Macroline-type indole alkaloids

Table 3 Macroline-type indole alkaloids—cont d...

The stem-bark extract of the Malayan Alstonia macrophylla provided in addition to seven known alkaloids, three new indole alkaloids, lO-methoxyaflinisine (334), 10-methoxy-cathafoline (335) and alstonerinal (336) [226]. The latter is a type A macroline and coeluted with the known type B macroline, alstonerine (337) during chromatography, and proved resistant to further resolution by chromatography or fractional crystallization. Eventually a pure sample was obtained by reduction of a mixture of 336 and 337 to yield the isomeric alcohols 338 and 339, followed by oxidation of338 to yield alstonerinal (336). 

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. 

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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