The study has no external funding; all costs are covered by ESHRE. There are no competing interests.

Important changes took place in the structure of costs of ART in the Human Reproduction Unit of the Virgen de las Nieves University Hospital between 1998 and 2003. Some techniques were discontinued, while others gained importance. Technological advances and structural innovations, together with a "learning effect," modified the structure of ART-related costs.

RESUMEN.-En este artículo se presenta una aproximación biomimética a la síntesis enantioselectiva de achillifolina, una lactona sesquiterpénica natural aislada de Achillea millefolium subsp. Millenium. La ciclación carbocatiónica de epoxi-costunolida es la etapa clave de la secuencia sintética. Esta ciclación transanular permite la formación del esqueleto de 1,4-epoxi-ciclodecano presente en (+)-achillifolina.PALABRAS CLAVES: Achillifolina, carbocatión, ciclación, síntesis, terpenos ABSTRACT.-In this paper, an approximation biomimetic synthesis of achillifoline, a natural sesquiterpene lactone isolated from Achillea millefolium subsp. Millenium, is presented. Carbocationic cyclization of epoxycostunolide is the key step of the synthetic sequence. This transannular cyclization, allows the formation of the skeleton of 1,4-epoxy-cyclodecane presents in achillifoline.

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