[Benzyl] [Trityl] [PMP] [Allyl] [pMB] [Back to Carb. Synthesis]

Bn - (benzyl) ether

Standard Protection Procedure

To a solution of sodium hydride (1.3 eq per -OH) in DMF, the glycoside (dissolved in DMF) is added drop wise at 0° under an inert atmosphere.  The mixture is stirred for 30 minutes at 0° and benzyl bromide (1.3 eq per -OH) is added drop wise.  *Note - a catalytic amount of TBAI or crown ether can be added.  The reaction is stirred at room temperature until complete by TLC (usually 16 h) and methanol is added slowly to quench the reaction.  The solution is then diluted with chloroform and water, extracted 3 times with water and once with brine.  The organic layer is dried (sodium sulfate) and concentrated in vacuoThe resulting residue is purified by flash chromatography (SiO2) if necessary.
OR
To a solution of the glycoside in DCM, benzyl trichloroacetimidate (2 eq per -OH) is added drop wise (as a solution in cyclohexane - see third reference) with TfOH (catalytic - >1mol%).  The result is stirred at room temperature under inert atmosphere until complete by TLC (usually overnight).  Saturated aqueous sodium bicarbonate is added and the mixture is diluted with DCM.  The organic layer is extracted once with water, once with brine, dried (sodium sulfate), and concentrated in vacuo.  The resulting residue is purified by flash chromatography (SiO2) if necessary.
Removal
The glycoside is dissolved in 1:1 MeOH:tBuOH and palladium hydroxide (0.1 eq) is added at room temperature.  A hydrogen atmosphere is added (balloon pressure) and the reaction is stirred until complete by TLC (usually 16 h).  The mixture is then filtered and concentrated.  *Note - catalytic glacial acidic acid may be added if the reaction isn't complete.  The resulting residue is purified by flash chromatography (SiO2) if necessary.
References
    J. Org. Chem., 1979, 44, 3442.
    J. Am. Chem. Soc., 1971, 93, 1746.
[Back to Top] [Back to Carbohydrate Synthesis]

Tr - (triphenyl methyl) or trityl ether

Standard Protection Procedure

To a solution of the glycoside, trityl chloride (1.1 eq for primary over secondary, 1.5 eq for each -OH otherwise), and triethylamine (1.5 eq for primary over secondary, 2 eq for each -OH otherwise) stirring in DMF under an inert atmosphere at room temperature, DMAP (0.05 eq) is added.  The reaction is stirred until complete by TLC (usually overnight) and then poured into ice-water.  The mixture is extracted with chloroform and the organic layer is washed with saturated aqueous ammonium chloride and water, dried (sodium sulfate), and concentrated in vacuoThe resulting residue is purified by flash chromatography (SiO2) if necessary.
Removal
The glycoside is dissolved in ethanol and 5% palladium on charcoal is added under a hydrogen atmosphere.  The reaction is stirred until complete by TLC (usually overnight) and filtered.  The solution is concentrated and the residue is purified by flash chromatography (SiO2) if necessary.
References
    Tet. Lett., 1979, 2, 95-98.
    JOC, 1978, 18, 2877-2881.
[Back to Top] [Back to Carbohydrate Synthesis]

pMB - (para-methoxy benzyl) ether

Standard Protection Procedure

To a solution of sodium hydride (1.3 eq per -OH) in DMF, the glycoside (dissolved in DMF) is added drop wise at 0° under an inert atmosphere.  The mixture is stirred for 30 minutes at 0° and para-methoxybenzyl bromide (1.3 eq per -OH) is added drop wise.  *Note - a catalytic amount of TBAI or crown ether can be added.  The reaction is stirred at room temperature until complete by TLC (usually 16 h) and methanol is added slowly to quench the reaction.  The solution is then diluted with chloroform and water, extracted 3 times with water and once with brine.  The organic layer is dried (sodium sulfate) and concentrated in vacuoThe resulting residue is purified by flash chromatography (SiO2) if necessary.
Removal
The glycoside is dissolved in DCM/H2O 20:1 and DDQ (up to 10 eq) is added at room temperature under an inert atmosphere.  The reaction is stirred until complete by TLC (usually 24 h, may require heat) and diluted with DCM.  The solution is extracted with saturated aqueous sodium bicarbonate, dried (sodium sulfate), and concentrated in vacuo.  Product can then be purified by column chromatography if necessary.  The resulting residue is purified by flash chromatography (SiO2) if necessary.
References
    JACS, 1992, 114, 2524-2536.
    JACS, 1996, 118, 9265-9270.
[Back to Top] [Back to Carbohydrate Synthesis]

Allyl - (allyl) ether

Standard Protection Procedure

To a solution of sodium hydride (1.3 eq per -OH) in DMF, the glycoside (dissolved in DMF) is added drop wise at 0° under an inert atmosphere.  The mixture is stirred for 30 minutes at 0° and ally bromide (1.3 eq per -OH) is added drop wise.  *Note - a catalytic amount of TBAI or crown ether can be added.  The reaction is stirred at room temperature until complete by TLC (usually 16 h) and methanol is added slowly to quench the reaction.  The solution is then diluted with chloroform and water, extracted 3 times with water and once with brine.  The organic layer is dried (sodium sulfate) and concentrated in vacuoThe resulting residue is purified by flash chromatography (SiO2) if necessary.
OR
To a solution of the glycoside in DCM, benzyl trichloroacetimidate (2 eq per -OH) is added drop wise (as a solution in cyclohexane - see third reference) with TfOH (catalytic - >1mol%).  The result is stirred at room temperature under inert atmosphere until complete by TLC (usually overnight).  Saturated aqueous sodium bicarbonate is added and the mixture is diluted with DCM.  The organic layer is extracted once with water, once with brine, dried (sodium sulfate), and concentrated in vacuo.  The resulting residue is purified by flash chromatography (SiO2) if necessary.
Removal
The glycoside is dissolved in AcOH:water 20:1 and Palladium chloride (1.5 eq) followed by sodium acetate (5 eq) is added.  The mixture is stirred under an inert atmosphere at room temperature until complete by TLC (usually overnight).  Ethyl acetate is added and the mixture is extracted 2 times with saturated aqueous sodium bicarbonate.  The organic layer is then extracted once with brine, dried (sodium sulfate), and concentrated in vacuo.  The resulting residue is purified by flash chromatography (SiO2) if necessary.
References
    Tet. Lett., 1997, 40, 13,509-13,556.
    JOC, 1973, 18, 3224.
    J. Chem. Soc. Perkin Trans. I, 1985, 2247-2250.
    JACS, 1991, 113, 2092-2112.
[Back to Top] [Back to Carbohydrate Synthesis]

PMP - (p-methoxyphenyl) ether

Standard Protection Procedure

To a solution of the glycoside in THF under an inert atmosphere is added triphenylphosphine (1.3 eq), diethylazocarboxylate (1.3 eq), and p-methoxyphenol (3 eq).  The resulting solution is heated to 80° and stirred until complete by TLC (usually 2 h).  The mixture is concentrated in vacuo and purified by flash chromatography (SiO2).
Removal
The glycoside is dissolved in acetonitrile:water 4:1 at room temperature under an inert atmosphere and CAN (5 eq) is added.  The mixture is stirred until complete by TLC (usually less than 1 h) and diluted with chloroform.  The resulting solution is washed with water and saturated sodium chloride solution.  The organic layer is dried (sodium sulfate) and concentrated in vacuo.  The residue can then be purified by flash chromatography (SiO2) if necessary.
References
    Tet. Lett., 1988, 29, 1389-1390.
    Heterocycles, 1990, 31, 1555-1563.
[Back to Top] [Back to Carbohydrate Synthesis]