Stereoselective Synthesis of the C27-C48 Moiety of Aflastatin A by a Carbohydrate Strategy Using a Tin(II)-Mediated Aldol Reaction

The C27-C48 segment of aflastatin A was synthesized by using d-mannoside and l-erythrulose derivatives as chiral building blocks. The aldol reaction of undecan-2-one with mannolactone and a subsequent reduction gave the C37 and C39 stereogenic centers with high selectivity. Another aldol reaction of a tin(II) enolate of a protected erythrulose (C27-C30 segment) with a C31-C48 aldehyde segment gave the C30,C31-syn adduct with the desired stereochemistry. Deprotection of the assembled product proceeded smoothly to give the C27-C48 segment of aflastatin A containing a contiguous polyol moiety.