Macroline-related alkaloids

The amino acid derived carboxy group can be utilized as a functionality for further synthetic manipulations, e.g. for cyclization reactions to 1,3-bridged P-carbolines, using the Dieckmann reaction, a promising stereocontrolled approach to macroline-related alkaloids (Scheme 14). > ... 

Synthesis of Sarpagine/Macroline-Related Indole Alkaloids... 

Pandicine (312), an air-sensitive, amorphous alkaloid from the leaves of Pandacastrum saccharatum Pichon, has a novel structure composed of macroline and highly oxygenated tabersonine units.135 Its structure was elucidated mainly by comparison of its H and 13C n.m.r. spectra with those of the macroline unit in villalstonine and the oxygenated tabersonine unit in cryophylline. There is at present no definitive proof for the relative stereochemistry of the two components of the pandicine molecule that depicted in (312) is simply based on the stereochemistry deduced for related monomers, namely talcarpine and hazuntinine. Presumably the ease of oxidation of pandicine is due to the facile formation of the quinonoid species (313). 

Alstonisidine (alkaloid A) [C42H48N4O4 mp 325° [a] — 234° (EtOH)] was first isolated by Elderfield and Gilman from the aerial bark of Alstonia muelleriana 48) but its structure (56) has only recently been elucidated 39). The indoline portion of this structure resembles macroline (57) and may well be derived from it or from a common precursor the second unit is related to quebrachidine (58) and the linkage between the two components is of a novel kind. 

Advances in the chemistry of macroline, sarpagine, and ajmaline-related indole alkaloids 06T8655. 

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. " ... 

Illustrated in Tables 2—6 are the structures of the recently isolated (since year 2000) sarpagine-related indole alkaloids, along with their key physicochemical properties. They have been classified into sarpagine-type, macroline-type, ajmaline-type, sarpagine/macroline oxindoles, and bisindole alkaloids containing sarpagine/macroHne monomeric units for ease of illustration. 

Table 5 Macroline/sarpagine-related oxindole alkaloids...

Indole alkaloids of the sarpagjne/macroline/aimaline type comprise one of the largest groups of structurally related indole natural products. New alkaloids of this type are being isolated with an increasing frequency... 

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