Tokunaru Horie

13C NMR spectral assignment of the A-ring of polyoxygenated flavones

Abstract The 13 C NMR spectra of polyhydroxyflavones were systematically examined by using about 70 examples which have a 4-methoxyphenyl B-ring, such as 5,6,7-, 5,7,8 and 5,6,8-trioxygenated and 5,6,7,8-tetraoxygenated flavones and flavonols, and the following results were obtained. In the 13 C NMR spectra of flavones, the signals at the 2-, 3- and 4-positions in the C-ring were hardly affected by the substituents on the A-ring except for those at the 5-position and shifted regularly by introduction of a methoxy or hydroxy group at the 3-position. The signals at the 5- to 10-positions in the A-ring were greatly affected by the substituents and oxygenated patterns on the A-ring and exhibited the respective characteristic pattern reflecting the A-ring substituents without the effects of the substituents on the B- and C-rings. The substituent effects on the A-ring were estimated from the spectral data. Consequently, it is found that the structures of polyhydroxyflavones can be correctly defined by their 13 C NMR spectral assignment. Additionally, we examined the structures of some natural flavones previously reported.

Arachidonate 5-lipoxygenase and its new inhibitors

The 5-lipoxygenases of guinea pig peritoneal polymorphonuclear leukocytes and of rat basophilic leukemia cells have been solubilized, purified partially by affinity chromatography, and shown to convert arachidonic acid principally to 5-hydroperoxy-6,8,11,14- eicosatetraenoic acid. The activity of both 5-lipoxygenases is calcium dependent and enhanced by adenosine triphosphate and other nucleotides in the presence of calcium ion. Both 5-lipoxygenase activity and leukotriene generation by sensitized guinea pig lung tissue challenged with antigen were suppressed substantially by specific benzoquinone and flavonoid inhibitors. The in vivo significance of the findings will be explored with potent and selective lipoxygenase inhibitors, which are delineated in the 5-lipoxygenase model systems.

Synthesis of 5,8-dihydroxy-6,7-dimethoxyflavones and revised structures for some natural flavones

Abstract Six 5,8-dihydroxy-6,7-dimethoxyflavones and three 8-hydroxy-5,6,7-trimethoxyflavones were synthesized from 2′,5′-dihydroxy-3′,4′,6′-trimethoxyacetophenone by adapting the selective O -alkylation and dealkylation, and the differentiation between the flavones and their isomeric 6-hydroxyflavones was clarified by 1 H NMR and UV spectra. Four natural flavones proposed as 5,8-dihydroxy-6,7-dimethoxyflavones, must have other structures and three are shown to be the isomeric 5,7-dihydroxy-6,8-dimethoxyflavones. A flavone, isolated from Ageratum conyzoides , is correctly identified as 8-hydroxy-5,6,7,3′,4′,5′-hexamethoxyflavone, but the structure of a flavone, isolated from Helichrysum , is revised to the isomeric 7-hydroxy-5,6,8-trimethoxyflavone.

DEHYDRATION INDUCED BY INTRAMOLECULAR REDOX CHARACTER OF A STABLE ALLYLIDENETRIBUTYLPHOSPHORANE

Abstract An air and moisture stable P-ylide, dimethyl fluorenylidenetributylphosphoranylidene-succinate acts as a new type of dehydrating agent for synthesizing acid anhydride, ester, and amide. The ylide is most suitable for inducing these reactions in analogous P-ylides. The reaction is considered to be caused by internal reductive and oxidative nature of the P-ylide.

Three flavone glycosides from citrus sudachi

Abstract Three flavone glycosides, sudachiins B, C and D, were isolated from the green peel of Citrus sudachi . On the basis of UV, 1 H NMR and 13 C NMR spectral data sudachiins B and C were identified as sudachiin A 6″- (3-hydroxy-3-methyl)glutarateand 7- O -β-D-glucosyl sudachitin 6″-(3-hydroxy-3-methyl)glutarate, respectively. Sudachiin D was found to be a unique glycoside in which sudachiin A and 7- O -β-D-glucosylsudachitin were esterified at their 6″-positions with 3-hydroxy-3-methylglutaric acid.

Revised structure of a natural flavone from Ageratum conyzoides

Abstract The structure of a natural flavone from Ageratum conyzoides , assumed to be 5,6,8,3′,4′,5′-hexamethoxyflavone, is revised to 5,6,7,3′,4′,5

3,5-Dihydroxy-7,8-dimethoxyflavones and revised structures for some natural flavones

Abstract Seven 3,5-dihydroxy-7,8-dimethoxyflavones were synthesized from the corresponding 3,5,7,8-tetramethoxyflavones using selective demethylation and protection of 3- or 5- methoxy group, and their properties were clarified by the UV and 1 H NMR spectral data. The structures of the four natural flavones were revised as follows: the three flavones, isolated from Heteromma simplicifolium , are 5,7-dihydroxy-3,8,3′,4′-tetramethoxyflavone, 5,7-dihydroxy-3,8,3′,4′,5′-pentamethoxyflavone, and 5,7,4′-trihydroxy-3,8,3′-trimethoxyflavone, respectively; the flavone glycoside, isolated from Rudbeckia bicolor , is proposed to be 3,5,4′-trihydroxy-6,7-dimethoxyflavone 3-rhamnoside.

Diinsertion of fluorenylidene into a sulfur-sulfur bond of diaryl disulfides

Abstract Upon irradiation (>340 nm) of a benzene solution of diazofluorene with di- p -tolyl- or di- p -anisyl disulfide, the corresponding 9,9′-bis(arylmercapto)bifluorenyl was afforded in moderate to good yield accompanied by formation of 9,9′-bis(arylmercapto)fluorene. The major reaction pathway is considered to be a disulfur ylide formation followed by two times of successive Stevens rearrangement or by concerted electron redistribution via [2,3]sigmatropic rearrangement.

Revised structure of a natural flavone from Tephrosia candida

Abstract The structure of a natural flavone, candirone from Tephrosia candida , assumed to be 5,4′-dihydroxy-3,6,8-trimethoxyflavone, is revised to 5,4′-dihydroxy-3,6,7-trimethoxyflavone, penduletin on the basis of spectral data.

Revised structure of a natural flavone from Artemisia lanata

Abstract The structure of a natural flavone from Artemisia lanata , thought to be 3,5-dihydroxy-7,8,3′,4′-tetramethoxyflavone, is revised to 5,3′-dihydroxy-3,6,7,4′-tetramethoxyflavone on the basis of spectral data.