1,5-Disubstituted indole derivatives as selective human neuronal nitric oxide synthase inhibitors

Abstract

A series of 1,6-disubstituted indole derivatives was designed, synthesized and evaluated as inhibitors of human nitric oxide synthase (NOS). By varying the basic amine side chain at the 1-position of the indole ring, several potent and selective inhibitors of human neuronal NOS were identified. In general compounds with bulkier side chains displayed increased selectivity for nNOS over eNOS and iNOS isoforms. One of the compounds, (R)-8 was shown to reduce tactile hyperesthesia (allodynia) after oral administration (30 mg/kg) in an in vivo rat model of dural inflammation relevant to migraine pain. Keywords1,6-Disubstitued indole derivatives; Nitric oxide; Nitric oxide synthase; Nitric oxide synthase inhibitors; Selective neuronal nitric oxide synthase inhibitors Nitric oxide (NO) is an inorganic free radical that has diverse roles both in normal and pathological processes, including the regulation of blood pressure, neurotransmission and macrophage defense systems. 1 NO is synthesized from the enzyme catalysis of L-arginine to L-citrulline by three isoforms of nitric oxide synthase (NOS): two constitutive forms in neuronal cells (nNOS) and endothelial cells (eNOS), and an inducible form in macrophage cells (iNOS). Overstimulation or overproduction of NO by nNOS and iNOS has been shown to play a key role in several disorders, including septic shock, arthritis, diabetes, ischemiareperfusion injury, pain and various neurodegenerative diseases. 2 However, any inhibitors to treat these conditions must avoid eNOS inhibition as this will lead to unwanted effects such as enhanced white cell and platelet activation, hypertension and atherogenesis. 3 Therefore, the development of selective NOS inhibitors is of considerable interest, both from a therapeutic perspective and also as specific pharmacological tools. 4 Although there is low homology among the three NOS primary sequences (~50%), the active sites of the enzymes appears to be relatively conserved with 16 out of 18 residues within 6 Å being identical, presumably explains the difficulty obtaining selective NOS The pharmacophore model we adopted for the arginine binding site of the NOS enzyme includes a guanidine isosteric group (amidine group) and a basic amine group, both attached to a central aryl scaffold (indole core) as shown in Figure 1. 4,15 The amidine group makes an important bidentate interaction with the conserved glutamic acid residue to achieve the necessary potency; whereas the basic amine is assumed to provide the nNOS isoform selectivity. 15 Our design strategy is based on an indole core as an aryl scaffold and exploring various basic amine side chains for achieving the NOS isoform selectivity. As part of our ongoing efforts to find small molecule selective nNOS inhibitors for treating CNS disorders, herein we report the synthesis and biological activity evaluations of a series of 1,6-disubstituted indole derivatives and in vivo activity of (R)-8 in a rat model relevant to migraine pain. 15 Two general approaches were undertaken for the prepa...

The Discovery of Potentially Selective Human Neuronal Nitric Oxide Synthase (nNOS) Inhibitors: A Combination of Pharmacophore Modelling, CoMFA, Virtual Screening and Molecular Docking Studies

“…Fifty-nine novel nNOS inhibitors were taken from the literature [15–17,21,22] with their biological activities in terms of IC 50 values; 49 compounds were used as a training set and the remaining 10 compounds were used as a test set, based on random selection. The compounds in the test set have a range of biological activity values similar to that of the training set.…”

TLQP Peptides in Amyotrophic Lateral Sclerosis: Possible Blood Biomarkers with a Neuroprotective Role

“…In patients, ALS related mutations were studied as follows: exon 6 of the TARDBP gene, and all five coding exons of the SOD1 gene were screened by polymerase chain reaction and sequenced using the Big-Dye Terminator v3.1 kit (Applied Biosystems Inc) and an ABI Prism 3130 Genetic Analyzer. A repeat-primed polymerase chain reaction assay was used to screen for the GGGGCC hexanucleotide expansion in the first intron of C9ORF72 (DeJesus-Hernandez et al, 2011;Renton et al, 2011). ALS patients studied showed either of: TARDBP-A382T mutation (n=16), SOD1-G93A mutation (n=3); expansion in the C9ORF72 gene (n=5), or no identifiable ALS-related mutation (n=20).…”

Recent Advances Toward Improving the Bioavailability of Neuronal Nitric Oxide Synthase Inhibitors

“…Many compounds in this class (for example, 32–36 ) exhibited submicromolar nNOS inhibition (Figure 7), but suffered from low selectivities, especially over eNOS. [39–44] However, compounds 32–36 were shown to reverse thermal hyperalgesia in vivo in the L 5 /L 6 spinal nerve ligation model of neuropathic pain. Although 32 only had a nNOS/eNOS selectivity of 33-fold, it was devoid of any significant vasoconstrictive effects in human coronary arteries, which is associated with the inhibition of human eNOS.…”