Diastereoselective Synthesis of 1-Deoxygalactonojirimycin, 1-Deoxyaltronojirimycin, and N-Boc-(2S,3S)-3-Hydroxypipecolic Acid via Proline Catalyzed α-Aminoxylation of Aldehydes

Recent advances in the total synthesis of polyhydroxylated alkaloids via chiral oxazines

This review summarizes recently established methodologies developed for the enantioselective and diastereoselective synthesis of chiral 1,3-oxazines. These compounds are of interest as advanced synthetic intermediates in the total synthesis of structurally complex and biologically active polyhydroxylated alkaloids such as (+)-1-deoxynojirimycin, (-)-anisomycin, (+)-castanospermine, (+)-casuarine, (-)-conduramine F-1, (-)-sphingofungin B, Neu5Ac methyl ester, and other natural products. The devised synthetic approach aims to offer a direct, efficient, and adaptable method for obtaining both pure enantiomers and pure diastereomers. It revolves around utilizing chiral building blocks like syn,syn-, syn,syn,anti-, syn,anti-, syn,anti,syn-, anti,syn-, anti,syn,syn-, and anti,syn,anti-oxazines. By integrating oxazine chemistry with established and innovative transformations, this approach enabled the synthesis of 30 polyhydroxylated amines across various studies conducted between 2007 and 2022.

Preparation of 1,6-di-deoxy-d-galacto and 1,6-di-deoxy-l-altro nojirimycin derivatives by aminocyclization of a 1,5-dicarbonyl derivative

Iminosugars are known glycosidase inhibitors which are the subject of drug development efforts against several diseases. The access to structurally-related families of iminosugars is of primary importance for running structure-activity relationship studies. In this work, the double reductive amination (aminocyclization) reaction of a dicarbonyl derivative of the l-arabino series, in turn obtained from lactose, is reported. Different ratios of 1,6-di-deoxy-d-galacto and 1,6-di-deoxy-l-altro nojirimycin derivatives were obtained depending on the amine employed in this transformation which provided an insight into the effects of their structure on the outcome of the reaction. Of particular interest were the results obtained when two enantiomeric amino acids (d-Phe-OMe and l-Phe-OMe) were used, which resulted in the inversion of the reaction stereoselectivity.

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.

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.

Stereoselective synthesis of (+)-1-deoxyaltronojirimycin

A stereocontrolled, facile and high-yield approach for producing (+)-altroDNJ, has been developed starting from the inexpensive commercial cis 2-butene-1,4-diol. Sharpless epoxidation and a subsequent dihydroxylation were used for the introduction of all stereocentres; finally, the ring closure under basic conditions afforded the piperidine heterocycle.

[1,4]-sigmatropic rearrangement of chiral nitrones and their utilization in the synthesis of new iminosugars

A new mechanism of nitrone epimerization via [1,4]-sigmatropic rearrangement was proposed and a set of epimeric iminosugars was synthesized.