Synthesis and kinetic study of the homolyse of biomolecules usable like theranostic agents

Ce travail est présenté en 2 parties. La première partie aborde la synthèse stéréocontrôlée de 2 séries de carbonucléosides de structures méthylènecyclopropane. Les molécules cibles sont des analogues de l’entécavir, une prodrogue utilisée en trithérapie pour lutter contre le VHB. Les synthèses des carbonucléosides cibles de la série I utilisent un chiron commun, un alcool obtenu par désymétrisation enzymatique d’un diol méso. La transformation chimique de cet intermédiaire clé permet d’obtenir le carbonucléoside (+)-17 en 8 étapes mettant en œuvre comme étapes cruciales un réarrangement de Curtius et la construction de la base uracile avec un rendement global de 23%. Le carbonucléoside appartenant à la série II, a été synthétisé en 10 étapes mettant en jeu une réaction de Mitsunobu, une acylation chimique et contrairement à l’approche précédente, la désymétrisation enzymatique d’un diol méso n’a pas permis d’obtenir le carbonucléoside cible énantiopure. La seconde partie est consacrée à l’activation et l’homolyse des alcoxyamines pour une application en théranostique. La synthèse de l’alcoxyamine modèle présente un groupement vinyl pyridine et un nitroxyde SG1. L’activation est réalisée par protonation, oxydation, méthylation et benzylation de la partie pyridyle et met en évidence l’importance de la polarité. Elle a permis d’obtenir des espèces hautement labiles qui libèrent un radical alkyle et le nitroxyde SG1, avec notamment des valeurs de la constante de dissociation kd plus élevées et donc des énergies d’activation Ea plus faibles par rapport à l’alcoxyamine non activée.This work is presented in 2 parts. The first part is dedicated to the stereocontrolled synthesis of 2 series of carbonucleosides of methylenecyclopropane structure. The target molecules are analogs of entecavir, a prodrug used in triple therapy to fight against HBV. The syntheses of the carbonucleosides targets of the series I use a common chiron, an alcohol obtained by enzymatic desymmetrization of meso-diol. For example, the chemical transformation of this key intermediate allows to obtain carbonucleoside (+)-16 in 8 steps as crucial steps involving a Curtius rearrangement and the construction of the uracil base with 23% overall yield. The carbonucleoside belonging to the series II was first synthesized in 10 steps involving a reaction of Mitsunobu, a chemical acylation. Howerer the enzymatic desymmetrization of a meso-diol did not get the target carbonucleoside in an enantiopur form. The second part is dedicated to the activation and the homolysis of the alcoxyamines for a theranostic application. The synthesis of the model alcoxyamine is made from vinyl pyridine and nitroxide SG1. Activation is carried out by protonation, oxidation, methylation and benzylation of the pyridyl part and highlights the importance of polarity. It allowed getting highly labile species that release an alkyl radical and nitroxide SG1, with notably higher kd dissociation constant values and therefore activation energies Ea lower compared to the alcoxyamine not enabled

Synthesis and Biological Evaluation of Methylenecyclopropane Analogues of Nucleosides

International audienceStarting from a chiral methylenecyclopropane building block, readily obtained by enzymatic desymmetrization of a meso-diol, two types of methylenecyclopropane analogues of nucleosides were synthesized. The first type of nucleosides was obtained from the direct coupling of the chiral building block with 6-chloropurine under Mitsunobu reaction conditions followed by the functionalization of the purine base. The second type of nucleosides featured a Curtius rearrangement as the key step and the uracil heterocycle was then constructed by a linear methodology. These derivatives were evaluated as potential agents against important viral pathogens. None of the new compounds had significant antiviral activity at a concentration of 100 g/mL, which was the highest concentration tested

Synthesis and biological evaluation of methylenecyclopropane analogues of nucleosides

Starting from a chiral methylenecyclopropane building block, readily obtained by enzymatic desymmetrization of a meso-diol, two types of methylenecyclopropane analogues of nucleosides were synthesized. The first type of nucleosides was obtained from the direct coupling of the chiral building block with 6-chloropurine under Mitsunobu reaction conditions followed by the functionalization of the purine base. The second type of nucleosides featured a Curtius rearrangement as the key step and the uracil heterocycle was then constructed by a linear methodology. These derivatives were evaluated as potential agents against important viral pathogens. None of the new compounds had significant antiviral activity at a concentration of 100 μg/mL, which was the highest concentration tested. © 2013 Georg Thieme Verlag Stuttgart New York.status: publishe

Hyperfine Coupling Constants of beta-Phosphorylated Nitroxides: A Tool to Probe the Cybotactic Effect by Electron Paramagnetic Resonance

International audienceNitrogen hyperfine coupling constants (hcc) aN of nitroxides measured by electron paramagnetic resonance are used to probe the cybotactic effect of solvents. A few articles (Janzen et al., Can. J. Chem. in 1982 for aH beta and Deng et al., J. Fluorine Chem. in 2002, both for aH beta and aF beta) dealt with the cybotactic effect on the hcc of atoms (hydrogen H, fluorine F, and phosphorus P) in beta positions of nitroxides. They show either no significant change or an increase in a beta with aN. However, an early report by Il'Yasov et al. (Theor. Exp. Chem. 1976, 656) described a dramatic change in aP beta with the solvent and an anti-correlation of aP beta with aN. We decided to reinvestigate that work using the N-(2-methylpropyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl radical that carries both hydrogen and phosphorus atoms on the same carbon attached to the nitroxy moiety and that is highly persistent, in contrast to the nitroxide used by Il'Yasov. We observe the same trends as those observed by Il'Yasov, except that the solvent cybotactic effect on aN and aP beta is dramatically weaker in our case. We showed that aP beta is correlated to both the cohesive pressure c and the normalized Reichardt polar constant ETN, and that hydrogen-bonding donor solvents exhibit a specific behavior

Chemically Triggered C-ON Bond Homolysis of Alkoxyamines. 5. Cybotactic Effect

International audienceIn a recent work (Org. Lett. 2012, 14, 358), we showed that the rate constant k(d) of the chemically activated C-ON bond homolysis of alkoxyamines was subject to solvent effects. However, we showed that solvent effects were weak for the nonactivated alkoxyamine 1 (diethyl (1-(tert-butyl(1-(pyridin-4-yl)ethoxy)amino)-2,2-dimethylpropyl)phosphon ate) and its N+-O- oxide activated version 3. On the other hand, the activated N-methylated version 2 of 1 experienced a strong solvent effect for a radical reaction, i.e., a 24-fold increase in kd from tert-butylbenzene (tBuPh) to 2,2,2-trifluoroethanol (TFE). Good correlations were observed with the normalized Reichardt solvent polarity constant E-T(N) and the nitrogen hyperfine coupling constant of the released nitroxide a(N,SGI), meaning that the stabilization of the nitroxide played an important role in C-ON bond homolysis in alkoxyamines. The Kalmet-Abboud-Taft relationships described successfully the solvent effect for each diastereoismer of 1 and 2, as for example with the minor diastereoisomer of 1 log(k(d)'/s(-1)) = -4.84 + 0.37 pi* + 0.21 alpha and that of 2 log(k(d)'/s(-1)) = -3.11 + 0.37 pi* + 0.47 alpha, with pi* being the polarity/polarizability and a the hydrogen bond donor (HBD) ability of the solvent. Surprisingly, the HBD effect is larger for 2 than for 1, whereas no extra lone pair is available in 2. This amazing effect was ascribed to the solvation of the counteranion, which is expected to be better solvated in a HBD solvent

Chemically triggered C-ON bond homolysis of alkoxyamines. Part 4: solvent effect

International audienceIn a recent work (Org. Lett., 2012, 14, 358), we showed that the rate constants k(d) for the C-ON bond homolysis of chemically activated alkoxyamines were subject to solvent effects. We then investigated solvent effects on the non-activated alkoxyamine 1 ((diethyl(1-(tert-butyl(1-(pyridin-4-yl)ethoxy) amino)-2,2-dimethylpropyl) phosphonate) and its N+-O- oxide activated version 2, using 14 solvents exhibiting different solvent parameters - dipolar moments mu, dielectrical constants epsilon, cohesive pressures c, Reichardt solvent polarity constants E-T, viscosity eta, hydrogen bond donor and hydrogen bond acceptor constants alpha and beta, respectively, and nitrogen hyperfine coupling constants a(N). Weak solvent effects were observed both for 1 (4-5-fold from n-octane to 2,2,2-trifluoroethanol TFE) and for 2 (2-fold from n-octane to water) although k(d) increased 27-fold in n-octane and 19-fold in TFE from 1 to 2. It was shown that the C-ON bond homolysis rate constant k(d) increased with the a(N) values, meaning that the stabilization of the nitroxide was the main factor involved in the solvent effect. Approaches relying on the Koppel-Palm and Kalmet-Abboud-Taft relationships failed to describe the solvent effect for all diastereoisomers of 1 and 2. Nevertheless, the solvent polarity/polarizability (pi*) and hydrogen bond donor (alpha) properties are the main effects involved in the solvent effects at TS and on products

Chemically Triggered C-ON Bond Homolysis in Alkoxyamines. 6. Effect of the Counteranion

International audienceWe showed (J. Org. Chem. 2012, 77, 9634) that the activation by methylation of pyridyl-based alkoxyamine 1 increased with the hydrogen bond donor properties of solvents. In this paper, activation of 1 by protonation with acids, CF3COOH and CSA, in tert-butylbenzene (t-BuPh) and in H2O/MeOH afforded, with CF3COOH, k(d) 28-fold larger in H2O/MeOH than in t-BuPh, whereas it was only 4-fold larger when CSA was used. This puzzling observation was ascribed to the dissociation of the intimate ion pair

Preparation of both enantiomers of a synthon for novel nucleoside analogs by enzymatic desymmetrization of a meso-diol with a methylene cyclopropane skeleton

International audienceThe enzymatic desymmetrization of methylenecyclopropane diol or its corresponding diacetate derivative, generated from a [2+1] cycloaddition between dioxepin and methylchlorocarbene, is described. After screening five commercial lipases, the two enantiomers of acetic acid 2-hydroxymethyl-3-methylene-cyclopropylmethyl ester are obtained in high yields and excellent enantioselectivities by using PFL or LPP in organic solvent. The stereostructure of the desymmetrization products was established by X-ray analysis. We also reported a new example with this non racemic chiral building block where the sign of optical rotation is dramatically solvent dependent and inverted. Using these enantiopure building blocks, a synthesis of novel nucleoside analogs is also presented. (C) 2011 Elsevier Ltd. All rights reserved

Chemically Triggered C–ON Bond Homolysis of Alkoxyamines. 5. Cybotactic Effect

In a recent work (Org. Lett. 2012, 14, 358), we showed that the rate constant <i>k</i>_d of the chemically activated C–ON bond homolysis of alkoxyamines was subject to solvent effects. However, we showed that solvent effects were weak for the nonactivated alkoxyamine <b>1</b> (diethyl (1-(<i>tert</i>-butyl­(1-(pyridin-4-yl)­ethoxy)­amino)-2,2-dimethylpropyl)­phosphonate) and its N⁺O^– oxide activated version <b>3</b>. On the other hand, the activated <i>N</i>-methylated version <b>2</b> of <b>1</b> experienced a strong solvent effect for a radical reaction, i.e., a 24-fold increase in <i>k</i>_d from <i>tert</i>-butylbenzene (<i>t</i>BuPh) to 2,2,2-trifluoroethanol (TFE). Good correlations were observed with the normalized Reichardt solvent polarity constant <i>E</i>_T^N and the nitrogen hyperfine coupling constant of the released nitroxide <i>a</i>_N,SG1, meaning that the stabilization of the nitroxide played an important role in C–ON bond homolysis in alkoxyamines. The Kalmet–Abboud--Taft relationships described successfully the solvent effect for each diastereoismer of <b>1</b> and <b>2</b>, as for example with the minor diastereoisomer of <b>1</b> log­(<i>k</i>_d′/s^–1) = −4.84 + 0.37π* + 0.21α and that of <b>2</b> log­(<i>k</i>_d′/s^–1) = −3.11 + 0.37π* + 0.47α, with π* being the polarity/polarizability and α the hydrogen bond donor (HBD) ability of the solvent. Surprisingly, the HBD effect is larger for <b>2</b> than for <b>1</b>, whereas no extra lone pair is available in <b>2</b>. This amazing effect was ascribed to the solvation of the counteranion, which is expected to be better solvated in a HBD solvent

Chemically triggered C-ON bond homolysis in alkoxyamines. Part 7. Remote polar effect

WOS:000334301600003International audienceIn a recent work (Org. Lett. 2012, 14, 358-361), we showed that the activation by benzylation of alkoxyamine 1 (diethyl (1-(tert-butyl(1-(pyridin-4-yl)ethoxy)amino)-2,2-dimethylpropyl)phosphon ate) afforded a surprisingly large C-ON bond homolysis rate constant k(d). Taking advantage of the easy preparation of para-X-benzyl-activated alkoxyamines 2 and of the presence of a shielding methylene group between the two aromatic moieties, we investigated the long range (10 bonds between the X group and the C-ON bond) polar effect for X=H, F, OMe, CN, NO2, NMe2, +NHMe2,Br-. It was observed that the effect was weak (4-fold) and mainly due to the zwiterionic mesomeric forms generated by the presence of group X on the para position, i.e. k(d) increased for CN and NO2 and decreased for OMe, NMe2 and +NMe2H,Br-. DFT calculations at the B3LYP/6-31G(d,p) level were performed to determine orbital interactions (natural bond orbital (NBO) analysis), Mulliken and NBO charges which support the reactivity described. Copyright (c) 2014 John Wiley & Sons, Ltd