CONFORMATION OF 5-AMINO-5-DEOXYPENTONOLACTAMS

Four configuration isomers of 5-amino-5-deoxy-D-pentonolactam 1a-4a an d their tri-O-acetyl derivatives 1b-4b were studied using NMR and CD s pectroscopy. For all compounds chemical shifts of the H-1 and C-13 nuc lei as well as of vicinal coupling constants were obtained. Comparison of the observed (3)J(H, H) with those calculated for various conforma tions by a modified Karplus relationship led to the assignment of pred ominant conformation H-3(4)(D) or H-4(3)(D) to the lactams 1a-4a and 1 b-4b in solution. The most important factor for determining the confor mation seems to be the pseudoequatorial position of the substituent on the carbon next to the carbonyl group. The results of the CD spectra of the lactams 1a-4a in water, interpreted according to the currently used rules, agreed with the NMR results.