Synthesis of symmetric fluorescently labeled poly(ethylene glycols) using phosphoramidites of pyrenebutanol and their characterization by MALDI mass spectrometry

We report the synthesis and characterization of a series of poly(ethylene oxide) [PEG] polymers in which two pyrene groups are separated by a common EO(87) chain, and flanked by tails of varying EO(x) length. These polymers were prepared by reacting HO-EO(87)-OH (M(n) = 3841, M(w)/M(n) = 1.01) with four different N,N-diisopropylphosphoramidites containing both pyrene (Py) and MeO-EO(x)-substituents. In this way, polymers of the form EO(x)-Py-EO(87)-Py-EO(x) (with MeO end groups) were obtained, with x = 2, 12, 17, and 47. These polymers are particularly useful for studying cyclization kinetics via pyrene excimer formation for two points labeled by pyrenes within the interior of a polymer chain. The polymers were characterized by NMR, size exclusion chromatography, and matrix-assisted laser desorption (MALDI) mass spectroscopy. The MALDI results were particularly informative since each of the oligomers of each of the components could be identified in each mass spectrum.