Synthesis of l-altro-1-Deoxynojirimycin, d-allo-1-Deoxynojirimycin, and d-galacto-1-Deoxynojirimycin from a Single Chiral Cyanohydrin

Cyclisations and Strategies for Stereoselective Synthesis of Piperidine Iminosugars

This personal account focuses on synthesis of polyhydroxylated piperidines, a subset of compounds within the iminosugar family. Cyclisations to form the piperidine ring include reductive amination, substitution via amines, iminium ions and cyclic nitrones, transamidification (N-acyl transfer), addition to alkenes, ring contraction and expansion, photoinduced electron transfer, multicomponent Ugi reaction and ring closing metathesis. Enantiomerically pure piperidines are obtained from chiral pool precursors (e. g. sugars, amino acids, Garner's aldehyde) or asymmetric reactions (e. g. epoxidation, dihydroxylation, aminohydroxylation, aldol, biotransformation). Our laboratory have contributed cascades based on reductive amination from glycosyl azide precursors as well as Huisgen azide-alkene cycloaddition. The latter's combination with allylic azide rearrangement has given substituted piperidines, including those with quaternary centres adjacent to nitrogen.

Enantioselective synthesis of cyanohydrins catalysed by hydroxynitrile lyases - a review

The first enantioselective synthesis was the selective addition of cyanide to benzaldehyde catalysed by a hydroxynitrile lyase (HNL). Since then these enzymes have been developed into a reliable tool in organic synthesis. HNLs to prepare either the (R)- or the (S)-enantiomer of the desired cyanohydrin are available and a wide variety of reaction conditions can be applied. As a result of this, numerous applications of these enzymes in organic synthesis have been described. Here the examples of the last decade are summarised, the enzyme catalysed step is discussed and the follow-up chemistry is shown. This proves HNLs to be part of main stream organic synthesis. Additionally the newest approaches via immobilisation and reaction engineering are introduced.

Application of sequential proline-catalyzed α-chlorination and aldol reactions in the total synthesis of 1-deoxygalactonojirimycin

A short enantioselective total synthesis of 1-deoxygalactonojirimycin (migalastat) has been achieved that does not rely on chiral pool starting materials or biocatalysis. Instead, this synthesis exploits a one-pot proline-catalyzed α-chlorination and aldol reaction of a commercially available aldehyde to assemble the entire carbon skeleton in a single step. The key role played by a nitrogen protecting group in the final epoxide opening reaction is highlighted as is the amenability to access structural analogues using this route.

Efficient diastereoselective synthesis of a new class of azanucleosides: 2'-homoazanucleosides

Azanucleosides, sugar-modified nucleoside analogues containing a 4' nitrogen atom, have shown a lot of therapeutic potential, e.g. as anti-cancer and antiviral agents. We report the synthesis of a series of 2'-homoazanucleosides, in which the nucleobase is attached to the 2'-position of the pyrrolidine ring via a methylene linker. A suitable orthogonally protected iminosugar was synthesized by ring closing metathesis and dihydroxylation as key steps and further converted to a series of 8 nucleoside analogues through Mitsunobu reaction with suitably protected nucleobases. The 5' position of the adenine analogue was then further derivatized with thiols to afford 2 additional compounds. The final compounds were evaluated for biological activity.

Chiral disubstituted piperidinyl ureas: a class of dual diacylglycerol lipase-α and ABHD6 inhibitors

Inhibitors of diacylglycerol lipases and α,β-hydrolase domain containing protein 6 (ABHD6) are potential leads for the development of therapeutic agents for metabolic and neurodegenerative disorders. Here, we report the enantioselective synthesis and structure activity relationships of triazole ureas featuring chiral, hydroxylated 2-benzylpiperidines as dual inhibitors of DAGLα and ABHD6. The chirality of the carbon bearing the C2 substituent, as well as the position of the hydroxyl (tolerated at C5, but not at C3) has profound influence on the inhibitory activity of both DAGLα and ABHD6, as established using biochemical assays and competitive activity-based protein profiling on mouse brain extracts.

Six-Step Syntheses of (-)-1-Deoxyaltronojirimycin and (+)-1-Deoxymannonojirimycin from N-Z-O-TBDPS-l-serinal

Highly stereoselective six-step syntheses of (-)-1-deoxyaltronojirimycin (altro-DNJ) and (+)-1-deoxymannojirimycin (manno-DNJ) from N-Cbz-O-TBDPS-l-serinal are described. Key transformations involve a two-step preparation of a functionalized dihydropyridin-3-one as a common intermediate followed by Luche reduction and dihydroxylation (for altro-DNJ). The same sequence employing an epoxidation/epoxide opening in place of dihydroxylation furnishes manno-DNJ.

CuAAC click chemistry with N-propargyl 1,5-dideoxy-1,5-imino-D-gulitol and N-propargyl 1,6-dideoxy-1,6-imino-D-mannitol provides access to triazole-linked piperidine and azepane pseudo-disaccharide iminosugars displaying glycosidase inhibitory properties

Protecting group-free synthesis of 1,2:5,6-di-anhydro-D-mannitol, followed by ring opening with propargylamine and subsequent ring closure produced a separable mix of piperidine N-propargyl 1,5-dideoxy-1,5-imino-D-gulitol and azepane N-propargyl 1,6-dideoxy-1,6-imino-D-mannitol. In O-acetylated form, these two building blocks were subjected to CuAAC click chemistry with a panel of three differently azide-substituted glucose building blocks, producing iminosugar pseudo-disaccharides in good yield. The overall panel of eight compounds, plus 1-deoxynojirimycin (DNJ) as a benchmark, was evaluated as prospective inhibitors of almond β-glucosidase, yeast α-glucosidase and barley β-amylase. The iminosugar pseudo-disaccharides showed no inhibitory activity against almond β-glucosidase, while the parent N-propargyl 1,5-dideoxy-1,5-imino-D-gulitol and N-propargyl 1,6-dideoxy-1,6-imino-D-mannitol likewise proved to be inactive against yeast α-glucosidase. Inhibitory activity could be reinstated in the former series by appropriate substitution on nitrogen. The greater activity of the piperidine could be rationalized based on docking studies. Further, potent inhibition of β-amylase was observed with compounds from both the piperidine and azepane series.

Palladium-catalyzed vicinal amino alcohols synthesis from allyl amines by in situ tether formation and carboetherification

Vicinal amino alcohols are important structural motifs of bioactive compounds. Reported herein is an efficient method for their synthesis based on the palladium-catalyzed oxy-alkynylation, oxy-arylation, or oxy-vinylation of allylic amines. High regio- and stereoselectivity were ensured through the in situ formation of a hemiaminal tether using the cheap commercially available trifluoroacetaldehyde in its hemiacetal form. The obtained compounds are important building blocks, which can be orthogonally deprotected to give either free alcohols, amines, or terminal alkynes.

Metathesis access to monocyclic iminocyclitol-based therapeutic agents

By focusing on recent developments on natural and non-natural azasugars (iminocyclitols), this review bolsters the case for the role of olefin metathesis reactions (RCM, CM) as key transformations in the multistep syntheses of pyrrolidine-, piperidine- and azepane-based iminocyclitols, as important therapeutic agents against a range of common diseases and as tools for studying metabolic disorders. Considerable improvements brought about by introduction of one or more metathesis steps are outlined, with emphasis on the exquisite steric control and atom-economical outcome of the overall process. The comparative performance of several established metathesis catalysts is also highlighted.

Imino sugars and glycosyl hydrolases: historical context, current aspects, emerging trends

Forty years of discoveries and research on imino sugars, which are carbohydrate analogues having a basic nitrogen atom instead of oxygen in the sugar ring and, acting as potent glycosidase inhibitors, have made considerable impact on our contemporary understanding of glycosidases. Imino sugars have helped to elucidate the catalytic machinery of glycosidases and have refined our methods and concepts of utilizing them. A number of new aspects have emerged for employing imino sugars as pharmaceutical compounds, based on their profound effects on metabolic activities in which glycosidases are involved. From the digestion of starch to the fight against viral infections, from research into malignant diseases to potential improvements in hereditary storage disorders, glycosidase action and inhibition are essential issues. This account aims at combining general developments with a focus on some niches where imino sugars have become useful tools for glycochemistry and glycobiology.

The synthesis and biological evaluation of 1-C-alkyl-L-arabinoiminofuranoses, a novel class of α-glucosidase inhibitors

The asymmetric synthesis of 1-C-alkyl-l-arabinoiminofuranoses 1 was achieved by asymmetric allylic alkylation (AAA), ring closing metathesis (RCM), and Negishi cross coupling as key reactions. Some of the prepared compounds showed potent inhibitory activities towards intestinal maltase, with IC(50) values comparable to those of commercial drugs such as acarbose, voglibose, and miglitol, which are used in the treatment of type 2 diabetes. Among them, the inhibitory activity (IC(50)=0.032μM) towards intestinal sucrase of 1c was quite strong compared to the above commercial drugs.