Quinolizidines. XVI. Chiral syntheses of 9-demethylcephaeline and 10-demethylcephaeline

In order to establish the structure of the Alangium alkaloid demethylcephaeline, chiral syntheses of the two possible alternative structures, (-)-9-demethylcephaeline (1) and (-)-10-demethylcephaeline (2), have been accomplished through a "cincholoipon-incorporating route." The synthesis of (-)-2 started with an initial condensation of the tricyclic acid (-)-12b, prepared from the ester (-)-11b by alkaline hydrolysis, with 3-benzyloxy-4-methoxyphenethylamine and proceeded through the intermediates (-)-13b, (+)-15b, and (-)-14b. The 1\u27-epimers (-)-18b and (-)-17 were also produced in this reaction sequence. A parallel sequence of conversions starting with (+)-15a afforded (-)-1 via the intermediate (-)-14a, together with the 1\u27-epimer (-)-16 via (-)-18a. Unfortunately, however, lack of a sufficient amount of natural (-)-demethylcephaeline for a detailed and direct comparison precluded identification of either (-)-1 or (-)-2 with this alkaloid, leaving its chemistry incomplete

Quinolizidines. XV. A Racemic Synthesis of 10-Demethyltubulosine, an Alkaloid from Alangium lamarckii

The racemic synthesis of the Alangium lamarckii alkaloid 10-demethyltubulosine (2) has been accomplished for the first time via a "lactim ether route, "which included the intermediates (±)-7,(±)-8,(±)-10,and (±)-9. The 1\u27α-H isomers (±)-12 and (±)-11 were also obtained through this synthetic route. The assignments of the configuration at C-1\u27of (±)-2,(±)-9,(±)-11,and (±)-12 were based on four criteria, namely, the ratio of products from the catalytic reduction of (±)-10,thin-layer chromatographic mobility, and ^1H and ^C nuclear magnetic resonance spectral features. The identity of synthetic (±)-2 with (-)-demethyltubulosine from A. lamarckii unequivocally established the structure of this alkaloid

Quinolizidines. XXIV. : Syntheses of Ankorine Congeners in Different Oxidation States

8-Hydroxyprotoemetine [(-)-2f], an aldehyde of biogenetic interest, has been synthesized for the first time from the tricyclic ester (-)-5 through the intermediate (-)-6. Wolff-Kishner reduction of (-)-2f produced the 2-ethyl congener (-)-2g. As a result of these syntheses, the circular dichroism (CD) spectra of (-)-2f・HClO_4 and (-)-2g in 0.1 N aqueous HCl and in EtOH, together with those of the Alangium alkaloids ankorine (2d) and alancine (2e), are now availale

Quinolizidines. X. Stereospecific Syntheses of (±)-9-Demethylpsychotrine and (±)-10-Demethylpsychotrine

With the aim of establishing the structure of the Alangium alkaloid desmethylpsychotrine, stereospecific syntheses of two alternative structures, (±)-9-demethylpsychotrine (1) and (±)-10-demethylpsychotrine (2), have been achieved through a"lactim ether route."The synthesis of (±)-1 started with an initial condensation of the lactim ether 6,derived from the translactam ester 5,with 3-benzyloxy-4-methoxyphenacyl bromide (7a) and proceeded through the intermediates 8a, 9a, 10c, 10a, 11a, 12a, 13a, 14a, and 15a. A parallel sequence of conversions starting with 6 and 4-benzyloxy-3-methoxyphenacyl bromide (7b) produced (±)-2. The ^C nuclear magnetic resonance spectra of (±)-1 and (±)-2 confirmed their endocyclic double bond structure in the dihydroisoquinoline moiety. Spectral comparison of (±)-1 and (±)-2 with natural desmethylpsychotrine suggested formula 1 to be the most likely structure of this alkaloid

Quinolizidines. XI. Structure determination of the Alangium alkaloid desmethylpsychotrine through synthetic incorporation of ethyl cincholoiponate into (+)-9-demethylpsychotrine

With a view to establishing the structure of the Alangium alkaloid desmethylpsychotrine, (+)-9-demethylpsychotrine [(+)-1] has been synthesized from ethyl cincholoiponate [(+)-6] and 3-benzyloxy-4-methoxyphenacyl bromide by the "cincholoipon-incorporating method" through the intermediates (+)-7,8,10-(+)-14,and (+)-17-(+)-22. The identity of synthetic (+)-1 with natural desmethylpsychotrine unequivocally established the structure of this alkaloid