Youness Touati-Jallabe

Cyclic enkephalins with a diversely substituted guanidine bridge or a thiourea bridge: Synthesis, biological and structural evaluations

Two series of 22 and 15 atom cyclic enkephalins incorporating a diversely substituted guanidine bridge have been prepared to assess the potential effect of the bridge substitutions on their opioid activity profile. The most notable results were obtained with the shortest cyclic analogues, which showed a significant variation of their binding affinity toward μ and δ opioid receptors in relation to bridge substitution. NMR studies were performed to rationalize these data. Some small analogues were found to exist as at least one major and one minor stable forms, which could be separated by chromatography. In particular, the compounds 13 and 14 with a cyclic substituent were separated in three isomers and the basis of this multiplicity was explored by 2D NMR spectroscopy. All compounds were agonists with slight selectivity for the μ opioid receptor. Compounds 7a (thiourea bridge) and 10a (N-Me-guanidine bridge) showed nanomolar affinity toward μ receptor, the latter being the more selective for this receptor (40-fold).

Further characterization of a putative serine protease contributing to the γ-secretase cleavage of β-amyloid precursor protein.

The 3-alkoxy-7-amino-4-chloro-isocoumarins JLK-6 and JLK-2 have been shown to markedly reduce the production of Amyloid β-peptide (Aβ) by Amyloid-β Precursor Protein (APP) expressing HEK293 cells by affecting the γ-secretase cleavage of APP, with no effect on the cleavage of the Notch receptor. This suggested that these compounds do not directly inhibit the presenilin-dependent γ-secretase complex but more likely interfere with an upstream target involved in γ-secretase-associated pathway. The mechanism of action of these compounds is unknown and there are high fundamental and therapeutical interests to unravel their target. Isocoumarin compounds were previously shown to behave as potent mechanism-based irreversible inhibitors of serine proteases, suggesting that the JLK-directed target could belong to such enzyme family. To get further insight into structure-activity relationships and to develop more potent isocoumarin derivatives, we have synthesized and evaluated a series of isocoumarin analogues with modifications at positions 3, 4 and 7. In particular, the 7-amino group was substituted with either acyl, urethane, alkyl or aryl groups, which could represent additional interaction sites. Altogether, the results highlighted the essential integrity of the 3-alkoxy-7-amino-4-chloro-isocoumarin scaffold for Aβ-lowering activity and supported the involvement of a serine protease, or may be more generally, a serine hydrolase. The newly reported 7-N-alkyl series produced the most active compounds with an IC(50) between 10 and 30μM. Finally, we also explored peptide boronates, a series of reversible serine protease inhibitors, previously shown to also lower cellular Aβ production. The presented data suggested they could act on the same target or interfere with the same pathway as isocoumarins derivatives.