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1. The β-phosphorus hyperfine coupling constant in nitroxides: 6. Solvent effects in non-cyclic nitroxides

Author

Paul Brémond, Raphael Bikanga, Lionel Bosco, Sylvain R. A. Marque, Gérard Audran, Paulin Nkolo, Teddy Butscher, Institut de Chimie Radicalaire (ICR), Aix Marseille Université (AMU)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Lab Substances Naturelles (LASUNA), Université des Sciences et Techniques de Masuku [Franceville, Gabon] (USTM), Laboratoire de Substances Naturelles et de Synthèses Organométalliques (LASNSOM), Unité de Recherche en Chimie [Université des Sciences et Techniques de Masuku] (URCHI), Ecole Doctorale des Sciences Fondamentales et Appliquées [Université des Sciences et Techniques de Masuku] (EDSFA), Université des Sciences et Techniques de Masuku (USTM)-Université des Sciences et Techniques de Masuku (USTM)-Ecole Doctorale des Sciences Fondamentales et Appliquées [Université des Sciences et Techniques de Masuku] (EDSFA), and Université des Sciences et Techniques de Masuku (USTM)-Université des Sciences et Techniques de Masuku (USTM)

Subjects
ALKOXYAMINE, Nitroxide mediated radical polymerization, Radical, HOMOLYSIS, 010402 general chemistry, Photochemistry, 01 natural sciences, Biochemistry, PROBES, law.invention, ELECTRON-PARAMAGNETIC-RESONANCE, law, Polarizability, RADICALS, [CHIM]Chemical Sciences, Molecule, Physical and Theoretical Chemistry, Electron paramagnetic resonance, 010405 organic chemistry, Chemistry, Hydrogen bond, Organic Chemistry, 0104 chemical sciences, Homolysis, NITROGEN, Solvent effects, POLARITY
Abstract

International audience; In two recent articles (Org. Biomol. Chem., 2015 and 2016), we showed that changes in the phosphorus hyperfine coupling constant a(P) at position beta in beta-phosphorylated nitroxides can be dramatic. Such changes were applied to the titration of water in organic solvents and conversely of organic solvents in water. One of the molecules tested was a non-cyclic nitroxide meaning that a thorough investigation of the solvent effect on the EPR hyperfine coupling constant is timely due. In this article, we show that the aP of persistent non-cyclic beta-phosphorylated nitroxides decrease with the normalized polarity Reichardt's constant ENT. The Koppel-Palm and Kalmet-Abboud-Taft relationships were applied to gain deeper insight into the effects influencing a(N) and a(P): polarity/polarizability, hydrogen bond donor properties, and the structuredness of the cybotactic region.

Published
2016

2. C-ON bond homolysis of alkoxyamines: when too high polarity is detrimental

Author

Gigmes, Didier, Nkolo, Paul, Audran, Gérard, Bikanga, Raphaël, Brémond, Paul, Marque, Sylvain, Roubaud, Valérie, Institut de Chimie Radicalaire (ICR), Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU), Laboratoires de Substances Naturelles et de Synthèses Organométalliques (LASNSOM), Université des Sciences et Techniques de Masuku [Franceville, Gabon] (USTM), Institut Lavoisier de Versailles (ILV), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Aix Marseille Université (AMU)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Substances Naturelles et de Synthèses Organométalliques (LASNSOM), Unité de Recherche en Chimie [Université des Sciences et Techniques de Masuku] (URCHI), Ecole Doctorale des Sciences Fondamentales et Appliquées [Université des Sciences et Techniques de Masuku] (EDSFA), Université des Sciences et Techniques de Masuku (USTM)-Université des Sciences et Techniques de Masuku (USTM)-Ecole Doctorale des Sciences Fondamentales et Appliquées [Université des Sciences et Techniques de Masuku] (EDSFA), and Université des Sciences et Techniques de Masuku (USTM)-Université des Sciences et Techniques de Masuku (USTM)

Subjects
chemistry.chemical_classification, Nitroxide mediated radical polymerization, 010405 organic chemistry, Stereochemistry, Organic Chemistry, Nitroxyl, 010402 general chemistry, 01 natural sciences, Biochemistry, Medicinal chemistry, 0104 chemical sciences, Homolysis, chemistry.chemical_compound, Reaction rate constant, chemistry, Polar effect, [CHIM]Chemical Sciences, Methanol, Physical and Theoretical Chemistry, Solvent effects, Alkyl, ComputingMilieux_MISCELLANEOUS
Abstract

Throughout the last decade, the effect of electron withdrawing groups (EWGs) has been known to play a role - minor or moderate depending on the nitroxyl fragment R1R2NO - in the change in the homolysis rate constant (kd) for C-ON bond homolysis in alkoxyamines (R1R2NOR). It has been shown that the effect of EWGs on kd is described by a linear relationship with the electrical Hammett constant σI. Since then, linear multi-parameter relationships f(σRS,ν,σI) have been developed to account for the effects involved in the changes in kd, which are the stabilization of the released radical (σRS) and the bulkiness (ν) and polarity (σI) of the alkyl fragment. Since a decade ago, new results have been published highlighting the limits of such correlations. In this article, previous multi-parameter linear relationships are amended using a parabolic model, i.e. (σI,nitroxide - σI,alkyl)2, to describe the effect of EWGs in the alkyl fragment on kd. In contrast to previous studies, these improved linear multi-parameter relationships f(σRS,ν,ΔσI2) are able to account for the presence of several EWGs on the alkyl fragment, R. An unexpectedly strong solvent effect - a ca. 1500-fold increase in kd - from tert-butylbenzene to the water/methanol mixture is also observed for 3-((2,2,6,6-tetramethylpiperidin-1-yl)oxyl)pentane-2,4-dione 1b in comparison to a ca. 5-fold increase in kd that is generally observed.

Published
2017

3. Normal, Leveled, and Enhanced Steric Effects in Alkoxyamines Carrying a beta-Phosphorylated Nitroxyl Fragment

Author

Gérard Audran, Paul Brémond, Raphael Bikanga, Jean-Patrick Joly, Sylvain R. A. Marque, Paulin Nkolo, Institut de Chimie Radicalaire (ICR), Aix Marseille Université (AMU)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Substances Naturelles et de Synthèses Organométalliques (LASNSOM), Unité de Recherche en Chimie [Université des Sciences et Techniques de Masuku] (URCHI), Ecole Doctorale des Sciences Fondamentales et Appliquées [Université des Sciences et Techniques de Masuku] (EDSFA), Université des Sciences et Techniques de Masuku (USTM)-Université des Sciences et Techniques de Masuku (USTM)-Ecole Doctorale des Sciences Fondamentales et Appliquées [Université des Sciences et Techniques de Masuku] (EDSFA), Université des Sciences et Techniques de Masuku (USTM)-Université des Sciences et Techniques de Masuku (USTM), Lab Substances Naturelles (LASUNA), Université des Sciences et Techniques de Masuku [Franceville, Gabon] (USTM), and Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)

Subjects
Steric effects, family, 010405 organic chemistry, Chemistry, Stereochemistry, Organic Chemistry, Nitroxyl, mediated polymerization, 010402 general chemistry, 01 natural sciences, on bond homolysis, 0104 chemical sciences, Homolysis, chemistry.chemical_compound, Reaction rate constant, Fragment (logic), styrene, Phosphorylation, [CHIM]Chemical Sciences, polar, rate-constant, free-radical polymerization, polymers, bearing
Abstract

International audience; The design of new R1R2NOR3 alkoxyamines for various applications relies on the accurate prediction of two kinetic parameters, the C-ON bond homolysis rate constant (k(d)) and its re-formation rate constant (k(c)). Relationships to describe the steric and polar effects of the R1R2NO fragment ruling k(d) have been developed. For all cyclic nitroxyl fragments, the steric effect is described as the sum of the bulkiness of the R-1 and R-2 groups (i.e., normal steric effect), while for the noncyclic nitroxyl fragment (except for one case), a leveled steric effect is assumed. In this work, we show that the normal steric effect also applies to noncyclic nitroxyl fragments and that for one case an enhanced steric effect is also observed, i.e., experimental k(d) \\textgreater 5-fold larger than the predicted value.

Published
2017

4. Hyperfine coupling constants of beta-phosphorylated nitroxides: Subtle interplay between steric strain, hyperconjugation, and dipole-dipole interactions

Author

Paul Brémond, Gérard Audran, Raphael Bikanga, Sylvain R. A. Marque, Paulin Nkolo, Valérie Roubaud, Institut de Chimie Radicalaire (ICR), Aix Marseille Université (AMU)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Substances Naturelles et de Synthèses Organométalliques (LASNSOM), Unité de Recherche en Chimie [Université des Sciences et Techniques de Masuku] (URCHI), Ecole Doctorale des Sciences Fondamentales et Appliquées [Université des Sciences et Techniques de Masuku] (EDSFA), Université des Sciences et Techniques de Masuku (USTM)-Université des Sciences et Techniques de Masuku (USTM)-Ecole Doctorale des Sciences Fondamentales et Appliquées [Université des Sciences et Techniques de Masuku] (EDSFA), Université des Sciences et Techniques de Masuku (USTM)-Université des Sciences et Techniques de Masuku (USTM), Lab Substances Naturelles (LASUNA), Université des Sciences et Techniques de Masuku [Franceville, Gabon] (USTM), and Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)

Subjects
Polarity (physics), Solvent effect, 010402 general chemistry, Hyperconjugation, Photochemistry, 01 natural sciences, Biochemistry, nitrogen, Hyperfine coupling, Drug Discovery, [CHIM]Chemical Sciences, Physics::Chemical Physics, mri, solvent polarity, 010405 organic chemistry, Chemistry, Hydrogen bond, Organic Chemistry, Nitroxides, electron-transfer, Condensed Matter::Mesoscopic Systems and Quantum Hall Effect, 0104 chemical sciences, Solvent, Dipole, Crystallography, parameter, resonance, Multi-parameter analysis, Solvent effects, solvation, probes, esr, EPR spectroscopy
Abstract

International audience; Solvent effects in beta-phosphorylated nitroxides show that nitrogen and phosphorus hyperfine coupling constants a(N) and a(p), increase and decrease with increasing polarity, polarizity, and Hydrogen Bond Donor effects of solvents, respectively. In a series of articles, it was shown that the driving interaction controlling the change in a(p) is the maximization of the N+center dot O-center dot center dot center dot center dot center dot center dot P+-O- dipole - dipole interaction. In this work, we show that the steric strain in Spiro beta-phosphotylated nitroxides affords the opposite trend for a(p) that is, a(p) increases with increasing solvent properties features. (C) 2017 Elsevier Ltd. All rights reserved.

Published
2017

5. How intramolecular hydrogen bonding (IHB) controls the C-ON bond homolysis in alkoxyamines

Author

Mariya V. Edeleva, Paul Brémond, Raphael Bikanga, Valérie Roubaud, Gérard Audran, Sylvain R. A. Marque, Jean-Patrick Joly, Paulin Nkolo, Institut de Chimie Radicalaire (ICR), Aix Marseille Université (AMU)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Substances Naturelles et de Synthèses Organométalliques (LASNSOM), Unité de Recherche en Chimie [Université des Sciences et Techniques de Masuku] (URCHI), Ecole Doctorale des Sciences Fondamentales et Appliquées [Université des Sciences et Techniques de Masuku] (EDSFA), Université des Sciences et Techniques de Masuku (USTM)-Université des Sciences et Techniques de Masuku (USTM)-Ecole Doctorale des Sciences Fondamentales et Appliquées [Université des Sciences et Techniques de Masuku] (EDSFA), Université des Sciences et Techniques de Masuku (USTM)-Université des Sciences et Techniques de Masuku (USTM), N. N. Vorozhtsov Novosibirsk Institute of Organic Chemistry, ANR-14-CE16-0023,NORMATHER,Etude et inhibition de l'activation des cellules endothéliales dans la vascularisation physiologique et pathologique de la rétine.(2014), Lab Substances Naturelles (LASUNA), Université des Sciences et Techniques de Masuku [Franceville, Gabon] (USTM), Institut de Chimie Radicalaire ( ICR ), Aix Marseille Université ( AMU ) -Centre National de la Recherche Scientifique ( CNRS ), Lab Substances Naturelles ( LASUNA ), Université des Sciences et Techniques de Masuku, ANR-14-CE16-0023,NORMATHER,Etude et inhibition de l’activation des cellules endothéliales dans la vascularisation physiologique et pathologique de la rétine. ( 2014 ), and Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Aix Marseille Université (AMU)

Subjects
family, Protonation, 010402 general chemistry, Photochemistry, chemistry, 01 natural sciences, Biochemistry, Medicinal chemistry, chemistry.chemical_compound, Reaction rate constant, [ CHIM.ORGA ] Chemical Sciences/Organic chemistry, polar, Physical and Theoretical Chemistry, Alkyl, chemistry.chemical_classification, 010405 organic chemistry, Hydrogen bond, Chemistry, [CHIM.ORGA]Chemical Sciences/Organic chemistry, Organic Chemistry, Nitroxyl, constants, 0104 chemical sciences, 3. Good health, Homolysis, Intramolecular force, derivatives, nitroxyl fragment, Solvent effects, free-radical polymerization
Abstract

International audience; Recent amazing results (Nkolo et al., Org. Biomol. Chem., 2017, 6167) on the effect of solvents and polarity on the C-ON bond homolysis rate constants kd of alkoxyamine R1R2NOR3 led us to re-investigate the antagonistic effect of intramolecular hydrogen-bonding (IHB) on kd. Here, IHB is investigated both in the nitroxyl fragment R1R2NO and in the alkyl fragment R-3, as well as between fragments, that is, the donating group on the alkyl fragment and the accepting group on the nitroxyl fragment, and conversely. It appears that IHB between fragments (inter IHB) strikingly decreases the homolysis rate constant kd, whereas IHB within the fragment (intra IHB) moderately increases kd. For one alkoxyamine, the simultaneous occurrence of IHB within the nitroxyl fragment and between fragments is reported. The protonation effect is weaker in the presence than in the absence of IHB. A moderate solvent effect is also observed.

Published
2017

6. One-pot microwave-assisted synthesis and antimalarial activity of ferrocenyl benzodiazepines

Author

Jean-Bernard Lekana-Douki, Philippe Grellier, Fousseyni S. Touré Ndouo, Gabin Mwande-Maguene, Sylvain Pellegrini, Jacques Lebibi, Till Bousquet, Jouda Jakhlal, Lydie Pelinski, Elisabeth Mouray, Unité de Catalyse et Chimie du Solide - UMR 8181 (UCCS), Centrale Lille Institut (CLIL)-Université d'Artois (UA)-Centrale Lille-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Lille, Département de Parasitologie, Mycologie et Médecine Tropicale, Faculté de Médecine-Université de Libreville, Molécules de Communication et Adaptation des Micro-organismes (MCAM), Muséum national d'Histoire naturelle (MNHN)-Centre National de la Recherche Scientifique (CNRS), Lab Substances Naturelles (LASUNA), Université des Sciences et Techniques de Masuku [Franceville, Gabon] (USTM), Université d'Artois (UA)-Centrale Lille-Institut de Chimie du CNRS (INC)-Université de Lille-Centre National de la Recherche Scientifique (CNRS), Laboratoire de Substances Naturelles et de Synthèses Organométalliques (LASNSOM), Unité de Recherche en Chimie [Université des Sciences et Techniques de Masuku] (URCHI), Ecole Doctorale des Sciences Fondamentales et Appliquées [Université des Sciences et Techniques de Masuku] (EDSFA), Université des Sciences et Techniques de Masuku (USTM)-Université des Sciences et Techniques de Masuku (USTM)-Ecole Doctorale des Sciences Fondamentales et Appliquées [Université des Sciences et Techniques de Masuku] (EDSFA), and Université des Sciences et Techniques de Masuku (USTM)-Université des Sciences et Techniques de Masuku (USTM)

Subjects
chemistry.chemical_classification, biology, 010405 organic chemistry, Chemistry, Condensation, Plasmodium falciparum, General Chemistry, 010402 general chemistry, biology.organism_classification, 01 natural sciences, Microwave assisted, Catalysis, 3. Good health, 0104 chemical sciences, Amino acid, [SDV.MP]Life Sciences [q-bio]/Microbiology and Parasitology, Materials Chemistry, [CHIM]Chemical Sciences, Organic chemistry, ComputingMilieux_MISCELLANEOUS
Abstract

An efficient synthesis of 1,4-benzodiazepin-2-ones is described by condensation between 2-aminobenzophenone and Boc-protected amino acids via microwave-assisted irradiation. This produces higher yields in shorter reaction times than with traditional methods. The antiplasmodial activity of the corresponding ferrocenyl benzodiazepines was evaluated in vitro against Plasmodium falciparum F32 (chloroquine-sensitive) and FCB1 and K1 (chloroquine-resistant) strains and gabonese clinical isolates.

Published
2011

7. Toxicity, Antibacterial, and Phytochemical Analyses of Antrocaryon klaineanum Pierre Extracts.

Author

Sima Obiang C, Ndong Mba T, Ondo JP, Ngoua Meye Misso RL, Orango Bourdette JO, Otogo N'Nang E, Mbogho Abogho J, Jolinom Mbot E, Obame Engonga LC, and Nsi Emvo E

Abstract

Medicinal plants are traditionally used in Gabon to treat several types of illnesses. The study's purpose was to determine the toxic, antibacterial, and anti-inflammatory effects of Antrocaryon klaineanum Pierre extracts and to characterize their phytochemical compounds. Toxicity was evaluated on frog tadpoles ( Phrynobatrachus africanus Hallowell). The microorganism susceptibility test was performed by the diffusion method, while minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were evaluated using the microdilution technique. Anti-inflammatory activity was tested through protein denaturation and membrane stabilization methods. Chromatography and molecular network techniques were used to characterize chemical compounds. The lethality test showed that the lethal concentration (LC 50 ) increased from 110.03 ± 1.25 to 15.86 ± 2.21  μ g/mL after 24 and 96 hours of exposure. In tadpoles exposed to 7.81  μ g/mL extract, the first mortalities (12.5%) were observed on the fifth day of exposure. A relative decrease in mature erythrocytes exposed to plant extracts was observed. The antibacterial activity shows that the Ak F 2 , Ak F 3 , and Ak F 4 fractions (from the water-ethanol crude extract) gave the greatest antibacterial activities compared to the other extracts. The water, water-acetone, and water-ethanol extracts showed good inhibition of denaturation. The haemolysis test shows that the extracts exhibited good anti-inflammatory activities. Phytochemical characterisation revealed four major compounds, including monogallate epicatechin and hydroxy-ergostadian. The molecular network revealed five main clusters. Our study shows that A. klaineanum Pierre could be a promising natural product for the isolation of molecules with potential biological activities., Competing Interests: The authors declare that there are no conflicts of interest regarding the publication of this paper., (Copyright © 2023 Cédric Sima Obiang et al.)

Published
2023
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8. Homolytic and Heterolytic Cleavage of β-Ether Linkages in Hardwood Lignin by Steam Explosion.

Author

Obame SN, Ziegler-Devin I, Safou-Tchima R, and Brosse N

Subjects
Ether chemistry, Hydrolysis, Lignin isolation & purification, Magnetic Resonance Spectroscopy, Molecular Structure, Molecular Weight, Plant Extracts isolation & purification, Steam analysis, Burseraceae chemistry, Lignin chemistry, Plant Extracts chemistry, Wood chemistry
Abstract

Steam-explosion lignin (SEL) was extracted with ethanol from steam-exploded hardwood (okoumé, Aucoumea klaineana Pierre) pretreated at various severities after neutral or acidic impregnation. The SELs were subjected to structural characterization by 2D HSQC NMR, 31 P NMR, and SEC and compared with milled-wood lignin (MWL). A strong decrease in the β- O-4 content is observed with increasing steam-explosion severity accompanied by a gradual increase in molecular mass. Cα-oxidized S units (S', Hibbert's ketones) were quantified by NMR and used as a marker of the hydrolytic mechanism; naphthol was used as a carbonium-ion scavenger. It has been observed that mixed reactions of hydrolysis and homolysis are involved, but the SEL is mainly cleaved homolytically, favoring recondensation through radical coupling even at low reaction severity. However, acidic preimpregnation of wood prior to steam explosion enhanced the carbonium-ion pathway.

Published
2019
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9. Probing for the presence of glucosinolates in three Drypetes spp. (Drypetes euryodes (Hiern) Hutch., Drypetes gossweileri S. Moore, Drypetes laciniata Hutch.) and two Rinorea spp. (Rinorea subintegrifolia O. Ktze and Rinorea woermanniana (Büttner) Engl.) from Gabon.

Author

Montaut S, De Nicola GR, Agnaniet H, Issembe Y, Rollin P, and Menut C

Subjects
Chromatography, High Pressure Liquid methods, Gabon, Glucosinolates chemistry, Glucosinolates isolation & purification, Plant Bark chemistry, Plant Extracts chemistry, Plant Leaves chemistry, Plant Roots chemistry, Seeds chemistry, Glucosinolates analysis, Magnoliopsida chemistry
Abstract

Drypetes euryodes (Hiern) Hutch., Drypetes gossweileri S. Moore, Drypetes laciniata Hutch. (Putranjivaceae), Rinorea subintegrifolia O. Ktze, and Rinorea woermanniana (Büttner) Engl. (Violaceae) from Gabon were probed for the presence of glucosinolates (GLs). When present, the GLs were identified and quantified by HPLC analysis. 2-Hydroxy-2-methyl GL (1) was the major GL in the cork of D. euryodes. Moreover, 4-hydroxybenzyl GL (2) was the major GL in the seed of D. gossweileri whereas the bark contained 2 as the minor GL and benzyl GL (3) was the major one. In addition, 4-methoxybenzyl GL (4), 3-methoxybenzyl GL (5), and 3 were found in the root of R. subintegrifolia. However, no GL was detected in D. laciniata (leaf and stem), D. euryodes (leaf and stem), and R. woermanniana (leaf and stem-branch). Our results support the hypothesis of the existence of GLs in plants of the Putranjivaceae and Violaceae families (order Malpighiales).

Published
2017
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10. Antidiabetic potential of two medicinal plants used in Gabonese folk medicine.

Author

Agnaniet H, Mbot EJ, Keita O, Fehrentz JA, Ankli A, Gallud A, Garcia M, Gary-Bobo M, Lebibi J, Cresteil T, and Menut C

Subjects
Chromatography, High Pressure Liquid, Diabetes Mellitus drug therapy, Gabon, Glycoside Hydrolase Inhibitors therapeutic use, Humans, Hypoglycemic Agents therapeutic use, Medicine, African Traditional, Phenols therapeutic use, Phytotherapy, Plant Bark, Plant Extracts therapeutic use, Plant Leaves, Diabetes Mellitus metabolism, Glycoside Hydrolase Inhibitors pharmacology, Hypoglycemic Agents pharmacology, Phenols pharmacology, Plant Extracts pharmacology, Rubiaceae chemistry, alpha-Glucosidases metabolism
Abstract

Background: Diabetes mellitus is a metabolic disorder which is rising globally in rich and developing countries. In the African region this rate is the highest, with 20 million diagnosed diabetics. Despite a noticeable progress in the treatment of diabetes mellitus by synthetic drugs, the search for new natural anti-diabetic agents is going on. Nauclea diderrichii (De Wild.) Merr. (ND) and Sarcocephalus pobeguinii Hua ex Pellegr. (SP) are used as traditional medicines in Gabon for the treatment of different diseases, especially in the case of diabetes. The aim of this study was to evaluate the antidiabetic potential of these two medicinal plants traditionally used in Gabon., Methods: Pharmacological (inhibitory action on α and β-glucosidases) and toxicological (effect on human T cell proliferation) studies were conducted on aqueous extracts of ND (leaves and bark) and SP (bark) collected in Gabon. All raw extracts were analyzed by HPTLC and their content in phenolic compounds was determined by using standard method. The most active extracts were submitted to preparative HPLC in order to evidence the most efficient subfractions by biological evaluation., Results: The results showed that two extracts from ND were potent α-glucosidase inhibitors, the leaf extract being more active that the bark extract: the first one was more than 60 fold more active than Acarbose, which is an oral medication used to treat type 2 diabetes; the extract from SP bark was less efficient. The HPLC subfractions of the extracts of ND leaves and SP bark were tested in the same experimental conditions. In each case, the most active subfractions still show very potent inhibitory effect on α-glucosidase (80-90% inhibition at 0.1 mg/mL). The most efficient extract, from ND leaves, was also characterized by the highest percentage of phenolic compounds, which suggests a relationship between its inhibitory potential on α-glucosidase and its content in phenolic compounds. Conversely, only a moderate inhibitory activity of the three extracts was observed on β-glucosidase., Conclusion: These results clearly indicated that active compounds present in N. diderrichii and S. pobeguinii leaves or/and bark were selective and highly potent inhibitors of α-glucosidase and validate their popular use for the treatment of diabetes.

Published
2016
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