Abscisic acid structure

Physiologically, violaxanthin is an important component of the xanthophyU cycle a high light stress-induced de-epoxidation of the violaxanthin pool to the more photoprotective zeaxanthin is mediated by violaxanthin de-epoxidase (VDE). Violaxanthin and neoxanthin, an enzymatically (NXS)-produced structural isomer, are the precursors for the abscisic acid (ABA) biosynthetic pathway (Figure 5.3.1, Pathway 4 and Figure 5.3.2). In non-photosynthetic tissues, namely ripe bell peppers, antheraxanthin and violaxanthin are precursors to the red pigments, capsanthin and capsorubin, respectively (Figure 5.3.3B). 

FIGURE 1.5 Structures of auxin and abscisic acid derivatives of cytokinin. 

The second example described here is dormant seeds from Rosa canina. Extracts of these seeds also inhibit germination of seeds of several plants (10). In Figure 5 a scheme is given for extraction and separation oF"three different inhibitor compounds. All these are present in the acid fraction. The first essential step is chromatography on Sephadex LH-20, which separates inhibitor I from inhibitor II and III. Inhibitor I was identified as abscisic acid. The other two inhibitors were separated by methylation with diazomethane, fractional distillation, and column chromatography. The second inhibitor is the a-pyrone 1 . Reaction with diazomethane transforms it into the bi-cyclic compound 19. This bicyclic compound is even more active than the parent a-pyrone 1 . Since we sought structural requirements for bioactivity here also,we tested several synthetic a-pyrones ( 0 - 22) for bioactivity. These compounds had no inhibitory activity. We alio tested the cyclopropane derivatives 23 and 24 In Table II, the bioactivity of the bicyclic compound T9 and two such derivatives is compared. The presence of several carboxylic acid groups seems to be essential (or at least helpful) for bioactivity in this case also. 

X-Ray Crystallography. The crystal and molecular structure of dl-2-cis-A-trans-abscisic acid (7-trans-9-cis, carotenoid numbering) has been determined by the X-ray method. X-Ray crystallographic data are presented for the retinal derivative (107). ... 

Violaxanthin also functions as a precursor to the plant hormone abscisic acid. Compare the structure of the latter (Fig. 22-4) with those of carotenoids. Oxidative cleavage of violaxanthin or related epoxy-carotenoids initiates the pathway of synthesis of this hormone.142 143... 

There are cases where HPLC separation is performed not in order to quantify the alcohols but as a technique for the purification of the analytes to be subjected to further instrumental analysis. This is the case, for example, with the identification and determination of the structure of an abscisic acid in starfruit extract (Averrhoa carambola L.). The separation and purification of the analytes was carried out also with HPLC using a mobile phase of diethyl ether, whereas the structure was elucidated by H and UC-NMR (6). In a similar way, to separate the sterols and alkanols from the unsaponifiable matter from olive oils on a silica column, a gradient composed of hexane/diethyl ether was chosen in an offline system (7), whereas an online HPLC-HRGC system uses as its mobile phase hexane/isopropanol (8). 

Figure 1. Structures of (-)-)-abscisic acid (ABA) and of 2-trans-abscisic acid...

Neoxanthin, a precursor of the plant hormone abscisic acid, is an allenic xantho-phyll recognized as the last product of carotenoid synthesis in green plants. A cDNA for neoxanthin synthase (NSY) was isolated from tomato cv. Philippino using a molecular approach based on the mechanistic and structural similarities of NSY to two other closely related carotenogenic enzymes, lycopene cyclase (LCY) and capsanthin-capsorubin synthase (CCS) (Bouvier et al., 2000). 

Terpenoids, which are also known as isoprenoids, constitute the most abundant and structurally diverse group of plant secondary metabolites, consisting of more than 40,000 different chemical structures. The isoprenoid biosynthetic pathway generates both primary and secondary metabolites that are of great importance to plant growth and survival. Among the primary metabolites produced by this pathway are phytohormones, such as gibberellic acid (GA), abscisic acid (ABA), and cytokinins the carotenoids, such as chlorophylls and plastoquinones involved in photosynthesis the ubiquinones required for respiration and the sterols that influence membrane stmcture (see also Steroid and Triterpene Biosynthesis) (Fig. 1). Monoterpenoids (CIO), sesquiterpenoids (Cl5), diterpenoids (C20), and... 

ABSTRACT More than 100 abscisic acid (ABA) analogs have been reported so far. Some were synthesized to clarify structure-activity relationships, and others were developed as tools for investigating the molecular mechanism of ABA action. These analogs, especially those that can be useful tools for studying ABA reception and catabolic inactivation, are summarized together with their design concepts, structural properties and bioactivities. 

In structural terms these fungal metabolites are analogous to the iridoid monoterpenoids cf. Chapter 1). Recent studies on the biosynthesis of cyclonerodiol,cyclonerotriol, and abscisic acid (25) are described in Chapter 6. 

In 1963 abscisic acid was first identified and characterized by Frederick Addicott and colleagues. In 1965 the chemical structure of ABA was defined, and in 1967 it was formally called abscisic acid. 

Until the discovery of brassinolide by USDA scientists in 1979, it was thought that only five groups (indole auxins, gibberellins, cytokinins, abscisic acid, and ethylene) of hormones were responsible for regulating plant growth and development. Following this discovery, a number of compounds similar to brassinolide both in structure and physiological activity were isolated from different parts of plants. On the basis of published... 

Metabolite C , derived from metabolism of (+)-abscisic acid by tomato shoots, has been assigned structure (27) and on methylation rearranged to the methyl... 

Mass spectrometry is the most recently introduced technique to be widely applied to carotenoid structural studies. Many spectra are recorded by Enzell et Recent advances include the recognition that a loss of 106 and 92 m.u. (rationalised as xylene and toluene) is characteristic of the polyene chain. The remaining fragments on either side of the polyene may be recognised by bisallylic fission. Ketonic carotenoids show characteristic fragmentation. MacMillan and Gaskin were able to detect 0.3 pg of abscisic acid or phaseic acid using... 

Degraded Carotenoids. Several new natural products have structures similar to carotenoid end-groups and thus may be considered as degraded carotenoids. A new abscisic acid (31) metabolite from seeds of Robinia pseudacacia has been identified as the 3-hydroxy-3-methylglutaryl ester of hydroxyabscisic acid (32). 

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