Synthesis of Purpurin Imide Derivatives by Modification of Peripheral Functional Groups of Methyl Pheophorbide-a

Abstract

A series of novel purpurin-18 imide derivatives exhibiting long wavelength absorption and amphiphilicity were obtained from methyl pheophorbide-a (MPa) by modification of the peripheral functional groups. The vinyl group at 3-position was oxidized with OsO4 and NaIO4 to form the formyl group and the Grignard reaction of this aldehyde with the alkyl magnesium bromide was carried out to give the corresponding 3-(1-hydroxylalkyl) pheophorbide-a. The E-ring of these chlorines was converted into anhydride ring to give purpurin derivatives by air oxidation. The trans-32-alkyl purpurin derivatives were obtained by dehydration of hydroxyl group at 31-position. The N-hydroxyl purpurin imide was generated by treatment of the anhydride ring with hydroxylamine hydrochloride. The 31-alkylacyl-N-hydroxyl purpurin imides were obtained by oxidation of hydroxyl group at 31-position. The acylation of N-hydroxyl group was completed to afford N-acyloxy purpurin imides. The photocytoxicity of several compounds in vitro were tested.