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Conformational studies on indole alkaloids from Flustra foliacea by NMR and molecular modeling
Author(s) -
MoralesRíos Martha S.,
SantosSánchez Norma F.,
SuárezCastillo Oscar R.,
JosephNathan Pedro
Publication year - 2002
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1080
Subject(s) - chemistry , steric effects , pyrrolidine , molecular mechanics , stereochemistry , ring (chemistry) , nuclear magnetic resonance spectroscopy , indole test , twist , two dimensional nuclear magnetic resonance spectroscopy , heteronuclear single quantum coherence spectroscopy , envelope (radar) , molecular model , proton nmr , computational chemistry , molecular dynamics , organic chemistry , telecommunications , radar , geometry , mathematics , computer science
1 H and 13 C NMR assignments for 1a–4a and 1b–4b were obtained using HSQC, HMBC and NOESY techniques. Differences and ambiguities from literature assignments are reconciled. For the pyrrolidine C‐ring, the combined use of NMR spectroscopy and molecular mechanics calculations revealed that this ring exists in a dynamic conformational equilibrium between twist ( 2 T 1 ) and envelope‐twist ( 1 E– 1 T 2 ) conformations. In chloroform‐ d 1 , the 1 H NMR coupling constants indicate that the pyrrolidine ring is biased in favor of the envelope‐twist conformation. Steric requirements of the N ‐prenyl group enhanced the envelope‐twist ( 1 E– 1 T 2 ) conformation populations. Copyright © 2002 John Wiley & Sons, Ltd.