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CHERIF, CLAVEL, AND MONNERET
Dilution with ethyl acetate (50 mL) was followed by filtration through a celite pad. The
filtrate was washed with brine, dried over MgSO4 and concentrated in vacuo. Flash
chromatography of the residue on a silica gel column eluting with 9:1 cyclohexane/EtOAc
afforded 0.35 g (49%) of 6 as a syrup; Rf (cyclohexane-EtOAc, 2:1) 0.85; [a]D20 + 84° (c
0.85, CDCl3); 1H NMR (CDCl3) d 7.32À6.97 (m, 25 H, H Ar), 5.50 (d, 1H, J= 3.6 Hz, H-10),
5.47 (s, 1H, H-7), 5.34 (d, 1H, J= 0.7 Hz, H-1), 4.97 and 4.43 (2d, 2H, J =10.9 Hz, CH2Ph),
4.86 and 4.78 (2d, 2H, J =12 Hz, CH2Ph), 4.82 and 4.43 (2d, 2H, J =12.3 Hz, CH2Ph), 4.37
(m, 3H, H), 4.18 (dd, 1H, J=4.8 Hz, J=10.18 Hz, H-60b), 3.97 (t, 1H, J= 9.2 Hz, H-30), 3.92
(dd, 1H, J= 2.3 Hz, J =1 Hz, H-2), 3.88 (t, 1H, J=10.1 Hz, H-60a), 3.73 (m, 1H, H-5 or H-50),
3.63 (dd, 1H, J= 3.6 Hz, J=8 Hz, H), 3.57 (t, 1H, J= 9.1 Hz, H), 2.59 (m, 2H, S-CH2-CH3),
1.26 (t, 3H, S-CH2-CH3).
Phenyl 2-O-Acetyl-3-O-benzyl-4,6-O-benzylidene-a-D-thiomannopyranoside
(7). A solution of phenyl 3-O-benzyl-4,6-O-benzylidene-a-D-thiomannopyranoside[9]
(1 g, 2.22 mol) in pyridine (20 mL) was stirred at room temperature for 5 h in the presence
of Ac2O (3 mL). Subsequent dilution with ethyl acetate, followed by washings with
aqueous solution of H2SO4, with water and with a saturated aqueous solution of sodium
hydrogencarbonate led to isolation of 1.3 g of crude product. Flash chromatography of the
residue on a silica gel column eluting with 9:1 cyclohexane/EtOAc afforded 1 g (92%) of 7
1
as a syrup; Rf (cyclohexane-EtOAc, 4:1) 0.76; [a]D20 + 113° (c 1, CDCl3); H NMR
(CDCl3) d 7.56À7.24 (m, 15H, Ar), 5.65 (s, 1H, H-7), 5.62 (dd, 1H, J2,3 = 3.4 Hz, J2,1 = 1.4
Hz, H-2), 5.46 (d, 1H, J= 1 Hz, H-1), 4.71 (s, 2H, CH2Ph), 4.44À3.90 (m, 4H, H-4, H-5, H-
6a, H-6b), 3.86 (dd, 1H, J2,3 =3.4 Hz, J3,4 =9,5 Hz, H-3), 2.16 (s, 3H, OAc); MS (DCI/
NH3) m/z 510 [M + NH4]+, 493 [M +H]+.
Anal. Calcd for C28H28O6S (492.59): C, 68.27; H, 5.73. Found: C, 68.12; H, 5.89.
Methyl O-(2-O-Acetyl-3-O-benzyl-4,6-O-benzylidene-a-D-mannopyranosyl)-
(1 2)-3-O-benzyl-4,6-O-benzylidene-a-D-mannopyranoside (9). A solution of 7
!
(0.530 g, 1.07 mmol) and 8 [9] (0.308 g, 0.82 mol) in anhydrous CH2Cl2 containing 4 A
˚
molecular sieves (0.4 g) and 2,6-di-tert-butyl-4-methylpyridine (170 mg, 0.8 mmol) was
stirred for 20 min at rt. Then, dimethyl(methylthio)sulfonium triflate (DMTST) [prepared
extemporaneously by dropwise addition of methyl trifluoromethanesulfonate (375 mL,
3.31mmol) to methyl disulfide (293 mL, 3.31 mmol)] was added and stirring was
maintained for 2.5 h before filtration over a celite pad. The solution was washed with
brine and dried over MgSO4. Concentration in vacuo, followed by flash chromatography
using cyclohexane/EtOAc (9:1) as eluent, gave 9 (0.3 g, 48%) as a syrup; Rf (cyclohexane-
EtOAc, 2:1) 0.66; [a]D20+4.5° (c 1, CDCl3); 1H NMR (CDCl3) d 7.41À 7.21 (m, 20H, Ar),
5.67 and 5.66 (2s, 2H, H-7 and H-70), 5.16 (d, 1H, J= 1.43 Hz, H-1), 4.88 and 4.72 (2d, 2H,
J=11.5 Hz, OCH2-Ph), 4.78 and 4.66 (2d, J=12 Hz, OCH2-Ph), 4.69 (s, 1H, H-10), 4.29 (m,
2H, H-6, H-60), 4.10À3.77 (m, 8H, H-2, H-20, H-3, H-30, H-4, H-4, H-5, H-50), 3.36 (s, 3H,
OCH3), 2.15 (s, 3H, Ac); MS (DCI/NH3) m/z 772 [M + NH4]+.
Methyl O-(3-O-Benzyl-4,6-O-benzylidene-a-D-mannopyranosyl)-(1 2)-3-O-
!
benzyl-4,6-O-benzylidene-a-D-mannopyranoside (10). A methanolic solution (20
mL) of 9 (0.25 g, 0.33 mmol) was stirred for 2 h in the presence of sodium methoxide
(100 mg). The solution was neutralized by addition of IRC50 H+ Amberlite and filtered.
Flash chromatography using cyclohexane-EtOAc (85:15) led to 10 (0.23 g, 98%). Rf