α-glucosidase (IC₅₀ = 79.88 μM) [2]
α-amylase (IC₅₀ > 250 μM) [2]

Quercimeritrin exhibited selective inhibitory activity against α-glucosidase with an IC₅₀ value of 79.88 μM, while its IC₅₀ against α-amylase was greater than 250 μM, indicating weak inhibition of α-amylase [2].
The inhibition kinetics of Quercimeritrin on α-glucosidase were determined using Lineweaver-Burk plots. All lines intersected in the negative direction of the γ-axis, Vmax remained constant, and Km decreased with increasing inhibitor concentration, indicating a competitive inhibition mechanism [2]. For α-amylase, Quercimeritrin also showed competitive inhibition, but its Km value for α-amylase was much higher than that for α-glucosidase, suggesting a higher affinity for α-glucosidase [2].
Fluorescence quenching experiments showed that Quercimeritrin quenched the intrinsic fluorescence of both α-glucosidase and α-amylase in a concentration-dependent manner. The quenching constants (Ksv) increased with temperature (from 0.17 to 0.21 × 10⁵ L/mol for α-glucosidase and 0.13 to 0.18 × 10⁵ L/mol for α-amylase at 300.15–310.15 K). The Kq values were much greater than the dynamic quenching maximum collision constant (2.0 × 10¹⁰ L/mol), indicating static quenching due to formation of a ground-state complex [2].
The binding constant (Ka) of Quercimeritrin with α-glucosidase (0.41 ± 0.06 × 10⁵ M at 310.15 K) was greater than that with α-amylase (0.26 ± 0.01 × 10⁵ M at 310.15 K), and the number of binding sites (n) was approximately 1 for both enzymes. Thermodynamic parameters (ΔH < 0, ΔS < 0) indicated that hydrogen bonding and van der Waals forces were the main binding forces, and the binding was spontaneous (ΔG < 0) [2].
Synchronous fluorescence spectra showed that with increasing Quercimeritrin concentration, the fluorescence intensity of α-glucosidase decreased at both Δλ = 15 nm (Tyr residues) and Δλ = 60 nm (Trp residues), with a significant redshift in the Trp residue peak, indicating a change in the microenvironment near Trp residues [2].
Molecular docking revealed that Quercimeritrin docked into the active pocket of α-glucosidase with an intermolecular energy of -81.17 kcal/mol, forming hydrogen bonds with ARG202, ASP203, ASP327, TRP406, ASP443, and ASP542, as well as hydrophobic interactions. The docking score for α-glucosidase was much higher than that for α-amylase [2].
In an anti-angiogenesis study using HUVEC (human umbilical vein endothelial cells), Quercimeritrin at 100 μM suppressed HUVEC proliferation (Fig. 3, reference [3]). However, it did not inhibit HUVEC tube formation on reconstituted basement membrane (less than 20% inhibition, Table 1, reference [3]). The effect on HUVEC chemotaxis was not examined due to insufficient sample [3].

In an in vivo starch load test using db/db diabetic mice, oral administration of Quercimeritrin at 100 mg/kg (low-dose group) and 200 mg/kg (high-dose group) significantly reduced postprandial blood glucose levels. The low-dose group showed a similar hypoglycemic effect to the acarbose group (100 mg/kg), while the high-dose group had a significantly lower blood glucose level than both the control and acarbose groups. The area under the glucose curve (AUC) was reduced by 19.0% at 100 mg/kg and 24.5% at 200 mg/kg, compared to a 20.31% reduction with acarbose [2].
In an ex vivo rat aortic ring angiogenesis assay, Quercimeritrin at 100 μM inhibited microvessel outgrowth, but its inhibitory effect was weaker than that of quercetin and isoquercitrin (quercetin 3-O-β-D-glucose). Rutin (quercetin 3-O-β-D-glucose-[1,6]-O-α-L-rhamnose) had no effect [3].

The in vitro α-glucosidase activity assay was performed using spectrophotometry. In phosphate buffer (pH 6.8), 0.5 U/mL α-glucosidase and p-nitrophenyl-D-glucopyranoside (pNGP, 0.6 mM) substrate were used. Test compounds and acarbose were dissolved in DMSO to form 10 mM stock solutions, then serially diluted with phosphate buffer. In 96-well plates, 10 μL of compound, 40 μL of enzyme solution, and 100 μL of potassium phosphate buffer were pre-incubated at 37°C for 10 min. Then 50 μL of substrate was added and incubated at 37°C for 20 min. Absorbance was measured at 405 nm. Inhibition percentage was calculated as [(Abscontrol - Abssample)/Abscontrol] × 100, and IC₅₀ values were calculated using nonlinear fitting (logit method) [2].
The in vitro α-amylase activity assay was performed similarly using 5 U/mL α-amylase and 2-chloro-4-nitrophenyl α-D-maltotrioside (G3-CNP, 0.6 mM) as substrate. The same pre-incubation and measurement conditions (37°C, 20 min, absorbance at 405 nm) were applied [2].
Inhibition kinetic analysis was performed at different substrate concentrations. The Lineweaver-Burk equation 1/v = (Km/Vmax)(1/[S]) + 1/Vmax was used to calculate Vmax and Km values. Reactions with a series of compound concentrations and substrates (pNaPG for α-glucosidase, G3-CNP for α-amylase) were tested [2].
Fluorescence quenching experiment: Quercimeritrin solutions (0–200 mM, 1.0 mL) were used to titrate α-glucosidase (1.0 mL, 2 U/mL) or α-amylase (1.0 mL, 2 U/mL) and equilibrated for 5 min. Fluorescence intensity was measured at 295–500 nm (emission) with excitation at 280 nm at different temperatures (305.15, 310.15, 315.15 K). Synchronous fluorescence spectra were determined at Δλ = 15 nm and Δλ = 60 nm (260–320 nm). Stern-Volmer equation F₀/F = 1 + Kqτ₀[Q] = 1 + Ksv[Q] was used to calculate quenching constants. Binding constants and number of binding sites were calculated using log[(F₀-F)/F] = logKa + n log[Q]. Thermodynamic parameters were calculated using Van 't Hoff equation lnKa = -ΔH/RT + ΔS/R and ΔG = ΔH - TΔS [2].

HUVEC proliferation assay: HUVEC were dispersed with trypsin and suspended in HuMedia EG2 medium at 15,000 cells/mL. A 100 μL cell suspension was plated onto 96-well culture plates and incubated at 37°C in 5% CO₂ for 24 h. The medium was replaced with fresh medium containing 0–100 μM of Quercimeritrin or other polyphenolic compounds. After 72 h, 10 μL of WST-1 reagent was added and incubated for 4 h at 37°C. Absorbance at 450 nm was measured. Quercimeritrin at 100 μM suppressed HUVEC proliferation (Fig. 3, reference [3]).
Tube formation assay: Solid gels were prepared on a 96-well plate using an In Vitro Angiogenesis Assay Kit. HUVEC (1 × 10⁵ cells/mL) in HuMedia EG-2 containing 0–100 μM of Quercimeritrin were seeded at 100 μL per well onto the gel surface. Cells were incubated for 12 h at 37°C in 5% CO₂. Tube formation was observed under an inverted light microscope at 40× magnification. The total length of tube structures was measured. Quercimeritrin at 100 μM showed less than 20% inhibition (no significant effect) (Table 1, reference [3]).
Chemotaxis assay (modified Boyden chamber): Microporous membranes (8 μm) of 24-well cell culture inserts were coated with 0.1% gelatin. HUVEC were detached, resuspended in Medium 199 with 0.1% BSA, and seeded in the upper chamber (1.0 × 10⁵ cells/400 μL). The lower well was filled with 400 μL of Medium 199 containing 0.1% BSA and 10 ng/mL VEGF with or without compound. After 6 h at 37°C, non-migrated cells were removed. Migrated cells on the lower surface were fixed with methanol, stained with Diff-Quik™, and counted in five fields per membrane at 200× magnification. The effect of Quercimeritrin on chemotaxis was not examined in this study [3].

Postprandial blood glucose measurement: db/db mice (diabetic) and C57BL/6J mice (blank controls) were used. After 1 week of acclimation, db/db mice were randomly divided into four groups (n=10 per group): normal saline (model group), 100 mg/kg acarbose (positive control), 100 mg/kg Quercimeritrin (low-dose group, LD), and 200 mg/kg Quercimeritrin (high-dose group, HD). C57BL/6J mice served as normal blank controls. After overnight fasting, mice received oral administration of 10 mL/kg normal saline (model), 100 mg/kg acarbose in normal saline, 100 mg/kg Quercimeritrin in normal saline, or 200 mg/kg Quercimeritrin in normal saline. All mice were given starch (2 g/kg) orally 60 min after treatment. Blood samples were taken from the caudal vein and blood glucose was measured at 0, 30, 60, and 120 min. The area under the curve (AUC) was calculated using the trapezoidal rule [2].
Rat aortic ring angiogenesis assay: Male Wistar rats (body weight ~200 g) were sacrificed under diethyl ether anesthesia. The thoracic aorta was removed, washed with RPMI 1640 medium, turned inside out, and cut into 1–1.5 mm segments. Collagen gel was prepared with 8 volumes of porcine tendon collagen solution (3 mg/mL), 1 volume of 10× Eagle's MEM, and 1 volume of reconstitution buffer (0.08 M NaOH, 200 mM HEPES). Each aortic segment was placed in a 6-well plate, covered with 0.5 mL of gel matrix, and allowed to gel at 37°C for 20 min, then overlaid with 2 mL of RPMI 1640 medium containing 1% ITS+. Quercimeritrin (100 μM) or vehicle was added. Incubation was carried out for 10 days at 37°C in 5% CO₂, with medium changed on day 7. Capillary length was measured from the cut end of the aortic segment to the approximate mean point of capillary using phase-contrast microscopy and Adobe Photoshop software. Quercimeritrin at 100 μM showed weaker inhibitory effect than quercetin and isoquercitrin but stronger than rutin (Fig. 2, reference [3]).

[1]. Chemical constituents from the rhizome of Polygonum paleaceum and their antifungal activity. J Asian Nat Prod Res. 2017 Jan;19(1):47-52.

Quercetin 7-O-α-L-rhamnoside is a quercetin O-glycoside with a structure in which quercetin is linked to the α-L-rhamnosyl moiety at position 7 via a glycosidic bond. It is a metabolite. It is an α-L-rhamnoside, a monosaccharide derivative, a tetrahydroxyflavone, a quercetin O-glycoside, and also a flavonol compound. Its function is related to α-L-rhamnosyl. It has been reported that stylidocleome brachycarpa, Thulinella chrysantha, and other organisms with relevant data have been found to contain stylidocleome B.

---

Quercimeritrin was identified as a highly effective selective inhibitor of α-glucosidase through virtual screening and in vitro enzyme activity assays among 12 flavonoid glycosides. Its selective inhibition mechanism involves higher binding affinity to α-glucosidase via non-covalent bonds (mainly hydrogen bonds) with amino acid residues in the active pocket, leading to conformational changes and formation of an enzyme-inhibitor complex that blocks substrate binding [2].
In structure-activity relationship analysis, glycosylation at the A7 position (as in Quercimeritrin) significantly enhanced α-glucosidase inhibitory activity compared to glycosylation at the C3 position. The OH groups at B4' and B5' positions were also favorable for α-glucosidase inhibition [2].
In anti-angiogenesis studies, the attachment of a glucose at position C-3 (isoquercitrin) was critical for anti-angiogenic activity, while glycosylation at position C-7 (Quercimeritrin) gave weaker activity, and diglycosylation (rutin) was ineffective [3].

C21H20O11

448.3769

448.1

22007-72-3

5748601

White to yellow solid powder

1.7±0.1 g/cm3

801.1±65.0 °C at 760 mmHg

174-175℃ (methanol )

283.8±27.8 °C

0.0±3.0 mmHg at 25°C

1.755

1.72

7

11

3

32

741

5

C[C@H]1[C@@H]([C@H]([C@H]([C@@H](O1)OC2=CC(=C3C(=C2)OC(=C(C3=O)O)C4=CC(=C(C=C4)O)O)O)O)O)O

QPHXPNUXTNHJOF-XNFUJFQVSA-N

InChI=1S/C21H20O11/c1-7-15(25)17(27)19(29)21(30-7)31-9-5-12(24)14-13(6-9)32-20(18(28)16(14)26)8-2-3-10(22)11(23)4-8/h2-7,15,17,19,21-25,27-29H,1H3/t7-,15-,17+,19+,21-/m0/s1

2-(3,4-dihydroxyphenyl)-3,5-dihydroxy-7-[(2S,3R,4R,5R,6S)-3,4,5-trihydroxy-6-methyloxan-2-yl]oxychromen-4-one

Vincetoxicoside B

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: This product requires protection from light (avoid light exposure) during transportation and storage.

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO : ~100 mg/mL (~223.03 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (5.58 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

---

Solubility in Formulation 2: ≥ 2.5 mg/mL (5.58 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

---

 (Please use freshly prepared in vivo formulations for optimal results.)