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Concept
Rose Bengale
Résumé
Rose bengal (4,5,6,7-tetrachloro-2',4',5',7'-tetraiodofluorescein) is a stain. Rose bengal belongs to the class of organic compounds called xanthenes. Its sodium salt is commonly used in eye drops to stain damaged conjunctival and corneal cells and thereby identify damage to the eye. The stain is also used in the preparation of Foraminifera for microscopic analysis, allowing the distinction between forms that were alive or dead at the time of collection.
A form of rose bengal is also being studied as a treatment for certain cancers and skin conditions. The cancer formulation of the drug, known as PV-10, is currently undergoing clinical trials for melanoma, breast cancer. and neuroendocrine tumors. The company also has formulated a drug based on rose bengal for the treatment of eczema and psoriasis; this drug, PV-10, is currently in clinical trials as well.
Rose bengal was originally prepared in 1882 by Swiss chemist Robert Ghnem, as an analogue of fluorescein. Rudolf Nietzki at the University of Basel identified the principal constituents of rose bengal as iodine derivatives of di- and tetra-chlorofluorescein. The compound was originally used as a wool dye. Its name derives from rose (flower) and Bengal (region); it is printed as rose bengal or Rose Bengal in the scientific literature.
Despite its complicated photochemistry involving several species, rose bengal is also used in synthetic chemistry to generate singlet oxygen from triplet oxygen. The singlet oxygen can then undergo a variety of useful reactions, particularly [2 + 2] cycloadditions with alkenes and similar systems.
Rose bengal can be used to form many derivatives that have important medical functions. One such derivative was created so to be sonosensitive but photoinsensitive, so that with a high intensity focused ultrasound, it could be used in the treatment of cancer. The derivative was formed by amidation of rose bengal, which turned off the fluorescent and photosensitive properties of rose bengal, leading to a usable compound, named in the study as RB2.
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