Short synthesis of hydroxylated thiolane and selenolane rings from mono-benzylated pentitols and aldoses dithioacetals bis-thionocarbonates as bis-electrophilic substrates

1-O-Benzylpentitols (with d-arabino, d-lyxo, d,l-xylo and d,l-ribo configurations) and aldoses dibenzyldithioacetals (with l-arabino, d-lyxo, d-xylo, d-ribo, d-galacto, d-gluco and d-manno configurations) were directly and efficiently transformed into their cyclic bis-thionocarbonate derivatives (61-73%) by reaction with diimidazolyl thione (Im₂CS) in 1,4-dioxane. These bis-electrophilic adducts react regioselectively with Na₂S·9H₂O or Se/NaBH₄ to lead regioselectively to the corresponding thiolane and selenolane rings in good yields for a short synthesis (47-65%).     

Trihydroxy-2-thiaquinolizidine derivatives as a new class of bicyclic glycosidase inhibitors

Trihydroxy-2-thiaquinolizidines, a new class of bicyclic dideoxy-iminohexitol glycosidase inhibitor derivatives with nominally the d-gluco, l-ido, d-manno and l-gulo configurations were synthesized. X-ray analyses indicated that the preferred conformation for d-gluco and d-manno derivatives was a flat trans-fused system. Unlike deoxynojirimycin, the compound with d-gluco configuration was selective for α-glucosidases (yeast and rice) and showed no inhibitory activity towards β-glucosidase (almond), α-galactosidase (green coffee beans), α-galactosidase (E. coli) and α-mannosidase (jack bean), while the l-ido derivative was specific for β-glucosidase (almond).     

Bifidobacterium longum l-Arabinose Isomerase—Overexpression in Lactococcus lactis, Purification, and Characterization

Bifidobacterium longum NRRL B-41409 l-arabinose isomerase (l-AI) was cloned and overexpressed in Lactococcus lactis using a phosphate-depletion-inducible expression system. The purified B. longum l-AI was characterized using d-galactose and l-arabinose as the substrates. The enzyme was active and stable at acidic pH with an optimum at pH 6.0?C6.5. The enzyme showed the highest activity at 55?°C during a 20-min incubation at pH 6.5. The K _m value was 120?mM for l-arabinose and 590?mM for d-galactose. The V _max was 42?U mg^?1 with l-arabinose and 7.7?U mg^?1 with d-galactose as the substrates. The enzyme had very low requirement for metal ions for catalytic activity, but it was stabilized by divalent metal ions (Mg²⁺, Mn²⁺). The enzyme bound the metal ions so tightly that they could not be fully removed from the active site by EDTA treatment. Using purified B. longum l-AI as the catalyst at 35?°C, equilibrium yields of 36?% d-tagatose and 11?% l-ribulose with 1.67?M d-galactose and l-arabinose, respectively, as the substrates were reached.     

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.     

Fragmentation of carbohydrate anomeric alkoxyl radicals. Synthesis of highly functionalized chiral vinyl sulfones

The reaction of derivatives of 3-acetyl-d-glucal, 3-acetyl-l-rhamnal, 3-acetyl-d-galactal, and 3-acetyl-d-lactal with sodium benzenesulfinate in acid medium catalyzed by HgSO₄ afforded diastereoisomeric mixtures of the corresponding 2,3-dideoxy-3-(phenylsulfonyl)-hexopyranoses through a Ferrier rearrangement. The anomeric alkoxyl radical fragmentation of these γ-hydroxy sulfones using the system (diacetoxyiodo)benzene and iodine gave vinyl sulfones with structures of 1,2-dideoxy-4-O-formyl-2-(phenylsulfonyl)-pent-1-enitol and configurations d-erythro, l-erythro, and d-threo at the two stereogenic centers.     

An efficient synthesis of d-ribo- and l-lyxo-phytosphingosine from d-tartaric acid

The preparations of d-ribo- and l-lyxo-phytosphingosines (1, 2) are described. Chelation-controlled addition of tetradecylmagnesium bromide to pentylidene-protected d-threitol aldehyde 6 afforded the key intermediate tetrol 7, providing the desired l-lyxo stereochemistry of phytosphingosine. Inversion at C4 of intermediate 7 provided the d-ribo stereochemistry.     

Expedious synthesis of polyhydroxylated selena and thia-heterocycles via Se and S-ring closure of α,ω-dibromoalditols

The selena and thiaanhydro alditols (with xylo, ribo, d-arabino, erythro, d,l-threo and d-manno configuration) were easily and expeditiously synthesized in good to excellent yields by reaction of selenure and sulfur ions as binucleophiles with α,ω-dibromoalditols as bis-electrophilic substrates. With the 1,6-dibromo-d-glucitol derivative as substrate, only the corresponding thiepane derivative was obtained while the selenaheterocyclistation attempte led to complex mixture.     

Short synthesis of new salacinol analogues and their evaluation as glycosidase inhibitors

Versatile synthesis of some analogues of the naturally-occurring α-glucosidase inhibitor salacinol (1), involving thioanhydro alditol moieties with erythro, d,l-threo, xylo, ribo, d-arabino and d-manno configurations is described. Nucleophilic attack at the least-hindered carbon atom of an l- or d-protected erythritol cyclic sulfate by the thioanhydro alditol sulfur atom yielded the desired zwitterionic compounds. In addition, the preparation of the cyclic sulfates of 2,4-O-benzylidene-d-erythritol and 2,4-O-isopropylidene-l-erythritol was improved. Enzyme inhibition tests showed that most of the new compounds were weak but specific inhibitors, while good inhibitory activity was found for a six-membered ring analogue (β-glucosidase: K_i=16 μM).     

An efficient approach to d-threo-3-hydroxyaspartic acid for the synthesis of novel l-threo-oxazolines as selective blockers of glutamate reversed uptake

An efficient, stereoselective synthetic strategy to d-threo-3-hydroxyaspartic acid was developed. Starting from l-(2S,3S)-N-benzoyl-3-hydroxyaspartic acid dimethyl ester by a Deoxo-fluor-catalyzed cyclization reaction, an inversion of configuration at the β-center (erythro isomer), was observed. A base-induced epimerization reaction led to the d-trans-isomer, which was hydrolyzed to give d-threo-3-hydroxyaspartic acid with excellent stereoselectivity and overall yield. Starting from d-threo-3-hydroxyaspartic acid, l-threo-oxazolines can be stereoselectively synthesized.     

Diastereo- and enantioseparation of a N-Boc amino acid with a zwitterionic quinine-based stationary phase: Focus on the stereorecognition mechanism

A chiral chromatography method enabling the simultaneous diastereo- and enantioseparation of N^α-Boc-N⁴-(hydroorotyl)-4-aminophenylalanine [Boc-Aph(Hor)-OH, 1] was optimized with a quinine-based zwitterionic stationary phase. The polar-ionic eluent system consisting of ACN:MeOH:water—49.7:49.7:0.6 (v/v/v) with formic acid (4.0 mM) and diethylamine (2.5 mM), allowed the successful separation of the four acid stereoisomers: α_d,d-/d,l-1 = 1.08; α_d,l-/l,d-1 = 1.08; α_l,d-/l,l-1 = 1.40.     

Synthesis and glycosidase inhibitory activity of aminocyclitols with a C6- or a C7-ring

The synthesis of carbasugars and various aminocyclitols, related to voglibose and acarbose used in the treatment of non-insulino-dependant diabetes, is described from C₂-symmetrical bis-epoxides derived from d-mannitol. The methodology involves two key steps: a domino alkylation-cyclization with 2-lithio-1,3-dithiane derivatives, and reduction or reductive amination with a primary amine. These compounds have been evaluated as inhibitors of several glycosidases, and this study indicates notably that the l-ido or d-manno 1-aminocycloheptane-3,4,5,6-tetrol are inhibitors of α-d-glucosidase with K_i in the micromolar range.     

Determination of Kynurenine and Tryptophan in Human Plasma by Stacking-Micellar Electrokinetic Chromatography

Kynurenine and tryptophan are important biomarkers for disorders in nervous and immune systems, while the low content of kynurenine in human plasma makes the determination by routine approaches difficult. In this work, an on-line preconcentration method for capillary electrophoresis was developed for the quantification of kynurenine and tryptophan. A concomitant sweeping phenomenon was observed due to the combination of micellar electrokinetic chromatography and stacking. The poor sensitivity in capillary electrophoresis was improved so that the determination of low concentrations of kynurenine became possible. Parameters that may affect the efficiency of the on-line concentration were systematically investigated and optimized. A large volume sample injection was employed for sampling at 100 mbar for 112 sec. A voltage of ?20 kV was applied, and the ionic sample matrix was removed with stacking while analytes were kept in the capillary. The voltage was switched to +18 kV and micellar electrokinetic chromatography was performed for separation and determination of kynurenine and tryptophan. Based on peak heights, the concentration factors for kynurenine and tryptophan were 33 and 31, respectively. The analytical performance of the established method was studied; good linearity of kynurenine was observed in the range of 0.3–30 µM (R² = 0.9988), and 0.3–60 µM (R² = 0.9963) was obtained for tryptophan. LODs of 0.15 µM for kynurenine and 0.30 µM for tryptophan were obtained. The optimum method was successfully tested in human plasma; kynurenine and tryptophan were well identified, which suggests that this method has potential for the analysis of biological samples.     

Stereoselective synthesis of C-glycosylphosphonates from their ketols. Reconsideration of an abandoned route

Isosteric phosphonate analogues of glycosyl 1-phosphates have been obtained by addition of LiCH₂P(O)(OMe)₂ to glyconolactones followed by Et₃SiH–TMSOTf reductive dehydroxylation of the resultant ketols. The compounds prepared include four β-linked pyranose derivatives (d-galacto, 2-azido-2-deoxy-d-galacto, d-gluco, d-manno) and one β-linked furanose derivative (d-manno). In the latter case the ketol was activated as its 2-acetate. In agreement with an observation in another laboratory, the dehydroxylation of a model ketol phosphonate failed with the use of Et₃SiH–BF₃·Et₂O.     

A tethered aminohydroxylation route to l-arabino-[2R,3S,4R] and l-xylo-[2R,3S,4S]-C18-phytosphingosines

A concise and highly efficient synthesis of l-arabino-[2R,3S,4R] and l-xylo-[2R,3S,4S]-C₁₈-phytosphingosines has been achieved. The synthetic strategy features the Sharpless kinetic resolution and tethered aminohydroxylation as the key steps.     

Simultaneous determination of plasma creatinine,uric acid,kynurenine and tryptophan by high‐performance liquid chromatography: method validation and in application to the assessment of renal function

A high‐performance liquid chromatography with ultraviolet detection method has been developed for the simultaneous determination of a set of reliable markers of renal function, including creatinine, uric acid, kynurenine and tryptophan in plasma. Separation was achieved by an Agilent HC‐C₁₈ (2) analytical column. Gradient elution and programmed wavelength detection allowed the method to be used to analyze these compounds by just one injection. The total run time was 25 min with all peaks of interest being eluted within 13 min. Good linear responses were found with correlation coefficient >0.999 for all analytes within the concentration range of the relevant levels. The recovery was: creatinine, 101 ± 1%; uric acid, 94.9 ± 3.7%; kynurenine, 100 ± 2%; and tryptophan, 92.6 ± 2.9%. Coefficients of variation within‐run and between‐run of all analytes were ≤2.4%. The limit of detection of the method was: creatinine, 0.1 µmol/L; uric acid, 0.05 µmol/L; kynurenine, 0.02 µmol/L; and tryptophan, 1 µmol/L. The developed method could be employed as a useful tool for the detection of chronic kidney disease, even at an early stage. Copyright © 2014 John Wiley & Sons, Ltd.     

Efficient syntheses of optically pure chiro- and allo-inositol derivatives, azidocyclitols and aminocyclitols from myo-inositol

Efficient routes for the syntheses of optically pure and hitherto unknown l-chiro- and d-allo-inositol derivatives, azido- and aminocyclitols of l-chiro-configuration, diazido- and diaminocyclitols of d-allo-configuration from economically viable myo-inositol are described. These routes provide access to synthetically flexible 1,2:4,5-di-O-isopropylidene-chiro-inositol and 1,6:3,4-di-O-isopropylidene-allo-inositol, which are otherwise difficult to synthesize directly from their parent inositols. A one pot methodology that allows rapid access to both chiro- and allo-inositol derivatives has also been developed. Investigations on the glycosidase inhibitory properties of these novel azido- and amino-inositols unraveled the potentials of these classes of compounds as novel class of glycosidase inhibitors. Both d and l forms of these cyclitols could be synthesized from myo-inositol in gram scales and hence by exploiting the difference in reactivities of cis- and trans-ketals, a variety of protected derivatives, which are useful for the synthesis of unnatural phosphoinositols and natural products, can be synthesized.     

Synthesis of C-glycosidically linked ADP glycero-β-d-manno-heptose analogues

C-Glycosides of l-glycero-d-manno- and d-glycero-d-manno-heptose containing either (S)- or (R)-2-hydroxypropyl aglycons are easily accessible compounds via condensation of reducing heptoses with pentane-2,4-dione. 2′,3′-Di-O-acetyl adenosine was transformed into the corresponding 5′-O-cyanoethyl N,N-diisopropylaminophosphoramidite derivative, which was coupled in fair yields to the O-acetylated diastereoisomeric C-glycosidic alcohols. Oxidation of the phosphite triesters followed by deprotection furnished four ADP-heptose analogues, wherein the heptosyl phosphate moiety had been replaced by a three carbon-skeleton. The compounds serving as substrate analogues will be used for co-crystallization experiments with ADP heptosyl transferases.     

1-C-Alkyl imino-d-xylitol and -l-arabinitol derivatives obtained via nucleophilic addition to pentose-derived N-tert-butanesulfinyl imines: sugar- versus chiral auxiliary-induced stereoselectivity

The stereoselective synthesis of 1-C-alkyl iminosugars in the d-xylo and l-arabino series as potential drugs for the treatment of lysosomal diseases has been achieved. The key step involves nucleophilic addition to pentodialdofuranose-derived imines generated using enantiopure tert-butanesulfinamide. Depending on the pentofuranose configuration and structure, the stereoselectivity of this reaction was found to be controlled either by the sugar moiety or by the stereogenic sulfur center.     

A unified approach to mesityl amino acids based on Sharpless dihydroxylation

Enantioselective syntheses of two mesityl (2,4,6-trimethylphenyl) amino acids are described. Starting from ethyl 3-mesityl-2-propenoate both enantiomeric dihydroxy esters 5 were prepared in excellent yield and enantiomeric purity (>99% ee) by Sharpless dihydroxylation. Each diol was converted into ethyl 3-azido-2-hydroxy-3-mesitylpropanoate 3 which is the common intermediate. Compound (2S,3S)-3 was transformed into Fmoc-d-mesitylglycine d-1 and Fmoc-l-mesitylalanine l-2 through two four-step-sequences.     

Synthesis of d-gluco-, l-ido-, d-galacto-, and l-altro-configured glycaro-1,5-lactams from tartaric acid

The d-gluco-, l-ido-, d-galacto-, and l-altro-configured glycaro-1,5-lactams 1-4 were prepared from the known tartaric anhydride 5 via the aldehyde 6. These lactams are known (1) or potential (2-4) inhibitors of β-d-glucuronidases and α-l-iduronidases. Olefination of 6 to the (E)- and (Z)-alkenes 7 or 8, followed by reagent or substrate controlled dihydroxylation, lactonization, azidation, reduction, and deprotection led in 10 steps and in overall yields of 11-20% to the title lactams.