•The C32- and C20-positions of methyl pyropheophorbide-a were iodinated.•Phenyliodine bis(trifluoroacetate) and I2 were used as iodination agents.•The C32-iodinated derivative of methyl pyropheophorbide-a is novel.•The C32-I atom could be removed selectively by treating with NaN3.•The 3-vinyl-20-iodo derivative was successfully prepared.A chlorophyll derivative possessing an iodine atom at the C3-moiety was synthesized from methyl pyropheophorbide-a for the first time using phenyliodine bis(trifluoroacetate) and I2. The use of larger amounts of reagents resulted in additional iodination at the C20-position, thus affording the 3,20-diiodo derivative. The iodine atom at the C3-moiety of the 3,20-diiodo derivative could be removed selectively by treating with NaN3, thus affording the 3-vinyl-20-iodo derivative.

•Radical reactions of a vinyl chlorin induced by thiols and AIBN were examined.•Thiyl radicals attacked regioselectively at the sole C3-vinyl group.•The anti-Markovnikov sulfanyl adducts were obtained as major products.•The radical reaction competed with co-oxidation that gave a formyl chlorin.Radical reactions of a C3-vinylated chlorophyll derivative, methyl pyropheophorbide-a, which were induced by thiols and the conventional initiator azobisisobutyronitrile (AIBN) were examined in vitro for the first time. Thiyl radicals attacked regioselectively at the sole C3-vinyl group, and the anti-Markovnikov sulfanyl adducts were obtained as major products. The other peripheral substituents, as well as the chlorin macrocycle, remained intact. The AIBN-induced radical reaction competed with co-oxidation that afforded the C3-formyl chlorin. This method can open new routes to derivatization of vinyl chlorins.

The C3-vinyl group of a chlorophyll derivative, methyl pyropheophorbide-a, was converted into the formyl group by a novel one-pot reaction with thiophenol at room temperature. The mild reaction can provide insight into development of ‘green’ catalysts displacing OsO4 or O3, and into elucidation of unknown biosynthetic processes of chlorophyll-d.A chlorophyll-a derivative (3-vinyl-chlorin) was smoothly converted into the corresponding chlorophyll-d derivative (3-formyl-chlorin) under mild conditions: treatment with thiophenol in an acidic solution at room temperature.

A preference for one of the two axial ligand-binding sites on the central metal atom of chlorophylls (Chls) and bacteriochlorophylls (BChls) was confirmed. In recently reported crystallographic data on PS2 and LHC2 complexes, there are 42 Chl molecules whose fifth ligands were identified; 33 of 42 molecules bound the fifth ligand at the axial position where the C132-methoxycarbonyl group protrudes (denoting as the ‘back’-type isomer). Among 151 (B)Chl a/b molecules found in eight types of (B)Chl proteins including PS2 and LHC2, 124 molecules (82%) are the ‘back’-type isomers. Such a statistical selection was observed not only for Chl a but also for Chl b and BChls a/b, indicating that the C3-, C7-, and C8-substituents as well as the macrocyclic π-conjugates would have little influence on the ligand-binding site. Computational examinations revealed that the energetic gap between the ‘back’ and its opposite ‘face’ complexes was inherent to (B)Chls and that the C132-methoxycarbonyl moiety contributed relatively greatly to the diastereomeric preference in the ligand binding. Nomenclature of the two distinguishable sides on chlorophyllous macrocycles, as well as the two asymmetric ligand-binding sites, is also discussed.It was confirmed that in photosynthetic proteins (bacterio)chlorophylls prefer the fifth ligand-binding on the one side of the π-macrocycle.

Chlorophyll-a (Chl-a) was readily converted into Chl-d under mild conditions without any enzymes. Treatment of Chl-a dissolved in dry tetrahydrofuran (THF) with thiophenol and acetic acid at room temperature successfully produced Chl-d in 31% yield. During the acidic oxidation, removal of the central magnesium, pheophytinization, was sufficiently suppressed. This mild pathway can give insights into the yet unidentified Chl-d biosynthesis.Highlights► Chlorophyll-d was synthesized in one-step from Chlorophyll-a in vitro. ► The reaction required neither hazardous reagents nor any enzymes. ► This is a possible model reaction of the Chlorophyll-d biosynthesis.