Antimicrobial activity and stability of protonectin with D-amino acid substitutions.

The misuse and overuse of antibiotics result in the emergence of resistant bacteria and fungi, which make an urgent need of the new antimicrobial agents. Nowadays, antimicrobial peptides have attracted great attention of researchers. However, the low physiological stability in biological system limits the application of naturally occurring antimicrobial peptides as novel therapeutics. In the present study, we synthesized derivatives of protonectin by substituting all the amino acid residues or the cationic lysine residue with the corresponding D-amino acids. Both the D-enantiomer of protonectin (D-prt) and D-Lys-protonectin (D-Lys-prt) exhibited strong antimicrobial activity against bacteria and fungi. Moreover, D-prt showed strong stability against trypsin, chymotrypsin and the human serum, while D-Lys-prt only showed strong stability against trypsin. Circular dichroism analysis revealed that D-Lys-prt still kept typical α-helical structure in the membrane mimicking environment, while D-prt showed left hand α-helical structure. In addition, propidium iodide uptake assay and bacteria and fungi killing experiments indicated that all D-amino acid substitution or partially D-amino acid substitution analogs could disrupt the integrity of membrane and lead the cell death. In summary, these findings suggested that D-prt and D-Lys-prt might be promising candidate antibiotic agents for therapeutic application against resistant bacteria and fungi infection. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

Synthesis of Chiral α-Trifluoromethylamines with 2,2,2-Trifluoroethylamine as a "Building Block".

The ß-isocupreidine, a cinchonine derived alkaloid, catalyzed asymmetric SN2'-SN2' reaction between N-2,2,2-trifluoroethylisatin ketimines and MBH type carbonates was realized in a simple and efficient way. A series of chiral α-trifluoromethylamines were prepared with excellent yields and stereoselectivities. A subsequent and easy process of deprotection gave γ-trifluoromethyl-α-methylenelactam in a stereoselective manner.

Highly Enantioselective Cascade Reaction Catalyzed by Squaramides: the Synthesis of CF3-Containing Chromanes.

A catalytic asymmetric method for the synthesis of 2-CF3 chromanes has been described. Generally, the squaramide-catalyzed cascade reaction of 2-hydroxychalcones with ß-CF3-nitroalkenes gave the CF3-containing heterocyclic compounds bearing three contiguous stereogenic centers in excellent yields, diastereoselectivities, and enantioselectivities.

The asymmetric synthesis of CF3-containing spiro[pyrrolidin-3,2'-oxindole] through the organocatalytic 1,3-dipolar cycloaddition reaction.

A new strategy for the construction of optically active 5'-CF3 spiro[pyrrolidin-3,2'-oxindole] was described. A series of unprecedented 1,3-dipoles were obtained by condensation of CF3CH2NH2 with isatins. The 1,3-dipolar cycloaddition reactions of these ketimines with enals gave the products bearing four contiguous stereogenic centers in excellent yields, diastereoselectivities and enantioselectivities.

Improving enzymatic production of ginsenoside Rh2 from Rg3 by using nonionic surfactant.

In this study, several nonionic surfactants were tried to improve the enzymatic hydrolysis of ginsenoside Rg3 into Rh2 which was catalyzed at 50 degrees C and pH 5.0 by a crude glucosidase extracted from Fusarium sp. ECU2042. Among the biocompatible nonionic surfactants, polyethylene glycol 350 monomethyl ether was shown to be the best. After optimizing some influencing factors on the reaction, the conversion of Rg3 (5 g/l) with 10 g/l crude enzyme reached almost 100% in the presence of the nonionic surfactant (7.5%, w/v), which was 25% higher than that in buffer without any surfactant. Furthermore, the enzyme stability was affected faintly by the surfactant.

Bioproduction of glycolic acid from glycolonitrile with a new bacterial isolate of Alcaligenes sp. ECU0401.

Alcaligenes sp. ECU0401 has been isolated from soil samples with high nitrilase activity against glycolonitrile using the enrichment culture technique. The preferred carbon/nitrogen sources and metal ions were sodium acetate, a composite of peptone and yeast extract, and Cu(2+), respectively. Glycolic acid was obtained in a yield of 96.5% after 14 h of biotransformation from a total of 200 mM glycolonitrile in the mode of sequential addition during the cultivation of Alcaligenes sp. ECU0401 in a 5-L jar fermenter. Fifty micromolars of glycolonitrile could be hydrolyzed in a yield of 94.1% by resting cells after 36 h. The microbial nitrilase system could hydrolyze various nitriles with high activity, and no amidase activity and glycolic acid were observed in hydrolyzing glycolamide. It significantly exhibited high enantioselectivity in the hydrolysis of mandelonitrile and 2-chloromandelonitrile (>99.9% e.e.( p )). Efficient biocatalyst recycling was achieved as a result of immobilization in glutaraldehyde/polyethylenimine cross-linked carrageenan with immobilized cells exhibiting a biocatalyst productivity of 1,042.2 g glycolic acid per gram dry cell weight after 29 batch recycles.

Synthesis of novel salidroside esters by lipase-mediated acylation with various functional acyl groups.

Salidroside, a natural glycoside, was enzymatically derived for the first time into novel esters using lipase as biocatalyst. The reaction system of glycoside acylation was optimized, and the effect of solvent nature, concentrations of substrate and biocatalyst, and acyl donors' structure on the acylation was studied. In the optimal system, various structures of acyl donors, either natural or unnatural, including short alkyl acyl groups, long chain acyl groups and acyl donors with aryl group were connected to molecular backbone of the glycoside, forming various structures of novel glycoside esters.