SYNTHESIS AND CHARACTERIZATION OF PURE ISOMERS OF IODOACETAMIDOTETRAMETHYLRHODAMINE

The isomeric benzoylnitrobenzoate esters 5 and 6, prepared by condensa tion of 4-nitrophthalic anhydride and 3-(dimethylamino)phenol followed by esterification, were separated by fractional crystallisation and t heir structures assigned by NOE difference spectroscopy. Reduction of the nitro group in each compound followed by acetylation and ester hyd rolysis gave the isomeric acetamido acids 7 and 8, which were efficien tly condensed with 3-(dimethylamino) phenol in the presence of trimeth ylsilyl polyphosphate to give the acetamidorhodamines 9 and 10, respec tively. These compounds were converted by standard means into the pure 6- and 5- (iodoacetamido)tetramethylrhodamines 1 and 2. The visible s pectroscopic properties of the compounds were examined and accurate ex tinction coefficients determined.