Structural determination of dihydro- and tetrahydrogeranylgeranyl groups at the 17-propionate of bacteriochlorophylls-a

In the final stage of bacteriochlorophyll (BChl) biosynthesis, the presence of BChl-a molecules possessing dihydrogeranylgeranyl and tetrahydrogeranylgeranyl groups at the 17-propionate has been reported. However, the molecular structures of such BChls-a have not yet been determined in terms of the positions of CC double bonds in the 172-ester. In this study, we isolated significant amounts of such pure BChls-a from Rhodopseudomonas palustris and determined their structures by both mass spectrometry and 1H and 13C NMR spectroscopy. The determined structures enable us to discuss a stepwise reduction from a geranylgeranyl to phytyl substituent.