(2S,4R)-1-((S)-20-amino-2-(tert-butyl)-4-oxo-6,9,12,15,18-pentaoxa-3-azaicosanoyl)-4-hydroxy-N-(4-(4-methylthiazol-5-yl)benzyl)pyrrolidine-2-carboxamide hydrochloride

FPN75233, also known as (S,R,S)-AHPC-PEG5-NH2 hydrochloride, is a ProTAC building block. This conjugate contains a von Hippel-Lindau (VHL)-recruiting ligand and a PEGylated crosslinker with pendant amine for reactivity with a carboxyl group on the target ligand. When used with other protein degrader building blocks with a pendant amine parallel synthesis can be used to more quickly generate ProTAC libraries that feature variation in crosslinker length composition and E3 ligase ligand. This product has no formal name at the moment.