Chemical Constituents from the Leaves of Ligustrum robustum and Their Bioactivities

Abstract

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.

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 Ligustrum robustum

“…In the previous phytochemical studies [ 2 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ], about 90 chemical constituents, including trans - p -hydroxycinnamic acid, 34 trans - p -hydroxycinnamic acid esters ( Figure 1 ), flavonoid glycosides, lignan glycosides, and other compositions, were isolated and identified from the leaves of L. robustum .…”

“…In our previous biological investigations [ 14 , 15 , 16 , 17 ], the chemical compositions isolated from the leaves of L. robustum were tested, and the results showed that (1) trans - p -hydroxycinnamic acid displayed stronger α -glucosidase inhibitory activity than the positive control acarbose; (2) trans - p -hydroxycinnamic acid and several trans - p -hydroxycinnamic acid esters displayed no weaker fatty acid synthase (FAS) inhibitory activities than the positive control orlistat; (3) trans - p -hydroxycinnamic acid and a lot of trans - p -hydroxycinnamic acid esters revealed stronger 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) ammonium salt (ABTS) radical scavenging effects than the positive control L-(+)-ascorbic acid and revealed moderate α-amylase inhibitory activities. What is more, trans - p -hydroxycinnamic acid esters might be hydrolyzed with catalysis of carboxylesterase or gastric acid in vivo [ 18 , 19 ] and release trans - p -hydroxycinnamic acid, meaning that trans - p -hydroxycinnamic acid esters are the prodrugs of trans - p -hydroxycinnamic acid.…”

“…What is more, trans - p -hydroxycinnamic acid esters might be hydrolyzed with catalysis of carboxylesterase or gastric acid in vivo [ 18 , 19 ] and release trans - p -hydroxycinnamic acid, meaning that trans - p -hydroxycinnamic acid esters are the prodrugs of trans - p -hydroxycinnamic acid. In addition, it was reported that natural products with inhibitory activities on α-glucosidase, α-amylase, and FAS as well as an antioxidant effect might be a new resource to prevent diabetes and its complications, which affected nearly 10.5% of the population in the world and led to serious mortality [ 17 ]. Therefore, trans - p -hydroxycinnamic acid and its esters isolated from L. robustum might be a novel resource for preventing diabetes and its complications.…”

Monoterpenoid Glycosides from the Leaves of Ligustrum robustum and Their Bioactivities (II)

“…Present anti-diabetic agents, including insulin, metformin, α-glucosidase inhibitors acarbose and N-substituted iminosugar C-glycoside [2], can deal with hyperglycemia, whereas their function to prevent the complications of diabetes is not ideal. Recent research [3] indicated that antioxidant natural ingredients with inhibitory actions on fatty acid synthase (FAS), α-glucosidase, and α-amylase might be a novel resource for preventing diabetes and its complications.…”

“…Ligustrum robustum (Roxb.) Blume, a shrub of the Oleaceae family, is widespread in Southwest China, Vietnam, Burma, Cambodia, and India [3]. The leaves of L. robustum, containing 3.96-3.99 mg•g −1 trans-p-hydroxycinnamic acid and 202.6-210.6 mg•g −1 total transp-hydroxycinnamic acid esters [4], have 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 [3].…”