Studies in chlorin chemistry. 3. A practical synthesis of c,d-ring symmetric chlorins of potential utility in photodynamic therapy.

C,D-ring symmetric chlorins 8 were prepared in 47−85% yield, on scales up to several hundred milligrams, by condensation of appropriately substituted bis-formyldihydrodipyrrins 6 and dipyrromethane bis-carboxylic acids 7 in 5% TFA/CH2Cl2 (25 examples). Target chlorins were chosen to systematically probe the effect of lipophilic and hydrophilic substituents on tissue partitioning and cellular membrane penetration in photodynamic therapy (PDT).