Stereochemical Studies of N,N'-Diacetyl-N,N'-dimethyl-1,2-diamino-1,2-diphenylethanes and their Mono- and Di-thio Analogues by NMR and CD Spectroscopy and by Molecular Mechanics Calculations

The R*,R* and R*,S* diastereomers of N,N'-diacetyl-N,N'-dimethyl-l,2-diamino- 1,2-diphenylethane and their mono- and di-thio analogues (1-6) have been studied by 1H and 13C NMR spectroscopy and by empirical force-field calculations (MMP2-85). The NMR spectral data (chemical shifts, coupling constants and NOE) clearly show that al1 compounds exist in the anti conformation with the Z,Z configuration for the (thio)amide groups. The same result is obtained by the force-field calculations. Four of the compounds (2, 3, 4 and 6) are chiral and have been resolved into enantiomers by chromatography on triacetylcellulose. The CD spectra of the first eluted enantiomers of 4 and 6 could be reasonably well reproduced by calculations based on minimum energy geometries for the S,S enantiomers, whereas no agreement could be reached for 2 and 3. This agrees with the results of the force-field calculations, which predict one predominant conformer for each of 4 and 6 , but significant amounts of two rotamers (both anti ZZ) for each of 2 and 3.