Stereoselective synthesis of 1,4-dideoxy-1,4-imino-d-allitol and formal synthesis of (2S,3R,4S)-3,4-dihydroxyproline

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.

A short, efficient, and stereoselective total synthesis of a pyrrolidine alkaloid: (-)-codonopsinine

An efficient total synthesis of antibiotic (-)-codonopsinine 1 with an overall yield of 44% was achieved from d-alanine as a chiral template. The key steps in our strategy are modified Sharpless asymmetric dihydroxylation reaction and the highly stereoselective intramolecular acid-catalyzed amidocyclization.

Synthesis ofd- andl-2,3-trans-3,4-cis-4,5-trans-3,4-Dihydroxy-5-hydroxymethylproline and Tripeptides Containing Them

Enantiomerically pure (-)-(1R,4R,5R,6S)- and (+)-(1S,4S,5S,6R)-7-(tert-butoxycarbonyl)-5,6-exo-isopropylidenedioxy-7-azabicyclo[2.2.1]hept-2-one ((-)-3 and (+)-3) have been obtained from the Diels-Alder adduct of N-(tert-butoxycarbonyl)pyrrole and 2-bromo-1-(p-toluenesulfonyl)acetylene, including the Alexakis optical resolution of ketone (+/-)-3 via formation of cyclic aminals with (1R,2R)-diphenylethylenediamine. Compounds (-)-3 and (+)-3 were converted into d- and l-2,3-trans-3,4-cis-4,5-trans-N-(tert-butoxycarbonyl)-5-hydroxymethyl-3,4-isopropylidenedioxyprolines (-)-4 and (+)-4, respectively. Applying the Boc and Fmoc strategies of peptide synthesis, these compounds were used to construct two tripeptides containing the d- or l-2,3-trans-3,4-cis-4,5-trans-3,4-dihydroxy-5-hydroxymethylproline.