Quinolizidines. XXVIII. Racemic and chiral syntheses of ochromianine, an indoloquinolizidine alkaloid from Neisosperma miana

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A full account is given of the first racemic and chiral syntheses of 11-methoxydihydrocorynantheol [(-)-1], a candidate structure for the Neisosperma alkaloid ochromianine. Coupling of (±)-trans-6-ethoxy-3-ethyl-2,3,4,5-tetrahydro-4-pyridineacetic acid ethyl ester [(±)-6] with 2-chloro-1-(6-methoxy-1H-indol-3-yl)ethanone (4) in the presence of KBr produced the lactam ketone (±)-7,which was then converted into the lactam (±)-9 through the oxazolium salt (±)-8. Bischler-Napieralski cyclization of (±)-9 followed by catalytic hydrogenation gave the tetracyclic ester (±)-11. On reduction with LiAlH_4,(±)-11 yielded the racemic target (±)-1. A parallel synthetic route starting from (+)-6 and 4 afforded the chiral target (-)-1 via (+)-7,8,(+)-9,and (-)-11. Identity of synthetic (-)-1 with ochromianine unequivocally established the structure and absolute stereochemistry of this alkaloid.
公益社団法人日本薬学会の論文
1991-01-25