Fluorocyclopropane-Containing Proline Analogue: Synthesis and Conformation of an Item in the Peptide Chemist's Toolbox

Over the years, numerous modifications to the structure of proline have been made in order to tune its effects on bioactive compounds. Notably, the introduction of a cyclopropane ring or a fluorine atom has produced interesting results. Herein, we describe the synthesis of a proline containing fluorocyclopropane. This modified amino acid was inserted into a tripeptide, whose conformation was studied by nuclear magnetic resonance and density functional theory calculations.

High Pressure promoted Dearomatization of Nitroarenes by [4+2] Cycloadditions with Silyloxydienes

Simple nitroarenes such as nitronaphthalenes and nitroquinolines smoothly undergo dearomatizing [4+2] cycloadditions with silyloxydienes under 16 kbar. Highly functionalized 3-dimensional polycyclic adducts bearing a tetrasubstituted carbon centre at the ring...

Drug Repurposing: Deferasirox Inhibits the Anti-Apoptotic Activity of Mcl-1

Introduction

With the aim of repositioning commercially available drugs for the inhibition of the anti-apoptotic myeloid cell leukemia protein, Mcl-1, implied in various cancers, five molecules, highlighted from a published theoretical screening, were selected to experimentally validate their affinity toward Mcl-1.

Results

A detailed NMR study revealed that only two of the five tested drugs, Torsemide and Deferasirox, interacted with Mcl-1. NMR data analysis allowed the complete characterization of the binding mode of both drugs to Mcl-1, including the estimation of their affinity for Mcl-1. Biological assays evidenced that the biological activity of Torsemide was lower as compared to the Deferasirox, which was able to efficiently and selectively inhibit the anti-apoptotic activity of Mcl-1. Finally, docking and molecular dynamics led to a 3D model for the Deferasirox:Mcl-1 complex and revealed the positioning of the drug in the Mcl-1 P2/P3 pockets as well as almost all synthetic Mcl-1 inhibitors. Interestingly, contrary to known synthetic Mcl-1 inhibitors which interact through Arg263, Deferasirox, establishes a salt bridge with Lys234.

Conclusion

Deferasirox could be a potential candidate for drug repositioning as Mcl-1 inhibitor.

Binding mode of Pyridoclax to myeloid cell leukemia-1 (Mcl-1) revealed by nuclear magnetic resonance spectroscopy, docking and molecular dynamics approaches

Myeloid cell leukemia-1 (Mcl-1) is an anti-apoptotic member of the Bcl-2 family proteins. Its amplification is one of the most frequent genetic aberrations found in human cancers. Pyridoclax, a promising BH3 mimetic inhibitor, interacts directly with Mcl-1 and induces massive apoptosis at a concentration of 15 µM in combination with anti-Bcl-x_L strategies in chemo-resistant ovarian cancer cell lines. In this study, a combined experimental and theoretical approach was used to investigate the binding mode of Pyridoclax to Mcl-1. The representative poses generated from dynamics simulations compared with NMR data revealed: (i) Pyridoclax bound to P1 and P2 pockets of Mcl-1 BH3 binding groove through its styryl and methyl groups establishing mainly hydrophobic contacts, (ii) one of the ending pyridines interacts through electrostatic interaction with K234 side chain, a negatively charged residue present only in this position in Mcl-1. Communicated by Ramaswamy H. Sarma.

The facile dearomatization of nitroaromatic compounds using lithium enolates of unsaturated ketones in conjugate additions and (4+2) formal cycloadditions

The dearomatization of conventional nitroarenes by lithiated enolates derived from methyl vinyl ketones easily takes place, following a formal (4+2) cycloaddition process. While nitroindoles react readily with in situ generated conjugated enolates, the deaggregation of these latter species using HMPA extends the reaction scope to the more aromatic nitronaphthalenes and pyridines.

Characterization of Milkisin, a Novel Lipopeptide With Antimicrobial Properties Produced By Pseudomonas sp. UCMA 17988 Isolated From Bovine Raw Milk

Biosurfactants such as lipopeptides are amphiphilic compounds produced by microorganisms such as bacteria of the genera of Pseudomonas and Bacillus. Some of these molecules proved to have interesting antimicrobial, antiviral, insecticide, and/or tensioactive properties that are potentially useful for the agricultural, chemical, food, and pharmaceutical industries. Raw milk provides a physicochemical environment that is favorable to the multiplication of a broad spectrum of microorganisms. Among them, psychrotrophic bacterial species, especially members of the genus Pseudomonas, are predominant and colonize milk during cold storage and/or processing. We isolated the strain Pseudomonas sp. UCMA 17988 from raw cow milk, with antagonistic activity against Listeria monocytogenes, Staphylococcus aureus, and Salmonella enterica Newport. Antimicrobial molecules involved in the antagonistic activity of this strain were characterized. A mass spectrometry analysis highlighted the presence of four lipopeptides isoforms. The major isoform (1409 m/z), composed of 10 carbons in the lipidic chain, was named milkisin C. The three other isoforms detected at 1381, 1395, and 1423 m/z, that are concomitantly produced, were named milkisin A, B, and D, respectively. The structure of milkisin, as confirmed by nuclear magnetic resonance analyses, is closely related to amphisin family. Indeed, the peptidic chain was composed of 11 amino acids, 6 of which are conserved among the family. In conclusion, Pseudomonas sp. UCMA 17988 produces new members of the amphisin family which are responsible for the antagonistic activity of this strain.

2D 7Li Ultrafast CT-COSY: a new tool for the rapid measurement of tiny homonuclear lithium scalar couplings

We report on the first examples of ⁷Li Ultrafast (UF) CT-COSY spectra from lithiated samples and on the usefulness of these experiments for the quantitative estimation of the ²J_7Li–7Li in a much shorter time.

Radical Cyclisation of α-Halo Aluminium Acetals: A Mechanistic Study

α-Bromo aluminium acetals are suitable substrates for Ueno-Stork-like radical cyclisations affording γ-lactols and acid-sensitive methylene-γ-lactols in high yields. The mechanistic study herein sets the scope and limitation of this reaction. The influence of the halide (or chalcogenide) atom X (X=Cl, Br, I, SPh, SePh) in the precursors α-haloesters, as well as influence of the solvent and temperature was studied. The structure of the aluminium acetal intermediates resulting from the reduction of the corresponding α-haloesters has been investigated by low-temperature (13) C-INEPT diffusion-ordered NMR spectroscopy (DOSY) experiments and quantum calculations, providing new insights into the structures of these thermally labile intermediates. Oxygen-bridged dimeric structures with a planar Al2 O2 ring are proposed for the least hindered aluminium acetals, while monomeric structures seem to prevail for the most hindered species. A comparison against the radical cyclisation of aluminium acetals derived from allyl and propargyl alcohols with the parent Ueno-Stork has been made at the BHandHLYP/6-311++G(d,p) level of theory, highlighting mechanistic similarities and differences.

1H Pure Shift DOSY: a handy tool to evaluate the aggregation and solvation of organolithium derivatives

The first successful application of ¹H PS-DOSY for a quantitative estimation of the degree of solvation and aggregation state of organolithium derivatives.

The conformation of tetrafluorinated methyl galactoside anomers: crystallographic and NMR studies

The first single-crystal X-ray diffraction study of tetrafluorinated monosaccharide derivatives is presented. Both α- and β-methyl 2,3-dideoxy-2,2,3,3-tetrafluoro-d-galactopyranoside anomers adopt the (4)C(1) conformation. The values for the C1-O1 and C1-O5 bond lengths and the O5-C1-O1-CH(3) dihedral angles are in line with what can be expected from the anomeric and exo-anomeric effects. The chair conformations are slightly distorted, presumably due to repulsion between 1,3-diaxial C-O and C-F bonds. The asymmetric unit of both compounds contains up to three independent molecules, which differ in the conformation of the hydroxymethyl group (including in one case a 'forbidden'gg rotamer). The molecular packing of the β-anomer shows a clear segregation between fluorinated and hydrophilic domains, while for the α-anomer the regions of fluorine segregation are broken by interleafing of OMe groups. There is one close OH⋯F contact, which is likely to arise from the crystal packing. NMR studies show that the two anomers also adopt a (4)C(1) conformation in solution (D(2)O, CDCl(3)).

Flexible porous metal-organic frameworks for a controlled drug delivery

Flexible nanoporous chromium or iron terephtalates (BDC) MIL-53(Cr, Fe) or M(OH)[BDC] have been used as matrices for the adsorption and in vitro drug delivery of Ibuprofen (or alpha- p-isobutylphenylpropionic acid). Both MIL-53(Cr) and MIL-53(Fe) solids adsorb around 20 wt % of Ibuprofen (Ibuprofen/dehydrated MIL-53 molar ratio = 0.22(1)), indicating that the amount of inserted drug does not depend on the metal (Cr, Fe) constitutive of the hybrid framework. Structural and spectroscopic characterizations are provided for the solid filled with Ibuprofen. In each case, the very slow and complete delivery of Ibuprofen was achieved under physiological conditions after 3 weeks with a predictable zero-order kinetics, which highlights the unique properties of flexible hybrid solids for adapting their pore opening to optimize the drug-matrix interactions.

Tautomerism and 1H, 13C and 15N NMR spectral assignments of some nitro derivatives of malonic acid diamide

Because of its reactivity, malonic acid diamide (1) was initially identified as an alternative precursor for the development of a new class of high-density insensitive energetic materials possessing low sensitivity to thermal decomposition and detonation by impact. Nitration of 1 was studied under different conditions and led to three different tautomeric forms (2-4) of nitromalonic acid diamine. Using stronger oxidation conditions the oxadiazole 5 was generated in one step. We report the full 1H, 13C and 15N NMR structural characterization of these compounds in DMSO together with thermal, infrared, mass spectrometric and x-ray analysis. Experimental data obtained for 4 are compatible with an enol-imine form. Our interpretation is consistent with calculated 1H and 13C NMR spectra (ACD).

A novel reactivity pattern of nitro-benzofuroxans and -benzofurazans: the heterodienic behaviour of the five-membered ring

Evidence is presented that the N3C9C8N fragment of the annelated ring of some nitro-activated benzofuroxans and benzofurazans acts as a heterodiene contributor upon treatment with cyclohexadiene, thus highlighting a new facet of the reactivity of this class of heterocycles.

A data-mining approach to spacer oligonucleotide typing of Mycobacterium tuberculosis

MOTIVATION

The Direct Repeat (DR) locus of Mycobacterium tuberculosis is a suitable model to study (i) molecular epidemiology and (ii) the evolutionary genetics of tuberculosis. This is achieved by a DNA analysis technique (genotyping), called sp acer oligo nucleotide typing (spoligotyping ). In this paper, we investigated data analysis methods to discover intelligible knowledge rules from spoligotyping, that has not yet been applied on such representation. This processing was achieved by applying the C4.5 induction algorithm and knowledge rules were produced. Finally, a Prototype Selection (PS) procedure was applied to eliminate noisy data. This both simplified decision rules, as well as the number of spacers to be tested to solve classification tasks. In the second part of this paper, the contribution of 25 new additional spacers and the knowledge rules inferred were studied from a machine learning point of view. From a statistical point of view, the correlations between spacers were analyzed and suggested that both negative and positive ones may be related to potential structural constraints within the DR locus that may shape its evolution directly or indirectly.

RESULTS

By generating knowledge rules induced from decision trees, it was shown that not only the expert knowledge may be modeled but also improved and simplified to solve automatic classification tasks on unknown patterns. A practical consequence of this study may be a simplification of the spoligotyping technique, resulting in a reduction of the experimental constraints and an increase in the number of samples processed.