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DOI: 10.1055/s-0029-1217356
A Mild, Highly Efficient, and Chemoselective Deprotection of Trityl Ethers of Carbohydrates and Nucleosides Using Iodine Monobromide [¹]
Publikationsverlauf
Publikationsdatum:
12. Juni 2009 (online)
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Abstract
Iodine monobromide in dichloromethane-methanol or acetonitrile constitutes an effective reagent for the deprotection of O-trityl and O-dimethoxytrityl ethers of carbohydrates and nucleosides. Acid-labile functionalities (acetals, O-p-methoxybenzyl ethers, etc.) as well as base-labile groups (esters and amides) are stable under these conditions; and the method has been found to be superior to the hitherto known literature methods.
Key words
interhalogen - iodine monobromide - trityl ether - carbohydrate - nucleoside - chemoselective deprotection
- 1 Iodine and its Interhalogen Compounds:
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References and Notes
The workup and isolation of the product are also a lot more convenient in the present case as the literature method³ makes use of glacial AcOH as the solvent for the reaction.
18Treatment of 5 with HBr/AcOH reagent in CH2Cl2 as described for 3 led to the formation of a mixture of 1,2-O- and 3,4-O-isopropylidene-d-galactoses and d-galactose as judged by TLC and ¹H NMR spectroscopy.
19
Typical Procedure
for Conversion of 3 → 4
Method
A
IBr (1.2 mL of a 1 M soln in CH2Cl2,
1.2 mmol) was added to a soln of 3 (562
mg, 1 mmol) in MeCN (10 mL) and was stirred until TLC (EtOAc-hexanes,
2:3) showed completion of the reaction. The reaction mixture was
then diluted with CH2Cl2 and was washed successively
with dilute aq Na2S2O3 and Na2CO3 soln,
dried (Na2SO4), concentrated to dryness under
reduced pressure and was purified by column chroma-tography (silica
gel; EtOAc-hexanes, 2:3) to yield crystals (308 mg, 95%)
of 4.
Alternatively, after the
completion of the reaction, the workup can also be carried out by
stirring the reaction mixture with Amberlite IRA-400 (hydroxide
form) resin to get a colourless solution. Filtration, concentration
of the filtrate under reduced pressure, and chromatography as described
above afforded 4.
Method
B
The reaction was carried out by the same procedure
as described above but CH2Cl2-MeOH
(9:1) was used as the solvent instead of MeCN. The product was obtained
in practically the same yield.