Sinapic residue

The stability of anthocyanins is increased by acylation (Dougall et al. 1997). These acylated anthocyanins may occur naturally as in the case of an anthocyanin from the purple yam (Yoshida et al. 1991). This anthocyanin has one sinapic residue attached through a disaccharide and was found to be stable at pH 6.0 compared to other anthocyanins without acylation. Dougall et al. (1977) were able to produce stable anthocyanins by acylation of carrot anthocyanins in cell cultures. They found that a wide range of aromatic acids could be incorporated into the anthocyanin. 

Depending on the identity, number and position of the acyl residues, these acids may be divided into the following groups mono-esters of caffeic, p-coumaric and ferulic acid di-, tri- and tetra-esters of caffeic acid [14,15] mixed di-esters of caffeic and ferulic acid or caffeic and sinapic acid [16] mixed esters of caffeic acid with dibasic aliphatic acids (e.g., oxalic, succinic) [17]. 

Finally, a fourth class of alkaloids has been discovered, apparently specific to the leaves of P. Lyallii (57). It consists of two unseparable products, 37 and 38, in the ratio 2 to 1, which readily give lyaloside (23) on mild methanolysis, along with two esters, namely, methyl ferulate and methyl sinapate (39 and 40, respectively). Elucidation of their structure was essentially based on NMR considerations (57). Graphical correlations between 1H- and 13C-NMR spectra, associated with analysis of the residual constant coupling during a step by step [200 Hz per 200 Hz from 0 (TMS) to 2000 Hz] off-resonance procedure, permitted the precise assignment of all the carbon atoms of the products (58). 

The pigmentation of red cabbage is caused by cyanidin derivatives which are acylated with various phenolic acids. Cyanidin 3-sophoroside-5-glucoside and its derivatives acylated with malonic acid and one or two residues of /7-coumaric, ferulic or sinapic acids have also been detected [59 60]. The relative stability of these pigments seems to be related to their degree of acylation. 

Fig. 3.8 Phenolic acids extracted from wheat stubble, wheat straw from half buried litter bags, and wheat stubble/soybean (no-till) soil. Phenolic acids isolated and quantified were caffeic acid (CAF), ferulic acid (FER), p-coumaric acid (PCO), p-hydroxybenzoic acid (POH), sinapic acid (SIN), syringic acid (SYR), and vanillic acid (VAN). Becausep-coumaric acid was so high in comparison to other phenolic acids in wheat residues, data are presented twice, once with p-coumaric acid (a) and once without p-coumaric acid (b). Because phenolic acids were so low in the soil they are also presented in (c). The absence of standard error bars for wheat straw and soil indicates that the error bars are too small to be visible. Figures based on data from Blum et al. (1991, 1992). Plenum Publishing Corporation, data used with permission of Springer Science and Business Media...

In the families of the Apocyanaceae, Loganiaceae, Rubiaceae, and Euphorbiaceae, indole alkaloids of complicated structure are found which can be arranged in different groups. We may take reserpine from Rauwolfia serpentina as an example. A sinapic acid residue is present as part of the molecule, in addition to the basic skeleton of tryptophan and two 5 C units (Fig. 130). 

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