Ervatamine-type alkaloids

The seeds of Centaurea moschata contain alkaloids with a 5-hydroxyindole structural unit, namely moschamine 87, moschamindole 88, and moschaminindolol 89 <1997MI189>. Ervatamine-type indole alkaloids, for example, 6-oxo-16,20-episilicine 90, 16,20-episilicine, and 6,16-didehydro-20-episilicine have been isolated from Ervatamia officinalis <2005HCA2537>. 

The chemical conversion of alkaloids of the vobasine type into those of the ervatamine type can readily be effected, using a modified Polonovski reaction. This involves formation of an N-oxide and its rearrangement, using trifluoroacetic anhydride as reagent. Dregamine (65) has been converted into 20-epi-ervatamine... 

Quite the most intriguing new indole alkaloidal structural type to appear this year is that of ervatamine (17b) which occurs, together with 20-epi-ervatamine (17c) and 19,20-dehydroervatamine (17a), in Ervatamia orientalis.26a A description of the degradations (Scheme 5) which led to the structural assignments is included in this sub-section on the basis of a possible biogenetic relationship to alkaloids in this class (see below). 

Applying the Potier-Polonovski reaction, vobasine-type indole alkaloids such as vobasine, dregamine, and tabernaemontanine could be transformed into dehydroervatamine, 20-epiervatamine, and ervatamine, respectively (70). 

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