Kinetic and Thermodynamic Approach to Design of Processes for Enzymatic Synthesis of Betalactams

An optimal way to design an enzymatic process for the production of betalactam antibiotics based on thermodynamic and kinetic studies is described. The study was performed on model reactions involving synthesis of cephalosporin-acids (cephalotin, cefazolin, cefoxitin) using immobilised cephalosporin-acid synthetase from Escherichia coli as biocatalyst, and aminocephalosporins (cephalexin) using immobilised cells of Xanthomonas rubrilineans containing the aminocephalosporin synthetase. The possibility of direct synthesis of cephalotin and cefoxitin was shown, the main equilibrium parameters were determined and the operation conditions were evaluated. The maximum key amino acid conversion to product of approximately 90% for cefoxitin and cephalotin was achieved using initial concentrations of the corresponding key amino acids of 0.05 λM and, respectively, 2-fold and 4-fold molar excess of the carboxylic acids. Cefazolin and cephalexin production by enzymatic synthesis with using of corresponding biocatalyst with a mechanism of action involving the acylenzyme intermediate was shown possible. The kinetic parameters of the process were estimated and the relationship between the maximum antibiotic yield and the initial concentrations of the substrate and nucleophile in the kinetically controlled synthesis was determined. The technologies for cefazolin and cephalexin enzymatic synthesis were designed and the cefazolin technology was optimised. Maximum yields of cefazolin and cephalexin of more than 90% were predicted by the kinetic model using 4-6-fold molar excess of the acylating agents and maximum yields of approximately 85% were achieved in experiments.     

Enzymatic Synthesis of Ethyl-glucoside Monooleate with Lipase in Solvent-free Medium

Ethylglucoside monooleate was synthesized by esterification between ethylglucoside and oleic acid with immobilized lipase from Candida antarctica in a solvent-free system. It was shown that a stirred tank reactor was suitable for the enzymatic reaction process involving substrates with low miscibility, in which the biocatalyst was recycled five times without significant activity loss. Removal of the co-product, water, from the reaction medium by carrying out the reaction under reduced pressure benefited the esterification reaction and increased the monooleate yield up to 97% within 8 hours.     

Enzymatic Synthesis of Ethyl-glucoside Monooleate with Lipase in Solvent-free Medium

Ethylglucoside monooleate was synthesized by esterification between ethylglucoside and oleic acid with immobilized lipase from Candida antarctica in a solvent-free system. It was shown that a stirred tank reactor was suitable for the enzymatic reaction process involving substrates with low miscibility, in which the biocatalyst was recycled five times without significant activity loss. Removal of the co-product, water, from the reaction medium by carrying out the reaction under reduced pressure benefited the esterification reaction and increased the monooleate yield up to 97% within 8 hours.     

Thermodynamic and Kinetic Framework of Selenocysteyl-tRNASec Recognition by Elongation Factor SelB

SelB is a specialized translation elongation factor that delivers selenocysteyl-tRNA^Sec (Sec-tRNA^Sec) to the ribosome. Here we show that Sec-tRNA^Sec binds to SelB·GTP with an extraordinary high affinity (K_d = 0.2 pm). The tight binding is driven enthalpically and involves the net formation of four ion pairs, three of which may involve the Sec residue. The dissociation of tRNA from the ternary complex SelB·GTP·Sec-tRNA^Sec is very slow (0.3 h⁻¹), and GTP hydrolysis accelerates the release of Sec-tRNA^Sec by more than a million-fold (to 240 s⁻¹). The affinities of Sec-tRNA^Sec to SelB in the GDP or apoforms, or Ser-tRNA^Sec and tRNA^Sec to SelB in any form, are similar (K_d = 0.5 μm). Thermodynamic coupling in binding of Sec-tRNA^Sec and GTP to SelB ensures at the same time the specificity of Sec- versus Ser-tRNA^Sec selection and rapid release of Sec-tRNA^Sec from SelB after GTP cleavage on the ribosome. SelB provides an example for the evolution of a highly specialized protein-RNA complex toward recognition of unique set of identity elements. The mode of tRNA recognition by SelB is reminiscent of another specialized factor, eIF2, rather than of EF-Tu, the common delivery factor for all other aminoacyl-tRNAs, in line with a common evolutionary ancestry of SelB and eIF2.     

Utilization of Proteases from Aspergillus Species for Peptide Synthesis via the Kinetically Controlled Approach

We examined Aspergillus melleus protease (Amano protease P) and A. oryzae protease (Amano protease A) as catalysts for peptide bond formation via the kinetically controlled approach. As the coupling efficiency was only moderate, even with a good amino acid substrate as the carboxyl component, in acetonitrile as a solvent (with or without a small amount of added water) that we had mainly employed previously in α-chymotrypsin catalyzed couplings, other solvent systems were sought. In 1,1,1,3,3,3-hexafluoro-2-propanol-DMF (1:1) without added water, these Aspergillus proteases were found to remain active for a long period of time and to be utilizable for peptide synthesis when the carbamoylmethyl ester was employed as the acyl donor, though the coupling efficiencies were dependent rather largely on the combination of the amino acid residues at the coupling site. The superiority of the carbamoylmethyl ester to conventional esters, for example the methyl ester, was once again established. Furthermore, some segment condensations were also achieved by the same procedure.     

Design,synthesis and biological evaluation of piperazino-enaminones as novel suppressants of pro-Inflammatory cytokines

Infection triggers the release of pro-inflammatory cytokines (TNF-alpha and IL-6). Over-production, however, cause tissue injury seen in severe asthma. The ability of enaminone E121 to reduce pro-inflammatory cytokines in our laboratory encouraged further examination of its structural scaffold. Piperazino-enaminones were designed by incorporating n-arylpiperazine motif into the aromatic enaminone. Four possible modifications were explored systematically. Synthesis was accomplished by amination of the corresponding methyl/ethyl 2,4-dioxo-6-(substituted)cyclohexane-carboxylate.. Sixteen novel compounds were synthesized. Biological activity was tested in J774 macrophages stimulated with lipopolysaccharides. The release of cytokines was measured via ELISA. Four compounds significantly suppressed TNF-alpha and IL-6 release in dose-dependent manner.     

Chemical and Enzymatic Synthetic Methods for Asymmetric Oxidation of the C-C Double Bond

A number of synthetically useful methods for asymmetric oxidation of the C-C double bond are briefly reviewed. This includes chemical asymmetric epoxidation, such as Sharpless, Julia, and Jacobsen epoxidation, asymmetric cis-dihydroxylation of olefins, monooxygenase-catalyzed epoxidation, dioxygenase-catalyzed cis-dihydroxylation of aromatics, and trans-dihydroxylation of C-C double bond catalyzed by a monooxygenase and an epoxide hydrolase. The catalytic system, substrate range, enantioselectivity, synthetic application, and scope and limitation of each method are described.     

Design,synthesis and biological activity of a novel ethylenediamine derivatives as H1 receptor antagonists

In this study, a series of novel ethylenediamine compounds were obtained by structural modification of the lead compounds with thonzylamine, and using the principle of modifying by bioisostere formation and modification with alkyl groups. In vitro assay, the biological activities showed that the target compounds have good properties in inhibiting mast cell degranulation and releasing histamine and β-aminohexidase, such as the compounds 5c, 5g, 5k, 5l and 5o, especially of compound 5k to mast cell degranulation is IC₅₀ = 0.0106 ± 0.001 μmol?L^?1, histamine release was IC₅₀ = 0.0192 ± 0.005 μmol?L^?1 and β-hexosaminidase release was IC₅₀ = 0.0455 ± 0.002 μmol?L^?1 in vitro. At the same time, in vivo biological activities assay results showed that have a good Histamie induce bronchospasm effect with relatively long duration and good protective effect in vivo, among which the protective effect of compound 5k was 79.74 ± 0.30%, compounds 5c, 5g, 5k, 5l and 5o could inhibit the capillary permeability of increasing which were caused by histamine.     

Enzymatic determination of choline acetyltransferase by coenzyme A cycling and its application to analysis of single mammalian neurons

Abstract: An enzymatic assay for choline acetyltrans-ferase was developed by measuring acetyl-coenzyme A (acetyl-CoA) formed from CoASH and acetylcholine (ACh). This method is extremely sensitive and may be applied to the analysis of microgram to nanogram crude samples. The method is, however, not useful when choline acetyltransferase is present in very low concentrations. The basis of this method is to amplify a small amount of synthesized acetyl-CoA in the assay mixture by using an enzymatic amplification reaction, CoA cycling. This amplification mechanism made it possible to perform microassays (13 nl-2.2 μl of assay volume) of freeze-dried sections prepared from cerebral cortex, striatum, and hippocampus of mice and single cell bodies isolated from freeze-dried sections of rabbit spinal cords. These samples were weighed and added directly to the reaction mixture. The activities of the above cerebral regions, assayed with 1,500–2,000-fold amplification, corresponded well to the results previously reported by other workers. The average activity of single anterior horn cells, determined with 64,000–420,000-fold amplification, was 40-fold higher than that of rabbit cerebral cortex, and the specific activities on a dry weight basis were widely distributed among individual neurons. No activity was detected in the noncholinergic dorsal root ganglion cells or in cerebellar cortex.     

Enzymatic (13)C labeling and multidimensional NMR analysis of miltiradiene synthesized by bifunctional diterpene cyclase in Selaginella moellendorffii

Diterpenes show diverse chemical structures and various physiological roles. The diversity of diterpene is primarily established by diterpene cyclases that catalyze a cyclization reaction to form the carbon skeleton of cyclic diterpene. Diterpene cyclases are divided into two types, monofunctional and bifunctional cyclases. Bifunctional diterpene cyclases (BDTCs) are involved in hormone and defense compound biosyntheses in bryophytes and gymnosperms, respectively. The BDTCs catalyze the successive two-step type-B (protonation-initiated cyclization) and type-A (ionization-initiated cyclization) reactions of geranylgeranyl diphosphate (GGDP). We found that the genome of a lycophyte, Selaginella moellendorffii, contains six BDTC genes with the majority being uncharacterized. The cDNA from S. moellendorffii encoding a BDTC-like enzyme, miltiradiene synthase (SmMDS), was cloned. The recombinant SmMDS converted GGDP to a diterpene hydrocarbon product with a molecular mass of 272 Da. Mutation in the type-B active motif of SmMDS abolished the cyclase activity, whereas (+)-copalyl diphosphate, the reaction intermediate from the conversion of GGDP to the hydrocarbon product, rescued the cyclase activity of the mutant to form a diterpene hydrocarbon. Another mutant lacking type-A activity accumulated copalyl diphosphate as the reaction intermediate. When the diterpene hydrocarbon was enzymatically synthesized from [U-(13)C(6)]mevalonate, all carbons were labeled with (13)C stable isotope (>99%). The fully (13)C-labeled product was subjected to (13)C-(13)C COSY NMR spectroscopic analyses. The direct carbon-carbon connectivities observed in the multidimensional NMR spectra demonstrated that the hydrocarbon product by SmMDS is miltiradiene, a putative biosynthetic precursor of tanshinone identified from the Chinese medicinal herb Salvia miltiorrhiza. Hence, SmMDS functions as a bifunctional miltiradiene synthase in S. moellendorffii. In this study, we demonstrate that one-dimensional and multidimensional (13)C NMR analyses of completely (13)C-labeled compound are powerful methods for biosynthetic studies.     

Enzymatic Routes for the Synthesis of Rhododendrin and Epi-Rhododendrin

The synthesis of (R)- and (S)-3-(4-hydroxyphenyO-1-methylpropyl-β-D-glucopyranosides has been achieved by two enzymatic steps, namely an oxido-reduction step involving alcohol dehydrogenases from different origin for the preparation of both aglycones in enantiomeric pure form, and a transglycosidation step involving a thermophilic β-glucosidase from the archaeon Sulfolobus solfataricus.     

Enzymatic hydrolysis and simultaneous saccharification and fermentation of alkali/peracetic acid-pretreated sugarcane bagasse for ethanol and 2,3-butanediol production

The enzymatic digestibility of alkali/peracetic acid (PAA)-pretreated bagasse was systematically investigated. The effects of initial solid consistency, cellulase loading and addition of supplemental β-glucosidase on the enzymatic conversion of glycan were studied. It was found the alkali-PAA pulp showed excellent enzymatic digestibility. The enzymatic glycan conversion could reach about 80% after 24 h incubation when enzyme loading was 10 FPU/g solid. Simultaneous saccharification and fermentation (SSF) results indicated that the pulp could be well converted to ethanol. Compared with dilute acid pretreated bagasse (DAPB), alkali-PAA pulp could obtain much higher ethanol and xylose concentrations. The fermentation broth still showed some cellulase activity so that the fed pulp could be further converted to sugars and ethanol. After the second batch SSF, the fermentation broth of alkali-PAA pulp still kept about 50% of initial cellulase activity. However, only 21% of initial cellulase activity was kept in the fermentation broth of DAPB. The xylose syrup obtained in SSF of alkali-PAA pulp could be well converted to 2,3-butanediol by Klebsiella pneumoniae CGMCC 1.9131.     

Synthesis of CMP-9'-modified-sialic acids as donor substrate analogues for mammalian and bacterial sialyltransferases

Cytidine-5'-monophospho-sialic acid (CMP-Neu5Ac) derivatives bearing a phenyl group in which the tether length between the phenyl group and the 9-position of Neu5Ac varied were synthesized and evaluated as substrates for sialyltransferases. In the synthesis of the compounds, a coupling reaction between methyl 5-acetamido-4,7,8-tri-O-acetyl-9-azido-3,5,9-trideoxy-beta-D-glycero-D-galacto-2-nonulopyranosonate and 2-cyanoethyl 2',3'-O,N4, triacetylcytidine-5'-yl N,N-diisopropylphosphoramidite was carried out and the phosphite derivative thus obtained was oxidized and then deprotected to yield CMP-9'-azido-Neu5Ac. Modification of the 9-amino group prepared by reduction of the azido groups was performed by the use of several phenyl-substituted alkylcarboxylic acid derivatives. Using these CMP-9'-modified-Neu5Ac analogues bearing the phenyl-substituted alkyl-amide group, sialyltransferase assays were performed with both rat liver alpha-(2-->6)-sialyltransferase and Photobacterium alpha-(2-->6)-sialyltransferase. These 9-modified analogues could be transferred to disaccharide acceptors, and a practical enzymatic synthesis using CMP-9'-modified-Neu5Ac yielded sialoside analogues and sialylglycoproteins in good yield. These experiments demonstrate that the Photobacterium sialyltransferase can be used in the synthesis of sialoside analogues having a large substituent at the 9-position of Neu5Ac.     

Design and synthesis of highly potent HIV-1 protease inhibitors with novel isosorbide-derived P2 ligands

The design, synthesis, and biological evaluation of a series of six HIV-1 protease inhibitors incorporating isosorbide moiety as novel P2 ligands are described. All the compounds are very potent HIV-1 protease inhibitors with IC₅₀ values in the nanomolar or picomolar ranges (0.05–0.43 nM). Molecular docking studies revealed the formation of an extensive hydrogen-bonding network between the inhibitor and the active site. Particularly, the isosorbide-derived P2 ligand is involved in strong hydrogen bonding interactions with the backbone atoms.     

Search for Microorganisms Producing Cephalosporin Acylase and Enzymatic Synthesis of Cephalosporins

Microorganisms were tested for production of cephalosporin acylase. Some bacteria showed strong acylase activity for all of cephalexin, cephaloridine, cephalotin, penicillin G and ampicillin. Some showed a rather specific activity for cephalexin. Pseudomonas melanogenum KY 3987 showed specific activity only for cephalexin and ampicillin which contain a side chain of d-phenylglycine. Most of these acylase-producing bacteria had the ability to synthesize cephalexin and other cephalosporins from 7-aminocephem compounds and organic acid esters. Among them, Ktuyvera citrophila KY 7844 was one of the most promising organisms for enzymatic synthesis of cephalosporins. This organism had the ability to catalyze N-acylation of 7-aminocephem compound not only with α-amino acid ester, but also with such acid esters as 1-(1 H)-tetrazolylacetate methylester which has no α-amino group.     

Synthesis of hexa- to tridecasaccharides related to Shigella dysenteriae type 1 for incorporation in experimental vaccines

Hexa- to tridecasaccharides corresponding to the O-specific polysaccharide (O-SP) of the Gram-negative bacterium Shigella dysenteriae type 1 were synthesized in solution phase. The syntheses utilized tetra-, octa-, and dodecasaccharide intermediates that represent one to three contiguous tetrasaccharide repeating units of the O-SP [Synlett2003, 743]. These compounds were glycosylated with mono-, di-, and trisaccharide trichloroacetamidates, which were synthesized in this study. The excellent stereodirecting effect of 4,6-O-benzophenone ketals in glycosylation reactions of 2-azido-2-deoxy-glucopyranosyl donors was demonstrated. The free oligosaccharides were characterized by 1H and 13C NMR spectroscopy and by high-resolution mass spectrometry. The oligosaccharides described herein contain the 5-(methoxycarbonyl)pentyl aglycon for eventual attachment to immunogenic carriers using a recently published protocol [J. Org. Chem.2005, 70, 6987].     

Enzymatic degradation and electrospray tandem mass spectrometry as tools for determining the structure of cationic starches prepared by wet and dry methods

Cationic starches from various semi-technical processes, two 'wet' (slurry and paste modification) and two 'dry' procedures (dry modification and extrusion), each type in a DS range from 0.03 to 0.1, were investigated by electrospray ionisation mass spectrometry (ESIMS) and tandem mass spectrometry (ESIMS2) after enzymatic degradation with alpha-amylase and subsequent glucoamylase digestion. For comparison, chemically derived cationic oligosaccharides were also analysed by ESIMS. The cationisation pattern in the glucosyl units was analysed by GLC after methanolysis, permethylation and Hofmann elimination. Results from ESIMS are discussed and interpreted with respect to enzyme susceptibility, monomer composition and physical properties of the different types of cationic starches.     

Enzymatic characterization of peptidic materials isolated from aqueous solutions of ammonium cyanide (pH 9) and hydrocyanic acid (pH 6) exposed to ionizing radiation

The enzymatic digestion of some radiolytically produced peptidic materials was examined. The substrates were compounds isolated from 0.1 molar solutions of NH₄CN (pH 9) and HCN (pH 6), after their exposure to rays from a⁶⁰Co source (15–20 Mrad doses). Commercial proteolytic enzymes pronase and aminopeptidase M were used. The examined materials were of composite nature and proteolytic action was systematically observed after their subsequent purification. In some fractions the effect was found to be positive with up to 30% of peptide bonds cleaved with respect to the amino acid content. These findings support our previous conclusions on the free radical induced formation of peptidic backbones without the intervention of amino acids. Some side effects were also noted which might be of interest in observations on enzymatic cleavage of other composite peptidic materials of abiotic origin.     

Simple and Rapid Enzymatic Method for the Synthesis of Single-Strand Oligonucleotides Containing Trifluorothymidine

To investigate the mechanism of trifluorothymidine (TFT)-induced DNA damage, we developed an enzymatic method for the synthesis of single-strand oligonucleotides containing TFT-monophosphate residues. Sixteen-mer oligonucleotides and 14-mer 5′-phosphorylated oligonucleotides were annealed to the template of 25-mer, so as to empty one nucleotide site. TFT-triphosphate was incorporated into the site by DNA polymerase and then ligated to 5′-phosphorylated oligonucleotides by DNA ligase. The synthesized 31-mer oligonucleotides containing TFT residues were isolated from the 25-mer complementary template by denaturing polyacrylamide electrophoresis. Using these single-strand oligonucleotides containing TFT residues, the cleavage of TFT residues from DNA, using mismatch uracil-DNA glycosylase (MUG) of E.coli origin, was compared with that of 5-fluorouracil (5FU) and 5-bromodeoxyuridine (BrdU). The TFT/A pair was not cleaved by MUG, while the other pairs, namely, 5FU/A, 5FU/G, BrdU/A, BrdU/G, and TFT/G, were easily cleaved from each synthesized DNA. Thus, this method is useful for obtaining some site-specifically modified oligonucleotides.