Evaluation of amidoxime derivatives as prodrug candidates of potent bis-cationic antimalarials.

Plasmodium falciparum is responsible for most of the cases of malaria and its resistance to established antimalarial drugs is a major issue. Thus, new chemotherapies are needed to fight the emerging multi-drug resistance of P. falciparum malaria, like choline analogues targeting plasmodial phospholipidic metabolism. Here we describe the synthesis of amidoxime derivatives as prodrug candidates of reverse-benzamidines and hybrid compounds able to mimic choline, as well as the design of a new series of asymmetrical bis-cationic compounds. Bioconversion studies were conducted on amidoximes in asymmetrical series and showed that amidoxime prodrug strategy could be applied on C-alkylamidine moieties, like benzamidines and that N-substituents did not alter the bioconversion of amidoximes. The antimalarial activity of the three series of compounds was evaluated in vitro against P. falciparum and in vivo against P. vinckei petteri in mice.

PBN derived amphiphilic spin-traps. II/Study of their antioxidant properties in biomimetic membranes.

The work reported herein deals with the evaluation of the antioxidant properties of bitailed amphiphilic α-phenyl-N-tert-butylnitrone derivatives (BPBNs) towards oxidation of an unsaturated lipid, the 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLoPC). Oxidation was induced either by UV light irradiation or radical initiators, i.e. the water soluble AAPH and the Fenton reaction, and the antioxidant evaluation was carried out using two biomimetic systems, namely Langmuir monolayers and large unilamellar vesicles. Measurement of the molecular area and the membrane fluidity of pure nitrone monolayers before and after UV-irradiation demonstrated the better stability and antioxidant properties of B17PBN, the derivative with two C17H35 alkyl chains, compared to its analogue B11PBN with two C11H23 alkyl chains. At only 5% molar ratio of nitrone in mixed DLoPC/nitrone monolayers, a complete inhibition of the molecular area decrease was observed for B17PBN whereas B11PBN showed lower protection. The oxidation of mixed DLoPC/nitrones large unilamellar vesicles in the presence of free radicals arising from AAPH decomposition or Fenton reaction was assessed by measuring lipid conjugated dienes and thiobarbituric acid reactive substances on the whole series of nitrone, i.e. C11-, C13-, C15- and C17-based compounds. Compared to the saturated 1,2-dimyristoyl-sn-glycero-3-phosphocholine, all bitailed amphiphilic nitrones were able to decrease conjugated dienes and TBARS in both oxidative paradigms, demonstrating therefore antioxidant property. The inhibition of phospholipids oxidation was increased when increasing the concentration of nitrone with the two B11PBN and B13PBN derivatives exhibiting higher potency. This study underlines the importance in the choice of a model membrane system when evaluating the potency of antioxidants against lipid oxidation.

Hydrophosphinylation of unactivated terminal alkenes catalyzed by nickel chloride.

The room-temperature hydrophosphinylation of unactivated monosubstituted alkenes using phosphinates (ROP(O)H2) and catalytic NiCl2 in the presence of dppe is described. The method is competitive with prior palladium-catalyzed reactions and uses a much cheaper catalyst and simple conditions. The scope of the reaction is quite broad in terms of unactivated terminal olefins, proceeds at room temperature, often avoids chromatographic purification, and allows one-pot conversion to various organophosphorus compounds.

Synthesis of Z-alkenyl phosphorus compounds through hydroalumination and carbocupration of alkynyl precursors.

The stereocontrolled synthesis of Z-alkenylphosphine-borane complexes is easily accomplished via the hydroalumination or carbocupration of alkynyl precursors. Z/E ratios are generally higher than 95/5. These reactions are stereocomplementary to our olefination approach.

Mixed 1,1-bisphosphorus compounds: synthesis, alkylation, and Horner-Wadsworth-Emmons olefination reactions.

Mixed 1,1-bisphosphorus compounds were prepared by the reaction between a phosphonate diester anion and a P(III) chlorophosphine, or its P(V) borane complex. After deprotonation either in situ or in a separate step, the resulting products can be alkylated or reacted with carbonyl compounds. A variety of olefination products were obtained, generally with high E-stereoselectivity. The reaction is competitive with other methods for the synthesis of alkenyl phosphorus compounds, and in the case of trisubstituted alkenes, regio- and stereocontrolled olefination provides products not easily accessible via any other process. The deprotection of phosphine-borane adducts was also demonstrated. Overall, a variety of novel organophosphorus reagents and products were synthesized easily and in good yields.

Amphiphilic amide nitrones: a new class of protective agents acting as modifiers of mitochondrial metabolism.

Our group has demonstrated that the amphiphilic character of alpha-phenyl-N-tert-butyl nitrone based agents is a key feature in determining their bioactivity and protection against oxidative toxicity. In this work, we report the synthesis of a new class of amphiphilic amide nitrones. Their hydroxyl radical scavenging activity and radical reducing potency were shown using ABTS competition and ABTS(+) reduction assays, respectively. Cyclic voltammetry was used to investigate their redox behavior, and the effects of the substitution of the PBN on the charge density of the nitronyl atoms, the electron affinity, and the ionization potential were computationally rationalized. The protective effects of amphiphilic amide nitrones in cell cultures exposed to oxidotoxins greatly exceeded those exerted by the parent compound PBN. They decreased electron and proton leakage as well as hydrogen peroxide formation in isolated rat brain mitochondria at nanomolar concentration. They also significantly enhanced mitochondrial membrane potential. Finally, dopamine-induced inhibition of complex I activity was antagonized by pretreatment with these agents. These findings indicate that amphiphilic amide nitrones are much more than just radical scavenging antioxidants but may act as a new class of bioenergetic agents directly on mitochondrial electron and proton transport.

Spin trapping and cytoprotective properties of fluorinated amphiphilic carrier conjugates of cyclic versus linear nitrones.

Nitrones have been employed as spin trapping reagent as well as pharmacological agent against neurodegenerative diseases and ischemia-reperfusion induced injury. The structure-activity relationship was explored for the two types of nitrones, i.e., cyclic (DMPO) and linear (PBN), which are conjugated to a fluorinated amphiphilic carrier (FAC) for their cytoprotective properties against hydrogen peroxide (H(2)O(2)), 3-morpholinosynonimine hydrochloride (SIN-1), and 4-hydroxynonenal (HNE) induced cell death on bovine aortic endothelial cells. The compound FAMPO was synthesized and characterized, and its physical-chemical and spin trapping properties were explored. Cytotoxicity and cytoprotective properties of various nitrones either conjugated and nonconjugated to FAC (i.e., AMPO, FAMPO, PBN, and FAPBN) were assessed using a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium (MTT) reduction assay. Results show that of all the nitrones tested, FAPBN is the most protective against H(2)O(2), but FAMPO and to a lesser extent its unconjugated form, AMPO, are more protective against SIN-1 induced cytotoxicity. However, none of the nitrones used protect the cells from HNE-induced cell death. The difference in the cytoprotective properties observed between the cyclic and linear nitrones may arise from the differences in their intrinsic antioxidant properties and localization in the cell.

Design and synthesis of amidoxime derivatives for orally potent C-alkylamidine-based antimalarial agents.

Within the frame of the design of prodrug candidates to deliver a C-alkylamidine antimalarial agent, we showed that specific O-substitutions were needed on the alkylamidoxime structure. Among the newly synthesized molecules, bis-oxadiazolone and bis-O-methylsulfonylamidoxime derivatives induced a complete clearance of parasitemia in mice after oral administration.

Fluorinated amphiphilic amino acid derivatives as antioxidant carriers: a new class of protective agents.

The use of classical antioxidants is limited by their low bioavailabilities, and therefore, high doses are usually required to display significant protective activity. In a recent article (J. Med. Chem. 2003, 46, 5230) we showed that the ability of the alpha-phenyl-N-tert-butylnitrone (PBN) to restore the viability of ATPase-deficient human skin fibroblasts was greatly enhanced by grafting it on a fluorinated amphiphilic carrier. With the aim of extending this concept to other antioxidants, we present here the design, the synthesis, and the physicochemical measurements of a new series of fluorinated amphiphilic antioxidant derivatives. The hydroxyl radical scavenging activity and the radical reducing potency of these newly designed compounds were respectively demonstrated in an ABTS competition and an ABTS(*+) reduction assay. We also showed that the protective effects of amphiphilic antioxidants derived from PBN, Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) or lipoic acid (5-[1,2]-dithiolan-3-ylpentanoic acid) in primary cortical mixed cell cultures exposed to oxidotoxins are greatly improved compared to their parent compounds in the following rank-order: (1) PBN, (2) Trolox, and (3) lipoic acid. In contrast, the protective activity of indole-3-propionic acid was slightly decreased by grafting it on the amphiphilic carrier. Similar observations were made in in vivo experiments using aquatic invertebrate microorganisms, called rotifers, which were exposed to lethal concentrations of nonselective (H(2)O(2)) and mitochondria-selective (doxorubicin) oxidotoxins. The conclusion of these studies is that fluorinated amphiphilic PBN, Trolox, and lipoic acid derivatives exhibit very potent protective activities in in vitro and in vivo experiments. The findings demonstrated herein therefore strongly suggest that the amphiphilic character enhances the bioavailability of the antioxidants and allows for a selective targeting of mitochondria.