5-Fluoro-2′-deoxycytidine was synthesized by treating 5-fluoro-2′-deoxyuridine with 2,4,6-trimethylphenol in the presence of 1-methylpyrrolidine and trifluoroacetic anhydride, followed by aminolysis. Among N-acetyl, pivaloyl, and benzoyl, N-acetyl was found to be suitable for the protection of the exocyclic amine of 5-fluoro-2′-deoxycytidine because of the stability of the N⁴-protected nucleoside under acidic conditions and its ease of removal after solid-phase synthesis. This modified nucleoside was incorporated into d(CG)₆ sequences through the phosphoramidite chemistry-based solid-phase synthesis. Circular dichroism experiments suggest that replacement of 2′-deoxycytidine with 5-fluoro-2′-deoxycytidine does not lead to detectable conformational changes, either in the B- or Z-form. ¹⁹F NMR spectroscopy of d(CG)₆ containing 5-fluoro-2′-deoxycytidine revealed that B/Z-DNA transition induced by sodium chloride is likely initiated at terminal ends, leading to unwinding at the middle of duplexes, and eventual switch of handedness when sodium chloride concentration reaches a threshold value.

中文翻译：

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5-氟-2'-脱氧胞苷作为探针通过¹⁹ F NMR光谱研究B / Z-DNA的转变

通过在1-甲基吡咯烷和三氟乙酸酐存在下用2,4,6-三甲基苯酚处理5-氟-2'-脱氧尿苷来合成5-氟-2'-脱氧胞苷，然后进行氨解。在N-乙酰基，新戊酰基和苯甲酰基中，由于N ^4-保护的核苷在酸性条件下的稳定性及其稳定性，发现N-乙酰基适合于保护5-氟-2'-脱氧胞苷的环外胺。固相合成后易于去除。将此修饰的核苷掺入d（CG）₆通过基于亚磷酰胺化学的固相合成进行测序。圆二色性实验表明，用5-氟-2'-脱氧胞苷替换2'-脱氧胞苷不会导致可检测的构象变化，无论是B型还是Z型。含有5-氟-2'-脱氧胞苷的d（CG）_6的¹⁹ F NMR光谱显示，氯化钠诱导的B / Z-DNA过渡可能在末端引发，导致双链体中间解开，并最终转换氯化钠浓度达到阈值时的惯性。