Total quantification and extraction of shikimic acid from star anise (llicium verum) using solid-state NMR and cellulose-dissolving aqueous hydroxide solutions

Many pharmaceutically relevant molecules are still extracted directly from lignocellulosic biomass sources. As this can be a bottleneck in supply, total quantification followed by total extraction are desirable processes to ensure as much as possible is obtained, at the optimal time in the growth cycle. Herein we report the application of solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy to quantify shikimic acid present inside Chinese star anise (or star aniseed, llicium verum). Subsequently, methanol soxhlet extraction is compared with conventional aqueous hydroxides (i.e. sodium hydroxide) and cellulose-dissolving aqueous hydroxides (i.e. tetraethylammonium and tetrabutylammonium hydroxide) for shikimic acid isolation. Methanol extraction isolated ca. 6.6±0.1 wt% (wt%) shikimic acid (post-purification), and solid-state NMR confirmed extraction was incomplete even after 72 h. Conversely, dissolution of the star anise at room temperature in tetrabutylammonium hydroxide ([N₄₄₄₄]OH) allowed isolation of ca. 14.0±0.6 wt% shikimic acid (post-purification). Solid state NMR confirmed the star anise initially contained 19±3 wt% shikimic acid, which was quantitatively extracted after dissolution in the aqueous hydroxide solution. The solubility of the star anise and the kinetics of the shikimic acid extraction were also briefly evaluated.