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Structural Studies of Norditerpenoid Alkaloids: Conformation Analysis in Crystal and in Solution States
Author(s) -
Zeng Ziyu,
KociokKöhn Gabriele,
Woodman Timothy J.,
Rowan Michael G.,
Blagbrough Ian S.
Publication year - 2021
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.202100179
Subject(s) - chemistry , steric effects , cyclohexane conformation , crystal structure , protonation , stereochemistry , ring (chemistry) , crystallography , nuclear magnetic resonance spectroscopy , aconitine , molecule , organic chemistry , hydrogen bond , ion , chromatography
Conformational analyses are presented of several pharmacologically important norditerpenoid alkaloids (NDAs), in crystal and in solution states. Crystal data of 8 NDAs (4 free bases and 4 salts) were obtained, in which crassicauline A, aconitine HCl, and methyllycaconitine HClO 4 are reported for the first time. 1D/2D NMR spectroscopies of 7 NDAs (5 free bases and 2 salts) were recorded comprehensively. Crystal conformations of NDAs are described with a revised cyclohexane ring nomenclature. The A/E‐rings of NDA‐free bases exist in twisted‐chair/twisted‐chair conformations, leading to examples of the 1 H NMR effect of steric compression shown in the A‐ring. The A/E‐rings of NDA salts adopt boat/chair crystal conformations, as does the protonated synthetic [3.3.1]azabicycle in its crystal lattice. However, in aqueous solutions at physiological pH, this protonated analogue adopts a true chair/true chair conformation where the NDA salts retain their twisted boat/twisted chair conformations.