Density functional theory study of the preferred conformation of geissoschizine

摘要

Density functional theory(DFT) study of the hitherto proposed structurs of geissoschiine(1) has proved that the strucure(1A) having hydrogne bond between the enol hydroxyl and Nb functions iwth a trans-quinolizindine-type C/D ring and twistboat D ring(proposed by van Tamelen and Wright) is the most stable one.A strong contribution of the zwitterionic species (1a') to 1a is suggested together with the reasons by 1a' was not foudn as a local minimum.Calculations of ~1H-adn ~(13)C-NMR chemical shifts based on this structure also support its structure.