Clickable PEG conjugate obtained by “clip” photochemistry: Synthesis and characterization by quantitative 19F NMR

In this paper, we describe a grafting methodology associated to a quantitative 19F NMR method (qNMR) for the conjugation of small molecules on a PEG building block aimed at click chemistry applications in the domain of drug delivery systems. Acetylenic PEG (PEG-yne) was first derivatized with a fluorinated benzyl amine (TagF6) by means of photografting of a trifluoromethylphenyl diazirine bifunctional linker (TPD-clip). The amount of TagF6 grafted on PEG-yne was calculated by NMR using an internal standard (trifluoroethanol) and adjusting of the acquisition and processing parameters. NMR is used as a valuable alternative to the complex procedures often employed for the quantification of functionalities on biomaterials. The accuracy of the qNMR methodology was attested by controlling its linearity, the determination of limits of quantification and the percentage of recovery. A good assessment of the TagF6 grafting rates was obtained after taking into account the inherent unspecific adsorption that occurs on materials. This versatile methodology that combines simple chemistry and a common analytical tool was, in a second time, applied to the preparation of a PEG conjugated with a RGD (Arg-Gly-Asp) peptidomimetic in a controlled manner.

A fluorinated probe and a RDG peptidomimetic were easily conjugated to an alkyne terminated PEG in three steps from a commercial α-methoxy-ω-hydroxy-PEG via a “clip photochemistry” process occurring in solid phase. To avoid the tricky procedures of material characterization a routine 19F qNMR protocol was developed.Figure optionsDownload as PowerPoint slideHighlights
► Grafting of NHS esters on alkyne terminated PEG with trifluoromethylphenyl diazirine.
► Preservation of the alkyne function during chemical derivatizations.
► Easy conjugation of fluorinated probe and peptidomimetic on PEG.
► Development, validation and application of a quantitative 19F NMR protocol.