Sinapate/sinapic acid

Ionization can be improved in many cases by placing the sample in a matrix formed from sinapic acid, nicotinic acid, or other materials. This variant of laser desorption is known as matrix-assisted laser desorption ionization (MALDI). The vaporized acids transfer protons to sample molecules (M) to produce protonated ions [M + H]+. 

Sinapine acid sulphate, CjgH240jN. HSO4. SHjO, crystallises in leaflets, m.p. 127° (188°, dry). The thiocyanate, CigHj OjN. SCN. HjO, forms pale yellow needles, m.p. 178° iodide, m.p. 185-6°. When the thiocyanate is warmed with alkalis there is formed choline and sinapic acid, the acid was investigated by Remsen and Coale, and... 

Recent scientific investigations of natural polyphenols have demonstrated their powerful antioxidant property (Niki et al, 1995). Several classes of polyphenols have been chemically identified. Some of these are grape polyphenols, tea polyphenols, soy polyphenols, oligomeric proanthocyanidines (OPA) and other natural polyphenols of the flavone class. Rice bran polyphenols are different from the above in that they are p-hydroxy cinnamic acid derivatives such as p-coumaric acid, ferulic acid and p-sinapic acid. Tricin, a flavone derivative, has also been isolated from rice bran. 

Among the hydroxycinnamic acids, anthocyanins acylated with sinapic acid are not widespread in foods they have been isolated only in black carrots " and red cabbages." Anthocyanins that are acylated with p-hydroxybenzoic acid were only found in black carrots " and sweet potatoes. This acyl group was located within the 6 position of a glucoside moiety. 

Gupta JK, C Jebsen, H Kneifel (1986) Sinapic acid degradation by the yeast Rhodotorula graminis. J Gen Microbiol 132 2793-2799. 

Takahama, U. Oniki, T. Effects of ascorbate on the oxidation of derivatives of hydroxycinnamic acid and the mechanism of oxidation of sinapic acid by cell wall-bound peroxidases. Plant Cell Physiol. 1994, 35, 593-600. 

Hydroxy cinnamic acids are included in the phenylpropanoid group (C6-C3). They are formed with an aromatic ring and a three-carbon chain. There are four basic structures the coumaric acids, caffeic acids, ferulic acids, and sinapic acids. In nature, they are usually associated with other compounds such as chlorogenic acid, which is the link between caffeic acid and quinic acid. 

The MALDI-TOF technique was first developed for the analysis of large biomolecules (Karas and others 1987). This technique presents some interesting characteristics. Of these, the high speed of analysis and the sensitivity of the technique have been pointed out as important advantages compared with other methods. In MALDI the samples are cocrystallized with a matrix that is usually composed of organic compounds, such as 3,5-dimethoxy-4-hydroxycinnamic acid (sinapic acid), 2, 4, 6 -trihydroxyacetophenone, a-cyano-4-hydroxycinnamic acid (alpha-cyano or alpha-matrix), and 2,5-dihydroxybenzoic acid (DHB). After the cocrystallization, the laser is fired and the matrix absorbs energy and allows a soft ionization of the samples. Afterward the ions are analyzed by a TOF mass spectrometer. 

A series of subsequent reactions after PAL first introduces a hydroxyl at the 4-position of the ring of cinnamic acid to form p- or 4-coumaric acid (i.e., 4-hydroxycinnamic acid). Addition of a second hydroxyl at the 3-position yields caffeic acid, whereas O-methylation of this hydroxyl group produces ferulic acid (see Fig. 3.3). Two additional enzymatic reactions are necessary to produce sinapic acid. These hy-drocinnamic acids are not found in significant amounts in plant tissue because they are rapidly converted to coenzyme A esters, or glucose esters. These activated intermediates form an important branch point because they can participate in a wide range of subsequent reactions. 

The 4-coumarate CoA ligase (4CL EC 6.2.1.12) enzyme activates 4-coumaric acid, caffeic acid, ferrulic acid, and (in some cases) sinapic acid by the formation of CoA esters that serve as branch-point metabolites between the phenylpropanoid pathway and the synthesis of secondary metabolites [46, 47]. The reaction has an absolute requirement for Mg " and ATP as cofactors. Multiple isozymes are present in all plants where it has been studied, some of which have variable substrate specificities consistent with a potential role in controlling accumulation of secondary metabolite end-products. Examination of a navel orange EST database (CitEST) for flavonoid biosynthetic genes resulted in the identification of 10 tentative consensus sequences that potentially represent a multi-enzyme family [29]. Eurther biochemical characterization will be necessary to establish whether these genes have 4CL activity and, if so, whether preferential substrate usage is observed. 

Figure 6. Separation of free phenolic acids. 1, Caffeic acid 2, p-coumaric acid 3, sinapic acid. Column 18 cm x 0.22 mm I.D. 3-um Spherisorb ODS. Mobile phase methanol-water-acetic acid (20 75 5). Detection TIC (ions of m/z <60 suppressed). Ion source temperature 210 C.

Pg, pelargonidin Cy, cyanidin Dp, delphinidin Pn, peomdin Pt, petumdin Mv, malvidin glc, glucose gal, galactose xyl, xylose rha, rhamnose cou, p-coumaric acid fer, ferulic acid sin, sinapic acid mal, malonic. 

Notes ace, acetic acid oxa, oxalic acid mal, malonic acid sue, succinic acid mly, malic acid hba,/ -OH-benzoic acid gao, gallic (tri-OH-benzoyl) acid cum, / -coumaric acid caf, caffeic acid fer, ferulic acid sin, sinapic acid hca, 3,5-diOHcinnamic acid tar, tartaric acid ara, arabinose xyl, xylose rha, rhamnose gal, galactose glc, glucose glu, glucuronic acid 2-(xyl)glc, sambubiose 2-(xyl)gal, lathyrose 2-(rha)glc, neohesperidose 6-(rha)gal, robinose 6-(rha)glc, rutinose 2-(glc)glc, sophorose 3-(glc)glc, laminariobiose 6-(glc)glc, gentiobiose. 

Present at the 3-hydroxyl of kaempferol in mono- or diacylated form with sinapic acid. 

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