On-line CD detection in chiral separation of spiro-lambda(4)-sulfanes

Enantiomers of chiral spiro-lambda(4)-sulfanes with equatorial diaryl and a xial bis(acyloxy), (alkoxy)-(acyloxy) or (acylamino)-(acyloxy) S-substituen ts were separated on a Kromasil-based chiral sorbent, namely on O,O'-bis(3, 5-dimethylbentoyl)-N,N'-diallyl-L-tartardiamide silica CSP, by using n-hexa ne (or n-heptane)-dioxane (or 2-propanol) isocratically mixed mobile phases , Direct chiral separation was monitored by a homemade HPLC-CD system consi sting of a circular dichroism (CD) spectrophotometer (Jobin-Yvon Model III Dicrograph) and a high performance liquid chromatograph. The system was use d in conjunction with HPLC-UV to study the chemical and stereochemical puri ty of the samples. By the stopped-flow technique CD spectra were measured i n the 350-230 nm spectral range. Monitoring at a selected wavelength enable d high-sensitivity detection. Racemic spiro-lambda(4)-sulfanes were also se parated into pure enantiomers on preparative scale. Regardless of the struc tural type of diaryl-spiro-lambda(4)-sulfanes, the first-eluted enantiomer was always found to show a CD spectrum marked by an intense positive band n ear 240 nm and a negative one at approximate to 210 nm (positive couplet) t hat allows prediction of absolute configuration.