Conformational studies on tocinamide and deaminotocinamide by 220 MHz nuclear magnetic resonance spectroscopy.

The 220 MHz spectra of tocinamide and deaminotocinamide, the ring moieties of oxytocin and of deamino-oxytocin, respectively, were investigated in [U-(2)H]dimethylsulfoxide solution. Extensive decoupling and exchange experiments allow complete spectral assignment and determination of many coupling constants. Circular dichroism spectra assigned a right-hand screw sense to the C-S-S-C group. The conformations of tocinamide and deaminotocinamide are different from each other and from those suggested for the ring portions of oxytocin and deamino-oxytocin. The relationship of this difference to biological activity is commented upon. The importance of the interaction of the side chain with the ring in oxytocin and deamino-oxytocin is emphasized.