<jats:p><jats:bold>Macrocarpamine, a new bisindole alkaloid from <jats:italic>Alstonia macrophylla</jats:italic> W<jats:sc>ALL</jats:sc>.</jats:bold><jats:p>A new bisindole alkaloid give the name (−)‐macrocarpamine (<jats:bold>3</jats:bold>) was isolated from the bark of Alstonia macrophylla W<jats:sc>ALL</jats:sc>. Under pyrolytic conditions <jats:bold>3</jats:bold> is cleaved into the two known bases (+)‐pleiocarpamine (<jats:bold>2</jats:bold>) and (−)‐anhydro macrosalhin‐methin (<jats:bold>5</jats:bold>) <jats:italic>(Scheme 1)</jats:italic>. The structure of <jats:bold>3</jats:bold> (including relative configuration) was deduced on the basis of chemical evidence and from its UV.‐, IR.‐, NMR.‐ and mass spectroscopic data.