Synthesis of 18-formylated B-ring reduced chlorophyll derivative as a heme A analog and effect of the 18-substituent on optical properties

Abstract

Methyl 17,18-didehydro-pyrobacteriopheophorbides-a possessing the 18-formyl and hydroxymethyl groups as chlorophyllous analogs of hemes A and I, respectively, were prepared by chemically modifying the corresponding 18-methyl counterpart via 17,18-cis-dihydroxylation and successive acidic mono-dehydration. As an increase of the oxidation degree in the 18-substituent (CH3 < CH2OH < CHO), the Soret and Qx absorption bands in dichloromethane were red-shifted, the Qy maxima were blue-shifted, and the relative intensities of the Qy over Soret bands decreased. The 18-formylated chlorin was less fluorescent than the 18-(hydroxy)methylated chlorins. The substitution effect was comparable to that at the 7-position in D-ring reduced chlorins, including chlorophylls-a/b.