title: 1H, 13C, 15N NMR analysis of sildenafil base and citrate (Viagra) in solution, solid state and pharmaceutical dosage forms.
abstract: Sildenafil citrate (SC) (Viagra) and sildenafil base in pure form are easily and unequivocally characterized by multinuclear NMR spectroscopy. Analysis of chemical shifts indicates that: (i) N6-H forms intramolecular hydrogen bonds, (ii) N25 is protonated in the salt and (iii) intermolecular OH...N hydrogen bonds involving N2 and N4 are present in the solid sildenafil citrate. 13C CPMAS NMR method has been proposed for the identification and quantitation of Viagra in its pharmaceutical formulations.
authors.affiliation: Department of Physical Chemistry, Faculty of Pharmacy, Medical University of Warsaw, Banacha 1, 02097 Warsaw, Poland. wawer@pluton.farm.amwaw.edu.pl
authors.forename: Iwona
authors.initials: I
authors.lastname: Wawer
authors.forename: Maciej
authors.initials: M
authors.lastname: Pisklak
authors.forename: Zdzisław
authors.initials: Z
authors.lastname: Chilmonczyk
mesh_terms: D002247:Carbon Isotopes; D004304:Dosage Forms / Q000592:standards*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D015394:Molecular Structure; D009587:Nitrogen Isotopes; D019999:Pharmaceutical Solutions / Q000592:standards; D010879:Piperazines / Q000032:analysis* / Q000737:chemistry / Q000592:standards; D011522:Protons; D011687:Purines; D000068677:Sildenafil Citrate; D013450:Sulfones
chemical_list: D002247:Carbon Isotopes; D004304:Dosage Forms; D009587:Nitrogen Isotopes; D019999:Pharmaceutical Solutions; D010879:Piperazines; D011522:Protons; D011687:Purines; D013450:Sulfones; D000068677:Sildenafil Citrate