One‐Pot Cascade Reactions using Fructose‐6‐phosphate Aldolase: Efficient Synthesis of D‐Arabinose 5‐Phosphate,D‐Fructose 6‐Phosphate and Analogues

One‐pot multienzymatic reactions have been performed for the synthesis of 1‐deoxy‐D ‐fructose 6‐phosphate, 1,2‐dideoxy‐D ‐arabino‐hept‐3‐ulose 7‐phosphate, D ‐fructose 6‐phosphate and D ‐arabinose 5‐phosphate. The whole synthetic strategy is based on an aldol addition reaction catalysed by fructose‐6‐phosphate aldolase (FSA) as a key step of a three or four enzymes‐catalysed cascade reaction. The four known donors for FSA – dihydroxyacetone (DHA), hydroxyacetone (HA), 1‐hydroxy‐2‐butanone (HB) and glycolaldehyde (GA) – were used with D ‐glyceraldehyde 3‐phosphate as acceptor substrate. The target phosphorylated sugars were obtained in good to excellent yields and high purity.     

Redesign of the Phosphate Binding Site of L‐Rhamnulose‐ 1‐Phosphate Aldolase towards a Dihydroxyacetone Dependent Aldolase

The aldol addition of unphosphorylated dihydroxyacetone (DHA) to aldehydes catalyzed by L ‐rhamnulose‐1‐phosphate aldolase (RhuA), a dihydroxyacetone phosphate‐dependent aldolase, is reported. Moreover, a single point mutation in the phosphate binding site of the RhuA wild type, that is, substitution of aspartate for asparagine at position N29, increased by 3‐fold the of aldol addition reactions of DHA to other aldehyde acceptors rather than the natural L ‐lactaldehyde. The RhuA N29D mutant modified the optimum enzyme design for the natural substrate and changed its catalytic properties making the aldolase more versatile to other aldol additions of DHA.     

A Thermostable Aldolase for the Synthesis of 3‐Deoxy‐2‐ulosonic Acids

A stereochemically promiscuous 2‐keto‐3‐deoxygluconate aldolase has been used as an efficient biocatalyst to catalyse the aldol reaction of pyruvate with C₃‐ and C₄‐aldoses to afford syn‐ and anti‐3‐deoxy‐2‐ulosonic acids in poor to good de. A continuous flow bioreactor containing immobilised aldolase has been developed that enables gram quantities of C₆‐ and C₇‐3‐deoxyhept‐2‐ulosonic acids to be produced in an efficient manner.     

Synthesis of the Ammonium Salt of 6‐Amino‐2‐hydroxy‐ 3,5‐dinitropyrazine and a Comparison of its Properties with those of Ammonium 3,5‐Diaminopicrate (ADAP)

The ammonium salt of 6‐amino‐2‐hydroxy‐3,5‐dinitropyrazine has been synthesised from 2,6‐dimethoxy‐3,5‐dinitropyrazine and its properties (DSC, crystal structure, impact sensitiveness and thermochemical properties) are compared with the analogous benzene derivative, ammonium 3,5‐diaminopicrate.     

Synthesis, 3D‐QSAR,and Structural Modeling of Benzolactam Derivatives with Binding Affinity for the D2 and D3 Receptors

A series of 37 benzolactam derivatives were synthesized, and their respective affinities for the dopamine D₂ and D₃ receptors evaluated. The relationships between structures and binding affinities were investigated using both ligand‐based (3D‐QSAR) and receptor‐based methods. The results revealed the importance of diverse structural features in explaining the differences in the observed affinities, such as the location of the benzolactam carbonyl oxygen, or the overall length of the compounds. The optimal values for such ligand properties are slightly different for the D₂ and D₃ receptors, even though the binding sites present a very high degree of homology. We explain these differences by the presence of a hydrogen bond network in the D₂ receptor which is absent in the D₃ receptor and limits the dimensions of the binding pocket, causing residues in helix 7 to become less accessible. The implications of these results for the design of more potent and selective benzolactam derivatives are presented and discussed.     

An Engineered Biocatalyst for the Synthesis of Glycoconjugates: Utilization of β1,3‐N‐Acetyl‐D‐glucosaminyltransferase from Streptococcus agalactiae Type Ia Expressed in Escherichia coli as a Fusion with Maltose‐Binding Protein

A fusion protein composed of β1,3‐N‐acetyl‐D ‐glucosaminyltransferase (β1,3‐GlcNAcT) from Streptococcus agalactiae type Ia and maltose‐binding protein (MBP) was produced in Escherichia coli as a soluble and highly active form. Although this fusion protein (MBP‐β1,3‐GlcNAcT) did not show any sugar‐elongation activity to some simple low‐molecular weight acceptor substrates such as galactose, Galβ(1→4)Glc (lactose), Galβ(1→4)GlcNAc (N‐acetyllactosamine), Galβ(1→4)GlcNAcβ(1→3)Galβ(1→4)Glc (lacto‐N‐tetraose), and Galβ(1→4)GlcβCer (lactosylceramide, LacCer), the multivalent glycopolymer having LacCer‐mimic branches (LacCer mimic polymer, LacCer primer) was found to be an excellent acceptor substrate for the introduction of a β‐GlcNAc residue at the O‐3 position of the non‐reducing galactose moiety by this engineered enzyme. Subsequently, the polymer having GlcNAcβ(1→3)Galβ(1→4)Glc was subjected to further enzymatic modifications by using recombinant β1,4‐D ‐galactosyltransferase (β1,4‐GalT), α2,3‐sialyltransferase (α2,3‐SiaT), α1,3‐L ‐fucosyltransferase (α1,3‐FucT), and ceramide glycanase (CGase) to afford a biologically important ganglioside; Neu5Aα(2→3)Galβ(1→4)[Fucα(1→3)]GlcNAcβ(1→3)Galβ(1→4)GlcCerα(IV3Neu5Acα,III3Fucα‐nLc4Cer) in 40% yield (4 steps). Interestingly, it was suggested that MBP‐β1,3‐GlcNAcT could also catalyze a glycosylation reaction of the LacCer mimic polymer with N‐acetyl‐D ‐galactosamine served from UDP‐GalNAc to afford a polymer carrying trisaccharide branches, GalNAcβ(1→3)Galβ(1→4)Glc. The versatility of the MBP‐β1,3‐GlcNAcT in the practical synthesis was preliminarily demonstrated by applying this fusion protein as an immobilized biocatalyst displayed on the amylose resin which is known as a solid support showing potent binding‐affinity with MBP.     

Synthesis and characterization of the feed ratio of polyethylene oxide (0 ∼ 10 wt % PEO) in the nylon‐6/PEO copolymer system

In this work, we have synthesis nylon‐6/polyethylene oxide (PEO) copolymer system based on feed ratio of PEO (0～ 10 wt %) through condensation polymerization in a pilot scale. The structure of copolymer was confirmed by Fourier transform infrared (FTIR) spectroscopy and verified by ¹H nuclear magnetic resonance (¹HNMR). The thermal properties were investigated by differential scanning calorimetry (DSC) and indicated both melting temperature (T_m) and cold crystallization temperature (T_c) appearing unapparent decreased while increased PEO content in copolymers. The incorporation of PEO into the nylon‐6 chain reduced its tensile strength, modulus, and heat distortion temperature (HDT). The notched Izod impact strength of and ductility of the copolymers improved significantly as the PEO content was increased. The plasticizing effect was caused by the soft segments from PEO, which increases the mobility of the molecular chain in the copolymers. The results of mechanical tests agree closely with dynamic mechanical analysis (DMA) measurements. A rheological investigation revealed that neat nylon‐6 and its copolymer displayed similar behavior. The crystalline structure was examined by wide‐angle X‐ray diffraction (WAXD). The results demonstrate that the addition of a little PEO altered the crystallization from the α form to the γ form, mainly owing to the breaking parts of the original H‐bonds by the incorporation of ether groups. A mechanism of interaction between the amide and the ether group in nylon‐6/PEO copolymers is proposed. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A novel polymer chemodosimeter for the detection of mercury ions: Synthesis and fluorescence “turn‐on” responses of fluorene‐based conjugated polymer with reactive pendent N,N‐diethyl‐2‐(4‐phenoxy)‐thioacetamide

A novel conjugating polyfluorene bearing N,N‐diethyl‐2‐(4‐phenoxy)‐thioacetamide as side chain was designed for the detection of Hg(II) ions. It was synthesized through postfunctionalization of acetamide‐based polyfluorene derivative. Upon the addition of Hg(II) ions, the thioacetamide groups of this polymer side chains were specifically reacted with Hg(II) ions, leading to this chemodosimeter with higher selectivity for Hg(II) over other metal ions tested under the same conditions. In addition, on the basis of the effect of fluorescent signal amplifications originated from electron transmission along the backbone, this designed conjugated polyfluorene with pendent reactive thioacetamide reached ultra high sensitivity for the detection of mercury ions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Enantioselective Benzylic Hydroxylation with Pseudomonas monteilii TA‐5: A Simple Method for the Syntheses of (R)‐Benzylic Alcohols Containing Reactive Functional Groups

Highly enantioselective benzylic hydroxylations of benzene derivatives ( 1–4 ) containing reactive functional groups were achieved for the first time with Pseudomonas monteilii TA‐5 as biocatalyst, giving the corresponding (R)‐benzylic alcohols 5 – 8 in 93–99% ee as the only products. Preparative biotransformations were demonstrated by the biohydroxylation of 1 and 2 with resting cells of P. monteilii TA‐5 to afford (R)‐ 5 in 94% ee and 66% yield and (R)‐ 6 in 94% ee and 56% yield, respectively. The highly enantioselective biohydroxylations represent a simple access to (R)‐benzylic alcohols containing reactive functional groups that are useful pharmaceutical intermediates and versatile chiral building blocks.     

2,6‐Diisopropoxyphenyl(dicyclohexyl)phosphine: A New Ligand for Palladium‐Catalyzed Amination Reactions of Aryl Chlorides with Potassium Hydroxide as the Base

A new, readily available monophosphine tetrafluoroborate salt [ L2 ⋅ HBF₄ ] was developed for the palladium‐catalyzed amination reaction of aryl chlorides in moderate to high yields with the cheap and easily available potassium hydroxide as the base. The reaction enjoys a wide scope, lower reaction temperatures, shorter reaction times, high yields, and low catalyst loading when compared to some of same amination reactions reported in the literature. Based on a kinetic study, ³¹P NMR measurements, and DFT calculations, a mechanism involving a 1:1 Pd/L species is proposed.