Synthesis of Silicon Phthalocyanines Bearing Two Cholesterol Moieties

Abstract

The binding of two cholesterol moieties on each side of silicon phthalocyanine is performed by reacting dihydroxysilicon phthalocyanine with chlorocholesteryloxydiphenylsilane, bis(triflate)silicon phthalocyanine with cholesterol or dichlorosilicon phthalocyanine with cholesterol alcoholate. Metallated phthalocyanines are used as photosensitizers in photodynamic therapy of cancer cells. In this area, a long triplet lifetime can get high yield of O2, O2° and/or HO° involved in cytotoxic effects.1 Silicon phthalocyanines are of great interest because Si coordination degree allows the binding of two axial ligands which may have a lipophilic character. They also create steric hindrance on each side of the phthalocyanine ring limiting thereby stack aggregation usually encountered in solution for the planar molecular structure.2 Such a phenomenon is responsible for a decrease of the lifetime of electronically excited states such as the triplet lifetime, probably by increasing internal conversion.3 Therefore, the binding of two cholesterol molecules on each side of silicon phthalocyanine may lead to a macrocyclic dye with good solubility in lipophilic medium, high potency in cell membrane recognition and good photophysical properties as already shown for other silicon phthalocyanine derivatives.4 We report herein four methods for Sicholesterol linking.