Molecular disorder in (‒)-encecanescin

Area of Science:

• Natural Product Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Eupatorium aschembornianum is a plant source of natural compounds.
• (‒)-Encecanescin (1) is a specific compound isolated from this plant.
• Understanding molecular conformation is crucial for structure-activity relationship studies.

Purpose of the Study:

• To isolate and elucidate the structure of (‒)-Encecanescin (1).
• To investigate the conformational behavior of (‒)-Encecanescin using computational methods.
• To validate experimental NMR data with theoretical calculations.

Main Methods:

• Isolation of (‒)-Encecanescin from Eupatorium aschembornianum leaves.
• Structure elucidation using 1D and 2D NMR techniques (gHSQC, gHMBC, NOESY).
• Conformational analysis via Monte Carlo searches, molecular mechanics, and DFT calculations (B3LYP/6-31G* and B3LYP/6-311++G(d,p)).
• Calculation of magnetic isotropic shielding tensors using GIAO/B3LYP/6-311++G(d,p).

Main Results:

• (‒)-Encecanescin (1) was successfully isolated and its structure confirmed.
• Two conformers were observed in the crystal structure due to molecular disorder.
• Computational modeling identified the three most stable conformers (2-4).
• A strong linear correlation was established between experimental and calculated NMR chemical shifts for protons and carbon atoms.

Conclusions:

• The study provides accurate molecular models for the conformational behavior of (‒)-Encecanescin.
• The findings validate the use of DFT calculations for predicting NMR properties.
• This work enhances the understanding of (‒)-Encecanescin's structure and conformational dynamics.