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Belactosins and hormaomycins are peptide natural products containing 3-(2-aminocyclopropyl)alanine and 3-(2-nitrocyclopropyl)alanine residues, respectively, with opposite stereoconfigurations of the cyclopropane ring. Herein we demonstrate that the heme oxygenase-like enzymes BelK and HrmI catalyze the N-oxygenation of l-lysine to generate 6-nitronorleucine. The nonheme iron enzymes BelL and HrmJ then cyclize the nitroalkane moiety to the nitrocyclopropane ring with the desired stereochemistry found in the corresponding natural products. We also show that both cyclopropanases remove the 4-proS-H of 6-nitronorleucine during the cyclization, establishing the inversion and retention of the configuration at C4 during the BelL and HrmJ reactions, respectively. This study reveals the unique strategy for stereocontrolled cyclopropane synthesis in nature.

Nitroalkanes such as nitromethane, nitroethane, 1-nitropropane (1NP), and 2-nitropropane (2NP), derived from anthropogenic activities, are hazardous environmental pollutants due to their toxicity and carcinogenic activity. In nature, 3-nitropropionate (3NPA) and its derivatives are produced as a defense mechanism by many groups of organisms, including bacteria, fungi, insects, and plants. 3NPA is highly toxic as its conjugate base, propionate-3-nitronate (P3N), is a potent inhibitor of mitochondrial succinate dehydrogenase, essential to the tricarboxylic acid cycle, and can inhibit isocitrate lyase, a critical enzyme of the glyoxylate cycle. In response to these toxic compounds, several organisms on the phylogenetic scale express genes that code for enzymes involved in the catabolism of nitroalkanes: nitroalkane oxidases (NAOs) and nitronate monooxygenases (NMOs) (previously classified as nitropropane dioxygenases, NPDs). Two types of NMOs have been identified: class I and class II, which differ in structure, catalytic efficiency, and preferred substrates. This review focuses on the biochemical properties, structure, classification, and physiological functions of NMOs, and offers perspectives for their in vivo and in vitro applications. • Nitronate monooxygenases (NMOs) are key enzymes in nitroalkane catabolism. • NMO enzymes are involved in defense mechanisms in different organisms. • NMO applications include organic synthesis, biocatalysts, and bioremediation.

Sajjad Ahmad,1 Mater H Mahnashi,2 Bandar A Alyami,2 Yahya S Alqahtani,2 Farhat Ullah,1 Muhammad Ayaz,1 Muhammad Tariq,3 Abdul Sadiq,1 Umer Rashid4 1Department of Pharmacy, Faculty of Biological Sciences, University of Malakand, Khyber Pakhtunkhwa, Pakistan; 2Department of Pharmaceutical Chemistry, College of Pharmacy, Najran University, Najran, Saudi Arabia; 3Department PCB, Rokhan University, Jalalabad, Nangrahar, Afghanistan; 4Department of Chemistry, COMSATS University Islamabad, Abbottabad Campus, Abbottabad, 22060, PakistanCorrespondence: Abdul SadiqDepartment of Pharmacy, Faculty of Biological Sciences, University of Malakand, Chakdara, 18000 Dir (L), Khyber Pakhtunkhwa, PakistanTel +92 301 2297 102Email sadiquom@yahoo.comUmer RashidDepartment of Chemistry, COMSATS University Islamabad, Abbottabad Campus, Abbottabad, 22060, PakistanTel +92-334 5171999Email umerrashid@cuiatd.edu.pkBackground: Organocatalytic asymmetric Michael addition is a strong approach for C-C bond formation. The objective of the study is to design molecules by exploiting the efficiency of Michael Adducts. We proceeded with the synthesis of Michael adducts by tailoring the substitution pattern on maleimide and trans-β-nitro styrene as Michael acceptors. The synthesized compounds were evaluated for dual cyclooxygenases (COX) and lipoxygenase (LOX) inhibition.Methods: The compounds (4, 9– 11) were synthesized through Michael additions. The cyclooxygenases (COX-1 and 2) and lipoxygenase (5-LOX) assays were used for in vitro evaluations of compounds. After the acute toxicity studies, the in vivo analgesic potential was determined with acetic acid induced writhing, tail immersion, and formalin tests. Furthermore, the possible roles of adrenergic and dopaminergic receptors were also studied. Extensive computational studies were performed to get a better understanding regarding the binding of this compound with protein target.Results: Four Michael adducts (4, 9– 11) were synthesized. Compound 4 was obtained in enantio- and diastereopure form. The stereopure compound 4 showed encouraging COX-1 and-2 inhibitions with IC50 values of 128 and 65 μM with SI of 1.94. Benzyl derivative 11 showed excellent COX-2 inhibition with the IC50 value of 5.79 μM and SI value 7.96. Compounds 4 and 11 showed good results in in vivo models of analgesia like acetic acid test, tail immersion, and formalin tests. Our compounds were not active in dopaminergic and adrenergic pathways and so were acting centrally. Through extensive computational studies, we computed binding energies, and pharmacokinetic predictions.Conclusion: Our findings conclude that our synthesized Michael products (pyrrolidinedione 4 and nitroalkane 11) can be potent centrally acting analgesics. Our in silico predictions suggested that the compounds have excellent pharmacokinetic properties. It is concluded here that dual inhibition of COX/LOX pathways provides a convincing step towards the discovery of safe lead analgesic molecules.Keywords: Michael products, succinimides, cyclooxygenase, lipoxygenase, analgesic, molecular docking, adrenergic and dopaminergic

A nitrile N-oxide-functionalized polypeptide was synthesized by a two-step method involving the combination of ring-opening polymerization of an α-amino acid N-carboxyanhydride monomer using a primary amine initiator containing a nitroalkane group and a subsequent terminal conversion. The catalyst-free grafting reaction of the formed functionalized peptide with rubbers containing double bonds was achieved with high efficiency. A nitrile N-oxide-functionalized polypeptide was synthesized by a two-step method involving the combination of ring-opening polymerization of an amino acid N-carboxyanhydride (NCA) monomer using a primary amine initiator containing a nitroalkane group and a subsequent terminal conversion. The formed peptide was fully characterized by NMR, FT-IR, and MALDI-TOF MS measurements. The catalyst-free grafting reaction of the formed functionalized peptide with rubbers containing double bonds was achieved with high efficiency via an environmentally benign process. These results surely contributed to the development of novel peptide-grafted polymers.

A facile one-pot, three component reaction has been developed using aldehydes, nitroalkane and sodium azide with zinc oxide nanocatalyst for the synthesis of 4-aryl-NH-1,2,3-triazoles. ZnO nanoparticles with controlled size (15–25 nm) and morphology were prepared using a sonochemical strategy. Structural and morphological study revealed the growth of well crystalline particles along the c axis i.e. [0001] direction due to higher surface energy. The catalysis protocol used in this work offers an efficient and highly economical alternative to the existing methods since the reactions proceed smoothly in green solvent polyethyleneglycol (PEG) 400 under aerobic condition. The reaction has a broad substrate scope resulting in excellent yields of the desired products. The catalyst recovery part was tricky at the initial stages; however an alternative route was successfully introduced to recover the former and reused it for the next cycles of catalytic reaction with excellent retentivity in the catalytic activity. The observed high catalytic efficacy with no significant activity loss using recovered catalyst is mainly due to the retention of morphology and crystal structure of ZnO nanoparticles after many catalytic reactions.

Experimental 13C kinetic isotope effects (KIEs) and DFT calculations are used to evaluate the mecha-nism and the origin of enantioselectivity in the C(sp2)‒H alkylative desymmetrization of cyclopentene-1,3-diones using nitroalkanes as the alkylating agent. An unusual combination of an inverse (~0.980) and a normal (~1.030) KIE is observed on the bond-forming carbon atoms of the cyclopentene-1,3-dione and nitroalkane, respectively. These data provide strong support for a mechanism involving reversible carbon-carbon bond-formation followed by rate- and enantioselectivity-determining nitro-group elimination. The theoretical free energy profile and predicted KIEs indicate that this elimination event occurs via an E1cB pathway. The origin of remote stereocontrol is evaluated by distortion-interaction and SAPT0 analyses of the enantiomeric E1cB transition states.

Nitroolefins are important synthetic intermediates in the field of organic synthesis as well as in medicinal chemistry. The high reactivity of nitroalkenes due to the polarized double bond which enables them to act as Michael acceptor in conjugate addition reactions, or as a dienophile in cycloaddition makes it an essential synthetic handle for accessing complex molecules. The classical method to prepare nitroolefins is indeed the Henry nitroaldol reaction, where a carbonyl compound and nitroalkane are condensed in presence of base. Direct nitration of olefin, on the other hand, serves as a useful alternative as olefins are abundant, have broad commercial availability and easy to manipulate. In this context, numerous methods have been developed over the last few decades, focusing on direct nitration of styrene and aliphatic olefins. Furthermore, thorough literature search revealed that implementation of this class of reactions are gaining momentum as a preferred pathway to access nitroolefins, despite the presence of a powerful technique such as Henry reaction. In this review, we aim to cover recent advances in direct olefin nitration and their importance in accessing biorelevant molecules, total synthesis targets and future outlook in this specific research area.

Nitroalkanes react specifically with aldehydes, providing rapid, stable, and chemoselective protein bioconjugation. These nitroalkylated proteins mimic key post-translational modifications (PTMs) of proteins and can be used to understand the role of these PTMs in cellular processes. Demonstrated here is the substrate scope of this bioconjugation by attaching a variety of tags, such as NMR tags, fluorescent tags, affinity tags, and alkyne tags, to proteins. The structure and enzymatic activity of modified proteins remain conserved after labeling. Notably, the nitroalkane group leads to easy characterization of proteins by mass spectrometry because of its distinct fingerprint pattern. Importantly, the nitro-alkylated peptides provide a new handle for site-selective fluorination of peptides, thus installing a specific probe to study peptide-protein interactions by 19 F NMR spectroscopy. Furthermore, nitroalkane reagents can be used for the late-stage diversification of peptides and for the synthesis of peptide staples.

A great number of reports have described asymmetric catalytic Henry reactions using nitromethanes as pronucleophiles, but far more challenging is diastereoselective catalytic Henry reactions using substituted higher nitroalkanes instead of nitromethane to generate chiral β-nitro alcohol scaffolds with four adjacent stereogenic centers in a one-pot operation. This review summarizes the current state and applications of such reactions involving complex nitroalkane coupling with various carbonyl compounds for resolving double chiral centers with high enantio- and diastereoselectivities.

Polyesters that have a nitrile N-oxide function at the initiation end were prepared and applied to a catalyst-free click reaction for star polymer synthesis. They were obtained by an initial living ring-opening polymerization of lactide and lactones with an alcohol-bearing nitroalkane as the initiator, followed by conversion of the nitroalkane to a nitrile N-oxide function. The resulting polymer and block copolymer nitrile N-oxides showed very high reactivity toward a hexakis(alkenyl) core to give the corresponding star polymers via complete conversion.

In this study, a thermophilic facultative anaerobic strain Geobacillus thermoglucosidasius W-2 was found to degrade nitroalkane under both aerobic and anaerobic conditions. Bioinformatical analysis revealed three putative nitroalkane-oxidizing enzymes (Gt-NOEs) genes from the W-2 genome. The three identified proteins Gt2929, Gt1378, and Gt1208 displayed optimal activities at high temperatures (70, 70, and 80 °C, respectively). Among these, Gt2929 exhibited excellent degradation capability, pH stability, and metal ion tolerance for nitronates under aerobic condition. Interestingly, under anaerobic condition, only Gt1378 still maintained high activity for 2-nitropropane and nitroethane, indicating that the W-2 strain utilized various pathways to degrade nitronates under aerobic and anaerobic conditions, respectively. Taken together, the first revelation of thermophilic nitroalkane-degrading mechanism under both aerobic and anaerobic conditions provides guidance and platform for biotechnological and industrial applications.

Conventional amide synthesis is a mainstay in discipline-spanning applications, and it is a reaction type that historically developed as a singular paradigm when considering the carbon-nitrogen bond-forming step. Umpolung amide synthesis (UmAS) exploits the unique properties of an α-halo nitroalkane in its reaction with an amine to produce an amide. The "umpolung" moniker reflects its paradigm-breaking C-N bond formation on the basis of evidence that the nucleophilic nitronate carbon and electrophilic nitrogen engage to form a tetrahedral intermediate (TI) that is an unprecedented functional group, a 1,1,1-halo-amino-nitro alkane (HANA). Studies probing HANA transience have failed to capture this (presumably) highly reactive intermediate. We report here the direct observation of a HANA, its conversion thermally to an amide functionality, and quantitative analysis of this process using computational techniques. These findings validate the HANA as a functional group common to UmAS and diverted UmAS, opening the door to its targeted use and creative manipulation.

The work illustrates multicomponent reaction of aldehydes, nitroalkanes and sodium azide for the metal-free synthesis of N-unsubstituted-1,2,3-triazoles using anthranilic acid as an organocatalyst under microwave irradiation. This is the first ever green protocol to synthesize 4-aryl-NH-1,2,3-triazoles from aromatic aldehyde, nitroalkane and sodium azide under microwave condition and offers broad substrate scope with good to excellent yields. Furthermore, using this efficient protocol gram scale synthesis of biologically important molecules were successfully carried out.

The rapid expansion of aquaculture industry brings about significant environmental concerns, especially nitrogen pollution. Compared to nitrogen bioconversion implemented by the conventional autotrophic nitrifiers and anaerobic denitrifiers, bacteria capable of heterotrophic nitrification-aerobic denitrification (HNAD) in mariculture environments have yet to be well understood. In this study, twenty-five species of new halophilic HNAD bacteria were isolated and identified from mariculture water. By these strains co-cultured in the synthetic mariculture water (ammonia: 5 mg/L, C/N: 5, salinity: 30‰), microbial dynamic analysis showed that ammonia were mainly removed by dominant genera of Marinomonas, Marinobacterium, Halomonas, and Cobetia which simultaneously had positive correlations to total nitrogen removal. Metagenomic annotations revealed that inorganic-N was converted into gaseous-N and organic-N by these HNAD bacteria through nitrogen metabolism pathways of assimilation, partial nitrification, nitroalkane oxidation, nitrate/nitrite dissimilation reduction, and denitrification. Among them, due to the interspecific coexistence and cooperation, Marinomonas communis & Halomonas titanicae, Marinomonas communis & Cobetia marina, Marinomonas aquimarina & Halomonas titanicae, and Marinomonas aquimarina & Cobetia marina exhibited significantly better inorganic-N removal efficiency and stability. The four novel bacterial consortia could transform approximately 60% of initial ammonia into intracellular organic-N (18–20%) and gaseous-N (36–38%), which were significantly higher than those of their single strains. These findings will contribute to understanding and developing the culturable HNAD bacteria as promising candidates for nitrogen pollution control and water bioremediation in mariculture or other saline environments.

The acidity ladder scale in [BMPY][NTf2] was successfully expanded toward the weak acidity region for about five more pK units compared to the previously established one. This allows the acidities of a series of 13 aliphatic and aromatic nitroalkanes to be determined accurately by the UV–vis spectroscopic method. The acidity of nitroalkane in [BMPY][NTf2] covers ∼8 pK units and is significantly weaker than those in DMSO and water. The Hammett plot for 4-substituted phenylnitromethanes shows an excellent linearity with a slope of 2.06, which is rather close to that in DMSO but significantly larger than that in water (0.80). The regression analyses reveal that the solvation behavior of [BMPY][NTf2] on the acidic dissociations of C–H acids is similar to that of DMSO.

A mild base-catalyzed protocol for the synthesis of substituted nitroalkane derivatives has been developed under continuous flow using a microreaction technique. This transformation basically involves the 1,6-conjugate addition of nitroalkanes to p-quinone methides, leading to the substituted nitroalkanes in good to excellent yields.

Nitroalkane oxidase (NAO) and nitronate monooxygenase (NMO) are two different types of nitroalkane oxidizing flavoenzymes identified in nature. A previous study suggested that the hypothetical protein PA4202 from Pseudomonas aeruginosa PAO1 is NMO and utilizes only anionic nitronates. However, the structural similarity between the PA4202 protein and Streptomyces ansochromogenes NAO has motivated investigation for what features of the two enzymes differentiate between the NAO and NMO activities. Herein, we report the crystal structure of PA4202 in a ternary complex with a neutral nitroethane (NE) and flavin mononucleotide (FMN) cofactor to elucidate the substrate recognition mechanism using a site-directed mutagenesis. The ternary complex structure indicates that the NE is bound with an orientation, which is poised for the proton transfer to H183 (which is the essential first catalytic step with nitroalkanes), and subsequent reactions with FMN. Moreover, a kinetic study reveals that the catalytic reactions of the wild type and H183 mutants PA4202s with nitroalkane substrates may yield the products of hydrogen peroxide and nitrite that are specified to NAO, although they show a low catalytic efficiency. Our results provide the first structure-based molecular insight into the substrate binding property of the hypothetical protein PA4202, including the interactions with neutral nitroalkanes as the substrate.

A method is reported for the catalytic direct coupling of allylic alcohols and nitroalkanes. In the allylation process, the synergistic action of palladium complexes and titanium(IV) alkoxide facilitates the formation of nitronate and π-allylpalladium intermediate. In the cases of reluctant allylations, typically with sterically demanding nitroalkanes, we found the addition of substoichiometric amount of DBU greatly facilitates the desired transformation. We also accomplished a total synthesis of (±)-adalinine through a homoallyl nitroalkane derived from Seebach's reagent.

Reactions of the type X• + HCR2CH2NO2 → XH + R2C=CH2 + N•O2 are exothermic, due to the breaking of weak C–N bonds and the formation of energy-intensive C=C bonds. Quantum chemistry calculations of the transition state using the reactions of Et• and EtO• with 2-nitrobutane shows that such reactions can be categorized as one-step, due to the extreme instability of the intermediate nitrobutyl radical toward decay with the formation of N•O2. Kinetic parameters that allow us to calculate the energy of activation and rate constant of such a reaction from its enthalpy are estimated using a model of intersecting parabolas. Enthalpies, energies of activation, and rate constants are calculated for a series of reactions with the participation of Et•, EtO•, RO•2, N•O2 radicals on the one hand and a series of nitroalkanes on the other. A new kinetic scheme of the chain decay of nitroalkanes with the participation of abstraction reactions with concerted fragmentation is proposed on the basis of the obtained data.

An unprecedented organocatalytic three-component domino Knoevenagel/vinylogous Michael reaction starting from simple enolizable aldehydes, malononitrile, and nitroolefins is reported. This facile two-step domino process provides a straightforward stereoselective route to multifunctional vinyl malononitrile products (up to 82 % yield, 85:15 d.r.) containing a nitroalkane moiety, and contributes to the development of sustainability and atom economy. The application of the obtained domino products for synthesis of highly functionalized o-terphenyls (of high interest for materials science and medicinal chemistry) through subsequent new three-step domino reaction involving cyclization-tautomerization-aromatization steps, has been demonstrated.

An efficient, environmentally friendly, one-pot three-component synthesis of a series of 2H-chromene-based imidazo[1,2-a]pyridines had been designed and were synthesized. This protocol was developed by the reaction of substituted 2H-chromene aldehydes and 2-aminopyridine in a mixture of nitroalkane and DMF under microwave irradiation at 60W, 100°C in 15 min with the presence of FeCl3 as the catalyst. The products were obtained in excellent yields with high functional group tolerance. All these compounds had been investigated further in vitro for evaluation of antibacterial potency by agar-well diffusion method against human pathogenic Gram-positive and Gram-negative bacteria, with the determination of minimum inhibitory concentration (MIC) values. Indeed, compound 13i strongly inhibited peptide deformylase (MIC = 16 μg/ml) in the Gram-negative Escherichia coli, in silico. From structure-activity relationships based on the biological and molecular docking results and the potent antibacterial activities, it could be stated that the selected synthetic compounds could be used as potent drugable antibacterial agents.