The GLC and TLC resolution of diastereoisomeric polyhydroxystearates and assignment of configurations

Trifluoroacetate (TFA) derivatives of methyl 12-hydroxystearate, methyl ricinoleate, five positional isomers of methylthreo- anderythro-dihydroxystearate, four diastereoisomeric methyl 9,10–12-trihydroxystearates, and four racemic diastereoisomeric methyl 9,10–12,13-tetrahydroxystearates were prepared and analyzed by gas-liquid chromatography (GLC). The isomericthreo- anderythro-dihydroxystearates that had not previously been resolved by GLC were separated. Excellent resolution of the diastereoisomeric pairs of methylthreo- anderythro-9,10–12-triand and methylerythro, erythro- andthreo, threo-9,10–12,13-tetrahydroxystearates was obtained by GLC of their TFA derivatives. Analyses of these high-molecular-weight compounds were carried out on polar and nonpolar packed columns used routinely for methyl ester analysis. The various methyl mono-, di-, tri-, and tetrahydroxysterate esters were also analyzed by thin-layer chromatography (TLC) on Silica Gel G adsorbent layers and on Silica Gel G impregnated with sodium arsenite. Relative and absolute configurations were assigned to the various diastereoisomeric tri- and tetrahydroxysterates based on information obtained from GLC, TLC, synthetic ratios, and molecular-models. A micro hydroxylation method that gives quantitative yields ofthreo- anderythro-dihydroxy acids from various concentrations of C₁₈ monoene geometrical isomers was developed. Subsequent GLC analysis of the isomeric methyl dihydroxy TFA derivatives allows the quantitative determination of double-bond configuration on small samples without expensive or specialized equipment. Presented at the AOCS Meeting, Los Angeles, April 1966. under appointment from Oak Ridge Associated Universities. An operating unit of the Oak Ridge Associated Universities, under contract with the US Atomic Energy Commission.