Reduction Processes in Biosynthesis of Chlorophyll Molecules: Chemical Implication of Enzymatically Regio- and Stereoselective Hydrogenations in the Late Stages of Their Biosynthetic Pathway

Photosynthetically active chlorophyll molecules are biosynthesized from 5-aminolevulinic acid through protoporphyrin IX. The multistep enzymatic transformations were well investigated, but their pathways and reaction mechanisms have not been fully elucidated in the late stages. The biosynthetic pathways of (bacterio)chlorophylls from protoporphyrin IX are here described from a chemical viewpoint, especially focusing on the reduction processes of the C=C double to C–C single bonds. The regioselective and stereoselective trans-hydrogenation is performed in the enzymatic reductions.