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    • Compound was obtained as a yellow crystal

    2022-06-20

    Compound was obtained as a yellow crystal (acetone). And the molecular formula of was established as CHO on the basis of a quasi-molecular ion at / 331.0799 [M+H] (calcd. for 331.0818) in its HR-ESI-MS. Compound showed H and C NMR similar to those of T0070907 . However, The H NMR spectrum of contained three hydroxy proton signals at 12.22 (1H, s), 12.09 (1H, s), 11.22 (1H, br.s), and only two methoxy proton signals at 3.90 (3H, s), 3.85 (3H, s). HMBC correlations between the methoxy proton signal ( 3.90) and 151.8, and long-range correlations between the aromatic hydrogen signal H-4 ( 7.49), methyl proton signal 2.32 and 151.8 suggested the methoxy group ( 3.90) attached to C-2, methyl group attached to C-3. Besides, hydroxy proton signal at 12.22 has a HMBC correlation to 151.8, displayed the hydroxy proton was located at C-1. δ 12.09 is another α hydroxy proton signal, linked at C-8 inferred from the two carbonyl groups ( 191.1 and 180.5) displaying a different chemical shift. In addition, the methoxy proton signal at 3.85 and H-5 ( 7.21), 8-OH (δ 12.09) were all correlated with 139.9, indicating that the methoxy group was attached to C-7. The remaining hydroxyl group can only be attached to C-6. Based on all data, compound 2 was identified as 1,6,8-trihydroxy-2,7-dimethoxy-3-methylanthraquinone, a new compound 2,7-dimethoxyemodin (). Its H and C NMR data were shown in . Compared with the structure reported in literature, compound is 3-methyl-2, 8-dihydroxy-1, 7-dimethoxy anthraquinone, named 7-methoxy obtusifolin. However, the H and C NMR data of compound have not been fully reported. Therefore, the H and C NMR signals of compound have been reasonably assigned according to HMQC and HMBC spectra (). The inhibitory effects against α-glucosidase of all 15 compounds isolated from were determined with 4-Nitrophenyl --glucopyranoside (PNPG) as substrate., Results are expressed as the IC (μg/mL). At the same concentration level as the tested sample, acarbose showed strong inhibitory activity against -glucosidase. And most of the components had an inhibitory effect on -glucosidase, and the IC values of the compounds , , , and were 50.60 ± 1.10, 22.57 ± 0.07, 60.09 ± 1.40, and 80.01 ± 2.66 μg/mL, respectively (See and ). The antioxidant activities of compound – were examined on experiments of 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging., Except compounds (IC 3.03 ± 0.31 μg/mL) and (IC 78.40 ± 2.39 μg/mL), the free radical scavenging capacities of other compounds were weak. The IC value of free radical scavenging of compound was lower than that of positive control (ascorbic acid, IC 6.48 ± 2.30 μg/mL), which meant that compound had better antioxidant activity (See ). In summary, fifteen small polar components including two novel anthraquinone aglycones ( and ) were isolated from . The H and C NMR data of 7-methoxy obtusifolin () were follow-up reported. Among these compounds, rubrofusarin (, IC 3.03 ± 0.31 μg/mL) showed stronger free radical scavenging capacity than ascorbic acid. Most of the components had inhibitory effect on α-glucosidase, which could be consistent with the hypoglycemic effect of in modern pharmacological research. Among the fifteen compounds, physicon () had the strongest inhibitory effect on α-glucosidase (weaker than acarbose), and the IC value was 22.57 ± 0.07 μg/mL.
    Introduction Prolonged high blood glucose levels (hyperglycaemia) is a characteristic sign of diabetes mellitus (DM) (American Diabetes Association, 2009). According to American Diabetes Association (2009), the disorder is characterized by improper functioning or secretion of insulin hormone from the pancreas or abnormal glucose homeostasis. Excessive and frequent intake of quickly digestible carbohydrates may also lead to prolonged elevation in the blood glucose level (O’Keefe & Bell, 2007). Over time, the continued postprandial state where the blood glucose is high (postprandial hyperglycaemia) may increase glycation and increase the risk of metabolic dysfunctions. In combination with other factors this may in turn increase the risk of type 2 diabetes where uncontrolled high blood glucose levels can contribute to a number of complications such as blindness, cardiovascular complications, renal failure, foot ulcers and need for limb amputation (Ceriello et al., 2006, O’Keefe and Bell, 2007, Szablewski, 2001).