A new approach to the C28 fatty acid chain of the marine natural products schulzeines B and C: a concise diastereoselective total synthesis of(−)-schulzeine B

An enantioselective approach to the C28 fatty acid chain of the marine natural products schulzeines B and C was established based on the l-tartaric acid derived C4 chiron 11 via successive 1,4-bis-chain elongation reactions and catalytic asymmetric hydrogenation. The chiral tricyclic core 8 was constructed via a diastereoselective Pictet–Spengler cyclization reaction (dr = 89:11) of the l-glutamic acid derived precursor 13. On this basis, a concise total synthesis of (−)-schulzeine B (5) was disclosed.