The asymmetric synthesis of the C15C23unit of Leptomycin B (LMB) is described. All four stereocenters of the C15C23unit were prepared from one building block exhibiting only one stereocenter. This building block was synthesized via either an enzymatic transformation or starting from a chiral reagent.Key words: Leptomycin, natural product synthesis, enzymatic transformation, Aldol reaction, Pseudomonas fluorescence lipase (PFL).