Synthesis of 8-C-glucosylflavones.
The syntheses of orientin, parkinsonin A, isoswertiajaponin, and parkinsonin B, which are 8-C-beta-D-glucopyranosyl-3',4',5,7-tetrahydroxyflavone, 5-methyl orientin, 7-methyl orientin, and 5,7-dimethyl orientin, respectively, are reported herein. The C-glucosyl phloroacetophenone derivatives were obtained via a regio- and stereoselective O-->C glycosyl rearrangement. Aldol condensation of the C-glucosyl phloroacetophenone derivatives with 3,4-bisbenzyloxybenzaldehyde afforded the corresponding C-glucosylchalcones. Construction of the flavone system by reaction with I(2)-Me(2)SO, followed by the elimination of the 5-benzyl protecting group in the flavone structure, yielded an orientin derivative and a isoswertiajaponin derivative. Methylation of the orientin derivatives with dimethyl sulfate afforded the parkinsonin A derivative, the isoswertiajaponin derivative, and the parkinsonin B derivative. Finally, hydrogenolysis of these C-glucosylflavone derivatives led to the four 8-C-glucosylflavones. The NMR spectra of these C-glucosylflavones showed a duplication of signals corresponding to a major rotamer, along with a minor one. Based on NOESY experiments in Me(2)SO at ambient temperature, they adopted conformations in which the H-2"and H-4" protons in the glucose moiety were oriented toward the B-ring in the flavone structure.
Kumazawa
T
T
Department of Chemistry and Chemical Engineering, Faculty of Engineering, Yamagata University, Jonan 4-3-16, Yonezawa, Yamagata 992-8510, Japan. kumazawa@chem.yz.yamagata-u.ac.jp
Kimura
T
T
Matsuba
S
S
Sato
S
S
Onodera
J
J
D000975:Antioxidants / Q000138:chemical synthesis / Q000737:chemistry; D005419:Flavonoids / Q000138:chemical synthesis* / Q000737:chemistry; D005960:Glucosides / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010944:Plants / Q000737:chemistry
D000975:Antioxidants; D005419:Flavonoids; D005960:Glucosides; C065886:orientin