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Dumbbell-Type Fullerene-Steroid Hybrids: A Join Experimental and Theoretical Investigation for Conformational, Configurational, and Circular Dichroism Assignments.

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Title: Dumbbell-Type Fullerene-Steroid Hybrids: A Join Experimental and Theoretical Investigation for Conformational, Configurational, and Circular Dichroism Assignments.
Authors: Ruíz, Alberto1, Morera-Boado, Cercis2, Almagro, Luis1, Coro, Julieta1, Maroto, Enrique E.3, Herranz, María Ángeles3, Filippone, Salvatore3, Molero, Dolores4, Martínez-Álvarez, Roberto3, de la Vega, José M. Garcia5, Suárez, Margarita1 msuarez@fq.uh.cu, Martín, Nazario3 nazmar@quim.ucm.es
Source: Journal of Organic Chemistry. 4/18/2014, Vol. 79 Issue 8, p3473-3486. 14p.
Subjects: Fullerenes, Steroids, Dichroism, Ring formation (Chemistry), Cyclopropanation
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. [ABSTRACT FROM AUTHOR]
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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. [ABSTRACT FROM AUTHOR]
ISSN:00223263
DOI:10.1021/jo500178t