Regiospecific Aryl Nitration And Consequent Derivation Of Meso-Tetraarylporphyrins

Numerous studies have been focused on synthesis and applications of porphyrin derivatives. Aminoporphyrins resulting from reduction of nitropoprhyrins were essential precursors of many novel porphyrin compounds. In the present paper, regiospecific aryl nitration and consequent derivation of meso-tetraarylporphyrins were studied.With excessive nitric acid of different concentrations as the nitrating agent, regiospecific of meso-tetraphenylporphyrin (TPP) were investigated in detail. It was concluded that nitration was conducted stepwisely at the para postion of the phenyl ring. Yield of nitrated porphyrins vibrated fiercely with different concentrations of nitric acid. It was found that nitration with 80% nitric acid (w/w, d = 1.45) could afford over 90% yield of mono nitrated TPP. Solvent took a significant effect on proportion between isomers of di-nitrated TPP.Using classical diazotisation of anilines, 5-(4-aminophenyl)-10,15,20-triphenyl-porphyrin was converted to a series of meso-tetraarylporphyrins (TAPs) with different substituents, including 5-(4-hydroxylphenyl)-10,15,20-triphenylporphyrin (80%), 5-(4-chlorophenyl)-10,15,20-triphenylporphyrin (74%), 5-(4-iodinphenyl)-10,15,20-triphenylporphyrin (76%), 5-(4-hydrazinephenyl)-10,15,20-triphenylporphyrin (67%) and 5-(4-bisphenyl)-10,15,20-triphenylporphyrin (32%). Therefore an efficient way of synthesizing unsymmetrically substituted TAPs was developed.Effects of hydroxyl, acetamino and nitro groups at para position of aryl ring on the nitration of TAP were investigated. Nitrations of both hydroxyl- and acetamino-substituted porphyrins were found to take place at the adjacent position of the substituent in the very aryl ring, whereas nitro group was guided into para positions of unsubstituted phenyl ring during the nitration of nitro-substituted porphyrin. When porphyrin containing a pyridyl and three phenyls was nitrated, para positions of two phenyls were substituted. The results were compatible with the substituent effect on electrophilic substitution reactions of aryl compounds, indicating that nitration onTAP was in the mechanism of electrophilic reaction.Valine and nitroxyl functional group were introduced into amino-substituted TPP respectively, and photocytotoxicities of the resulting porphyrins were tested. Compared w ith t heir p recursors, t he p orphyrins w ith t he functional groups s howed improved in vitro photocytotoxicity against tumor cells and relative low photocytotoxicity to the normal cells.