Phytol

Chemical degradation of chlorophyll gives a number of substances including phytol The constitution of phytol is given by the name 3 7 11 15 tetramethyl 2 hexadecen 1 ol How many stereoisomers have this constitution" ... 

Green coloration, present in many vegetable oils, poses a particular problem in oil extracted from immature or damaged soybeans. Chlorophyll is the compound responsible for this defect. StmcturaHy, chlorophyll is composed of a porphyrin ring system, in which magnesium is the central metal atom, and a phytol side chain which imparts a hydrophobic character to the stmcture. Conventional bleaching clays are not as effective for removal of chlorophylls as for red pigments, and specialized acid-activated adsorbents or carbon are required. 

Phytol [505-06-5] (111) and isophytol [150-86-7] (112) are important intermediates used in commercial synthesis of Vitamins E and K. There is a variety of synthetic methods for their manufacture. Chlorophyll [479-61-8] is a phytyl ester. 

Although all four tocopherols have been synthesized as their all-rac forms, the commercially significant form of tocopherol is i7//-n7i a-tocopheryl acetate. The commercial processes ia use are based on the work reported by several groups ia 1938 (15—17). These processes utilize a Friedel-Crafts-type condensation of 2,3,5-trimethylhydroquinone with either phytol (16), a phytyl haUde (7,16,17), or phytadiene (7). The principal synthesis (Fig. 3) ia current commercial use iavolves condensation of 2,3,5-trimethylhydroquiQone (13) with synthetic isophytol (14) ia an iaert solvent, such as benzene or hexane, with an acid catalyst, such as ziac chloride, boron trifluoride, or orthoboric acid/oxaUc acid (7,8,18) to give the all-rac-acetate ester (15b) by reaction with acetic anhydride. Purification of tocopheryl acetate is readily accompHshed by high vacuum molecular distillation and rectification (<1 mm Hg) to achieve the required USP standard. 

Hydrolysis of chlorophyll using sodium hydroxide produces the moderately water-soluble sodium salts of chlorophyllin, phytol and methanol (145). The magnesium ia chlorophyllin may be replaced by copper. The sodium copper chlorophyllin salt is heat stable, and is ideal for coloring foods where heat is iavolved, such as ia canning (146). 

Although /3-oxidation is universally important, there are some instances in which it cannot operate effectively. For example, branched-chain fatty acids with alkyl branches at odd-numbered carbons are not effective substrates for /3-oxidation. For such species, a-oxidation is a useful alternative. Consider phy-tol, a breakdown product of chlorophyll that occurs in the fat of ruminant animals such as sheep and cows and also in dairy products. Ruminants oxidize phytol to phytanic acid, and digestion of phytanic acid in dairy products is thus an important dietary consideration for humans. The methyl group at C-3 will block /3-oxidation, but, as shown in Figure 24.26, phytanic acid a-hydroxylase places an —OFI group at the a-carbon, and phytanic acid a-oxidase decar-boxylates it to yield pristanie add. The CoA ester of this metabolite can undergo /3-oxidation in the normal manner. The terminal product, isobutyryl-CoA, can be sent into the TCA cycle by conversion to succinyl-CoA. 

At present, it is evident that diaeetylene ean be used for the ereation of profitable pilot-seale faeilities to produee simple and funetionalized thiophenes, pyrroles, pyrazoles, pyrimidines, pyridines, and other heteroeyeles, as well as vitamins A and PP, geraniole, phytole derivatives, and many other high-prieed speeialty ehemieals. 

Abbott, R. J. 1981. The keel petal colour polymorphism of Lotus corniculatus L. in Scotland. New Phytol. 88 549-553. 

Rainey, F. 1946. Quinine hunters in Ecuador. National Geographic Magazine 89 341-363. Rajakaruna, N., Siddiqui, M. Y., Whitton, J., Bohm, B. A. and Glass, A. D. M. 2003. Differential responses to Na+/K+ and Ca2+/Mg2+ in two edaphic races of Lasthenia californica (Asteraceae) complex A case for parallel evolution of physiological traits. New Phytol. 

Since carotenoids are isoprenoids, they share a common early pathway with other biologically important isoprenoids such as sterols, gibberellins, phytol and the terpenoid quinones (Fig. 13.3). In all cases, these compounds are derived from the C5 isoprenoid, isopentenyl diphosphate (IPP). Until a few years ago it was believed that a single pathway from the Cg precursor mevalonic acid (MVA) formed IPP, which itself was synthesised from hydroxymethylglutaryl coenzyme A (HMG CoA) by the action of HMG... 

Since carotenoids are derived for the central isoprenoid pathway (Fig. 13.3), the regulation of their formation must involve a co-ordinated flux of isoprenoid imits into this branch of the pathway as well as into others such as the biosynthesis of sterols, gibberellins, phytol and terpenoid quinones. An imderstanding of the complexities of regulation of the pathway is necessary in order to target the regulatory steps for genetic manipulation. 

From these stractural features it is interesting to note that each molecule of chlorophylls a and b consists of a hydrophilic part (tetrapyrrole macrocycle) and a hydrophobic portion (long terpenoid chain of phytol esterifying the acid group at C-17). Figure 2.1.2 shows the structures and nomenclature of chlorophylls a and b and their major breakdown derivatives. 

The early stages of catabolism correspond to the replacement of Mg by two H atoms under acidic conditions and/or by the action of Mg-dechelatase and the cleavage of the phytol chain by the enzyme chlorophyllase. The still greenish intermediates are pheophytins, chlorophyUides, and pheophorbides with intact tet-rapyrrole rings. - ... 

In addition to the porphyrin nucleus, the phytol tail that esterifies the propionic acid side chain at C-17 may be hydrolyzed enzymatically during storage or processing. Cleavage of the phytol chain during digestion is unlikely. Free phytol is quickly... 

Thomas, H., Chlorophyll a symptom and a regulator of plastid development. New PhytoL, 136, 163, 1997. 

Hortensteiner, S., Vicentini, F., and Matile, P., Chlorophyll breakdown in senescent cotyledons of rape, Brassica napus L. enzymatic cleavage of pheophorbide a in vitro, New Phytol, 129, 237, 1995. 

Arnhold, T, Ehnazar, M.M.A., and Nau, H., Prevention of vitamin A teratogenesis by phytol or phytanic acid results from reduced metabolism of retinol to the teratogenic metabolite, all frara-retinoic acid, Toxicol. Sci., 66, 274, 2002. 

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