Flavonoids acylation

Flavonoids acylated with hydroxycinnamic acids show a UV spectrum of the flavonoid overlapped with that of the acid, this last being the main one. They are characterized by a maximum with a high absorption 330nm (310-335 nm), and eventually can show a small maximum that coincides with the flavonoid band II ( 255-268 nm) and a shoulder at higher wavelengths that reflects the flavonoid Band I (Vallejo et ah, 2004). In polyacylated flavoneglycosides, in which two or even three hydroxycinnamate molecules are attached to the flavonoid... 

In flavonoids acylated with aliphatic acids, the most common acids are acetic and malonic. In the MS fragmentation of the dicarboxylic acids (as malonic acid), a first loss of 44 mass units is observed (loss of the carboxylic radical, CO2), and this is due to decarboxylation. 

The sugars attached to the anthocyanin molecule are in order of relative abundance glucose, rhamnose, galactose, xylose, arabinose, and glucuronic acid. The molecule may also contain one or more of the acyl acids p-coumaric, caffeic, and ferulic or the aliphatic acids malonic and acetic esterified to the sugar molecules. Extracts of anthocyanins invariably contain flavonoids, phenolic acids, catechins and polyphenols. The net result is that it is impossible to express the chemical composition accurately. Specifications usually present tinctorial power, acidity, per cent solids, per cent ash and other physical properties. 

The cacao plant, Theobroma cacao, is the source of chocolate which is well known and highly prized in international commerce. The cacao pods contain beans which are fermented and pressed to provide a brown liquid which is the raw material for chocolate. The press cake is ground and sold as cocoa and it also provides a brown colorant. The pods, beans, shells, husks and stems have also been suggested as colorants. They contain a very complex mixture of acyl acids, leucoanthocyanins, flavonoid polymers, tannins, and catechin-type polymers.33... 

The anthocyanins exist in solution as various structural forms in equilibrium, depending on the pH and temperature. In order to obtain reproducible results in HPLC, it is essential to control the pH of the mobile phase and to work with thermostatically controlled columns. For the best resolution, anthocyanin equilibria have to be displaced toward their flavylium forms — peak tailing is thus minimized and peak sharpness improved. Flavylium cations are colored and can be selectively detected in the visible region at about 520 nm, avoiding the interference of other phenolics and flavonoids that may be present in the same extracts. Typically, the pH of elution should be lower than 2. A comparison of reversed-phase columns (Ci8, Ci2, and phenyl-bonded) for the separation of 20 wine anthocyanins, including mono-glucosides, diglucosides, and acylated derivatives was made by Berente et al. It was found that the best results were obtained with a C12 4 p,m column, with acetonitrile-phosphate buffer as mobile phase, at pH 1.6 and 50°C. 

Typical NMR Chemical Shift Values of Acyl Moieties of Acylated Flavonoid Glycosides Recorded in DMSO-c/6 (D) or CD3OD (M) with Various Proportions of CF3COOD (T) or Acetone (A)... 

The application of standardized UV (or UV-Vis) spectroscopy has for years been used in analyses of flavonoids. These polyphenolic compounds reveal two characteristic UV absorption bands with maxima in the 240 to 285 and 300 to 550 nm range. The various flavonoid classes can be recognized by their UV spectra, and UV-spectral characteristics of individual flavonoids including the effects of the number of aglycone hydroxyl groups, glycosidic substitution pattern, and nature of aromatic acyl groups have been reviewed in several excellent books. ... 

Teng, R. et al.. Two new acylated flavonoid glycosides from Morina nepalensis var. alba Hand.-Mazz, Magn. Reson. Chem., 40, 415, 2002. 

Parejo, I. et al.. Characterization of acylated flavonoid-O-glycosides and methoxylated flavonoids from Tagetes Maxima by liquid chromatography coupled to electrospray ionization tandem mass spectrometry. Rapid Commun. Mass Spectrom., 18, 2801, 2004. 

Many other compounds are involved in flavonoid biosynthesis in some species, for example, as donors for methylation or aromatic or aliphatic acylation. For intact plants, these are generally accepted to be available in the cell for the reaction to proceed if the appropriate modification activity is present. 

Schwinn, K.E. et al.. Expression of an Antirrhinum majus UDP-glucose flavonoid-3-0-glucosyltransferase transgene alters flavonoid glycosylation and acylation in lisianthus (Eustoma grandiflorum Grise.). Plant ScL, 125, 53, 1997. 

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