- Biomimetic synthesis of (±)-galanthamine and asymmetric synthesis of (-)-galanthamine using remote asymmetric induction
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(±)-Galanthamine (1) was synthesized in excellent yield by applying PIFA-mediated oxidative phenol coupling of N-(4-hydroxy)phenethyl-N-(3′, 4′,5′-trialkoxy)benzyl formamide (15b) as a key step. Because of the symmetrical characteristics of the pyrogallol moiety in the substrate (15b), the phenol coupling resulted in a sole coupling product except for volatile components from the oxidizing agent. On the basis of the successful results of the above strategy, (-)-galanthamine (1) was synthesized by employing a novel remote asymmetric induction, where conformation of the seven-membered ring in the product of the phenol coupling was restricted by forming a fused-chiral imidazolidinone ring with D-phenylalanine on the benzylic C-N bond of the tri-O-alkylated gallyl amino moiety. The conformational restriction and successive debenzylation of the protected hydroxyl groups on the pyrogallol ring caused diastereoselective cyclization to yield a cyclic ether having the desired stereochemistry for the synthesis of (-)-1.
- Node, Manabu,Kodama, Sumiaki,Hamashima, Yoshio,Katoh, Takahiro,Nishide, Kiyoharu,Kajimoto, Tetsuya
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p. 1662 - 1679
(2007/10/03)
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- Total synthesis of (-)-galanthamine by remote asymmetric induction
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A pivotal intramolecular Michael addition to form a fused 5,7,5 ring system and the skeleton of (-)-galanthamine (1) was completely controlled by a remote chiral imidazolidinone auxiliary derived from D-phenylalanine (see scheme). This total synthesis of the allylic alcohol 1 avoids the corresponding enone narwedine, a highly allergenic intermediate in previous syntheses of 1.
- Kodama, Sumiaki,Hamashima, Yoshio,Nishide, Kiyoharu,Node, Manabu
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p. 2659 - 2661
(2007/10/03)
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