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Acilación regioselectiva de diolos y triolos: el efecto cianuro

Peng Peng¹, Michael Linseis¹, Rainer F Winter¹

¹Department of Chemistry, University of Konstanz , D-78457 Konstanz, Germany.

Journal of the American Chemical Society

|April 23, 2016

Resumen

Los investigadores descubrieron un nuevo "efecto cianuro" para la protección directa de los carbohidratos, lo que permite la O-acilación regioselectiva de grupos hidroxi específicos. Este método utiliza el doble enlace de hidrógeno para la síntesis eficiente de bloques de construcción de carbohidratos protegidos.

Área de la Ciencia:

Química de los carbohidratos
Síntesis orgánica
Estereoquímica

Sus antecedentes:

La síntesis de oligosacáridos y la modificación de carbohidratos requieren bloques de construcción protegidos regioselectivamente.
Los métodos actuales para obtener estos bloques de construcción son a menudo indirectos y de varios pasos.
Los métodos de protección directa para grupos hidroxi específicos son muy deseables en la química de los carbohidratos.

Objetivo del estudio:

Desarrollar un método directo para la protección regioselectiva del grupo hidroxi en los carbohidratos.
Investigar el papel del doble enlace de hidrógeno en el logro de la regioselectividad durante la O-acilación.
Para permitir la síntesis de productos controlados cinéticamente en la química de los carbohidratos.

Principales métodos:

Se utiliza cianuro de benzoilo o cianuro de acetil como agentes acilantes a bajas temperaturas (-78 °C).
Se utiliza el DMAP (4-dimetilaminopiridina) como catalizador.
Se estudió la regioselectividad en varios galacto-, fuco- y manopyranósidos protegidos y no protegidos.
Los hallazgos confirmados mediante la espectroscopia de resonancia magnética nuclear (RMN) y los cálculos de la teoría funcional de la densidad (TFD).

Principales resultados:

Se ha logrado una O-acilación axial termodinámicamente desfavorable de 1,2-cis-diols utilizando el "efecto cianuro".
Demostró que las capacidades de enlace de hidrógeno del ion cianuro dirigen la acilación regioselectiva, incluso en posiciones estéricamente obstaculizadas.
Se observó que la acilación axial de 4-O en triolos fue más rápida que la acilación del grupo 6-hidroxi primario.
No mostró migración de acilo bajo las condiciones de reacción, lo que permite el aislamiento de productos cinéticos.

Conclusiones:

El "efecto cianuro" surge de la doble unión de hidrógeno, mejorando la nucleofilicidad de los grupos hidroxi axiales.
Este método proporciona una ruta directa a los bloques de construcción de carbohidratos regioselectivamente protegidos.
Los resultados ofrecen un avance significativo para la síntesis eficiente de oligosacáridos y la modificación estructural de los carbohidratos.

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