title: Diastereoselective synthesis of bridged polycyclic alkaloids via tandem acylation/intramolecular Diels-Alder reaction.
abstract: A mild and efficient stereoselective synthesis of hexacyclic indole alkaloids with a tetrahydro-β-carboline motif has been developed by utilizing the Pictet-Spengler reaction and tandem N-acylation followed by intramolecular Diels-Alder cyclization. Initially, a diene unit was installed in the tetrahedron β-carboline skeleton through Pictet-Spengler cyclization of the corresponding aldehyde with tryptophan ester. The dienophile moiety was introduced by N-acylation of tetrahydro-β-carboline. Successive, in situ, [4 + 2] intramolecular Diels-Alder cycloaddition of the activated dienophile and conjugated diene containing intermediate furnished bridged polycyclic heterocycles with high diastereoselectivity. Formation of four new rings, five new covalent bonds, and five new chiral centers with excellent stereoselectivity is the key feature of this strategy. The diastereoselective formation of product was attributed to intramolecular chirality transfer through a chiral amino acid. The stereoselective outcome of this tandem reaction was confirmed by X-ray crystallographic studies. The developed synthetic strategy was also explored on a soluble polymer support to incorporate the advantage of rapid synthesis and a high-throughput workup process toward the development of a green synthetic protocol for polycyclic alkaloids.
authors.affiliation: Department of Applied Chemistry, National Chiao Tung University , Hsinchu 300-10, Taiwan, Republic of China.
authors.forename: Chih-Hau
authors.initials: CH
authors.lastname: Chen
authors.forename: Gorakh S
authors.initials: GS
authors.lastname: Yellol
authors.forename: Cheng-Hsun
authors.initials: CH
authors.lastname: Tsai
authors.forename: Prashant B
authors.initials: PB
authors.lastname: Dalvi
authors.forename: Chung-Ming
authors.initials: CM
authors.lastname: Sun
mesh_terms: D000215:Acylation; D000470:Alkaloids / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D061565:Cycloaddition Reaction; D006572:Heterocyclic Compounds, Bridged-Ring / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D011083:Polycyclic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D000470:Alkaloids; D006572:Heterocyclic Compounds, Bridged-Ring; D011083:Polycyclic Compounds