Synthesis of l-prolinol substituted novel optically active phthalocyanines

The novel optically active Pc-4 (neutral) and Pc-5 (ionic), zinc(II) phthalocyanines having four N-benzyl protected l-prolinol unit were synthesized. l-prolinol has binucleophilic character and can be anchored to phthalonitrile derivative from both nitrogen and oxygen atoms. In order to overcome this problem and to enhance the solubility of phthalonitrile (S)-(-)-3 and the target phthalocyanines, the nitrogen atom of l-prolinol was first protected with benzyl chloride. All the compounds were characterized by 1H and 13C NMR, MALDI–TOF MS, IR, UV–vis, and Circular Dichroism (CD) spectroscopy. Pc-4 is highly soluble in most common organic solvents, whereas ionic Pc-5 is soluble in water. The CD results showed that the chiral information was transferred from the peripheral chiral l-prolinol side chains to the phthalocyanine chromophore at the molecular level.

Research highlights
► A novel chiral l-prolinol-anchored Pc with high solubility in common solvents.
► Cyclotetramerization results in optically active target Pc.
► Nitrogen on the periphery enables HCl salt formation to afford water soluble Pc.
► CD signals prove the chiral information transfer from l-prolinol to Pc chromophores.