Efficient synthesis of pyropheophorbide-a and its derivatives

A new and simplified method of preparing hexyloxy pyropheophorbide-a (HPPH), a promising agent used in photodynamic therapy, is described. This method is carried out in two processing steps, replacing an older method requiring five steps. This is accomplished by means of a Dieckmann condensation and subsequent thermal decarboxylation, both occurring in the same high-boiling solvent, thus reversing the long-standing trend in which naturally occurring chlorin derivatives with exocyclic rings are often subjected to conditions that open this ring to obtain chlorin derivatives. In the new process, a raw material without an exocyclic ring is used to construct a product containing the exocyclic ring. The new method does not require cryogenic processing or chromatography, removing the most significant obstacles to large-scale preparation of HPPH and its homologues.