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 language | English |
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Pages (from-to) | 18797-18805 |
Journal | RSC Advances |
Issue number | 32 |
Early online date | 18 May 2020 |
DOIs | |
Publication status | Published - 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