References:
A. Bax and M. Ikura (1991) J. Biomol. NMR 1 99-104. (Link to Article)
S. Grzesiek and A. Bax (1992) J. Magn. Reson. 96 432-440. (Link to Article)

Minimum labelling: ¹⁵N, ¹³C

Dimensions: 3

The magnetisation is passed from ¹H to ¹⁵N and then to ¹³CO. From here it is transferred to ¹³Cα and the chemical shift is evolved. The magnetisation is then transferred back via ¹³CO to ¹⁵N and ¹H for detection. The chemical shift is only evolved for the ¹H^N, the ¹⁵N^H and the ¹³Cα, but not for the ¹³CO. This results in a spectrum which is like the HNCA, but which is selective for the Cα of the preceding residue.

This experiment can be useful for backbone assignment when used in conjunction with the HNCA, HNCO and HN(CA)CO if the CBCANNH and CBCA(CO)NNH spectra are of bad quality.