Bienal de Química: Síntesis orgánica, historia, glicobiología y ribosomas.
La tercera jornada de la XXXIII Reunión Bienal de la RSEQ fue muy intensa. Asistí a dos conferencias plenarias, dos conferencias invitadas, tres comunicaciones de póster seleccionados y a una sesión de presentaciones flash. Los temas fueron variados: metodológía sintética, moléculas complejas de quiralidad plana, interacciones carbohidrato-proteína, historia de la química y la toxicología, y ribosomas, RNA, proteínas y su significado biológico. Los resúmenes y mis impresiones se indican a continuación,
El día 27 de julio comenzó con la conferencia plenaria del profesor Gregory Fu (MIT), que expuso resultados de reacciones de acoplamiento catalizadas por paladio. Describió el acoplamiento de haluros de alquilo con alquilboranos catalizado por paladio (0) en presencia de fosfinas sencilla con impedimento estérico. Se puede partir de la olefina, la cual se hidrobora al borano. El método se aplica a tosilatos y a electrófilos alquílicos secundarios, realizándose estudios mecanísticos. Describió reacciones de Suzuki de haluros secundarios con organozincicos catalizado por complejos de níquel. En presencia de fosfinas quirales se obtuvieron altos rendimientos y buenos excesos enantioméricos. El método se aplicó a la síntesis de productos naturales. También se describieron reacciones de Suzuki con bromuros de alquilo secundario catalizadas por complejos de níquel. El estudio mecanístico de la reacción indica que es es de orden uno en borano y en catalizador y de orden cero en el electrófilo. Describió reacciones tandem de alquilboración y acoplamiento de Suzuki y su aplicación en síntesis asimétrica usando ligandos quirales (diaminas); así como reacciones de Suzuki dirigida por un sustituyente del sustrato. Otros resultados descritos fueron la reacción de Negishi de haluros de propargilo y arilzinc, la reacción de Hiyama (trialcoxisilanos como núcleofilos promovida por diaminas quirales y la aplicación de la reacción de Suzuki catalizada por níquel a la resolución cinética de α-cetoamidas. Esta resolución cinética no es demasiado eficiente (E = 1’8). Este resultado se explica por la formación de un radical y la baja selectividad se debe a la etapa de adición oxidativa.
En definitiva, Fu mostró un amplio repertorio de reacciones de utilidad sintética; pero demasiado metodológico. En mi opinión hubo una diferencia sustancial con la conferencia de Hartwig (en el fondo y la forma). Mientras que los dos explicaron “química” muy similar, Hartwig fue mucho más didáctico, explicando la base del diseño de las reacciones y haciendo una exposición dónde se apreciaba el desarrollo de las ideas. La charla de Fu fue una exposición de muchos resultados experimentales útiles, pero sin explicar los fundamentos del desarrollo del proyecto.
Una copia del resumen se puede descargar aquí.
En el simposio de Didáctica e Historia de la Química, el profesor José R. Bertomeu (Universidad de Valencia) impartió una conferencia invitada sobre la vida y obra de Mateu Orfila (1787-1853), que ha sido objeto de un libro reciente editado por el conferenciante. Me gustó mucho la conferencia, tanto por el personaje histórico (posiblemente el “padre” de la toxicología química) como por la exposición realzada por Bertomeu. Aparte de numerosos detalles humanos y científicos de Orfila, el conferenciante puso en contexto histórico los hechos; haciendo hincapié en aspectos sociales de la época. Es bien conocido que en esa época, el uso de venenos era bastante frecuente, especialmente el arsénico; por lo que Orfila se especializó en la determinación de venenos; siendo la máxim autoridad de la época. En mi twitter he recomendado la lectura de The Elements of Murder. A History of Poison, de Emsley. También recomiendo The Arsenic Century: How Victorian Britain was Poisoned at Home, Work, and Play, de Whorton. Debido a que la siguiente conferenciante de esta sesión no se presentó, la conferencia y discusión con Bertomeu se pudo prolongar un poco más.
Una copia del resumen de la conferencia de Bertomeu se puede descargar aquí.
La siguiente conferenciante plenaria fue Ada Yonath (Weizmann Institue of Science), Premio Nobel de Química en 2009. La conferencia fue espectacular, tanto desde el punto de vista formal como del fondo; describiendo muchísimos resultados experimentales y lanzando hipótesis interesantes. Partiendo del dogma central de la biología molecular (DNA a RNA a proteína), presentó a los ribosomas como la fábrica que produce proteínas continuamente a través de la descodificación de la información genética. Los ribosomas son universales. Una célula de mamífero puede contener millones de ribosomas. En una bacteria en reposo pueden existir 100000. La eficacia de los ribosomas es impresionante: generan de 15 a 40 enlaces peptídicos por segundo, prácticamente sin errores. Expuso con detalle (incluso ayudándose de videos) la traducción a nivel molecular. Posteriormente se centró en el estudio estructural de los ribosomas, identificando al RNA como la molécula fundamental para el funcionamiento del ribosoma. Estos hechos parecen confirmar la hipótesis de que, evolutivamente, el RNA fue anterior a las proteínas (la hipótesis del mundo-RNA). El RNA no es un catalizador eficiente pero sí es una eficaz máquina de hacer proteínas. Desde el punto de vista estructural, existe simetría en la subunidad mayor del ribosoma, un hecho muy interesante, y además está muy conservada evolutivamente. Yonath explicó que las moléculas de RNA tiene las siguientes propiedades: autoreplicante, autoplegables y autodimerizables con capacidad catlítica.
Evolutivamente, propone que existió un protorribosoma, que fue una enzima dimérica producida por duplicación o fusión de genes. Esta hipótesis tiene importates implicaciones en el mundo prebiótico y recordó que la función es superior a secuencia desde un punto evolutivo (algo ya conocido en enzimología). A continuación pasó a discutir el posible origen del código genético. Yonath propone la hipótesis de que en origen del ancestro del código genético el protorribosoma jugó un papel fundamental. Con actividad catalítica, los sustratos del protorribosoma pudieron ser dipéptidos y estos eligieron el codón que les codificaba (posiblemente a través de interacciones no covalentes). Especula sobre los posibles primeros aminoácidos en la evolución: ¿glicina, alanina?, por ser los más sencillos; ¿histidina?, por su capacidad catalítica; ¿lisina, arginina?, por ser básicos; ¿fenilalanina, triptófano?, por ser aromñaticos; etc. En definitiva, los ribosomas son moléculas ancestrales y usan proteínas para ser máquinas más eficaces de fabricación de proteínas.
En la última parte de la conferencia se centró en el diseño de antibióticos que actúan por inhibición de la síntesis de proteínas en el ribosoma. Debido a que estas estructuras celulares están muy conservadas evolutivamente, es difícil tener fármacos selectivos que actúen sólo sobre el microorganismo y no sobre el anfitrión. Estos fármacos (por ejemplo, cloranfenicol, clindomicin, eritromicina o azitromicina) o son naturales o están inspirados en la naturaleza. Los microorganismos usan los antibióticos naturales como armas para defenderse de otros microorganismos. El mecanismo de acción de estos compuestos es deteniendo la función del ribosoma uniéndose a sitios fundamentales del mismo.
Aunque la conferencia fue más larga de lo previsto (80 minutos), disfruté escuchándola, pues aprendí muchísimo. No hay copia del resumen de la conferencia en el libro de resúmenes.
La sesión de tarde la comencé asistiendo a la ponencia de la Dra. Sonsoles Martín-Santamaría (Universidad San Pablo-CEU), póster seleccionado en el simposio de Química Biológica. Expuso resultados sobre las interacciones carbohidrato-proteína, analizando las bases moleculares de esta interacción por una combinación de métodos experimentales y computacionales. También presentó resultados de la interacción de oligosacáridos con catión calcio.
Una copia del resumen de la comunicación se puede descargar aquí.
Posteriormente asistí a las presentaciones flash del simposio de Didáctica e Historia de la Química; donde se presentaron comunicaciones sobre el uso el ordenador en resolución de problemas; el centenario de la conferencia Solvay y la física moderna; herramientas informáticas para prevención de riesgos laborales en el laboratorio de química analítica; y Robert Bunsen como innovador.
A continuación Jesús Arsuaga (Universidad Rey Juan Carlos) impartió una comunicación seleccionada sobre los orígenes de la química física, desde Lavoisier a Pauling; con una visión muy particular sobre este asunto. Hubo una intensa discusión sobre estos orígenes y el papel que otros científicos han hecho en esta disciplina y la relación con otras áreas de la química y de la física. Creo que fue una incorporación de última hora al programa y no hay resumen de la comunicación en el libro de resúmenes.
A continuación asistí a la entrega de los premios y la proyección de los videos del concurso Reacciona, una iniciativa de la RSEQ-STV, en colaboración con las dos universidades valencianas y la Ciudad de las Artes y las Ciencias. Los videos ganadores, realizados por alumnos de ESO-Bachillerato o universitarios, tenían un contenido muy adecuado y una realización cuidada. Los videos los podéis descargar de youtube.
La última conferencia invitada del día corrió a cargo de la profesora Mª Carmen Carreño (Universidad Autónoma de Madrid). Siempre es un placer escuchar a Carmen Carreño, por lo bien que explica su investigación, que es muy interesante y original. Su conferencia trató principalmente sobre ferroceno[4]helienoquinona; que son compuestos con quiralidad plana que pueden tener aplicaciones tecnológicas. Se obtienen por resolución cinética a través de reacciones de Diels-Alder con sulfóxidos quirales. También describió la síntesis de ácidos borónicos derivados de quinonas y su aplicación a la la reacción de Diels-Alder, dónde se produce una desborilación que puede tener utilidad sintética; de esta manera, el grupo dihidroxiborano (ácido borónico) es un controlador sintético útil. Finalmente, se describieron las aplicaciones de quinoles en síntesis de productos naturales.
Una copia del resumen de la conferencia se puede descargar aquí.
Bernardo Herradón-G.
CSIC
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