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Equilibrar el control cinético y termodinámico: el mecanismo de ciclización del carbocatión por la ciclase de
1Department of Chemistry and Supercomputing Institute, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Journal of the American Chemical Society
|October 16, 2003
Resumen
La ciclasa de escualeno-hopeno (SHC) utiliza un potencial QM/MM para simular la ciclización del carbocatión. El control cinético dicta la distribución del producto, favoreciendo la formación de hopanoides sobre otras vías.
Área de la Ciencia:
- La bioquímica es la bioquímica.
- Química computacional es la química computacional.
- Enzimología Enzimología.
Sus antecedentes:
- La ciclasa de escualeno-hopeno (SHC) cataliza una compleja reacción de ciclización.
- Comprender el mecanismo de la biosíntesis de los hopanoides es crucial en la bioquímica.
Objetivo del estudio:
- Investigar la dinámica molecular de la ciclización de escualeno a hopeno.
- Elucidar el mecanismo de ciclización del carbocatión dentro del SHC.
- Determinar los factores que controlan la distribución del producto.
Principales métodos:
- Potencial combinado mecánico cuántico y mecánico molecular (QM/MM).
- Simulaciones de energía libre y construcción de superficies de energía libre.
- Simulaciones de dinámica molecular.
Principales resultados:
- La cascada de ciclización de carbocationes implica un equilibrio entre el control termodinámico y el cinético.
- La expansión de anillos de cinco a seis miembros no es una vía viable para la formación de anillos C o D.
- Dos vías concertadas asincrónicas se originan a partir del intermediario del catión ciclohexilo A/B-bicíclico.
- Estas vías conducen a distintos esqueletos tetraciclicos y pentacíclicos de los hopanoides.
Conclusiones:
- La distribución de productos en SHC de tipo silvestre se rige por el control cinético.
- El rendimiento del 99% de los hopanoides pentacíclicos se explica por la favorabilidad cinética.
- El mecanismo destaca el intrincado control sobre la compleja biosíntesis de productos naturales.
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