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 journalArticlepeer-review

11 Citations (SciVal)

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
JournalRSC Advances
Issue number32
Early online date18 May 2020
DOIs
Publication statusPublished - 31 Dec 2020

Funding

We thank Carbosynth Ltd. (UK) for the donated condelphine (7). We thank Zarqa University, Jordan, for the Studentship to Mr Ashraf M. A. Qasem. We thank the University of Bath for the partial support of Dr Ziyu Zeng.

ASJC Scopus subject areas

  • General Chemistry
  • General Chemical Engineering

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