Synthesis of Gly-ψ[(Z)CF═CH]-Phe, a Fluoroalkene Dipeptide Isostere, and Its Incorporation into a Leu-enkephalin Peptidomimetic

Abstract

A new Leu-enkephalin peptidomimetic designed to explore the hydrogen bond acceptor ability of the third peptide bond has been prepared and studied. This new analog is produced by replacing the third amide of Leu-enkephalin with a fluoroalkene. An efficient and innovative synthesis of the corresponding dipeptide surrogate Fmoc-Gly-ψ[(Z)CF═CH]-Phe-OH is described. The key step involves the alkylation of a tin dienolate from the less hindered face of its chiral sulfonamide auxiliary derived from camphor. Once its synthesis was complete, its incorporation into the peptidomimetic sequence was achieved on a solid support with chlorotrityl resin following the Fmoc strategy. The peptidomimetic was characterized using competition binding with [I]-deltorphin I on membrane extracts of HEK293 cells expressing the mouse delta opioid receptor (DOPr) and based on its abilities to inhibit the electrically induced contractions of the mouse vas deferens and to activate the ERK1/2 signaling pathway in DRGF11/DOPr-GFP cells. Together with our previous observations, our findings strongly suggest that the third amide bond of Leu-enkephalin primarily acts as a hydrogen bond acceptor in DOPr. Consequently, this amide bond can be successfully replaced by an ester, a thioamide, or a fluoroalkene without greatly impacting the binding or biological activity of the corresponding analogs. The lipophilicity (LogD) of the active analog was also measured. It appears that fluoroalkenes are almost as efficient at increasing the lipophilicity as normal alkenes.

Synthesis and Opioid Activity of Tyr1‐ψ[(Z)CF=CH]‐Gly2 and Tyr1‐ψ[(S)/(R)‐CF3CH‐NH]‐Gly2 Leu‐enkephalin Fluorinated Peptidomimetics

“…Although a 60‐fold decrease from the parent compound 5 , this activity confirms that the Tyr 1 ‐Gly 2 amide is not essential for binding to the DOPR . These results contrast the six‐fold decreased binding affinity in Gly 3 ‐Phe 4 fluoroalkene peptidomimetic . At the MOPR, a similar activity trend emerged with 6 being the only active analogue, albeit 45‐fold less active than 5 .…”

“…[24] These results contrast the six-foldd ecreased binding affinity in Gly 3 -Phe 4 fluoroalkenep eptidomimetic. [58] At the MOPR, as imilar activity trend emerged with 6 being the only active analogue, albeit 45-foldl ess active than 5.W hile the fluoroalkene modification did not impart as ignificant change to the m/d selectivity,t his substructure will likelys tabilize the probe towardp roteolytic metabolism. Additionally,t he lack of activity seen with (S)-7 and (R)-8 gives further insighti nto the SAR aroundt he amide bond, specificallyt hat the receptors do not toleratet he ( Ta ble1), as previously demonstrated for trifluoroethylamine substitution at Gly 3 -Phe 4 (30-to 110-foldd ecreasei na ffinity), and at Gly 2 -Gly 3 (non-measurable affinity).…”

Incorporating a Monofluoroalkene into the Backbones of Short Peptides: Evaluating the Impact on Local Hydrophobicity

“…Although log P is still the reference value for hydrophobicity, a good correlation with φ 0 is observed . Furthermore, because only a few examples of evaluation of the lipophilicities of fluorinated peptides/peptidomimetics are present in the literature, the use of this parameter would allow comparison with the work of Brigaud and co‐workers …”

“…Different examples of its use as a peptide bond isostere, its incorporation into larger peptides and its biological activity have been published over the years . Interestingly, only one group has reported a quantitative measure of the hydrophobicity of a peptidomimetic containing a monofluoroalkene system: the β‐sheeted Leu‐enkephalin . In that case, no general conclusion about the effect of the incorporation of the fluoroalkene moiety can be drawn, due to the conformational effect.…”

Exploration of the fifth position of leu‐enkephalin and its role in binding and activating delta (DOP) and mu (MOP) opioid receptors

“…The remaining leucine is viewed as the residue responsible for the specificity (ie the “address”; Figure ) . We have shown previously that a systematic replacement of the amide bonds contained in Leu‐enkephalin was useful to explore and understand their role and involvement in the interaction of Leu‐enkephalin with DOP . In the present study, we investigated the role of the fifth position of Leu‐enkephalin in binding and activating DOP and MOP.…”