13C and 1H NMR investigations of quinic acid derivatives: Complete spectral assignment and elucidation of preferred conformations

✍ Scribed by Angelina Flores-Parra; Dora Marina Gutiérrez-Avella; Rosalinda Contreras; Françoise Khuong-Huu

• Publisher: John Wiley and Sons
• Year: 1989
• Tongue: English
• Weight: 551 KB
• Volume: 27
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/mrc.1260270607

✦ Synopsis

The 'H and 13C NMR spectra of 23 quinic acid derivatives are reported. The complete assignment of the 'H NMR spectra using selective proton decoupling experiments allowed the conformation of the six membered ring to be established from vicinal coupling constants and the calculation of dihedral angles. The ''C spectral assignments were made by consideration of substituent effects and comparison within the series. In some cases the similarities in chemical shifts did not allow unambiguous assignments; the chemical shifts were then calculated from empirical parameters.

KEY WORDS I3C and 'H NMR assignment Conformation Quinic acid derivatives

Introduction

A series of quinic acid derivatives were prepared during the synthetic approach to the enterocine antibiotic.lV2 Here we describe the complete 'H and I3C NMR characterization of these compounds, which allowed the conformation of the six-membered ring to be derived.

The proton coupling constants of quinic acid (l), the parent compound of this series, demonstrated the existence of a conformational equilibrium. This finding led us to investigate the conformer equilibrium ratio and to re-examine the 13C NMR data previously reported by Kelley et aL3 EXPERIMENTAL Compounds