Differences and sums of traces within, COSY spectra (DISCO) for the extraction of coupling constants: ‘Decoupling’ after the measurement

A procedure is proposed for obtaining coupling constants from phase‐sensitive H,H‐COSY spectra. For this purpose, firstly pseudo‐one‐dimensional spectra are created by co‐addition of individual traces of cross‐peaks, and by a similar addition of diagonal peaks in a spectrum which is phase corrected to pure‐absorption line shapes. The sum and difference of the pseudo‐one‐dimensional spectra of a cross‐peak and its diagonal peak give two spectra, with a pattern in which the active coupling ceases to exist (‘spin decoupling’) but is shifted by half the value of the same. If diagonal peaks are not available owing to overlapping signals, sums and differences of the pseudo‐one‐dimensional spectra of two cross‐peaks can be applied to simplify spectral patterns for the evaluation of J values. The procedure is demonstrated with the example of the AMXY spin system of a tyrosine, and the complex pattern of the Pro⁸ spin system of the cyclic decapeptide antamanide. The conformation of the Pro⁸ ring, derived from the coupling constants thus obtained, is of the _γE type.