Serendipitous discovery of a pH-dependant atropisomer bond rotation: toward a write-protectable chiral molecular switch?

J Chromatogr B Analyt Technol Biomed Life Sci. 2008 Nov 1;875(1):118-21. doi: 10.1016/j.jchromb.2008.08.028.

Abstract

Owing to slow rotation of a sterically constrained dimethylamide substituent, two slowly interconverting enantiomers of a preclinical candidate for pharmaceutical development, 1, (6-(3-Chloro-4-fluoro-benzyl)-4-hydroxy-2-methyl-3,5-dioxo-2,3,5,6,7,8-hexahydro-[2,6]naphthyridine-1-carboxylic acid dimethylamide) are observed by chiral chromatography. Isolation of pure enantiomer by preparative chiral chromatography followed by enantiopurity analysis over time allowed for a study of the kinetics of enantiomer interconversion under a variety of conditions. Relatively slow racemization was observed in alcohol solvents, with a half life on the order of 5-10 h. A dramatic influence of aqueous buffer pH on racemization was noted, with higher pH leading to rapid racemization within a few minutes, and lower pH leading to essentially no racemization for periods up to a week. A hypothesis explaining this unusual effect of pH on carboxamide bond rotation is offered, and some suggestions for potential utility of such a system are considered.

MeSH terms

  • Amides / chemistry*
  • Chromatography, High Pressure Liquid / methods*
  • Circular Dichroism
  • Dimethylamines / chemistry*
  • Hydrogen-Ion Concentration
  • Naphthyridines / chemistry*
  • Optical Rotation*
  • Spectrophotometry, Ultraviolet

Substances

  • (6-(3-chloro-4-fluoro-benzyl)-4-hydroxy-2-methyl-3,5-dioxo-2,3,5,6,7,8-hexahydro-(2,6)naphthyridine-1-carboxylic acid dimethylamide)
  • Amides
  • Dimethylamines
  • Naphthyridines