Tetrazoles as carboxylic acid isosteres: chemistry and biology

Transition-metal-free multinitrogenation of amides by C-C bond cleavage: a new approach to tetrazoles

A metal-free brand-new one-pot multinitrogenation of amides for the chemo- and regioselective synthesis of 1,5-disubstituted tetrazoles has been developed. By means of electrophilic amide activation, and further C-C bond cleavage and rearrangement, a diverse set of functionalized 1,5-DST derivatives were selectively constructed under mild conditions. As showcased in the mechanisms, the chemoselectivity is easily switched by the selection of the starting materials in the reaction.

Fragment-Based Discovery of Inhibitors of the Bacterial DnaG-SSB Interaction

In bacteria, the DnaG primase is responsible for synthesis of short RNA primers used to initiate chain extension by replicative DNA polymerase(s) during chromosomal replication. Among the proteins with which Escherichia coli DnaG interacts is the single-stranded DNA-binding protein, SSB. The C-terminal hexapeptide motif of SSB (DDDIPF; SSB-Ct) is highly conserved and is known to engage in essential interactions with many proteins in nucleic acid metabolism, including primase. Here, fragment-based screening by saturation-transfer difference nuclear magnetic resonance (STD-NMR) and surface plasmon resonance assays identified inhibitors of the primase/SSB-Ct interaction. Hits were shown to bind to the SSB-Ct-binding site using 15N-¹H HSQC spectra. STD-NMR was used to demonstrate binding of one hit to other SSB-Ct binding partners, confirming the possibility of simultaneous inhibition of multiple protein/SSB interactions. The fragment molecules represent promising scaffolds on which to build to discover new antibacterial compounds.

Computational assessment of thioether isosteres

Replacement of the sulfur atom in biologically active diaryl and heteroaryl thioethers (Ar-S-Ar', HAr-S-Ar, and HAr-S-HAr') with any of several one-atom or two-atom linkers can be expected to reduce the susceptibility of the analogue to metabolic oxidation, a well-documented problem for thioethers intended for medicinal chemistry applications. Ab initio calculations indicate how well various proposed thioether isosteric groups, including some new and unusual ones, may perform structurally and electronically in replacing the bridging sulfur atom. Four of these are calculationally evaluated as proposed substructures in Axitinib analogues. The predicted binding behavior of the latter within two different previously crystallographically characterized protein-Axitinib binding sites (VEGFR2 kinase and ABL1 T315I gatekeeper mutant kinase), and an assessment of their suitability and anticipated shortcomings, are presented.

Synthesis and biological evolution of hydrazones derived from 4-(trifluoromethyl)benzohydrazide

Reflecting the known biological activity of isoniazid-based hydrazones, seventeen hydrazones of 4-(trifluoromethyl)benzohydrazide as their bioisosters were synthesized from various benzaldehydes and aliphatic ketones. The compounds were screened for their in vitro activity against Mycobacterium tuberculosis, nontuberculous mycobacteria (M. avium, M. kansasii), bacterial and fungal strains. The most antimicrobial potent derivatives were also investigated for their cytostatic and cytotoxic properties against three cell lines. Camphor-based molecule, 4-(trifluoromethyl)-N'-(1,7,7-trimethylbicyclo[2.2.1]heptan-2-ylidene)benzohydrazide, exhibited the highest and selective inhibition of M. tuberculosis with the minimum inhibitory concentration (MIC) of 4 µM, while N'-(4-chlorobenzylidene)-4-(trifluoromethyl)benzohydrazide was found to be superior against M. kansasii (MIC = 16 µM). N'-(5-Chloro-2-hydroxybenzylidene)-4-(trifluoromethyl)benzohydrazide showed the lowest MIC values for gram-positive bacteria including methicillin-resistant Staphylococcus aureus as well as against two fungal strains of Candida glabrata and Trichophyton mentagrophytes within the range of ≤0.49-3.9 µM. The convenient substitution of benzylidene moiety at the position 4 or the presence of 5-chloro-2-hydroxybenzylidene scaffold concomitantly with a sufficient lipophilicity are essential for the noticeable antimicrobial activity. This 5-chlorosalicylidene derivative avoided any cytotoxicity on two mammalian cell cultures (HepG2, BMMΦ) up to the concentration of 100 µM, but it affected the growth of MonoMac6 cells.

N-Alkylated 1,4-Diazabicyclo[2.2.2]octane-Polyethylene Glycol Melt as Deep Eutectic Solvent for the Synthesis of Fisher Indoles and 1H-Tetrazoles

1,4-Diazabicyclo[2.2.2]octane (DABCO)-based ionic liquids (ILs) 2-4 were synthesized by the N-alkylation of DABCO using alkyl halides of varying chain lengths (C₂, C₅, and C₇). The N-alkylated DABCO-ILs were mixed with polyethylene glycols (PEGs) of varying molar masses as hydrogen bond donors (HBDs) to prepare new deep eutectic solvents (DESs). These DABCO-PEG-based DESs were successfully employed for the synthesis of a variety of indoles 7a-7h (by Fischer indole synthesis) and 1H-tetrazoles 9a-9i (by click chemistry). For comparison, DESs of DABCO-ILs with different alcohols (as HBD) were also prepared and investigated for the synthesis of indoles. Although comparable yields were observed in DES-containing alcohols and PEGs, the use of PEG as HBD in DES (as an alternative to alcohols) provides a much safer, nonvolatile, and environmentally benign reaction medium for synthetic reactions. The first successful application of PEG-polymer-based DES as benign reaction media for organic syntheses offers exciting opportunities to be explored in the realm of green synthesis.

Microwave alkylation of lithium tetrazolate

ABSTRACT

N1-substituted tetrazoles are interesting ligands in transition metal coordination chemistry, especially in the field of spin crossover. Their synthesis is performed in most cases according to the Franke-synthesis, using a primary amine as reagent introducing the substitution pattern. To enhance flexibility in means of substrate scope, we developed a new protocol based on alkylation of lithium tetrazolate with alkyl bromides. The N1-N2 isomerism of the tetrazole during the alkylation was successfully suppressed by use of highly pure lithium tetrazolate and 30 vol.% aqueous ethanol as solvent, leading to pure N1-substituted products. The feasibility of this reaction was demonstrated by a selection of different substrates.

GRAPHICAL ABSTRACT

Copper(i) catalyzed oxidative hydrolysis of Ugi 3-component and Ugi-azide reaction products towards 2° α-ketoamides and α-ketotetrazoles

Catalytic Cu(i) mediated C–N oxidation of Ugi-3-component and Ugi-azide reaction products affords 2° α-ketoamides 1 and α-ketotetrazoles 2.

N,N-Dimethylpyridin-4-amine (DMAP) based ionic liquids: evaluation of physical properties via molecular dynamics simulations and application as a catalyst for Fisher indole and 1H-tetrazole synthesis

N,N-dimethylpyridin-4-amine (DMAP) based ionic liquids (ILs) as new and efficient catalysts for the facile synthesis of indoles (via Fischer indole synthesis), and 1H-tetrazoles (via click chemistry).

Synthesis of chiral (tetrazolyl)methyl-containing acrylates via silicon-induced organocatalytic kinetic resolution of Morita–Baylis–Hillman fluorides

A new approach for the asymmetric installation of a (tetrazolyl)methyl group via Si/F activation using organocatalytic kinetic resolution of racemic MBH-fluorides.

Functional AdoMet Isosteres Resistant to Classical AdoMet Degradation Pathways

S-adenosyl-l-methionine (AdoMet) is an essential enzyme cosubstrate in fundamental biology with an expanding range of biocatalytic and therapeutic applications. We report the design, synthesis, and evaluation of stable, functional AdoMet isosteres that are resistant to the primary contributors to AdoMet degradation (depurination, intramolecular cyclization, and sulfonium epimerization). Corresponding biochemical and structural studies demonstrate the AdoMet surrogates to serve as competent enzyme cosubstrates and to bind a prototypical class I model methyltransferase (DnrK) in a manner nearly identical to AdoMet. Given this conservation in function and molecular recognition, the isosteres presented are anticipated to serve as useful surrogates in other AdoMet-dependent processes and may also be resistant to, and/or potentially even inhibit, other therapeutically relevant AdoMet-dependent metabolic transformations (such as the validated drug target AdoMet decarboxylase). This work also highlights the ability of the prototypical class I model methyltransferase DnrK to accept non-native surrogate acceptors as an enabling feature of a new high-throughput methyltransferase assay.

An Efficient Passerini Tetrazole Reaction (PT-3CR)

A sonication accelerated, catalyst free, simple, high yielding and efficient method for the Passerini-type three component reaction (PT-3CR) has been developed. It comprises reaction of an aldehyde/ketone, a isocyanide and a TMS-azide in methanol:water (1:1) as the solvent system. Use of sonication not only accelerated the rate of the reaction but also provided up to quantitative yields. This reaction is applicable to a broad scope of aldehyde/ketone and isocyanides.

A combined experimental and theoretical study of the tautomeric and conformational properties of (5-phenyl-tetrazol-2-yl)-acetic acid methyl ester

The tautomeric and conformational properties of a new tetrazole derivative are studied in a combined approach that includes the analysis of the experimental vibrational data together with theoretical calculation methods, especially in terms of natural bond orbital (NBO) population analysis. Moreover, the molecular and crystal structure was determined by single crystal X-ray diffraction. The compound crystallized as the 2-tautomeric form, monoclinic space group P21/c with Z=4, a=10.0630(14), b=8.2879(11), c=12.8375(18) Å, β=105.546(3)°, V=1031.5(2) Å(3). The tetrazole and phenyl rings are coplanar with the acetate group oriented perpendicular to the plane. The NBO analysis showed that delocalizing interactions of the lpp(N2) lone pair orbital contributes to a strong resonance interactions with both adjacent π(∗)(N3N4) and π(∗)(N1C5) antibonding orbitals of the tetrazole group.

Solvent-free 1H-tetrazole, 1,2,5,6-tetrahydronicotinonitrile and pyrazole synthesis using quinoline based ionic fluoride salts (QuFs): thermal and theoretical studies

The role of ionic liquids as catalyst and solvent to mediate organic reactions is well documented.