Stereochemical effects in some acronycine derivatives

The stereochemical effects of 18 natural and synthetic 1,2-dihydro-1,2-disubstituted acronycine derivatives are reported. The conformation of the pyran D ring was determined by using J couplings and NOEs derived from 1D 1H and 2D NOESY spectra and molecular mechanics calculations. In the case of the 1-hydroxy derivatives the influence of the solvent, concentration and temperature on the 1H chemical shifts suggests that aggregation phenomena take place in solution through the formation of an intermolecular hydrogen bond. Aggregation in the gas phase was confirmed by electrospray ionization mass Spectra. The assignment of the 13C chemical shifts was made by 2D NMR techniques. A correlation between the relative stereochemistry at C(1) and C(2) on the D ring and the methyl group carbon chemical shifts was established.