Gas chromatographic separation of chiral 2-hydroxy acids and 2-alkyl-substituted carboxylic acids

✍ Scribed by Wilfried A. König; Ingrid Benecke

• Publisher: Elsevier Science
• Year: 1980
• Tongue: English
• Weight: 317 KB
• Volume: 195
• Category: Article
• ISSN: 1873-3778
• DOI: 10.1016/s0021-9673(00)96823-7

✦ Synopsis

Gas chromatographic methods are preferentially applied for the determination of the con.@uration of opticahy active compounds, especially when only small and impure sampks are availabIe_ Besides the biological relevance of a certain cunfiguration, the quantitative measurement of enantiomer composition in asymmetric syntheses has increasing importance.

Direct enaatiomer resoiution on chiraI stationary phases has been used as the most ekgant method for stereochemical assignments in the Geld of amino acids and amine&-', based on the fundamental investigations of Gil-Av and co-workers. Only recently the enantiomers of 2-hydroxy acids could be separated OQ special chiral stationary phases as G-trifiuoroacetyLhy&oxy acid isopropyl esters5.

Alternatively, chiral compounds may be separated as diastereomeric derivatives on achiral stationary phases. As in amino acids two functional groups are available in hydroxy acids for introducing a chiral substituent. Both techniques have been used befare~xo_ For amino acids (+)-3-methylbutan-24 proved to 'be an exceknt reagent to form d&te-eomeric esters, which could be very well resolved as N-pentafluoropropionyl derikives.

in this mper we report on the separation of the (f)-3-methyl-2-butyl esters of G-trifluoroacMyIated (0-TFA) or G-trimethylsilylatcd (0-TMS) 2-hydroxy acids and of branched carboxyhc acids.

EXPEREMENTAL

Mater&z&

(f)-3-Methylbut was prepared, as described by Halpem and Westky:*, by esterifkation of L-valine with racemic 3-methylbutan-2-01 and fractional crystilization of the _@oluene su!phonic acid salt_ After two crystahizations and alkaline