105.4851, [(M + Na)+, calcd for
C53H78NaO23: 1105.4830].
Alcohol 5. To trisaccharide 25 (44.0 mg, 0.06 mmol) was added a
methanol solution of anhydrous hydrazine (0.35 mL of a 0.29 M
solution in methanol, 0.10 mmol). The reaction mixture was stirred at
0 °C for 4 h and concentrated. The residue was purified by flash
chromatography (1:1 hexanes-ethyl acetate) to afford 26 mg (72%)
Characterization data for hexasaccharide r-3: [R]25D -55.3° (c
0.76, CHCl3); 1H NMR (300 MHz, CDCl3) δ 6.95 (d, J ) 9.3 Hz, 2H,
arom), 6.81 (d, J ) 9.0 Hz, 2H, arom), 5.30 (m, 1H), 5.05 (m, 1H),
5.02 (dd, J ) 9.3, 1.8 Hz, 1H), 4.96 (br s, 2H), 4.91 (br s, 1H), 4.68
(app t, J ) 9.3 Hz, 1H), 4.67 (app t, J ) 9.3 Hz, 1H), 4.53 (d, J ) 8.1
Hz, 1H), 4.51 (d, J ) 8.1 Hz, 1H), 4.00-3.75 (overlapping signals,
9H), 3.52-3.25 (complex m, 7H), 2.45-2.25 (complex m, 4H), 2.12
(s, 3H), 2.07 (s, 3H), 2.06 (s, 3H), 2.05 (s, 3H), 2.04 (s, 3H), 1.95-
1.45 (complex m, 12H), 1.35 (d, J ) 6.0 Hz, 3H), 1.25-1.20
(overlapping signals, 12H), 1.11 (d, J ) 6.6 Hz, 3H); 13C NMR (75
MHz, CDCl3) δ 170.7, 170.1, 170.0, 169.9, 169.8, 155.2, 151.0, 118.2,
114.5, 100.0, 99.8, 98.1, 92.8, 92.6, 82.4, 81.5, 77.2, 75.1, 75.0, 71.3,
71.1, 71.0, 70.4, 70.1, 69.6, 69.2, 68.8, 67.2, 66.4, 65.1, 55.6, 36.5,
36.0, 35.8, 35.5, 24.0, 23.6, 22.7, 21.4, 21.3, 21.1, 21.0, 20.9, 20.1,
18.1, 17.8, 17.6, 17.0; HRMS(FAB) m/z 1105.4869, [(M + Na)+, calcd
for C53H78NaO23: 1105.4830].
of alcohol 5 as an amorphous solid: [R]25 -69.7° (c 1.29, CHCl3);
D
IR (CHCl3) 1742, 1505, 1216, 1051 cm-1; 1H NMR (300 MHz, CDCl3)
δ 6.95 (d, J ) 9.0 Hz, 2H), 6.81 (d, J ) 9.0 Hz, 2H), 5.07 (m, 1H),
5.02 (dd, J ) 9.6, 2.1 Hz, 1H), 4.92 (br s, 1H), 4.69 (app t, J ) 9.3
Hz, 1H), 4.53 (dd, J ) 9.6, 1.8 Hz, 1H), 3.88 (q, J ) 6.6 Hz, 1H),
3.84-3.75 (m, 1H), 3.77 (s, 3H), 3.55 (br s, 1H, -OH), 3.52 (m, 1H),
3.40 (superimposed m, 2H), 2.36 (m, 2H), 2.07 (s, 3H), 2.06 (s, 3H),
1.42-1.95 (m, 6H), 1.35 (d, J ) 6.3 Hz, 3H), 1.23 (d, J ) 6.6 Hz,
3H), 1.19 (d, J ) 6.6 Hz, 3H); 13C NMR (75 MHz, CDCl3) δ 170.1,
169.9, 155.1, 150.9, 118.1, 114.4, 99.9, 98.1, 92.8, 81.5, 74.9, 71.2,
71.0, 70.3, 70.1, 67.2, 66.3, 55.6, 36.5, 35.8, 25.5, 23.3, 21.3, 20.9,
18.1, 17.8, 17.1; HRMS(FAB) m/z 605.2582 [(M + Na)+, calcd for
C29H42NaO12: 605.2574].
Hexasaccharide 3. Glycosyl phosphite 27 (18 mg, 0.027 mmol)
and glycosyl acceptor 5 (19 mg, 0.032 mmol) were concentrated from
benzene (3 × 4 mL). Anhydrous toluene (0.8 mL) was introduced,
and the resultant solution cooled to -94 °C. TMSOTf (2 µL of 0.5 M
solution in dichloromethane, 0.001 mmol) was added to the solution,
and the mixture was stirred for 5 min and quenched with triethylamine
(0.5 mL). The resulting mixture was allowed to warm to 0 °C, passed
through a plug of silica gel, and flushed with EtOAc (40 mL), and the
filtrate was concentrated. The residue was purified by HPLC (65:35
hexanes-ethyl acetate, 5 mL/min) to afford 6.2 mg (21%) of hexas-
accharide 3 and 6.7 mg (23%) of the corresponding R isomer, both
Acknowledgment. This paper is dedicated to Professor Carl
R. Johnson on the occasion of his 60th birthday. Support by
the American Cancer Society (DHP-154) and the Welch
Foundation (A-1230) is gratefully acknowledged. G.A.S. is an
Alfred P. Sloan Fellow (1996-1998) and Eli Lilly Grantee
(1996-1998). We thank Mr. Jianjun Lu for the preparation of
early intermediates. High-resolution mass spectra were obtained
at Texas A&M University Mass Spectrometry Service Center
by Drs. Lloyd Sumner and Barbara P. Wolf on a VG Analytical
70S high resolution, double focusing, sectored (EB) mass
spectrometer. Funds to purchase the VG magnetic instrument
came from National Science Foundation Grant CHE-8705697.
amorphous solids. Hexasaccharide
3 exhibited the following
1
characteristics: [R]25 -71.0° (c 0.62, CHCl3); H NMR (400 MHz,
D
CDCl3) δ 6.94 (d, J ) 9.2 Hz, 2H, arom), 6.81 (d, J ) 9.2 Hz, 2H,
arom), 5.04 (m, 1H, 3a), 5.00 (dd, J ) 12.0, 2.4 Hz, 1H, 1a), 4.95 (br
s superimposed m, 2H, 1f, 3d), 4.91 (br s, 1H, 4f), 4.78 (br s, 1H, 1c),
4.67 (overlapping app t, J ) 9.6, J ) 9.6 Hz, 2H, 4b, 4e), 4.49
(overlapping signals, 3H, 1b, 1d, 1e), 3.95 (q, J ) 6.0 Hz, 1H, 5f),
3.79 (s superimposed m, 6 H, -OMe, 3b, 5c, 3e), 3.49 (m, 1H, 5a),
3.42 (br s, 1H, 4c), 3.40-3.24 (complex m, 5H, 5b, 5d, 5e, 4a, 4d),
2.42 (ddd, J ) 12.0, 5.1, 2.0 Hz, 1H), 2.22 (overlapping signals, 2H),
2.12 (s, 3H, -OAc), 2.06 (s, 3H, -OAc), 2.06 (s, 3H, -OAc), 2.05
Supporting Information Available: Experimental proce-
dure and characterization data for compounds 6, 13, 17-21,
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JA973348B