A fast, efficient and stereoselective synthesis of hydroxy-pyrrolidines

Efficient synthesis for each of the eight stereoisomers of the iminosugars lentiginosine and 1,4-dideoxy-1,4-imino-D-arabinitol (DAB)

Herein, we describe the efficient, diastereoselective syntheses of the iminosugars 1,4-dideoxy-1,4-imino-D-arabinitol (DAB) 1b, lentiginosine 3a, and the seven stereoisomers of each of these iminosugars starting from 4-benzoyl-6-deoxy-6-iodoglycopyranosides 47 with yields ranging from 38 % to 68 % for the DAB and isomers 1a-1h and from 44 % to 89 % for the lentiginosine and isomers 3a-3h. We also report the syntheses of the eight stereoisomers of the 4-benzoyl-6-deoxy-6-iodoglycopyranosides 47 from commercially available sugars. Key to the iminosugar syntheses is a single multistep reaction that converts the 4-benzoyl-6-deoxy-6-iodoglycopyranosides 47 to a vinyl pyrrolidine through a one-pot zinc mediated reductive elimination, followed by a reductive amination and finally an intramolecular nucleophilic substitution. Strategic selection of the amine utilized in the reductive amination and the functionalization of the intermediate carbon-carbon double bond provides access to a vast array of iminosugars.

Synthesis and glycosidase inhibition of 3,4,5-trihydroxypiperidines using a one-pot amination-cyclisation cascade reaction

Trihydroxypiperidines are a therapeutically valuable class of iminosugar. We applied a one-pot amination-cyclisation cascade reaction to synthesise 3,4,5-trihydroxypiperidine stereoisomers in three steps from commercially available pentoses and in excellent overall yields. Using our methodology, the yields of the syntheses of meso-1, meso-2 and 3L are the highest reported to date. The synthetic methodology was readily extended to the three-step synthesis of N-alkyl derivatives by replacing the ammonia nitrogen source with a primary amine. The trihydroxypiperidines and N-alkyl analogues were screened for enzyme inhibitory activity using Fabrazyme (Fabry disease), GCase (Gaucher's disease), Agrobacterium sp. β-glucosidase, and Escherichia coli β-galactosidase. N-Phenylethyl 3,4,5-trihydroxypiperidine (N-phenylethyl-1-(3R,4R,5S)-piperidine-3,4,5-triol) showed good inhibitory activity of Fabrazyme (Ki = 46 μM). This activity was abolished when the N-phenylethyl group was removed or replaced with a non-aromatic alkyl chain.

An Amination-Cyclization Cascade Reaction for Iminosugar Synthesis Using Minimal Protecting Groups

The development of a one-step amination-cyclization cascade reaction for the synthesis of N-substituted iminosugars from iodo-pentoses and hexoses is reported. This novel methodology allows for the stereoselective conversion of easily accessible iodo-aldoses and iodo-ketoses into iminosugars in a single step, in highly efficient yields (63-95%), and in aqueous media. Furthermore, the use of functionalized amines allows for the synthesis of N-functionalized iminosugars without additional steps. To illustrate this methodology, a number of biologically important iminosugars were prepared, including 1-deoxynojirimycin, (3S,4R,5S,6R)-azepane-3,4,5,6-tetraol, and N-functionalized 1-deoxymannojirimycins.

A novel and environmental friendly synthetic route for hydroxypyrrolidines using zeolites

A critical step in the synthesis of the hydroxypyrrolidines, 1,4-dideoxy-1,4-imino-l-lyxitol and 1,4-dideoxy-1,4-imino-d-lyxitol, from the corresponding d-sugars is the synthesis of O-methyl 2,3-O-isopropylidenepentofuranoses. Instead of applying homogeneous catalysis process with conventional inorganic acid catalysts like HCl and HClO₄, it was found that heterogeneous catalysis using zeolites could be used for the one-pot synthesis of O-methyl 2,3-O-isopropylidenepentofuranoses directly from d-sugars, MeOH and acetone at mild condition. The best catalyst was H-beta zeolite containing a Si/Al molar ratio of 150, where a yield of >83% was obtained. The overall yields of the five-step procedure to 1,4-dideoxy-1,4-imino-l-lyxitol and 1,4-dideoxy-1,4-imino-d-lyxitol were 57% and 50%, respectively. This synthetic procedure has several advantages such as competitive overall yield, reduced number of steps, and mild reaction conditions. Furthermore, the zeolite catalyst can be easily recovered from the reaction mixture and reused with no loss of activity.

Synthesis and anti-tuberculosis activity of glycitylamines

A series of glycitylamines, which were prepared in few steps from readily available carbohydrates, were tested for their ability to inhibit tuberculosis growth in an Alamar Blue BCG colourimetric assay. Several derivatives, including (2R,3R)-1-(hexadecylamine)pent-4-ene-2,3-diol, (2R,3R)-1-(hexadecylmethylamino)pent-4-ene-2,3-diol and 5-deoxy-5-hexadecylmethylamino-D-arabinitol, were prepared in good to excellent (44-90%) overall yield and exhibited micromolar (20-41μM) inhibitory activity that was similar to the first line tuberculosis (TB) drug ethambutol (39μM) in the same assay. The ease and low cost of the synthesis of the glycitylamines offers definite advantages for their use as potential TB drugs.

Amino-functionalized iminocyclitols: synthetic glycomimetics of medicinal interest

A review on the syntheses and biological activities of unnatural glycomimetics highlighting the effect of replacement of hydroxyl groups of natural iminosugars by amino functionalities is presented.

Quantification of plant cell wall monosaccharides by reversed-phase liquid chromatography with 2-aminobenzamide pre-column derivatization and a non-toxic reducing reagent 2-picoline borane

In this report, we described a sensitive method for quantifying plant cell wall monosaccharides using chemical derivatization, reversed-phase high performance liquid chromatography separation with ultraviolet detection (HPLC-UV). Monosaccharides were derivatized with 2-aminobenzamide (2-AB) by reductive amination to increase the hydrophobicity and detected by ultraviolet absorption for HPLC-UV analysis. A non-toxic reductant, 2-picoline borane was utilized to replace the traditionally used sodium cyanoborohydride (NaCNBH3) to avoid the formation of toxic by-products. Experimental conditions were optimized using glucose as a model system to achieve a high reaction yield of 99%. Under the optimized conditions, we demonstrated that the derivatization yields of several saccharides with 2-AB using 2-picoline borane were all slightly higher than those observed using NaCNBH3. In plants, cell wall monosaccharides consist of arabinose, fucose, galactose, galacturonic acid, glucose, glucuronic acid, mannose, rhamnose, and xylose. Using our method, we successfully quantified these monosaccharides from Arabidopsis cell wall by HPLC-UV, and we obtained a good linearity at a wide dynamic range over five orders (1pmol through 10nmol of injection amount), a detection limit of ∼0.1pmole, and a high precision and accuracy.

Regio- and stereoselective oxygenation of proline derivatives by using microbial 2-oxoglutarate-dependent dioxygenases

We evaluated the substrate specificities of four proline cis-selective hydroxylases toward the efficient synthesis of proline derivatives. In an initial evaluation, 15 proline-related compounds were investigated as substrates. In addition to l-proline and l-pipecolinic acid, we found that 3,4-dehydro-l-proline, l-azetidine-2-carboxylic acid, cis-3-hydroxy-l-proline, and l-thioproline were also oxygenated. Subsequently, the product structures were determined, revealing cis-3,4-epoxy-l-proline, cis-3-hydroxy-l-azetidine-2-carboxylic acid, and 2,3-cis-3,4-cis-3,4-dihydroxy-l-proline.

Design and synthesis of mimics of the T7-loop of FtsZ

Mimics of the T7-loop of the bacterial cell division protein FtsZ have been designed and synthesized. The design is based on the X-ray cocrystal structure of P. aeruginosa FtsZ:SulA. Fast Rigid Exhaustive Docking (FRED) was employed to select compounds that can mimic the key interacting residues. Bicyclic oxazolidinones 1a-d were selected for further study and synthesized from a key bicyclic aziridine intermediate, which is synthesized from a readily available unsaturated aldehyde and amides derived from α-amino acids.