Plants of the genus Kopsia (Apocynaceae) continue to
provide novel indole alkaloids with intriguing carbon
skeletons.1–18 Recent examples of unusual alkaloids
from Kopsia which are notable for possessing novel ring
systems and which were postulated to derive from
known monoterpenoid indole precursors through pathways
involving deep-seated rearrangements and/or loss
of key fragments include, inter alia, the cage indole
arbophylline,1 the three-nitrogen pentacyclic indole arboflorine,
2 the tetracyclic indole mersicarpine,3 and the
tetracyclic quinolinic alkaloid, mersilongine.4 We now
report the isolation and structure elucidation of another
novel alkaloid from the leaf extract of Kopsia arborea,
namely, arboricinine (2), representing an intriguing regioisomer
of the new deplancheine-type indole alkaloid,
arboricine (1).