Synthesis of nor-C-linked neuraminic acid disaccharide: A versatile precursor of C-analogs of oligosialic acids and gangliosides

Article abstract of DOI:10.1021/jo0623787

(Chemical Equation Presented) The Neu5Acα(2,8)Neu5Ac disaccharide is an important constituent of tumor related antigen, however, the O-linkage is catabolically unstable. Vaccination with a catabolically stable sialic acid C-glycoside analog might enhance

Full text of DOI:10.1021/jo0623787

can reappear in adulthood diseases such as Wilms tumor of the
kidney,6 small cell lung carcinoma,7 and various malignant
neuroendocrine tumors, such as neuroblastoma, pheochromocy-
toma, and medullary thyroid carcinoma.8 The precise function
of PSA has not yet been established. The most well-
demonstrated property of PSAs is in cell-cell interaction and
adhesion, and it is postulated that alteration of PSA glycans in
NCAM reduces cell adhesion and may be involved in invasive
metastasis.7
Synthesis of Nor-C-linked Neuraminic Acid
Disaccharide: A Versatile Precursor of
C-Analogs of Oligosialic Acids and Gangliosides
Xuejun Yuan, Dino K. Ress, and Robert J. Linhardt*
Department of Chemistry and Chemical Biology, Rensselaer
Polytechnic Institute, Troy, New York 12180
linhar@rpi.edu
ReceiVed NoVember 18, 2006
PSAs are also expressed widely in bacteria. Structural
mimicry of PSAs may result in immune tolerance, attenuating
host-tumor and host-pathogen immune reactions.9a PSA capsules
found in Escherichia coli K-235 to the capsular polysaccharides
of Neisseria meningtidis group B and in Pasteurella hemeolytica
serotype A2 have identical structures.10 The role and importance
of different capsular polysaccharides in the pathogenicity of
several strains of E. coli have been established. A large
proportion of cases of bacteremia and urinary tract infections
are caused by strains containing Neu5Ac in their capsular
structure.11 Similarly, over 80% of neonatal meningitis is caused
by strains having PSA capsules. The virulence of these
organisms is attributable to structural mimicry between their
common R(2f8) PSA capsular polysaccharide and human tissue
counterpart, which allows the bacteria to evade immune
surveillance. The poor immunogenicity of the group B menin-
gococcal PSA has made it difficult to formulate a protective
polysaccharide-based vaccine against meningococcal meningitis.12
The Neu5AcR(2,8)Neu5Ac disaccharide is an important
constituent of tumor related antigen, however, the O-linkage
is catabolically unstable. Vaccination with a catabolically
stable sialic acid C-glycoside analog might enhance immu-
nogenicity. The synthesis of Neu5Ac nor-C-disaccharide
20R/S, corresponding to versatile precursors of C-analogs
of oligosialic acid and gangliosides, is reported. The synthesis
of the protected acceptor was not straightforward, as ester,
silyl ether, and isopropylidene protection failed to afford
desired C-linked disaccharide. Allyl ether protection of
hydroxyl groups and acetyl protection of the acetamido
facilitated the successful synthesis of the 8-aldehyde neurami-
nyl acceptor. Samarium mediated C-glycosylation afforded
the desired nor-C-disaccharide as a mixture of two separable
diastereomers.
The glycosidic oxygen linkage in PSAs, susceptible to the
enzymatic action of extracellular sialidases,13 represents an
important target for modification in the rational design of PSA-
based therapeutics. PSAs are also prone to spontaneous chemical
depolymerization through the protonation of glycosidic oxygens
by the adjacent internal carboxylic acid residues.14 Neu5AcR-
(2,8)Neu5Ac 2 is also an important constituent of gangliosides
GD2 and GD3, well-known melanoma-associated antigens,
Sialic acids, among the most important saccharides in living
systems, are often found at nonreducing end of glycans.1 They
are involved in many biological phenomena, such as recognition,
cell interactions, neuronal transmission, ion transport, reproduc-
tion, differentiation, epitope masking, and epitope protection.
Sialic acids are also associated with pathological processes
including infection, inflammation, cancer, and in neurological,
cardiovascular, endocrinological, and autoimmune diseases.2
Polysialic acids (PSAs, 1) are naturally occurring helical,
linear homopolymers composed entirely of negatively charged
sialic acid residues joined by R(2f8), R(2f9), or R(2f8)/R-
(2f9) alternating ketosidic linkages3 and are commonly found
N-linked to a neural cell adhesion molecule (NCAM). NCAM
is a cell adhesion molecule that plays a pivotal role in
embryogenesis and the developmental biology of organogen-
esis.4 PSAs are spatially and temporally expressed during
development and disappear soon after birth. In adult mammals,
PSA expression is limited to selected regions of hippocampus,
where neuronal generation and axonal plasticity persists.5 PSAs
(6) Rothbard, J. B.; Brackenbury, R.; Cunningham, B. A.; Edelman, G.
M. J. Biol. Chem. 1982, 257, 11064-11069.
(7) (a) Roth, J.; Zuber, C.; Wagner, P.; Taatjes, D. J.; Weisgerber, C.;
Heitz, P. U.; Goridis, C.; Bitter-Suermann, D. Proc. Natl. Acad. Sci. U.S.A.
1988, 85, 2999-3003. (b) Scheidegger, E. P.; Lackie, P. M.; Papay, J.;
Roth, J. Lab. InVest. 1994, 70, 95-106.
(8) (a) Margolis, R. K.; Margolis, R. U. Biochem. Biophys. Res. Commun.
1983, 116, 889-894. (b) Livingston, B. D.; Jacobs, J. L.; Glick, M. C.;
Troy, F. A. J. Biol. Chem. 1988, 263, 9443-9448. (c) Komminoth, P.;
Roth, J.; Schrroder, S.; Saremaslani, P.; Heitz, P. U. Lab. InVest. 1995, 72,
424-431. (d) Moolenaar, C. E.; Muller, E. J.; Schol, D. J.; Figdor, C. G.;
Bock, E.; Bitter-Suermann, D.; Michalides, R. J. Cancer Res. 1990, 50,
1102-1106.
(9) (a) Roth, J.; Zuber, C. Lab. InVest. 1990, 62, 55-60. (b) Roth, J.;
Zuber, C.; Wagner, D.; Blaha, I.; Bitter-Suermann, D.; Heitz, P. U. Am. J.
Path. 1988, 133, 227-240.
(10) (a) Barry, G. T.; Goebel, W. F. Nature 1957, 179, 206. (b)
Bhattacharjee, A. K.; Jennings, H. J.; Kenny, C. P.; Martin, A.; Smith, I.
C. J. Biol. Chem. 1975, 250, 1926-1932.
* To whom correspondence should be addressed. Phone: 518-276-3404.
Fax: 518-276-3405. Homepage: http://www-heparin.rpi.edu.
(1) Angata, T.; Varki, A. Chem. ReV. 2002, 102, 439-469.
(2) Varki, A. Glycobiology 1992, 2, 25-40.
(3) Reglero, A.; Rodrigues-Aparicio, L. B.; Luengo, J. M. Int. J. Biochem.
1993, 25, 1517-1527.
(4) Finne, J. J. Biol. Chem. 1982, 257, 11966-11970.
(5) Hoffman, S.; Sorkin, B. C.; White, P. C.; Brackenbury, R.; Mail-
hammer, R.; Rutishauer, U.; Cunningham, B. A.; Edelman, G. M. J. Biol.
Chem. 1982, 257, 7720-7729.
(11) Kaijser, B.; Hanson, L. A.; Jodal, V.; Linden-Johnson, G.; Robbins,
J. B. Lancet 1977, 1, 664-666.
(12) Pon, R. A.; Lussier, M.; Yang, Q.; Jennings, H. J. J. Exp. Med.
1997, 11, 1929-1938.
(13) Troy, F. A.; McCloskey, M. A. J. Biol. Chem. 1979, 254, 7377-
7387.
(14) Manzi, A. E.; Higa, H. H.; Diaz, S.; Varki, A. J. Biol. Chem. 1994,
269, 23617-23624.
10.1021/jo0623787 CCC: $37.00 © 2007 American Chemical Society
Published on Web 03/20/2007
J. Org. Chem. 2007, 72, 3085-3088
3085

SCHEME 1
SCHEME 2
considered attractive targets for vaccine-based anticancer therapy.15
C-Glycosides are resistant to chemical and enzymatic degrada-
tion, and vaccination with C-glycosides might enhance immu-
nogencity16 or be of utility in understanding biological recog-
nition at the molecular level.17 Herein, we report the synthesis
of nor-C-linked R(2f8) Neu5Ac disaccharide, a versatile
precursor of PSA, GD2, and GD3 C-analogs.
Retrosynthetic analysis (Scheme 1) suggests that glycosylation
of acceptor 5 with Neu5Ac phenyl sulfone donor 4 should afford
protected nor-C-disaccharide target 3.16a The success of this
synthetic route relies on the design and application of acceptor
5, which we envision could be synthesized starting from the
previously reported sialic acid thiophenyl glycoside 8,16b using
an orthogonal protection strategy followed by exposure and
oxidation of the C-9 hydroxyl group.
The stability of trialkylsilyl ether masking group made it an
attractive candidate as temporary protecting group (P′′) for the
9-hydroxyl group. In initial attempts, starting from Neu5Ac
phenyl thioglycoside 8, C-9 hydroxyl was protected as t-
butyldimethylsilyl (TBDMS) ether.17 Peracetylation, followed
by selective deprotection of the 9-OH using TBAF,18 resulted
in acetyl migration over a wide range of conditions (pH 3-9).19
Persilylation of hydroxyl groups in 8 using a more aggressive
silylating reagent, TBDMS-OTf,20 selective deprotection of C-9
hydroxyl group,21 and Swern oxidation afforded desired alde-
hyde acceptor 5 (PdTBDMS).19 SmI2 mediated C-glycosylation
with Neu5Ac sulfone donor 4 (P′dAc), failed to afford the
desired C-linked Neu5Ac disaccharide 3.19 Molecular modeling
of 5 (PdTBDMS) suggested the 9-aldehyde group was crowded
and suggested the 7,8-hydroxy groups might be better protected
as a smaller of isopropylidene ketal. Selective TBDMS protec-
tion of 4- and 9-hydroxyl groups resulted in 9 (Scheme 2).
Treatment with dimethyl acetone ketal in the presence of a
catalytic amount of tosic acid resulted in loss of the 9-O-
TBDMS group, affording the undesired 8,9-O-isopropylidene
derivative 10. The t-butyldiphenylsilyl (TBDPS) ether 11 was
prepared22 to enhance the acid stability of the protection group
at the C-9. Successful protection of the 7,8-hydroxyl groups as
isopropylidene was followed by exposure of the 9-hydroxyl
group using TBAF (11f12). Unfortunately, 12 was insuf-
ficiently stable, due to its strained 5-membered ring, showing
50% decomposition within one week at room temperature.
Modeling suggested allyl protection should allow C-glyco-
sylation with the bulky nucleophile 4. The ease of introduction,
electron-donating properties, orthogonality, and ease of removal
made OAll an ideal protecting group for synthesis of desired
aldehyde acceptor 5.23 Regioselective protection of 8,9-diol of
8 gave 13 in 94% yield, which was then regioselectively
opened24 affording the 9-p-methoxybenzyl (PMB) ether 14
(Scheme 3). Perallylation of 15 under standard conditions
(15) (a) Riemer, A. B.; Fo¨rster-Waldl, E.; Bra¨mswig, K. H.; Pollak, A.;
Zielinski, C. C.; Pehamberger, H. Lode, H. N.; Scheiner, O.; Jensen-Jarolim,
E. Eur. J. Immunol. 2006, 36, 1267-1274. (b) Seyfried, T. N.; Yu, R. K.
Mol. Cell. Biochem. 1985, 68, 3-10.
(18) Corey, E. J.; Venkateswarlu, A. J. Am. Chem. Soc. 1972, 94, 6190-
6191.
(19) Ress, D. K. Doctoral Dissertation, Department of Chemistry,
University of Iowa, 2005.
(20) (a) Robins, M. J.; Samano, V.; Johnson, M. D. J. Org. Chem. 1990,
55, 410-412. (b) Otera, J.; Nozaki, H. Tetrahedron Lett. 1986, 27, 5743-
5746.
(16) (a) Vlahov, I. R.; Vlahova, P. I.; Linhardt, R. J. J. Am. Chem. Soc.
1997, 119, 1480-1481. (b) Du, Y.; Linhardt, R. J.; Vlahov, I. R.
Tetrahedron 1998, 54, 9913-9959. (c) Dino, K. R.; Baytas, S. N.; Wang,
Q.; Mun˜oz, E. M.; Tukuzoki, K.; Tomiyama, H.; Linhardt, R. J. J. Org.
Chem. 2005, 70, 8197-8200. (d) Bazin, H. G.; Du, Y.; Polat, T.; Linhardt,
R. J. J. Org. Chem. 1999, 64, 7254-7259. (e) Du, Y.; Polat, T.; Linhardt,
R. J. Tetrahedron Lett. 1998, 39, 5007-5010. (f) Yuan, X.; Linhardt, R. J.
Curr. Top. Med. Chem. 2005, 5, 1393-1430.
(21) Kawai, A.; Hara, O.; Hamada, Y.; Shiara, T. Tetrahedron Lett. 1988,
29, 6331-6334.
(22) Wood, W. W.; Rashid, A. Tetrahedron Lett. 1987, 28, 1933-1936.
(23) Kimbonguila, A. M.; Boucida, S.; Guibe´, F.; Loffet, A. Tetrahedron
1997, 53, 12525-12538.
(17) Chaudhary, S. K.; Herbandez, O. Tetrahedron Lett. 1979, 20, 99-
102.
(24) Demchenko, A. V.; Boons, G. J. Chem.-Eur. J. 1999, 5, 1278-
1283.
3086 J. Org. Chem., Vol. 72, No. 8, 2007

SCHEME 3
TABLE 1. Modeling on SGI SYBYL 6.0 (TRIPOS Force Field and
a Dielectric Constant Set to 4.8) Compared with NMR Experimental
Data
confirmed by a JC1, H3ax ) 8.5 Hz and JC1, H3eq < 1.0 Hz for
less polar isomer, and a JC1, H3ax ) 9.0 Hz and JC1, H3eq < 1.0
Hz for the other, as measured by selective 13C NMR
decoupling.16b The stereochemistry of newly generated bridge-
carbon was determined by ROESY, NOESY, and TCOSY
experiments and the less polar diastereomer assigned as S and
the more polar as R. Data from computational molecular
modeling are in excellent agreement with NMR experimental
data (Table 1). NOE was only observed between two protons
with the closest through-space distance. Differences observed
in the H-3ax chemical shifts coincide with the stereochemistry
assignments at the C-9 position in both diastereomers. In the
20S, the 9′-hydroxyl group points toward H-3ax, resulting in
downfield chemical shift of H-3ax. A large coupling constant
between H-9′ and H8′ is consistent with the dihedral angle of
178.8° in the structure of the S diastereomer.16d
distance (Å)
H3eq-H9′
2.83
3.46
3.28
3.03
H3eq-H(OH9′)
H3ax-H9′
3.20
2.28, NOE observed,
δ
H3ax 1.88 ppm
H3ax-H(OH9′)
2.29, NOE observed,
H3ax 2.25 ppm
3.96 Å
δ
dihedral angle (deg)
178.8
7.0 Hz
H9′-C9′-C8′-H8′
JH-9′,H-8′
57.9
1.5 Hz
Experimental Section
Methyl[phenyl5-acetamido-endo-8,9-O-(p-methoxy)-benzyl-
idene-3,5-dideoxy-2-thio-d-glycero-R-D-galacto-non-2-ulo-
pyranosid]onate (13). Neu5Ac phenyl sulfide 8 (1.00 g, 2.41
mmol) was dissolved in CH3CN (100 mL), and anisaldehyde
dimethyl acetal (3.3 mL, 19.4 mmol) and camphorsulfuric acid (56.0
mg, 0.20 mmol). The reaction mixture was stirred for overnight
and neutralized with trimethylamine (pH ) 7) and solvent was
evaporated under reduced pressure. The residue was dissolved in
CH2Cl2 (100 mL) and washed with saturated aqueous NaHCO3 (60
mL) and water (3 × 25 mL). The organic phase was dried over
anhydr. MgSO4 and filtered, and the filtrate was concentrated under
vacuum. The residue was purified by flash chromatography (CH2-
Cl2-CH3OH, v/v 10:1) to afford 13 as light-yellow foam (1.46 g,
94%, endo/exo 1:1).
Methyl[phenyl 5-acetamido-9-O-(p-methoxy)benzyl-3,5-dideoxy-
2-thio-D-glycero-R-D-galacto-non-2-ulopyranosid]onate (14). BH3·
NMe3 (297 mg, 4.10 mmol) and AlCl3 (530 mg, 3.98 mmol) were
added to a solution of 13 (360 mg, 0.66 mmol) in anhydrous THF
(60 mL) with activated molecular sieves (4 Å, 1.80 g) at 0 °C.
After stirring at 0 °C for 4 h and at room temperature overnight,
the reaction mixture was filtered over a pad of Celite and solids
resulted in unexpected lactamization affording 15. A mixture
of BaO and Ba(OH)2·8H2O25 gave the desired, albeit transes-
terified, allylated compound 16 in 75% yield. If the ratio of
BaO and Ba(OH)2·8H2O was altered in any way, the methyl
ester was hydrolyzed. N-acetylation of 16 afforded 17 in 80%
yield.26 Deprotection of the PMB gave 9-hydroxyl derivative
18,26 which was oxidized to the corresponding aldehyde acceptor
19 in 70% yield.27 C-Glycosylation of the aldehyde 19 with
Neu5Ac sulfone donor 4 in the presence of freshly prepared
16a
SmI2 gave the desired nor-R(2,8)-C-neuraminic acid disac-
charide 20 in 35% yield, as a diastereomeric mixture (R/S 1:1)
at the bridge hydroxymethylene group. The two diastereomers
were separated by flash chromatography.
1H NMR shows the expected resonances of the C-3/3′
methylene and the C-4/4′ protons of ulosonic acid skeleton in
the 5C2 conformation.28 The R-configuration of the products was
(25) Guo, Z.-C.; Han, L.; Hu, B.; Cao, C.-S. Youji Huaxue (Chinese)
2004, 24, 946-949.
(26) Gizur, T.; Harsanyi, K. Syn. Commun. 1990, 20, 2365-2371.
(27) Dess, D. B.; Martin, J. C. J. Org. Chem. 1983, 48, 4155-4156.
(28) Haverkamp, J. F. G.; Van Halbeek, H.; Dorland, L.; Vliegenthart,
J. F. G.; Pfeil, R.; Schauer, R. Eur. J. Biochem. 1982, 122, 305-311.
J. Org. Chem, Vol. 72, No. 8, 2007 3087

were washed with CH3CN (3 × 25 mL). The combined filtrate
was concentrated in vacuum. The residue was dissolved in ethyl
acetate (30 mL) and washed with saturated aqueous NaHCO3 (30
mL) and water (3 × 20 mL). The organic phase was dried over
MgSO4 and filtered, and the filtrate was concentrated in vacuum.
The residue was purified by flash column chromatography
(CH2Cl2/MeOH20:1),affording14assnow-whitefoam(190mg,52.7%).
Allyl[phenyl 4,7,8-tri-O-allyl-5-acetamido-9-O-(p-methoxy)-
benzyl-3,5-dideoxy-2-thio-D-glycero-R-D-galacto-non-2-ulopyra-
nosid]onate (16). BaO (420 mg, 2.74 mmol) and Ba(OH)2·8H2O
(564 mg, 1.8 mmol) were added to a solution of 14 (160 mg, 0.30
mmol) in anhydrous DMF (10 mL) under stirring. Half an hour
later, AllBr (0.54 mL, 6.2 mmol) was added dropwise to the above
mixture. The mixture was stirred under argon at r.t. for 10 h. The
reaction was quenched with TsOH, the reaction mixture was filtered
over a pad of celite, and the solids were washed with CH3CN (3 ×
20 mL). The combined filtrate was rotary evaporated under vacuum
to dryness, leaving a yellow oil-like liquid residue. The residue
was subject to flash column chromatography (CH2Cl2-MeOH, v/v
35:1) to afford 16 (150 mg, 73.6%) as yellow oil-like liquid.
Allyl[phenyl 4,7,8-tri-O-allyl-5-(N-acetylacetamido)-9-O-(p-
methoxy)benzyl-3,5-dideoxy-2-thio-D-glycero-R-D-galacto-non-
2-ulopyranosid]onate (17). A solution of 16 (150 mg, 0.208 mmol)
and TsOH·H2O (10 mg, 0.05 mmol) in isopropenyl acetate (5 mL)
was kept at 60 °C for 6 h. The reaction mixture was neutralized by
addition of Et3N. The resulting solution was concentrated under
vacuum. The residue was purified by flash silica gel column
chromatography (petroleum ether-EtOAc, v/v 4:1), affording 17 as
a light-yellow oil-like liquid (0.123 g, 77.4%).
Allyl [phenyl 4,7,8-tri-O-allyl-5-(N-acetylacetamido)-3,5-
dideoxy-2-thio-D-glycero-R-D-galacto-non-2-ulopyranosid]-
onate (18). Cerium ammonium nitrate (348 mg, 0.60 mmol) was
added to a solution of 17 (120 mg, 0.18 mmol) in a mix solvent
(CH3CN/H2O 10:1) under stirring. The reaction mixture was stirred
for 5 h at r.t. Then it was concentrated under vacuum. The residue
was dissolved in ethyl acetate (15 mL), and the resulting solution
was washed with saturated Na2SO3 aqueous solution (5 mL) and
water (3 × 5 mL), consecutively. The organic phase was concen-
trated to dryness, and the resulting residue was subject to flash
chromatography (petroleum ether-EtOAc, v/v 5:1), affording 18 (60
mg, 60%) as a colorless liquid.
Allyl[phenyl 4,7,8-tri-O-allyl-5-(N-acetylacetamido)-3,5-di-
deoxy-2-thio-D-glycero-R-D-galacto-non-2-(9-oxa-ulopyranosid)]-
onate (19). Dess-Martin solution (15 wt %) (0.64 mL, 0.30 mmol)
was added dropwise to a solution of 18 (48 mg, 0.079 mmol) in
anhydr. CH2Cl2 (5.0 mL) under stirring at 0 °C. The reaction
mixture was kept at 0 °C for 30 min and was stirred overnight at
r.t. It was diluted with ethyl ether (15 mL) and poured into 0.1 N
sodium thiosulfate saturated with NaHCO3 (5 mL). The organic
layer was washed sequentially with saturated aqueous NaHCO3,
brine, and water. The organic phase was concentrated under
vacuum. The residue was purified on flash column chromatography
(petroleum ether-EtOAc, v/v 10:1), giving 19 (33 mg, 70%) as a
colorless liquid.
Methyl 5-Acetamido-4,7,8,9-tetra-O-acetyl-2,6-anhydro-3,5-
dideoxy-2-C- {(S)-hydroxy-[9′-(allyl(phenyl4′,7′,8′-tri-O-allyl-5-
(N-acetylacetamido)-3′,5′-dideoxy-2′-thio-D-glycero-R-D-galacto-
oct-2′-ulopyranosid)onate)methyl]}-D-erythro-L-manno-
nononate (20). A solution of compounds 19 (30 mg, 0.050 mmol)
and 4 (60 mg, 0.10 mmol) in CH2Cl2 (2 mL) was evaporated to
dryness and the resulting residue dried overnight under high
vacuum. The dried residue placed under argon was added a solution
of freshly prepared SmI2 (0.1 N, 5.0 mL) and the reaction mixture
was stirred for 1 h at r.t. The reaction mixture was diluted with
ethyl ether, washed successively with 0.1 N HCl, saturated aqueous
Na2S2O3 in NaHCO3, and distilled water, dried over anhydr. MgSO4,
and filtered. The filtrate was evaporated under vacuum to dryness
and purified by column chromatography (petroleum ether-EtOAc,
v/v 3:1f1:1) in a total yield of (S)-20 (9.5 mg) and (R)-20 (9.5
mg) corresponding to 35.0%.
(S)-20: [R]2D5 ) -17.5 (c 0.01, CHCl3); H NMR (500 MHz,
1
CDCl3) δ (ppm): 1.53 (1H, dd, JH-3ax′, H-3eq′ 12.9 Hz, JH-3ax′, H-4′
) 10.8 Hz, H-3ax′), 2.01, 2.04, 2.09, 2.17, 2.30, 2.31, 2.36 (21H,
7s, CH3CO), 2.25 (1H, t, JH-3ax,H-4 ) 10.5 Hz, H-3ax), 2.78 (1H,
t, JH-3eq′,H-4 ) 5.0 Hz, H-3eq′), 2.80 (1H, t, JH-3eq,H-4 ) 5.0 Hz,
H-3eq), 3.45 (1H, m, H-7′), 3.49 (1H, dd, JH-9′,OH-9′ ) 4.5 Hz,
JH-9′,H-8′ ) 7.0 Hz, H-9′), 3.70 (1H, m, CH2CHAll), 3.72 (3H, s,
COOCH3), 3.77 (1H, dd, JH-5′,H-4′ ) 10.0 Hz, JH-5′,H-6′ ) 10.0
Hz, H-5′), 3.78-3.83 (3H, m, CH2CHAll), 3.88 (2H, m, CH2-
CHAll), 3.94 (1H, d, JOH-9′,H-9′ ) 4.5 Hz, OH-9′), 3.96-3.99 (1H,
m, CH2CHAll), 4.01 (1H, dd, J
) 5.0 Hz, J
)
H-9a,H-9b
H-9a,H-8
12.5 Hz, H-9a), 4.03-4.11 (2H, m, CH2CHAll), 4.12 (1H, m, H-4′),
4.14 (1H, m, H-6), 4.19 (2H, m, CH2CHAll), 4.29 (1H, m, H-8′),
4.34 (1H, dd, JH-7,H-8 ) 11.0 Hz, JH-7,H-6 ) 2.5 Hz, H-7), 4.63
(1H, m, CH2dCHAll), 4.71 (1H, dd, JH-6′,H-7′ ) 2.5 Hz, JH-6′,H-5′
) 9.5 Hz, H-6′), 4.75 (1H, d, JNH,H-5 ) 5.0 Hz, NH), 4.79 (1H,
oct, JH-5,H-4 ) 10.0 Hz, JH-5,H-6 ) 9.0 Hz, JH-5,NH ) 5.0 Hz,
H-5), 4.85 (1H, oct, JH-4,H-3ax ) 10.5 Hz, JH-4,H-5 ) 10.0 Hz,
JH-4,H-3eq ) 5.0 Hz, H-4), 5.16 (5H, m, CH2dCHAll), 5.25-5.38
(2H, m, CH2dCHAll), 5.41 (1H, m, H-8), 5.48-5.51 (1H, m, CH2d
CHAll),5.52 (1H, dd, J
) 12.5 Hz, J
) 2.0 Hz,
H-9b,H-8
H-9b,H-9a
H-9b), 5.66-6.11 (3H, m, CH2dCHAll), 7.65-7.77 (5H, m, Ph);
13C NMR (75 MHz, CDCl3): 21.0, 21.5, 23.4, 25.4, 28.0, 29.9,
30.6, 35.4, 40.3, 50.0, 52.6, 60.2, 67.1, 68.0, 70.9, 72.0, 72.3, 73.0,
73.3, 77.4, 84.8, 87.8, 95.2, 116.6, 116.9, 117.6, 120.6, 125.7, 129.2,
130.2, 131.8, 134.3, 135.1, 137.0, 154.3, 168.6, 169.9, 170.4, 170.7,
171.0, 171.2, 175.2, 176.0; HR-ESIMS calcd for C51H68N2O21NaS
[M + Na]+ 1099.3933, found m/z 1099.3937.
(R)-20: [R]2D5) -5.7 (c 0.01, CHCl3); 1H NMR (500 MHz,
CDCl3) δ: 1.68 (1H, dd, JH-3ax′,H-3eq′ ) 12.5 Hz, JH-3ax′,H-4′
)
10.8 Hz, H-3ax′), 1.88 (1H, t, JH-3ax,H-4 ) 10.5 Hz, H-3ax), 1.89,
1.98, 2.03, 2.04, 2.14, 2.20, 2.24 (15H, s, CH3CO), 2.48 (1H,
JH-3eq,H-4 ) 5.0 Hz, JH-3eq,H-3ax ) 12.5 Hz, H-3eq), 2.78 (1H,
JH-3eq′,H-4′ ) 4.5 Hz, JH-3eq′,H-3ax′ ) 12.5 Hz, H-3eq′), 3.49 (2H,
m, CH2CHAll), 3.51 (1H, m, H-9a), 3.62-3.72 (2H, m, CH2CHAll),
3.74 (3H, s, COOCH3), 3.81 (1H, m, H-4′), 3.82-3.87 (2H, m,
CH2CHAll), 3.92 (1H, dd, J H-9b,H-8 ) 5.0 Hz, J H-9b,H-9a ) 12.5
Hz, H-9b), 3.97 (1H, m, H-7′), 4.02 (1H, m, JH-5,H-4 ) 10.0 Hz,
JH-5,H-6 ) 10.0 Hz, H-5), 4.06-4.18 (2H, m, CH2CHAll), 4.19
(1H, m, H-8′), 4.21 (1H, m, H-6), 4.58-4.63 (1H, m, CH2dCHAll),
4.71-4.76 (1H, m, CH2dCHAll), 5.08-5.14 (2H, m, CH2d
CHAll), 4.84 (1H, oct, JH-4,H-3ax ) 10.5 Hz, JH-4,H-5 ) 10.0 Hz,
JH-4,H-3eq ) 5.0 Hz, H-4), 5.17 (1H, dd, JH-6′,H-7′ ) 2.5 Hz,
JH-6′,H-5′ ) 9.5 Hz, H-6′), 5.19-5.28 (2H, m, CH2dCHAll), 5.29
(1H, dd, JH-7,H-8 ) 11.0 Hz, JH-7,H-6 ) 2.5 Hz, H-7), 5.31 (1H,
t, JH-9′,H-8′ ) 1.5 Hz, H-9′), 5.33-5.36 (2H, m, CH2dCHAll), 5.38
(1H, dd, JH-5′,H-4′ ) 10.0 Hz, JH-5′,H-6′ ) 10.0 Hz, H-5′), 5.42
(1H, m, OH), 5.43 (1H, m, H-8), 5.57-5.60 (2H, m, H-5 and NH),
5.76-6.00 (4H, m, CH2dCHAll), 7.35-7.63 (5H, m, Ph); 13C
NMR (75 MHz, CDCl3) δ (ppm): 21.1, 21.1, 21.5, 21.6, 23.5, 23.8,
32.0, 35.3, 50.0, 52.6, 53.0, 63.0, 66.5, 68.11, 68.9, 70.0, 70.0, 71.5,
73.2, 73.3, 74.6, 75.7, 80.6, 87.8, 115.8, 116.9, 117.2, 119.6, 129.0,
129.6, 129.7, 131.8, 134.9, 135.3, 135.5, 136.8, 168.5, 169.8, 170.5,
170.6, 170.7, 171.0, 171.1, 171.3; HR-ESIMS calcd for C51H68N2O21-
NaS [M + Na]+ 1099.3933, found m/z 1099.3939.
Acknowledgment. We thank Dr. Scott McCallum and Dr.
Herb Schwartz for their help with 2D NMR and support from
NIH AI065786; X. Y. would thank Dr. Zhang Zhenqing for
discussion on this work.
Supporting Information Available: 1H and 13C NMR spectra
for compounds 9-21 and HR ESI-MS spectra for 20R and 20S,
general methods, and the synthesis and characterization of 9-19,
and 21. This material is available free of charge via the Internet at
http://pubs.acs.org.
JO0623787
3088 J. Org. Chem., Vol. 72, No. 8, 2007