Recent progress in the chemistry of indole alkaloids and mould metabolites

Abstract

Volume 38 in the Manske-Brossi series of alkaloid monographs contains a review of recent work on the ergot alkaloids;' and Volume 39 includes a survey of the betalains2" and a summary of recent syntheses and antitumour activity of ellipticine and related alkaloids.2* In a second review, the same author has discussed synthetic approaches to the ellipticine group via metalation and cycloaddition ~h e m i s t r y . ~ Volume 5 in the series ' Studies in Natural Product Chemistry' contains chapters on applications of NMR spectroscopy to structure el~cidation,~" and the mass spectrometry of the

Recent progress in the chemistry of the monoterpenoid indole alkaloids

“…44 ( )-Anhydromacrosalhine methine 82, one of the components of the bisindole alkaloid, macrocarpamine, has been obtained by partial synthesis from (+)-ajmaline 83, and also by total synthesis. 45 The hemicaetal 84, previously prepared 46 from ajmaline as shown in Scheme 16, was first dehydrated to deoxyalstonerine 85. Since allylic bromination at C-19 in 85 failed, it was subjected to regioselective oxyselenation by means of N-(phenylselenyl)phthalimide.…”

“…The product, however, did not contain the meloscine ring system, but was shown, by X-ray crystal structure analysis, to have the structure 191, and is clearly the result of a remarkable rearrangement in which carbon atoms 6 and 16 have exchanged positions via two 1,5-sigmatropic shifts (Scheme 29). This result prompted a reassessment of the rearrangement of 5-cyanovincadifformine 16-chloroindolenine 192, which had earlier 46 been postulated to give the -carboline derivative 193. Reinterpretation of the NMR spectrum of this product, which was very similar to that of of 191, led to its reformulation as the -carboline derivative 194 (Scheme 30).…”

“…103 The long-range 1 H, 15 N couplings and 15 N chemical shifts have been assigned for navelbine (5 -noranhydrovinblastine) by application of gradient-enhanced HMQC for the observation of long-range heteronuclear couplings at natural abundance. 104 Kuehne and Bandarage 105 have improved the enantioselectivity of an earlier synthesis 46 of vinblastine by making use of a chiral auxiliary derived from ferrocene for the construction of the vital intermediate 270. In this improved approach the indoloazepine ester 152 was alkylated on N b by 2-diphenylphosphinyl-(S)--ferrocenylethyl acetate 271, and the product 272 was condensed with the chiral protected aldehyde 273, under milder conditions than are normally adopted for condensations of this kind.…”

Recent progress in the chemistry of indole alkaloids and mould metabolites

“…Three new alkaloids have been isolated134 from RauwolJia serpentinu cell cultures grown in the presence of added ajmaline, in addition to raumacline (232) and its derivatives, which were described earlier,54. 98 and (in trace amounts) suaveoline. The first of these new alkaloids was shown to be 6a-hydroxyraumacline (233), a conclusion which was confirmed by partial synthesis of (233) from ajmaline (234), via the knowngx intermediate (235) (Scheme 38).134a The second alkaloid was shown from its spectroscopic data to be simply isoraumacline (236) again this was confirmed by partial synthesis, on this occasion from isoajmaline (237) via the intermediate (238), the route followed being exactly analogous to that used in the conversion of ajmaline into raumacline (Scheme 38).…”

Recent progress in the chemistry of the monoterpenoid indole alkaloids

“…Apodihydrocinchonamine (30) is a new alkaloid found in the leaves of Isertia haenkeana DC., together with dihydroquinamine (3 1) and epidihydroquinamine (32). '* A thorough analysis of the NMR spectra of these last two alkaloids resulted in the elucidation of their stereochemistry, and a complete reinterpretaton of the spectroscopic and physical data earlier reported.…”