Nuckoddes and nucleotides : part 28 [ 1 ] . l 3 C - NMR spectra of 2 ' - deoxycytldine and 3 - deaza - 2 ' - deoxycytidine

3-D*aza-2'-d*ozycytidin* (d(3-d*azaC)) it a structural analogu* of 2'-d*ozycytidin* (dC) and was shown to react in a different manner as a S'-triphosphate [2] and at a template nucleotide [3] on in vitro polymerization. In thit connection the tautomeric equilibrium of d(3-d*azaC) with its imino-enol form was investigated by C-NMR spsctroscopy. Using solvents with gradually changing hydrmtion properties (dimethyl sulfozide/water miztures) d(3-d*azaC) was measured and compared to dC the tautomeric equilibrium of which is mostly on th* amino-lactam sid* in both solvents (cf. Figure and Table}. The assignments of the H-decoupled signals are bas*d on H, C hetaronuclear correlation sp«ctra (data not shown) and on C-NMR spectra of cytidine from th* literature. Th* assignment of C(4) and C(2) of d(3-d*azaC) was confirmed by a fully coupled C-NMR spectrum in dg-dimethyl sulfozid* (JCH(163.05 ppm) = 6.2 Hz, broad*n*d doublet; JCH(157.74 ppm) = 9.7 Hz, doublet). The H-NMR spectrum of d(3-deazaC) in dg-dimelhyl sulfozide shows two ami no protons at 6.1 ppm (not thown). Therefore, du* to th* relatively small differences b*tw**n th* curves of the same carbon atom of both substrates (Figured it is concluded that no substantial thift of th* taulomeric equilibrium toward* th* imino-enol form of d(3-d*azaC) tak*t plac* through th* replacement of dimethyl sulfozid* with wal*r. I thank Prof. Ch. Tamm for his interest in th*s* investigations. They were supported by th* Swiss National Sci*nc* Foundation. Iihli;C-NME Data of dC (I) and of d(3Referencet: [1] Part 27: Charezuk, R. & Tamm, Ch. deazaC) 0 0 .(Hl-deeouple d algous In ppm (1987) Helv. Chim. Acta 70, 717-725. [2] Wachtl, M., relaliw to external TMS.) Kohler, P. Si Tamm, Ch. (1980) Helv. Chim. Acta 63, 2495-2302. [3] Charcruk, R., Tamra, Ch., Suri, B. Si Bickle, Th. A. (1986) Nucleic Adds Res. 14, 9530.