4-Fluoroprolines: Conformational Analysis and Effects on the Stability and Folding of Peptides and Proteins

Abstract

Proline is unique among proteinogenic amino acids because a pyrrolidine ring links its amino group to its side chain. This heterocycle constrains the conformations of the main chain and thus templates particular secondary structures. Proline residues undergo post-translational modification at the 4-position to yield 4-hydroxyproline, which is especially prevalent in collagen. Interest in characterizing the effects of this modification led to the use of 4-fluoroprolines to enhance inductive properties relative to the hydroxyl group of 4-hydroxyproline and to eliminate contributions from hydrogen bonding. The strong inductive effect of the fluoro group has three main consequences: enforcing a particular pucker upon the pyrrolidine ring, biasing the conformation of the preceding peptide bond, and accelerating cis/trans prolyl peptide bond isomerization. These subtle, yet reliable modulations make 4-fluoroproline–incorporation a complement to traditional genetic approaches for exploring structure–function relationships in peptides and proteins, as well as for endowing peptides and proteins with conformational stability.

Fluorinated Prolines as Conformational Tools and Reporters for Peptide and Protein Chemistry

“…The synthesis and main uses of 4-fluoroprolines has been thoroughly described recently in an excellent review by Raines and Newberry. 43…”

Comparative effects of trifluoromethyl- and methyl-group substitutions in proline

“…91 Another common modification is hydroxylation in position 4; finally extensive experimental data have addressed 4-fluoroprolines. 19,20 For this reason, we compared the lipophilicity of the 4-substituted proline derivatives in Fig. 10.…”

“…Several unique biological phenomena associated with the presence of Pro in polypeptide structures have been investigated through the substitution with structural analogues of Pro (ProAs). ProAs were shown to impact translation yields 13,14 and velocities, 15 folding kinetics, [16][17][18] protein structural stability, [19][20][21][22][23][24][25] aggregation properties, 17,26 biological potency of peptides 27,28 and more. In each individual case, changes resulting from the substitution of a Pro with an analogue were attributed to structural differences or are rationalized using data obtained from experimental molecular models.…”

Hydrolysis, polarity, and conformational impact of C-terminal partially fluorinated ethyl esters in peptide models

“…The hydrophobicity [ 23 – 24 ], conformational equilibria [ 25 ], and the thermodynamic [ 26 – 29 ] and kinetic [ 30 – 31 ] folding profiles can be altered by the presence of even a single fluorinated amino acid in the sequence. Perhaps the most studied molecules exhibiting such effects are the proline analogues, with the proline-to-fluoroproline exchange providing the first proof-of-principle and experimental basis for a number of subsequent conceptual studies [ 32 ]. For example, these were used to demonstrate the impact of non-canonical amino acids in proteins [ 33 ].…”