Stereoselective synthesis of rapamycin fragment to build a macrocyclic toolbox.

A stereoselective synthesis of a rapamycin fragment is developed and further utilized toward building a macrocyclic chemical toolbox. The amino alcohol moiety embedded in the 22-membered macrocyclic ring allowed for the addition of a variation in the chiral side chain. The key reactions leading to the synthesis of the rapamycin-derived pyran fragment include the following: (i) Paterson aldol, (ii) stereoselective β-OH carbonyl reduction, and (iii) regio- and stereoselective intramolecular oxy-Michael reaction. The other piece needed for building the macrocyclic diversity was obtained from the coupling of various amino alcohol moieties with S-pipecolic acid.