1. The carbon-13 nmr spectra of formycin and formycin B were just presented by T. R. Krugh at the 13th ENC, Asilomar, California, 1972. Krugh suggested that the line broadening observed in the spectra of the formycins was caused by tauto-merism of the labile proton.
2. The assignments are based on off-resonance decoupling data and comparison with certain model compounds. A manuscript describing the experimental details and all model compounds studied is in preparation.
3. All chemical shifts were corrected for temperature with regard to the standard employed. The method used is described in Table I.
4. Carbon-13 magnetic resonance. X. Six-membered nitrogen heterocycles and their cations