The 1α-hydroxy-A-rings of norditerpenoid alkaloids are twisted-boat conformers.

ABSTRACT: The skeletal conformations of naturally occurring norditerpenoid alkaloids fix their substituent functional groups in space, thereby directing their bioactivities. Solution conformations of the A-rings of 4 selected norditerpenoid alkaloid free bases: mesaconitine, karacoline (karakoline), condelphine, and neoline (bullatine B), were analysed by NMR spectroscopy and single-crystal X-ray crystallography. They adopt twisted-chair, twisted-boat, twisted-boat, twisted-boat conformations, respectively. That the A-ring is stabilised in a boat conformer by an intramolecular H-bond from 1α-OH to the N-ethyl tertiary amine is also confirmed in the condelphine single crystal data. The conformations are a result of through-space repulsion between 12-H_e' and atoms attached to C1 (in

SUBMITTER: Zeng Z 

PROVIDER: S-EPMC9053968 | biostudies-literature | 2020 May

REPOSITORIES: biostudies-literature