The Continuum in 5-Fluorocytosine. Toward Salt Formation

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• 作者：Cec铆lia C. P. da Silva ; Rebeka de Oliveira ; Juan C. Tenorio ; Sara B. Honorato ; Alejandro P. Ayala ; Javier Ellena
• 刊名：Crystal Growth & Design
• 出版年：2013
• 出版时间：October 2, 2013
• 年：2013
• 卷：13
• 期：10
• 页码：4315-4322
• 全文大小：433K
• 年卷期：v.13,no.10(October 2, 2013)
• ISSN：1528-7505

文摘

5-Fluorocytosine (5-FC) was crystallized with complementary dicarboxylic acids, aiming to achieve a controlled synthesis of structures based on the 螖pK_a rule proposed in the salt鈥揷ocrystal continuum study and to provide structural information helpful in the comprehension of its supramolecularity. Although 5-FC tends to be basic, pK_a = 3.26, only three salts are reported. In this way, new 5-FC salts were obtained, the fumaric, maleic and oxalic ones, all crystallizing in the monoclinic space group P2₁/c. In the 5-FC oxalate and fumarate cases, the acid molecules are placed on an inversion center in a fashion that each half molecule exhibits one terminal donor鈥揳cceptor site, leading to the constitution of a 5-FC鈥揳cid鈥?-FC heterodimer. Such a heterodimer is observed in only one donor鈥揳cceptor site of the maleate of 5-FC, whose acid molecule exhibits a closed chain architecture. Infrared and Raman spectra recorded for the three compounds complement the salt characterization on the basis of the extent of proton transfer. Thermal analysis evidence that the salt formation decreases the melting point of the new compounds, ranking this molecule as a coformer candidate to improve the physical properties of other drugs.