Design and Synthesis of Novel Phenothiazinium Photosensitiser Derivatives

A high-yielding approach towards N-(2-aminoethyl)-Azure B has been established and extended towards the preparation of a functionalized peptide-dye synthetic precursor; Boc-protected 3-(alkylamino)phenothiazin-5-ium TFA. This has been utilized in a series of reactions with various amines towards nine novel 3,7-disubstituted phenothiazin-5-ium derivatives. Cleavage of the Boc group in the 3,7-disubstituted salts allowed a further seven novel dyes to be prepared and these have been utilized in a practical methodology designed for the synthesis of 13 novel phenothiazine-peptide conjugates. These peptide-photosensitizer vectors consist of a covalent attachment of a tethered dye to various protected amino acid moieties including the cell-penetrating peptide (CPP) octa-arginine and exhibit intense absorption maxima in the 623650 nm regions of the visible spectrum. The main goal of the studies is the design of cell-compatible photosensitisers that may be employed in photodynamic therapy. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)