Structure-activity relationships of methoctramine-related polyamines as muscular nicotinic receptor noncompetitive antagonists. 3. Effect of inserting the tetraamine backbone into a macrocyclic structure

Identification of a 2,4-diaminopyrimidine scaffold targeting Trypanosoma brucei pteridine reductase 1 from the LIBRA compound library screening campaign

The LIBRA compound library is a collection of 522 non-commercial molecules contributed by various Italian academic laboratories. These compounds have been designed and synthesized during different medicinal chemistry programs and are hosted by the Italian Institute of Technology. We report the screening of the LIBRA compound library against Trypanosoma brucei and Leishmania major pteridine reductase 1, TbPTR1 and LmPTR1. Nine compounds were active against parasitic PTR1 and were selected for cell-based parasite screening, as single agents and in combination with methotrexate (MTX). The most interesting TbPTR1 inhibitor identified was 4-(benzyloxy)pyrimidine-2,6-diamine (LIB_66). Subsequently, six new LIB_66 derivatives were synthesized to explore its Structure-Activity-Relationship (SAR) and absorption, distribution, metabolism, excretion and toxicity (ADMET) properties. The results indicate that PTR1 has a preference to bind inhibitors, which resemble its biopterin/folic acid substrates, such as the 2,4-diaminopyrimidine derivatives.

Novel class of quinone-bearing polyamines as multi-target-directed ligands to combat Alzheimer's disease

One of the characteristics of Alzheimer's disease (AD) that hinders the discovery of effective disease-modifying therapies is the multifactorial nature of its etiopathology. To circumvent this drawback, the use of multi-target-directed ligands (MTDLs) has recently been proposed as a means of simultaneously hitting several targets involved in the development of the AD syndrome. In this paper, a new class of MTDLs based on a polyamine-quinone skeleton, whose lead (memoquin, 2) showed promising properties in preclinical investigations (Cavalli et al. Angew. Chem., Int. Ed. 2007, 46, 3689-3692), is described. 3-29 were tested in vitro against a number of isolated AD-related targets, namely, AChE and BChE, and Abeta aggregation (both AChE-mediated and self-induced). Furthermore, the ability of the compounds to counteract the oxidative stress in a human neuronal-like cellular system (SH-SY5Y cells) was assayed, in both the presence and absence of NQO1, an enzyme able to generate and maintain the reduced form of quinone.

Targeting acetylcholinesterase to treat neurodegeneration

Neurodegenerative disorders, such as Alzheimer's disease, are often characterised by the degeneration of the cholinergic system. Thus, the aim of many treatment regimens is to support this system either by means of muscarinic agonists or by inhibitors of acetylcholinesterase (AChE), the latter being able to increase the concentration of acetylcholine. However, both pharmacological groups of drugs can only help in the beginning of the progressive disease. The finding that the occupation of the peripheral anionic site of AChE is able to stop the formation of the amyloid plaque led to the development of bivalent ligands that occupy both the active and the peripheral site. This dual action might be more beneficial for treatment of Alzheimer s disease than simple inhibition of the acetylcholine hydrolysis. Thus, the new bivalent ligands are the focus of this review.

Selective Oxygenation of 4,4‘-Dimethylbiphenyl with Molecular Oxygen, Catalyzed by 9-Phenyl-10-methylacridinium Ion via Photoinduced Electron Transfer

Photooxygenation of 4,4'-dimethybiphenyl with oxygen occurs efficiently in the presence of 9-phenyl-10-methylacridinium perchlorate (AcrPh(+)ClO(4)(-)) under visible light irradiation in O(2)-saturated chloroform (CHCl(3)) to yield 4-(4'-methylphenyl)benzaldehyde as a main oxygenated product. Prolonged photoirradiation afforded the further oxygenated product, 4,4'-diformylbiphenyl. The reactive radical intermediates involved in the photocatalytic cycle have successfully been detected by laser flash photolysis and electron spin resonance (ESR) measurements. The photocatalytic mechanism for the oxygenation of 4,4'-dimethybiphenyl via photoinduced electron transfer from 4,4'-dimethybiphenyl to the singlet excited state of AcrPh(+) is clarified based on the dependence of quantum yields on concentrations of substrates and the detected radical intermediates.

AMPA receptor ligands: Synthetic and pharmacological studies of polyamines and polyamine toxins

Alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptors (AMPAR), subtype of the ionotropic glutamate receptors (IGRs), mediate fast synaptic transmission in the central nervous system (CNS), and are involved in many neurological disorders, as well as being a key player in the formation of memory. Hence, ligands affecting AMPARs are highly important for the study of the structure and function of this receptor, and in this regard polyamine-based ligands, particularly polyamine toxins, are unique as they selectively block Ca2+ -permeable AMPARs. Indeed, endogenous intracellular polyamines are known to modulate the function of these receptors in vivo. In this study, recent developments in the medicinal chemistry of polyamine-based ligands are given, particularly focusing on the use of solid-phase synthesis (SPS) as a tool for the facile generation of libraries of polyamine toxin analogues. Moreover, the recent development of highly potent and very selective AMPAR ligands is described. Additionally, we provide a detailed account on the mechanism and site of action of AMPAR blockade by polyamine-based ligands, including examples of how these ligands are used as tools to study AMPAR, and a comparison with their action on other ionotropic receptors.

Cholinergic nicotinic receptors: competitive ligands, allosteric modulators, and their potential applications

Discovery of the important role played by nicotinic acetylcholine receptors (nAChRs) in several CNS disorders has called attention to these membrane proteins and to ligands able to modulate their functions. The existence of different subtypes at multiple levels has complicated the understanding of this receptor's physiological role, but at the same time has increased the efforts to discover selective compounds in order to improve the pharmacological characterization of this kind of receptor and to make the possible therapeutical use of its modulators safer. This review focuses on the structure of new ligands for nAChRs, agonists, antagonists and allosteric modulators, and on their possible applications.

Polymethylene tetraamine backbone as template for the development of biologically active polyamines

The concept that polyamines may represent a universal template in the receptor recognition process is embodied in the design of ligands for different biological targets. As a matter of fact, the insertion of different pharmacophores onto the polymethylene tetraamine backbone can tune both affinity and selectivity for any given receptor. The application of this approach provided a prospect of modifying benextramine (1). structure to achieve specific recognition of muscarinic receptors that led to the discovery of methoctramine (2). which is widely used as a pharmacological tool for muscarinic receptor characterization. In turn, appropriate structural modifications performed on the structure of methoctramine led to the discovery of new polyamines endowed with high affinity and selectivity for (a). muscarinic receptor subtypes, (b). G(i) proteins, and (c). muscle-type nicotinic receptors. Thus, polyamines tripitramine (9) and spirotramine (33), among others, were designed, which were shown to be highly selective for muscarinic M(2) and M(1) receptors, respectively. Several polyamines have been discovered, which inhibit noncompetitively a closed state of the nicotinic receptor. These ligands, such as 66, resulted in important tools for elucidating the mode and site of interaction of polyamines with the ion channel. It was discovered that reducing the flexibility of the diaminohexane spacer of methoctramine led to polyamines, such as 70, which are endowed with a biological profile significantly different from that of the prototype. Most likely, tetraamine (70) is a potent activator of G(i) proteins. Finally, the universal template approach formed the basis for modifying benextramine (1) structure to the design of ligands, which display affinity for acetylcholinesterase and muscarinic M(2) receptors. Thus, these polyamines, such as caproctamine (78), could have potential in the investigation of Alzheimer disease.