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).