ABSTRACT
Herein, a new method for the elucidation of the absolute configuration of chiral secondary alcohols is proposed. This method is an alternative for a widely used approach reported by Mosher and Dale and similar methods that are based on the 1H NMR shift (δ) changes of protons that are attached to the substituents of the oxymethine carbon atom. The presented method is not based on tracking the chemical shift changes and utilizes stereochemically defined monosaccharides as chiral probes. A secondary alcohol is glycosylated, and the resulting glycoside is subjected to NMR studies. The observation of dipolar couplings between the protons of the monosaccharide moiety and the protons of the secondary alcohol moiety via the NOESY/ROESY spectra enables the determination of the absolute configuration of the oxymethine carbon atom.
Subject(s)
Alcohols/chemistry , Monosaccharides/chemistry , Esters , Glycosides/chemistry , Molecular Structure , Nuclear Magnetic Resonance, Biomolecular , Protons , StereoisomerismABSTRACT
Nystatin A1 , a polyene macrolide antifungal antibiotic, in a slightly basic or acidic solution undergoes an intramolecular transformation, yielding a structural isomer, the translactonization product, iso-nystatin A1 with lactone ring diminished by two carbon atoms. Structural evidence is provided by advanced NMR and Mass Spectrometry (MS) studies. Molecular dynamics simulations and quantum mechanics calculations gave the insight into the course and mechanism of the transformation and its effect on the conformation of the subject molecule. Copyright © 2016 John Wiley & Sons, Ltd.
Subject(s)
Antifungal Agents/chemistry , Nystatin/analogs & derivatives , Nystatin/chemistry , Chromatography, High Pressure Liquid , Isomerism , Lactones/chemistry , Magnetic Resonance Spectroscopy , Mass Spectrometry , Models, Molecular , Molecular Conformation , Molecular Dynamics SimulationABSTRACT
The candicidin D stereostructure was established based on NMR studies including DQF-COSY, ROESY, HSQC and HMBC experiments. The relative configurations of the candicidin D stereogenic centers were assigned as the following: 9R*, 11S*, 13S*, 15R*, 17S*, 18R*, 19S*, 21R*, 36S*, 37R*, 38S*, 40S* and 41S*. The geometry of the heptaene chromophore was defined as 22E, 24E, 26Z, 28Z, 30E, 32E and 34E.
