A New Route to 3-Amino Sugars. A Concise Synthesis of l-Daunosamine and d-Ristosamine Derivatives

An asymmetric aldol strategy has been developed for the synthesis of l-daunosamine and d-ristosamine derivatives starting from noncarbohydrate precursors. Lithium and boron enolate mediated aldol reactions of 12 with O-TBS lactaldehyde gave non-Evans syn and Evans syn aldol products, respectively, with high selectivity. The chemical efficiency of the lithium enolate reactions were higher than the corresponding reactions with the boron enolates. Curtius rearrangement of lactone acids 23 and 26 gave the corresponding N-BOC amino lactones 30 and 32 in 64% and 62%, respectively, with complete retention of configuration. Lactone 30 was converted by a two-step sequence to N-benzoyldaunosamide 40. The overall yield for the amino sugar 40 was 18% over six steps. Similarly, lactone 32 was converted to N-benzoylristosamide 42 with an overall yield of 18% starting from 12.