The imidazol and imidazoline derives have many advantages in therapy. For the synthesis of new imidazoline derives, the authors implemented the ethylene diamene cyclization from nitril compounds differently substituted. Then, a dehydrogenation of these imidazolines leaded to the imidazol derives. The last reaction consisted of the condensation of these imidazolines and imidazoles. The authors subjected their synthesized products to an ophthalmic protective evaluation (anti-oedema, secondary anti-hyperemia) on the experimental ocular irritancy models
Imidazolines ; Cyclization

Terpenes are the largest group of natural products and contain the widest assortment of structural types. Terpene cyclization is also the most complex reaction found in nature. For a long time, terpenoids with diverse structures have attracted natural product chemists to explore their biosynthesis mechanism. Such a large number of terpene skeletons are catalyzed by enzymes called terpene synthase. Sesquiterpene synthase is a kind of terpene synthase, which can catalyze the cyclization of linear precursor farnesyl pyrophosphate(FPP) to sesquiterpene skeletons. Sesquiterpene synthase cyclize a single precursor FPP into many sesquiterpene skeletons. With the continuous discovery of sesquiterpene synthase, the cyclization mechanism of sesquiterpene synthase has been studied deeply. In recent years, with the development and improvement of isotope labeling of substrate FPP and structural analysis of sesquiterpene synthase, the structure and cyclization mechanism of sesquiterpene synthase have been studied more systematically and accurately. In this review, we reviewed the progress of the research methods on the mechanism of sesquiterpene cyclization by substrate isotope labeling and protein structure, as well as the summary and prospect of sesquiterpene synthase research.
Cyclization ; Sesquiterpenes ; Terpenes

Isopeptide bond-mediated molecular superglue is the irreversible covalent bond spontaneously formed by the side chains of lysine (Lys) and asparagine/aspartic acid (Asn/Asp) residues. The peptide-peptide interaction is specific, stable, and can be achieved quickly without any particular physicochemical factor. In the light of recent progress by domestic and foreign researchers, here we summarize the origin, assembly system and mechanism of isopeptide bond reaction, as well as the molecular cyclization and protein topological structure mediated by it. The prospect for its application in synthetic vaccine, hydrogel and bacterial nanobiological reactor is further discussed.
Cyclization ; Lysine ; Peptides ; chemistry ; Proteins

Although the number of sesterterpenoids is fewer than other terpenoids reported, they have presented a wide range of biological activities and medicinal value. Reported filamentous fungal sesterterpene synthases are special on bifunctional two catalytically independent domains: prenyltransferase and terpene cyclase, but less specific on substrates selection and diverse ways of cyclization. This article reviews the research advances in filamentous fungal sesterterpenoids and their synthases, especially describes filamentous fungal sesterterpenoids and the structure and function characteristics of sesterterpene synthase.
Cyclization ; Fungi ; chemistry ; enzymology ; Sesterterpenes ; chemistry

Proteins, which exist mainly in linear form in vivo, are easily affected by the change of ambient temperature and pH. The application of proteins (enzymes) in the fields of industrial catalyzing, food manufacturing and medicine are restricted due to their properties. The cyclic structure of natural cyclic peptides confers high thermal stability on itself; such mechanism can be referred to in further enhancement of the thermal stability and transformation of the structure of enzymes. This article reviewed the latest progress in the domestic and international studies on protein cyclization and summarized the traditional methods (such as protein trans-splicing, expressed protein ligation and sortase-catalyzed transpeptidation) in protein cyclization. A novel method based on SpyTag/SpyCather-mediated enzyme cyclization was discussed in more detail.
Cyclization ; Peptides, Cyclic ; chemistry ; Protein Processing, Post-Translational ; Proteins ; chemistry

Current interest in the regioselective N-functionalization of tetraazacycloalkanes (cyclen and cyclam) stems mainly from their complexes with radioactive metals for applications in diagnostic (64Cu, 111In, 67Ga) and therapeutic (90Y) medicine, and with paramagnetic ions for magnetic resonance imaging (Gd+3). Selective methods for the N-substitution of cyclen and cyclam is a crucial step in most syntheses of cyclen and cyclam-based radiometal complexes and bifunctional chelating agents. In addition, mixing different pendent groups to give hetero-substituted cyclen derivatives would be advantageous in many applications for fine-tuning the compound's physical properties. So far, numerous approaches for the regioselective N-substitution of tetraazacycloalkanes and more specifically cyclen and cyclam are reported. Unfortunately, none of them are general and every strategy has its own strong points and drawbacks. Herein, we categorize numerous regioselective N-alkylation methods into three strategies, such as 1) direct substitution of the macrocycle, 2) introduction of the functional groups prior to cyclization, and 3) protection/functionalization/deprotection. Our discussion is also split into the methods of mono- and tri-functionalization and di-functionalizataion based on number of substituents. At the end, we describe new trials for the new macrocycles which form more stable metal complexes with various radiometals, and briefly mention the commercially available tetraazacycloalkanes which are used for the biconjugation of biomolecules.
Chelating Agents ; Coordination Complexes ; Cyclization ; Ions ; Ligands* ; Magnetic Resonance Imaging ; Metals

To study the oxidative alkaline-degradation products of PQS (Panax quinquefolium saponin), two compounds were isolated from the crude product of oxidative alkaline-degradation by silica gel column chromatography, Sephadex LH-20 column chromatography and recrystallized methods. On the basis of spectroscopic analysis, their structures were established as (12R, 20S, 24R)-20, 24; 12, 24-diepoxy-24-deisopropyl-dammarane-3beta-ol (1) and (20S, 24R)-20, 24-epoxydammarane-3beta3, 12beta, 25-triol (2). Compounds 1 and 2, dammarane type triterpene with cyclization at the side chain, were obtained for the first time from alkaline-degradation products of total ginsenosides of Panax quinquefolium L., compound 1 is a new compound.
Cyclization ; Oxidation-Reduction ; Panax ; chemistry ; Sapogenins ; chemistry ; Saponins ; chemistry ; Steroids ; chemistry ; Triterpenes ; chemistry

Japanese encephalitis virus (JEV) is a member of mosquito-borne flaviviruses. To investigate whether there is a cis-acting genetic element in the coding region of the JEV C protein, which is required for viral replication, we generated four mutants by introducing a various size of deletions in each structural protein-coding region, designated as pJEV/Rep/deltaCC/LUC, pJEV/Rep/deltaC/LUC, pJEV/Rep/deltaprM/LUC, and pJEV/Rep/deltaE/LUC, of these, all replicons except for pJEV/Rep/deltaCC/LUC were competent in replication. Since pJEV/Rep/deltaCC/LUC is the same as pJEV/Rep/ deltaC/LUC except for an additional 5' deletion (nt 132~201) in the coding region of the C protein, this region appeared to be essential for RNA replication. This is consistent with the proposed cyclization sequence motif in the 5' region of the C gene, which has been recently shown to be required for replication in other mosquito-borne flaviviruses such as DV, YFV, KUN, and WNV. Thus, our results suggest that a cis-acting genetic element in the coding region of the JEV C protein may play an important role in RNA replication. This study will facilitate the current understanding of JEV RNA replication.
Asian Continental Ancestry Group* ; Capsid Proteins ; Clinical Coding* ; Cyclization ; Encephalitis Virus, Japanese* ; Encephalitis, Japanese* ; Flavivirus ; Humans ; Replicon ; RNA

The capacity for thermal tolerance is critical for industrial enzyme. In the past decade, great efforts have been made to endow wild-type enzymes with higher catalytic activity or thermostability using gene engineering and protein engineering strategies. In this study, a recently developed SpyTag/SpyCatcher system, mediated by isopeptide bond-ligation, was used to modify a rumen microbiota-derived xylanase XYN11-6 as cyclized and stable enzyme C-XYN11-6. After incubation at 60, 70 or 80 ℃ for 10 min, the residual activities of C-XYN11-6 were 81.53%, 73.98% or 64.41%, which were 1.48, 2.92 or 3.98-fold of linear enzyme L-XYN11-6, respectively. After exposure to 60-90°C for 10 min, the C-XYN11-6 remained as soluble in suspension, while L-XYN11-6 showed severely aggregation. Intrinsic and 8-anilino-1-naphthalenesulfonic acid (ANS)-binding fluorescence analysis revealed that C-XYN11-6 was more capable of maintaining its conformation during heat challenge, compared with L-XYN11-6. Interestingly, molecular cyclization also conferred C-XYN11-6 with improved resilience to 0.1-50 mmol/L Ca²⁺ or 0.1 mmol/L Cu²⁺ treatment. In summary, we generated a thermal- and ion-stable cyclized enzyme using SpyTag/SpyCatcher system, which will be of particular interest in engineering of enzymes for industrial application.
Animals ; Cyclization ; Endo-1,4-beta Xylanases ; chemistry ; metabolism ; Enzyme Stability ; Industrial Microbiology ; methods ; Microbiota ; Protein Engineering ; Rumen ; enzymology ; microbiology ; Temperature

Peptide cyclization, a pivotal approach to modifying linear precursors of proteins and pepticles, has been used to enhance their biological activities and serum stabilities. Recently, sortase A (SrtA) from Staphyloccus aureus becomes a promising new technology for efficiently incorporating site specific modifications into proteins, conjugating the cell surface and cyclizing the linear peptides. In this study, we constructed two recombinant expression systems, one with chitin binding domain and the other with six-histidine tag and chitin binding domain on the N-terminal of SrtA, separately. The results of enzymatic kinetics indicate that the two recombinant tags do not impair the transpeptidase activity of SrtA compared with the standard reaction reported under the same reaction condition. The two synthesized peptides with N-ternimal three glycines and C-terminal penta-amino acid motif, LPETG, were cyclized using immobilized and recycled SrtA. The SrtA-based cyclization promises to represent a simple method for easy and efficient enzymatic synthesis of large cyclic peptides.
Aminoacyltransferases ; metabolism ; Bacterial Proteins ; metabolism ; Cyclization ; Cysteine Endopeptidases ; metabolism ; Enzymes, Immobilized ; metabolism ; Kinetics ; Peptides ; metabolism ; Peptides, Cyclic ; biosynthesis ; Staphylococcus aureus ; enzymology