Tocopherol synthesis

Tebbe reaction 148 Tetracyclin synthesis 190 Tetrazole synthesis 17 Tetrodotoxin synthesis 136 Tocopherol synthesis 142 Tonantzitlolone synthesis 188 Triazine synthesis 17 Triclavulone synthesis 102... 

The stereochemical consequences of the cyclization of some 3-(2,5-dihydroxyphenyl)pro-pan-l-ols (247) have been investigated, with a view to optimizing the chiral economy of a tocopherol synthesis from (S)-chroman-2-carboxylic acid (81JOC2445). It was observed that acid-catalyzed dehydration occurred with retention of configuration and it was proposed (79JA6710) that the process involved the formation of a hemiketal through nucleophilic attack by the side-chain hydroxy group on the keto tautomer. 

Synthesis of the enantiomerically pure (5)-chroman-2-carbaldehyde (257) follows a similar route to the above, but the chirality is introduced through the ketone (256) (82CC205). A particularly interesting feature of this synthesis is the derivation of the diol (255) from 2-methyl-3-(2-furyl)propenal using fermenting baker s yeast. Furthermore, the fermentation also produces the chiral alcohol (258), a source of the C15 unit which is the second component along with the aldehyde (257) in an a-tocopherol synthesis. 

A detailed survey of chroman and tocopherol synthesis has been published (81HC<36)59) and earlier reviews are of interest <40CRV(27)287,77E555). 

Sattler, S.E. Cahoon, E.B. Coughlan, S.J. DellaPeima, D. 2003. Characterization of tocopherols cyclases from higher plants and cyanobacteria. Evolutionary implications for tocopherols synthesis and function. Plant Physiol. 132 2184-2195. 

Gan Fanyuna, Xu Chun, Zheng Guangzhi. 1992 Effect of ginseng-oligosaccharin M on the growth rate and a-tocopherol synthesis in cultured cell of Carthamus tinctorius. Acta Phytophysiologica Sinica, 18 355-360. 

Soil, J. Schultz, G. (1979). Comparison of geranylgeranyl and phytyl substituted methylquinols in the tocopherol synthesis of spinach chloroplasts. Biochem.Bioph. Res. Co., 91, 715-720. 

Table 3.2 shows some results of tocopherol synthesis obtained with different MgF2 based catalysts. Both crystalline MgF2 (entry 1) and HS-MgF2 prepared with very little or no water (entries 7 and 8) were not at all active, even after prolonged reaction time. As crystalline MgF2 exhibits almost no acidity its inactivity was to be expected. On the other hand, a HS-MgF2 catalyst prepared with 71% aqueous HF resulted in total conversion of isophytol and almost 100% selectivity to (all-rac)-[a]-tocopherol (entry 6). The activities of the catalysts do not correspond to their respective numbers of acid centres (Table 3.2). Likewise, the F MAS NMR spectra do not correspond to the activity.

Table 3.2 Influence of the key surface features and the reaction parameters on the catalytic performances of tocopherol synthesis...

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