Total synthesis of calonyctin A2, a macrolidic glycolipid with plant growth-promoting activity

Calonyctin A2, a tetrasaccharidic glycolipid having a 22-membered macrolidic structure, has been synthesized by the assembly of three 6-deoxygenated thioglycoside intermediates. The short-step synthesis was achieved by preparation of the most complicated b–c disaccharide unit from phenyl 2,2′:4,6:4′,6′-tri-O-benzylidene-1-thio-β- d -laminaribioside without any glycosidation reaction and by regioselective macrolactonization.