Phenothiazinium photosensitisers: choices in synthesis and application

The use of phenothiazinium dyes in the photodynamic therapy of cancer and its related antimicrobial protocols, e.g. blood product decontamination, has been mainly limited to a few commercially available dyes, such as Methylene Blue, the Azure stains and Toluidine Blue O. Novel Methylene Blue derivatives are scarce in the literature, and yet there are various synthetic routes available to furnish sufficient candidate compounds for properly organised programmes of photosensitiser design and development to be carried out. In this review, consideration is given to the types of phenothiazinium derivative required for the various photodynamic applications currently under examination, and also to the synthetic strategies involved in their preparation. (C) 2003 Elsevier Science Ltd. All rights reserved.