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

Autor: Zeng Z; Department of Pharmacy and Pharmacology, University of Bath Bath BA2 7AY UK prsisb@bath.ac.uk., Qasem AMA; Department of Pharmacy and Pharmacology, University of Bath Bath BA2 7AY UK prsisb@bath.ac.uk., Kociok-Köhn G; Material and Chemical Characterisation (MC2), University of Bath Bath BA2 7AY UK., Rowan MG; Department of Pharmacy and Pharmacology, University of Bath Bath BA2 7AY UK prsisb@bath.ac.uk., Blagbrough IS; Department of Pharmacy and Pharmacology, University of Bath Bath BA2 7AY UK prsisb@bath.ac.uk.
Jazyk: angličtina
Zdroj: RSC advances [RSC Adv] 2020 May 18; Vol. 10 (32), pp. 18797-18805. Date of Electronic Publication: 2020 May 18 (Print Publication: 2020).
DOI: 10.1039/d0ra03811c
Abstrakt: 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 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.
Competing Interests: There are no conflicts to declare.
(This journal is © The Royal Society of Chemistry.)
Databáze: MEDLINE
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