Tautomerism and Site of Protonation of 1-Methylcytosine: Proof by Nuclear Magnetic Resonance Spin-Spin Coupling

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Science  20 Dec 1963:
Vol. 142, Issue 3599, pp. 1569-1571
DOI: 10.1126/science.142.3599.1569


New nuclear magnetic resonance data lead to a completely unambiguous proof that the predominant tautomeric form of 1-methylcytosine is the amino form and that in acid solution the molecule protonates at 3-N. The close similarity of the nuclear magnetic resonance spectra of this compound to the spectra of the cytosine nucleosides indicates that these structures also exist in the nucleosides. These conclusions are reached on the basis of the spectra of analogs labeled with N15 and of the proton spin decoupling measurements made at low temperature.