A new synthesis of the fungallipo-chitooligosaccharideMyc-IV (C16:0, S), which was recently reported to be a major symbioticsignalling molecule in arbuscularmycorrhiza, is described. Key steps include the oxidative cleavage of a 4,6-O-benzylidene acetal to prepare a disaccharidic glycosyl acceptor, and stereoselective glycosylations with 2-methyl-5-tert-butylphenyl thioglycosyl donors.