Enantiodivergent synthesis of both antipodes of hydroxy-exo-brevicomin from l-(+)-tartaric acid

An enantiodivergent approach to both antipodes of hydroxy-exo-brevicomin was achieved from a common chiral precursor l-(+)-tartaric acid. The strategy utilizes the elaboration of a keto-Weinreb amide and successive stereoselective reductions.     

Stereoselective syntheses of γ-alkyl (aryl)-α,β-dihydroxy-γ-butyrolactones and naturally occurring lipid guggultetrol

γ-Oxo-butyramides derived from tartaric acid serve as excellent precursors for the synthesis of γ-alkyl (aryl)-α,β-dihydroxy-γ-butyrolactones and for the synthesis of tetrols containing three contiguous stereogenic centres. The methodology presented here is general for the synthesis of γ-alkyl (aryl)-α,β-dihydroxy-γ-butyrolactones. Utility of the chiral building block was demonstrated by the synthesis of naturally occurring lipid guggultetrol.     

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 novel and stereospecific synthesis of (+)-exo-brevicomin

A novel and stereospecific synthesis of (+)-exo-brevicomin is disclosed. The key step of the reaction sequence employs the sulfinyl moiety as an intramolecular nucleophile to functionalize an alkene π-complexed to a bromonium ion.     

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.     

Selective hydroxyl protection of (+)-noviose via improved synthesis

Coumarin antibiotics are biologically important molecules embedded with (+)-noviose as signature moiety. A challenging problem concerning the synthesis of these molecules and their analogues is the difficulty in selective protection of the two non-anomeric OHs of (+)-noviose. In order to provide a useful solution to this problem, we report here a new strategy of (+)-noviose synthesis, modified from Musicki’s previous study. Dihydrofuranone 8 was thus prepared from l-arabinose and was employed as key intermediate to provide previously unknown 3-O-BOM-Noviose 9 in seven steps (40% overall yield). Compound 9 was then efficiently converted into noviose 1,2-acetonide 6 (66%, two steps), which was otherwise only available from controlled degradation of naturally occurring novobiocin 1.     

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.     

An efficient synthesis of l-allono-1,4-lactone from 2,3:5,6-di-O-isopropylidene-d-mannono-1,4-lactone

We reported herein an efficient synthesis of l-allono-1,4-lactone from 2,3:5,6-di-O-isopropylidene-d-mannono-1,4-lactone in five steps. The key feature of this method involved a one-pot, ‘double inversion’ procedure at the stereocenters of C-4 and C-5 of d-mannono-1,4-lactone to afford the target molecule.     

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.     

Total synthesis of (+)-lentiginosine from d-glucose

A total synthesis of (+)-lentiginosine, a potent and selective amyloglucosidase inhibitor, is reported from a d-glucose-derived epoxide in 38% overall yield. In this synthesis, ambient conditions and readily available starting materials and reagents are used.     

A facile synthesis of a new trihydroxy piperidine derivative and (+)-proto-quercitol from d-(−)-quinic acid

We described herein the new synthesis of a trihydroxy piperidine derivative (1,4,5-trideoxy-1,5-imino-d-ribo-hexitol) and (+)-proto-quercitol from d-(−)-quinic acid, both are considered as inhibitors for glycosidases.     

Synthesis of (+)-amberketal and its analog from l-abietic acid

(+)-Amberketal (1) and its analog (2) have been synthesized from commercially available l-abietic acid (3) by a selective reduction of an unsaturated aldehyde in the presence of a ketone and simultaneous reduction of an iodide using an aqueous suspension of Raney Ni as the key step.     

Total synthesis of d-(+)-biotin

A total synthesis of d-(+)-biotin is described starting from d-(+)-glucosamine using acyliminium chemistry.     

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.     

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.     

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.     

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.     

New pyrano[3,4-b]indoles from 2-hydroxymethylindole and l-dehydroascorbic acid

2-Hydroxymethylindole reacts with l-dehydroascorbic acid under mild conditions to give (3R,3aR,10cS)-3-[(1S)-1,2-dihydroxyethyl]-3a,10c-dihydroxy-3a,5,6,10c-tetrahydrofuro[3′,4′:5,6]pyrano[3,4-b]indol-1(3H)-one. Its tosyl derivative undergoes cyclization to form a pentacyclic ketal derivative.     

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.