Synthesis of Optically Pure Cyclometalated Iridium(III) Complex‐Peptide Hybrids and Their Anticancer Activity.

We report on the synthesis of optically pure cyclometalated iridium(III) complex-peptide hybrids as amphiphilic peptide conjugates (IPH-ACs) from Δ- and Λ-Ir(tpyCO2H)3 (tpy: 2-(4’-tolyl)pyridine) by optical resolution via diastereomeric intermediates conjugated with the chiral alcohol, (1R,2R)-2-aminocyclohexanol ((R,R)-11).  Spectroscopic spectra of the optically pure IPH-ACs that were prepared from Δ- and Λ-Ir(tpyCO2H)3 are reported.  It was found that both optically pure IPH-ACs induce paraptotic cell death in Jurkat cells and the EC50 values were evaluated by MTT assays.  We also performed TEM analyses of Jurkat cells treated with Λ-13 to observe morphological changes that occurred, and cytoplasmic vacuolization, a characteristic feature of paraptosis, was observed.  The intracellular uptake of IPH-ACs by the cells measured by ICP-MS (inductively coupled plasma-mass spectrometry) was higher for the Λ-forms and the EC50 values of the Λ-forms were slightly lower than those of the Δ-IPH-ACs.  The intrinsic cytotoxicity of the IPH-ACs, taking into account the fact that the intracellular uptake and the intrinsic cytotoxicity is almost equal for the Δ- and Λ-forms, suggests that the difference in cytotoxicity against Jurkat cells is due to the selectivity in the intracellular uptake of each stereoisomer.