One-pot inversion of d-mannono-1,4-lactone for the practical synthesis of l-ribose

l-Ribose was synthesized in a concise manner from d-mannono-1,4-lactone using one-pot inversion conditions. Treatment of d-mannono-1,4-lactone with piperidine, followed by mesylation-induced S_N2-type O-alkylation, afforded the desired one-pot inversion in an optimum yield, and the following straightforward transformations provided l-ribose in good yields.     

Improved synthesis of 6-amino-6-deoxy-d-galactono-1,6-lactam and d-mannono-1,6-lactam from corresponding unprotected d-hexono-1,4-lactones

Regioselective bromination of unprotected d-galactono-1,4-lactone and d-mannono-1,4-lactone with PPh₃/CBr₄ led to 6-bromo-6-deoxy derivatives. These intermediates were treated with LiN₃ and hydrogenated to give 6-amino-6-deoxy-d-galactono-1,6-lactam (8) and 6-amino-6-deoxy-d-mannono-1,6-lactam (13) in 74 and 67% overall yield, respectively.     

A convenient synthesis of l-ribose from d-fructose

An efficient method for the stereoselective synthesis of l-ribose was accomplished starting from commercially inexpensive d-fructose. The intermediates in the process can serve as versatile precursors for the preparation of l-nucleoside analogues.     

A highly efficient synthesis of unnatural l-sugars from d-ribose

A preparative and short synthesis of l-ribose and l-apiose was accomplished starting from d-ribose via stereoselective cis-dihydroxylation and C2-hydroxymethylation, respectively. These l-sugars can serve as versatile intermediates for the synthesis of l-nucleosides.     

Synthesis of 6-amino-6-deoxy-d-gulono-1,6-lactam and l-gulono-1,6-lactam derived from corresponding 5,6-O-sulfinyl hexono-1,4-lactones

Syntheses of 6-amino-6-deoxy-2,3-O-isopropylidene-d-gulono- and l-gulono-1,6-lactams 3 and 4 from corresponding glycono-1,4-lactones are described. Activation of the primary hydroxyl group requires 5,6-cyclic sulfite intermediate to obtain 6-azido-6-deoxy derivatives, which are cyclized after reduction.     

Efficient synthesis of new N-alkyl-d-ribono-1,5-lactams from d-ribono-1,4-lactone

d-Ribono-1,4-lactone was treated with ethylamine in DMF to afford N-ethyl-d-ribonamide 9a in quantitative yield. Bromination of amide 9a by the system SOBr₂ in DMF or PPh₃/CBr₄ in pyridine led, after acetylation, to epoxide 7. However, treatment of amide 9a with acetyl bromide in dioxane followed by acetylation gave 2,3,4-tri-O-acetyl-5-bromo-5-deoxyl-N-ethyl-d-ribonamide 10a. Methanolysis of 10a, with sodium methoxide, afforded the N-ethyl-d-ribonolactam 11a in 51% overall yields. Using this method, N-butyl, N-hexyl, N-dodecyl, and N-benzyl-d-ribonolactams 11b-e were obtained in good yields (48-53%).     

New building blocks for peptide and depsipeptide synthesis: hexafluoroacetone protected l-homoisoserine and d,l-homoisocysteine derivatives

Efficient syntheses of l-homoisoserine and d,l-homoisocysteine derivatives starting from l-malic and d,l-thiomalic acid using hexafluoroacetone as protecting and activating agent are described. The new compounds are interesting building blocks for the preparation of non-natural peptides and depsipeptides as well as for the construction of new GABA derivatives.     

Novel synthesis of 5-thio-hexopyranoside: preparation of 5-thio-d- and l-glucose and 1,6-anhydro-5-thio-l- and d-altrose

Asymmetric synthesis of both d- and l-isomers of 5-thioglucose and 1,6-anhydro-5-thioaltrose are described. The key intermediates, l- and d-threose diethylacetal derivatives, were derived by chemical transformation from d-xylose or d-arabinose and by Sharpless asymmetric dihydroxylation from γ-hydroxycrotylaldehyde diethylacetal. They transformed to γ-thiiranyl diethylacetal via trans-2,3-epoxy alcohol in seven steps. Acetic acid-promoted cyclization of γ-thiiranyl diethylacetal gave 5-thiopyranoside. Removal of the protected groups under the acidic conditions afforded 5-thio-d- and l-glucose and 1,6-anhydro-5-thio-l- and d-altrose, respectively.     

Racemization behavior of l,l-lactide during heating

To control the depolymerization process of poly(l-lactic acid) into l,l-lactide for feedstock recycling, the racemization of l,l-lactide as a post-depolymerization reaction was investigated. In the absence of a catalyst, the conversion to meso-lactide increased with increase in the heating temperature and time at a higher rate than the conversion into oligomers. The resulting high composition of meso-lactide suggests that the direct racemization of l,l-lactide had occurred in addition to the known racemization mechanism that occurs on the oligomer chains. In the presence of MgO, the oligomerization rapidly proceeded to reach an equilibrium state between monomers and oligomers. The equilibrium among l,l-, meso-, and d,d-lactides was found to be a convergent composition ratio l,l-:meso-:d,d-lactides = 1:1.22:0.99 (wt/wt/wt) after 120 min at 300 °C. This composition ratio also indicates that in addition to the known racemization reaction on the oligomer chains, direct racemization among the lactides is also a frequent occurrence.     

Synthesis of l,l-puromycin

l,l-Puromycin, a diastereomer of the natural peptidyl nucleoside antibiotic puromycin, has been synthesized from l-xylose in 13 steps.     

Synthesis of homochiral 2-C-perfluoroalkyl substituted d- and l-riboses

Homochiral 2-C-perfluoroalkyl substituted d- and l-riboses were synthesized via Barbier, Grignard and Ruppert type reactions. The influence of the size of the perfluoroalkyl groups, attached to C-2, on the furanose/pyranose as well as on the α-furanose/β-furanose and α-pyranose/β-pyranose ratio in solution was studied.     

New low-molecular weight gelators based on l-valine and l-isoleucine with various terminal groups

New low-molecular weight gelators based on l-valine and l-isoleucine, which have various terminal groups such as ester, carboxyl, and carboxylate, function as a good organogelator that form an organogel in many organic solvents. In addition, the sodium salt compounds form not only organogels but also a hydrogel in the presence of a cationic surfactant.     

An efficient synthesis of d-ribo-C18-phytosphingosine and l-arabino-C18-phytosphingosine from d-fructose

d-ribo-C₁₈-phytosphingosine and l-arabino-C₁₈-phytosphingosine were synthesised starting from commercially inexpensive d-fructose. Metal-mediated fragmentation and stereoselective reduction were used as key steps to provide the hydrophilic portion of d-ribo and l-arabino phytosphingosines. Grubbs’ cross-metathesis and hydrogenation allowed the incorporation of hydrophobic tail.     

Intermolecular/interionic interactions in l-isoleucine-, l-proline-, and l-glutamine-aqueous electrolyte systems

Speed of sound and density values for ternary systems (amino acid + salt + water): l-isoleucine/l-proline/l-glutamine in aqueous solutions of 1.5 M KCl, 1 M KNO₃, and 0.5 M K₂SO₄ have been measured for several concentrations of amino acids at different temperatures (303.15, 308.15, 313.15, 318.15, and 323.15 K). Using speed of sound and density data, the thermodynamic parameters such as isentropic compressibility (κ_s), change in isentropic compressibility (Δκ_s) and relative change (Δκ_s/κ₀) in isentropic compressibility have been computed. The isentropic compressibility values decrease with increase in the amino acid concentration as well as with temperature. The decrease in κ_s values with increase in concentration of l-isoleucine/l-proline/l-glutamine in 1.5 M KCl, 1 M KNO₃, and 0.5 M K₂SO₄ has been ascribed to an increase in the number of incompressible zwitterions in solutions, and the formation of ‘zwitterions-ions’ and ‘zwitterions-water dipole’ entities in solutions. The decrease in κ_s values with increase in temperature has been attributed to the corresponding decrease of κ_relax (a relaxational part of compressibility), which is dominant over the corresponding increase of κ_∞ (an instantaneous part of compressibility). The trends of variation of Δκ_s and Δκ_s/κ₀ with variations in solute concentration and temperature have also been discussed in terms of solute-solute and solute-solvent intermolecular/interionic interactions operative in the systems.     

An efficient synthesis of selectively functionalized d-rhamnose derivatives

d-Rhamnose is an important component of bacterial lipopolysaccharides. This paper describes a short and highly efficient synthesis of d-rhamnose from d-mannose. The synthesis of selectively C-4 modified d-rhamnosides and 6-deoxy-d-talosides as potential building blocks for complex oligosaccharide synthesis is also discussed.     

A new and short synthesis of naturally occurring 1-deoxy-l-gulonojirimycin from tri-O-benzyl-d-glucal

A new and short synthesis of naturally occurring 1-deoxy-l-gulonojirimycin from tri-O-benzyl-d-glucal, via a regioselective intramolecular cyclization of an amino triol intermediate, is described. Its absolute configuration was deduced from the single crystal X-ray analysis of compound 11.     

Characterization and release of triptolide-loaded poly (d,l-lactic acid) nanoparticles

Triptolide (TP), which has immunosuppressive effect, anti-neoplastic activity, anti-fertility function and severe toxicities on digestive, urogenital, blood circulatory system, was used as a model drug in this study. TP-loaded poly (d,l-lactic acid) (PLA) nanoparticles were prepared by the modified spontaneous emulsification solvent diffusion method (modified-SESD method). Dynamic light scattering system (DLS), transmission electron microscope (TEM), atomic force microscopy (AFM), differential scanning calorimetry (DSC), X-ray powder diffractometry and Fourier transform infra-red spectroscopy (FT-IR) were employed to characterize the nanoparticles fabricated for size and size distribution, surface morphology, the physical state of drug in nanoparticles, and the interaction between the drug and polymer. Encapsulation efficiency (EE) and the in vitro release of TP in nanoparticles were measured by the reverse phase high-performance liquid chromatography (RP-HPLC). The produced nanoparticles exhibited a narrow size distribution with a mean size of approximately 150 nm and polydispersity index of 0.088. The morphology of the nanoparticles exhibited a fine spherical shape with smooth surfaces without aggregation or adhesion. TP-entrapped in nanoparticles was found in the form of amorphous or semicrystalline. It was found that a weak interaction existed between the drug and polymer. In all experiments, more than 65% of EE were obtained. The in vitro release profile of TP from nanoparticles exhibited a typical biphasic release phenomenon, namely initial burst release and consequently sustained release. In this case, the particle size played an important role for the drug release. The modified-SESD method was a potential and advantage method to produce an ideal polymer nanoparticles for drug delivery system (DDS).     

Influence of cellulose nanowhiskers on the hydrolytic degradation behavior of poly(d,l-lactide)

This paper reports the preparation of bionanocomposites based on poly(d,l-lactide) and cellulose nanowhiskers (PDLLA/CNWs) and studies the influence of the CNWs on the hydrolytic degradation behavior of the polylactide. The hydrolytic degradation process was studied in a phosphate buffer medium through the sample weight loss and also by FTIR, DSC and TGA measurements. The presence of CNWs induced a strong delay in the hydrolytic degradation of the PDLLA, even when the concentration of the nanofillers was only 1%. This effect was related to the physical barrier created by the highly crystalline CNWs that inhibited water absorption and hence retarded the hydrolytic degradation of the bionanocomposites. In addition, the incorporation of cellulose nanocrystals in the PDLLA also made the biopolymer more thermally stable, increasing the initial temperature of mass loss even after the degradation in phosphate medium. The results presented here show the possibility of controlling the biodegradability and prolonging the service life of a polylactide through the incorporation of a small quantity of nanofillers obtained from renewable materials.     

Amperometric simultaneous sensing system for d-glucose and l-lactate based on enzyme-modified bilayer electrodes

An amperometric biosensor system which uses screen-printed electrodes to simultaneously detect d-glucose and l-lactate has been developed and applied for simple and rapid determination of d-glucose and l-lactate levels in lactic fermenting beverages. The system was constructed from three-dimensionally layered electrodes. Taking into consideration the effects of easily oxidized substances contained in the samples, ferricyanide ions, which are electrochemically oxidized at a lower voltage, were chosen as a mediator. A linear relationship between steady-state current and concentration was found over a range of 1-100 mM (d-glucose) and 1-50 mM (l-lactate); the variation coefficients were 1.43% (n = 10) and 3.50% (n = 10) for the d-glucose and l-lactate sensors, respectively. When applied to lactic fermenting beverages, there was good agreement between the results obtained by the proposed sensing system and those obtained by the HPLC method. Using the proposed method, assays were completed within 5 min.     

Swelling and hydrolytic degradation of poly(d,l-lactic acid) in aqueous solutions

Low molecular weight poly(lactic acid) was synthesized by direct polycondensation of lactic acid. The oligomers were characterized by viscometry, light scattering, and gel permeation chromatography (GPC). The swelling behaviour of tablets made of the above polymer immersed in buffer solutions at 37 °C was studied. In the same experiments, the hydrolytic stability of d,l-PLA was assessed by measuring the weight loss after drying the tablets. In order to inhibit any degradation due to bacteria, formaldehyde was added in the solution as biostatic factor. The effect of an incorporated drug on the swelling behaviour of d,l-PLA tablets was also considered. It was found that the incorporation of drug in d,l-PLA tablets increases their swelling index, probably due to the creation of additional porosity in the specimens or other interaction between drug and polymeric matrix.