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Extensive NMR Studies (extensive + nmr_studies)
Selected AbstractsTemperature and solvent dependent NMR studies on mangiferin and complete NMR spectral assignments of its acyl and methyl derivativesMAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2006Shaheen Faizi Abstract 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. Copyright © 2006 John Wiley & Sons, Ltd. [source] Pakistolides A and B, Novel Enzyme Inhibitory and Antioxidant Dimeric 4-(Glucosyloxy)Benzoates from Berchemia pakistanicaHELVETICA CHIMICA ACTA, Issue 2 2004Naveen Mukhtar Pakistolides A and B, novel dimeric , -(glucosyloxy)benzoates were isolated from Berchemia pakistanica and assigned structures 1 and 2 on the basis of extensive NMR studies. In addition, the known compounds 7,5,-dimethoxy-3,5,2,-trihydroxyflavone (=3,5-dihydroxy-2-(2-hydroxy-5-methoxyphenyl)-7-methoxy-4H -1-benzopyran-4-one), 4,,5-dihydroxy-3,6,7-trimethoxyflavone (=5-hydroxy-2-(4-hydroxyphenyl)-3,6,7-trimethoxy-4H -1-benzopyran-4-one), 5,6-dihydroxy-4,7-dimethoxy-2-methylanthracene-9,10-dione, and 1,3,4-trihydroxy-6,7,8-trimethoxy-2-methylanthracene-9,10-dione were reported for the first time from the genus Berchemia. Both 1 and 2 showed significant , -glucosidase and lipoxygenase inhibitory activities, while 2 also showed antioxidant potential. [source] Structure determination of new steroids from Abutilon pakistanicum by NMR techniquesMAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2008Munawar Hussain Abstract Two new steroids provisionally named as pakisteroid-A (1) and pakisteroid-B (2) have been isolated in crystalline form from Abutilon pakistanicum. Their structures have been assigned as 3- O -,- D -glucopyranosyl-stigmasta-5,11(12)-diene (1) and 24,-ethylcholesta-5, 9(11), 22E-trien-3,-benzoate (2), respectively through extensive NMR studies. Copyright © 2008 John Wiley & Sons, Ltd. [source] Structural determination of diterpenes from Daphne genkwa by NMR spectroscopyMAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2006Kalsoom Akhtar Abstract Five daphnane type diterpenes have been isolated from the chloroform soluble fraction of Daphne genkwa. The structure of the new compound (1) was assigned as 5,-hydroxyresiniferonol-6,,7,-epoxy-12,-acetoxy-9,13,14- ortho -2E -decenoate by extensive NMR studies. Copyright © 2006 John Wiley & Sons, Ltd. [source] | ||||||||||