Summary NMR

The configurational analysis based on the extensive use of the proton-proton and carbon-proton NMR coupling constants, also known as J-based configurational analysis (JAB) or Murata methodology, is a standard tool that allows the determination of the relative stereochemistry of asymmetric centers in acyclic systems with large conformational freedom.
We were able to apply successfully this methodology to new natural products that we have isolated (eg. dysithiazolamide) or to a new synthetic analogues such as 5,6-epoxycholestanes, whose relative stereochemistry could not be solved by classical methods. Carbon-proton coupling constants are obtained by two-dimensional NMR methods and they are also compared with those obtained by theoretical calculations by density functional theory methods (DFT).
Our main goal is to solve the limitation of this J-based configurational analysis on acyclic systems where the existence of multiple conformer equilibrium precludes the application of the Murata methodology.
Thus, we have developed the called temperature-dependent J-based configurational analysis, a new strategy based on the measurement comparison of coupling constants at different temperatures in order to the resolution of complex conformer equilibria in flexible acyclic systems. This is achieved by considering the observed tendencies in these values which allows applying the JBA methodology to determine the relative configuration.