SYNTHESIS AND CONFORMATIONAL-ANALYSIS OF A BRIDGED ANABASINE AND RELATED-COMPOUNDS - A NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY AND MOLECULAR MODELING STUDY

The synthesis and conformational analysis of a ''bridged'' anabasine, 5,8,9,10,11,11a-hexahydro-6H-pyrido[2,1-f][1,6] naphthyridine (5), and related compounds are reported. Conformational assignments were made using NMR data (including coupling constants, homonuclear Overhauser e ffects, and 2D correlations) and the results of molecular mechanics (M M2) calculations. The tricyclic compounds have trans-quinolizidine rin g fusion with a chair-shaped piperidine ring. The center ring shows a half-chair conformation for the title compound, and a half-boat shape for its 6-oxo derivative. Calculated vicinal coupling constants are in good agreement with those obtained experimentally.