Enantiomeric derivatives of tokinolide B: absolute configuration and biological properties.

The enantiomeric lactams (-)-8, (+)-8, (+)-9, and (-)-9 were formed by the reaction of the dimeric phthalide rac-tokinolide B (rac-3) with (R)-(+)-α-methylbenzylamine and (S)-(-)-α-methylbenzylamine. The absolute configurations of compounds 8 and 9 were assigned by experimental and theoretically calculated electronic circular dichroism methods for (+)-8 and (-)-9. Compounds 3, 5, (-)-8, (+)-8, (+)-9, and (-)-9 displayed cytotoxic activity toward several human tumor cell lines, with (-)-8 and (-)-9 being the most potent.