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Escisión endocíclica en glucósidos con grupos protectores cíclicos 2,3-trans
Hiroko Satoh1, Shino Manabe, Yukishige Ito
1National Institute of Informatics (NII), Tokyo 101-8430, Japan. hsatoh@nii.ac.jp
Journal of the American Chemical Society
|March 23, 2011
Resumen
Una vía endocíclica explica la anomerización de los glucósidos con grupos protectores cíclicos bajo catálisis ácida débil. La tensión del anillo interno, que no protege la conformación del grupo, impulsa principalmente esta reacción de endoclavaje.
Área de la Ciencia:
- Química de los carbohidratos Química de los carbohidratos
- Mecanismos de reacción orgánica.
- Química computacional es la química computacional.
Sus antecedentes:
- La anomerización de los glucósidos generalmente implica una escisión exocíclica, pero los compuestos con grupos protectores cíclicos 2,3-trans muestran una vía endocíclica.
- Esta escisión endocíclica (endocleavage) se observa en condiciones más suaves (ácidos débiles de Lewis o Brønsted) en comparación con los glucósidos típicos.
Objetivo del estudio:
- Investigar el mecanismo de reacción y los factores promotores del endoclavado en glucósidos con grupos protectores cíclicos 2,3-trans.
- Racionalizar la anomerización observada de las configuraciones β (1,2-trans) a α (1,2-cis) bajo condiciones específicas.
Principales métodos:
- Se emplearon cálculos de mecánica cuántica (QM) para estudiar las vías de reacción y las energías del estado de transición (TS).
- Se llevaron a cabo estudios experimentales, incluidas las reacciones de anomerización de los tioglucósidos con el éterato de trifluoruro de boro (BF(3) ·OEt(2).
Principales resultados:
- Un modelo simple predijo con precisión las energías TS basadas en la tensión del anillo fundido, correlacionándose bien con los cálculos de QM y la reactividad experimental.
- Se encontró una excelente concordancia entre las energías TS previstas y calculadas, lo que respalda el mecanismo endocíclico propuesto.
Conclusiones:
- El estudio apoya firmemente el predominio del mecanismo endocíclico sobre la vía exocíclica para esta clase de glucósidos.
- La cepa del anillo interno se identifica como el factor primario que mejora el endocleavage, con la conformación del grupo protector que juega un papel secundario.
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