Sinapic acid esters

Lorenzen, M., Racicot, V., Stack, D., Chappie, C., 1996, Sinapic acid ester metabolism in wild type and a sinapoylglucose-accumulating mutant of Arabidopsis, Plant Physiol. 112 1625-1630. 

Linscheid, M., Wendisch, D. and Strack, D. (1980) The structures of sinapic acid esters and their metabolism in cotyledons of Raphanus sativus. Z. Naturforsch., 35c, 907. 

The analysis of mutants of the phenylpropanoid pathway in Arabidopsis, as outlined in this review, has led to numerous revisions of the pathway over the past decade. The presently accepted pathway clarifies some of the contradictory data of the past, but also poses new questions for which we do not yet have answers. For example, a growing body of evidence suggests that neither ferulic acid nor sinapic acid are intermediates in phenylpropanoid biosynthesis. This is problematic in that many plant cell walls contain esterified ferulic acid, " and sinapic acid esters are major soluble secondary metabolites in Arabidopsis leaves and seeds. If the most current model of the pathway is correct, how are these molecules synthesized ... 

STRACK, D., Sinapic acid ester fluctuations in cotyledons of Raphanus sativus., Z. PflanzenphysioL, 1977, 84,139-154. 

Sakushima A, Coskun M, Tanker M, Tanker N. A sinapic acid ester from Boreava orientalis. Phytochemistry 1994 35 1481-1484. 

Enzymatic reduction of sinapic acid ester content in canola meal using polyphenol oxidase from the fungus T. versicolor... 

Lacki K, Duvnjak Z. 1996. Comparison of 3 methods for the determination of sinapic acid ester content in enzymatically treated canola meals. Applied Microbiology and Biotechnology, 45(4) 530-537. 

Thies W. 1991. Determination of the phytic acid and sinapic acid esters in seeds of rapeseed and selection of genotypes with reduced concentrations of these compounds. Lipid/Fett, 93(2) 49-52. 

The main phenolic compounds of rapeseed meal are commonly sinapic acid (Figure 15.3a) and its derivatives—sinapine the choline ester of sinapic acid (Figure 15.3b), or as the glucosidic ester, glucopyranosyl sinapate. About 80-90% of all the phe-nolics in the meal are sinapic acid esters (SAEs) as discussed earlier. Thus, 70% methanolic rapeseed meal extracts of the meal have been classified into free-pheno-lics, esterifled phenolics and released-phenolics according to Krygier et al. (1982). Krygier et al. (1982) extracted free and esterified phenolics, which were methanol soluble and demonstrated that only a small fraction of the total phenolic compounds of rapeseed occurs as free sinapic acid (Koski et al., 2002 Vuorela et al., 2003). 

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. 

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]. 

Broccoli florets and leafy cruciferous vegetables will be the major source of sugar esters and of conjugated sinapic acid (10 mg/100 g). Tomato and tomato products are likely to be the major source of glucosides at up to 13 mg/100 g in total, and possibly the second richest source of conjugate p-coumaric acid (3 mg/100 g). 

Polyphenolic phytochemicals are classified into three major groups phenolic acids, fla-vonoids, and tannins. Phenolic acids include hydroxybenzoic, hydroxyphenylacetic, and hydroxycinnamic acids (Figure 11.3.3). Hy-droxycinnamic acids are the most widely distributed of the phenolic acids in plant tissues. The important hydroxycinnamic acids are p-coumaric, caffeic, ferulic, and sinapic acids. Most hydroxycinnamic acids are rarely encountered in the free state in nature. They occur as glucose esters and, more frequently, as quinic acid esters (Herrmann, 1989). Phenolic acids are usually detected at wavelengths between 210 and 320 nm. In general, the polarity of phenolic acids is increased mainly by the hy-... 

As discussed in Section 7, the general phenylpropanoid pathway originally included the biosynthesis of the hydroxycinnamic acids caffeic acid (3.32), femlic acid (3.33), 5-hydroxyferulic acid (3.34), and sinapic acid (3.35) from />coumaric acid (3.30), as well as the corresponding CoA-esters... 

Figure 3-13. Sinapoyl ester metabolism catalyzed by the enzymes (a) UDP-glucose sinapic acid glucosyltransferase (SGT), (b) sinapoylglucose malate sinapoyltransferase (SMT), (c) sinapoylglucosexholine sinapoyltransferase (SCT), and (d) sinapoylcholinesterase (SCE).

Suberins or polyestolides are related to cutins. These are complex polymers composed of co-hydroxy monobasic acids linked by ester bonds. They also contain a,P-dibasic acids esterified with diols, as well as ferulic and sinapic acid moieties. Suberins are enriched with molecules having 16 and 18 carbon atoms. They also have ethyl-enic and hydroxyl functionalities, and ester and ether cross-linking can occur. 

Suberins. The cork cells in the outer bark contain polyestolides or su-berins. The suberin content in the outer layer of the cork oak bark (cork) is especially high and amounts to 20-40% in the periderm of birch bark. Polyestolides are complicated polymers composed of co-hydroxy monobasic acids which are linked together by ester bonds. In addition, they contain a,/3-dibasic acids esterified with bifunctional alcohols (diols) as well as ferulic and sinapic acid moieties. The chain lengths vary but suberins are enriched with molecules having 16 and 18 carbon atoms. There are also double bonds and hydroxyl groups through which ester and ether cross-links are possible. The outer layer of the epidermis contains so-called cutin, which is heavily branched and has a structure similar to suberin. 

Sinapic acid (and esters) c h12o, Haluk and Metche 1986... 

Hydroxycinnamic acids possess a C6-C3 skeleton and formally belong to the group of phenylpropanoids. The different compounds present in wine are mainly derived from the hydroxycinnamic acids caffeic acid, p-coumaric acid, ferulic acid, and sinapic acid (Fig. 9C.2). These derivatives can be present in cis- and trans-configured forms, while the trans forms are more stable and therefore more prevalent. In wine HCA are present in low amounts in their free form, while the depside forms, i.e. esters of l-(-i-)-tartaric acid, are predominant. The ubiquitous chlorogenic acids, esters of HCA and quinic acid, cannot be found in wine but are replaced by the tartaric acid esters instead (Ong and Nagel 1978 Singleton et al. 1978 Somers etal. 1987). 

L-Phenylalanine,which is derived via the shikimic acid pathway,is an important precursor for aromatic aroma components. This amino acid can be transformed into phe-nylpyruvate by transamination and by subsequent decarboxylation to 2-phenylacetyl-CoA in an analogous reaction as discussed for leucine and valine. 2-Phenylacetyl-CoA is converted into esters of a variety of alcohols or reduced to 2-phenylethanol and transformed into 2-phenyl-ethyl esters. The end products of phenylalanine catabolism are fumaric acid and acetoacetate which are further metabolized by the TCA-cycle. Phenylalanine ammonia lyase converts the amino acid into cinnamic acid, the key intermediate of phenylpropanoid metabolism. By a series of enzymes (cinnamate-4-hydroxylase, p-coumarate 3-hydroxylase, catechol O-methyltransferase and ferulate 5-hydroxylase) cinnamic acid is transformed into p-couma-ric-, caffeic-, ferulic-, 5-hydroxyferulic- and sinapic acids,which act as precursors for flavor components and are important intermediates in the biosynthesis of fla-vonoides, lignins, etc. Reduction of cinnamic acids to aldehydes and alcohols by cinnamoyl-CoA NADPH-oxido-reductase and cinnamoyl-alcohol-dehydrogenase form important flavor compounds such as cinnamic aldehyde, cin-namyl alcohol and esters. Further reduction of cinnamyl alcohols lead to propenyl- and allylphenols such as... 

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