Complete assignment of the noncarbonylic carbon-13 resonances of Tendamistat

H. Kessler, P. Schmieder, W. Bermel

Biopolymers (1990) 30, 465-475

The complete assignment of all noncarbonylic carbon-13 resonances at natural abundance of the a-amylase inhibitor Tendamistat is presented. Such an assignment can help solve ambiguities in the proton spectrum and forms the basis for further measurements to obtain more structural or dynamic information. Using a non-enriched sample, the low sensitivity due to the small gyromagnetic ratio of 13C to 1H and the low natural abundance of 13C requires sensitive methods to obtain interpretable spectra. Thus all the NMR techniques used incorporate proton detection. With three different techniques, the HMQC, the HMQC with TOCSY-transfer, and the HMBC, a complete assignment based on the published proton chemical shifts was possible with spectra recorded in a reasonable time. Especially the HMBC, which yields correlations via 1H-13C long-range couplings, proved to be extremely valuable in the assignment procedure.