Facile Synthesis of Pyridyl Rosamines as Potential Photosensitizers

Rosamines represent one of the most promising groups of xanthene dyes. Their excellent photophysical properties allow their widespread application. Their use as photosensitizers in photodynamic therapy has recently gained considerable attention. Here, we report the facile, effective, microwave-assisted synthesis of rosamine dyes. Pyridylbenzaldehyde derivatives were reacted with 1,3-dialkylaminophenols or 8-hydroxyjulolidine in toluene without any additive. The resulting pyridyl rosamines were investigated for their cytotoxic effect against the A431 human epidermoid carcinoma cell line to estimate their potential as photosensitizers. The compounds displayed light-induced toxicity in the submicromolar or occasionally in the low nanomolar range. One of the julolidine-based derivatives exhibited a phototoxic index above 100, indicating an increase in light-induced cytotoxic efficacy of two orders of magnitude compared to its negligible dark toxicity. This compound is a particularly promising candidate for the development of novel pyridyl-rosamine-based photosensitizers for photodynamic therapy of skin cancer.