Synthesis and Biological Application of Isosteviol-Based 1,3-Aminoalcohols

Starting from isosteviol, a series of diterpenoid 1,3-aminoalcohol derivatives were stereoselectively synthesised. The acid-catalysed hydrolysis and rearrangement of natural stevioside gave isosteviol, which was transformed to the key intermediate methyl ester. In the next step, Mannich condensation of diterpenoid ketone, paraformaldehyde, and secondary amines resulted in the formation of 1,3-aminoketones with different stereoselectivities. During the Mannich condensation with dibenzylamine, an interesting N-benzyl → N-methyl substituent exchange was observed. Reduction of 1,3-aminoketones produced diastereoisomeric 1,3-aminoalcohols. Alternatively, aminoalcohols were obtained via stereoselective hydroxy-formylation, followed by oxime preparation, reduction, and finally, reductive alkylation of the obtained primary aminoalcohols. An alternative 1,3-aminoalcohol library was prepared by reductive amination of the intermediate 3-hydroxyaldehyde obtained from isosteviol in two-step synthesis. Cytotoxic activity of compounds against human tumour cell lines (A2780, SiHa, HeLa, MCF-7 and MDA-MB-231) was investigated. In our preliminary study, the 1,3-aminoalcohol function and N-benzyl substitution seemed to be essential for the reliable antiproliferative activity. To extend their application, a diterpenoid condensed with 2-phenylimino-1,3-thiazine and -1,3-oxazine was also attempted to prepare, but only formation of thioether intermediate was observed.

Naturally Occurring Oxazole Structural Units as Ligands of Vanadium Catalysts for Ethylene-Norbornene (Co)polymerization

1,3-Oxazole and 4,5-dihydro-1,3-oxazole are common structural motifs in naturally occurring peptides. A series of vanadium complexes were synthesized using VCl3(THF)3 and methyl substituted (4,5-dihydro-1,3-oxazol-2-yl)-1,3-oxazoles as ligands and analyzed using NMR and MS methods. The complexes were found to be active catalysts both in ethylene polymerization and ethylene-norbornene copolymerization. The position of methyl substituent in the ligand has considerable impact on the performance of (co)polymerization reaction, as well as on the microstructure, and thus physical properties of the obtained copolymers.

Challenges in the Highly Selective [3 + 1]-Cycloaddition of an Enoldiazoacetamide to Form a Donor–Acceptor Cis-Cyclobutenecarboxamide

A substituted donor–acceptor cyclobutenecarboxamide is synthesized with modest enantiocontrol through a chiral copper(I) complex catalyzed [3 + 1]-cycloaddition reaction of α-acyl diphenylsulfur ylides with 3-siloxy-2-diazo-3-butenamides. With a methyl substituent on the 4-position of the 3-butenamide, the cis-vicinal-3,4-disubstituted cyclobutenecarboxamide is formed with >20:1 diastereocontrol. Donor-acceptor 3-methyl-2-siloxycyclopropenecarboxamide is rapidly formed from the reactant enoldiazoamide and undergoes catalytic ring opening to give only the Z-γ-substituted metallo-enolcarbene. Elimination from 3-siloxy-2-diazo-3-pentenamide to form the conjugated 3-siloxy-2,4-pentadienamide is competitive but minimized at low temperature.

Analysis of β-lactone formation by clinically observed carbapenemases informs on a novel antibiotic resistance mechanism

An important mechanism of resistance to β-lactam antibiotics is via their β-lactamase–catalyzed hydrolysis. Recent work has shown that, in addition to the established hydrolysis products, the reaction of the class D nucleophilic serine β-lactamases (SBLs) with carbapenems also produces β-lactones. We report studies on the factors determining β-lactone formation by class D SBLs. We show that variations in hydrophobic residues at the active site of class D SBLs (i.e. Trp105, Val120, and Leu158, using OXA-48 numbering) impact on the relative levels of β-lactones and hydrolysis products formed. Some variants, i.e. the OXA-48 V120L and OXA-23 V128L variants, catalyze increased β-lactone formation compared with the WT enzymes. The results of kinetic and product studies reveal that variations of residues other than those directly involved in catalysis, including those arising from clinically observed mutations, can alter the reaction outcome of class D SBL catalysis. NMR studies show that some class D SBL variants catalyze formation of β-lactones from all clinically relevant carbapenems regardless of the presence or absence of a 1β-methyl substituent. Analysis of reported crystal structures for carbapenem-derived acyl-enzyme complexes reveals preferred conformations for hydrolysis and β-lactone formation. The observation of increased β-lactone formation by class D SBL variants, including the clinically observed carbapenemase OXA-48 V120L, supports the proposal that class D SBL-catalyzed rearrangement of β-lactams to β-lactones is important as a resistance mechanism.

Influence of the Nucleophilic Ligand on the Reactivity of Carbonyl Rhenium(I) Complexes towards Methyl Propiolate: A Computational Chemistry Perspective

A comparative theoretical study on the reactivity of the complexes [ReY(CO)3(bipy)] (Y = NH2, NHMe, NHpTol, OH, OMe, OPh, PH2, PHMe, PMe2, PHPh, PPh2, PMePh, SH, SMe, SPh; bipy = 2,2′-bipyridine) towards methyl propiolate was carried out to analyze the influence of both the heteroatom (N, O, P, S) and the alkyl and/or aryl substituents of the Y ligand on the nature of the product obtained. The methyl substituent tends to accelerate the reactions. However, an aromatic ring bonded to N and O makes the reaction more difficult, whereas its linkage to P and S favour it. On the whole, ligands with O and S heteroatoms seem to disfavour these processes more than ligands with N and P heteroatoms, respectively. Phosphido and thiolato ligands tend to yield a coupling product with the bipy ligand, which is not the general case for hydroxo, alcoxo or amido ligands. When the Y ligand has an O/N and an H atom the most likely product is the one containing a coupling with the carbonyl ligand, which is not always obtained when Y contains P/S. Only for OMe and OPh, the product resulting from formal insertion into the Re-Y bond is the preferred.

Positional Isomerism in the N^N Ligand: How Much Difference Does a Methyl Group Make in [Cu(P^P)(N^N)]+ Complexes?

The synthesis and structural characterization of 5,6′-dimethyl-2,2′-bipyridine (5,6′-Me2bpy) are reported, along with the preparations and characterizations of [Cu(POP)(5,6′-Me2bpy)][PF6] and [Cu(xantphos)(5,6′-Me2bpy)][PF6] (POP = bis(2-(diphenylphosphanyl)phenyl)ether, xantphos = 4,5-bis(diphenylphosphanyl)-9,9-dimethyl-9H-xanthene). Single-crystal X-ray structure determinations of [Cu(POP)(5,6′-Me2bpy)][PF6] and [Cu(xantphos)(5,6′-Me2bpy)][PF6] confirmed distorted tetrahedral copper(I) coordination environments with the 5-methylpyridine ring of 5,6′-Me2bpy directed towards the (C6H4)2O unit of POP or the xanthene unit of xantphos. In the xantphos case, this preference may be attributed to C–H…π interactions involving both the 6-CH unit and the 5-methyl substituent in the 5-methylpyridine ring and the arene rings of the xanthene unit. 1H NMR spectroscopic data indicate that this ligand orientation is also preferred in solution. In solution and the solid state, [Cu(POP)(5,6′-Me2bpy)][PF6] and [Cu(xantphos)(5,6′-Me2bpy)][PF6] are yellow emitters, and, for powdered samples, photoluminescence quantum yields (PLQYs) are 12 and 11%, respectively, and excited-state lifetimes are 5 and 6 μs, respectively. These values are lower than PLQY and τ values for [Cu(POP)(6,6′-Me2bpy)][PF6] and [Cu(xantphos)(6,6′-Me2bpy)][PF6], and the investigation points to the 6,6′-dimethyl substitution pattern in the bpy ligand being critical for enhancement of the PLQY.

Wide-Antimicrobial Spectrum of Picolinium Salts

Nosocomial infections, which greatly increase morbidity among hospitalized patients, together with growing antibiotic resistance still encourage many researchers to search for novel antimicrobial compounds. Picolinium salts with different lengths of alkyl chains (C12, C14, C16) were prepared by Menshutkin-like reaction and evaluated with respect to their biological activity, i.e., lipophilicity and critical micellar concentration. Picolinium salts with C14 and C16 side chains achieved similar or even better results when in terms of antimicrobial efficacy than benzalkoniums; notably, their fungicidal efficiency was substantially more potent. The position of the methyl substituent on the aromatic ring does not seem to affect antimicrobial activity, in contrast to the effect of length of the N-alkyl chain. Concurrently, picolinium salts exhibited satisfactory low cytotoxicity against mammalian cells, i.e., lower than that of benzalkonium compounds, which are considered as safe.

Synthesis of internally alkylated azuliporphyrins

Examples of internally alkylated azuliporphyrins were prepared by MacDonald-type “3 + 1” condensations. 2-Methyl- and 2-ethylazulene reacted with an acetoxymethylpyrrole in the presence of an acid catalyst to give azulitripyrranes. Following cleavage of the terminal protective groups, condensation with a diformylpyrrole in the presence of hydrochloric acid and oxidation with ferric chloride afforded 21-alkylazuliporphyrins. An azulene dialdehyde similarly reacted with an [Formula: see text]-methyltripyrrane to generate a 23-methylazuliporphyrin. The products could only be isolated in protonated form and the free-base internally alkylated azuliporphyrins proved to be unstable. Nevertheless, the dications are highly diatropic and the internal alkyl group resonances were shifted upfield to beyond -3 ppm. Reaction of a 23-methylazuliporphyrin with palladium(II) acetate primarily afforded a palladium(II) complex with loss of the internal methyl substituent. However, two palladium(II) benzocarbaporphyrins were also identified that were formed by sequential oxidative ring contraction and methyl group migration. Internally alkylated azuliporphyrins provide new insights into the reactivity of the system and the results show that the introduction of alkyl substituents within porphyrinoid cavities greatly modifies the properties of these structures.

Effect of methyl substituent on the solubility of 1,4-benzoquinone derivatives in n-octanol/water system

The solubility of the compound is a crucial task for new drug design. Quinone is a promising candidate to develop as a new drug. In this research, the synthesis of 1,4-benzoquinone derivatives, that is, 2-(5-bromoamyl)-3,5-dimethyl-1,4-benzoquinone (2a) and 2-(5-bromoamyl)-5-methyl-1,4-benzoquinone (2b) were carried out by decarboxylation and insertion reaction of alkyl bromides. The product 2a and 2b are purified using SiO2 gel column chromatography and analyzed by UV-Visible, FT-IR, and NMR. The yield of 2a is 13.75%, and 2b is 4.04%. The solubility of 2a and 2b, expressed by log P, is measured in the n-octanol/water (3:7 (v/v)) system by the shake flask method. The log P of 2a and 2b are 2.99 and 1.36, respectively. It is showed that the log P of 2a is higher compared to 2b. The presence of two methyl substituents on the quinone ring of 2a supports the increase of hydrophobicity of the compound in the n-octanol/water system.