| Autor: |
Pablo Englebienne, Nicolas Moitessier, Yves Chapleur |
| Rok vydání: |
2005 |
| Předmět: |
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| Zdroj: |
Tetrahedron. 61:6839-6853 |
| ISSN: |
0040-4020 |
| DOI: |
10.1016/j.tet.2005.04.060 |
| Popis: |
A novel concept of regioselective transformation of secondary hydroxyl groups in carbohydrates is presented. First, the relative reactivity of the free hydroxyl groups of onoprotected d -glucose derivatives was assessed using acetylation as a model reaction. As a result, acylation of these polyols gave a mixture of monosubstituted products in which the 3- O functionalized derivatives predominated. Novel hydrogen bond acceptor protecting groups were next designed to modulate the 4-OH and 3-OH reactivity in the hope to mediate higher regioselective transformations. A molecular modeling study later validated by spectroscopic analysis predicted additional intramolecular hydrogen bonds between the hydroxyl groups and pyridyl-containing protecting groups. Taking advantage of this induced hydrogen bond network, we achieved regioselective acetylation of the hydroxyl group at position 3 without protecting any secondary hydroxyl groups of the carbohydrate moiety. This designed protecting/directing group increased the nucleophilicity and the steric hindrance of position 3. As a result, optimization of the reaction conditions enabled the monoacetylation (not affected by steric hindrance) of 6- O -protected glucopyranosides at position 3 and selective silylation (affected by steric hindrance) of position 2 in high isolated yields and regioselectivities. This result certainly opens doors to the regioselective open glycosylation of carbohydrates. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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