Efficient Large Scale Syntheses of 3-Deoxy- d -manno-2-octulosonic acid (Kdo) and Its Derivatives

Article abstract of DOI:10.1021/acs.orglett.5b00901

An efficient method to rapidly synthesize 3-deoxy-d-manno-2-octulosonic acid (Kdo) and its derivatives in large scale has been developed. Starting from d-mannose, the di-O-isopropylidene derivative of Kdo ethyl ester was prepared in three steps on a scale of more than 40 g in one batch in an overall yield of 75-80% without any intermediate purification. Kdo, Kdo glycal, and 2-acetylated Kdo ester were synthesized quickly in high yield from a di-O-isopropylidene derivative of Kdo ethyl ester. 2-Deoxy-β-Kdo ester was obtained with high stereoselectivity via the epimerization of the α-isomer using t-BuOH as a proton source.

Full text of DOI:10.1021/acs.orglett.5b00901

Letter
pubs.acs.org/OrgLett
Efficient Large Scale Syntheses of 3‑Deoxy‑D‑manno-2-octulosonic
acid (Kdo) and Its Derivatives
Yingle Feng, Jie Dong, Fangyuan Xu, Aiyun Liu, Li Wang, Qi Zhang, and Yonghai Chai*
School of Chemistry and Chemical Engineering, Shaanxi Normal University, Xi’an, Shaanxi 710119, P. R. China
S
* Supporting Information
ABSTRACT: An efficient method to rapidly synthesize 3-deoxy-D-manno-2-
octulosonic acid (Kdo) and its derivatives in large scale has been developed.
Starting from D-mannose, the di-O-isopropylidene derivative of Kdo ethyl
ester was prepared in three steps on a scale of more than 40 g in one batch in
an overall yield of 75−80% without any intermediate purification. Kdo, Kdo
glycal, and 2-acetylated Kdo ester were synthesized quickly in high yield from
a di-O-isopropylidene derivative of Kdo ethyl ester. 2-Deoxy-β-Kdo ester was
obtained with high stereoselectivity via the epimerization of the α-isomer
using t-BuOH as a proton source.
Kdo (3-deoxy-D-manno-2-octulosonic acid), an unusual 8-
carbon acidic sugar, is an essential constituent of the cell wall
lipopolysaccharides (LPS) of Gram-negative bacteria.1 The
transformation of Kdo to CMP-Kdo, catalyzed by the enzyme
CMP-Kdo synthetase (CKS), is a key reaction in the
biosynthesis of LPS, which renders CKS a promising
pharmaceutical target in the development of new classes of
antibiotics.2 Kdo-containing oligosaccharides have been chemi-
cally synthesized for the development of Gram-negative
bacteria vaccines.3 However, the difficulty of Kdo isolation
from natural sources results in an extremely high cost ($41/mg,
Sigma-Aldrich) of Kdo production, which thereby hampers the
extensive exploration of Kdo-related chemistry and biology. As
a result, highly efficient syntheses of Kdo and its derivatives are
necessary for research on Kdo-containing oligosaccharides and
CKS inhibitors based on the Kdo skeleton, such as 2-deoxy-β-
Kdo and 8-NH2-2,8-dideoxy-β-Kdo.4
Many chemical and enzymatic syntheses of Kdo and its
derivatives have been developed, mainly using D-mannose, D-
arabinose, or other small organic molecules as starting
materials.5 These protocols used the Wittig reaction,
Horner−Wadsworth−Emmons reaction (HWE reaction),
Diels−Alder reaction, ring-closing metathesis, and other
metal-mediated reactions to build the skeleton of Kdo.
However, most of these methods required multiple steps to
construct Kdo and its derivatives. The Cornforth reaction6a has
been efficiently applied to the synthesis of Kdo by condensation
of oxalacetic acid with D-arabinose.1,6b−d This method provides
a short route to Kdo, but the difficulty in separation of the 4-
epimer of Kdo could not be neglected. Moreover, Kdo
derivatives could not be rapidly accessed via this method.
We envisioned that the di-O-isopropylidene derivative of
Kdo ethyl ester 4 might be rapidly synthesized via Horner−
Wadsworth−Emmons reaction between protected mannose 1
and phosphate ester7 2 followed by desilylation. Then, ester 4
could be employed to finish the syntheses of Kdo, 2-acetylated
Kdo, glycal, and 2-deoxy-β-Kdo in short steps.
Isopropylidenation of D-mannose with 2,2-dimethoxypro-
pane and a catalytic amount of TsOH·H2O gave 1,8 which was
used directly for the next step without purification (Table 1).
Table 1. Synthesis of Compound 3 via HWE Condensation
c
entry
base (equiv)
solvent
toluene
temp (°C)
yield
1
2
3
4
LiHMDS
NaH
100
100
100
100
80
72%
trace
28%
trace
55%
85%
73%
56%
62%
88%
toluene
toluene
toluene
toluene
toluene
toluene
DCE
t-BuOK
t-BuONa
t-BuOLi
t-BuOLi
t-BuOLi
t-BuOLi
t-BuOLi
t-BuOLi
a
5
a
6
100
120
reflux
reflux
50
a
7
8
9
1,4-dioxane
b
10
THF
a
b
1.2 equiv of compound 2 was added. 1.3 equiv of compound 2 was
c
added. 1.2 equiv of base was used.
The key reaction, HWE condensation between 1 and
phosphate ester 2 in the presence of different bases (including
LiHMDS, NaH, t-BuOK, t-BuONa, and t-BuOLi, entries 1−5,
respectively), was investigated. The condensation worked
smoothly to provide the desired product 3 in 88% isolated
yield (entry 10) when t-BuOLi as the base9 and THF as the
solvent were used. Phosphate ester 2, which is commercially
Received: March 28, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.5b00901
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
available, was readily synthesized according to Horne’s
procedure7c using ethyl glyoxylate hydrate as starting material.
As an important intermediate, Kdo ethyl ester 4 and Kdo
methyl ester have been widely used in the field of Kdo-related
synthetic chemistry. Many methods have been reported to
synthesize those Kdo esters.10,5c,j With HWE product 3 in
hand, we explored the deprotection of the TBS group under
different conditions (Table 2) to complete the synthesis of the
Acylation of Kdo ester 4 in the presence of pyridine/Ac2O
led to 2-acetylated Kdo ester 7 in quantitative yield, which also
can be used in the glycosidations of Kdo derivatives.15
With the large scale synthesis of Kdo ester 4 in hand, we
attempted to directly deoxygenate the C-2 hydroxyl group of
Kdo ester 4 to finish the synthesis of 2-deoxy-β-Kdo and 8-
NH2-2,8-dideoxy-β-Kdo, both of which are potent inhibitors of
CMP-Kdo synthase4 and have been studied by many
groups.10d,g,15,16 When Et3SiH or NaBH3CN with different
Lewis acids was applied to the direct deoxygenation,17 no
desired product was formed (Scheme 2). Deoxygenation of 4
with SmI215,16d,18 afforded the ring-opened product 8 instead of
the desired product with a 1:1 ratio of the R and S
configuration at the C-2 position.
Table 2. Optimization of the Desilylation Conditions for 3
Scheme 2. Direct Deoxygenation of 4
entry
reagent (equiv)
TBAF (1 equiv)
time
yield (%)
1
2
3
4
5 min
3 h
67
a
TBAF (1 equiv)
quant
73
a
KF (1 equiv)
6 h
HF·Py (1.5 equiv)
10 h
quant
a
20% AcOH aqueous was added.
key intermediate-di-O-isopropylidene derivative of Kdo ethyl
ester 4. Treatment of 3 with TBAF or KF11a gave the ester 4
only in moderate yield, but a quantitative yield was achieved
when HF·Py11b or the combined system of TBAF with 20%
AcOH aqueous solution5c,11c was used. Deprotection under
more acidic conditions led to more side reactions.
As the desilylation conditions were now well established, we
examined the synthesis of 4 directly from D-mannose without
intermediate purification. As expected, 4 was prepared on a
scale of more than 40 g in one batch in 75−80% overall yield.
Compared to those reported methods, our current approach
can be used to efficiently synthesize 4 on a large scale starting
from cheap material and reagents without intermediate
purification and heavy metal pollution (Scheme 1). After
The deoxygenation of 2-acetylated Kdo ester 7 in the
presence of Et3SiH or NaBH3CN with different Lewis acids did
not give the desired product either. When compound 7 was
treated with SmI2 in the presence of ethylene glycol,16d 2-
deoxy-β-Kdo 9 was obtained in 71% yield along with 13% of
the α-isomer (Scheme 3). Careful control of the reaction
conditions was necessary. Otherwise, over-reduction would
occur to form compound 10.
Scheme 3. Reduction with SmI2
Scheme 1. Synthesis of Kdo and Kdo Derivates from 4
Considering the low stereoselectivity, the low solubility of
SmI2 in THF, and the strict oxygen-free conditions, the SmI2-
mediated deoxygenation of 2-acetylated Kdo ester was not
suitable for the large scale synthesis of 2-deoxy-β-Kdo. We
exploited Burke’s epimerization protocol to afford the β-
isomer.16g As we mentioned above, Kdo glycal 6 was
synthesized on a large scale. The quantitative hydrogenation
of 6 gave 2-deoxy-α-Kdo 11 on more than a 10-g scale in the
presence of a catalytic amount of 10% Pd/C (Scheme 4).
Epimerization of the α-isomer 11 to the β-isomer 9 was
explored under different conditions. A 3:1 ratio of the β and α
isomers was obtained when 1.2 equiv of LDA was used as the
base and aqueous NH4Cl was the proton source;16g the ratio
was increased to 5:1 with t-BuOH as the proton source.
Surprisingly, only a trace amount of the β-isomer was obtained
when AcOH was used as a proton source. The epimerization
did not favor the β-isomer when LiTMP, t-BuOLi, or NaOMe
was used as the base. Gratifyingly, the ratio of β/α was greatly
increased to 10:1 when 2.5 equiv of LDA as the base and t-
BuOH as a proton source were used. Finally, 2-deoxy-β-Kdo 9
was prepared in 85% yield on a scale of 10 g under the
succeeding in the efficient synthesis of Kdo ester 4, we
completed the syntheses of Kdo ammonium salt, 2-acetylated
Kdo ester, and Kdo glycal on a large scale. Deprotection and
hydrolysis of Kdo ester 4 provided Kdo ammonium salt 5 in
almost quantitative yield on the basis of a reported
procedure.5g,12 Treatment of compound 4 with MsCl/Et3N13
provided the Kdo glycal 6 in 80% yield, which has been widely
used as a donor for construction of Kdo glycoside.3e,14
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DOI: 10.1021/acs.orglett.5b00901
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Chen, W. X.; Boons, G. J. J. Am. Chem. Soc. 2012, 134, 14255.
(c) Yang, Y.; Martin, C. E.; Seeberger, P. H. Chem. Sci. 2012, 3, 896.
(d) Yang, Y.; Oishi, S.; Martin, C. E.; Seeberger, P. H. J. Am. Chem.
Soc. 2013, 135, 6262. (e) Pradhan, T. K.; Lin, C. C.; Mong, K. K. T.
Org. Lett. 2014, 16, 1474. (f) Yi, R.; Ogaki, A.; Fukunaga, M.;
Nakajima, H.; Ichiyanagi, T. Tetrahedron 2014, 70, 3675. (g) Pokorny,
B.; Kosma, P. Org. Lett. 2015, 17, 110. (h) Pokorny, B.; Kosma, P.
Chem.Eur. J. 2015, 21, 305.
Scheme 4. Synthesis of 2-β-Kdo 9 via the Epimerization of α-
Isomer 11
(4) (a) Hammond, S. M.; Claesson, A.; Jansson, A. M.; Larsson, L.
̋
G.; Pring, B. G.; Town, C. M.; Ekstrom, B. Nature 1987, 327, 730.
(b) Claesson, A.; Luthman, K.; Gustafsson, K.; Bondesson, G. Biochem.
Biophys. Res. Commun. 1987, 143, 1063.
(5) (a) Li, L. S.; Wu, Y. L. Curr. Org. Chem. 2003, 7, 447 and
references cited therein. (b) Hekking, K. F. W.; van Delft, F. L.; Rutjes,
F. P. J. T. Tetrahedron 2003, 59, 6751. (c) Kuboki, A.; Tajimi, T.;
Tokuda, Y.; Kato, D.; Sugai, T.; Ohira, S. Tetrahedron Lett. 2004, 45,
4545. (d) Hartmann, K.; Kim, B. G.; Linker, T. Synlett 2004, 2728.
(e) Kim, B. G.; Schilde, U.; Linker, T. Synthesis 2005, 1507. (f) Kikelj,
V.; Plantier-Royon, R.; Portella, C. Synthesis 2006, 1200. (g) Hekking,
K. F. W.; Moelands, M. A. H.; van Delft, F. L.; Rutjes, F. P. J. T. J. Org.
Chem. 2006, 71, 6444. (h) Adachi, H.; Kondo, K.; Kojima, F.;
Umezawa, Y.; Ishino, K.; Hotta, K.; Nishimura, Y. Nat. Prod. Res. 2006,
20, 361. (i) Ichiyanagi, T.; Sakamoto, N.; Ochi, K.; Yamasaki, R. J.
Carbohydr. Chem. 2009, 28, 53. (j) Pradhan, T. K.; Lin, C. C.; Mong,
K. K. T. Synlett 2013, 24, 0219. (k) Gillingham, D. G.; Stallforth, P.;
Adibekian, A.; Seeberger, P. H.; Hilvert, D. Nat. Chem. 2010, 2, 102.
(l) Camci-Unal, G.; MizaNur, R. M.; Chai, Y. H.; Pohl, N. L. Org.
Biomol. Chem. 2012, 10, 5856.
(6) (a) Cornforth, J. W.; Firth, M. E.; Gottschalk, A. Biochem. J. 1958,
68, 57. (b) Mcnicholas, P. A.; Batley, M.; Redmond, J. W. Carbohydr.
Res. 1986, 146, 219. (c) Shirai, R.; Ogura, H. Tetrahedron Lett. 1989,
30, 2263. (d) Winzar, R.; Philips, J.; Kiefel, M. J. Synlett 2010, 583.
(7) (a) Itoh, H.; Kaneko, T.; Tanami, K.; Yoda, K. Bull. Chem. Soc.
Jpn. 1988, 61, 3356. (b) Nakamura, E. Tetrahedron Lett. 1980, 22, 663.
(c) Horne, D.; Gaudino, J.; Thompson, W. J. Tetrahedron Lett. 1984,
25, 3529.
optimized conditions. The ammonium salt of 2-deoxy-β-Kdo
was also synthesized according to the reported procedure.5g
With the compound 9 in hand, we proceeded directly to the
synthesis of 8-NH2-2,8-dideoxy-β-Kdo ethyl ester,5h which will
be used in the further investigation of CKS inhibitors in our
laboratory.
In summary, we have developed an efficient route for the
large-scale synthesis of Kdo and its derivatives. Without
intermediate purification and heavy metal pollution, Kdo
ester 4 was prepared in three steps starting from D-mannose.
Kdo, Kdo glycal, and 2-acetylated Kdo ester were rapidly
afforded in high yield from 4. Highly stereoselective synthesis
of 2-deoxy-β-Kdo was achieved in 85% yield via epimerization.
Finally, 8-NH2-2,8-dideoxy-β-Kdo ester was prepared according
to the reported procedure. Further studies on the CKS
inhibitors based on 2-deoxy-β-Kdo and 8-NH2-2,8-dideoxy-β-
Kdo are in progress in our laboratory.
(8) (a) Krohn, K.; Boerner, G.; Gringard, S. J. Org. Chem. 1994, 59,
6069. (b) Drew, K. N.; Gross, P. H. J. Org. Chem. 1991, 56, 509.
(9) (a) Petroski, R. J.; Weisleder, D. Synth. Commun. 2001, 31, 89.
(b) Fox, R. J.; Lalic, G.; Bergman, R. G. J. Am. Chem. Soc. 2007, 129,
14144.
(10) (a) Imoto, M.; Kusumoto, S.; Shiba, T. Tetrahedron Lett. 1987,
28, 6235. (b) van der Klein, P. A. M.; Boons, G. J. P. H.; Veeneman, G.
H.; van der Marel, G. A.; van Boom, J. H. Tetrahedron Lett. 1989, 30,
5477. (c) Boons, G. J. P. H.; van der Klein, P. A. M.; van der Marel, G.
A.; van Boom, J. H. Recl. Trav. Chim. Pays-Bas 1990, 109, 273.
ASSOCIATED CONTENT
* Supporting Information
Experimental procedures, characterization data and NMR
spectra. The Supporting Information is available free of charge
on the ACS Publications website at DOI: 10.1021/
acs.orglett.5b00901.
■
S
AUTHOR INFORMATION
Corresponding Author
■
(d) Lubineau, A.; Auge,
́
J.; Lubin, N. Tetrahedron 1993, 49, 4639.
(e) Sato, K.; Miyata, T.; Tanai, I.; Yonezawa, Y. Chem. Lett. 1994, 23,
*E-mail: ychai@snnu.edu.cn.
Notes
́
́
ez-Herrera, F. J.; Sarabia-Garcla, F. Tetrahedron Lett. 1994,
129. (f) Lop
35, 6705. (g) Lop
1997, 53, 3325. (h) Reiner, M.; Schmidt, R. R. Tetrahedron: Asymmetry
2000, 11, 319. (i) Wardrop, D. J.; Zhang, W. M. Tetrahedron Lett.
2002, 43, 5389.
́
ez-Herrera, F. J.; Sarabia-Garcla, F. Tetrahedron
́
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(11) (a) Ruan, Q.; Penning, T. M.; Blair, I. A.; Harvey, R. G. J. Org.
This work was supported by the Fundamental Research Funds
for the Central Universities (No. GK200902005), Shaanxi
Provincial Natural Science Foundation (No. 2010JM2010), the
National Natural Science Foundation of China (Nos.
21072122, 21472119), and Ministry of Science and Technology
(No. 2012ZX09502-001-001). All of the financial support is
gratefully acknowledged.
Chem. 2008, 73, 992. (b) Paterson, I.; Chen, D. Y.; Acena, J. L.;
̃
Franklin, A. S. Org. Lett. 2000, 2, 1513. (c) Zimmerman, H. E.; Wang,
P. F. J. Org. Chem. 2003, 68, 9226.
(12) (a) Gao, J. M.; Harter, R.; Gordon, D. M.; Whitesides, G. M. J.
̈
Org. Chem. 1994, 59, 3714. (b) Schlessinger, R. H.; Pettus, L. H. J. Org.
Chem. 1998, 63, 9089.
(13) Wong, M. K.; Chung, N. W.; He, L.; Wang, X. C.; Yan, Z.; Yang,
Y. C.; Tang, D. J. Org. Chem. 2003, 68, 6321.
(14) (a) Tanaka, H.; Takahashi, D.; Takahashi, T. Angew. Chem., Int.
Ed. 2006, 45, 770. (b) Qian, Y. X.; Feng, J. H.; Parvez, M.; Ling, C. C.
J. Org. Chem. 2012, 77, 96.
(15) Boons, G. J. P. H.; van Delft, F. L.; van der Klein, P. A. M.; van
der Marel, G. A.; van Boom, J. H. Tetrahedron 1992, 48, 885.
(16) References for synthesis of 2-deoxy-β-Kdo and its analogs:
REFERENCES
■
(1) Unger, F. M. Adv. Carbohydr. Chem. Biochem. 1981, 38, 323.
(2) (a) Ray, P. H.; Benedict, C. D.; Grasmuk, H. J. Bacteriol. 1981,
145, 1273. (b) Goldman, R. C.; Bolling, T. J.; Kohlbrenner, W. E.;
Kim, Y.; Fox, J. L. J. Biol. Chem. 1986, 261, 15831.
(3) (a) Oscarson, S. Carbohydr. Chem. 2012, 38, 40 and references
cited therein. (b) Boltje, T. J.; Zhong, W.; Park, J.; Wolfert, M. A.;
(a) Luthman, K.; Orbe, M.; Wag
́
lund, T.; Claesson, A. J. Org. Chem.
C
DOI: 10.1021/acs.orglett.5b00901
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
1987, 52, 3777. (b) Tamao, K.; Nakajo, E.; Ito, Y. J. Org. Chem. 1987,
52, 4414. (c) Ohrui, H.; Morita, M.; Meguro, H. Carbohydr. Res. 1992,
224, 319. (d) Hanessian, S.; Girard, C. Synlett 1994, 863. (e) Sarabia-
́
́ ́
Garcla, F.; Lopez-Herrera, F. J.; Pino-Gonzalez, M. S. Tetrahedron Lett.
1994, 35, 6709. (f) Craig, D.; Pennington, M. W.; Warner, P.
Tetrahedron Lett. 1995, 36, 5815. (g) Burke, S. D.; Sametz, G. M. Org.
Lett. 1999, 1, 71. (h) Kumaran, G.; Mootoo, D. R. Tetrahedron Lett.
2001, 42, 3783. (i) Luthman, K.; Claesson, A. Carbohydr. Res. 1987,
166, 233. (j) Tadanier, J.; Lee, C.; Whittern, D.; Wideburg, N.
Carbohydr. Res. 1990, 201, 185. (k) Claesson, A.; Jansson, A. M.;
̋
Pring, B. G.; Hammond, S. M.; Ekstrom, B. J. Med. Chem. 1987, 30,
2309. (l) Norbeck, D. W.; Rosenbrook, W.; Kramer, J. B.;
Gramprovnik, D. J.; Lartey, P. A. J. Med. Chem. 1989, 32, 625.
(m) Pring, B. G.; Jansson, A. M.; Persson, K.; Andersson, I.; Gagner-
Milchert, I.; Gustafsson, K.; Claesson, A. J. Med. Chem. 1989, 32, 1069.
(17) (a) Terauchi, M.; Abe, H.; Matsuda, A.; Shuto, S. Org. Lett.
2004, 6, 3751. (b) Tanis, P. S.; Infantine, J. R.; Leighton, J. L. Org. Lett.
2013, 15, 5464.
(18) (a) Kusuda, K.; Inanaga, J.; Yamaguchi, M. Tetrahedron Lett.
1989, 30, 2945. (b) Hanessian, S.; Girard, C.; Chiara, J. L. Tetrahedron
Lett. 1992, 33, 573.
D
DOI: 10.1021/acs.orglett.5b00901
Org. Lett. XXXX, XXX, XXX−XXX