Cyclization Activity Research Articles

Micelle-Dependent Spontaneous Formation of Gold(I) in Nanodendritic Chloride-Bridged Particles with Catalytic Activity for Cyclization of Alkynylanilines in an Aqueous Environment

Micelle-Dependent Spontaneous Formation of Gold(I) in Nanodendritic Chloride-Bridged Particles with Catalytic Activity for Cyclization of Alkynylanilines in an Aqueous Environment

Evolution and diversification of carboxylesterase-like [4+2] cyclases in aspidosperma and iboga alkaloid biosynthesis

Monoterpene indole alkaloids (MIAs) are a large and diverse class of plant natural products, and their biosynthetic construction has been a subject of intensive study for many years. The enzymatic basis for the production of aspidosperma and iboga alkaloids, which are produced exclusively by members of the Apocynaceae plant family, has recently been discovered. Three carboxylesterase (CXE)-like enzymes from Catharanthus roseus and Tabernanthe iboga catalyze regio- and enantiodivergent [4+2] cycloaddition reactions to generate the aspidosperma (tabersonine synthase, TS) and iboga (coronaridine synthase, CorS; catharanthine synthase, CS) scaffolds from a common biosynthetic intermediate. Here, we use a combined phylogenetic and biochemical approach to investigate the evolution and functional diversification of these cyclase enzymes. Through ancestral sequence reconstruction, we provide evidence for initial evolution of TS from an ancestral CXE followed by emergence of CorS in two separate lineages, leading in turn to CS exclusively in the Catharanthus genus. This progression from aspidosperma to iboga alkaloid biosynthesis is consistent with the chemotaxonomic distribution of these MIAs. We subsequently generate and test a panel of chimeras based on the ancestral cyclases to probe the molecular basis for differential cyclization activity. Finally, we show through partial heterologous reconstitution of tabersonine biosynthesis using non-pathway enzymes how aspidosperma alkaloids could have first appeared as "underground metabolites" via recruitment of promiscuous enzymes from common protein families. Our results provide insight into the evolution of biosynthetic enzymes and how new secondary metabolic pathways can emerge through small but important sequence changes following co-option of preexisting enzymatic functions.

Facets in metal halide perovskite nanocrystals for the photoinduced electron transfer annulation reaction

In terms of accelerated charge-carrier dynamics and suitable adsorption behaviors for the substrate and intermediate, Cube with exposed four (110) and two (002) facets exhibited higher activity for photocatalytic cascade cyclization compared to Poly.

Altering glycopeptide antibiotic biosynthesis through mutasynthesis allows incorporation of fluorinated phenylglycine residues.

Glycopeptide antibiotics (GPAs) are peptide natural products used as last resort treatments for antibiotic resistant bacterial infections. They are produced by the sequential activities of a linear nonribosomal peptide synthetase (NRPS), which assembles the heptapeptide core of GPAs, and cytochrome P450 (Oxy) enzymes, which perform a cascade of cyclisation reactions. The GPAs contain proteinogenic and nonproteinogenic amino acids, including phenylglycine residues such as 4-hydroxyphenylglycine (Hpg). The ability to incorporate non-proteinogenic amino acids in such peptides is a distinctive feature of the modular architecture of NRPSs, with each module selecting and incorporating a desired amino acid. Here, we have exploited this ability to produce and characterise GPA derivatives containing fluorinated phenylglycine (F-Phg) residues through a combination of mutasynthesis, biochemical, structural and bioactivity assays. Our data indicate that the incorporation of F-Phg residues is limited by poor acceptance by the NRPS machinery, and that the phenol moiety normally present on Hpg residues is essential to ensure both acceptance by the NRPS and the sequential cyclisation activity of Oxy enzymes. The principles learnt here may prove useful for the future production of GPA derivatives with more favourable properties through mixed feeding mutasynthesis approaches.

Algal Kainoid Synthases Exhibit Substrate-Dependent Hydroxylation and Cyclization Activities.

FeII/α-ketoglutarate-dependent dioxygenases (Fe/αKG) make up a large enzyme family that functionalize C-H bonds on diverse organic substrates. Although Fe/αKG homologues catalyze an array of chemically useful reactions, hydroxylation typically predominates. Microalgal DabC uniquely forms a novel C-C bond to construct the bioactive pyrrolidine ring in domoic acid biosynthesis; however, we have identified that this kainoid synthase exclusively performs a stereospecific hydroxylation reaction on its cis substrate regioisomer. Mechanistic and kinetic analyses with native and alternative substrates identified a 20-fold rate increase in DabC radical cyclization over β-hydroxylation with no observable 1,5-hydrogen atom transfer. Moreover, this dual activity was conserved among macroalgal RadC1 and KabC homologues and provided insight into substrate recognition and reactivity trends. Investigation of this substrate-dependent chemistry improves our understanding of kainoid synthases and their biocatalytic application.

Brønsted ionic liquids as catalysts for synthesis of 2-pyrazoline derivatives from ketazines: A combined experimental and theoretical approach

Brønsted ionic liquids (BILs) were designed and applied to catalyze intramolecular cyclization of ketazines to 2-pyrazoline derivatives. Under the optimal conditions as 90 °C, 15 mol% [PsBim][CF3SO3] dosage and 4 h, the conversion rate and selectivity of the reaction are up to 98 % and 99 % respectively. Through the substrate screening, it shows that the steric hindrance of the R group in ketazines is a big factor of cyclization activities, following the order of methyl (98 %) > ethyl (93 %) > n-propyl (87 %) > n‑butyl (81 %) > isopropyl (52 %) > isobutyl (46 %)> neobutyl (13 %). Moreover, the results of the density functional theory (DFT) calculations indicate that the cations and anions of BIL can synergistically participate in the ketazines configuration transformation step so as to significantly reduce the Gibbs free barrier energy from 30.65 to 20.12 kcal/mol, thereby promoting the cyclization reaction to synthesize 2-pyrazoline derivatives.

Economical synthesis of γ-cyclodextrin catalyzed by oriented cyclodextrin glycosyltransferase displayed on bacterial polyhydroxyalkanoate nanogranules

BackgroundThe advantages of γ-cyclodextrin (γ-CD) include its high solubility, ability to form inclusion complexes with various poorly water-soluble molecules, and favorable toxicological profile; thus, γ-CD is an attractive functional excipient widely used in many industrial settings. Unfortunately, the high cost of γ-CD caused by the low activity and stability of γ-cyclodextrin glycosyltransferase (γ-CGTase) has hampered large-scale production and application.ResultsThis study reports the in vivo one-step production of immobilized γ-CGTase decorated on the surface of polyhydroxyalkanoate (PHA) nanogranules by the N-terminal fusion of γ-CGTase to PHA synthase via a designed linker. The immobilized γ-CGTase-PHA nanogranules showed outstanding cyclization activity of 61.25 ± 3.94 U/mg (γ-CGTase protein) and hydrolysis activity of 36,273.99 ± 1892.49 U/mg, 44.74% and 18.83% higher than that of free γ-CGTase, respectively. The nanogranules also exhibited wider optimal pH (cyclization activity 7.0–9.0, hydrolysis activity 10.0–11.0) and temperature (55–60 °C) ranges and remarkable thermo- and pH-stability, expanding its utility to adapt to wider and more severe reaction conditions than the free enzyme. A high yield of CDs (22.73%) converted from starch and a high ratio (90.86%) of γ-CD in the catalysate were achieved at pH 9.0 and 50 °C for 10 h with 1 mmol/L K+, Ca2+, and Mg2+ added to the reaction system. Moreover, γ-CGTase-PHA beads can be used at least eight times, retaining 82.04% of its initial hydrolysis activity and 75.73% of its initial cyclization activity.ConclusionsThis study provides a promising nanobiocatalyst for the cost-efficient production of γ-CD, which could greatly facilitate process control and economize the production cost.

Rhodium-Catalyzed C–H Activation of 2-Arylquinazolinones and Cyclization with Elemental Sulfur via C–S/S–N Bond Formation to Access 7H-Benzo[4,5]isothiazolo[3,2-b]quinazolinones

AbstractAn efficient method for the synthesis of 7H-benzo[4,5]isothiazolo[3,2-b]quinazolin-7-ones by the reaction of 2-arylquinazolin-4(3H)-ones and elemental sulfur is described. The rhodium-catalyzed C–H activation of 2-arylquinazolinones and cyclization with elemental sulfur via one-step formation of C–S/N–S bonds to give the corresponding 7H-benzo[4,5]isothiazolo[3,2-b]quinazolinones is realized in good to high yields with good functional group tolerance.

Cyclodextrin Glucanotransferase of Alkalophilic Strain <i>Caldalkalibacillus mannanilyticus</i> IB-OR17-B1

Extracellular cyclodextrin glucanotransferase (CGTase, K.F.2.1.19) was characterized for the first time in a strain of bacteria of the species Caldalkalibacillus mannanilyticus IB-OR17-B1. The enzyme was isolated from the culture supernatant using ultrafiltration and affinity adsorption on corn starch. The specific activity of the CGTase was increased in 18-fold as a result of purification with the enzyme yield 56%. The molecular mass of the purified enzyme was 70 kDa according to the denaturing electrophoresis in polyacrylamide gel. The CGTase of C. mannanilyticus IB-OR17-B1 demonstrated a maximal cyclizing activity under pH 8 and temperature 60°C, respectively, and it was stable in the pH range 7–10 and temperatures ≤70°C. The thermal stability of the enzyme under 70°C increased by 10–15% in the presence 5–10 mM of calcium and magnesium salts. The cations of Ag+, Cu2+, Zn2+, Fe2+ and Fe3+ in concentration 5 mM inhibited a CGTase activity by 90, 26, 23, 18 and 11%, respectively. The purified CGTase under optimal conditions and enzyme-substrate ratio 1 U/g converted a potato starch during 24 h to mixture of α-, β- and γ-cyclodextrins with mass ratio 38.8 : 52.6 : 8.6 and yield 42%.

Production of jet fuel range hydrocarbons using a magnetic Ni–Fe/SAPO-11 catalyst for solvent-free hydrodeoxygenation of jatropha oil

A novel, multifunctional Nix–Fe/SAPO-11 catalyst was synthesized and characterized, and its activity was evaluated for the solvent-free hydrodeoxygenation of jatropha oil. The catalyst has a spherical structure and moderate acid strength, and exhibited excellent cyclization and deoxidation activity. The inclusion of iron facilitated the dispersion of active components. Consequently, the iron-nickel alloy particle size remained small, resulting in an optimal distribution of the product. The composition of the products is linear alkanes (59.83%), isoparaffins (4.16%), aromatics (8.41%), and naphthenes (12.03%), where jet fuel components are relatively high, accounting for 55.04% of C8–C16 hydrocarbons. Interestingly, the iron present in the catalyst allowed the use of an external magnetic field for the rapid separation and recycling of the catalyst. Despite multiple uses, the recycled catalyst maintained high activity following five cycles, with hydrocarbon content consistently above 85%. The synergic effect of the metallic and acid sites of the catalyst, let to realize one-pot hydrodeoxygenation, isomerization, aromatization, and cracking of substrate forming bio-jet fuel range hydrocarbons.

Palladium-Catalyzed Aerobic Oxidative Spirocyclization of Alkyl Amides with Maleimides via β-C(sp3)-H Activation.

An efficient method for the synthesis of bicyclic spirodiamine molecules via β-C(sp3)-H bond activation of aliphatic amides, followed by cyclization with maleimides, has been developed. The reaction proceeds through an amide-directed β-C(sp3)-H bond activation of alkyl amides and subsequent cyclization with maleimides. The methodology is highly compatible with a wide variety of maleimides. Amides derived from biologically active aliphatic and fatty acids were also found to be highly compatible with the protocol. A palladacycle was synthesized and found to be the active intermediate in this reaction. A plausible reaction mechanism was also proposed to account for this spirocyclization.

Rh(III)-catalyzed C–H/C–C activation of benzoylacetonitriles and cyclization with CF3-imidoyl sulfoxonium ylides to 3-trifluoromethyl-isoquinolones

A Rh(III)-catalyzed C–H&C–C activation/annulation of benzoylacetonitriles and CF3-substituted imidoyl sulfoxonium ylides (TFISYs) has been disclosed, which provide a facile access to biologically important 3-trifluoromethyl-isoquinolones. The transformation proceeds with the cleavage of one C–H bond and one unusual C–C bond of benzoylacetonitriles, along with the removal of a molecule of dimethyl sulfoxide (DMSO) and acetonitrile (CH3CN). The reaction has notable merits of low amounts of catalyst loading, mild conditions, a broad substrate scope, high efficiency, and scalability.

Deciphering the biosynthesis of a novel lipid in Mycobacterium tuberculosis expands the known roles of the nitroreductase superfamily

Mycobacterium tuberculosis's (Mtb) success as a pathogen is due in part to its sophisticated lipid metabolic programs, both catabolic and biosynthetic. Several of Mtb lipids have specific roles in pathogenesis, but the identity and roles of many are unknown. Here, we demonstrated that the tyz gene cluster in Mtb, previously implicated in resistance to oxidative stress and survival in macrophages, encodes the biosynthesis of acyl-oxazolones. Heterologous expression of tyzA (Rv2336), tyzB (Rv2338c) and tyzC (Rv2337c) resulted in the biosynthesis of C12:0-tyrazolone as the predominant compound, and the C12:0-tyrazolone was identified in Mtb lipid extracts. TyzA catalyzed the N-acylation of l-amino acids, with highest specificity for l-Tyr and l-Phe and lauroyl-CoA (kcat/KM= 5.9± 0.8×103M-1s-1). In cell extracts, TyzC, a flavin-dependent oxidase (FDO) of the nitroreductase (NTR) superfamily, catalyzed the O2-dependent desaturation of the N-acyl-L-Tyr produced by TyzA, while TyzB, a ThiF homolog, catalyzed its ATP-dependent cyclization. The substrate preference of TyzB and TyzC appear to determine the identity of the acyl-oxazolone. Phylogenetic analyses revealed that the NTR superfamily includes a large number of broadly distributed FDOs, including five in Mtb that likely catalyze the desaturation of lipid species. Finally, TCA1, a molecule with activity against drug-resistant and persistent tuberculosis, failed to inhibit the cyclization activity of TyzB, the proposed secondary target of TCA1. Overall, this study identifies a novel class of Mtb lipids, clarifies the role of a potential drug target, and expands our understanding of the NTR superfamily.

SARM1, an Enzyme Involved in Axon Degeneration, Catalyzes Multiple Activities through a Ternary Complex Mechanism.

Sterile alpha and toll/interleukin receptor (TIR) motif containing protein 1 (SARM1) is an NAD+ hydrolase and cyclase involved in axonal degeneration. In addition to NAD+ hydrolysis and cyclization, SARM1 catalyzes a base exchange reaction between nicotinic acid (NA) and NADP+ to generate NAADP, which is a potent calcium signaling molecule. Herein, we describe efforts to characterize the hydrolysis, cyclization, and base exchange activities of TIR-1, the Caenorhabditis elegans ortholog of SARM1; TIR-1 also catalyzes NAD(P)+ hydrolysis and/or cyclization and regulates axonal degeneration in worms. We show that the catalytic domain of TIR-1 undergoes a liquid-to-solid phase transition that regulates not only the hydrolysis and cyclization reactions but also the base exchange reaction. We define the substrate specificities of the reactions, demonstrate that cyclization and base exchange reactions occur within the same pH range, and establish that TIR-1 uses a ternary complex mechanism. Overall, our findings will aid drug discovery efforts and provide insight into the mechanism of recently described inhibitors.

Overview of Amino Acid Modifications by Iron- and α-Ketoglutarate-Dependent Enzymes

Modified amino acids are important building blocks in both natural biomolecules and synthetic small-molecule drugs. Here, we review the roles of iron- and α-ketoglutarate-dependent dioxygenases in the oxidative modification of amino acids, focusing on C–H hydroxylation and halogenation. Recent engineering approaches to alter substrate specificity, improve catalytic efficiency, and install non-native activities are also discussed, along with several applications in complex molecule synthesis. We conclude with a brief discussion on recent discoveries of unique oxidative cyclization activities on amino acids by several family members and contemporary challenges in expanding both the biocatalytic utility and the reaction scope of the enzyme family.

Enzymatic formation of cyclic maltooligosaccharides for the application of quercetin inclusion complex

To improve the applicability of quercetin (QCT), we produced a QCT and cycloamylose (CA-QCT) inclusion complex based on the cyclization activity of cyclodextrin glucanotransferase (CGTase; EC 2.4.1.19). The encapsulated QCT was purified using recycling preparative high-performance liquid chromatography, and its formation was analyzed using matrix-assisted laser desorption/ionization-time of flight mass spectrometry. The water solubility of CA-QCT was 55,000-fold higher than that of QCT. CA-QCT had 97 % stability for one week at pH 8 in a 4 °C water bath. According to a 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity assay, CA-QCT activity in aqueous solution was 24 times higher than that of an equal amount of QCT in aqueous solution. In an anti-inflammatory assay using lipopolysaccharide-induced RAW264.7 macrophages, CA-QCT in aqueous solution decreased nitric oxide production in a similar manner to QCT in dimethyl sulfoxide (DMSO). Additionally, even under aqueous conditions, CA-QCT more effectively inhibited the production of inflammatory mediators, such as interleukin-1β, interleukin-6, and cyclooxygenase, compared with QCT dissolved in DMSO.

Identification of crucial amino acid residues involved in large ring cyclodextrin synthesis by amylomaltase from Corynebacterium glutamicum

Amylomaltase can be used to synthesize large ring cyclodextrins (LR-CDs), applied as drug solubilizer, gene delivery vehicle and protein aggregation suppressor. This study aims to determine the functional amino acid positions of Corynebacterium glutamicum amylomaltase (CgAM) involved in LR-CD synthesis by site-directed mutagenesis approach and molecular dynamic simulation. Mutants named Δ167, Y23A, P228Y, E231Y, A413F and G417F were constructed, purified, and characterized. The truncated CgAM, Δ167 exhibited no starch transglycosylation activity, indicating that the N-terminal domain of CgAM is necessary for enzyme activity. The P228Y, A413F and G417F produced larger LR-CDs from CD36-CD40 as compared to CD29 by WT. A413F and G417F mutants produced significantly low LR-CD yield compared to the WT. The A413F mutation affected all tested enzyme activities (starch tranglycosylation, disproportionation and cyclization), while the G417F mutation hindered the cyclization activity. P228Y mutation significantly lowered the kcat of disproportionation activity, while E231Y mutant exhibited much higher kcat and Km values for starch transglycosylation, compared to that of the WT. In addition, Y23A mutation affected the kinetic parameters of starch transglycosylation and cyclization. Molecular dynamic simulation further confirmed these mutations’ impacts on the CgAM and LR-CD interactions. Identified functional amino acids for LR-CD synthesis may serve as a model for future modification to improve the properties and yield of LR-CDs.

Synthesis, intramolecular cyclization and anti-inflammatory activity of substituted 2-(2-(Furan-2-carbonyl)hydrazono)-4-oxobutanoic Acids

A method was proposed for the synthesis of substituted 2-(2-(furan-2-carbonyl)hydrazono)-4-oxobutanoic acids by the reaction of substituted 2,4-dioxobut-2-enoic acids with furan-2-carbohydrazide. It was found that substituted 2-(2-(furan-2-carbonyl)hydrazono)-4-oxobutanoic acids undergo intramolecular cyclization in the presence of propionic anhydride to form the corresponding N'-(2-oxofuran-3(2H)-ylidene)furan-2-carbohydrazides. The anti-inflammatory activity of the obtained compounds was studied. It was found that the obtained compounds have pronounced anti-inflammatory activity.

Synthesis, Intramolecular Cyclization, and Anti-inflammatory Activity of Substituted 2-[2-(4-R-Benzoyl)hydrazinylidene]-4-oxobutanoic Acids

Synthesis, Intramolecular Cyclization, and Anti-inflammatory Activity of Substituted 2-[2-(4-R-Benzoyl)hydrazinylidene]-4-oxobutanoic Acids

Fully bio-based poly (pentamethylene glutaramide) with high molecular weight and less glutaric acid cyclization via direct solid-state polymerization

Poly (pentamethylene glutaramide) (PA55) has broad application prospects because all the polymeric monomers can be obtained from biomass fermentation. However, it is very difficult to obtain PA55 with high molecular weight by conventional melt polymerization (MP) due to the cyclization of glutaric acid. Thermodynamics and kinetics studies illustrated that the cyclization activity of glutaric acid increased with increasing temperature. Solid-state polymerization can be carried out at a low temperature and effectively avoid the occurrence of side reactions. Herein, we successfully inhibited the cyclization ratio of glutaric acid at low polymerization temperature via direct solid-state polymerization (DSSP) and obtained high molecular weight PA55 (ηr = 1.99, Mn = 19 kg·mol−1), which was much higher than that of MP (ηr = 1.52, Mn = 6 kg·mol−1). PA55 possessed a high melting temperature (Tm = 241 °C), excellent thermal stability (Td5 = 408 °C) and high water absorption (>13 wt%). Besides, the cyclization of glutaric acid related to polymerization methods, temperature and time was studied systematically, the ratio of imide ring could be controlled at <3 mol% via DSSP.