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Stereochemical Assignment of Diastereomeric Imidazolidinone‐Ring‐Containing Bicyclic Sugar‐Peptide Adducts: NMR Spectroscopy and Molecular Calculations
Author(s) -
Roščić Maja,
Eklund Robert,
Nordmark EvaLisa,
Horvat Štefica,
Widmalm Göran
Publication year - 2004
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.200400391
Subject(s) - chemistry , diastereomer , bicyclic molecule , ring (chemistry) , intramolecular force , stereochemistry , moiety , nuclear magnetic resonance spectroscopy , chemical shift , adduct , organic chemistry
A combination of NMR spectroscopy and molecular simulations is used to determine trans / cis configurational features of two diastereomeric bicyclic imidazolidinone compounds obtained by intramolecular cyclization of the monosaccharide ester of leucine‐enkephalin related to D ‐glucose. The stereochemical assignment of the five‐membered imidazolidinone ring system was performed by consideration of long‐range proton‐proton coupling observed between protons at C2 and C4 in the COSY spectrum of the major isomer only. A long‐range 4 J H,H coupling across the nitrogen atoms is larger in the trans isomer than in the cis . In addition, comparison of these results with the NMR spectroscopic data obtained for the major isomer of D ‐galactose‐related imidazolidinone and those previously obtained by X‐ray methods for the corresponding minor isomer, show that the substituents attached to the imidazolidinone ring moiety in the studied compounds preferentially adopt the trans (2 R ,4 S ) orientation. The experimental results were complemented by density functional theory calculations of NMR‐observable parameters, such as 1 H and 13 C chemical shifts and 4 J H,H coupling constants, performed on simplified imidazolidinone ring systems. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)