Formation of protoporphyrin IX from carboxylic- and amino-derivatives of 5-aminolevulinic acid

N-f-ALA showed an outstanding stability in water solutions even at pH 7. However, it induced no PPIX neither in WiDr cells in vitro, nor in mouse skin in vivo. A probable reason is lack of an enzyme that can cleave the bond between the formyl group and ALA. Thus, steric hindrance may prevent processing of the compound into porphobilinogen. N-f-ALA did not inhibit PpIX formation from ALA and is unable to enter the heme cycle. Generation of ALA from its derivatives, therefore, seems to be an essential step in PPIX synthesis.