The synthesis of fluorescein-diacrylate (FL-DA) and four-functional fluoresceins (FL) by Michael addition of secondary amines to FL-DA was investigated. FL-DA was successfully synthesized at the ∼ 100 g level. Diallyl amine (DAA) reacted with FL-DA instantaneously. Diethanolamine (DEA) also reacted within 5 min but was unstable and hydrolyzed back to FL. Michael addition of aminodiols with longer carbon chains and diethyl-amino-diacetate (DIDA) was slower but could be accelerated using Candida antarctica lipase B (CALB) as a biocatalyst. The structure of tetrafunctional fluorosceins was confirmed by 13C and 1H NMR. High resolution Mass Spectrometry (HRMS) demonstrated the formation of very pure tetraallyl- and tetraethylacetate-fluoresceins. These multifuntional fluoresceins are good candidates for the
synthesis of imaging agents for a wide variety of applications.
Synthesis and characterization of Four-functional fluoresceins