New indole aldehydic alkaloids of Strychnos variabilis

Two isomeric pairs of novel indoline aldehydic alkaloids have been isolated from the root barks of Strychnos variabillis. The isomerism finds its origin in the facile isomerisation of C16 and is set up rapidly at room temperature. So, they could be the biogenetic starting point of two series of alkaloids which have a different stereochemistry for C16: the "retuline" series and the epimer "isoretuline" series.