Download PDF
Synlett 2002(9): 1409-1416
DOI: 10.1055/s-2002-33605
LETTER
© Georg Thieme Verlag Stuttgart · New York

Solid-phase Synthesis of Oligosaccharides Using Novel Alkyne-type Linkers: Selection of Reactive Sites on the Support by Sonogashira Reaction

Minoru Izumi, Koichi Fukase*, Shoichi Kusumoto
Department of Chemistry, Graduate School of Science, Osaka University 1-1 Machikaneyama, Toyonaka, Osaka 560-0043
e-Mail: koichi@chem.sci.osaka-u.ac.jp;
Further Information

Publication History

Received 6 June 2002
Publication Date:
17 September 2002 (online)

    Permissions and Reprints All articles of this category

Abstract

Two new alkyne-type linkers having alkynylmethyloxy moieties were elaborated for solid-phase synthesis of oligosaccharides. A propargyl glycoside-type linker between a sugar residue and a solid support was formed by the Sonogashira reaction of a propargyl glycoside with polymer-supported iodobenzene. A pro­pargyl ester-type linker was also constructed by the same reaction of a 4-(proparygyloxycarbonyl)benzyl glycoside with the latter. Both linkers are stable against acids such as TFA but can be readily cleaved with this acid after conversion to the corresponding alkyne-cobalt complex by treatment with Co2(CO)8. The latter ester linker is generally advantageous in that mild cleavage liberates a product as its carboxybenzyl glycoside which is readily purified. The Sonogashira reaction was found to proceed only at spatially reactive sites on the solid support where the reagent accesses readily, so that the subsequent reactions including glycosylation on solid phase proceeded smoothly to result in high total yields of the desired oligosaccharides.

Key words

oligosaccharides - solid-phase synthesis - carbohydrates - glycosylations - cross-coupling

17

Commercially available from Mimotopes Pty. Ltd. (http://www.mimotopes.com). Solid-phase oligosaccharide synthesis on SynPhase Crown see ref. [3b] and ref. [7]

18

3: Mp: 98 °C; [α]D 22 = +13 (c 1.10, CHCl3); ESI-Mass (positive) m/z 509.3 [(M + Na)+]; 1H NMR (CDCl3) δ = 7.48-7.24 (15 H, m, PhCH × 3), 5.54 (1 H, s, PhCH), 5.05 (1 H, d, J = 3.0 Hz, H-1), 4.93-4.73 (4 H, m, PhCH2 × 2), 4.51 (1 H, t, J = 9.0 Hz, H-3), 4.30 (2 H, d, J = 3.0 Hz, OCH2-CCH), 4.26 (1 H, dd, J = 10.4, 5.2 Hz, H-6a), 3.88-3.86 (1 H, m, H-5), 3.75-3.72 (2 H, m, H-2 and H-4), 3.62 (1 H, d, J = 5.2 Hz, H-6b), 2.47 (1 H, t, J = 3.0 Hz, OCH2-CCH). Found: C, 73.79; H, 6.11%. Calcd for C30H30O6: C, 74.06; H, 6.21%.

19

5: Mp: 162 °C; [α]D 22 = +37 (c 1.00, CHCl3); ESI-Mass (positive) m/z 629.3 [(M + Na)+]; 1H NMR (CDCl3) δ = 8.00 (2 H, m, CC6H4CO2Me), 7.50-7.21 (17 H, m, PhCH × 3 + CC6H4CO2Me), 5.56 (1 H, s, PhCH), 5.10 (1 H, d, J = 3.6 Hz, H-1), 4.93-4.73 (4 H, m, PhCH2 × 2), 4.54 (2 , d, J = 3.0 Hz, OCH2-CCH), 4.26 (1 H, dd, J = 10.3, 4.9 Hz, H-6a), 4.09 (1 H, t, J = 9.1 Hz, H-3), 3.95-3.92 (1 H, m, H-5), 3.92 (3 H, s, CC6H4CO2Me), 3.71 (1 H, d, J = 10.3 Hz, H-6b), 3.65-3.61 (2 H, m, H-2 and H-4). Found: C, 72.92; H, 5.75%. Calcd for C38H36O8·1/2H2O: C, 72.48; H, 5.92%.

20

6: ESI-Mass (negative) m/z 605.2 [(M - H)-]; 1H NMR (CDCl3) δ = 8.00 (2 H, m, CC6H4CO2H), 7.50-7.21 (17 H, m, PhCH × 3 + CC6H4CO2H), 5.56 (1 H, s, PhCH), 5.10 (1 H, d, J = 3.6 Hz, H-1), 4.93-4.73 (4 H, m, PhCH2 × 2), 4.54 (2 H, d, J = 3.0 Hz, OCH2-CCH), 4.26 (1 H, dd, J = 10.3, 4.9 Hz, H-6a), 4.09 (1 H, t, J = 9.1 Hz, H-3), 3.95-3.92 (1 H, m, H-5), 3.71 (1 H, d, J = 10.3 Hz, H-6b), 3.65-3.61 (2 H, m, H-2 and H-4). Found: C, 72.24; H, 5.78%. Calcd for C37H34O8·1/2H2O: C, 72.18; H, 5.73%. A typical procedure for introduction of a monosaccharide 6 on solid support. ArgoPore resin (NH2-LL: 0.28 mmol/g) (100mg, 28.0 µmol) was placed in a polypropylene tube (Varian) fitted with a filter, and washed with 5% diisopropylamine in CH2Cl2 and then CH2Cl2. Compound 6 (38.9 mg, 56.0 µmol), HOBt (18.9 mg, 140 µmol), CH2Cl2 (3.0 mL), and DIC (8.8 µL, 56.0 µmol) were added to the tube, successively. The reaction mixture was shaken for 3 d with Rotator RT-50 (Taitech) and filtered. The resin was washed with CH2Cl2 and the residual amino groups on the resin were then capped with acetic anhydride (1.0 mL) and triethylamine (1.0 mL) in CH2Cl2 (2.0 mL) by shaking for 30 min. The resin was washed successively with DMF, MeOH, and CH2Cl2.

21

A typical procedure for introduction of 4-iodobenzoic acid 8 on solid support. SynPhaseTM resin (NH2-HL: 35.0 µmol) was placed in a polypropylene tube (Varian) fitted with a filter, and washed with 5% diisopropylamine in CH2Cl2 and then CH2Cl2. Compound 8 (17.4 mg, 70.0 µmol), HOBt (23.6 mg, 175 µmol), CH2Cl2 (3.0 mL), and DIC (11.0 µL, 70.0 µmol) were added to the tube, successively. The reaction mixture was shaken for 3 d with Rotator RT-50 (Taitech) and filtered. The resin was washed with CH2Cl2 and the residual amino groups on the resin were then capped with acetic anhydride (1.0 mL) and triethylamine (1.0 mL) in CH2Cl2 (2.0 mL) by shaking for 30 min. The resin was washed successively with DMF, MeOH, and CH2Cl2.

22

A typical procedure for Sonogashira coupling of monosaccharide 3 on solid support. SynPhaseTM resin 9 (NH2: 35.0 µmol) was placed in a polypropylene tube (Varian) fitted with a filter, and washed with THF. CuI (2.6 mg, 14.0 µmol), Pd(PPh3)4 (8.1 mg, 7.0 µmol), THF (2.5 mL), TEA (2.5 mL) and 3 (34.1 mg, 70.0 µmol) were added to the tube, successively. The reaction mixture was shaken for 24 h with Rotator RT-50 (Taitech) and filtered. The resin was washed with DMF, MeOH and CH2Cl2 to give 7.

23

A typical cleavage reaction of alkynylmethyloxy linker: The ArgoPoreTM resin 7 (100 mg of ArgoPoreTM resin) was shaken with a mixture of Co2(CO)8 (14.4 mg, 42.0 µmol) in CH2Cl2 (3.0 mL) at room temperature for 1 h. After the reaction mixture was filtered, the resin was washed with DMF and CH2Cl2 (3.0 mL). The resin was shaken with TFA (0.5 mL) in CH2Cl2 (4.0 mL) and water (0.5 mL) at room temperature for 12 h and then filtered. The resin was then washed with ethyl acetate. The organic layer was combined, washed with saturated NaHCO3 solution and brine, dried over MgSO4, and concentrated in vacuo. The residue was purified with preparative silica gel TLC (CHCl3-MeOH = 5:1) to give colorless solid 10. Yield 5.1 mg (75%). ESI-Mass (positive) m/z 383.1 [(M + Na)+]; 1H NMR (CDCl3) δ = 7.35-7.24 (10 H, m, PhCH × 2), 5.24 (1 H, d, J = 3.63 Hz, H-1), 4.93-4.63 (4 H, m, PhCH2 × 2), 4.26 (1 H, dd, J = 10.4, 5.2 Hz, H-6a), 3.84-3.73 (2 H, m, H-6b), 3.71-3.62 (1 H, m, H-5), 3.57-3.52 (2 H, m, H-2 and H-4), 2.19 (2 H, d, J = 8.3 Hz, OH × 2).

25

The typical procedure for glycosylation on solid-support: The monosaccharide resin 11 (62% loading) (100 mg of ArgoPoreTM resin) was washed with dry CH2Cl2 (3 mL). To the resin were added Molecular Sieves 4A beads, 8-12 mesh (200 mg), a solution of a glycosyl trichloroacetimidate 12 (38.9 mg, 56.0 µmol) in dry CH2Cl2 (3.0 mL), and TMSOTf (8.8 µL, 56.0 µmol), successively. The reaction mixture was shaken with Rotator RT-50 (Taitech) at room temperature for 3 h. The solution was removed by filtration and the resin was washed with CH2Cl2 and ether. After Molecular Sieves 4Å beads were removed by picking with forceps, the resins were washed with DMF and CH2Cl2.

26

14: ESI-Mass (positive) m/z 905.4 [(M + Na)+]; 1H NMR (CDCl3) δ = 7.34-7.21 (30 H, m, PhCH × 6), 5.01 (1/2 H, d, J = 3.2 Hz, H-1α), 4.93-4.43 (14 H, m, PhCH2 × 6, H-1′α, H-1′β, H-1β), 3.84-3.73 (4 H, m, H-2, H-3, H-3′, and H-4′), 3.76-3.62 (4 H, m, H-4, H-5, H-2′, and H-5′), 3.57-3.37 (4 H, m, H-6, and H-6′), 2.50 (2 H, s, OH × 2).

28

17: ESI-Mass (positive) m/z 541.1 [(M + Na)+]; 1H NMR (CDCl3) δ = 7.48-7.24 (15 H, m, PhCO × 2 and PhCH2), 5.94-5.88 (1 H, m, OCH2CH=CH2), 5.75 (1 H, d, J = 9.6 Hz, H-2), 5.37-5.26 (2 H, m, OCH2CH=CH2), 5.24 (1 H, t, J = 9.6 Hz, H-3), 5.05 (1 H, d, J = 3.6 Hz, H-1), 4.93-4.73 (4 H, m, PhCH2 and OCH2CH=CH2), 4.26 (1 H, dd, J = 10.4, 5.2 Hz, H-6a), 3.88-3.86 (1 H, m, H-5), 3.75-3.72 (1 H, m, H-4), 3.62 (1 H, d, J = 5.2 Hz, H-6b).

29

18: ESI-Mass (positive) m/z 763.2 [(M + Na)+]; 1H NMR (CDCl3) δ = 8.00-7.24 [24 H, m, PhCO × 2, PhCH2, and C13H9-CH2-OCO(Fmoc)], 5.94-5.88 (1 H, m, OCH2CH=CH2), 5.75 (1 H, d, J = 9.6 Hz, H-2), 5.56 (1 H, dd, J = 9.6, 7.9 Hz, H-4), 5.37-5.26 (2 H, m, OCH2CH=CH2), 5.24 (1 H, t, J = 9.6 Hz, H-3), 5.05 (1 H, d, J = 3.6 Hz, H-1), 4.93-4.73 (4 H, m, PhCH2 and OCH2CH=CH2), 4.26 (1 H, dd, J = 10.4, 5.2 Hz, H-6a), 3.94 [1 H, d, J = 10.3 Hz, C13H9-CH2-OCO(Fmoc)], 3.88-3.86 (1 H, m, H-5), 3.75-3.72 (1 H, m, H-4), 3.62 (1 H, d, J = 5.2 Hz, H-6b).

30

20: Mp: 144 °C; [α]D 24 = +134 (c 1.00, CHCl3); ESI-Mass (positive) m/z 895.2 [(M + Na)+]; 1H NMR (CDCl3) δ = 8.01 (2 H, m, OCH2C6H4CO2CH2-CCH), 7.48-7.25 (17 H, m, PhCH2 × 3, and OCH2C6H4CO2CH2-CCH), 4.71 (1 H, d, J = 8.6 Hz, H-1), 4.88-4.45 (8 H, m, PhCH2 × 3 and OCH2C6H4CO2H), 4.51 (1 H, t, J = 9.1 Hz, H-3), 4.26 (1 H, dd, J = 10.4, 5.2 Hz, H-6a), 3.91 (2 H, d, J = 3.0 Hz, OCH2C6H4CO2CH2-CCH), 3.88-3.86 (1 H, m, H-5), 3.72 (1 H, d, J = 10.3 Hz, H-6b), 3.65-3.57 (2 H, m, H-2 and H-4), 2.47 (1 H, t, J = 3.0 Hz, OCH2C6H4CO2CH2-CCH).

31

A typical procedure for solid-phase glycosylation using a glycosyl trichloroacetimidate: The 4-O-Fmoc resin 21 (21% loading) (SynPhaseTM-NH2; 7.7 µmol) was washed with CH2Cl2 (3.0 mL). To the resin was added 25% piperidine in CH2Cl2 (3.0 mL). The reaction mixture was shaken with Rotator RT-50 (Taitech) at room temperature for 30 min. The solution was removed by filtration and the resin was washed with CH2Cl2, DMF and MeOH. The resin was then washed with 5% TMSOTf in dry CH2Cl2 and then dry CH2Cl2 (3 mL). Trichloroacetimidate 19 (19.5 mg, 23.1 µmol), dry CH2Cl2 (3.0 mL), and TMSOTf (0.3 µL, 1.5 µmol) were added. The reaction mixture was shaken with Rotator RT-50 (Taitech) at room temperature for 30 min to give resin-linked disaccharide 32.
Typical procedure of cleavage from solid support by alkali. SynPhase resin linked with disaccharide via alkynyl ester linker was shaken with a mixture of 28% CH3ONa in MeOH (1.0 mL), MeOH (1.0 mL) and CH2Cl2 (2.0 mL) at room temperature for 12 h. After the reaction mixture was filtered, EtOAc and 0.1 N aqueous HCl were added to the filtrate. The organic layer was combined, washed with saturated NaHCO3 solution and brine, dried over MgSO4, and concentrated in vacuo. The residue was purified with preparative silica gel TLC (CHCl3-MeOH = 5:1) to give the desired compound.
34: Yield 7.2 mg (quant.). ESI-Mass (positive) m/z 945.5 [(M + Na)+]; 1H NMR (CDCl3) δ = 7.84-7.21 (19 H, m, PhCH2 × 3 and OCH2C6H4CO2Me), 4.83-4.43 (10 H, m, PhCH2 × 3, OCH2C6H4CO2Me, H-1β, H-1′β, and H-1′′β), 3.93 (3 H, s, OCH2C6H4CO2Me), 3.84-3.60 (12H, m, H-2, H-3, H-4, H-5, H-2′, H-3′, H-4′, H-5′, H-2′′, H-3′′, H-4′′ and H-5′), 3.57-3.37 (4 H, m, H-6, H-6′, and H-6′′), 2.50 (4 H, s, OH × 7).