Structure elucidation of a new isoflavone by exclusive use of super(1)H NMR measurements

The leaves of Piscidia carthagenensis provided new 7,2',5'-trimethoxy-3',4'-methylenedioxy isoflavone (1), admixed with known 6,7-dimethoxy-3',4'-methylenedioxyisoflavone (2), and 5,4'-dihydroxy-7,2',5'-trimethoxyisoflavone (3), which were separated by ex...

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Bibliographic Details
Published in:Magnetic resonance in chemistry 2015-01, Vol.53 (10), p.860-865
Main Authors: Ortega, Alfredo R, Toscano, Ruben A, Hernandez-Barragan, Angelina, Alvarez-Cisneros, Celina, Joseph-Nathan, Pedro
Format: Article
Language:English
Subjects:
Crystal structure
Crystallography
Diffraction
Isoflavones
Nuclear magnetic resonance
Polymorphism
Solid state
Triclinic crystals
X-rays
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Summary:The leaves of Piscidia carthagenensis provided new 7,2',5'-trimethoxy-3',4'-methylenedioxy isoflavone (1), admixed with known 6,7-dimethoxy-3',4'-methylenedioxyisoflavone (2), and 5,4'-dihydroxy-7,2',5'-trimethoxyisoflavone (3), which were separated by extensive fractional solubillization. Selective irradiation of the H-5 "singlet" of 2 allowed distinction of the two methoxy group signals, whose chemical shift difference is only 0.004 ppm (1.2 Hz at 300 MHz). The super(1)H and super(13)C NMR data of 3 were assigned with the aid of HETCOR and gHMBC measurements. Although 1 looked inhomogeneous in the solid state, its solution structure followed from super(1)H NMR measurements, where it looked homogeneous. To clarify the solid state aspect and confirm the structure of 1, two types of crystals were mechanically separated and subjected to single crystal X-ray diffraction measurements. This study revealed polymorphism because of the concomitant presence of orthorhombic and triclinic crystals, but showed no atropisomerism. The structure of 3 was also verified by X-ray diffraction crystallography.
ISSN:0749-1581
1097-458X
DOI:10.1002/mrc.4278