Abstract
An ionic liquids-based ultrasound-assisted extraction (ILUAE) method was successfully developed for extracting shikimic acid from conifer needles. Eleven 1-alkyl-3-methylimidazolium ionic liquids with different cations and anions were investigated and 1-benzyl-3-methylimidazolium bromide solution was selected as the solvent. The conditions for ILUAE, including the ionic liquid concentration, ultrasound power, ultrasound time, and liquid-solid ratio, were optimized. The proposed method had good recovery (99.37%–100.11%) and reproducibility (RSD, n = 6; 3.6%). ILUAE was an efficient, rapid, and simple sample preparation technique that showed high reproducibility. Based on the results, a number of plant species, namely, Picea koraiensis, Picea meyeri, Pinus elliottii, and Pinus banksiana, were identified as among the best resources of shikimic acid.
Highlights
Shikimic acid is a white crystalline cyclitol, which is a precursor material for industrial synthesis of the important drug, oseltamivir phosphate (Tamiflu), which is an effective drug against the H5N1 influenza virus [1], especially if administered early
In order to investigate the effects of ionic liquids with different anions on extraction yield, 1-butyl-3-methylimidazolium ionic liquids with four kinds of anions (Cl−, Br−, NO3−, and BF4−) were studied by ionic liquids-based ultrasound-assisted extraction (ILUAE)
The extraction results of four different ionic liquid aqueous solutions with the same cation but different anions were shown in Figure 2(a), from which we can conclude that the anion of ionic liquids influenced the extraction yield of target analyte and [C4mim]Br and [C4mim]Cl were more efficient than other two ionic liquids, which was likely related to the great effect of anion on the overall hydrogen bond basicity of the 1-butyl-3-methylimdazolium based ionic liquids [41]
Summary
Shikimic acid is a white crystalline cyclitol, which is a precursor material for industrial synthesis of the important drug, oseltamivir phosphate (Tamiflu), which is an effective drug against the H5N1 influenza virus [1], especially if administered early. Shikimic acid (Figure 1) was first isolated from the fruit of Illicium religiosum by Eykman in 1885 [10]. Most of the shikimic acid required by the pharmaceutical industry was obtained from the fruits of Chinese plant star anise (I. verum) [11]. The fruits of this tree were reported that the content of shikimic acid ranged from 2 to 7% [12]; only I. verum resource could not satisfy its growing market demand as growing difficulties. Potential alternative resources of shikimic acid are urgently required. Shikimic acid is a widely occurring primary plant metabolite, which has been identified in some conifer needles with relative abundance distribution
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