Roger Escale

Symmetrical choline-derived dications display strong anti-kinetoplastid activity

OBJECTIVES to investigate the anti-kinetoplastid activity of choline-derived analogues with previously reported antimalarial efficacy. METHODS from an existing choline analogue library, seven antimalarial compounds, representative of the first-, second- and third-generation analogues previously developed, were assessed for activity against Trypanosoma and Leishmania spp. Using a variety of techniques, the effects of choline analogue exposure on the parasites were documented and a preliminary investigation of their mode of action was performed. RESULTS the activities of choline-derived compounds against Trypanosoma brucei and Leishmania mexicana were determined. The compounds displayed promising anti-kinetoplastid activity, particularly against T. brucei, to which 4/7 displayed submicromolar EC(50) values for the wild-type strain. Low micromolar concentrations of most compounds cleared trypanosome cultures within 24-48 h. The compounds inhibit a choline transporter in Leishmania, but their entry may not depend only on this carrier; T. b. brucei lacks a choline carrier and the mode of uptake remains unclear. The compounds had no effect on the overall lipid composition of the cells, cell cycle progression or cyclic adenosine monophosphate production or short-term effects on intracellular calcium levels. However, several of the compounds, displayed pronounced effects on the mitochondrial membrane potential; this action was not associated with production of reactive oxygen species but rather with a slow rise of intracellular calcium levels and DNA fragmentation. CONCLUSIONS the choline analogues displayed strong activity against kinetoplastid parasites, particularly against T. b. brucei. In contrast to their antimalarial activity, they did not act on trypanosomes by disrupting choline salvage or phospholipid metabolism, instead disrupting mitochondrial function, leading to chromosomal fragmentation.

Imidazo[1,2-a]quinoxalines: synthesis and cyclic nucleotide phosphodiesterase inhibitory activity.

A group of imidazo[1,2-a]quinoxalines have been synthesised from quinoxaline by condensation of an appropriate haloester or intramolecular cyclisation of a keto moiety on an intracyclic nitrogen atom. The reactivity of the heterocycle was explored through diverse reactions such as electrophilic substitution, lithiation and halogen-metal exchange to give access to a new series of derivatives. Confirmation of their structure was mainly performed by NMR, after careful assignment of the signals in comparison to previous attributions made on the parent imidazo[1,2-a]quinoxaline and discussion of available data in the literature. The cyclic nucleotide phosphodiesterase inhibitor activity of some of these derivatives has been assessed on isoenzymes type III and type lV. Compound 15, 4-(methylamino)imidazo[1,2-a]quinoxaline-2-carbonitrile, exhibited potent relaxant activity on smooth muscle, with a potency similar to the one measured with SCA 40, its structural analogue in the imidazo[1,2-a]pyrazine series.

Solid phase synthesis of phosphonopeptides from Fmoc phosphonodipeptides

Abstract The solid phase synthesis of two phosphonopeptides was carried out from a N-Fmoc protected dipeptide precursor containing the PN bond and a benzyl or allyl carboxylic protection easily removable under neutral conditions.

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.

N-substituted bis-C-alkyloxadiazolones as dual effectors: efficient intermediates to amidoximes or amidines and prodrug candidates of potent antimalarials.

A convenient route to N-substituted bis-C-alkylamidines possessing antiplasmodial activity and their oxadiazolone and amidoxime prodrug candidates, is described. These three families of compounds were available after a key N-alkylation step of the parent oxadiazolone 1a. Testing of the three compound classes in vitro and in vivo is also presented.

Aza-indolizine with bridgehead nitrogen. Metalation, halogen-metal exchange and directed ortho-lithiation in the imidazo[1,2-a]pyrazine series

Abstract The n-BuLi and lithium 2,2,6,6-tetramethylpiperidine (LTMP) metalation of imidazo[1,2-a]pyrazine heterocycles and subsequent quenching with electrophiles is described. Bromine atoms exhibit different behaviours towards lithiation depending on their positions (3 or 6) on the imidazo[1,2-a]pyrazine heterocycle. Halogen-metal exchange occurs readily with the bromine on position 3. On the contrary, bromine on position 6 only leads to C-5 substituted derivatives further to an ortho-directing effect.

Synthesis and Evaluation of Hybrid Bis-cationic Salts as Antimalarial Drugs

A new series of hybrid bis-cations has been synthesized as potent antimalarial agents. These drugs share two different cationic heads derived from bis-thiazolium and bis-amidine salts. Structure-activity relationships has been defined and pointed out that the linker plays a prior role for antimalarial activity leading to compounds with significant oral activity.

Cyclisation reactions of some 3-nitrosoimidazo[1,2-a]-pyridines and-pyrimidines. Ring-opening/ring-closure reactions with triethyl phosphite: reassignment by X-ray crystal structure and nuclear magnetic resonance

Deoxygenation of 3-nitroso-2-phenylimidazo[1,2-a]-pyridines and -pyrimidines with triethyl phosphite does not lead to the products described in the literature as pyrido- and pyrimido-imidazoindoles (3) and (4), but to the open-chain derivatives, N-(2-pyridyl)- and N-(2-pyrimidyl)-benzimidoyl cyanides (5) and (6). X-Ray crystallographic analysis confirms the structure of (5a): orthorhombic system with a= 24.377 (6), b= 11.729 (3), c= 7.534 (2)A, space group Pbca, Z= 8, d= 1.27 g/cm3, R= 0.061. Thermal ring-closure with triethyl phosphite of compounds (5) and (6) produced the 3-amino-2-phenylimidazo[1,2-a]-pyridines and -pyrimidines (8) and (9).

Substituted cyclohexane as conformationally-restricted: Analogues of the peptido-leukotrienes

Abstract A new class of potential leukotriene analogues is synthesized which attempts to restrict the conformationally mobile lipophilic chain. Biological evaluation shows weak agonist activity, giving key information on LTD 4 geometry to the receptor.

Reverse-benzamidine antimalarial agents: design, synthesis, and biological evaluation.

In the frame of the development of bis-cationic choline analogs, the RSA of bis-N-alkylamidines were studied and a new series of reverse-benzamidine derivatives was designed. Contrary to the lipophilicity, the basicity of alkylamidine compounds directly influences their antimalarial potencies.