Abstract
Chemical investigation of the endophytic fungus Aspergillus sp. 16-5B cultured on Czapek’s medium led to the isolation of four new metabolites, aspergifuranone (1), isocoumarin derivatives (±) 2 and (±) 3, and (R)-3-demethylpurpurester A (4), together with the known purpurester B (5) and pestaphthalides A (6). Their structures were determined by analysis of 1D and 2D NMR spectroscopic data. The absolute configuration of Compound 1 was determined by comparison of the experimental and calculated electronic circular dichroism (ECD) spectra, and that of Compound 4 was revealed by comparing its optical rotation data and CD with those of the literature. The structure of Compound 6 was further confirmed by single-crystal X-ray diffraction experiment using CuKα radiation. All isolated compounds were evaluated for their α-glucosidase inhibitory activities, and Compound 1 showed significant inhibitory activity with IC50 value of 9.05 ± 0.60 μM. Kinetic analysis showed that Compound 1 was a noncompetitive inhibitor of α-glucosidase. Compounds 2 and 6 exhibited moderate inhibitory activities.
Highlights
Diabetes is a group of metabolic diseases in which there are high blood sugar levels over a prolonged period and can cause many serious complications, including diabetic ketoacidosis, non-ketotic hyperosmolar coma, cardiovascular disease, stroke, kidney failure, etc. [1,2,3]
The structures of the known compounds were identified as purpuresters B (5) [18] (Table 3) and pestaphthalides A (6) [19] by comparison of their spectroscopic and optical rotation data with those reported in the literature
The structure of Compound 6 was further confirmed by single-crystal X-ray diffraction experiment using CuKα radiation [20] (Figure 5) (Cambridge Crystallographic Data Centre (CCDC) Number 1053019)
Summary
Diabetes is a group of metabolic diseases in which there are high blood sugar levels over a prolonged period and can cause many serious complications, including diabetic ketoacidosis, non-ketotic hyperosmolar coma, cardiovascular disease, stroke, kidney failure, etc. [1,2,3]. Health Organization reported that there are 387 million people living with diabetes worldwide in 2014, and the number would increase to 592 million in 2035 [4]. Endophytic fungi have been demonstrated to be a rich and reliable source of biologically-active and/or chemically-novel compounds [5,6,7]. Our research group has focused on the exploration of new bioactive metabolites from mangrove endophytic fungi collected from the South. 16-5B, from the leaves of Sonneratia apetala, had led to the isolation and characterization of four new compounds (1–4), as well as two previously reported compounds (5,6) (Figure 1). All compounds were evaluated for their α-glucosidase inhibitory activities. Structural elucidation, as well as evaluation of the biological activity of these compounds are reported
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