Published March 31, 2022
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Hypoglycemic flavonoids from Selaginella tamariscina (P.Beauv.) Spring
- 1. The First Hospital of Hunan University of Chinese Medicine, Changsha, 410007, PR China & Department of Pharmacy, Xiangya Hospital, Central South University, Changsha, Hunan, 410008, PR China
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Long, Hong-Ping, Liu, Jian, Xu, Ping-Sheng, Xu, Kang-Ping, Li, Jing, Tan, Gui-Shan (2022): Hypoglycemic flavonoids from Selaginella tamariscina (P.Beauv.) Spring. Phytochemistry (113073) 195: 1-8, DOI: 10.1016/j.phytochem.2021.113073, URL: http://dx.doi.org/10.1016/j.phytochem.2021.113073
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- urn:lsid:plazi.org:pub:FB30FFC1DD22FFCF313EFFB6F8413008
References
- Involvenflavone G (1) was obtained as a yellow amorphous powder. Its molecular formula was determined to be C31H24O10 by positive HREIMS at m/z 556.1388 [M]+ (calcd for C31H24O10, 556.1364), indicating 20 degrees of unsaturation. Analysis of the 1H and 13C NMR data (Table 1) of 1 suggested that it is a biflavonoid, as indicated by the characteristic resonances of two nonconjugated carbonyls at δ C 197.4 (C-4) and 196.8 (C-4''), as well as six doublets of doublets at δ H 5.47(1H, dd, J =13.0, 3.0 Hz, H-2), 3.30 (1H, dd, J =17.0, 13.0 Hz, H-3a), 2.75 (1H, dd, J =17.0, 3.0 Hz, H-3b), δ H 5.52(1H, dd, J =13.0, 3.0 Hz, H-2''), 3.27 (1H, dd, J = 17.0, 13.0 Hz, H-3''a), 2.70 (1H, dd, J =17.0, 3.0 Hz, H-3''b), which are typical spin patterns for the heterocycle ring of flavanone moieties (Long et al., 2015). Two sets of 1,3,4-trisubstituted aromatic signals at δ H 7.30 (2H, d, J = 2.0 Hz, H-2'/2'''), 7.31 (2H, dd, J = 8.0, 2.0 Hz, H-6'/6''') and 6.93 (2H, d, J = 8.0 Hz, H-5'/5'''), together with four protons with two sets of meta-coupled doublets at δ H 5.87 (1H, d, J =2.0 Hz, H-6), 5.89 (1H, d, J =2.0 Hz, H-8), δ H 6.08 (1H, d, J = 2.0 Hz, H-6''), 6.12 (1H, d, J = 2.0 Hz, H-8'') suggested that 1 contained two naringenin moieties. The linkage of the two flavonone moieties was determined from the HMBC spectrum (Fig. 2). The HMBC correlations from H-2' (δ H 7.30) to C-3''' (δ C 126.1), C-4' (δ C 155.6) and C-6' (δ C 127.5), and from H-2''' (δ H 7.28) to C-3' (δ C 126.1), C-4''' (δ C 155.6), and C-6''' (δ C 127.5) confirmed that they are linked by C-3' C-3''' bonds. The methoxyl group was confirmed to be located at C-7 by the HMBC correlations between the methoxyl protons (δ H 3.88) and C-7 (δ C 167.9). The ECD spectrum of compound 1 exhibited positive Cotton effects at 328 nm and negative Cotton effects at 293 nm, indicating S configurations at both C-2 and C-2'' (Aguilar et al., 2008). Based on the above evidence, the structure of 1 was elucidated, as shown in Fig. 1.
- Involvenflavone J (5) was isolated as a yellow amorphous powder with a molecular formula of C22H14O8 determined by the negative HRESIMS ion at m/z 405.0612 [M - H] (calcd for C22H13O8, 405.0616). A comprehensive analysis of the 1D and 2D NMR spectra (Table 2) of 5 suggested a carbon skeleton the same as the carbon skeleton of unciflavone D, a known flavonoid isolated from Selaginella uncinata (Zou et al., 2014). The only difference was the position of the carboxyl group, which was attached to C-7 in compound 5, confirmed by the correlations from H-6 to the carboxyl carbon (δ C 173.7), C-8 (δ C 108.0), and C-10 (δ C 101.6). Therefore, the structure of 5 was determined as shown, and the compound was named involvenflavone J.
- The two known compounds were identified as (2''S)-2'',3''-dihydrorobustaflavone (4) (Zou et al., 2013) and unciflavone E (6) (Zou et al., 2014) by comparison with NMR and MS data in the literature.