An Asymmetric Total Synthesis of Broussonetine C †

Broussonetine C, a member of the Broussonetia class, was first isolated from the branches of Broussonetia Kazinoki (a deciduous tree distributed throughout Japan, China and Taiwan) in 1997 by Kusano et al.([1,2]) and was assigned structure 1. All of the Broussonetines incorporate a 2,3,4,5-tetrasubstituted pyrrolidine unit as a key motif, probably the most synthetically challenging substructure associated with this class of natural product. Significantly, Broussonetine C was found to exhibit unique beta-galactosidase and beta-mannosidase activities.([1,2]) Such properties, coupled with the unique structure assigned to the alkaloid encouraged us to choose 1 as a novel synthetic target. Thus far, only one asymmetric total synthesis of this pyrrolidine alkaloid has been reported. ([3]) In this report we describe a synthesis of 1, starting from D-arabinose.