S. Grzesiek and A. Bax (1993) J. Biomol. NMR 3 185-204. (Link to Article)
Minimum labelling: 15N, 13C
This experiment is similar to the CBCAC(CO)NH: magnetisation is transferred from 1Hα and 1Hβ to 13Cα and 13Cβ, respectively, and then from 13Cβ to 13Cα. From here it is transferred first to13CO, then to 15NH and then to 1HN for detection. The chemical shift it not evolved on any of the carbon atoms. Instead, it is evolved on the 1Hα and 1Hβ, the 15NH and 1HN. This results in a three-dimensional spectrum with one nitrogen and two hydrogen dimensions.
This is a useful spectrum for obtaining Hα and Hβ assignments, but isn’t necessarily a must.