A number of fluorescein derivatives were synthesized and their fluorescent properties were studied. Phosphates of the fluorescein derivatives were tested for the alkaline phosphatase-linked fluorescence assay of membrane-bound DNA and were found to give high resolution for detection of DNA, in which DNA was detectable to the amount of 5 fg in the spot test and 0.1 pg in Southern blot hybridization.
3'-O-Aralkyl-5-(4-biphenylcarboxamido)- and 3'-O-aralkyl-5-N'-(3,5-dimethylphenyl)thioureido}fluorescein derivatives are prepared in high yield by alkylation of 5-(4-biphenylcarboxamido)and 5-N'-(3,5-dimethylyhenyl)thioureido}fluoresceins.