A positional scanning combinatorial library of peptoids as a source of biological active molecules: identification of antimicrobials.

A positional scanning library of N-alkylglycine trimers (peptoids) containing over 10 000 compounds has been synthesized on solid phase. The synthetic pathway involved the use of the submonomer strategy and a set of 22 commercially available primary amines as a chemical diversity source. The unbiased nature of the library allowed its screening against a variety of biological targets, leading to the identification of individual peptoids exhibiting remarkable biological activities (García-Martínez, C. et al. Proc. Natl. Acad. Sci. U.S.A. 2002, 99, 2374. Montoliu, et al. J. Pharm. Exp. Therap. 2002, 302, 29. Planells-Cases, R., et al. J. Pharm. Exp. Therap. 2002, 302, 163). In the present work, the screening of this library against a panel of Gram-positive and Gram-negative bacteria led to the identification of different compounds exhibiting antimicrobial activity.

A novel N-methyl-D-aspartate receptor open channel blocker with in vivo neuroprotectant activity.

Excitotoxicity has been implicated in the etiology of ischemic stroke, chronic neurodegenerative disorders, and very recently, in glioma growth. Thus, the development of novel neuroprotectant molecules that reduce excitotoxic brain damage is vigorously pursued. We have used an ionic current block-based cellular assay to screen a synthetic combinatorial library of trimers of N-alkylglycines on the N-methyl-D-aspartate (NMDA) receptor, a well known molecular target involved in excitotoxicity. We report the identification of a family of N-alkylglycines that selectively blocked the NMDA receptor. Notably, compound 3,3-diphenylpropyl-N-glycinamide (referred to as N20C) inhibited NMDA receptor channel activity with micromolar affinity, fast on-off blockade kinetics, and strong voltage dependence. Molecule N20C did not act as a competitive glutamate or glycine antagonist. In contrast, saturation of the blocker binding site with N20C prevented dizolcipine (MK-801) blockade of the NMDA receptor, implying that both drugs bind to the same receptor site. The N-alkylglycine efficiently prevented in vitro excitotoxic neurodegeneration of cerebellar and hippocampal neurons in culture. Attenuation of neuronal glutamate/NMDA-induced Ca(2+) overload and subsequent modulation of the glutamate-nitric oxide-cGMP pathway seems to underlie N20C neuroprotection. Noteworthy, this molecule exhibited significant in vivo neuroprotectant activity against an acute, severe, excitotoxic insult. Taken together, these findings indicate that N-alkylglycine N20C is a novel, low molecular weight, moderate-affinity NMDA receptor open channel blocker with in vitro and in vivo neuroprotective activity, which, in due turn, may become a tolerated drug for the treatment of neurodegenerative diseases and cancer.

Prevention of in vivo excitotoxicity by a family of trialkylglycines, a novel class of neuroprotectants.

Excitotoxicity has been implicated in the etiology of ischemic stroke and chronic neurodegenerative disorders. Hence, the development of novel neuroprotectant molecules that ameliorate excitotoxic brain damage is vigorously pursued. We used a neuroprotection-based cellular assay to screen a synthetic combinatorial library of N-alkylglycine trimers. Two compounds (6-1-2 and 6-1-10) that efficiently prevented excitotoxic neurodegeneration in vitro and in vivo were identified. Both molecules protected primary cultures of cerebellar neurons against glutamate-induced neuronal death with an efficiency equivalent to N-methyl-D-aspartate (NMDA) receptor antagonists. These trialkylglycines did not block appreciably the NMDA receptor channel, or attenuated glutamate-induced increase of Ca(2+), or affect the glutamate-nitric oxide-cGMP pathway. Intraperitoneal injection of both peptoids in mice attenuated > or = 80% ammonia-induced, NMDA receptor-mediated animal death. Furthermore, these two molecules reduced by > or = 50% the neurodegeneration in striatum in a rat model of cerebral ischemia. Neuroprotection against ischemia was associated with decreased activation of caspase-3, reflecting prevention of apoptotic neuronal death. Collectively, the results reported indicate that these trialkylglycines are new neuroprotectant leads with important in vivo activity against excitotoxicity, and that they act on a novel, yet-unrecognized cellular target. These lead compounds may become tolerated drugs for the treatment of acute and chronic neurodegenerative diseases with fewer side effects than NMDA receptor antagonists.

Attenuation of thermal nociception and hyperalgesia by VR1 blockers.

Vanilloid receptor subunit 1 (VR1) appears to play a critical role in the transduction of noxious chemical and thermal stimuli by sensory nerve endings in peripheral tissues. Thus, VR1 antagonists are useful compounds to unravel the contribution of this receptor to pain perception, as well as to induce analgesia. We have used a combinatorial approach to identify new, nonpeptidic channel blockers of VR1. Screening of a library of trimers of N-alkylglycines resulted in the identification of two molecules referred to as DD161515 [N-[2-(2-(N-methylpyrrolidinyl)ethyl]glycyl]-[N-[2,4-dichlorophenethyl]glycyl]-N-(2,4-dichlorophenethyl)glycinamide] and DD191515 [[N-[3-(N,N-diethylamino)propyl]glycyl]-[N-[2,4-dichlorophenethyl]glycyl]-N-(2,4-dichlorophenethyl)glycinamide] that selectively block VR1 channel activity with micromolar efficacy, rivaling that characteristic of vanilloid-related inhibitors. These compounds appear to be noncompetitive VR1 antagonists that recognize a receptor site distinct from that of capsaicin. Intraperitoneal administration of both trialkylglycines into mice significantly attenuated thermal nociception as measured in the hot plate test. It is noteworthy that these compounds eliminated pain and neurogenic inflammation evoked by intradermal injection of capsaicin into the animal hindpaw, as well as the thermal hyperalgesia induced by tissue irritation with nitrogen mustard. In contrast, responses to mechanical stimuli were not modified by either compound. Modulation of sensory nerve fibers excitability appears to underlie the peptoid analgesic activity. Collectively, these results indicate that blockade of VR1 activity attenuates chemical and thermal nociception and hyperalgesia, supporting the tenet that this ionotropic receptor contributes to chemical and thermal sensitivity and pain perception in vivo. These trialkylglycine-based, noncompetitive VR1 antagonists may likely be developed into analgesics to treat inflammatory pain.