ORGN 532 |
Progress toward the total synthesis of Upenamide
| Zhushou Luo, Kurt Kiewel, and Gary A. Sulikowski. Department of Chemistry, Texas A&M University, College Station, TX 77842 |
| Upenamide 1 is a structurally unique alkaloid isolated from the Indonesian marine sponge Echinochalina (Scheuer JOC 2000, 2858) and features a highly functionalized 20-membered macrocycle possessing both spirooxaquinolizidinone and hemiaminal ring systems. The structure of 1 was elucidated by a combination of spectroscopic techniques. However, the structural information currently available is in agreement with both 27S, 30R, 32R (1a) and 27R, 30S, 32S (1b) configurations due to the inability to assign the absolute stereochemistry of the DE ring. Our general strategy illustrates that the merger of optically active DE fragment (+)-2 and racemic BC fragement (±)-3 by stereoselective formation of the A ring followed by macrocyclization should afford both possible upenamide isomers simultaneously. b-Iodoenecarbamates 5 was used as starting material to construct (+)-2 via remarkably stereoselective cyclization of intermediate 4. A stereoselective Diels-Alder reaction coupled with an intramolecular Staudinger reductive cyclization of 6 were employed to construct spriocyclic fragment (±)-3. 
|
| |
|
|