Synthesis of chlorophyll-c derivatives by modifying natural chlorophyll-a

Chlorophyll- a (Chl- a ) was extracted from cyanobacterial cells and modified to methyl pyropheophorbide- a . The 3-vinyl-chlorin was transformed to zinc complex of the corresponding 3-acetyl-porphyrin. The zinc porphyrin was oxidized to give cis -7,8- and 17,18-dihydroxy-chlorins as well cis -7,8- cis -17,18-tetrahydroxybacteriochlorin. After zinc-demetallation, the isolated cis -7,8- and 17,18-diols were reduced at the 3-acetyl group and triply dehydrated under acidic conditions to afford two regioisomeric 3-vinyl-porphyrins, methyl divinyl-pyroprotopheophorbide- a possessing the 8-vinyl group and 17-propionate residue (one of the divinyl-protoChl- a derivatives) and methyl pyropheophorbide- c 1 possessing the 8-ethyl group and 17-acrylate residue (one of the Chl- c 1 derivatives), respectively. The resulting 7,8,17,18-tetrol was reduced and then acidically treated, giving five-fold dehydrated free base porphyrin, methyl pyropheophorbide- c 2 possessing the 3,8-divinyl groups and 17-acrylate residue (one of the Chl- c 2 derivatives). The visible absorption and fluorescence emission spectra of the three semi-synthetic 3-vinyl-porphyrins in dichloromethane were compared with those of the corresponding 8-ethyl-porphyrin bearing the 17-propionate residue, methyl pyroprotopheophorbide- a (one of the protoChl- a derivatives). The Soret and Qy absorption maxima were shifted to longer wavelengths with an increase of π-conjugation in a molecule: protoChl- a (8-CH 2 CH 3 /17-CH 2 CH 2 COOCH 3 )