3-Fluoro-4-hydroxyprolines: Synthesis, Conformational Analysis, and Stereoselective Recognition by the VHL E3 Ubiquitin Ligase for Targeted Protein Degradation

Andrea Testa, Xavier Lucas, Guilherme V. Castro, Kwok-Ho Chan, Jane E. Wright, Andrew C. Runcie, Morgan S. Gadd, William T. A. Harrison, Eun-Jung Ko, Daniel Fletcher, Alessio Ciulli* (Corresponding Author)

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

80 Citations (Scopus)
24 Downloads (Pure)


Hydroxylation and fluorination of proline alters the pyrrolidine ring pucker and the trans:cis amide bond ratio in a stereochemistry-dependent fashion, affecting molecular recognition of proline-containing molecules by biological systems. While hydroxyprolines and fluoroprolines are common motifs in medicinal and biological chemistry, the synthesis and molecular proper-ties of prolines containing both modifications i.e. fluoro-hydroxyprolines have not been described. Here we present a practical syn-thesis of all four diasteroisomers of 3-fluoro-4-hydroxyprolines (F-Hyps). Conformational preferences and the effect of fluorination on hydrogen bond donating capacity are elucidated by means of X-ray crystallography, NMR spectroscopy and quantum mechani-cal calculations. We exemplify an application of F-Hyps as novel building blocks for biomolecular recognition by incorporating them in HIF-1α peptides and small peptidomimetic ligands targeting the von Hippel-Lindau E3 ligase (VHL) – widely used as PROTAC (PROteolysis TArgeting Chimera) conjugates for targeted protein degradation. We found that VHL exhibits stereoselec-tive recognition of the (3R,4S)-F-Hyp over the corresponding (3S,4S) epimer and rationalize this preference through co-crystal structures and electrostatic potential calculations. Hyp substitution with (3R,4S)-F-Hyp into the BET degrader MZ1 retained bind-ing affinities and cellular degradation activities comparable to those of the parent PROTAC. In spite of a ~20-fold loss in binding affinity to VHL, incorporation of the (3S,4S) epimer into MZ1 led to Brd4-selective degradation at nanomolar concentration. We anticipate that the disclosed chemistry of 3-fluoro-4-hydroxyprolines and their application as VHL ligands for targeted protein deg-radation will be of wide interest to medicinal organic chemists, chemical biologists and drug discoverers alike.
Original languageEnglish
Pages (from-to)9299-9313
Number of pages15
JournalJournal of the American Chemical Society
Issue number29
Early online date27 Jun 2018
Publication statusPublished - 25 Jul 2018


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