Abstract
Seven pairs of enantiomeric isoflavones (1a/1b–7a/7b) were obtained from the ethyl acetate extract of the fruits of Maclura tricuspidata (syn. Cudrania tricuspidata), and successfully separated by chiral high-pressure liquid chromatography (HPLC). The structures and absolute configurations of the enantiomeric isoflavones were established on the basic of comprehensive spectroscopic analyses and quantum chemical calculation methods. Compounds 1, 1a, and 1b exhibited neuroprotective activities against oxygen-glucose deprivation/reoxygenation (ODG/R)-induced SH-SY5Y cells death with EC50 values of 5.5 µM, 4.0 µM, and 10.0 µM, respectively. Furthermore, 1, 1a, and 1b inhibited OGD/R-induced reactive oxygen species generation in SH-5Y5Y cells with IC50 values of 6.9 µM, 4.5 µM, and 9.5 µM, respectively.
Highlights
Known as brain ischemia or ischemic stroke, is one of the most common causes of mortality and morbidity, conducing to major negative social and economic consequences. The prevention of this disease is clearly an important public health priority. It occurs as a result of the cerebral blood flow is disrupted, leading to the starvation of oxygen and glucose to the affected area, causing of irreversible brain damage[15,16]
Seven pairs of enantiomeric isoflavones (1a/1b–7a/7b) were obtained from the ethyl acetate extract of the fruits of M. tricuspidata. These enantiomeric isoflavones were further purified by using chiral high-pressure liquid chromatography (HPLC), their structures with absolute configurations were established based on interpretation of their 1D and 2D NMR, and HRESIMS data together with electronic circular dichroism (ECD) calculations
The 1H and 13C NMR spectra resembled those of cudraisoflavone D (Supplementary S.24, Table 1)[6], except for the appearance of a 3-hydroxy-2,2-dimethyldihydropyran group [δH 3.07 (1 H, dd, J = 16.5, 5.5 Hz, Ha-1′′′), 2.73 (1 H, dd, J = 16.5, 7.5 Hz, Hb-1′′′), 3.89 (1 H, dd, J = 7.5, 5.0 Hz, H-2′′′), 1.35 (3 H, s, Me-4′′′), and
Summary
Compound 1 was determined as C25H26O7 by the HRESIMS [M + H]+ ion at m/z 439.1742 (calcd. for C25H25O7, 439.1757). In order to further confirm the results, the additional ECD calculations were carried out using the CAM-B3LYP and WB97XD functionals, which yielded consistent ECD results (Fig. 2) On this basis, the absolute configurations of 1a, 1b, 2a, and 2b were assigned as depicted, which were named as (2′′S,2′′′R)-cudraisoflavone U, (2′′R,2′′′S)-cu draisoflavone U, (2′′R,2′′′R)-cudraisoflavone U, and (2′′S,2′′′S)-cudraisoflavone U, respectively. The 1D NMR spectra resembled those of cudraisoflavone I (Supplementary S.24)[6] They differed in the presence of a 2-(1-hydroxy-1-methylethyl)dihydrofuran group [δH 3.20 (2 H, d, J = 8.5 Hz, H-1′′′), 4.76 (1 H, t, J = 8.5 Hz, H-2′′′), 1.18 (3 H, s, Me-4′′′), and 1.15 (3 H, s, Me-5′′′)] at the C-7 and C-8 positions instead of the furan group, confirmed by the HMBC cross-peaks H-1′′′/C-7 (δC 162.2), C-8 (δC 103.5) and C-9 (δC 152.3). The isolated compounds from M. tricuspidata could be promising candidates for the treatment of cerebral ischemia and more investigations are needed to understand their cellular mechanisms of action in the brain for fully exploring their neuroprotective potential
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