5 dl-CYCLEANINEの合成

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Cycleanine, (O,O-dimethylisochondodendrine), a bisbenzylisoquinoline alkaloid, was first isolated from Cyclea and Stephania genera (Menispermaceae), and the structure of which was elucidated as formula 1. The synthesis of this alkaloid, however, had remained unsuccessful. CuO-catalysed Ullmann condensation of dl-8-bromoarmepavine gave only 4a. Methylation of 4a with diazomethane followed by sodium-liquid ammonia fission gave proof for the structure 4a. In the course of an attempted synthesis of 4a by an alternative route, Bischler-Napieralski cyclization of amide 10 and 8 was effected, and it was found that, in both case, the cyclization proceeds in two directions i.e., ortho and pare positions with respect to the substituted phenoxyl group. Although cyclization products were not differentiated chromatographically, sodium-liquid ammonia treatment of N-methyl-tetrahydroisoquinolines, derived from the cyclization products, gave two phenolic bases 3a and 11. Synthesis of dl-cycleanine was achieved through Bischler-Napieralski reaction of cyclobisamide 22. N-CBZo-carboxylic acid (16) and amino ester (14) were condensed to give an amide (17), which was converted to the corresponding amino acid p-nitrophenyl ester (21). Intramolecular condensation of (21) afforded the cyclobisamide (22) in 17% yield. Bischler-Napieralski cyclization of 22 followed by NaBH_4 reduction and N-methylation gave a mixture of bisbenzylisoquinolines. dl-Cycleanine (A), diastereoisomer of cycleanine (B), and an isomer of cycleanine (C) were isolated in chrystalline state. The structure of the products were confirmed by IR, NMR, and mass spectral comparisons with natural cycleanine. The structure 25 for the isomeric base C was proved further by sodium-liq. ammonia treatment which gave 11 as the sole bisected product.
天然有機化合物討論会の論文
1966-09-15

5 dl-CYCLEANINEの合成

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