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

Ziyu Zeng, Ashraf M.A. Qasem, Gabriele Kociok-Köhn, Michael G. Rowan, Ian S. Blagbrough

Research output: Contribution to journalArticle

1 Citation (Scopus)

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 theN-ethyl tertiary amine is also confirmed in the condelphine single crystal data. The conformations are a result of through-space repulsion between 12-He′and atoms attached to C1 (in the equatorial positions). This causes the A-rings with 1α-OR always to be twisted whether in a chair or a boat conformation. The impact of these studies is in providing a detailed understanding of the shape of the A-ring of these important biologically active natural product alkaloids.

Original languageEnglish
Pages (from-to)18797-18805
Number of pages9
JournalRSC Advances
Volume10
Issue number32
Early online date18 May 2020
DOIs
Publication statusE-pub ahead of print - 18 May 2020

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)

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