N-Boc-4,4-difluoro-l-proline (CAS number 203866-15-3) is a tert-butoxycarbonyl (Boc) protected l-proline with two fluorine substituents at 4-position. N-Boc-4,4-difluoro-l-proline is an S-enantiomer, making it an excellent additive/catalyst in asymmetric reactions. In protein/peptide chemistry, N-Boc-4,4-difluoro-l-proline is introduced for conformational control favoring 78% cis-conformers. The conformation selectivity is also expressed in the 19F NMR spectrum which is a powerful tool to study the isomerization of peptides and proteins.
N-Boc-4,4-difluoro-l-proline is also applied as a molecular scaffold for synthesizing fibroblast activation protein, a trans-membrane serine protease.