Structure Reassignment of Melonine and Quantum-Chemical Calculations-Based Assessment of Biosynthetic Scenarios Leading to Its Revised and Original Structures

Melonine
is a basic monoterpene indole alkaloid (MIA) skeleton
from Melodinus philliraeoides that
was reported in 1983. The scarcity of its spectroscopic data questioned
the validity of its structure. This prompted us to reisolate this
molecule and to revise its structure into an unprecedented MIA scaffold.
DFT-validated biosynthetic paths to both this new core and the originally
reported form are proposed. The pathway to the original structure
of melonine seems to be thermodynamically feasible, and that compound
may exist as a natural product.