Swainsonine total synthesis

As an example of the usefulness of the Sharpless asymmetric epoxidation the enantioselective synthesis of (-)-swainsonine and an early note by Nicolaou on the stereocontrolled synthesis of 1, 3, 5...(2n + 1) polyols, undertaken in connection with a programme directed towards the total synthesis of polyene macrolide antibiotics, such as amphotericin B and nystatin Aj, will be discussed. 

An ab initio study of the 2 + 2-cycloadditions of allene to isocyanic acid and ketene to vinylimine found the reactions to be concerted and mostly asynchronous.28,29 The diastereoselective 2 + 2-cycloaddition of dichloroketene with a chiral enol ether (26) produced the cyclobutanone (27), which leads to a key intermediate (28) in (g) the total synthesis of the natural alkaloid (-)-Swainsonine (29) (Scheme 8).30 The... 

The absolute configuration of (-)-swainsonine (1) was deduced on the basis of its biosynthesis and unambiguous nuclear magnetic resonance assignments.The relative stereochemistry of swainsonine was determined by X-ray crystallography. Noncarbohydrates have been used for the total synthesis of swainsonine and its isomers.The first total synthesis of 1 has established its absolute stereochemistry as (15, 2i ,8i ,8ai )-... 

Polyhydroxylated indolizidine alkaloids, due to their biological activity, have attracted considerable synthetic interest. The total synthesis of ( —)-l-qp/-swainsonine (250) from the chiral imine 238 (Scheme 58) and the parallel synthesis of (+ )-2,8,8a-tri-qp/-swainsonine (252) from the enantiomeric threose A-benzylimine 251, prepared from natural L-tartaric acid, provide further examples of the utility of tartaric acid in meeting the challenge of complex syntheses. A stereospecific 4 + 4 homologation utilizing 2-(trimethylsiloxy)furan (178) pro-... 

The novel nitrenium ion-mediated alkene bis-functionalization used by Bowen and Wardrop in their synthesis of swainsonine (cf Scheme 76 Section 3.5.2) also featured in their total synthesis of (-f)-castanospermine (654) (Scheme 90). The derivatized xylopyranoside (+)-681, prepared in four steps fixrm D-xylose, was converted in stepwise fashion into lactone (—)-682 by rearrangement of the allyl ether to the corresponding enol ether, hydrolysis to a mixture of lactol anomers, and oxidation. Carefijl methano-lysis in the presence of camphorsulfonic acid and adjustment of the pH to 7... 

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