Indole alkaloids spectroscopy

Recently Isolated Sarpagine-Related Indole Alkaloids Spectroscopy... 

Two important books on the biogenesis of indole alkaloids have been published (5, 6), therefore we do not intend to cover the literature of the biogenesis of corynantheine- and yohimbine-type alkaloids. Our chapter begins with the structure elucidation of the alkaloids isolated during the past two decades and proceeds with the synthesis, transformation, as well as spectroscopy of the alkaloids in question. 

Results and data gathered on mass spectroscopy of various indole alkaloids have been summarized by Hesse (320). The derivation of the characteristic fragments of indolo[2,3-a]quinolizidines has been interpreted by Gribble and Nelson (321), who investigated C-3, C-5, C-6, C-20, and C-21 deuterated derivatives of octahydroindolo[2,3-a]quinolizine (1). Kametani et al. have observed and proved, with labeled compounds, a methyl transfer from the ester function of reserpine derivatives to the basic nitrogen atom during mass-spectroscopic measurement (322). 

Dr. Crabb has updated his review on alkaloids which appeared in Volume 6A of this series. This valuable report includes a timely account of the published work on indole alkaloids. A previous review on the 13C NMR spectroscopy of steroids has been brought up to date by Professor W. B. Smith. The more theoretical aspects of dynamic NMR are covered by Dr. Witanowski and his co-workers. Finally, it is a pleasure to include a review on 119Sn NMR spectroscopy for the first time in this series. 

The biosynthesis of terpenoid indole alkaloids from tryptophan has long been known.1,2 In new experiments with DL-[2-14C,2, 3 - 3C2]tryptophan [as (94)], this has been confirmed for vindoline (106).35 Incorporation measured by assay for radioactivity and by n.m.r. spectroscopy was the same, thus indicating an intact incorporation (with loss, of course, of the carboxy-group) (for discussion of the particular application of 13C labelling used here, see pp. 1-2). 

Three dimeric indole alkaloids of a new type, peceyline, peceylanine, and pelankine, have been isolated from a Sri Lankan apocynaceous plant, Petchia ceylanica Wight.876 The structures of these bases were determined mainly by n.m.r. spectroscopy. In their H spectra, all three alkaloids exhibit four aromatic singlets, one olefinic hydrogen multiplet, two methoxycarbonyl singlets, two N-methyl singlets, and two C-methyl doublets. One half of the non-aromatic carbon resonances in the 13C spectra show that one monomer unit is common to all three alkaloids, and inspection reveals that this unit must be based on vincorine... 

Another alkaloid example was studied by UIC C—N correlation spectroscopy [41]. Spectra of the indole alkaloid vincamine 20 were acquired as H-C HMBC with 2048 x 160 data points and H—N IMPEACH-HMBC with 1024 X 96 data points. The calculated correlation map was called C—N HMBC-IMPEACH. It provided a high number of correlations, which were considered to hamper structure elucidation more than to enhance. 

The latest structure for VLR (leurosine, vinleurosine) (55) was obtained primarily by analytical methods like i.r., n.m.r., and mass spectroscopy. No structure has yet been proposed for VRD (leurosidine, vinrosidine), leurosivine, or rovidine. An additional number of dimeric indole bases (24 out of the total of 72 alkaloids isolated) have been obtained from Catharanthus, but they seem to be devoid of anti-tumour activity. 

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