Absolute configuration reassignment of two chromanes from Peperomia obtusifolia (Piperaceae) using VCD and DFT calculations

Autor(es)

Batista, Jr., Joao Marcos ^{[1, 2]} ; Batista, Andrea N. L. ^[1] ; Rinaldo, Daniel ^[1] ; Vilegas, Wagner ^[1] ; Cass, Quezia B. ^[3] ; Bolzani, Vanderlan S. ^[1] ; Kato, Massuo J. ^[4] ; Lopez, Silvia N. ^{[1, 5]} ; Furlan, Maysa ^[1] ; Nafie, Laurence A. ^[2]

Afiliação do(s) autor(es)

^[1] Univ Estadual Paulista, Inst Quim, Dept Quim Organ, BR-14800900 Araraquara, SP - Brazil

^[2] Syracuse Univ, Dept Chem, Syracuse, NY 13244 - USA

^[3] Univ Fed Sao Carlos, Dept Quim, BR-13565905 Sao Carlos, SP - Brazil

^[4] Univ Sao Paulo, Inst Quim, Sao Paulo - Brazil

^[5] Univ Nacl Rosario, Fac Ciencias Bioquim & Farmaceut, RA-2000 Rosario, Santa Fe - Argentina

• Tipo de documento: Artigo Científico
• Fonte: TETRAHEDRON-ASYMMETRY; v. 21, n. 19, p. 2402-2407, OCT 7 2010.
• Citações Web of Science: 44

Resumo

Previous analysis of the ECD spectra of two prenylated benzopyrans isolated from Peperomia obtusifolia, by means of the helicity rule for the chromane chromophore, resulted in the incorrect assignment of their absolute configuration, (5) instead of (R) for a deduced P-helicity of the chromane ring for the (+)-enantiomers. This was discovered by the application of DFT calculations and VCD spectroscopy. Experimental and calculated (B3LYP/6-31G(d)) VCD and IR spectra were compared, and a definitive absolute configuration of (+)-1 and (+)-2 is reassigned directly in solution as (R). The assumption of equatorial positioning of bulky groups, shown here to be invalid for the title molecules, is the underlying cause of the previous incorrect assignment of absolute configuration. Moreover, TDDFT (B3LYP/6-311++G(2d,2p)//B3LYP/6-31G(d)) calculations of ECD spectra have shown that both P- and M-helicity of the heterocyclic ring, for a given absolute configuration, lead to the same sign for the (1)L(b) ECD band, thus bringing into question the validity of the empirical ECD helicity rule for chromane molecules. (C) 2010 Elsevier Ltd. All rights reserved. (AU)

• Processo FAPESP: 03/02176-7 - Conservação e uso sustentável da diversidade do Cerrado e da Mata Atlântica: diversidade química e prospecção de medicamentos potenciais - fase II
• Beneficiário: Vanderlan da Silva Bolzani
• Modalidade de apoio: Auxílio à Pesquisa - Programa BIOTA - Temático
• Processo FAPESP: 08/58658-3 - Estudo químico e biológico de benzopiranos naturais em espécies de Piperaceae e seus análogos
• Beneficiário: João Marcos Batista Junior
• Modalidade de apoio: Bolsas no Brasil - Doutorado Direto