Introduction Cassia singueana Del. (Fabaceae) is a rare medicinal plant used in the traditional medicine preparations to treat various ailments. The root of C. singueana is a rich source of anthraquinones that possess anticancer, antibacterial and antifungal properties. Objective The objective of this study was to develop an ultrasound‐assisted extraction (UAE) method for achieving a high extraction yield of anthraquinones using the response surface methodology (RSM), Box–Behnken design (BBD), and a recycling preparative high‐performance liquid chromatography (HPLC) protocol for isolation of anthraquinones from C. singueana. Methodology Optimisation of UAE was performed using the Box–Behnken experimental design. Recycling preparative HPLC was employed to isolate anthraquinones from the root extract of C. singueana. Results The BBD was well‐described by a quadratic polynomial model (R2 = 0.9751). The predicted optimal UAE conditions for a high extraction yield were obtained at: extraction time 25.00 min, temperature 50°C and solvent‐sample ratio of 10 mL/g. Under the predicted conditions, the experimental value (1.65 ± 0.07%) closely agreed to the predicted yield (1.64%). The obtained crude extract of C. singueana root was subsequently purified to afford eight anthraquinones. Conclusion The extraction protocol described here is suitable for large‐scale extraction of anthraquinones from plant extracts.

A new stilbene (1) was isolated from the root of Cassia sieberiana D. C. together with thirteen known compounds, one stilbene (2), three flavonoids (3–5), six anthraquinones (6–11), two triterpenes (12–13), and phytosterol (14). Their structures were identified using spectroscopic techniques and by comparison of the spectral data with those previously reported in the literature. Compounds 10 – 13 were isolated from C. sieberiana for the first time. Compounds 1, 2 and 3 exhibited significant inhibitory activity on 15-lipoxygenase with IC50 values of 2.62, 1.27 and 0.98 μM, respectively. Compounds 2 and 3 showed acetylcholinesterase inhibitory activity with IC50 values of 10.57 and 2.89 μM, respectively.

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Succinic acid is an important platform and/or commodity or specialty chemical with a broad range of applications. The metabolic role of pyruvate formatelyase A (pflA) in relation to succinate production in Escherichia coli under anaerobic conditions from glucose substrate remained largely unspecified. Herein we identified pflAgene for the first time, as a novel gene knockout target for increasing succinate production in E. coli. Guided by E. coli reconstruction iJO1366, we engineered the E. coli host metabolism by deleting the pflA, thereby causing the up-regulation of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which hypothetically increases the generation of NADH and the pool of phosphoenolpyruvate (PEP) in the central carbon metabolism, required for succinate production. This strategy produced succinic acid that is 4.78 fold (0.28g l-1 in 1day) from glucose substrate. This work elucidatesfor the first time that pflA is a novel gene deletion target for increasing succinic acid production in E. coli under anaerobic conditions. In addition, these results highlight the power of metabolic model in identifying novel gene deletion target and ultimately driving novel biological discovery.