title: A C-Glycosylflavone from Piper ossanum, a Compound Conformationally Controlled by CH/π and Other Weak Intramolecular Interactions.
abstract: The structure of the known 2''-O-α-rhamnosyl-4''-O-methylvitexin (apigenin-8-C-α-rhamnosyl-(1→2)-β-4-O-methylglucopyranoside), isolated from the leaves of Piper ossanum, was revised to acacetin-8-C-neohesperidoside (acacetin-8-C-α-rhamnosyl-(1→2)-β-glucopyranoside or 2''-O-α-rhamnosyl-4'-O-methylvitexin) (1). The NMR data and theoretical calculations established the preferred conformation of 1, which is controlled by CH/π interactions. This phenomenon explains the unusual chemical shifts of some protons in the molecule, besides other weak intramolecular interactions such as the anomeric effect, the Δ2 effect, and several hydrogen bonds.
authors.affiliation: Instituto Superior de Medicina Militar Dr. Luis Díaz Soto, Laboratorio de Medicina Herbaria, Avenida Monumental y Carretera del Asilo, Habana del Este, 11700, Ciudad de la Habana, Cuba.
authors.forename: María
authors.initials: M
authors.lastname: Larionova
authors.forename: Iraida
authors.initials: I
authors.lastname: Spengler
authors.forename: Clara
authors.initials: C
authors.lastname: Nogueiras
authors.forename: Leovigildo
authors.initials: L
authors.lastname: Quijano
authors.forename: Karla
authors.initials: K
authors.lastname: Ramírez-Gualito
authors.forename: Fernando
authors.initials: F
authors.lastname: Cortés-Guzmán
authors.forename: Gabriel
authors.initials: G
authors.lastname: Cuevas
authors.forename: José S
authors.initials: JS
authors.lastname: Calderón
mesh_terms: D018360:Crystallography, X-Ray; D003462:Cuba; D005419:Flavonoids / Q000737:chemistry* / Q000302:isolation & purification*; D006027:Glycosides / Q000737:chemistry* / Q000302:isolation & purification*; D006860:Hydrogen Bonding; D008968:Molecular Conformation; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D031701:Piper / Q000737:chemistry*; D018515:Plant Leaves / Q000737:chemistry
chemical_list: D005419:Flavonoids; D006027:Glycosides; C000605910:apigenin-8-C-alpha-rhamnosyl-(1-2)-beta-4-O-methylglucopyranoside