Cytotoxicity and DNA Interaction of the Enantiomers of 6-Amino-3-(chloromethyl)-l-[(5,6,7-trimethoxyindol-2-yl)carbonyl]indoline (Amino-seco-CI-TMI)

The enantiomers of the previously reported racemic 6-amino-3-(chloromethyl)-l-[(5,6,7trimethoxyindol-2-yl)carbonyl]indoline (amino-seco-CI-TMI) were prepared via resolution of a precursor by chiral HPLC. The only detectable product isolated from reaction of the racemic compound with calf thymus DNA, followed by thermal cleavage, was shown by mass spectrometry and two-dimensional NMR spectroscopy to be the adenine N3 adduct. Polyacrylamide gel electrophoresis assays with the racemate and with each enantiomer also showed adenine to be the only site of alkylation. While the racemic amino compound exhibited sequence selectivity identical to that of the previously characterized phenol analogue, the enantiomers exhibited distinctly different sequence selectivities, allowing the (+) enantiomer to be assigned the "natural" S configuration. The (4-)-(S) enantiomer is 3-fold more cytotoxic than the (-)-(R) enantiomer (IC50 values of 240 and 700 nM, respectively, in AA8 cells, after exposure for 4 h).