Synthesis of chiral 1-(2'-amino-2'-carboxyethyl)-1,4-dihydro-6,7-quinoxaline-2,3-diones: alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate receptor agonists and antagonists

Functionalized quinoxalinones as privileged structures with broad-ranging pharmacological activities

Quinoxalinones are a class of heterocyclic compounds which attract extensive attention owing to their potential in the field of organic synthesis and medicinal chemistry. During the past few decades, many new synthetic strategies toward the functionalization of quinoxalinone based scaffolds have been witnessed. Regrettably, there are only a few reports on the pharmacological activities of quinoxalinone scaffolds from a medicinal chemistry perspective. Therefore, herein we intend to outline the applications of multifunctional quinoxalinones as privileged structures possessing various biological activities, including anticancer, neuroprotective, antibacterial, antiviral, antiparasitic, anti-inflammatory, antiallergic, anti-cardiovascular, anti-diabetes, antioxidation, etc. We hope that this review will facilitate the development of quinoxalinone derivatives in medicinal chemistry.

Structure and vibrational frequencies of 6,7-dimethoxy-1,4-dihydro-1,3-quinoxalinedione based on density functional theory calculations: The role of pi-electron conjugation and back-donation

This work deals with the vibrational spectroscopy of 6,7-dimethoxy-1,4-dihydro-1,3-quinoxalinedione by means of quantum chemical calculations. The mid and far FT-IR and FT-Raman spectra are recorded in the condensed State. The fundamental vibrational frequencies and intensity of vibrational bands are evaluated using density functional theory (DFT) with the standard B3LYP/6-31G* method and basis set combination and is scaled using various scale factors which yields a good agreement between observed and calculated frequencies. The vibrational spectrum is interpreted with the aid of normal coordinate analysis based on scaled density functional force field. The results of the calculations are applied to simulate infrared and Raman spectra of the title compounds, which showed excellent agreement with the observed spectra. The infrared unscaled frequencies and intensities are used to disentangle the role played by back-donation in the title compound. For this purpose five other molecules are considered as references: ethane, dimethyl ether, anisole, p-nitro-anisole, and p-hydroxyanisole, in which back-donation has already been ascertained also experimentally. From the study of infrared intensities it is shown that no back-donation of electrons from the oxygen lone pairs takes place, independently of the conformation of the methoxy-group.

Synthesis and spectroscopic properties of lanthanide nitrate complexes with a new amide-based quinoxaline-2,3-dione ligand

Solid complexes of lanthanide nitrate with 1,4-di(N,N-di-n-butyl-acetamido)-quinoxaline-2,3-dione (L), [Ln(N03)3L.H2O] (Ln=La, Nd, Eu, Gd, Tb, Er), have been prepared and characterized by elemental analysis, IR, UV-vis spectra and conductivity measurements. The fluorescence property of the europium complex in solid state and in MeCN, acetone, AcOEt and THF was studied. Under the excitation, the europium complex exhibited characteristic emissions of europium. The result indicates that the triplet state energy level of the ligand matches better to the resonance level of Eu(III) than Tb(III) ion.

X-ray crystal structure of phenylglycine hydrazide: synthesis and spectroscopic studies of its transition metal complexes

Phenylglycine hydrazide was synthesized and investigated by X-ray crystallography. It crystallizes in the monoclinic space group P121/c with cell parameters a=5.9459 (18) Angstrom, b=5.1940 (16) Angstrom, c=26.7793 (83) Angstrom and Z=2. Its conformational changes, on complexation with transition metal ions Cu(II), Co(II), Ni(II), Mn(II) and Zn(II) has been studied on the basis of elemental analysis, magnetic moment and spectral (IR, (1)H NMR, UV-vis) studies. The bidentate nature of the ligand was confirmed on the basis of a comparative IR and NMR spectral studies. The trigonal bipyramidal geometries were observed for Cu(II), Ni(II) and Co(II) complexes, while it is octahedral for the remaining complexes. The conductivity data suggest them to be non-electrolytes.

Competitive AMPA receptor antagonists

Glutamic acid (Glu) is the major excitatory neurotransmitter in the mammalian central nervous system (CNS) where it is involved in the physiological regulation of different processes. It has been well established that excessive endogenous Glu is associated with many acute and chronic neurodegenerative disorders such as cerebral ischaemia, epilepsy, amiotrophic lateral sclerosis, Parkinson's, and Alzheimer's disease. These data have consequently added great impetus to the research in this field. In fact, many Glu receptor antagonists acting at the N-methyl-D-aspartic acid (NMDA), 2-amino-3-(3-hydroxy-5-methylisoxazol-4-yl)propionic acid (AMPA), and/or kainic acid (KA) receptors have been developed as research tools and potential therapeutic agents. Ligands showing competitive antagonistic action at the AMPA type of Glu receptors were first reported in 1988, and the systemically active 2,3-dihydroxy-6-nitro-7-sulphamoyl-benzo[f]quinoxaline (NBQX) was first shown to have useful therapeutic effects in animal models of neurological disease in 1990. Since then, the quinoxaline template has represented the backbone of various competitive AMPA receptor antagonists belonging to different classes which had been developed in order to increase potency, selectivity and water solubility, but also to prolong the "in vivo" action. Compounds that present better pharmacokinetic properties and less serious adverse effects with respect to the others previously developed are undergoing clinical evaluation. In the near future, the most important clinical application for the AMPA receptor antagonists will probably be as neuroprotectant in neurodegenerative diseases, such as epilepsy, for the treatment of patients not responding to current therapies. The present review reports the history of competitive AMPA receptor antagonists from 1988 up to today, providing a systematic coverage of both the open and patent literature.

Synthesis and biological activity of novel amino acid-(N'-benzoyl) hydrazide and amino acid-(N'-nicotinoyl) hydrazide derivatives

The coupling reaction of benzoic acid and nicotinic acid hydrazides with N-protected L-amino acids including valine, leucine, phenylalanine, glutamic acid and tyrosine is reported. The target compounds, N-Boc-amino acid-(N`-benzoyl)- and N-Boc-amino acid-(N`-nicotinoyl) hydrazides 5a-5e and 6a-6e were prepared in very high yields and purity using N-[(dimethylamino)-1H-1,2,3-triazolo[4,5-b]pyridin-1-yl- methylene]-N-methyl-methanaminium hexafluorophosphate N-oxide (HATU) as coupling reagent. The antimicrobial activity of the Cu and Cd complexes of the designed compounds was tested. The products were deprotected affording the corresponding amino acid-(N`-benzoyl) hydrazide hydrochloride salts (7a-7e) and amino acid-(N`- nicotinoyl) hydrazide hydrochloride salts (8a-8e). These compounds and their Cu and Cd complexes were also tested for their antimicrobial activity. Several compounds showed comparable activity to that of ampicillin against S. aureus and E. coli.

Inherent desensitisation-preventing properties of a novel, subtype-selective AMPA receptor agonist, (S)-CPW 399, as a possible explanation for its excitotoxic action in cultured cerebellar granule cells

The synthesis and pharmacological characterisation of (S)-CPW 399 as a novel, potent and subtype-selective agonist of the AMPA receptor was recently reported. Studies have been extended to investigate its excitotoxic action in primary cultures of mouse cerebellar granule cells. (S)-CPW 399 induced neuronal cell death in a time- and concentration-dependent manner (EC(50) approximately 70 microM) at 24-h exposure. (S)-CPW-induced neuronal death could be prevented by co-administration with either of the AMPA/kainate selective receptor antagonists 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX) and 6-nitro-7-sulphamoylbenzo[f]quinoxaline-2,3-dione (NBQX) or by the 2,3-benzodiazepine, GYKI 53655 (a selective AMPA receptor antagonist); while no protection was afforded by either the NMDA receptor antagonist D,L(+/-)-2-amino-5-phosphonopentanoate (APV) or by nifedipine (an L-type calcium channel antagonist) when used alone or in combination. Cyclothiazide, which blocks AMPA receptor desensitisation, caused minimal potentiation of (S)-CPW 399-induced neuronal death, supporting accumulating evidence that (S)-CPW 399 is a full AMPA receptor agonist that markedly prevents a receptor desensitised conformation. (S)-AMPA, (S)-willardiine (a naturally-occurring heterocyclic excitatory amino acid) and its halogenated derivative, (S)-5-fluorowillardiine, had no deleterious effect on neuronal viability when used alone but each, in the presence of cyclothiazide, induced a concentration-dependent excitotoxic cell death with a rank order of potency (fluorowillardiine>>AMPA=willardiine). (S)-CPW 399 stimulated an increase in intracellular free-calcium levels ([Ca(2+)](i)) in a concentration-dependent fashion (EC(50) approximately 5 microM) attaining a value of six-fold that of 'resting' cells at maximum stimulation; achieved at approximately 100 microM (S)-CPW 399. The (S)-CPW 399-stimulated increase in [Ca(2+)](i) was virtually abolished by GYKI 53655, NBQX, CNQX and by cobalt ions; markedly inhibited by nifedipine and marginally affected by D-APV. These results suggest that (S)-CPW 399 may be used as a pharmacological tool to aid in the investigation of the role of AMPA receptors in excitotoxicity and their molecular mechanisms of desensitisation.