Phytol structure

At the time that he received his Nobel Prize in 1930, Fischer was investigating the structure of the pigments chlorophyll a and b, magnesium complexes of a close relative of protoporphyrin IX. WiUstatter s early work had demonstrated a long-chain ester in chlorophyll and, around 1930, James B. Conant (1893-1978) at Harvard deduced its structure (phytol). Structures for the chlorophylls were finally solved by Fischer around 1940 and he also published the structure of bilirubin in 1942. Fischer worked in Munich before and throughout World War II. Following an AlHed bombing raid that destroyed his laboratory, Fischer committed suicide on March 31, 1945, five weeks before the war in Europe ended. 

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. 

L. Gea, L. Normand, B. Vian, and G. Gay, Structural aspects of ectomycorrhiza of Pinus pinaster (Ait.) Sol. formed by an lAA-overproducer mutant of Heheloma cylindrosporuni Romagnesi. New Phytol. 128 659 (1994). 

S. E. Smith and F. A. Smith, Structure and function of the interfaces in biotrophic symbiosis as they relate to nutrient transport. New Phytol. 114 (1990). 

Chabot, S. et al., Hyphal growth promotion in vitro of the VA mycorrhizal fungus, Gigaspora margarita Becker and Hall, by the activity of structurally specific flavonoid compounds under C02-enriched conditions. New Phytol, 122, 461, 1992. 

Head-to-tail rearrangement of four isoprene units results in the formation of diterpenes (C20H32), as seen also in Fig. 4.2. Diterpenes are generally found in resins, e.g. pimaric acid and abietic acid. Some diterpenoids are also constituents of essential oils, e.g. phytol [3, 7-14, 37, 52, 53]. Like sesquiterpenes, diterpenes are heavier than monoterpenes therefore, they require more energy to go to the vapour phase. For this reason, longer distillation times are necessary for their recovery. The DNP lists 118 different structural types for diterpenoids [37]. Important diterpenes found in essential oils will be detailed. Some representatives of volatile diterpenes are as in Structure 4.32. 

Phytol, a diterpene alcohol (3,7,11,15-tetramethyl-2-hexadecen-l-ol), occurs in two isomeric forms fraus-phytol 110 and czs-phytol 111 (Structure 4.33). Phytol was first isolated at the beginning of the nineteenth century during esterification of the chlorophyll molecule. It is a constituent of nettle and many essential oils. Another acyclic diterpene, geranylcitronellol 112, also occurs in essential oils. 

Knowledge of the chemical structures of the major vitamins was acquired during the 30 years after 1920, and some were identified as known compounds. They were classified as fat-soluble and water-soluble vitamins. The only heterocyclic compounds in the former class are the tocopherols (vitamin E). They were discovered through their action in preventing sterility in rats, but they appear to play an important part in the metabolism of skeletal muscle. Vitamin E deficiency appears to occur rarely in man, but vitamin E therapy is tried in a number of clinical disorders. The tocopherols may be isolated from vegetable oils, and synthetic a-tocopherol (61) is made by condensing trimethylhydroquinone with phytol or phytyl halides (Scheme 2). For medicinal use they may be converted into their acetates or succinates. 

Isoprenoid structures for carotenoids, phytol, and other terpenes start biosynthetically from acetyl coenzyme A (89) with successive additions giving mevalonate, isopentyl pyrophosphate, geranyl pyrophosphate, farnesyl pyrophosphate (from which squalene and steroids arise), with further build-up to geranyl geranyl pyrophosphate, ultimately to a- and /3-carotenes, lutein, and violaxanthin and related compounds. Aromatic hydrocarbon nuclei are biosynthesized in many instances by the shikimic acid pathway (90). More complex polycyclic aromatic compounds are synthesized by other pathways in which naphthalene dimerization is an important step (91). 

These compounds can be divided into two types, tocols and trienols. Although both types have the 6-chromanol ring structure and a phytol-like... 

This effect was seen only in hypoxia, not normoxia, was dose-dependent within the range 0.2-200 /rM, and provided a simple in vitro model for investigating the mode of action of the vitamin. By examining the structure-activity relationship of the response, compounds with a phytyl side-chain, phytol and vitamin K-l (phytomenadione), of similar length to vitamin E (9) were found to be also active, but compounds that had structures which resembled the chroman ring of the vitamin, vitamin K-3 (menaphthone) and Trolox, were antagonists of the responses to the phytol side-chain effects. 

Other studies have shown biological actions from these kinds of structure and indicate interrelationships between the chemicals in terms of their potencies. Tomita [229] found that the substances, vitamin A, vitamin K, vitamin E, /1-carotene, ubiquinone (15), phytol and squalene (16), from green-yellow vegetables could suppress the growth of tumour cells and enhance T-cell cytotoxicity, but /1-carotene, which does have both ends of the chain substituted with a bulky / -ionone ring on each end-group did not. Hydrophobic chain... 

Table 5.6. STRUCTURE-ACTIVITY RELATIONSHIP FOR COMPOUNDS CONTAINING THE PHYTOL SIDE-CHAIN AND CHROMANOL RING STRUCTURES RELATED TO VITAMIN E...

Write a structural formula for phytol and count the number of structural units capable of stereochemical variation. 

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.

You will notice that they are all aliphatic compounds with a scattering of double bonds and rings, few functional groups, and an abundance of methyl groups. A better definition (that is, a bio synthetically based definition) arose when it was noticed that all these compounds have 5n carbon atoms. Pinene and camphor are Cto compounds, humulene is Cl5> and phytol is C20 It seemed obvious that terpenes were made from a C5 precursor and the favourite candidate was isoprene (2-methylbuta-l,3-diene) as all these structures can be drawn by joining together 2-, 3-, or 4-isoprene skeletons end to end. Humulene illustrates this idea. 

Figure 5-2. Structure of Chi a, illustrating the highly conjugated porphyrin head (a closed chain tetrapyr-role) to which is attached a hydrocarbon phytol tail. The convention for numbering the various rings is also indicated with capital letters (formerly labeled as I through V). The solid lines to Mg indicate a resonating form with shared elections in the bonds, and the dashed lines indicate bonds with little election sharing at that moment (election sharing varies over time).

Jacquot JP, Lancelin JM, Meyer Y. Thioredoxins structure and function in plant cells. New Phytol. 1997 136 543-570. 

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