Phytol reactions

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. 

This enzyme [EC 3.1.1.14] catalyzes the hydrolysis of chlorophyll to produce phytol and chlorophyllide. The enzyme has also been reported to catalyze chlorophyllide transfer reactions (for example, in converting chlorophyll to methylchlorophyllide). 

While there are a number of acyclic diterpenes such as phytol, cyclization of these acyclic diterpenes, driven by various enzymes, leads to the formation of cyclic diterpenes. A number of other biogenetic reactions, e.g. oxidation, also bring in variation among these cyclic diterpenes. 

The concentration of dolichyl phosphate in eukaryotic tissues is very low and is probably rate-limiting for the glycosylation processes. Variation of the concentration in the endoplasmic-reticulum membranes is a possible way of controlling the rate of glycosylation. It is important to point out that the early steps in the dolichol biosynthesis are common to such other prenyl derivatives in plants as steroids, essential oils, hormones, phytol, and carotenes (see Scheme 1), and parameters affecting those reactions that may control the dolichol to dolichyl phosphate step could be another mechanism for regulation of the level of dolichyl phosphate. 

Figure 3. Geochemically reversible and irreversible reactions. Only the reactions are listed for which we have evidence from the fringelites, the fossil porphyrins, and the phytol-derived hydrocarbons (5).

The synthesis of Vitamin E, that is, a-tocopherol (5,7,8-trimethyltocol) in the past has been accomplished primarily by reacting trimethylhydroquinone (TMHQ) with isophytol (3,7,ll,15-tetramethylhexadec-l-en-3-ol) or phytol (3,7,ll,15-tetramethylhexadec-2-en-l-ol) in a condensation reaction. The reaction is well known and has been practiced for many years (Stalla-Bourdillon, Ind. Chim. Belg., 35, 13 (1970) "The Vitamins" Vol. 5, pages 168-223, Academic Press, New York, 1967). 

The condensation of allylic alcohols with phenolic compounds in the presence of an acid catalyst yields allylphenols. This reaction was used 86 in a synthesis of vitamin K (LXXVa) by condensing phytol with 2-methyl-l,4-naphthohydroquinone in dioxane with oxalic or trichloroacetic acid as catalyst the hydroquinone first formed was oxidized to... 

Figure 9.37 Chemical structures of chlorophylls-a and b which contain a propionic acid esterified to a C20 phytol chlorophylls-cj and C2 have an acrylic acid that replaces the propionic acid. Also included are the pheopigments, the four dominant tetrapyrrole derivatives of chloropigments (pheopigments) found in marine and fresh-water/estuarine systems (chlorophyllide, pheophorbide, pheophytin, pyropheophorbide.) More specifically, chlorophyllase-mediated de-esterification reactions (loss of the phytol) of chlorophyll yield chlorophyllides. Pheophytins can be formed when the Mg is lost from the chlorophyll center. Pheophorbides are formed from removal of the Mg from chlorophyllide or removal of the phytol chain from pheophytin, and pyrolyzed pheopigments, such as pyropheophorbide and pyropheophytin, are formed by removal of the methylcarboxylate group (-COOCH3) on the isocylic ring from the C-13 propionic acid group.

Oxidation reactions of this nature are common in the literature. For example, selenium dioxide in refluxing etiumolic solution brought about the allylic oxidative rearrangement geranyl acetate, which was further functionalized in a synthesis of the norsesquiterpenoid gytinidal (equation 46). This trans formation was also used in a total synthesis of phytol. Similarly, an a, -unsaturated aldehyde was obtained undm similar conditions in studies of a synthesis of pentalenic acid derivatives (equation 47). ... 

BF3 Et20 is useful for the condensation of allylic alcohols with enols. A classic example is the reaction of phytol in dioxane with 2-methyl-l,4-naphthohydroquinone 1-monoacetate to form the dihydro monoacetate of vitamin Ki (Eq. 30), which can be easily oxidized to the quinone [57]. 

Reactions in SCCO2 have also been used for the production of minor lipid components, such as tocopherols and sterol esters. The synthesis of D, L, ot-tocopherol in SCCO2 and nitrous oxide by condensation of trimethyUiydroquinone with iso-phytol in the presence of various Bronsted or Lewis acids as catalysts resulted in... 

Vitamin E, a-tocopherol, an effective antioxidant, is obtained as a diastereoisomeric mixture in the 2,3 (S),7 (R),11 (R), form and the natural 2,3 (R),7 (R), 11 (R), form (83) by the reaction of phytyl bromide with trimethylhydroquinone in the presence of zinc chloride (ref.86), the phytol required being obtained from chlorophyll. 

Phytol, CAS no. [150-86-7] C20H40O, an alcohol obtained by the decomposition of chlorophyll is an odorless liquid, BP 202—204°C/10mm Hg and has been used in the synthesis of vitamin E. On reaction with trimethyl hydroquinone phytol is converted to a-tocopherol, etc. 

The a,P-unsaturated nitriles can be converted to the corresponding a,P-unsaturated alcohols by two successive treatments with DlBAL-H. This reaction has been used in the synthesis of sarco-phytols A and T to produce the allylic alcohol in 71% yield " ... 

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