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El efecto desarmador del grupo 4,6-acetal sobre la reactividad de los glucósidos: torsional o electrónica?
Henrik Helligsø Jensen1, Lars Ulrik Nordstrøm, Mikael Bols
1Department of Chemistry, University of Aarhus, 8000 Aarhus C, Denmark.
Journal of the American Chemical Society
|July 30, 2004
Resumen
El grupo protector 4,6-acetal es el grupo protector 4,6-acetal.
Área de la Ciencia:
- Química de los carbohidratos Química de los carbohidratos
- Química orgánica es la química orgánica.
- Reacciones de glicosilación Reacciones de glicosilación.
Sus antecedentes:
- Se sabe que el grupo protector 4,6-acetal desactiva la transferencia de glicosilo.
- El mecanismo preciso (torsional vs. electrónico) de esta desactivación ha sido objeto de debate.
- Comprender este mecanismo es crucial para controlar las reacciones de glicosilación.
Objetivo del estudio:
- Para determinar si el efecto desactivador del grupo de protección 4,6-acetal es torsional o electrónico.
- Para investigar el papel de la fijación del 6-OH en la conformación tg.
- Para comparar las tasas de hidrólisis de los glucósidos conformacionalmente bloqueados y flexibles.
Principales métodos:
- Síntesis de moléculas de sonda conformacionalmente bloqueadas (18R y 18S) y análogos flexibles (21 y 26).
- Medición de las tasas de hidrólisis a pH 6.5 para las moléculas de la sonda y sus análogos.
- Comparación de las tasas de hidrólisis ácida para los correspondientes metil alfa-glucósidos (17S, 17R y 19).
Principales resultados:
- Las tasas de hidrólisis a pH 6,5 siguieron el orden: 21 > 18R > 18S > 26.
- El efecto desactivador del grupo 4,6-metileno es una combinación de factores torsionales y electrónicos.
- Los sacarídeos bloqueados en la conformación (4)C(1) mostraron una hidrólisis significativamente más lenta.
- Los rotameros de hidroximetil desactivan la hidrólisis de los glucósidos en el orden tg >> gt > gg.
Conclusiones:
- La desactivación por el grupo de protección 4,6-acetal es a la vez torsional y electrónica.
- La fijación del 6-OH en la conformación tg contribuye a la desactivación.
- Los glucósidos conformalmente bloqueados proporcionan información sobre los factores que influyen en las tasas de transferencia de glucosilo.
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