Abstract
Bisindole natural products consist of two monomeric indole alkaloid units as their obligate constituents. Bisindoles are more potent with respect to their biological activity than their corresponding monomeric units. In addition, the synthesis of bisindoles are far more challenging than the synthesis of monomeric indole alkaloids. Herein is reviewed the enantiospecific total and partial synthesis of bisindole alkaloids isolated primarily from the Alstonia genus of the Apocynaceae family. The monomeric units belong to the sarpagine, ajmaline, macroline, vobasine, and pleiocarpamine series. An up-to-date discussion of their isolation, characterization, biological activity as well as approaches to their partial and total synthesis by means of both synthetic and biosynthetic strategies are presented.
Highlights
Indole alkaloids are of extraordinary significance due to their structural diversity, medicinal properties and are an essential part of the drug discovery process [1].Their medicinal values are evident from folklore and their ethnopharmacological uses worldwide stem from ancient times [2,3,4,5]
This study study confirmed the conversion of the earliersarpagine by Woodward
Bi et al [86].15The from 49 following thereported same procedure reported for the total synthesis of alstonerine by enone
Summary
Indole alkaloids are of extraordinary significance due to their structural diversity, medicinal properties and are an essential part of the drug discovery process (see the Merck Index for details) [1]. This review is focused on the partial and total synthesis of bisindoles, as well as some dimeric indole alkaloids wherein at least one of the following monomeric units contains, as its obligate constituent, the sarpagine, macroline, ajmaline, vobasine, or pleiocarpamine systems. Because of the complexity of their structures, which are comprised of more than one alkaloidal partner, a convergent approach toward their synthesis is logical synthetically, as well as biosynthetically This breaks down to synthesis of the monomeric alkaloidal units, followed by a biomimetic-type condensation to arrive at the bisindole framework. As always one of the main hurdles in natural product related drug-discovery is that many natural products are present in very small quantities and cannot be isolated in quantities high enough to study their biological activity let alone structure-activity relationships This situation is exacerbated in the case of bisindole alkaloids. Biosynthetic between ajmaline reported by Stöckigt et al [62,63,64]
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