title: Configuration and conformation of alfentanil hydrochloride. Conformational study by NMR and theoretical calculations.
abstract: The configurational and conformational structure of alfentanil hydrochloride (1) was studied by nuclear magnetic resonance and theoretical calculations. Compound 1 is best described by equilibrium between two stereoisomeric piperidinium rings with the N-substituent always being in equatorial position. Nuclear magnetic resonance spectra demonstrate that, depending on the solvent, 1 adopts the conformation with an axial methoxymethylene group. Computations were crucial in determining the importance of the transannular attractive interaction between the positive charge at the piperidinium N-atom and the methoxymethyl group in position 4.
authors.affiliation: Departament de Química, Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain.
authors.forename: Carlos
authors.initials: C
authors.lastname: Jaime
authors.forename: Albert
authors.initials: A
authors.lastname: Virgili
authors.forename: Susana
authors.initials: S
authors.lastname: Portillo
authors.forename: Antoni
authors.initials: A
authors.lastname: Caparrós
authors.forename: Kepa K
authors.initials: KK
authors.lastname: Burusco
mesh_terms: D015760:Alfentanil / Q000737:chemistry*; D000701:Analgesics, Opioid / Q000737:chemistry*; D008968:Molecular Conformation; D066244:Proton Magnetic Resonance Spectroscopy / Q000379:methods*
chemical_list: D000701:Analgesics, Opioid; D015760:Alfentanil
keywords: DFT; NMR; alfentanil; conformational analysis; molecular mechanics; transannular interactions