A concise synthesis of (−)-lentiginosine via an anti,syn-oxazine

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.

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.

Recent applications of the Wittig reaction in alkaloid synthesis

The Wittig reaction is the chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide (the Wittig reagent) to afford an alkene and triphenylphosphine oxide. Noteworthy, this reaction results in the synthesis of alkenes in a selective and predictable fashion. Thus, it became as one of the keystone of synthetic organic chemistry, especially in the total synthesis of natural products, where the selectivity of a reaction is paramount of importance. A literature survey disclosed the existence of vast numbers of related reports and comprehensive reviews on the applications of this important name reaction in the total synthesis of natural products. However, the aim of this chapter is to underscore, the applications of the Wittig reaction in the total synthesis of one the most important and prevalent classes of natural products, the alkaloids, especially those showing important and diverse biological activities.

Novel stereocontrolled syntheses of tashiromine and epitashiromine

A novel stereocontrolled approach has been developed for the syntheses of tashiromine and epitashiromine alkaloids from cyclooctene β-amino acids. The synthetic concept is based on the azetidinone opening of a bicyclic β-lactam, followed by oxidative ring opening through ring C-C double bond and reductive ring-closure reactions of the cis- or trans-cyclooctene β-amino acids.

Enantioselective syntheses of (R)-pipecolic acid, (2R,3R)-3-hydroxypipecolic acid, β-(+)-conhydrine and (−)-swainsonine using an aziridine derived common chiral synthon

Concise total syntheses of (R)-pipecolic acid, (2R,3R)-3-hydroxypipecolic acid and formal syntheses of β-(+)-conhydrine, (−)-lentiginosine, (−)-swainsonine and -1,2-di-epi-swainsonine have been accomplished starting from a common chiral synthon.

Chirality extension of an oxazine building block en route to total syntheses of (+)-hyacinthacine A2 and sphingofungin B

Concise total syntheses of (+)-hyacinthacine A₂ and sphingofungin B were achieved by palladium(0)-catalyzed intramolecular oxazine formation and diastereoselective nucleophilic additions.