Long functionalized poly(ethylene glycol)s of defined molecular weight: Synthesis and application in solid-phase synthesis of conjugates

A concise synthesis of long-chain poly(ethylene glycol) (PEG) of defined molecular weight up to 29 ethyleneoxy units is described. These PEG diols were converted in a two-step synthesis into Fmoc-protected PEG amino acids, suitable as long linkers and compatible with solid-phase peptide synthesis. Long PEG chains (MW > 1000) can be readily synthesized with this method, which has the advantage of defined single molecular weight products over the comparable commercial polymers. The application of these PEG linkers to the synthesis of peptide-PEG-folate conjugates on a solid support was investigated. A method for the solid support synthesis of the targeting component of the conjugate, folic acid-cysteine, was developed, resulting in improved yields with respect to literature methods. The assembly of the peptide, PEG linker, and targeting group on solid support resulted in the synthesis of a conjugate of defined molecular weight and structure.