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==Chemical synthesis== [[Image:(R)-Liponic Acid Structural Formula V.1.svg|200px|R-isomer]] [[Image:(S)-Liponic Acid Structural Formula V.1.svg|200px|S-isomer]] SLA did not exist prior to chemical synthesis in 1952.<ref>{{cite journal |last1= Hornberger |first1= CS |last2= Heitmiller |first2= RF |last3= Gunsalus |first3= IC |last4= Schnakenberg |first4= GHF |last5= Reed |first5= LJ |display-authors= 4 |title= Synthesis of DL—lipoic acid |journal= [[Journal of the American Chemical Society]] |volume= 75 |issue= 6 |pages= 1273–7 |year= 1953 |doi= 10.1021/ja01102a003}}</ref><ref>{{cite journal |last1= Hornberger |first1= CS |last2= Heitmiller |first2= RF |last3= Gunsalus |first3= IC |last4= Schnakenberg |first4= GHF |last5= Reed |first5= LJ |display-authors= 4 |title= Synthetic preparation of lipoic acid |journal= [[Journal of the American Chemical Society]] |volume= 74 |issue= 9 |page= 2382 |year= 1952 |doi= 10.1021/ja01129a511|bibcode= 1952JAChS..74.2382H }}</ref> SLA is produced in equal amounts with RLA during achiral manufacturing processes. The racemic form was more widely used clinically in Europe and Japan in the 1950s to 1960s despite the early recognition that the various forms of LA are not bioequivalent.<ref name="Kleeman" /> The first synthetic procedures appeared for RLA and SLA in the mid-1950s.<ref>{{cite journal |pmid= 13294188 |last1= Fontanella |first1= L |title= Preparation of optical antipodes of alpha-lipoic acid |journal= Il Farmaco; Edizione Scientifica |volume= 10 |issue= 12 |year= 1955 |pages= 1043–5}}</ref><ref>{{cite journal |last1= Walton |first1= E |last2= Wagner |first2= AF |last3= Bachelor |first3= FW |last4= Peterson |first4= LH |last5= Holly |first5= FW |last6= Folkers |first6= K |display-authors= 4 |title= Synthesis of (+)-lipoic acid and its optical antipode |journal= [[Journal of the American Chemical Society]] |volume= 77 |issue= 19 |pages= 5144–9 |year= 1955 |doi= 10.1021/ja01624a057 }}</ref><ref>{{cite journal |last1= Acker |first1= DS |last2= Wayne |first2= WJ |title= Optically active and radioactive α-lipoic acids |journal= [[Journal of the American Chemical Society]] |volume= 79 |issue= 24 |pages= 6483–6487 |year= 1957 |doi= 10.1021/ja01581a033}}</ref><ref>{{cite journal |pmid= 14207116 |last1= Deguchi |first1= Y |last2= Miura |first2= K |title= Studies on the synthesis of thioctic acid and its related compounds. XIV. Synthesis of (+)-thioctamide |journal= Yakugaku Zasshi |volume= 84 |issue= 6 |date= June 1964 |pages= 562–3|doi= 10.1248/yakushi1947.84.6_562 |doi-access= free }}</ref> Advances in chiral chemistry led to more efficient technologies for manufacturing the single enantiomers by both classical resolution and [[asymmetric synthesis]] and the demand for RLA also grew at this time. In the 21st century, R/S-LA, RLA and SLA with high chemical and/or optical purities are available in industrial quantities. At the current time, most of the world supply of R/S-LA and RLA is manufactured in China and smaller amounts in Italy, Germany, and Japan. RLA is produced by modifications of a process first described by Georg Lang in a Ph.D. thesis and later patented by DeGussa.<ref>{{cite thesis |last= Lang |first= G |title= In Vitro Metabolism of a-Lipoic Acid Especially Taking Enantioselective Bio-transformation into Account |degree= Ph.D. |publisher= University of Münster |location= Münster, DE |year= 1992}}</ref><ref>{{cite patent |inventor1-last= Blaschke |inventor1-first= G |inventor2-last= Scheidmantel |inventor2-first= U |inventor3-last= Bethge |inventor3-first= H |inventor4= R Moeller, Beisswenger, T Huthmacher |title= Preparation and use of salts of the pure enantiomers of alpha-lipoic acid |country= US |number= 5281722 |status= patent |gdate= 1994-01-25 |assign1= DeGussa |fdate= 1992-11-12 |pridate= 1991-11-16 |postscript= .}}</ref> Although RLA is favored nutritionally due to its "vitamin-like" role in metabolism, both RLA and R/S-LA are widely available as dietary supplements. Both [[stereospecific]] and non-stereospecific reactions are known to occur ''in vivo'' and contribute to the mechanisms of action, but evidence to date indicates RLA may be the [[eutomer]] (the nutritionally and therapeutically preferred form).<ref name=Carlson08/><ref>{{cite journal |pmid= 11684397 |last1= Packer |first1= L |last2= Kraemer |first2= K |last3= Rimbach |first3= G |title= Molecular aspects of lipoic acid in the prevention of diabetes complications |journal= Nutrition |volume= 17 |issue= 10 |date= October 2001 |pages= 888–95 |doi= 10.1016/S0899-9007(01)00658-X}}</ref>
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