Anomalous AlCl3 induced U.V. shift of C-alkylated polyphenols

Phenolic Compounds of the Mulberry Tree and Related Plants

“…Presence of aluminum chloride induced a bathochromic shift of the 281 nm maximum. SHERIF et al had reported earlier that the aluminum chlorideinduced shift was not observed in the UV spectra of compounds containing a prenyl substituent ortho to a chela ted hydroxyl group (113). These data, together with the fact that chalcomoracin (103) Fig.…”

“…If the lH-NMR spectrum is taken into account, the absorption at about 285 nm can be ascribed to two conjugated carbonyl groups which are hydrogen bonded. These results led to the assumption that a prenyl unit is substituted on one of the positions adjacent to the two hydrogen bonded hydroxyl groups (113). From the spectral evidence, sanggenon C (164) seemed to be a Diels-Alder type adduct having a sanggenon A partial structure.…”

Phenolic Constituents of Licorice (Glycyrrhiza Species)

“…Various methods exist for determining the position of substitution, such as (a) the Gibbs test for ftavonoids having no hydroxyl group at C-2' or C-3', (b) the anomalous aluminum induced UV shift, (c) cyclization reactions (6-prenylftavonoids afford two products because of cyclization to 5-0H or 7-0H, 8-prenylftavonoids afford only one product by cyclization to 7-0H), (d) chemical shifts of the vinyl methyl signals of the prenyl group in the IH NMR spectra (this is only appropriate for flavanones), (e) chemical shifts of an aromatic proton on ring A and the methylene protons of the prenyl group (useful for flavones and isoflavones), (I) shifts of chromene protons after acetylation of a 5-hydroxyl group (for this opportunity for a cyclization reaction must exist), (g) chemical shifts of C-6 and C-8 carbons, etc. (398)(399)(400)(401)(402)(403)(404)(405). These methods are not always applicable as shown in Table 4 and may therefore lead to errors.…”

“…using UV spectrometry (383, 415) since SHERIF et aZ. had reported earlier that 6-alkyl(alkenyl)flavonoids do not exhibit the aluminum-induced shift due to chelation as a result of steric hindrance (399). However, the chemical shifts of the 5-0H of the Morus flavones indicated that the compounds were actually 6-geranylflavones.…”

Complete 13C and 1H NMR spectral assignments of two isoflavones from the roots of Dalbergia horrida

“…We report here the complete 1 H NMR and 13 C NMR spectra of dalspinin (1) and dalspinosin (2). In the case of 5,7-dihydroxyflavonoids, a few reported techniques have been useful in determining the positions of the substituents at C-6 or C-8 of flavonoids, including the Gibb's test, 5 aluminium chloride-induced UV shift, 6,7 chemical shift of the 5-OH signal 8 -10 and the chemical shift of the lone A-ring proton. 11 In the present study, the complete assignments of the protonated and non-protonated carbons and the position of the methoxyl group at C-6 in both 1 and 2 were assigned by interpretation of data from 2D NMR experiments such as HMQC and HMBC.…”