Structure–activity relationship of novel and known inhibitors of human dimethylarginine dimethylaminohydrolase-1: Alkenyl-amidines as new leads

Recent studies demonstrated that inhibition of dimethylarginine dimethylaminohydrolase (DDAH) activity could be a new strategy to indirectly affect nitric oxide (NO) formation by elevating Nω-methylated l-arginine (NMMA, ADMA) levels. This approach is an alternate strategy for the treatment of diseases associated with increased NO-concentrations. To date, three classes of potent inhibitors are known: (1) pentafluorophenyl sulfonates (IC50 = 16–58 μM, PaDDAH), which are also inhibitors for the arginine deiminase; (2) the most potent inhibitors are based on indolylthiobarbituric acid (IC50 = 2–17 μM, PaDDAH), which were identified by virtual modelling; and (3) l-arginine analogs, whose best representative is Nω-(2-methoxyethyl)-l-arginine (IC50 = 22 μM, rat DDAH). Based on these known structures, we aimed to develop inhibitors for the human DDAH-1 with improved potency and better relative selectivity for DDAH-1 over NOS. Particularly, the binding pocket of the guanidine-moiety was investigated by screening differently substituted guanidines, amidines and isothioureas in order to collect information on possible binding modes in the active site. All substances were tested in a plate-reader format and HPLC assay and several potent inhibitors were identified with Ki-values varying from 2 to 36 μM, with N5-(1-iminobut-3-enyl)-l-ornithine (l-VNIO) being the most potent inhibitor of the human DDAH-1 so far described. Besides these potent inhibitors alternate substrates for hDDAH-1 were identified as well.

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