Synthesis of chlorophyll-a homologs by Wittig and Knoevenagel reactions with methyl pyropheophorbide-d

The formyl group at the 3-position of methyl pyropheophorbide-d reacted with phosphorous ylides and activated methylene compounds to give efficiently the corresponding 3-(2-substituted ethenyl)chlorins compounds as a product of Wittig and Knoevenagel reactions. The trans-isomers of the synthetic chlorins, methyl 3(2)-substituted pyropheophorbide-a had visible bands absorbing longer wavelengths than the cis-isomers and the 3(2)-unsubstituted chlorin, methyl pyropheophorbide-a. 3(2),3(2)-Disubstitution strongly affected the absorption bands compared with the bands of the 3(2)-monosubstituted chlorins. The absorption, fluorescence and circular dichroism spectra were dependent upon the 3-substituents conjugated with the chlorin chromophore. (C) 1997 Elsevier Science Ltd.