Ajmaline group structure

Aldehyde 198 served as a key intermediate in a synthesis of the alkaloid ajmaline. The. Mannich aminomethylation transform triggers disconnection of two bonds in 198 to form dialdehyde 199, which by connective transform application can be converted to cyclopentene 200.58,59 The reduction in functional group reactivity and in structural complexity are both apparent by comparison of 198 and 200. 

The mass spectra of ajmaline type alkaloids can be divided into three main groups namely, ajmaline (17) and similar compounds widi a H-2P orientation, ajmalidine (15) and other compounds with a 17-keto group, and compounds with a H-2a configuration [e.g. quebrachidine (36)]. For the general features of the mass spectra of ajmaline alkaloids, and the determination of structures with the aid of mass spectra, see Refs. 198-202. 

CH3-C0-C=CH2 and >CH-CH20H follow from n.m.r. and i.r. spectra, that of the two AT-methyl groups from n.m.r. The constitution follows from the mass spectral decomposition which involves two principal fragmentation modes which are shown in Scheme 14. This scheme is supported by, amongst other things, examination of the spectra of 20,21-dihydromacroline (catalytic hydrogenation product), the so-called macralinol (ketone function reduced with lithium aluminium hydride), and structurally related derivatives of ajmaline. ... 

Of the 12 alkaloids belonging to this group occurring in Sri Lankan flora, 11 were encountered in Alstonia macrophylla Wall, of the family Apocynaceae, and the remaining alkaloid was isolated from Taberrtaemon-tana divaricata (L.) Br. ex Roem et Schult. of the same family. Six of the alkaloids were found to be new. Vincamajine (101) and its new derivative, 19-hydroxyvincamajine (102), are two alkaloids of the ajmaline subgroup present in A. macrophylla (82). The structure of 102 was elucidated with the aid of IR, H NMR, and low-resolution MS data. A. macrophylla also... 

The aerial parts of Lebanese Vinca libanotica Zucc. appear to contain 16 alkaloids, of which 12 have so far been isolated these include, in the present group, vincamajine (the major alkaloid), picrinine, quebrachidine, vincamidine, vin-camidine hydrate, herbamine, and herbadine. The structures earlier proposed for herbamine and herbadine have now been shownto be incorrect, and on the basis of mass spectral and 220 MHz n.m.r. data, have been shown to be (113) and (114) respectively. The n.m.r. spectrum of herbamine is very similar to that of vincamajine except for the non-equivalence of the C-21 protons in herbamine. Inspection of models, confirmed by n.m.r. studies in the ajmaline-2-epiajmaline series, indicates... 

Sarpagine-Ajmaline-Picraline Group. Raucaffrinoline from Rauwolfia caffra has been tentatively assigned a structure corresponding to 21,21-0-dihydro-perakine. 

Indole alkaloids of the sarpagme/ajmaline/macroline type comprise one of the most important groups of structurally related natural products. Many compounds of this class of alkaloids have been isolated mainly from the genera Alstonia and Rauwolfia of the family Apocynaceae. ° Much of the early isolation and stmctural work was performed on the Alstonia alkaloids in the laboratories of Elderfield and Schmid and was followed by the biomimetic interconversions of LeQuesne et al. " ... 

Rauwolfia alkaloids a group of about 50 structurally related indole alkaloids firom the roots and rhizomes of various species of Rauwolfa, Aspidosperma and Corynanihe. All R. a. contain a -carbolene skeleton they are classified into 3 types 1. yohimbine (cory-nanthine), 2. ajmaline, 3. serpentine. The large number of R. a. is due to the existence of stereoisomers. Thus Rauwolfia contains seven stereoisomers of yohimbine. 

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