Abstract
Almost all naturally occurring chlorophyll (Chl) pigments have a propionate-type ester group at the 17-position. The esterifying substituent is not directly attached to the conjugated π-system of Chl molecules and does not affect their electronic-absorption properties. Therefore, it has attracted less attention than other peripheral substituents. However, the hydrophobic ester group is thought to play an important role in stabilizing their complexation with peptides in photosynthetic apparatuses. In the final stage of Chl biosynthesis, the geranylgeranyl (GG) group of Chl-a is hydrogenated to yield phytylated Chl-a via the intermediates possessing dihydrogeranylgeranyl (DHGG) and tetrahydrogeranylgeranyl (THGG) groups. We found the accumulation of Chls-a having different ester groups in the centric diatom Chaetoceros calcitrans, and determined their structures by 1H / 13C NMR spectroscopy and mass spectrometry. The DHGG group has a single bond in C10-C11, and the THGG group has single bonds in C6-C7 and C10-C11. Interestingly, the structure in from that in BChl-a as determined previously in terms of DHGG of Chl-a was different in the positions of three C=C double bonds.
