title: Dumbbell-type fullerene-steroid hybrids: a join experimental and theoretical investigation for conformational, configurational, and circular dichroism assignments.
abstract: New [60]fullerene-steroid conjugates (4-6) have been synthesized by 1,3-dipolar cycloaddition and Bingel-Hirsch cyclopropanation reactions from suitably functionalized epiandrosterone and [60]fullerene. Since a new stereocenter is created in the formation of the Prato monoaduct, two different diastereomers were isolated by HPLC (4, 5) whose absolute configurations were assigned according to the highly reliable "sector rule" on fullerenes. A further reaction of the malonate-containing diastereomer 5 with a second C60 molecule has afforded dumbbell fullerene 6 in which the two fullerene units are covalently connected through an epiandrosterone moiety. The new compounds have been spectroscopically characterized and their redox potentials, determined by cyclic voltametry, reveal three reversible reduction waves for hybrids 4 and 5, whereas these signals are split in dumbbell 6. Theoretical calculations at semiempirical (AM1) and single point B3LYP/6-31G(d) levels have predicted the most stable conformations for the hybrid compounds (4-6), showing the importance of the chlorine atom on the D ring of the steroid. Furthermore, TDDFT calculations have allowed assignments of the experimentally determined circular dichroism (CD) of the [60]fullerene-steroid hybrids based on the sign and position of the Cotton effects, despite the exceptionally large systems under study.
authors.affiliation: Laboratorio de Síntesis Orgánica and ‡Laboratorio de Química, Computacional y Teórica, Facultad de Química, Universidad de la Habana , 10400-La Habana, Cuba.
authors.forename: Alberto
authors.initials: A
authors.lastname: Ruíz
authors.forename: Cercis
authors.initials: C
authors.lastname: Morera-Boado
authors.forename: Luis
authors.initials: L
authors.lastname: Almagro
authors.forename: Julieta
authors.initials: J
authors.lastname: Coro
authors.forename: Enrique E
authors.initials: EE
authors.lastname: Maroto
authors.forename: María Ángeles
authors.initials: MÁ
authors.lastname: Herranz
authors.forename: Salvatore
authors.initials: S
authors.lastname: Filippone
authors.forename: Dolores
authors.initials: D
authors.lastname: Molero
authors.forename: Roberto
authors.initials: R
authors.lastname: Martínez-Álvarez
authors.forename: José M
authors.initials: JM
authors.lastname: Garcia de la Vega
authors.forename: Margarita
authors.initials: M
authors.lastname: Suárez
authors.forename: Nazario
authors.initials: N
authors.lastname: Martín
mesh_terms: D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D037741:Fullerenes / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008962:Models, Theoretical; D008968:Molecular Conformation; D013237:Stereoisomerism; D013256:Steroids / Q000737:chemistry*
chemical_list: D037741:Fullerenes; D013256:Steroids