Dynamic aspects of the stereochemistry of phenothiazines in solution : Part 2. Segmental motion and conformational analysis of the side-chain in promazines

Some promazines and the model compound NN-dimethyl-3-phenylpropylamine have been studied, as protonated and unprotonated species, by 1H and 13C n.m.r. spectroscopy. 13C T1 relaxation times have shown that the mobility of the dimethylaminopropyl chain in chloroform solution varies depending on whether the chain is protonated or unprotonated, and whether it is attached to a phenyl or to a tricyclic system. Segmental motions were also detected in two compounds. The conformation of the side-chain has been deduced for different solvents. Remarkably, for protonated promazines the preferred conformations are gauche for the Cα-Cβ fragment and trans for the Cβ-Cγ in chloroform as well as in water solution, whereas the model compound exists preferentially in the fully extended trans–trans-conformation. In dioxan and in DMSO the population of the αβ-gauche forms decreases. The presence and the nature of the 2-substituent do not appear to have any effect, whereas the tricyclic system is predominant in the stabilization of the αβ-gauche form. This has been related to the ability of these molecules to aggregate in solution with a vertical stacking-type association.