- Email: [email protected]
Programmable one-pot synthesis of tumor-associated carbohydrate antigens Lewis X dimer and KH-1 epitopes
Tetrahedron Letters 52 (2011) 2132–2135
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Programmable one-pot synthesis of tumor-associated carbohydrate antigens Lewis X dimer and KH-1 epitopes Bin-Ling Tsai a,b, Jeng-Liang Han a, Chien-Tai Ren a, Chung-Yi Wu a,⇑, Chi-Huey Wong a,b,⇑ a b
Genomics Research Center, Academia Sinica, Taiwan Department of Chemistry, National Taiwan University, Taipei, Taiwan
a r t i c l e
i n f o
Article history: Available online 16 November 2010 Dedicated to Professor Harry Wasserman on the occasion of his 90th birthday
a b s t r a c t The total synthesis of the antigenic Lewis X (Lex) dimer and KH-1 epitopes by a reactivity-based programmable one-pot synthetic strategy is reported. This approach can minimize the protection–deprotection and purification steps. Using the reactivity-based one-pot synthetic method, the fully protected Lewis X (Lex) dimer and KH-1 epitopes were furnished in a facile manner, which were globally deprotected to give the Lex dimer and KH-1 epitopes. Ó 2010 Elsevier Ltd. All rights reserved.
Lewis X (Lex) dimer and KH-1, isolated by Hakomori in 1986,1 are tumor-associated carbohydrate antigens and considered as markers of colonic adenocarcinoma.1,2 They can be used to develop carbohydrate-based anticancer vaccines and carbohydrate microarray for diagnosis. Lex dimer has been synthesized via stepwise [3+2+3] or [3+3+2] strategies,3–6 soluble polymer supported synthesis,7 orthogonal, and iterative methods.8,9 Chemical synthesis of KH-1 was first reported by both Schmidt10 and Danishefsky11 independently in 1997. In 2004, Seeberger used the automated solid-phase synthesis to construct KH-1.12 Stepwise [4+3] strategy was used by Danishefsky13 and Boons14 independently in 2005. Our group has developed a programmable one-pot strategy for the synthesis of complex oligosaccharides.15–21 The methodology is based on the use of designer thioglycoside building blocks with defined relative reactivity values (RRVs) that are collected in the Optimer database.22 Herein, we report the use of this strategy to prepare antigens Lex dimer and KH-1 epitopes. From the structural point of view, the subtle difference between the epitope structure of dimeric LewisX (1) and KH-1 (2) is that the latter has an extra L-fucose with an a(1?2) linkage to the nonreducing end galactose moiety (the LewisY epitope). Accordingly, we designed a convergent synthetic approach utilizing a reactivity-based one-pot methodology (Scheme 1), in which 1 could be derived from the building blocks 3,22, 4,18 and 6 by one-pot glycosylation. In a similar manner, 2 could be prepared from the corresponding building blocks 3, 5,18 and 6. The disaccharides 4 and 5 could be prepared from thiogalatosides 722 and 8,22 respectively, with 9.22 The reducing end trisaccharide building block 6 in turn ⇑ Corresponding authors. E-mail addresses: [email protected] (C.-Y. Wu), [email protected]. edu.tw (C.-H. Wong). 0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2010.11.055
could be assembled from building blocks 3, 10 (RRV = 115),9 and 11 via a second one-pot glycosylation. To synthesize building blocks 4 and 5 (Scheme 2), we started by treating thiogalactoside 7 (RRV = 5200) with 9 (RRV = 282) in the presence of N-iodosuccinimide (NIS) and 0.1 equiv of triflic acid (TfOH) in CH2Cl2 at 35 °C to give disaccharide 12 in 43% yield. The levulinate (Lev) protecting group in 9 seems to be critical for increasing the yield. Replacement of the levulinoyl group with the benzoyl group resulted in a substantial decrease in product yield. Selective deprotection of the Lev ester in 12 by treatment with hydrazine hydrate in an acetic acid/pyridine mixture afforded building block 4 in 98% yield. Likewise, building block 5 was prepared from glycosylation of 8 (RRV = 4000) and 9 in a comparable yield. The synthesis of 11 was started from the known glycosyl bromide 14.23 Treatment of 4 with azido alcohol 15 in the presence of iodine and DDQ24 gave 16 exclusively in 71% yield. Deacetylation of 16 followed by benzylidene formation between C4–OH and C6–OH afforded 17 (91% for two steps). Compound 17 was converted into 11 by a three step sequence: protecting C3–OH in 17 as Lev ester, followed by reductive benzylidene ring cleavage and selective Lev deprotection. Next, we proceeded to the assembly of trisaccharide building block 18 via a one-pot sequential glycosylation (Scheme 3). To take advantage of the reactivity difference between C3–OH and C4–OH in building block 1125, thiogalactoside 10 was chosen to be the first glycosyl donor in order to introduce the galactose moiety in a desired regioselective manner. In a separate experiment, treatment of 11 with glycosyl donor 10 in the presence of NIS and a catalytic amount of TfOH in CH2Cl2 at 40 °C gave two regioisomers in a ratio of 10–1, in which the C4-isomer was obtained as the major product. Encouraged by these results, we further investigated the one-pot synthesis of 18. Building block 11 (1.0 equiv) was coupled
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B.-L. Tsai et al. / Tetrahedron Letters 52 (2011) 2132–2135
HO
OH O
HO
OH O
O OR 1 O O
HO
OH O
O NHAc
O O
OH
OH
O
OH HO
OH O
O
NHAc
OH NH2
HOOH 1 R1 = H 2 R 1 = α(1-2)-L-Fucose
OBn O
BnO STol OBn
O OBn BnO
O HO OR2
BnO
STol NHTroc
O
HO
4 R 2 = Bz 5 R2 = H
OBn O
BnO
OBn O
O OH O O
3
BnO
Ph O O
HO LevO
STol
OR3
OBn
OBn BnO
O
NHTroc 6
N3
Ph O O
OBn O
O
STol NHTroc
7 R 3 = Bz 8 R 3 = Lev
OBn O
OBn BnO
STol OBn
LevO
3
9
O
STol OLev
OBn O
HO HO
O
NHTroc
10
11
N3
Scheme 1. Retro-synthetic analysis of Lex dimer 1 and KH-1 2.
BnO
OBn O
BnO
+
STol
OR 3
HO LevO
7 = Bz 8 R 3 = Lev
OBn O
STol
NHTroc 9
R3
BnO Hydrazine hydrate/AcOH/pyridine
BnO
NIS / TfOH CH2 Cl2 , AW-300, -45 oC to -35 o C 41-43% OBn O OR2
98%
O HO
BnO OBn OBn O O O BnO STol LevO 3 R O NHTroc 12 R 3 = Bz 13 R 3 = Lev
OBn O
STol
NHTroc
4 R 2 = Bz 5 R2 = H 15
AcO AcO
OAc O TrocHN 14
Ph
O O HO
HO
N3 I2 , DDQ
Br
O TrocHN
CH3CN, AW-300, r.t 71%
O
N3 17
AcO AcO
OAc O
O
1) NaOMe, MeOH
N3
2) benzaldehyde dimethyl acetal CSA, CH 3CN, 40 o C 91% two steps
TrocHN 16
1) Levulinic acid, EDCI, DMAP (88%)
BnO HO HO
2) Triethylsilane, TFA,TFAA (89%) 3) Hydrazine hydrate/AcOH/pyridine (87%)
O
O
N3
TrocHN 11
Scheme 2. Synthesis of building blocks 4, 5 and 11.
with 10 (1.4 equiv) in the presence of NIS/TfOH (0.1 equiv) at 40 °C. After the complete consumption of 11 was confirmed by TLC, the temperature was cooled to 50 °C, and perbenzylated fucosyl building block 3 (1.2 equiv) was added, followed by the addition of NIS/TfOH. After the complete consumption of 3 was
confirmed by TLC analysis, trisaccharide 18 was obtained in 40– 47% yield after standard work up and purification and no regioisomer of 18 was detected. Building block 6 was then prepared by selective Lev deprotection of 18 under the conditions of hydrazine hydrate in an acetic acid/pyridine mixture.
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BnO
OBn O
HO HO
O
OBn O
STol OH NHTroc 5 RRV = 12000 Ph (a) O O
BnO
11 NHTroc (a)
OBn O
O HO
N3
STol OBn
O yield: 40~47%
OBn BnO
O
LevO
STol OLev
10
yield: 36.2%
(b)
O
OBn O
O
LevO
O OLev O O
O
Hydrazine hydrate
NHTroc
AcOH, Pyridine 89%
OBn
OBn BnO
OBn O
BnO
N3
18
6
BnO
O OBn
O O O
O OBn BnO
BnO OBn
78%
Ph O O
O OH O
(b)
O STol OBn OBn BnO 3 RRV = 72000
3
OBn O
OBn
OBn BnO
Ph O O
O NHTroc
O
O OH O O
20
OBn BnO
OBn O
O
HO
Ph O O
OBn O
O
NHTroc
OBn 6
RRV = 0
N3
O
NHTroc
OBn N3
Scheme 3. One-pot synthesis of trisaccharide building block 18.
Scheme 5. One-pot synthesis of fully protective KH-1 epitope.
With all the desired building blocks in hand, we examined the feasibility of one-pot synthesis of compounds 1 and 2. First, the reaction of glycosyl donor 3 with acceptor 4 and 5, respectively, was performed under various conditions in order to optimize the stereochemical outcome. It was found that the best result was obtained when the reaction was carried out in CH2Cl2 at 45 °C and activated by NIS/TfOH. The reaction temperature seems to be crucial for the success of this reaction; little products with poor anomeric selectivity and by-products derived from succinimde were observed when the reaction was carried out at lower temperature, such as 78 °C. For the reducing end trisaccharide 6, there was a distinct acceptor reactivity bias where C3–OH>>C2–OH was speculated for the reason of their steric accessibility.9 With these preliminary results in hand, we turned our attention to the one-pot synthesis of hexa-
saccharide 19, a precursor of 1 in a [1+2+3] fashion (Scheme 4). Perbenzylated fucosyl building block 3 (1.1 equiv, RRV = 7.2 104) was coupled with the less reactive disaccharide building block 4 (1.0 equiv, RRV = 5890) in the presence of NIS/TfOH at 45 °C. After the complete consumption of 3 was confirmed by TLC analysis, the reaction temperature was raised to 35 °C, and trisaccharide acceptor 6 (0.8 equiv, RRV = 0) was added, followed by the addition of NIS/TfOH. The second glycosylation was generally completed in 1 h at 35 °C as demonstrated by TLC analysis. The reaction was then worked up by the standard procedures to provide 19 in 41% yield (based on 6) after flash silica gel chromatography (EA/ Hexane = 1:2). Following the same reaction sequence, heptasaccharide 20, a precursor of 2 was prepared in a [1 2+2+3] fashion from corresponding building blocks 3 (2.2 equiv, RRV = 7.2 104), 5 (1.0 equiv, RRV = 1.2 104), and 6 (0.6 equiv, RRV = 0) in 36% yield (based on 6) (Scheme 5). To complete the synthesis, compounds 19 and 20 were subjected to global deprotection (Scheme 6). The process started with the removal of the Acyl and Troc protecting groups by alkali hydrolysis (1 N NaOH in THF at 50 °C for 24 h), followed by reacetylation of the exposed hydroxyl and amine functionalities with acetic anhydride in pyridine, and O-deacetylation with NaOMe in methanol to provide intermediate 21 and 22, respectively, in 56–62% yield. The rest of the protecting groups in 21 and 22 were removed by catalytic hydrogenolysis (H2, 20% Pd(OH)2/C, in MeOH/H2O/ AcOH) to afford the target molecules 1 and 2, respectively, in 61–80% yield. This approach extensively utilizes the diol functionality of the building blocks by introducing two of the same carbohydrate units simultaneously or taking the advantages of the distinct reactivity order of these hydroxyl groups for attachment of two different carbohydrates in a regioselective manner. Thus, the protection–deprotection steps are minimized, and we present a simple, elegant, convergent, and highly efficient reactivity-based programmable one-pot synthesis of LeX dimer 1 and KH-1 2 epitopes.
OBn O
BnO
OBn O
O STol HO OBz NHTroc 4 RRV = 5890 (a)
BnO
Ph O O
yield: 41.1% O OBn BnO 3
O OH O
(b)
STol OBn
OBn O
O
HO
O
O
NHTroc OBn
OBn BnO 6
RRV = 0
RRV = 72000
BnO BnO
OBn O
O OBz O O
OBn BnO
Ph O O
OBn O
OBn
O NHTroc 19
O OH
O O
O OBn BnO
OBn O
O
NHTroc
N3
OBn N3
Scheme 4. One-pot synthesis of fully protective Lex dimer epitope.
Acknowledgment This work was supported by Academia Sinica, Taiwan.
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BnO
OBn O
BnO
OBn O
O OR 4 O O
Ph O O O OH O
OBn
O
OBn BnO
OBn O
O
O NHTroc
1) 1N NaOH, THF, 50 o C O
2) Ac2O, Pyridine
NHTroc
OBn N3
OBn BnO
BnO
19 R = Bz 20 R4 = α(1-2)-L-perbenzylated Fucosyl 4
3) NaOMe, MeOH 56-62%
BnO
OBn O
O OR 5 O O
H 2, 20% Pd(OH)2/carbon MeOH /H 2 O/HOAc HO HO
OH O
O OR 1 O O
OH HO
OH
OH O
HO
O NHAc
OH O OH
O O
O
OH O
61-80%
OBn O
Ph O O
O NHAc
OBn
OBn BnO
O
O OH O O
OBn BnO
OBn O
O
NHAc
OBn N3
21 R4 = OH 22 R4 = α(1-2)-L-perbenzylated Fucosyl
O
NHAc
OH NH2
OH HO 1 R1 = H 2 R 1 = α(1-2)-L-Fucose
Scheme 6. Synthesis of Lex dimer and KH-1 epitopes.
Supplementary data Supplementary data associated with (full characterization of all new compounds (1–2, 6, 19 and 20) and copies of NMR spectra) this article can be found, in the online version, at doi:10.1016/ j.tetlet.2010.11.055. References and notes 1. Nudelman, E.; Levery, S. B.; Kaizu, T.; Hakomori, S. J. Biol. Chem. 1986, 261, 1247–1253. 2. Zhang, S. L.; CordonCardo, C.; Zhang, H. S.; Reuter, V. E.; Adluri, S.; Hamilton, W. B.; Lloyd, K. O.; Livingston, P. O. Int. J. Cancer 1997, 73, 42–49. 3. Sato, S.; Ito, Y.; Ogawa, T. Tetrahedron Lett. 1988, 29, 5267–5270. 4. Nicolaou, K. C.; Caulfield, T. J.; Kataoka, H.; Stylianides, N. A. J. Am. Chem. Soc. 1990, 112, 3693–3695. 5. Toepfer, A.; Kinzy, W.; Schmidt, R. R. Liebigs Ann. Chem. 1994, 449–464. 6. Bregant, S.; Zhang, Y. M.; Mallet, J. M.; Brodzki, A.; Sinay, P. Glycoconjugate J. 1999, 16, 757–765. 7. Zhu, T.; Boons, G. J. J. Am. Chem. Soc. 2000, 122, 10222–10223. 8. Tanaka, H.; Matoba, N.; Tsukamoto, H.; Takimoto, H.; Yamada, H.; Takahashi, T. Synlett 2005, 824–828. 9. Miermont, A.; Zeng, Y. L.; Jing, Y. Q.; Ye, X. S.; Huang, X. F. J. Org. Chem. 2007, 72, 8958–8961.
10. 11. 12. 13. 14. 15. 16. 17. 18. 19.
20. 21. 22. 23. 24. 25.
Hummel, G.; Schmidt, R. R. Tetrahedron Lett. 1997, 38, 1173–1176. Deshpande, P. P.; Danishefsky, S. J. Nature. 1997, 387, 164–166. Love, K. R.; Seeberger, P. H. Angew. Chem., Int. Ed. 2004, 43, 602–605. Spassova, M. K.; Bornmann, W. G.; Ragupathi, G.; Sukenick, G.; Livingston, P. O.; Danishefsky, S. J. J. Org. Chem. 2005, 70, 3383–3395. Buskas, T.; Li, Y.; Boons, G. J. Chem. Eur. J. 2005, 11, 5457–5467. Burkhart, F.; Zhang, Z. Y.; Wacowich-Sgarbi, S.; Wong, C. H. Angew. Chem., Int. Ed. 2001, 40. 1274. Mong, K. K. T.; Wong, C. H. Angew. Chem., Int. Ed. 2002, 41, 4087–4090. Mong, T. K. K.; Huang, C. Y.; Wong, C. H. J. Org. Chem. 2003, 68, 2135– 2142. Mong, T. K. K.; Lee, H. K.; Duron, S. G.; Wong, C. H. Proc. Natl. Acad. Sci. U.S.A. 2003, 100, 797–802. Lee, H. K.; Scanlan, C. N.; Huang, C. Y.; Chang, A. Y.; Calarese, D. A.; Dwek, R. A.; Rudd, P. M.; Burton, D. R.; Wilson, I. A.; Wong, C. H. Angew. Chem., Int. Ed. 2004, 43, 1000–1003. Lee, J. C.; Wu, C. Y.; Apon, J. V.; Siuzdak, G.; Wong, C. H. Angew. Chem., Int. Ed. 2006, 45, 2753–2757. Polat, T.; Wong, C. H. J. Am. Chem. Soc. 2007, 129, 12795–12800. Zhang, Z. Y.; Ollmann, I. R.; Ye, X. S.; Wischnat, R.; Baasov, T.; Wong, C. H. J. Am. Chem. Soc. 1999, 121, 734–753. Mitchell, S. A.; Pratt, M. R.; Hruby, V. J.; Polt, R. J. Org. Chem. 2001, 66, 2327– 2342. Kartha, K. P. R.; Aloui, M.; Field, R. A. Tetrahedron Lett. 1996, 37, 8807–8810. Zhang, Z. Y.; Niikura, K.; Huang, X. F.; Wong, C. H. Can. J. Chem. Rev. Can. Chim. 2002, 80, 1051–1054.
Contents lists available at ScienceDirect
Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet
Programmable one-pot synthesis of tumor-associated carbohydrate antigens Lewis X dimer and KH-1 epitopes Bin-Ling Tsai a,b, Jeng-Liang Han a, Chien-Tai Ren a, Chung-Yi Wu a,⇑, Chi-Huey Wong a,b,⇑ a b
Genomics Research Center, Academia Sinica, Taiwan Department of Chemistry, National Taiwan University, Taipei, Taiwan
a r t i c l e
i n f o
Article history: Available online 16 November 2010 Dedicated to Professor Harry Wasserman on the occasion of his 90th birthday
a b s t r a c t The total synthesis of the antigenic Lewis X (Lex) dimer and KH-1 epitopes by a reactivity-based programmable one-pot synthetic strategy is reported. This approach can minimize the protection–deprotection and purification steps. Using the reactivity-based one-pot synthetic method, the fully protected Lewis X (Lex) dimer and KH-1 epitopes were furnished in a facile manner, which were globally deprotected to give the Lex dimer and KH-1 epitopes. Ó 2010 Elsevier Ltd. All rights reserved.
Lewis X (Lex) dimer and KH-1, isolated by Hakomori in 1986,1 are tumor-associated carbohydrate antigens and considered as markers of colonic adenocarcinoma.1,2 They can be used to develop carbohydrate-based anticancer vaccines and carbohydrate microarray for diagnosis. Lex dimer has been synthesized via stepwise [3+2+3] or [3+3+2] strategies,3–6 soluble polymer supported synthesis,7 orthogonal, and iterative methods.8,9 Chemical synthesis of KH-1 was first reported by both Schmidt10 and Danishefsky11 independently in 1997. In 2004, Seeberger used the automated solid-phase synthesis to construct KH-1.12 Stepwise [4+3] strategy was used by Danishefsky13 and Boons14 independently in 2005. Our group has developed a programmable one-pot strategy for the synthesis of complex oligosaccharides.15–21 The methodology is based on the use of designer thioglycoside building blocks with defined relative reactivity values (RRVs) that are collected in the Optimer database.22 Herein, we report the use of this strategy to prepare antigens Lex dimer and KH-1 epitopes. From the structural point of view, the subtle difference between the epitope structure of dimeric LewisX (1) and KH-1 (2) is that the latter has an extra L-fucose with an a(1?2) linkage to the nonreducing end galactose moiety (the LewisY epitope). Accordingly, we designed a convergent synthetic approach utilizing a reactivity-based one-pot methodology (Scheme 1), in which 1 could be derived from the building blocks 3,22, 4,18 and 6 by one-pot glycosylation. In a similar manner, 2 could be prepared from the corresponding building blocks 3, 5,18 and 6. The disaccharides 4 and 5 could be prepared from thiogalatosides 722 and 8,22 respectively, with 9.22 The reducing end trisaccharide building block 6 in turn ⇑ Corresponding authors. E-mail addresses: [email protected] (C.-Y. Wu), [email protected]. edu.tw (C.-H. Wong). 0040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2010.11.055
could be assembled from building blocks 3, 10 (RRV = 115),9 and 11 via a second one-pot glycosylation. To synthesize building blocks 4 and 5 (Scheme 2), we started by treating thiogalactoside 7 (RRV = 5200) with 9 (RRV = 282) in the presence of N-iodosuccinimide (NIS) and 0.1 equiv of triflic acid (TfOH) in CH2Cl2 at 35 °C to give disaccharide 12 in 43% yield. The levulinate (Lev) protecting group in 9 seems to be critical for increasing the yield. Replacement of the levulinoyl group with the benzoyl group resulted in a substantial decrease in product yield. Selective deprotection of the Lev ester in 12 by treatment with hydrazine hydrate in an acetic acid/pyridine mixture afforded building block 4 in 98% yield. Likewise, building block 5 was prepared from glycosylation of 8 (RRV = 4000) and 9 in a comparable yield. The synthesis of 11 was started from the known glycosyl bromide 14.23 Treatment of 4 with azido alcohol 15 in the presence of iodine and DDQ24 gave 16 exclusively in 71% yield. Deacetylation of 16 followed by benzylidene formation between C4–OH and C6–OH afforded 17 (91% for two steps). Compound 17 was converted into 11 by a three step sequence: protecting C3–OH in 17 as Lev ester, followed by reductive benzylidene ring cleavage and selective Lev deprotection. Next, we proceeded to the assembly of trisaccharide building block 18 via a one-pot sequential glycosylation (Scheme 3). To take advantage of the reactivity difference between C3–OH and C4–OH in building block 1125, thiogalactoside 10 was chosen to be the first glycosyl donor in order to introduce the galactose moiety in a desired regioselective manner. In a separate experiment, treatment of 11 with glycosyl donor 10 in the presence of NIS and a catalytic amount of TfOH in CH2Cl2 at 40 °C gave two regioisomers in a ratio of 10–1, in which the C4-isomer was obtained as the major product. Encouraged by these results, we further investigated the one-pot synthesis of 18. Building block 11 (1.0 equiv) was coupled
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B.-L. Tsai et al. / Tetrahedron Letters 52 (2011) 2132–2135
HO
OH O
HO
OH O
O OR 1 O O
HO
OH O
O NHAc
O O
OH
OH
O
OH HO
OH O
O
NHAc
OH NH2
HOOH 1 R1 = H 2 R 1 = α(1-2)-L-Fucose
OBn O
BnO STol OBn
O OBn BnO
O HO OR2
BnO
STol NHTroc
O
HO
4 R 2 = Bz 5 R2 = H
OBn O
BnO
OBn O
O OH O O
3
BnO
Ph O O
HO LevO
STol
OR3
OBn
OBn BnO
O
NHTroc 6
N3
Ph O O
OBn O
O
STol NHTroc
7 R 3 = Bz 8 R 3 = Lev
OBn O
OBn BnO
STol OBn
LevO
3
9
O
STol OLev
OBn O
HO HO
O
NHTroc
10
11
N3
Scheme 1. Retro-synthetic analysis of Lex dimer 1 and KH-1 2.
BnO
OBn O
BnO
+
STol
OR 3
HO LevO
7 = Bz 8 R 3 = Lev
OBn O
STol
NHTroc 9
R3
BnO Hydrazine hydrate/AcOH/pyridine
BnO
NIS / TfOH CH2 Cl2 , AW-300, -45 oC to -35 o C 41-43% OBn O OR2
98%
O HO
BnO OBn OBn O O O BnO STol LevO 3 R O NHTroc 12 R 3 = Bz 13 R 3 = Lev
OBn O
STol
NHTroc
4 R 2 = Bz 5 R2 = H 15
AcO AcO
OAc O TrocHN 14
Ph
O O HO
HO
N3 I2 , DDQ
Br
O TrocHN
CH3CN, AW-300, r.t 71%
O
N3 17
AcO AcO
OAc O
O
1) NaOMe, MeOH
N3
2) benzaldehyde dimethyl acetal CSA, CH 3CN, 40 o C 91% two steps
TrocHN 16
1) Levulinic acid, EDCI, DMAP (88%)
BnO HO HO
2) Triethylsilane, TFA,TFAA (89%) 3) Hydrazine hydrate/AcOH/pyridine (87%)
O
O
N3
TrocHN 11
Scheme 2. Synthesis of building blocks 4, 5 and 11.
with 10 (1.4 equiv) in the presence of NIS/TfOH (0.1 equiv) at 40 °C. After the complete consumption of 11 was confirmed by TLC, the temperature was cooled to 50 °C, and perbenzylated fucosyl building block 3 (1.2 equiv) was added, followed by the addition of NIS/TfOH. After the complete consumption of 3 was
confirmed by TLC analysis, trisaccharide 18 was obtained in 40– 47% yield after standard work up and purification and no regioisomer of 18 was detected. Building block 6 was then prepared by selective Lev deprotection of 18 under the conditions of hydrazine hydrate in an acetic acid/pyridine mixture.
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B.-L. Tsai et al. / Tetrahedron Letters 52 (2011) 2132–2135
BnO
OBn O
HO HO
O
OBn O
STol OH NHTroc 5 RRV = 12000 Ph (a) O O
BnO
11 NHTroc (a)
OBn O
O HO
N3
STol OBn
O yield: 40~47%
OBn BnO
O
LevO
STol OLev
10
yield: 36.2%
(b)
O
OBn O
O
LevO
O OLev O O
O
Hydrazine hydrate
NHTroc
AcOH, Pyridine 89%
OBn
OBn BnO
OBn O
BnO
N3
18
6
BnO
O OBn
O O O
O OBn BnO
BnO OBn
78%
Ph O O
O OH O
(b)
O STol OBn OBn BnO 3 RRV = 72000
3
OBn O
OBn
OBn BnO
Ph O O
O NHTroc
O
O OH O O
20
OBn BnO
OBn O
O
HO
Ph O O
OBn O
O
NHTroc
OBn 6
RRV = 0
N3
O
NHTroc
OBn N3
Scheme 3. One-pot synthesis of trisaccharide building block 18.
Scheme 5. One-pot synthesis of fully protective KH-1 epitope.
With all the desired building blocks in hand, we examined the feasibility of one-pot synthesis of compounds 1 and 2. First, the reaction of glycosyl donor 3 with acceptor 4 and 5, respectively, was performed under various conditions in order to optimize the stereochemical outcome. It was found that the best result was obtained when the reaction was carried out in CH2Cl2 at 45 °C and activated by NIS/TfOH. The reaction temperature seems to be crucial for the success of this reaction; little products with poor anomeric selectivity and by-products derived from succinimde were observed when the reaction was carried out at lower temperature, such as 78 °C. For the reducing end trisaccharide 6, there was a distinct acceptor reactivity bias where C3–OH>>C2–OH was speculated for the reason of their steric accessibility.9 With these preliminary results in hand, we turned our attention to the one-pot synthesis of hexa-
saccharide 19, a precursor of 1 in a [1+2+3] fashion (Scheme 4). Perbenzylated fucosyl building block 3 (1.1 equiv, RRV = 7.2 104) was coupled with the less reactive disaccharide building block 4 (1.0 equiv, RRV = 5890) in the presence of NIS/TfOH at 45 °C. After the complete consumption of 3 was confirmed by TLC analysis, the reaction temperature was raised to 35 °C, and trisaccharide acceptor 6 (0.8 equiv, RRV = 0) was added, followed by the addition of NIS/TfOH. The second glycosylation was generally completed in 1 h at 35 °C as demonstrated by TLC analysis. The reaction was then worked up by the standard procedures to provide 19 in 41% yield (based on 6) after flash silica gel chromatography (EA/ Hexane = 1:2). Following the same reaction sequence, heptasaccharide 20, a precursor of 2 was prepared in a [1 2+2+3] fashion from corresponding building blocks 3 (2.2 equiv, RRV = 7.2 104), 5 (1.0 equiv, RRV = 1.2 104), and 6 (0.6 equiv, RRV = 0) in 36% yield (based on 6) (Scheme 5). To complete the synthesis, compounds 19 and 20 were subjected to global deprotection (Scheme 6). The process started with the removal of the Acyl and Troc protecting groups by alkali hydrolysis (1 N NaOH in THF at 50 °C for 24 h), followed by reacetylation of the exposed hydroxyl and amine functionalities with acetic anhydride in pyridine, and O-deacetylation with NaOMe in methanol to provide intermediate 21 and 22, respectively, in 56–62% yield. The rest of the protecting groups in 21 and 22 were removed by catalytic hydrogenolysis (H2, 20% Pd(OH)2/C, in MeOH/H2O/ AcOH) to afford the target molecules 1 and 2, respectively, in 61–80% yield. This approach extensively utilizes the diol functionality of the building blocks by introducing two of the same carbohydrate units simultaneously or taking the advantages of the distinct reactivity order of these hydroxyl groups for attachment of two different carbohydrates in a regioselective manner. Thus, the protection–deprotection steps are minimized, and we present a simple, elegant, convergent, and highly efficient reactivity-based programmable one-pot synthesis of LeX dimer 1 and KH-1 2 epitopes.
OBn O
BnO
OBn O
O STol HO OBz NHTroc 4 RRV = 5890 (a)
BnO
Ph O O
yield: 41.1% O OBn BnO 3
O OH O
(b)
STol OBn
OBn O
O
HO
O
O
NHTroc OBn
OBn BnO 6
RRV = 0
RRV = 72000
BnO BnO
OBn O
O OBz O O
OBn BnO
Ph O O
OBn O
OBn
O NHTroc 19
O OH
O O
O OBn BnO
OBn O
O
NHTroc
N3
OBn N3
Scheme 4. One-pot synthesis of fully protective Lex dimer epitope.
Acknowledgment This work was supported by Academia Sinica, Taiwan.
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B.-L. Tsai et al. / Tetrahedron Letters 52 (2011) 2132–2135
BnO
OBn O
BnO
OBn O
O OR 4 O O
Ph O O O OH O
OBn
O
OBn BnO
OBn O
O
O NHTroc
1) 1N NaOH, THF, 50 o C O
2) Ac2O, Pyridine
NHTroc
OBn N3
OBn BnO
BnO
19 R = Bz 20 R4 = α(1-2)-L-perbenzylated Fucosyl 4
3) NaOMe, MeOH 56-62%
BnO
OBn O
O OR 5 O O
H 2, 20% Pd(OH)2/carbon MeOH /H 2 O/HOAc HO HO
OH O
O OR 1 O O
OH HO
OH
OH O
HO
O NHAc
OH O OH
O O
O
OH O
61-80%
OBn O
Ph O O
O NHAc
OBn
OBn BnO
O
O OH O O
OBn BnO
OBn O
O
NHAc
OBn N3
21 R4 = OH 22 R4 = α(1-2)-L-perbenzylated Fucosyl
O
NHAc
OH NH2
OH HO 1 R1 = H 2 R 1 = α(1-2)-L-Fucose
Scheme 6. Synthesis of Lex dimer and KH-1 epitopes.
Supplementary data Supplementary data associated with (full characterization of all new compounds (1–2, 6, 19 and 20) and copies of NMR spectra) this article can be found, in the online version, at doi:10.1016/ j.tetlet.2010.11.055. References and notes 1. Nudelman, E.; Levery, S. B.; Kaizu, T.; Hakomori, S. J. Biol. Chem. 1986, 261, 1247–1253. 2. Zhang, S. L.; CordonCardo, C.; Zhang, H. S.; Reuter, V. E.; Adluri, S.; Hamilton, W. B.; Lloyd, K. O.; Livingston, P. O. Int. J. Cancer 1997, 73, 42–49. 3. Sato, S.; Ito, Y.; Ogawa, T. Tetrahedron Lett. 1988, 29, 5267–5270. 4. Nicolaou, K. C.; Caulfield, T. J.; Kataoka, H.; Stylianides, N. A. J. Am. Chem. Soc. 1990, 112, 3693–3695. 5. Toepfer, A.; Kinzy, W.; Schmidt, R. R. Liebigs Ann. Chem. 1994, 449–464. 6. Bregant, S.; Zhang, Y. M.; Mallet, J. M.; Brodzki, A.; Sinay, P. Glycoconjugate J. 1999, 16, 757–765. 7. Zhu, T.; Boons, G. J. J. Am. Chem. Soc. 2000, 122, 10222–10223. 8. Tanaka, H.; Matoba, N.; Tsukamoto, H.; Takimoto, H.; Yamada, H.; Takahashi, T. Synlett 2005, 824–828. 9. Miermont, A.; Zeng, Y. L.; Jing, Y. Q.; Ye, X. S.; Huang, X. F. J. Org. Chem. 2007, 72, 8958–8961.
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