Phytenes

Phytene is an example of a diterpene. It is found as the phytyl side chain in chlorophyll a and vitamin K. Haslene is an example of a sesterpene. It is an imsaturated and branched simple lipid synthesized by marine pennate diatoms. One of the largest femilies of terpenes... 

Examples of terpenes (a) isoprene, (b) phytene, which is a side chain of chlorophyll a, (c) squalene, (d) vitamin A, (e) haslene, (f) amyrin, and (g) cephalosporin. 

Figure 10. Postulated formation of C20 isoprenoid thiophenes and bithiophenes by incorporation of sulfur into phytenes. Different substrates lead to different thiophenes which is the major control for the thiophene ratio.

The selective generation of (poly)sulfide-linked molecules from the resin macromolecules at lower pyrolysis temperatures is exemplified b / Figure 10, which shows mass chromatograms of m/z 57 of the 358 and 610°C pyrolysates. At 358°C, phytenes and phytane dominate this mass... 

Brown, G. D. Phytene-l,2-diol from Artemisia annua. Phytochemistry, 1994, 36(6) 1553-1554. 

Figure 6. Reconstituted ion chromatogram (RIC) from gc-ms analysis of the aliphatic hydrocarbons of a Quaternary sediment from the Cariaco Trench (DSDP 15-147C-3-3). Peak assignments numbered peaks (solid) are n-alkanes A, pristane B, 2,6,10-trimethyl-7-(3-methylbutyl)dodecane C, phytane D, phytenes E, 2,6,10,15,19-pentamethyleicosane F, lycopane.

Further work is necessary to better understand and apply the obvious information present. For example, one wonders whether the high phytane/pristane ratio is the result of relatively high amounts of phytenes and/or diphytanylethers present in (halophilic) archaebacteria and is not at all an indication for anoxicity (46,47). 

Abundant Cis isoprenoid ketone, Z/E pristenal, and Z/E phytenal as well as phytol biomarker compounds were detected in the sinking particulate materials from the Yongshu Reef Lagoon and the continental shelf of the East China Sea (Figs. 5.28 and 5.29). This appears to be the first report of these compounds in China marine environment. Detection of these compounds in the studied regions is of some importance to understand the evolutional processes of acyclic isoprenoid compounds in the seawater column and their formative pathways in marine sediments. Their identifications were based on chromatographic retention time, mass spectrum features (Figs. 5.28 and 5.29), and comparison with those reported previously. The mass spectrum of phytol trimethylsilyl ether exhibits a base peak at mlz 143 and a molecular ion at mjz 368. Cig isoprenoid ketone has a base peak at mjz 58, a molecular... 

Fig. 5.29. Total ion chromatogram of ketone+aldehyde fractions in sinking particulate material from the Yongshu Reef Lagoon. A, Cis isoprenoid ketone B, Z pritenal C, E pristenal D, Z phytenal E, E phytenal (Duan et al., 1997) (With permission from Duan Y)...

Approximately 5 000 naturally abundant acyclic and cyclic diterpenes derived from the parent hydrocarbon phytane are known The (3i ,7i ,ll )-enantiomer of phy-tane has been found in meteorites, oil slate, other sediments and, last but not least, in human liver. Oil slate additionally eontains (-)-(3if,7if,llif)-phytanoic acid which has also been isolated from butter. 1,3(20)-Phytadiene is one among many constituents of tobacco Nicotiana tabacum (Solanaceae) -1,3-phytadiene and its (%)-isomer are found in zooplankton. Chlorophyll in the chloroplasts of plant cells exemplifies an ester of +)-(lE,lR, l/ )-2-phyten-l-ol usually referred to as phytol. 2,6,10,14-Phytatetraene-l,19-diol, better known as plaunotol, is the ehief constituent of the leaves of flie Thai medicinal plant Croton sublyratus (Euphorbiaceae) used as "plau noi" or "kelnac" as an antiulcerative. 

This class of fatty acids has the general formula of R-(CH2CH-CH3CH2CH2) -CH-C = CH-COOH, where R = H. These saturated and partially unsaturated multibranched fatty acids belong to the is-oprenoid acid family, and in nature, isoprenoid acids are often found in microorganisms and plants. Phytenic acid, whose systematic name is 3,7,11,15-tetramethyl-2-hexadecenoic acid (Figure 4), is one member of this class. 

Figure 4 Phytenic acid, or 3,7,11,15-tetramethyl-2-hex-adecenoic acid.

In this context, Woggon and coworkers [21e] appHed an asymmetric vinylogous aldol/Michael reaction in the total synthesis of a-tocopherol (44). They converted enantiomerically pure phytenal and substituted saHcylaldehyde 40 into lactol 42 (Scheme 8.13). Using proHnolether J -41 as the chiral organocatalyst, they obtained the lactol in 60% yield with a diastereomeric ratio of 97 3, which was measured after oxidation to the lactone 43. 

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