Glucose esters

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. 

Arsenate, which can apparently serve as glucose acceptor to the enzyme-D-glucose complex but which does not form a stable glucose ester, causes the rapid decomposition of both sucrose and D-glucose-l-phosphate in accordance with the following equations 44... 

Esterification of 2,4-D with plant constituents via conjugation formed the p-D-glucose ester of 2,4-D (Thomas et ah, 1964). 

Plant. Degrades in plants to N-glucoside, glucose ester, conjugates, and insoluble residues (Ashton and Monaco, 1991). 

It therefore appeared that a general mechanism for enzymatic esterification of phenolic acids with glucose was operative, whereas the reaction with other alcoholic moieties proceeded via carboxyl-activated acyl derivatives. [In this context it should be emphasized that glucose esters must not be confused with glucosides different enzymes are involved in the biosynthesis of these two types of phenolic glucose derivatives (36)]. 

Arjunglucosides I (163) and II (164) from Terminalia arjuna are the glucose esters of arjungenin and arjunolic acid respectively. "" The full details of the structure elucidation of arjungenin are included in this paper. Three lyxosides (165)—(167) have been obtained, together with 16a,21/8,22a,28-tetrahydroxyolean-12-en-3-... 

Crocus sativus L. Shi Hong Hua (Saffron) (root) Crocetin, crocetin geniobiose glucose ester, crocetin di-glucose ester, crotin, lycopene, beta-carotene.33-450 Ameliorating effect on ethanol-induced impairment of learning and memory. 

Crocetin di-glucose ester Crocetin geniobiose glucose ester... 

Fig- (3 ). Seasonal variation of crocetin glucose esters in C. sativus L. 

MeOH gradient solution (1 0 to 0 1) to yield crocetin di-glucose ester (0.41 g), crocetin gentiobiose glucose ester (5.10 g) and crocin (5.69 g). 

Crocin of 50 mg/kg ameliorated the blocking effect of ethanol on the LTP at approximately 84% compared to the control as indicated in Fig. (10). Crocetin gentiobiose glucose ester also antagonized the blocking effect of ethanol on the LTP dose-dependently. But die intensity is not so strong, about a half of crocin when compared the intensity of 50 mg/kg. On the other hand, crocetin di-glucose ester did not remove the inhibitory effect of ethanol on the LTP. 

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-... 

Saffron extract contains many carotenoids such as crocetin, crocetin di-glucose ester, crocetin gentiobiose glucose ester, and crocin (crocetin di-gentiobiose ester), whose chemical structures are shown in Figure 58.1. These carotenoids scavenge free radicals, especially superoxide anions, and so may protect cells from oxidative stress. Indeed, it has been demonstrated that these carotenoids are useful in sperm cryoconservation and in protecting heptocytes from toxins. 

FIGURE 58.1 Chemical structures of crocetin (A), crocetin diglucose ester (B), crocetin gentiobiose glucose ester (C), and crocin (D). 

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