NMR elucidation of a novel (S)‐pentacyclo‐undecane bis‐(4‐phenyloxazoline) ligand and related derivatives

Abstract

The NMR elucidation of a novel ligand (S)-pentacyclo-undecane bis-(4-phenyloxazoline) and related pentacyclo-undecane (PCU) derivatives is reported. Two-dimensional NMR proved to be a powerful technique in overcoming the difficulties associated with the elucidation of these compounds when only one-dimensional NMR data is utilized. A chiral substituent was introduced to both 'arms' of the PCU skeleton to produce derivatives 1-3. These derivatives display C(1) symmetry with all thecage atoms being nonequivalent. Owing to overlapping of peaks in the (1)H spectra, identification of these diastereomeric protons was very difficult. The (13)C spectra gave rise to clear splitting of the nonequivalent carbons. This is unusual compared to similar PCU derivatives with chiral substituents as splitting of all the diastereomeric cage carbons has not yet been reported. Nuclear Overhauser enhancement spectroscopy (NOESY) correlations of derivatives 1-3 confirm the different conformations of the molecule in which the side 'arms' occupy different orientations with respect to cage moiety.

Synthesis and NMR elucidation of novel pentacycloundecane‐based peptides

“…One would therefore expect a 3 J ‐coupling constant of about 2–3 Hz according to the Karplus relationship 33. However, in all our previous NMR studies5–11, 14, 28, 34 of the PCU skeleton, this fine coupling constant is never observed. The 1 H NMR spectrum of the peptide 2 (Fig.…”

“…The NOESY spectra of the PCU cage normally show5–10 correlations of H‐4a with H‐2 and H‐6, whereas H‐4s shows correlations with H‐9 and H‐10, also NOESY and COSY spectra of PCU cage normally show correlations of H‐4a (δ = 1.26 ppm) and H‐4s (δ = 1.72 ppm) with H‐3 and H‐5 (δ = 2.30 ppm and/or 2.15 ppm).…”

“…Our group has reported NMR studies of pentacycloundecane (PCU)‐based compounds in a bid to understand how the ‘cage’ skeleton relates to its side ‘arms’ (Fig 1). 5–11 As part of our studies to utilise NMR spectroscopy in the elucidation of PCU derivatives, the synthesis and NMR evaluation of two PCU peptides are reported herein.…”

NMR elucidation of novel SQ109 derivatives

“…NMR and computational study of 'cage' molecules such as pentacycloundecane and trishomocubane based compounds has been a major focus of our group for the past 5 years [25][26][27][28][29][30][31][32][33][34][35][36]. We recently reported the NMR elucidation of pentacycloundecane based tetraamines [37,38] which were screened for their anti-tuberculosis activities [39].…”

Synthesis and NMR elucidation of novel pentacyclo-undecane diamine ligands

“…However, the emergence of a range of standard 2D NMR techniques has helped a great deal in overcoming these problems. Our group has successfully used 2D NMR techniques to elucidate numerous PCU derivatives [12][13][14][15][16][17][18][19][20][21]. Odisitse et al [22] recently reported potent anti-inflammatory activity for the PCU diamine 9; this discovery led to the design and synthesis of compounds 3-8 which are currently being investigated as potential inflammatory agents while compounds 1 and 2 are precursors to 3 and 4. triethylamine was refluxed under nitrogen for 36 h to obtain the novel compounds 18 and 19.…”