EXPERIMENTAL
1. General procedures.
All reactions were performed in flame-dried modified Schlenk (Kjeldahl shape) flasks fitted with a glass stopped or rubber septa under a positive pressure of Argon. Air and moisture-sensitive liquids and solutions were transferred via syringe. Organic solutions were dried on MgSO4 and concentrate by a rotary evaporator below 40°C al ca. 25 Torr. Flash chromatography was performed employing 230-400 mesh silica gel. Analytical TLC was performed on Alugram SIL G/UV254 silica gel sheets ( Macherey_Nagel) with detection by 0.5% phosphomolybdic acid solution in 95% EtOH.
2. Materials.
Tri-O-acetyl-D-glucal, lipase from Candida Rugosa type VII CRL, pyridinium p-toluen sulfonate (PPTS), MeONa, PMBCl, Ph3PMeI, potassium hexamethyldisilazide (KHMDS), 1,3-dichlorobenzene, NaBH4, BnBr, NaH 60%, 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), PivCl, DMAP, MsCl, NaN3, PS-Ph3, TsCl, t-BuOK, AcONa, MCPBA 70%, Cu(OTf)2, TMSOTf, 10% Pd-C, MeONa, Ac2O were purchased from Aldrich and used without purification. 2-Iodoxybenzoic acid (IBX) was synthesized according to the literature methods. Deionized water. (iPr)2O, AcOH, MeOH, EtOH and Et2O were purchased from Aldrich and used without purification. 3,4-dihydro-2H-pyran (DHP) was purchased from Fluka and AW 300 molecular. Anhydrous CH2Cl2 over molecular sieves, anhydrous CH3CN over molecular sieves, anhydrous pyridine over molecular sieves, and anhydrous acetone were purchased from Aldrich and used without purification, anhydrous N,N- dimethylformamide (DMF) over molecular sieves purchased from Aldrich. Tetrahydrofuran (THF) was distilled from Na/benzophenone. Toluene and Et2O were distilled from sodium/benzophenone.
3. Instrumentation.
Infrared (IR) spectra were obtained using Cary 600 Series FTIR spectrometer. Data are presented as frequency absorption (cm-1). Proton and carbon-13 nuclear magnetic resonance (1H NMR and 13C NMR) spectra were recorded at 250 and 62.5 MHz, respectively using a Bruker Advance 250 MHz spectrometer; chemical shifts are expressed in parts per million (δ scale) and refer to residual protium in the NMR solvent [CDCl3: δ 7.26; CD3CN: δ 1.94, CD3OD: δ 3.31]. Data are presented as follows: chemical shift, multiplicity (s=singlet, d=doublet, t=triplet, m=multiplet and/or multiple resonances), integration, coupling costant in Hertz (Hz).
3,4-Di-O-acetyl-D-glucal (+)-2.12
A phospate buffer (NaH2PO4∙H2O/Na2HPO4, pH 7.0, 60 mL) was added to a solution of tri-O-acetyl-D-glucal (+)-2.11 (10.0 g, 36.73 mmol)22-23 in (i-Pr)2O (15.0 mL), and anhydrous acetone (5.0 mL). The mixture was treated with lipase CRL (lipase from Candida Rugosa type VII activity >700 unit/mg) (1.7 g) and anhydrous acetone (10 mL) was added. The reaction mixture was stirred for 12 h at room temperature.
Then, the reaction mixture was concentrated by rotary evaporator and the remaining solution was filtered on a pad of Celite® and extracted with AcOEt. The evaporation of the washed (brine) and dried (MgSO4) organic extracts afforded a crude reaction product (7.75 g, 36.73 mmol, 91.7% yield), which was subjected to a flash chromatography. Elution with a 6:4 hexane/AcOEt mixture afforded a viscous liquid consisting of a pure alcohol (+)-2.12 (4.667 g, 20.29 mmol, 55% yield).
(+)-2.12: Rf = 0.26 (1:1 hexane/AcOEt);
1H NMR (CDCl3) δ 6.49 (dd, 1HH1, J= 6.1, 1.2 Hz), 5.48-5.40 (m, 1HH3), 5.23 ( dd, 1HH2, J=9.0, 6.5 Hz), 4.79 (dd, 1HH4, J=5.9, 2.9 Hz), 4.06-3.95 (m, 1HH5), 3.83-3.65 (m, 2HH6-6’), 2.13 (s,3HAc), 2.07 (s, 3HAc);
13C NMR (CDCl3) δ 170.8, 170.6, 145.9, 99.1, 76.7, 68.4, 67.9, 60.0, 21.2, 20.9. Anal.
Calcd for C10H14O6: C, 52.17; H,6.13. Found: C, 52.23; H, 6.41.
6-O-(2-Tetrahydropyranyl)-3,4-di-O-acetyl-D-glucal 2.13
A solution of PPTS (0.153 g, 0.608 mmol, 0.02 equiv) in anhydrous CH2Cl2 (200.0 mL) was added dropwise at room temperature to a stirred solution of alcohol (+)-2.12 (6.922 g, 30.4 mmol) in DHP (4.10 mL, 45.6 mmol, 1.5 equiv) and the reaction mixture was stirred at the same temperature for 16 h. Dilution with CH2Cl2 and evaporation of the washed (saturated aqueous NaHCO3 and saturated aqueous NaCl) organic solution afforded a crude reaction product (9.27 g, 29.52 mmol, 97% yield), a liquid consisting of 6-OTHP protected diacetate 2.13, as a mixture of diasteroisomers, which was used in the next step without any purification.
2.13: Rf =0.48 (6:4 hexane/AcOEt);
1H NMR (CDCl3) δ 6.48 (dt, 1H, J= 6.0, 1.3 Hz), 5.17-5.38 (m, 2H), 4.75-4.85 (m, 1H), 4.53-4.70 (m, 1H), 4.17-4.30 (m, 1H), 3.69-4.00 (m, 2H), 3.40-3.68 (m, 2H), 2.06 and 2.07 (two singlets corresponding to two diasteroisomers, 3H), 2.03 and 2.04 (two singlets corresponding to two diasteroisomers, 3H), 1.43-1.92 (m, 6H);
13C NMR (CDCl3) δ 170.4, 169.5, 145.8, 99.3, 99.2, 98.6, 98.4, 75.3, 75.1, 74.9, 74.7, 67.7, 67.4, 65.3, 64.8, 62.1, 61.7, 30.3, 25.3, 21.0, 20.8, 19.2, 19.0. Anal. Calcd for.
C15H22O7: C, 57.32; H,7.05. Found: C, 57.38; H, 7.23;
FTIR (neat film) ν 1743, 1471, 1238, 1033 cm-1.
6-O-(2-Tetrahydropyranyl)-D-glucal 2.14
A solution of diacetate 2.13 (9.27 g, 29.51 mmol, 1.0 equiv) in MeOH (244.0 mL) was treated with MeONa (0.398 g, 7.38 mmol, 0.25 equival) and the reaction mixture was stirred for 12 h at room temperature. Dilution with MeOH and evaporation of the filtered organic solution afforded a crude reaction product, which was subjected to a flash chromatography. Elution with an 2:8 hexane/AcOEt mixture afforded a pale yellow liquid consisting of trans diol 2.14 (4.125 g, 17.93 mmol, 61% yield).
2.14: Rf = 0.30 (2:8 hexane/AcOEt);
1H NMR (CDCl3) δ 6.27 (dt, 1H, J= 6.0, 1.9 Hz), 4.65 (dt, 1H, J= 6.0, 1.5 Hz), 4.45-4.62 (m, 1H), 3.37-4.31 (m, 9H), 1.38-1.84 (m, 6H). 1H NMR (CD3CN) δ 6.29 (d, 1H, J= 6.0 Hz), 4.65 (dd, 1H, J= 6.0, 1.6 Hz), 4.54-4.60 (m, 1H), 4.13-4.38 (m, 9H), 1.41-1.80 (m, 6H);
13C NMR (CDCl3) δ 144.3, 144.2, 103.2, 102.8, 100.8, 100.7, 99.4, 77.5, 77.1, 76.6, 69.6, 69.5, 69.4, 66.7, 66.4, 64.4, 62.6, 31.1, 30.8, 30.4, 25.3, 25.1, 21.3, 20.6, 19.5. 13C NMR (CD3CN) δ 144.4, 144.3, 104.7, 104.6, 103.7, 103.5, 102.4, 100.1, 78.7, 78.6, 78.5, 78.0, 75.2, 69.5, 68.6, 67.3, 66.8, 65.6, 65.4, 63.4, 62.8, 31.9, 31.8, 31.4, 31.2, 26.1, 26.0, 20.6, 20.3. Anal. Calcd for C11H18O5: C, 57.38; H, 7.88. Found: C, 56.99; H, 7.95.
FTIR (neat film) ν 3398, 1647, 1350, 1232, 1126, 1080, 1026 cm-1.
3,4-Di-O-(p-methoxybenzyl)-6-O-(2-tetrahydropyranyl)-D-glucal 2.15
A solution of trans diol 2.14 (4.325 g, 18.80 mmol) in anhydrous DMF (40 mL) was added dropwise at 0°C to a suspension of 60%
NaH in mineral oil (2.256 g, 94.04 mmol, 5.0 quiv) in anhydrous DMF (40 mL). After stirring at 0°C for 15 minutes and then at room temperature for 30 minutes, the suspension was cooled at 0°C and p-methoxybenzylchloride (PMBCl) (6.38 mL, 47.02 mmol, 2.5 equiv.) was added dropwise. The reaction mixture was allowed to warm at room temperature and stirred for further 12 h. Dilution with Et2O and evaporation of the washed (brine) and dried (MgSO4) organic solution afforded a crude reaction product (9.145 g), which was subjected to a flash chromatography.
Elution with an 7:3 hexane/AcOEt mixture afforded the 3,4-di-O-para-methoxybenzyl (PMB)-derivative 2.15 (7.841 g, 89% yield), pure as a yellow oil.
2.15: Rf = 0.36 (7:3 hexane/AcOEt);
1H NMR (250 MHz, CDCl3) δ 7.17-7.36 (m, 4H), 6.78-6.97 (m, 4H), 6.40 (dd, 1H, J= 6.2, 3.1 and 1.3 Hz), 4.84 (ddd, 1H, J= 6.2, 2.7, 0.9 Hz), 4.55-4.82 (m, 2H), 4.77 (d, 1H, J= 10.8 Hz), 4.68 (d, 1H, J= 10.8 Hz), 4.49 (dd, 1H, J= 11.3 and 1.9 Hz), 4.13-4.22 (m, 1H), 3.95- 4.12 (m, 2H), 3.65-3.93 (m, 3H), 3.80 (s, 6H), 3.42-3.55 (m, 1H), 1.41-1.92 (m, 6H);
13C NMR (62.5 MHz, CDCl3) (2 diasteroisomers) δ 159.4, 144.8, 130.6, 129.7, 129.6, 113.9, 100.2, 100.0, 99.4, 99.2, 75.8, 75.6, 74.3, 73.6, 73.5, 70.4, 62.5, 62.2, 55.5, 30.7, 25.6, 19.7, 19.5. Anal. Calcd for C27H34O7: C, 68.92; H, 7.29. Found; C, 69.24; H, 7.55.
3,4-Di-O-(p-methoxybenzyl)-D-glucal (-)-2.16
3,4-Di-O-(p-methoxybenzyl)-derivative 2.15 (2.604 g, 6.40 mmol) was dissolved in a 1.5:2:1 AcOH/THF/H2O mixture (70 mL)27, the reaction mixture was heated at 45°C and stirred at the same temperature for 12 h. After dilution with Et2O and neutralization with solid NaHCO3 (60.0 g), evaporation of the washed (satured aqueous NaHCO3 and saturated aqueous NaCl) and dried organic solution afforded a crude solid product (2.20 g), which was subjected to a flash chromatography.
Elution with an 7:3 hexane/AcOEt mixture, afforded the primary alcohol (-)-2.16 (1.20 g, 3.11 mmol, 57%), pure as a yellow solid, m.p. 67-69°C.
(-)-2.16: Rf= 0.20 (7:3 hexane/AcOEt);
1H NMR (250 MHz, CDCl3), δ 7.21-7.32 (m, 4H), 6.84-6.92 (m, 4H), 6.39 (dd, 1HH1, J=6.2, 1.2 Hz), 4.87 (dd, 1HH2, J= 6.2, 2.7 Hz), 4.78 (d, 1H, J=11.1 Hz), 4.64 (d, 1H, J= 11.1 Hz), 4.60 (d, 1H, J= 11.1 Hz), 4.50 (d, 1H, J=11.1 Hz), 4.16-4.22 (m, 1H), 3.87-3.96 (m, 1H), 3.82-3.86 (m, 2H), 3.81 (s, 3H), 3.80 (s, 3H), 3.76 (dd, 1H, J= 8.4, 6.5 Hz);
13C NMR (62.5 MHz, CDCl3) δ 159.5, 159.4, 144.6, 130.3, 130.2, 129.9, 129.6, 114.0, 100.4, 77.4, 75.3, 74.3, 73.5, 70.5, 62.0, 55.4. Anal. Calcd for C22H26O6: C, 68.38; H, 6.78.
Found: C, 68.82; H, 6.53;
FTIR ν 3307.2, 1613.3, 1514.2, 1247.9, 1020.2, 812.4 cm-1. [α]20D -21.7 (c 0.6, CHCl3).
2-Formyl-3,4-di-(p-methoxybenzyloxy)-3,4-dihydro-2H-pyrane 2.17
IBX28 (3.28 g, 11.64 mmol, 3.0 equiv)was added to a solution of primary alcohol (-)-2.16 (1.50 g, 3.90 mmol) in anhydrous CH3CN (90 mL) and the reaction mixture was stirred at 45°C overnight. After cooling, the reaction mixture was filtered on a pad of Celite® that was
further eluted with AcOEt. Evaporation of the filtered solution afforded aldehyde 2.17 (1.50 g, > 99% yield), pure as a liquid, which was used in the next step without any purification.
2.17 Rf = 0.30 (7:3 hexane/AcOEt);
1H NMR (250 MHz, CDCl3) δ 9.53 (d, 1H, J=0.6 Hz), 7.20-7.34 (m, 2H), 7.09-7.17 (m, 2H), 6.79-6.93 (m,4H), 6.65 (d, 1HH1, J=6.2 Hz), 5.00-5.09 (m, 1HH2), 4.58 (d, 1HBenzylic, J=11.7 Hz), 4.51-4.59 (m, 1H), 4.29 (s, 2H), 4.01-4.06 (m, 1H), 3.81 (s, 3H-OCH3), 3.79 (s, 3H-OCH3), 3.71-3.78 (m, 1H).
13C NMR (62.5 MHz, CDCl3) δ 198.9, 159.6, 159.5, 145.0, 129.7, 129.6, 129.4, 114.0, 100.5, 79.4, 72.2, 71.6, 69.4, 66.9, 55.5. Anal. Calcd for C22H24O6: C, 68.74; H, 6.29.
Found: C, 69.02; H, 6.11.
1,5-Anhydro-di-O-(p-methoxybenzyl)-2,6,7-trideoxy-D-arabino-hept-1,6-dienitol (+)- 2.18
A solution 0.5 M of KHMDS in THF (11.18 mL, 5.59 mmol, 1.4 equiv) was added dropwise to a solution of Ph3PMe+I- (2.36 g, 5.83 mmol, 1.5 equiv) in anhydrous THF (20 mL) at -78°C, and the mixture was stirred at the same temperature for 30 min and at 0°C for 1 h. After cooling at -78°C, a solution of aldehyde 2.17 (1.50 g, 3.50 mmol) in anhydrous THF (19 mL) was added dropwise, and the reaction mixture was stirred at r.t. for 4 h. Dilution with Et2Oand filtration on Celite® pad afforded an organic solution which was washed (saturated aqueous NH4Cl, saturated aqueous NaHCO3, and saturated aqueous NaCl) and dried. Evaporation of the organic solution afforded a crude product which was filtered again on Fluorisil®-silica gel pad using hexane/AcOEt mixture as eluent at three different concentrations: 7:3, 1:1 and 3:7. Evaporation of the filtered solution of the first mixture afforded olefin (+)-2.18, practically pure as a solid (0.930 g). Evaporation of the filtered solution of the second mixture afforded a crude product (0.320 g) which was subjected to flash chromatography. Elution with 8:2 hexane/AcOEt mixture of the second mixture afforded olefin (+)-2.18, pure as a solid (0.070 g, 76% global yield)
(+)-2.18. Rf =0.43 (7:3 hexane/ACOEt);
1H NMR (250 MHz, CDCl3) δ 7.17-7.37 (m, 4H), 6.79-6.97 (m, 4H), 6.41 (d, 1H, J=6.2 Hz), 6.03 (ddd, 1H, J=17.2, 10.5 and 6.5 Hz), 4.70 (d, 1H, J=10.7 Hz), 4.60 (d, 1H, J=10.7), 4.57 (d, H, J=11.3 Hz), 4.51 (d, 1H, J=11.3 Hz), 4.29 (t, 1H, J=7.7 Hz), 4.12-4.20 (m, 1H), 3.80 (s, 6H9, 3.56 (dd, 1H, J=8.5 and 6.2 Hz);
13C NMR (62.5 MHz, CDCl3) δ 159.5, 159.4, 144.6, 134.6, 130.7, 130.4, 129.8, 129.5, 118.4, 113.9, 100.7, 78.2, 78.1, 75.3, 73.6, 70.6, 55.4 Anal. Calcd for C23H26O5: C, 72.23; H, 6.85. Found: C, 72.82; H, 6.73.
[α]20D = +1.1 (c 0.10, CHCl3).
3,4-di-O-(p-methoxybenzyl)-5a-carba-D-glucal (-)-2.20.
Olefin (+)-2.18 (1.40 g, 3.69 mmol) was dissolved in 1,3- dichlorobenzene (6.0 mL) and the reaction mixture was stirred for 2 h at 240°C. . The obtained aldehyde 2.19 was not isolated but directly reduced with NaBH4 (0.209 g, 5.53 mmol, 1.5 equiv) in a 2:1 THF/EtOH mixture (7.0 mL) to primary carba alcohol (-)-2.20, which was subjected to flash chromatography. Elution with 7:3 hexane/ACOEt mixture afforded primary alcohol (-)-2.20 (0.725 g, 54%).
(-)-2.20: Rf = 0.28 (1:1 hexane/AcOEt);
1H NMR (250 MHz, CDCl3) δ 7.19-7.39 (m, 4H), 6.80-6.95 (m, 4H), 5.62-5.81 (m, 2H), 4.91 (d, 1H, J= 11.0 Hz), 4.67 (d, 1H, J= 11.0 Hz), 4.66 (d, 1H, J= 11.2 Hz), 4.58 (d, 1H, J=
11.2 Hz), 4.15-4.25 (m, 1H), 3.81 (s, 3H), 3.80 (s, 3H), 3.49-3.67 (m, 3H), 1.57-2.22 (m, 3H);
13C NMR (62.5 MHz, CDCl3) δ 159.5, 159.4, 130.6, 130.1, 129.7, 128.9, 128.2, 127.0, 126.2, 114.1, 114.0, 82.1, 81.1, 74.1, 71.2, 66.0, 55.4, 40.7, 28.2. Anal. Calcd for C23H28O5: C, 71.85; H 7.34. Found: C,72.02; H, 7.43;
[α]20D = – 14.6 (c 0.52, CHCl3).
6-O-Benzyl-3,4-di-O-(p-methoxybenzyl)-5a-carba-D-glucal (+)-2.21.
A solution of primary alcohol (-)-2.20 (0.700 g, 1.82 mmol) in anhydrous DMF (4 mL) was added dropwise at 0°C to a suspension of 60% NaH in mineral oil ( 0.216 g, 5.47 mmol, 3.0 equiv) in anhydrous DMF (4 mL) and the resulting reaction mixture was stirred at the same temperature for 30 min and then at room temperature for 30 min. After cooling at 0°C, BnBr (0.42 mL, 3.64 mmol, 2.0 equiv) was added dropwise, and the mixture was stirred at room temperature overnight. After dilution with Et2O and ice, evaporation of the washed (satured aqueous NaCl) and dried organic layer, afforded a crude reaction mixture (0.911 g), which was subjected to flash chromatography. Elution with an 8:2 hexane/AcOEt mixture afforded monobenzyl-derivate (+)-2.21, pure as liquid (0.600 g, 70% yield).
(+)-2.21 Rf = 0.36 (8:2 hexane/AcOEt);
1H NMR (250 MHz, CDCl3) δ 7.15-7.40 (m, 9H), 6.80-6.92 (m, 4H), 5.61-5.81 (m, 2H) 4.81 (d, 1H, J= 10.5 Hz), 4.62 (s, 2H), 4.55 (d, 1H, J= 10.5 Hz), 4.50 (s, 2H), 4.10.4.21 (m, 1H) 3.81 (s, 3H), 3.53-3.71 (m, 3H), 2.20-2.31 (m, 2H), 1.99-2.15 (m, 1H);
13C NMR (62.5 MHz, CDCl3) δ 159.3, 138.8, 138.4, 132.4, 132.2, 129.8, 129.6, 129.2, 128.9, 128.6, 127.9, 127.8, 127.6, 113.9, 81.0, 79.4, 74.2, 73.2, 71.3, 70.7, 55.5, 39.5, 29.0.
Anal. Calcd for C30H34O5: C, 75.92; H, 7.22. Found. C, 76.04; H, 7.53;
[α]20D =+2.9 (c 0.83, CHCl3).
6-O-Benzyl-5a-carba-D-glucal (+)-2.22.
2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) (0.390 g, 1.71 mmol, 1.5 equiv) was added at room temperature to a solution of benzyl derivate (+)-2.21 (0.540 g, 1.14 mmol, 1.0 equiv) in 18:1 CH2Cl2/H2O mixture (31.05 mL) and the reaction solution was stirred at the same temperature for 3 h. After dilution with CH2Cl2,
evaporation of the washed (saturated aqueous NaHCO3, and satured aqueous NaCl) and dried organic solution, afforded a crude product (0.500 g), which was subjected to flash chromatography. Elution with 1:1 hexane/AcOEt mixture afforded trans diol (+)-2.22, pure as a liquid (0.140 g, 79% yield).
(+)-2.22: Rf = 0.18 (1:1 hexane/AcOEt);
1H NMR (250 MHz, CDCl3) δ 7.19-7.49 (m, 5H), 5.42-5.71 (m, 2H), 4.55 (s, 2H), 4.12- 4.24 (m, 1H), 3.49-3.76 (m, 3H), 1.85-2.24 (m, 3H);
13C NMR (62.5 MHz, CDCl3) δ 137.8, 128.7, 128.5, 128.1, 127.9, 127.0, 77.4, 74.0, 73.7, 73.5, 38.4, 28.4. Anal Calcd for C14H18O3: C, 71.77; H 7.74. Found: C, 72.02; H 7.43.
[α]20D =+40.8 (CHCl3, c 0.13).
6-O-Benzyl-3-O-pivaloyl-5a-carba-D-glucal (-)-2.23
A solution of trans diol (+)-2.22 (0.140 g, 0.6 mmol) in anhydrous CH2Cl2 (6.83 mL) was treated with DMAP (14.66 mg, 0.12 mmol, 0.2 equiv), pyridine (0.386 mL, 4.8 mmol, 8.0 equiv) and dropwise with PivCl (0.147 mL, 1.2 mmol, 2.0 equiv). After stirring 24 h at room temperature, dilution with AcOEt, evaporation of the washed (saturated aqueous NaHCO3 and brine) organic layer afforded a crude reaction product (0.460 g, >99% yield) consisting of the pivaloyl derivative (-)-2.23, pure as a yellow liquid, which was used in the next step without any further purification.
(-)-2.23: Rf = 0.40 (8:2 hexane/AcOEt);
1H NMR (CDCl3) δ 7.27-7.37 (m, 5H), 5.74 (ddd, 1H, J = 10.1, 4.5, 2.1 Hz), 5.41 (unresolved d, 1H, J = 10.1 Hz), 5.25-5.33 (m, 1H), 4.54 (d, 1H, J = 12.0 Hz), 4.48 (d, 1H, J
= 12.0 Hz), 3.79 (dd, 1H, J = 10.3, 7.7 Hz), 3.58-367 (m, 2H), 1.93-2.27 (m, 3H), 1.23 (s, 9H);
13CNMR (CDCl3) δ 179.5, 138.1, 129.3, 128.6, 127.9, 127.8, 125.4, 73.6, 73.5, 72.5, 39.6, 39.1, 28.2, 27.4;
[]20D =-0.76 (c 9.1, CHCl3).
6-O-Benzyl-4-O-mesyl-3-O-pivaloyl-5a-carba-D-glucal (-)-2.24
A solution of pivaloyl derivative (-)-2.23 (0.460 g, 1.45 mmol) in anhydrous pyridine (4.24 mL) was treated with MsCl (0.223 mL, 2.89 mmol, 2.0 equiv) at 0°C and the reaction mixture was stirred at the same temperature for 12 h. Dilution with Et2O and evaporation of the washed (10% aqueous HCl and ice, saturated aqueous NaHCO3 and brine) organic solution afforded a crude reaction product (0.300 g) consisting of O-mesyl derivative (-)-2.24, a yellow oil, which was used in the next step without any further purification.
(-)-2.24: Rf = 0.40 (8:2 hexane/AcOEt);
1HNMR (CDCl3) δ 7.27-7.39 (m, 5H), 5.80-5.91 (m, 1H), 5.50 (dt, 1H, J = 7.0, 2.1 Hz), 5.42 (dt, 1H, J = 9.9, 2.1 Hz), 5.02 (dd, 1H, J = 9.9, 7.2 Hz), 4.58 (d, 1H, J = 11.7 Hz), 4.47 (d, 1H, J = 11.7 Hz), 3.63 (dd, 1H, J = 9.5, 4.8 Hz), 3.54 (dd, 1H, J = 9.5, 2.3 Hz), 2.98 (s, 3H), 2.21-2.41 (m, 3H), 1.22 (s, 9H);
13CNMR (CDCl3) δ 178.4, 138.2, 130.0, 128.6, 128.0, 127.9, 124.1, 80.0, 73.3, 72.6, 38.8, 38.5, 28.1, 27.3;
[]20D =-0.76 (c 9.1, CHCl3).
6-O-Benzyl-3,4-anhydro-5a-carba-D-galactal (-)-2.25
MeONa (0.071 g, 20.52 mmol, 27.0 equiv) was added in three times (10.0 equiv initially, 10.0 equiv after 24 h and 7.0 equiv after 30 h) to a solution of O-mesyl-O-pivaloyl derivative (-)-2.24 (0.300 g, 0.76 mmol) in CH3CN (10.34 mL) at room temperature, and the reaction mixture was stirred for 48 h. Dilution with CH2Cl2 and evaporation of the washed (distilled water and brine) organic solution afforded a crude reaction product consisting of epoxide (-)-2.25 (0.110 g, 85%
yield) practically pure as a pale yellow oil, which was used in the next step without any further purification.
(-)-2.25: Rf = 0.40 (8:2 hexane/AcOEt);
1H NMR (250 MHz, CDCl3) δ 7.28-7.41 (m, 5H), 5.87–6.02 (m, 2H), 4.62 (d, 1HBenzylic, J
= 12.0 Hz), 4.55 (d, 1HBenzylic, J= 12.0 Hz), 3.52–3.70 (m, 3H), 3.28–3.33 (m, 1H), 2.02–
2.27 (m, 2H), 1.70–1.84 (m, 1H).
13C NMR (62.5 MHz, CDCl3) δ 138.4, 132.7, 128.5, 127.7, 123.2, 73.4, 73.0, 56.5, 47.8, 33.7, 24.7. Enantiomeric excess (ee) >99%. Anal. Calcd for C14H16O2: C, 77.75; H, 7.46.
Found: C, 77.86; H, 7.31.
[]20D =−3.9 (c 0.13, CHCl3).
6-O-Benzyl-3-deoxy-3-azido-5a-carba-D-glucal (+)-2.26
A solution of NaN3 (33.10 mg, 0.50 mmol, 1.1. equiv) in H2O ( 1.13 mL) was added to a solution of epoxide (-)-2.25(0.100 g, 0.46 mmol, 1.0 equiv) in distilled THF (1.13 mL) and the reaction mixture was stirred for 20 h at room temperature. After dilution with Et2O, evaporation of washed (brine) organic solution gave the trans azido alcohol (+)-2.26(0.105 g), as a yellow liquid, which was reduced without any purification.
(+)-2.26: Rf =0.54 (8:2 hexane/AcOEt)
1H NMR (CDCl3) δ 7.42-7.28 (m, 5H), 6.12-6.01 (m, 1HH2), 5.75-5.61 (m, 1HH1), 4.56 (d, 1HBenzylic, J=12.0 Hz), 4.51 (d, 1HBenzylic, J=12.0 Hz), 4.08-3.94 (m, 1H), 3.67 (d, 2H, J=4.5 Hz), 3.88-3.78 (m, 1H), 2.39-2.20 (m, 1H), 2.39-2.02 (m, 2H);
13C NMR (CDCl3) δ 137.6, 132.5, 128.7, 128.1, 121.3, 73.8, 72.8, 72.2, 60.1, 34.7, 24.8;
FTIR ν 3410, 2920, 22092, 1259, 1084, 798 cm-1; [α]D20=+172.5 (c= 1.7, CHCl3);
6-O-Benzyl-3-deoxy-3-amino-5a-carba-D-glucal (+)-2.27
Polymer-supported PPh3 (PS-PPh3, 3 mmol/g) (196 mg, 0.587 mmol, 1.17 equiv) was washed with CH2Cl2, Acetone and Methanol, dried at 60°C for 3 h and allowed to swell in THF/H2O 20:1 ( 6.422 mL) for 30 minutes without stirring. A solution of trans azido alcohol (+)-2.26 in
dry THF (1.27 mL) was added dropwise to the above prepared suspension of RS-PPh3 in THF/H2O and the reaction mixture was stirred for 48 h at room temperature. Dilution with AcOEt and evaporation of the filtered (Celite®) organic solution afforded a crude product (0.110 mg), consisting of trans amino alcohol (+)-2.27, as practically pure white crystalline solid, m.p. 96-98°C.
(+)-2.27: Rf =0,06 (9:1 AcOEt/MeOH);
1H NMR (CDCl3) δ 7.40-7.27 (m, 5H), 5.69 (ddt,1H, J=9.9, 3.3, 1.3 Hz), 5.63-5.54 (m, 1H), 4.52 (s, 2H), 3.73 (dd, 1H, J=6.7, 2.2 Hz), 3.66 (dd, 1H, J=6.7, 2.9 Hz), 3.59 (dd, 1H, J=9.2, 5.4 Hz), 3.29-3.22 (m, 1H), 2.15-2.07 (m,2H);
13C NMR (CDCl3) δ 137.9, 129.7, 128.6, 128.0, 127.8, 127.2, 76.1, 73.7, 72.6;
[α]20D = +21.1 (c= 1.2, CHCl3);
6-O-Benzyl-3-deoxy-3-(N-Tosylamino)-5a-carba-D-glucal (+)-2.28
Tosyl chloride (0.043 g, 0.226 mmol, 1.1 equiv) was added in a solution of trans amino alcohol (+)-2.27 (0.048 g, 0.206 mmol, 1.0 equiv) in pyridine (0.442 mL) at room temperature. The reaction mixture was stirred for 24h at the same temperature. Evaporation with Toluene afforded the N-Tosyl derivative as a brown crude residue, constituted by the monotosylated (+)-2.28 and the ditosylate 2.30 in ratio 60:40 (1H NMR). The crude was subjected to flash chromatography with a mixture 3:3:4 of hexane/AcOEt/CH2Cl2 to obtain the monotosylated (+)-2.28 (0.042 g, yield of 53.%) and the ditosylate 2.30 (0.028 g, 35% yield)
(+)-2.28: Rf =0.4 (1:1 hexane/AcOEt);
1H NMR (250 MHz CDCl3) δ 7.84 – 7.67 (m, 2H), 7.43 – 7.17 (m, 7H), 5.80 (m, 1HH2), 5.34 – 5.21 (m, 1HH1), 4.67 (d, J = 7.1 Hz, 1HNH), 4.47 (s, 2HBenzylic), 4.02 (m, 1H H4), 3.65- 3.56 (m, 3HH3-H6-6’), 2.40 (s, 3HTos), 2.14 – 1.88 (m, 3HAlkyl).
13C NMR (CDCl3) δ 131.07, 129.74, 128.49, 127.84, 127.57, 127.12, 123.10, 72.21, 53.43, 33.91, 24.08, 21.52;
FTIR ν 3488.9, 3272.1, 3087.8, 3062.6, 3029.7, 2962.5, 2922.5, 2855.6, 1651.9, 1598.2, 1495.2, 1453.4, 1260.7, 1090.5, 1025.3, 799.7 cm-1;
[α]20D= +61,023 (c=1,31)
6-O-Benzyl-4-O-Mesyl-3-deoxy-3-(N-Tosylamino)-5a-carba-D-glucal 2.29
Mesyl Chloride (0.02 mL, 2 equiv) was added at 0°C in a solution of trans N-Tosyl-amino alcohol (+)-2.28 (0.010 g, 0.026 mmol, 1 equiv) in pyridine (0.10 mL). The reaction mixture was stirred for 24h at room temperature. Evaporation with Toluene afforded the O-Mesyl- N-Tosyl derivative 2.29 as a crude residue with many pyridine salts, which was subjected to flash chromatography with a mixture 3:3:4 of hexane/AcOEt/CH2Cl2 (0.007 g, yield of 58%).
2.29: Rf =0,66 (3:3:4 hesane/AcOEt/CH2Cl2)
1H NMR (250 MHz, CDCl3) δ 7.98-7.92 (m, 2H), 7.34 – 7.02 (m, 7H), 6.6 (d, J = 7.125 Hz, 1HNH), 5.91 (d, J = 10.1 Hz, 1HH2), 5.29 (d, J = 10.1 Hz, 1HH1), 4.96 (bs, 1HH4), 4.49 (s, 2HBenz), 3.87 (bs, 1HH3), 3.46 (m, 2HH6-6’), 2.98 (s, 3HMes), 2.40 (s, 3HTos), 2.13 – 1.74 (m, 3HAlkyl).
13C NMR (CDCl3) δ 145.84, 143.54, 141.52, 138.12, 137.51, 131.15, 129.78, 128.48, 128.24, 128.03, 127.77, 127.27, 127.21, 121.64, 79.11, 73.17, 69.78, 50.82, 37.72, 33.01, 23.56, 21.57.
6-O-Benzyl-3-deoxy-3-(N-Tosylamino)- 4-O-Tosyl-5a-carba-D-glucal (-)-2.30
A solution of trans amino alcohol (+)-2.27 (0.110 g, 0.47 mmol, 1.0 equiv) in anhydrous pyridine (1.0 mL) was treated with an excess of tosyl-chloride (0.224 g, 1.18 mmol, 2.5 equiv). The reaction mixture was stirred for 72 h at room temperature and then coevaporated with toluene. The brown solid crude residue was subjected to flash chromatography with a mixture 9:1 of CH2Cl2/AcOEt. The pure di- N,O-tosyl derivative (-)-2.30 (0.135 g, yield of 53%) is a pale yellow solid, m.p. 136-138°C.
(-)-2.30: Rf =0,4(1:1 Hexane/AcOEt)
1H NMR (CDCl3) δ 7.87-7.20 (m, 4H), 7.41-7.18 (m, 9H), 5.93-5.81 (m, 1HH2), 5.26-5.16 (m, 1HH1), 4.81 (m, 1HH4,), 4.49 (m, 1HNH), 4.14 (s, 2HBenzylic), 3.93 (m, 1HH3), 3.14 (dd, J=
6.72, 9.16 Hz, 1HH6*),2.99 (dd, , J= 7.49, 9.16 Hz, 1H6’*), 2.42-2.35 (2s, 6HTos), 2.29 – 1.76 (m, 3HH5-Alkyl);
13C NMR (CDCl3) δ 145.24, 144.15, 138.48, 137.02, 133.28, 132.40, 130.15, 130.13, 128.65, 128.63, 127.81, 127.73, 127.62, 121.81, 78.77, 73.04, 70.29, 50.28, 33.09, 24.08, 21.94, 21.91;
FTIR ν 3277.9, 3089.3, 3064.0, 3033.4, 2962.7, 2918.9, 2853.9, 2801.9, 1922.4, 1810.5, 1710.3, 1655.1, 1597.9, 1495.4, 1363.0, 1335.0, 1261.8, 1188.7, 1173.6, 1093.6, 1074.9, 1041.3, 915.8 cm-1;
[α]D20
=-9.29 (c=2.78)
(3S*,4R*,5R*)5-(Benzyloxymethyl)-3,4-(N-Tosylazirido)-1-cyclohexene (+)-2.31
A solution of trans N-Tosylamino-O-Tosyl derivative (-)-2.30 (0.066 g, 0.122 mmol, 1 equiv) in CH3CN (1.9 mL) was treated with t-BuOK (0.0274 g, 0.244 mmol, 2 equiv) at room temperature and the reaction mixture was stirred for 1h and 30 minutes at room temperature. After dilution with Et2O, evaporation of the filtered (Celite®) organic solution afforded N-Tosyl aziridine (+)-2.31 (43.8 mg, 97% of yield) practically pure, as a pale yellow liquid.
(+)-2.31: Rf =0,66 (1:1 hexane/AcOEt);
1H NMR (CDCl3) δ 7.86-7.75 (m, 2H), 7.41-7.21 (m, 7H), 5.91-5.69 (m, 2HH1-2), 4.51 (d, J
= 11.64 Hz, 1HBenzylic), 4.44(d, J = 11.64 Hz, 1HBenzylic), 3.34 (dd, J= 9.07, 16.61 Hz, 1HH6*), 3.33-3.25 (m, 2HH3-6’*), 3.17-3.07(m, 1HH4), 2.51-2.4 (m, 1HH5), 2.43 (s, 3HTos), 2.18- 1.81(m, 2HAlkyl);
13C NMR (CDCl3) δ 144.73, 138.43, 135.85, 131.85, 129.97, 128.75, 128.05, 128.03, 127.92, 120.81, 73.49, 70.91, 66.23, 42.98, 36.22, 30.39, 24.01, 21.94;
FTIR ν 3062.0, 3032.6, 2919.4, 2853.0, 2190.8, 1642.4, 1598.0, 1495.3, 1453.81, 1320.9, 1155.6, 1089.6, 973.1, 949.1, 843.1, 813.7, 695.4, 670.4 cm-1;
[α]D20=+74,4 (c=0,51)
3-O-Acetyl-6-O-Benzyl-4-deoxy-4-(N-Tosylamino)-5a-carba-D-glucal 2.32
N-Tosyl aziridine (43.8 mg, 0.1185 mmol, 1 equiv) was dissolved in an aqueous DMF solution of (80%). AcONa (38.9 mg, 0.474 mmol, 4 equiv) was added to the resulting mixture that was stirred for 24 h at room temperature. Dilution with Et2O and evaporation of the washed organic solution (with brine) afforded a crude reaction product (0.044 mg) consisting of a 50:50 mixture of trans 3,4-N-(tosylamino)-acetoxy derivative 2.32 and trans 3,4-N-(tosylamino)-hydroxy derivative 2.33, which was used in the next step without any purification.
2.32: Rf =0.48 (1:1, hexane/AcOEt).
3-O-Acetyl-6-O-Benzyl-4-deoxy-4-(N-Tosylamino)-5a-carba-D-glucal 2.33
MeONa (1.94 mg, 0.036 mmol, 0.35 equiv) was added to a solution of mixture of 2.32 and 2.33 (44.0 mg, 0.102 mmol, 1 equiv) dissolved in MeOH (3.21 mL). The reaction mixture was stirred for 18 h at room temperature. Dilution with MeOH and evaporation of the filtered solution (Celite®) afforded a crude reaction product. Flash chromatography with a mixture 7:3 of hexane/AcOEt afforded a pure pale yellow product 2.33 (30.0 mg, 65% of yield).
2.33: Rf =0.40 (1:1, hexane/AcOEt) and Rf =0.15 (7:3, hexane/AcOEt);
1H NMR (CDCl3) δ 7.78-7.70 (m, 2H), 7.40-7.23 (m, 7H), 6.2 (d, J = 4.28 Hz, 1HNH), 5.70-5.53 (m, 2HH1-2), 4.39 (d, J = 11.72 Hz,1HBenzylic), 4.26 (d, J = 11.72 Hz, 1HHbenzylic), 4.24-4.18(m, 1HH3),3.98 (d, J = 2.28 Hz, 1HOH), 3.20 (dd, J =9.92, 3.09 Hz, 1HH6*), 2.98- 2.75 (m, 2HH4-6’*), 2.43 (s, 3HTos), 2.38-2.16 (m, 1H), 2.06-1.98 (m,2H),;
13C NMR (CDCl3) δ 143.89, 137.16, 136.35, 129.84, 129.81, 129.12, 128.72, 128.14, 127.72, 127.63, 126.11, 73.54, 73.25, 73.12, 62.14, 37.29, 28.86, 21.68.
6-O-Benzyl-4-deoxy-4-(N-Tosylamino)-1,2-anhydro-5a-carba-β-D,L-mannopyranose MCPBA (70%) (0.077 mg, 0.31 mmol, 1.2 equiv) was added to a solution of alcohol derivative 2.33 (0.101g, 0.26 mmol, 1 equiv) dissolved in anhydrous CH2Cl2 (5.02 mL) at 0°C. The reaction mixture was stirred for 18h at room temperature. Dilution with CH2Cl2 and evaporation of the washed organic solution (Na2SO3aq(10%), NaHCO3aq and brine) afforded a crude reaction product (0.094 g, yield of 89%), consisting of a 60:40 mixture of a diastereoisomeric epoxides, 2.34β and 2.34α, which was subjected to preparative TLC using a 4:6 mixture as eluant. Extraction of the two most intense bands afforded β the epoxide 2.34β (0.055 g, 58.5% of yield) and α epoxide 2.34α (0.035 g, 37%).
2.34β: Rf =0.10 (1:1, hexane/AcOEt);
1H NMR (250 MHz, Chloroform-d) δ 7.78-7.66 (m, 2H), 7.42-7.22 (m, 7H), 5.79 (d, J = 5.6 Hz, 1HNH), 4.32 (d, J = 11.8 Hz, 1HBenzylic), 4.17 (d, J = 11.8 Hz, 1HBenylicz), 3.84 (d, J = 8.8 Hz, 1HH3), 3.72 (bs, 1HOH), 3.38 (dd, J=4.0, 1.6 Hz, 1HH2ox), 3.24 (dd, J = 4.88, 4.0 Hz, 1HH1ox), 3.12-3.07 (m, 2HH4-6*), 2.79 (dd, J = 9.5, 7.5 Hz, 1HH6’*), 2.42 (s, 3HTos), 2.07-1.50 (m, 3HAlkylyc);
13C NMR (CDCl3) δ 143.99, 137.20, 136.58, 129.85, 128.73, 128.17, 127.73, 127.64, 73.47, 72.00, 57.94, 56.76, 52.80, 37.93, 27.21, 21.72;
FTIR ν 3528.1, 3233.2, 3002.3, 2962.0, 2927.3, 2899.6, 2859.7, 1152.6, 1090.5, 1030.1 cm-1.
6-O-Benzyl-4-deoxy-4-(N-Tosylamino)-1,2-anhydro-5a-carba-β-D,L-mannopyranose 2.34α
Rf =0.31 (1:1, hexane/AcOEt);
1H NMR (250 MHz, Chloroform-d) δ 7.77 – 7.65 (m, 2H), 7.45 – 7.19 (m, 7H), 6.21 (d, J = 4.9 Hz, 1HNH), 4.36 (d, J = 11.67 Hz,1HBenzylic), 4.34 (d, J = 2.37, 1HOH), 4.24 (d, J = 11.67 Hz,1HBenzylic), 3.89 (dd, J = 7.5, 2.1 Hz, 1HH3), 3.26 – 3.11 (m,
3HH1-2-6*), 2.81-2.68 (m, 2HH4-6’*), 2.43 (s, 3H), 2.08-1.98 (m, 1H), 1.90-1.75 (m, 1H), 1.52 – 1.39 (m, 1H);
13C NMR (CDCl3) δ 144.11, 136.97, 136.25, 129.91, 128.77, 128,24, 127.65, 127.56, 73,46, 72.90, 72.01, 61.66, 55.42, 52.33, 31.32, 29.82, 27.97, 21.73.
6-O-Benzyl-3-O-Acetyl-4-deoxy-4-(N-Tosylamino)-1,2-anhydro-5a-carba-β-D,L- mannopyranose 2.35
Epoxide 2.34(0.010 g, 0.025 mmol, 1 equiv) was dissolved in anhydrous pyridine (0.323 mL) and treated with Ac2O (0.161 mL) at 0°C. The reaction mixture was stirred at room temperature for 4 h. Co-evaporation of the reaction mixture with toluene afforded a product 2.35 (0.011 g) practically pure, which was used in the next step without any purification.
2.35: Rf =0.41 (1:1, hexane/AcOEt);
1H NMR (250 MHz, CDCl3) δ 7.76 -7.65 (m, 2H), 7.43-7.11 (m, 7H), 5.02 (dd, J= 9.75, 1.3, 1HH3), 4.87 (bs, 1HNH), 4.45 (d, J= 11.7 Hz, 1HBenzylic), 4.32 (d, J= 11.7 Hz, 1HBenzylic), 3.74-3.39 (m, 2HH4-6*), 3.34-3.20 (m, 3HH1ox-2ox-6’*), 2.40 (s, 3HTos), 2.46-1.85 (m, 3HAlkylic), 1.60 (s, 3HAcetyl);
13C NMR (CDCl3) δ 171.58, 143.20, 139.00, 138.07, 129.84, 129.68, 128.72, 128.52, 127.86, 127.82, 127.65, 127.18, 73.68, 73.32, 71.68, 54.88, 54.13, 53.11, 39.84, 29.82, 27.53, 21.57, 20.52;
IR ν 3280.4, 3063.1, 3028.7, 2957.8, 2921.5, 2855.5, 1729.0, 1234.3, 1156.9, 1092.2, 1026.2 cm-1.
(2-Azidoethyl)-3-O-acetyl-6-O-benzyl-4-deoxy-4-(N-tosylamino)-5a-carba--D,L- mannopyranoside 2.10
Epoxide 2.35 (11.0 mg, 0.024 mmol, 1 equiv) was dissolved in a solution 1.3 M 2-azido-
1-ethanol in CH2Cl2 (0.1 mL, 0.097 mmol, 4.0 equiv) and Cu(OTf)2 (2.64 mg, 0.0073 mmol, 0.3 equiv) was added. The reaction mixture was stirred for 18 h at room temperature. Dilution with CH2Cl2 and evaporation of the washed (1:1 NaHCO3/NH4Cl mixture and brine) and dried organic solution afforded a crude reaction mixture (10.7 mg) which was subjected to preparative TLC, using a 4:6 hexane/AcOEt mixture as the eluant. Extraction of the more intense band afforded carbamannoside 2.10 (6 mg, 46% yield), pure as yellow solid.
2.10: Rf =0.40 (1:1, hexane/AcOEt, two development);
1H NMR (CDCl3) δ 7.76-7.63 (m, 2H), 7.41 – 7.16 (m, 7H), 5.03 (dd, J = 10.5, 2.8 Hz, 1HH3), 4.57 (d, J = 9.0 Hz, 1HH2), 4.28 (s, 2HBenzylic), 4.05 (m, 1HOH), 3.89-3.52 (m, 4HH4-6*- 2H Alkylic), 3.46-3.21 (m, 4HH1-6’*-2H Alkylic), 2.39 (s, 3HTos), 2.21 – 1.84 (m, 3HAlkylic), 1.77 (s, 3HAcetyl),
13C NMR (CDCl3) δ 171.10, 143.06, 139.15, 138.58, 129.64, 128.39, 127.53, 127.48, 127.39, 127.07, 95.36, 77.32, 76.72, 73.92, 72.88, 71.05, 70.03, 68.34, 53.92, 50.86, 37.74, 29.81, 27.44, 21.56, 20.87;
FTIR ν 3726.4, 3707.6, 3625.9, 3594.9, 2360.3, 2340.5, 2107.5, 1732.3 cm-1.
Synthesis of a 1.3 N solution of 2-azido-1-ethanol in CH2Cl2
2-chloro-1-ethanol (1.75 mL, 26.07 mmol) was added to a solution of NaN3 (2.0 g, 30.77 mmol, 1.18 equiv) in distilled H2O (8.0 mL) ad the resulting reaction mixture was stirred at room temperature for 1 h, and then heated at 70°C for 3 days. After cooling the reaction mixture was diluted with brine and the aqueous phase was extracted 3 times with CH2Cl2. The combined organic extracts were dried over Na2SO4 and concentrated under vacuum (rotating evaporator) until about 20 mL.
An analytical amount of this solution was completely evaporated at the pump, and the resulting liquid residue examined by 1H NMR analysis. The concentrated solution of 2- azido-ethanol in CH2Cl2 was used as the reagent in the corresponding glycosylation
reactions.
Synthesis of 2,3,4,6-tetra-O-benzoyl-α-D-mannopyranosyl trichloroacetimidate (-)-1.00 A solution of 2,3,4,6-tetra-O-benzoyl-α-D-mannose (1.42 g, 2.38 mmol) in anhydrous CH2Cl2 (8.0 mL) was treated with Cl3CCN (1.0 mL, 12.0 mmol, 5.0 equiv) and DBU (18.0 µL, 0.12 mmol, 0.05 equiv) and the reaction mixture was stirred 3 h at room temperature. Evaporation of the reaction mixture afforded a crude product (2.04 g) which was subjected to flash chromatography. Elution with an 8:2 hexane/AcOEt mixture afforded 2,3,4,6-tetra-O-benzoyl-α-D-mannopyranosyl trichloroacetimidate (-)-1.00, pure as a white solid (1.11 g, 63% yield).55-56
(2-azidoethyl)-2-O-[2’, 3’, 4’, 6’-tetra-O-benzoyl-α-D-mannopyranosyl]-3-O-acetyl-6-O- benzyl-4-deoxy-4-(N-tosylamino)-5a-carba-α-D-mannopyranoside 2.36
The glycosyl-donor trichloroacetimidate (-)-1.00 (22.62 mg, 0.0305 mmol, 1.3 equiv) and the glycosyl-acceptor, the partially protected carbamannoside 2.10 (12.5 mg, 0.0235 mmol, 1.0 equiv) were dissolved in distilled toluene and dried overnight at the pump. Acid washed molecular sieves AW 300 were activated under vacuum and added to the reagents. The mixture was dissolved in dry CH2Cl2 (0.50 mL) and a catalytic amount of TMSOTf in CH2Cl2 (0.85 µL, 4.7·10-3 mmol, 0.2 equiv) was added under nitrogen at -20°C and the reaction mixture was stirred at the same temperature for 3h, monitoring by TLC (7:3 hexane/AcOEt, 3 runs).
Et3N (20.0 µL) was added and the mixture was diluted with CH2Cl2 and filtered through a Celite® pad. Evaporation of the solvent afforded a crude product (0.049 g), which was subjected to a preparative TLC. Elution with a 7:3 hexane/AcOEt mixture afforded the O-
and N-protected pseudomannobioside 2.36 (19.6 mg, 0.018 mmol, 75% yield), pure as a white solid.
2.36: Rf = 0.22 (7:3, hexane/AcOEt, 3 runs);
1H NMR (CDCl3) δ 8.20-7.70 (m, 9H), 7.69-7.09 (m, 20H), 6.17-6.04 (m, 2H), 5.86 (dd, J
= 10.2, 3.2 Hz, 1H), 5.79-5.63 (m, 2H), 5.19-5.16 (m, 1HAnomeric), 5.02 (dd, J =5.03, 2.8 Hz, 1H), 4.79-4.60 (m, 2H), 4.52 (s, 2H), 4.08 (bs, 1H), 3.94 – 3.74 (m, 2H), 3.73 – 3.42 (m, 2H), 3.45 – 3.34 (m, 1H), 3.23-3.17 (m, 2H), 2.37 (s, 3HTos), 2.20 (m, 1H), 1.90-1.74 (m, 2H), 1.51 (s, 3HAcetyl);
13C NMR (CDCl3) δ 171.71, 166.18, 165.79, 165.49, 165.17, 143.24, 138.89, 133.71, 133.36, 130.06, 130.00, 129.95, 129.90, 129.84, 129.82, 129.36, 129.21, 128.95, 128.80, 128.69, 128.65, 128.62, 128.56, 128.49, 128.45, 127.66, 127.52, 127.44, 99.81, 78.12, 77.36, 76.33, 73.16, 72.82, 71.47, 70.42, 69.96, 68.21, 67.03, 63.28, 54.53, 50.73, 38.03, 29.84, 28.30, 21.54, 20.36;
FTIR ν 3350.0, 3292.8, 3065.0, 2956.9, 2926.9, 2360.0, 2340.4, 2107.9, 1726.9, 1264.8, 1107.5, 1069.8, 1028.5 cm-1.
(2-aminoethyl)-2-O-[2’, 3’, 4’, 6’-tetra-O-benzoyl- α-D-mannopyranosyl]-3-O-acetyl-4- deoxy-4-(N-tosylamino)-5a-carba-α-D-mannopyranoside 2.37
Pseudomannobioside 2.36 (19.6 mg, 0.018 mmol) was dissolved in a 4:1 MeOH/anhydrous DMF mixture (0.8 mL) and 10% Pd-c (0.08 g) was added. The reaction mixture was hydrogenated (1 bar) at room temperature under hydrogen saturated atmosphere until reduction of the azide group and deprotection of the benzyl group were achieved, monitoring by analytical TLC (7:3 hexane/AcOEt, 3 runs). After 18 h the mixture was diluted with MeOH and filtered through a Celite® pad. The evaporation of the solvent afforded a crude reaction product (0.015 g), which was crystallized from diisopropyl ether. Evaporation of the solvent afforded a white oil, to afford the pure
partially-O-deprotected 1,2-pseudomannobioside 2.37 (0.007 g, 0.007 mmol, 80% yield), pure as a yellow solid.
2.37: Rf = 0.02 (7:3, hexane/AcOEt, 3 runs);
1H NMR (CDCl3) δ 8.20-7.70 (m, 8H), 7.69-7.09 (m, 16H), 6.19-6.04 (m, 2H), 5.86 (dd, J
= 10.2, 3.2 Hz, 1H), 5.75-5.65 (m, 2H), 5.18-5.16 (m, 1H), 5.02 (dd, J =5.03, 2.8 Hz, 1H), 4.79-4.60 (m, 2H), 4.08 (bs, 1H), 3.94 – 3.74 (m, 2H), 3.73 – 3.42 (m, 2H), 3.45 – 3.34 (m, 1H), 3.23-3.17 (m, 2H), 2.37 (s, 3HTos), 2.20 (m, 1H), 1.90-1.74 (m, 2H), 1.51 (s, 3HAcetyl).
1
H NMR SPECTRA
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