Synthesis and characterisation of pure isomers of iodoacetamidotetramethylrhodamine

Abstract

The isomeric benzoylnitrobenzoate esters 5 and 6, prepared by condensation of 4-nitrophthalic anhydride and 3-(dimethylamino)phenol followed by esterification, were separated by fractional crystallisation and their structures assigned by NOE difference spectroscopy. Reduction of the nitro group in each compound followed by acetylation and ester hydrolysis gave the isomeric acetamido acids 7 and 8, which were efficiently condensed with 3-(dimethylamino)phenol in the presence of trimethylsilyl polyphosphate to give the acetamidorhodamines 9 and 10, respectively. These compounds were converted by standard means into the pure 6- and 5-(iodoacetamido)tetramethylrhodamines 1 and 2. The visible spectroscopic properties of the compounds were examined and accurate extinction coefficients determined.