Editing Tocopherol (section)

===Synthetic all-racemic===
Synthetic vitamin E derived from petroleum products is manufactured as all-[[racemic]] α-tocopheryl acetate with a mixture of eight stereoisomers. In this mixture, one α-tocopherol molecule in eight molecules are in the form of ''RRR''-α-tocopherol (12.5% of the total).<ref>{{cite journal | vauthors = Weiser H, Riss G, Kormann AW | title = Biodiscrimination of the eight α-tocopherol stereoisomers results in preferential accumulation of the four 2R forms in tissues and plasma of rats | journal = The Journal of Nutrition | volume = 126 | issue = 10 | pages = 2539–49 | date = October 1996 | pmid = 8857515 | doi = 10.1093/jn/126.10.2539 | doi-access = free }}</ref>

The 8-isomer ''all-rac'' vitamin E is always marked on labels simply as '''dl-tocopherol''' or '''dl-tocopheryl acetate''', even though it is (if fully written out) {{chem name|dl,dl,dl-tocopherol}}. The present largest manufacturers of this type are [[DSM (company)|DSM]] and [[BASF]].

Natural α-tocopherol is the RRR-α (or ddd-α) form. The synthetic {{chem name|dl,dl,dl-α}} ("dl-α") form is not so active as the natural ddd-α ("d-α") tocopherol form. This is mainly due to reduced vitamin activity of the four possible stereoisomers that are represented by the ''l'' or ''S'' enantiomer at the first stereocenter (an S or l configuration between the chromanol ring and the tail, i.e., the SRR, SRS, SSR, and SSS stereoisomers).<ref name=Jensen>{{cite book |last1=Jensen |first1=S |last2=Lauridsen |first2=C |title=α-Tocopherol Stereoisomers |journal=Vitamins & Hormones |volume=76 |pages=281–308 |year=2007 |doi=10.1016/S0083-6729(07)76010-7 |pmid=17628178|isbn=9780123735928 }}</ref> The three unnatural "2R" stereoisomers with natural R configuration at this 2' stereocenter, but S at one of the other centers in the tail (i.e., RSR, RRS, RSS), appear to retain substantial RRR vitamin activity, because they are recognized by the [[alpha-tocopherol transfer protein]], and thus maintained in the plasma, where the other four stereoisomers (SRR, SRS, SSR, and SSS) are not. Thus, the synthetic all-rac-α-tocopherol, in theory, would have approximately half the vitamin activity of RRR-α-tocopherol in humans. Experimentally, the ratio of activities of the 8 stereoisomer racemic mixture to the natural vitamin, is 1 to 1.36 in the rat pregnancy model (suggesting a measured activity ratio of 1/1.36 = 74% of natural, for the 8-isomer racemic mix).<ref>"Taken together, these data indicate that of the eight stereoisomers (RRR, RSR, RRS, RSS, SRR, SSR, SRS, SSS) in all-rac-α-tocopherol, only the four 2R-forms (RRR, RSR, RSS, RRS) are recognized by α-TTP and maintained in the plasma. Indeed, the Food and Nutrition Board (Food and Nutrition Board and Institute of Medicine, 2000) has defined that only α-tocopherol, specifically the 2R-forms of α-tocopherol, can fulfill the human requirement for vitamin E. Thus, all-rac-α-tocopherol has only half the activity of RRR-α-tocopherol." Taken from the discussion in {{cite journal | vauthors = Lauridsen C, Engel H, Craig AM, Traber MG | title = Relative bioactivity of dietary RRR- and all-rac-α-tocopheryl acetates in swine assessed with deuterium-labeled vitamin E | journal = Journal of Animal Science | volume = 80 | issue = 3 | pages = 702–7 | date = March 2002 | pmid = 11890405 | doi = 10.2527/2002.803702x | url = http://jas.fass.org/cgi/reprint/80/3/702.pdf | access-date = 2008-03-12 | archive-url = https://web.archive.org/web/20081217124036/http://jas.fass.org/cgi/reprint/80/3/702.pdf | url-status = dead | archive-date = 2008-12-17 }}</ref>

Although it is clear that mixtures of stereoisomers are not so active as the natural ''RRR''-α-tocopherol form, in the ratios discussed above, specific information on any side effects of the seven synthetic vitamin E stereoisomers is not readily available.