Total syntheses of bengamides B and E

Total syntheses of the cytotoxic marine natural products bengamides B and E are described. Both bengamides are prepared via amide coupling of a protec ted polyhydroxylated lactone intermediate 9 with a suitably substituted ami nocaprolactam intermediate. Lactone 9 is prepared in five steps from commer cially available alpha-(D)-glucoheptonic gamma -lactone. The key reactions are a selective deprotection of a 1,2-acetonide in the presence of a 1,3-ac etonide and an (E)-selective olefination of an unstable aldehyde using a ge m-dichromium reagent. The bengamide B lactam intermediate 10 is prepared in seven steps from commercially available (5R)-5-hydroxy-L-lysine (12). The desired S-configuration at the gamma -OH lactam position is established usi ng the Mitsunobu reaction.