The phytochemical study on the leaves of Ligustrum robustum, which have been used as Ku-Ding-Cha, led to the isolation and identification of three new phenylethanoid glycosides and three new phenylmethanoid glycosides, named ligurobustosides R₁ (1b), R_2–3 (2), R₄ (3), S₁ (4b), S₂ (5), and S₃ (6), and five reported phenylethanoid glycosides (7–11). In the bioactivity test, (Z)-osmanthuside B₆ (11) displayed strong fatty acid synthase (FAS) inhibitory activity (IC₅₀: 4.55 ± 0.35 μM) as the positive control orlistat (IC₅₀: 4.46 ± 0.13 μM), while ligurobustosides R₄ (3) and S₂ (5), ligupurpuroside B (7), cis-ligupurpuroside B (8), ligurobustoside N (9), osmanthuside D (10), and (Z)-osmanthuside B₆ (11) showed stronger ABTS radical scavenging activity (IC₅₀: 2.68 ± 0.05~4.86 ± 0.06 μM) than the positive control L-(+)-ascorbic acid (IC₅₀: 10.06 ± 0.19 μM). This research provided a theoretical basis for the leaves of L. robustum as a tea with function in treating obesity and diabetes.

The leaves of Ligustrum robustum have been consumed as Ku-Ding-Cha for clearing heat and removing toxins, and they have been used as a folk medicine for curing hypertension, diabetes, and obesity in China. The phytochemical research on the leaves of L. robustum led to the isolation and identification of two new hexenol glycosides, two new butenol glycosides, and five new sugar esters, named ligurobustosides X (1a), X₁ (1b), Y (2a), and Y₁ (2b) and ligurobustates A (3a), B (3b), C (4b), D (5a), and E (5b), along with seven known compounds (4a and 6–10). Compounds 1–10 were tested for their inhibitory effects on fatty acid synthase (FAS), α-glucosidase, and α-amylase, as well as their antioxidant activities. Compound 2 showed strong FAS inhibitory activity (IC₅₀ 4.10 ± 0.12 μM) close to that of the positive control orlistat (IC₅₀ 4.46 ± 0.13 μM); compounds 7 and 9 revealed moderate α-glucosidase inhibitory activities; compounds 1–10 showed moderate α-amylase inhibitory activities; and compounds 1 and 10 displayed stronger 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) ammonium salt (ABTS) radical scavenging effects (IC₅₀ 3.41 ± 0.08~5.65 ± 0.19 μM) than the positive control l-(+)-ascorbic acid (IC₅₀ 10.06 ± 0.19 μM). This study provides a theoretical foundation for the leaves of L. robustum as a functional tea to prevent diabetes and its complications.

Trans-p-hydroxycinnamic acid and its esters in the leaves of Ligustrum robustum might be a new resource to prevent diabetes and its complications. In the present study, a new HPLC-UV method using hydrolyzation with sodium hydroxide for quantitation of trans-p-hydroxycinnamic acid and total trans-p-hydroxycinnamic acid esters in the leaves of L. robustum was developed, since it was difficult and troublesome to analyze no less than 34 trans-p-hydroxycinnamic acid esters by usual HPLC. The extract of L. robustum was hydrolyzed with sodium hydroxide at 80 °C for 2 h, and then, hydrochloride was added. HPLC analysis was performed in reverse phase mode using a C-18 column, eluting with methanol-0.1% acetic acid aqueous solution (40:60, v/v) in isocratic mode at a flow rate of 1.0 mL·min⁻¹ and detecting at 310 nm. The linear range for trans-p-hydroxycinnamic acid was 11.0–352.0 μg·mL⁻¹ (r² = 1.000). The limit of detection and limit of quantification were 2.00 and 6.07 μg·mL⁻¹, respectively. The relative standard deviations of intra-day and inter-day variabilities for trans-p-hydroxycinnamic acid were less than 2%. The percentage recovery of trans-p-hydroxycinnamic acid was 103.3% ± 1.1%. It is the first HPLC method using hydrolyzation for quantification of many carboxylic esters. Finally, the method was used successfully to determine trans-p-hydroxycinnamic acid and total trans-p-hydroxycinnamic acid esters in various extracts of the leaves of L. robustum. The 60–70% ethanol extracts of L. robustum showed the highest contents of free trans-p-hydroxycinnamic acid (3.96–3.99 mg·g⁻¹), and the 50–80% ethanol extracts of L. robustum displayed the highest contents of total trans-p-hydroxycinnamic acid esters (202.6–210.6 mg·g⁻¹). The method can be applied also to the quality control of the products of L. robustum.

Ligustrum robustum has been not only used as a heat-clearing and detoxicating functional tea (Ku-Ding-Cha) but also consumed as a hypotensive, anti-diabetic, and weight-reducing folk medicine. From the leaves of L. robustum, ten new monoterpenoid glycosides named ligurobustosides T₁₀ (1a), T₁₁ (1b), T₁₂ (2a), T₁₃ (2b), T₁₄ (3a), T₁₅ (3b), F₁ (4b), T₁₆ (5a), T₁₇ (5b), and E₁ (6b), together with five known ones (4a, 6a, 7, 8a, 8b), were separated and identified using the spectroscopic method and chemical method in this research. The results of biological tests exhibited that the fatty acid synthase (FAS) inhibitory action of compound 5 (IC₅₀: 4.38 ± 0.11 μM) was as strong as orlistat (IC₅₀: 4.46 ± 0.13 μM), a positive control; the α-glucosidase inhibitory actions of compounds 1–4 and 7–8, and the α-amylase inhibitory actions of compounds 1–8 were medium; the ABTS radical scavenging capacities of compounds 1–3 and 5–8 (IC₅₀: 6.27 ± 0.23 ~ 8.59 ± 0.09 μM) were stronger than l-(+)-ascorbic acid (IC₅₀: 10.06 ± 0.19 μM) served as a positive control. This research offered a theoretical foundation for the leaves of L. robustum to prevent diabetes and its complications.

The leaves of Ligustrum robustum have been applied as Ku-Ding-Cha, a functional tea to clear heat and remove toxins; and served as a folk medicine to deal with diabetes, obesity, and hypertension. Trans-p-hydroxycinnamic acid and its esters, which were isolated from the leaves of L. robustum, might be a new resource to prevent diabetes and its complications because of their strong -glucosidase and fatty acid synthase (FAS) inhibitory activities and antioxidant effect. However, the quantitative analytical method for trans-p-hydroxycinnamic acid and its esters in the leaves of L. robustum hasn’t been reported so far. In addition, it was difficult and troublesome to analyze no less than 34 trans-p-hydroxycinnamic acid esters by usual HPLC. Therefore, a new HPLC-UV method using hydrolyzation with sodium hydroxide for quantitation of trans-p-hydroxycinnamic acid and its esters in the leaves of L. robustum was developed in the present study. The optimal hydrolyzation conditions were as follows: 1 mL sodium hydroxide aqueous solution (1 M) was added into 1 mL the extract of L. robustum and incubated at 80 °C for 2 h , and then 1 mL hydrochloride (1 M) solution was added. HPLC analysis was performed in reverse phase mode using a C-18 column, eluting with methanol-0.1% acetic acid aqueous solution (40:60, v/v) in isocratic mode at a flow rate of 1.0 mL/min, and detecting at 310 nm. The analytical method was simple and rapid, which simplified greatly the analytical process. The method was validated in terms of linearity, limit of detection (LOD), limit of quantification (LOQ), precision, and accuracy. High linearity was demonstrated with correlation coefficient of 1.000 for trans-p-hydroxycinnamic acid. The LOD and LOQ values were 1.55 and 4.69 μg/mL, respectively. The relative standard deviations (RSD) of intra-day and inter-day variabilities for trans-p-hydroxycinnamic acid were less than 2%. The percentage recovery of trans-p-hydroxycinnamic acid was 101.2% ± 0.8%. Finally, the proposed method was applied successfully to the determination and comparison of the contents of trans-p-hydroxycinnamic acid and its esters in various extracts of the leaves of L. robustum. The 60%-70% ethanol extracts of L. robustum showed the highest contents of free trans-p-hydroxycinnamic acid (3.96-3.99 mg/g), and the 50%-80% ethanol extracts of L. robustum displayed the highest contents of trans-p-hydroxycinnamic acid esters (202.6-210.6 mg/g). The method can be applied also to the quality control of the products of L. robustum.