“…[10] Aretrosynthetic analysis for natural glycosides 5a-c [5a: (2S,3S)-wallichoside, 5b:( 2 R,3S)-wallichoside, 5c:p teroside B],t he precursors of the target natural glycosides 1-3,i s shown in Scheme 1. [11] Thetotal synthesis of 2 was investigated first (Scheme 2). Theaglycons 7a, 7b,and 9 are also natural products known as (2S,3S)-pterosin C, (2R,3S)-pterosin C, and (2R)-pterosin B, [10] respectively.T he b-hydroxyketone moieties of 7a and 7b could be constructed by an organocatalytic intramolecular asymmetric aldol reaction of the aromatic ketoaldehyde 11.A lthough the relative stereochemistry of the aldol reaction could not be predicted at this stage,b oth the syn and anti isomers were required because they are both constituents of the natural products, and the interconversion between them seemed possible by epimerization at C2.…”