A series of fifteen silver (I) quinoline complexes Q1–Q15 have been synthesized and studied for their biological activities. Q1–Q15 were synthesized from the reactions of quinolinyl Schiff base derivatives L1–L5 (obtained by condensing 2-quinolinecarboxaldehyde with various aniline derivatives) with AgNO3, AgClO4 and AgCF3SO3. Q1–Q15 were characterized by various spectroscopic techniques and the structures of [Ag(L1)2]NO3Q1, [Ag(L1)2]ClO4Q6, [Ag(L2)2]ClO4Q7, [Ag(L2)2]CF3SO3Q12 and [Ag(L4)2]CF3SO3Q14 were unequivocally determined by single crystal X-ray diffraction analysis. In vitro antimicrobial tests against Gram-positive and Gram-negative bacteria revealed the influence of structure and anion on the complexes′ moderate to excellent antibacterial activity. In vitro antioxidant activities of the complexes showed their good radical scavenging activity in ferric reducing antioxidant power (FRAP). Complexes with the fluorine substituent or the thiophene or benzothiazole moieties are more potent with IC50 between 0.95 and 2.22 mg/mL than the standard used, ascorbic acid (2.68 mg/mL). The compounds showed a strong binding affinity with calf thymus-DNA via an intercalation mode and protein through a static quenching mechanism. Cytotoxicity activity was examined against three carcinoma cell lines (HELA, MDA-MB231, and SHSY5Y). [Ag(L2)2]ClO4Q7 with a benzothiazole moiety and [Ag(L4)2]ClO4Q9 with a methyl substituent had excellent cytotoxicity against HELA cells.
We isolated and identified gallic and protocatechuic acids as the antidiabetic principles in Hibiscus sabdariffa using solvent extraction, column chromatographic fractionation, and nuclear magnetic resonance (NMR) spectroscopy. Ethylacetate fraction of the aqueous extract of H. sabdariffa inhibited α‐amylase and α‐glucosidase with IC50 of 411.73 and 433.93 μg/ml, respectively. Furthermore, fractions I and II obtained from column chromatography inhibited α‐amylase with IC50 of 27.03 and 20.12 μg/ml, and α‐glucosidase with IC50 of 24.30 and 22.29 μg/ml, respectively. In addition, the principles reduced the serum glucose and lipid peroxide levels of diabetic rats and with an improvement in the rat lipid profiles and antioxidant defenses. Fractions I and II were identified as protocatechuic acid and gallic acid, respectively, using 1H and 13C NMR. Protein–ligand docking showed that these compounds form multiple favorable interactions with the active‐site residues of the two glycosidases. Overall, protocatechuic and gallic acids emerge as natural antidiabetic agents.
Practical applications
Hibiscus sabdariffa (Zoborodo) is a refreshment drink for ceremonial gatherings in Nigeria. Also, its pharmacological use includes diabetes, hypertension, hyperlipidemia, metabolic syndrome, and hepatoprotection. The consumption of this food drink could improve diabetes, hypertension, dyslipidemia, metabolic syndrome, and liver disease. Furthermore, the inhibition of α‐amylase and α‐glucosidase could prevent diabetic complications associated with postprandial glucose. Developing the extract of H. sabdariffa calyx as food supplement could be used in managing diabetes and its associated complications such as dyslipidemia, hypertension, and metabolic syndrome.
The antidiabetic principles from methanolic leaf extract of Bryophyllum pinnatum were isolated. The leaf extract was fractionated on silica gel using column chromatography and identified using nuclear magnetic resonance (NMR) spectrometry. The ethylacetate fraction of the partitioned methanolic extract of B. pinnatum lowered blood glucose of alloxan‐induced diabetic rats and inhibited α‐amylase and α‐glucosidase with IC50 137.89 and 110.15 µg/mL, respectively. In addition to lowering blood glucose, fractions A and B inhibited α‐amylase with IC50 57.43 and 43.84 µg/mL and α‐glucosidase with IC50 11.15 and 25.79 µg/mL, respectively. 1H and 13C NMR showed that fractions A and B are quercetin and kaempeferol, respectively. Molecular docking revealed that kaempferol and quercetin interacted with amino acid residues that bind/hydrolyze substrate molecules These compounds reversed altered lipid profile and oxidative stress biomarkers. Our findings showed that kaempferol and quercetin are responsible for the antidiabetic activity of B. pinnatum.
Practical application
Bryophyllum pinnatum is an edible vegetable plant in some parts of Nigeria, and its consumption could improve diabetic condition and lower postprandial glucose. Furthermore, extract of the leaves could be developed into food supplements for managing diabetes and its associated complications including dyslipidaemia and oxidative stress.
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