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

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• 作者：Alberto Ru铆z ; Cercis Morera-Boado ; Luis Almagro ; Julieta Coro ; Enrique E. Maroto ; Mar铆a 脕ngeles Herranz ; Salvatore Filippone ; Dolores Molero ; Roberto Mart铆nez-脕lvarez ; Jos茅 M. Garcia de la Vega ; Margarita Su谩rez ; Nazario Mart铆n
• 刊名：Journal of Organic Chemistry
• 出版年：2014
• 出版时间：April 18, 2014
• 年：2014
• 卷：79
• 期：8
• 页码：3473-3486
• 全文大小：622K
• 年卷期：v.79,no.8(April 18, 2014)
• ISSN：1520-6904

文摘

New [60]fullerene-steroid conjugates (4鈥?b>6) have been synthesized by 1,3-dipolar cycloaddition and Bingel鈥揌irsch 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 鈥渟ector rule鈥?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鈥?b>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.