The antitumor drug gimatecan is available as nearly pure (S)-enantiomer. Neither pure (R) enantiomer nor a racemic (equal) mixture of the two enantiomers are available. To measure small quantities of (R)-enantiomer in nearly pure (S)-gimatecan, a preparation

Preparation was subjected to normal-phase chromatography on each of the enantiomers of a commercial, chiral stationary phase designated (S,S)- and (R,R)-DACH-DNB. Chromatography on the (R,R)-stationary phase gave a slightly asymmetric peak at tr = 6.10 min with retention factor k = 1.22. Chromatography on the (S,S)-stationary phase gave a slightly asymmetric peak at tr = 6.96 min with k = 1.50. With the (S,S)-stationary phase, a small peak with 0.03% of the area of the main peak was observed at 6.10 min.
(a) Explain the appearance of the upper chromatograms. Dashed lines are position markers, not part of the chromatogram. What would the chromatogram of pure (R)-gimatecan look like on the same two stationary phases?
(b) Explain the appearance of the two lower chromatograms and why it can be concluded that the gimatecan contained 0.03% of the (R)-enantiomer. Why is the (R)-enantiomer not observed with the (R,R)-stationary phase?
(c) Find the adjusted relative retention (α) and unadjusted relative retention („“) for the two enantiomers on the (S,S)-stationary phase.

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6.10|(R,R) chiral minstationary 6.96 | (S.S) chiral min stationary phase phase 6.96 6.10 min min R- 003% 0 3 6 912 15 0 3 6 9 12 15 Time (min)