Temperature and solvent dependent NMR studies on mangiferin and complete NMR spectral assignments of its acyl and methyl derivatives.
By employing concerted 1 and 2D NMR techniques, exact NMR spectral assignments have been made of the acyl (2-7) and methyl (8 and 9) derivatives of mangiferin (1) isolated from the leaves of Bombax ceiba. Derivatives 2, 8 and 9 have been reported in literature, while 3-7 represent new compounds. The acetates 2 and 3 were found to be unstable and were converted into the same penta-acetate 4 at room temperature. Extensive NMR studies on mangiferin (1) and its derivatives showed that H-4 exchanges with deuterium of the solvent molecule more easily. This exchange under acidic conditions occurred at that position (C-4) where electrophilic substitution reactions can easily take place. This is the first report describing the exchange of C-4 proton of mangiferin (1), or any other xanthone, with deuterium of solvent molecules.
Faizi
Shaheen
S
International Centre for Chemical Sciences, H.E.J. Research Institute of Chemistry, University of Karachi, Karachi-75270, Pakistan. shaheenfaizi@hotmail.com
Zikr-Ur-Rehman
Sadia
S
Ali
Muhammad
M
Naz
Aneela
A
D000107:Acetylation; D035163:Bombax / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008745:Methylation; D008968:Molecular Conformation; D018515:Plant Leaves / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D013696:Temperature; D044004:Xanthones / Q000737:chemistry* / Q000302:isolation & purification
D012997:Solvents; D044004:Xanthones; C013592:mangiferin