Tetrazole as a Replacement of the Electrophilic Group in Characteristic Prolyl Oligopeptidase Inhibitors

Abstract

4-Phenylbutanoyl-aminoacyl-2(S)-tetrazolylpyrrolidines were studied as prolyl oligopeptidase inhibitors. The compounds were more potent than expected from the assumption that the tetrazole would also here be a bioisostere of the carboxylic acid group and the corresponding carboxylic acids are at their best only weak inhibitors. The aminoacyl groups L-prolyl and L-alanyl gave potent inhibitors with IC 50 values of 12 and 129 nM, respectively. This was in line with typical prolyl oligopeptidase inhibitors; however, we did observe a difference with N-methyl-L-alanyl, which gave potent inhibitors in typical prolyl oligopeptidase inhibitors but not in our novel compound series. Furthermore, all studied 4-phenylbutanoyl-aminoacyl-2(S)-tetrazolylpyrrolidines decreased α-synuclein dimerization at the concentration of 10 μM, also when they were only weak inhibitors of the proteolytic activity of the enzyme with an IC 50 value of 205 μM. Molecular docking studies revealed that the compounds are likely to bind differently to the enzyme compared to typical prolyl oligopeptidase inhibitors represented in this study by 4-phenylbutanoyl-aminoacyl-2(S)cyanopyrrolidines.

Prolyl oligopeptidase inhibition reduces alpha‐synuclein aggregation in a cellular model of multiple system atrophy

“…In our previous studies, we have shown that a serine protease, prolyl oligopeptidase (PREP), increases aSyn oligomerization via direct protein‐protein interaction 15 , 16 and negatively regulates autophagy. 17 Importantly, small‐molecular PREP inhibitors can interfere with this interaction, leading to decreased aSyn aggregation, 15 , 18 , 19 and PREP inhibition or deletion also stimulates autophagy and increases the degradation of aSyn oligomers 16 , 17 , 18 and fibrils. 20 In aSyn‐based in vivo PD model, PREP inhibition has shown disease‐modifying impact by restoring an aSyn virus vector‐induced behavioural deficit.…”

2-Imidazole as a Substitute for the Electrophilic Group Gives Highly Potent Prolyl Oligopeptidase Inhibitors

“…We have also demonstrated that the effects of PREP ligands on αSyn dimerization and autophagy have no direct correlation to their IC 50 values. 15 , 16 Inhibition of the proteolytic activity has been thoroughly studied, but we are still learning how protein–protein interactions of PREP are regulated. PREP is a highly dynamic protein, where inhibitor binding restricts its conformational freedom, 17 and our working hypothesis is that the functions of PREP are dependent on what conformations PREP can adopt.…”

“…In our previous study, we showed that a tetrazole ring could be directly attached to the inhibitor structure at the position of the electrophilic group without the important carbonyl group, resulting in moderately potent inhibitors 1a – e , and that the tetrazole ring was not a bioisostere of a carboxylic acid group. 16 In addition, the tetrazoles demonstrated clearly disconnected structure–activity relationships (SARs) for inhibition of the proteolytic activity and modulation of αSyn dimerization. In the present study, other nitrogen-containing five-membered heteroaromatics with different hydrogen-bonding capabilities and charges at physiological pH were investigated.…”

“…The starting compounds 3 – 10 were synthesized analogously to the previously reported procedure. 16 These were then used to synthesize the different heteroaryls according to Scheme 1 . The tetrazoles 15 – 17 were synthesized from 3 – 6 according to the previously reported procedure.…”

“…The tetrazoles 15 – 17 were synthesized from 3 – 6 according to the previously reported procedure. 16 Compound 1a was reacted with MeI to obtain the methylated tetrazoles 18a and 19a . We first made an attempt to synthesize compound 20a by coupling 1,2,4-triazolylpyrrolidine to N -(4-phenylbutanoyl)- l -proline.…”