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Acaryochloris marinais a unique photosynthetic prokaryote containing chlorophyll(Chl)-das a major photoactive pigment (over 95%). The molecular structure of Chl-dis proposed as the 3-formyl analog of Chl-a.However, the stereochemistry of Chl-dat the 132-, 17- and 18-positions has not yet been established unambiguously. In the first part of this paper, we describe the determination of their stereochemistries to be 132-(R)-, 17-(S)- and 18-(S)-configurations by using 1H-1H NOE correlations in 1H-NMR and circular dichroism spectra as well as chemical modification of Chl-ato produce stereochemically defined Chl derivatives. In the second part of the paper, we report a facile synthesis of a self-aggregative Chl by modifying isolated Chl-d.Since Chl-dwas characterized by its reactive 3-formyl group, the formyl group was reduced with t-BuNH2BH3to afford the desirable Chl, 3-deformyl-3-hydroxymethyl-pyrochlorophyll-d(31-OH-pyroChl-d). The synthetic 31-OH-pyroChl-dmolecules spontaneously self-organized to form well-ordered aggregates in a non-polar organic solvent. The self-aggregates are a good model of major light-harvesting antenna systems of green photosynthetic bacteria, chlorosomes, in terms of the following three findings. (1) Both the red-shifted electronic absorption band above 750 nm and its induced reverse S-shape CD signal around 750 nm were observed in 0.5% (v/v) THF-cyclohexane. (2) The stretching mode of the 13-carbonyl group was downshifted by about 35 cm−1from the wavenumber of its free carbonyl. (3) The self-aggregates were quite stable on titration of pyridine to the suspension, in comparison with those of natural chlorosomal bacteriochlorophyll-dpossessing the 3-(1-hydroxyethyl) group.

Eight bacteriochlorophyll (BChl)-dhomologs and epimers were isolated from a strain of the green sulfur bacterium Chlorobium vibrioforme.By a combination of mass spectrometry and 1H-NMR spectroscopy using the chemical shifts of meso- and 31-protons and 1H–1H NOE correlations, the molecular structures were determined as (31R)-8-ethyl-12-methyl, (31R)-8-ethyl-12-ethyl, (31R)-8-propyl-12-methyl, (31S)-8-propyl-12-methyl, (31R)-8-propyl-12-ethyl, (31S)-8-propyl-12-ethyl, (31S)-8-isobutyl-12-methyl and (31S)-8-isobutyl-12-ethyl. The aggregation behavior of the epimerically pure BChls-din hydrophobic organic solvents was examined to investigate the absolute configuration of the 3-(1-hydroxyethyl) group as well as the bulkiness of the C8 and C12 side-chains by using electronic-absorption and fluorescence-emission spectroscopies. At high concentration of the BChls-din CH2Cl2, the absolute configuration of the 3-(1-hydroxyethyl) group governed the formation of a subunit as a building block for the subsequent higher assembly. Upon dilution of the resulting subunit with hexane, the bulkiness of the C8 and C12 side-chains were found to affect the association of the subunits differently: the bulkiness of the C8 side-chain acted as a promoter for the association due to a stabilized hydrophobic interaction among the relevant larger side-chain, whereas the bulkiness of the C12 side-chain acted as an inhibitor for that association due to introduction of a particular steric-hindrance around the side-chain in the aggregates.