Short Peptides with Uncleavable Peptide Bond Mimetics as Photoactivatable Caspase-3 Inhibitors

Abstract

Chemical probes that covalently interact with proteases have found increasing use for the study of protease function and localization. The design and synthesis of such probes is still a bottleneck, as the strategies to target different families are highly diverse. We set out to design and synthesize chemical probes based on protease substrate specificity with inclusion of an uncleavable peptide bond mimic and a photocrosslinker for covalent modification of the protease target. With caspase-3 as a model target protease, we designed reduced amide and triazolo peptides as substrate mimetics, whose sequences can be conveniently constructed by modified solid phase peptide synthesis. We found that these probes inhibited the caspase-3 activity, but did not form a covalent bond. It turned out that the reduced amide mimics, upon irradiation with a benzophenone as photosensitizer, are oxidized and form low concentrations of peptide aldehydes, which then act as inhibitors of caspase-3. This type of photoactivation may be utilized in future photopharmacology experiments to form protease inhibitors at a precise time and location.

1,4-Disubstituted 1,2,3-Triazoles as Amide Bond Surrogates for the Stabilisation of Linear Peptides with Biological Activity

“…The amide-to-triazole switch can lead to a higher success rate when compared to other established stabilisation methods such as in the case of BBN(7-14), where four novel peptidomimetics with conserved biological activity were identified whereas the reduction of amide bonds or N -methylation recognised only two novel promising compounds each [ 44 , 116 , 117 ]. On the other hand, in the case of protease inhibitors for caspase-3 or cathepsin K & S, the amide-to-triazole switch was not successful and more promising results were obtained with reduced amide bonds (for caspase-3) or the corresponding azapeptides (for cathepsin K & S) [ 99 , 104 ]. In the same way, additive or synergistic effects of combining multiple triazoles in one peptide appear to be difficult to anticipate based on the data of mono-substituted triazolo-peptidomimetics.…”

“…A lot of effort has been invested in studying their function and localisation. For example, Verhelst and co-workers investigated the possibility to develop a general strategy for the design of chemical probes that covalently interact with proteases [ 104 ]. Their idea was to design inhibitors based on known substrates by substituting the labile peptide bond with a metabolically stable surrogate and attach a photo-crosslinker to covalently inhibit the targeted enzyme.…”

Straightforward Synthesis of Various Chiral Pyrimidines Bearing Stereogenic Center at the C2 position, Including C-Terminal Peptide Isosters

“…This is also particularly desirable as N-heterocycles are considered as highly valuable C-terminal peptides isosteres but their access is still challenging. [9][10][11][12][13][14][15][16][17][18][19][20][21] We present herein our results in this field.…”

“…Scope and limitation for the use of various -chiral carboxamides.As previously stated, peptides with N-heterocyles C-terminal ends are highly desirable compounds. Indeed, C-terminal modified peptidomimetics have been used to limit the enzymatic degradation and to enhance the bioavaibility [9][10][11][12][13][14][15][16][17][18][19][20][21]. To this endeavour, pyrimidines 3ab' and 3ae' derived from Phenylalanine and Valine were deprotected in acidic conditions and then coupled to Cbz-Ala-OH in the presence of PyBOP to give the corresponding C-terminal modified pseudo-peptides 19 and 20 in 65 and 55% yields respectively (Scheme 5).…”

Gold-Catalyzed Amide/Carbamate-Linked N,O-Acetal Formation with Bulky Amides and Alcohols

“…1 H NMR (600 MHz, CDCl 3 , rotamer mixture) δ 7.88 (brd, 1H, J = 7.3 Hz), 7.49 (brd, 1H, J = 7.6 Hz), 7.41−7.42 (m, 1H), 7.27−7.30 (m, 1H), 5.52−5.80 (m, 2H), 5. 29 The Precursor 3d. Compound 3d was prepared from the N-Fmoc amine 1d (62.2 mg, 177 μmol) according to GP-1 and was obtained in a 41% yield (41.1 mg, 72.7 μmol) as a colorless oil after purification by column chromatography on silica gel (eluted with hexane/EtOAc = 10:1).…”