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.
Subject(s)
Candicidin/chemistry , Molecular Structure , Humans , Magnetic Resonance SpectroscopyABSTRACT
The absolute configurations of all the stereogenic centers of the antibiotic mycoheptin A(2) were established upon previously elaborated general procedure, consisting of DQF-COSY, NOESY, ROESY, HSQC and HMBC experiments as major tools. The structure of mycoheptin A(2) without stereochemistry of its aglycone has been reported before.
Subject(s)
Actinomyces/chemistry , Anti-Bacterial Agents/chemistry , Polyenes/chemistry , Magnetic Resonance Spectroscopy , Molecular Structure , StereoisomerismABSTRACT
The relative configurations of four stereogenic centers of the C33-C42 fragment of niphimycin A were assigned as 2S*, 3R*, 4S* and 6S*, based upon (1)H NMR analysis with double-quantum filtered COSY and nuclear Overhauser spectroscopy experiments. These data were then correlated with absolute configurations at C36 and C38 of niphimycin A, which were declared previously as 36S and 38S [3]. This allowed for the assignment of the absolute configurations at C34 and C35 of niphimycin A as 34S and 35R.
Subject(s)
Anti-Bacterial Agents/chemistry , Guanidines/chemistry , Magnetic Resonance Spectroscopy , Molecular StructureABSTRACT
D-Glucose, D-mannose and L-rhamnose were reacted with a racemic mixture of 2-butanol, and the resulting alpha-glycosides were analyzed by 1H NMR with COSY and NOESY experiments. Conformational analysis of alpha-glycosidic bonds performed with molecular modeling and appropriate heteronuclear long-range coupling measurements and combined with analysis of dipolar couplings observed in NOESY spectra allowed the assignment of absolute configuration in the aglycones of elucidated alpha-glycosides.
