Enantioseparation of chiral thiobarbiturates using cyclodextrin-modified capillary electrophoresis

The racemates of several chiral thiobarbiturates were separated by using di fferent cyclodextrins in capillary electrophoresis (CE). Six neutral and ne gatively charged cyclodextrins 1 (CDs) were employed as chiral separators w hereof five led to successful separation of enantiomeric thiobarbiturate pa irs. The CDs used were the native alpha -CD, beta -CD, gamma -CD, and hepta kis-(2,6-di-O-methyl)-beta -cyclodextrin (HDM) as well as heptakis-(2,3-di- O-methyl-6-sulfato)-beta -cyclodextrin (HDMS) and heptakis-(2,3-di-O-acetyl -6-sulfato)-beta -CD (HDAS). Five of the six chiral thiobarbiturates studie d could be resolved at a basic pH value of 9.4 and a phosphate buffer conce ntration of 100 mM in a fused-silica capillary. Structurally related substa nces showed a similar behavior in separation: 1 and 2 bearing the center of chirality in the side chain at C5 can be best separated using gamma -CD, t he N-alkyl-substituted compounds 3 and 4 as well as the N/S-dialkyl-substit uted compound 5 could be resolved with HDM. Using the neutral CDs, the migr ation times were relatively small (< 11 min). 3 and 4 could be also resolve d by means of the negatively charged HDMS. In the latter case, the migratio n time is twice as long as with HDM.