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Flavonoids from the leaves and twigs of Knema elegans
Biochemical Systematics and Ecology 88 (2020) 103991
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Biochemical Systematics and Ecology journal homepage: www.elsevier.com/locate/biochemsyseco
Flavonoids from the leaves and twigs of Knema elegans a
a
b
a
a
a,∗
Zhao Lu , Wen-Chao Wu , Mei Wang , Jia-Qian Zhang , Ye-Gao Chen , Rui Zhan , Li-Dong Shaob,∗∗ a b
T
School of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming, 650050, PR China School of Chinese Materia Medica, Yunnan University of Chinese Medicine, Kunming, 650050, PR China
ARTICLE INFO
ABSTRACT
Keywords: Knema elegans Knemavones Chemotaxonomy
Knema elegans, a tropical evergreen plant, belongs to Myristicaceae family. Phytochemical investigation on the leaves and twigs of K. elegans led to the isolation and identification of two new flavonoids knemavones A and B (1 and 2), along with fifteen known analogues (3–17). These compounds belong to four subtypes of flavonoids, including chalcones, flavanes, flavones, and isoflavones. The structures of 1 and 2 were elucidated by means of spectroscopic techniques, including HRESIMS, 1D, and 2D NMR experiments. Compounds 3–17 are isolated from the title plant for the first time. Moreover, the new chalcones 1 and 2 could serve as chemotaxonomic markers of K. elegans.
1. Subject and source
3. Present study
The genus Knema (Myristicaceae) is comprised of approximately 11 species. Members of genus Knema are tropical evergreen trees, and some species are used to extract industrial oil from the seeds (Sriphana et al., 2016; Wu et al., 2008). This sample was collected in Mengla County, Yunnan Province, China. A voucher specimen (No. 20170712R) has been deposited at the school of Chemistry and Chemical Engineering, Yunnan Normal University.
3.1. Extraction and isolation
2. Previous work To date, only the trunk wood of K. elegans collected in Thailand has been subjected to phytochemical work, which led to the isolation of two flavane derivates (Deng et al., 2005). Previous chemical investigation on other species of Knema genus revealed the presence of acetophenones (Geny et al., 2016; Sriphana et al., 2016; Zeng et al., 1994), lignans (Gonzaléz et al., 1993; Joshi et al., 1978; Pinto et al., 1990; Rangkaew et al., 2009a; Taher et al., 2017), isocoumarins (Kijjoa et al., 1991), flavonoids (Ismail et al., 2015; Gonzaléz et al., 1993; Mei et al., 2000, 2002; Rangkaew et al., 2009a; Zeng et al., 1994), alkyl or acyl resorcinols (Gonzaléz et al., 1993; Pinto et al., 1990), and phenylalkyl phenols (Akhtar et al., 2011; Alen et al., 2000; Geny et al., 2016; Gonzaléz et al., 1996; Kijjoa et al., 1991; Rangkaew et al., 2009b; Spencer et al., 1980; Zahir et al., 1993; Zeng et al., 1994).
∗
The twigs and leaves (17.5 Kg) of K. elegans were extracted with 70% aqueous acetone four times (four days for each time) at room temperature and filtered. The filtrate was evaporated in vacuo. Then the concentrate without acetone (10 L) was partitioned between EtOAc and H2O. The EtOAc portion (325 g) was isolated by CC (silica gel, gradient petroleum ether/acetone 20:1 to 0:1) to yield five fractions AE. Fractions A and E were left untreated. Fraction B (23.0 g) was further repeatedly subjected to CC (Silica gel petroleum ether/EtOAc 50:1 to 1:1; Silica gel CHCl3/acetone 50:1 to 5:1; Sephadex LH-20, CHCl3/MeOH 3:2) to give compounds 2 (5.6 mg), 3 (13.5 mg), and 16 (14.9 mg) (Fig. 1). Fraction C (48.1 g) was applied to a Sephadex LH-20 column eluting with CHCl3/MeOH (3:2) to provide three major fractions (C1–C3). Compound 4 (22.6 mg), 8 (14. mg), and 9 (15.2 mg) were obtained from Fr.C1 (4.1 g) by silica gel CC (CHCl3/acetone 30:1 to 5:1) and Sephadex LH-20 (MeOH). Fr.C2 (15.3 g) was purified on silica gel CC (CHCl3/acetone 20:1 to 2:1) and Sephadex LH-20 (CHCl3/MeOH 3:2) to furnish 5 (24 mg), 10 (30 mg), and 11 (4.1 mg). Fr. C3 (11.6 g) was subjected to silica gel column eluting with petroleum ether/EtOAc (10:1 to 1:1) and Sephadex LH-20 (CHCl3/MeOH 3:2) to give 12 (2.5 mg), 15 (35 mg), and 17 (5 mg) (Fig. 1). Fraction D (26.2 g) was applied to a Sephadex LH-20 column eluting
Corresponding author. Corresponding author. E-mail addresses: [email protected] (R. Zhan), [email protected] (L.-D. Shao).
∗∗
https://doi.org/10.1016/j.bse.2019.103991 Received 3 November 2019; Received in revised form 6 December 2019; Accepted 14 December 2019 0305-1978/ © 2019 Published by Elsevier Ltd.
Biochemical Systematics and Ecology 88 (2020) 103991
Z. Lu, et al.
Fig. 1. Structures of compounds isolated from K. elegans.
with CHCl3/MeOH (3:2) to provide two major fractions (D1–D2). Compound 1 (4.7 mg) and 7 (13.4 mg) was obtained from Fr.D1 (7.4 g) by silica gel CC (CHCl3/acetone 30:1 to 1:1) and Sephadex LH-20 (MeOH). Fr.D2 (12.3 g) was purified on silica gel CC (CHCl3/acetone 10:1 to 0:1) and then isolated on Sephadex LH-20 with CHCl3/MeOH (3:2) to furnish 6 (14.4 mg) 13 (6.5 mg), and 14 (7.6 mg) (Fig. 1). 3.2. Structure elucidation
Fig. 2. Key 1H-1H COSY and key HMBC (H→C) correlations for 1 and 2.
Compound 1 was obtained as a colorless oil. The HRESIMS pseudomolecular ion [M + Na]- at m/z 325.1056 is consistent with the molecular formula of C17H18O5, indicating 9 indices of hydrogen deficiency. The IR spectrum showed absorption bands for hydroxy group (3423 cm−1) and aromatic moieties (1505 cm−1) (Ma et al., 2014). Analysis of the 1H, 13C, and HSQC NMR data (Table 1) indicated the presence of two phenyl groups (five of those carbons were oxygenated, and four of which were protonated), four methylene groups (including a methylenedioxy group), and a methyl group. Above data suggested that 1 is a diarylpropane (reduced chalcone), similar to horsfielane A
(Du et al., 2017). 2D-NMR spectra highlighted the difference and helped to determine the structure of 1. Key HMBC correlations (Fig. 2) between H-1 and C-2′, H-6′ and C-2'/C-4′, as well as correlations between H-3′-Me and C-2'/C-3′, suggest that the 2′,4′-dihydroxy-3′-methylphenyl moiety is connected to C-1. The only difference was proved to be the connectivity of an additional hydroxy group at C-2″ in 1, which was verified by HMBC correlations from H-3 and H-6″ to C-2″, and further by the HRESIMS data. Therefore, compound 1 was deduced as 1-(2′,4′-dihydroxy-3′-methylphenyl)-3-(2″-hydroxy-4″,5″-methylenedioxyphenyl)-propane, named knemavone A. Indicated by HRESIMS (a [M - H]- peak at 301.1093), compounds 2 and 1 shared the same molecular formula of C17H18O5. Analysis of the NMR data of compound 2 suggested that 2 is also a reduced chalcone, which is similar to 1. Whereas, the assignment of a 2′-hydroxy-4′-methoxyphenyl group at C-1 of 2 was based on HMBC correlations from H-1, H-3′, and H-6′ to C-2′, along with correlations from H-OMe’ to C-4'. Thus, compound 2 was deduced as 1-(2′-hydroxy-4′-methoxylphenyl)-3-(2″hydroxy-4″,5″-methylenedioxyphenyl)-propane, named knemavone B. The structural characterizations of compounds 3–17 were performed by 1D NMR, MS, and comparison with data of those reported in the literature. These compounds were identified as virolane (3) (L. de Almeida et al., 1979), 1-(2′-hydroxy-4′-methoxyphenyl)-3-(4″-hydroxy3″-methoxyphenyl)-propane (4) (Yao et al., 2018), 1-(2′,4′-dihydroxy3′-methylphenyl)-3-(2″,-methoxy-4″,5″-methylenedioxyphenyl)-propane (5) (L. de Almeida et al., 1979), genistein (6) (Hanawa et al., 1991), tectorigenin (7) (Li et al., 2016), 5,7,2′-trihydroxy-4′-methoxyisoflavone (8) (F.O et al., 1976), formononetin (9) (Zeng et al., 1994), 2′,5,7-trihydroxy-4′-metoxyisoflavone (10) (F.O et al., 1976), 7,2′-dihydroxy-4′,5′-methylenedioxyisoflavone (11) (Kaimoyo and VanEtten, 2008), 2′-hydroxypseudobaptigenin (12) (Zhao et al., 2003), 3′,4′,7trihydroxyflavone (13) (Júnior et al., 2008), luteolin (14) (Júnior et al., 2008), quercetin (15) (Krasnov et al., 2006), (2R, 4R)-4′-hydroxy-3′-
Table 1 1 H- (500 MHz) and13C-NMR (125 MHz) data for 1–2 (δ in ppm and J in Hz). No.
1 2 3 1′ 2′ 3′ 4′ 5′ 6′ 1″ 2″ 3″ 4″ 5″ 6″ 3′-Me 4′-OMe OCH2O a
1a
2a
δH (mult. J, Hz)
δC (mult.)
δH (mult. J, Hz)
δC (mult.)
2.49, overlapped 1.71, m 2.49, overlapped
2.55, overlapped 1.79, m 2.55, overlapped
6.52, s 2.03, s
30.8 t 32.0 t 30.9 t 122.1 s 154.3 s 112.9 s 154.8 s 107.9 d 127.6 d 122.2 s 150.1 s 98.7 s 146.9 s 141.7 d 110.2 d 9.0 q
6.57, s
30.3 t 31.8 t 30.8 t 122.3 s 156.9 s 102.4 d 160.2 s 105.6 d 131.3 d 122.7 s 150.3 s 98.6 d 147.0 s 141.7 s 110.2 d
5.74, s
101.7 t
3.72, s 5.80, s
55.6 q 101.7 t
6.27, d, (8.2) 6.67, d, (8.2) 6.33, s
6.43, d, (2.4) 6.34, dd, (8.2,2.4) 6.95, d, (8.2) 6.36, s
Data were recorded in CD3OD. 2
Biochemical Systematics and Ecology 88 (2020) 103991
Z. Lu, et al.
Table 2 Flavonoids isolated from Knema genus. Species
Authorities
Parts
Subtypes
Compounds name
K. globularia
(Lam.) Warb.
twigs
flavone flavonol
luteolin quercetin-3-O-β-D-glucopyranoside, kaempferol, kaempferol-3-O-β-Dglucopyranoside, kaempferol-3-O-β-D-rutinoside, kaempferol-3-O-β-Dgalactopyranoside taxifolin catechin proanthocyanidin sulfuretin luteolin (+)-catechin, (−)-catechin 7,4′-dihydroxy-3′-methoxyflavan, 5,7,3′-trihydroxy-4′-methoxyflavan formononetin, biochanin A, 8-O-methylretusin 7,4′- dihydroxy-3′-methoxyflavan, myristinin D, myristinin A myristinins A and D 7,4′- dihydroxy-3′-methoxyflavan
K. laurina
Warb.
stem barks
K. K. K. K.
(Blanco) Merr. Warb. Warb. W.J.de Wilde
stem barks leaves trunk trunk
glomerate glauca elegans austrosiamensis
flavanone flavanol dimeric flavane aurone flavone flavanol flavane isoflavone flavane flavane flavane
Reference
methyl-6,7- methylenedioxy-4-O-2′-cycloflavan (16) (Peng et al., 2016), and 7,4′-dihydroxy-3′-methoxyjauan (17) (Ghosal et al., 1985), respectively.
Mei et al. (2002); Mei et al. (2000)
Ismail et al. (2015) Zeng et al. (1994) Rangkaew et al. (2009a) Deng et al. (2005) Gonzaléz et al. (1993)
CRediT authorship contribution statement Zhao Lu: Investigation, Methodology. Wen-Chao Wu: Investigation, Methodology. Mei Wang: Data curation. Jia-Qian Zhang: Data curation. Ye-Gao Chen: Writing - original draft. Rui Zhan: Writing - original draft, Supervision. Li-Dong Shao: Writing review & editing.
3.3. Knemavones Knemavone A, colorless oil; UV (MeOH) λmax (log ε): 302 (3.0), 204 (3.8) nm; IR (KBr) cm−1: 3532, 3423, 2943, 1620, 1501, 1447, 1176, 1040; 1H and 13C NMR data (CD3OD) see, Table 1; positive HRESIMS m/z 325.1056 [M + Na]+ (calcd for C17H18O5, 325.1046). Knemavone B, colorless oil; UV (MeOH) λmax (log ε): 301 (3.1), 288 (3.1), 203 (3.9) nm; IR (KBr) cm−1: 3508, 3396, 2922, 2856, 1620, 1522, 1175, 1040; 1H and 13C NMR data (CD3OD) see, Table 1; negative HRESIMS m/z 301.1093 [M - H]- (calcd for C17H18O5, 301.1081).
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements
3.4. Experimental
This project was supported in part by the National Natural Science Foundation of China (31460086 and 31860097), the Science and Technology Program of Yunnan Province (2017FB135), the Start-up Fund of Yunnan University of Chinese Medicine (2019YZG03), and the Discipline Funding of School of Chinese Materia Medica, Yunnan University of Chinese Medicine (2019ZY018).
The IR spectra were obtained by a Tensor 27 spectrophotometer using KBr pellets. The 1D and 2D NMR spectra were recorded on a Bruker DRX-500 MHz spectrometer with TMS as internal standard. Chemical shifts (δ) were expressed in ppm with reference to the solvent signals. The HRESIMS data were recorded on an Agilent G6230 TOF MS.
Appendix A. Supplementary data
4. Chemotaxonomic significance
Supplementary data to this article can be found online at https:// doi.org/10.1016/j.bse.2019.103991.
The genus Knema, an important representative of Myristicaceae family, is comprised of about 11 species. Species of Knema are tropical evergreen trees. Previous phytochemical investigations of six species of Knema led to the isolation of eight subtypes of flavonoids which were not only from the twigs, but also from the stem barks, leaves, and the trunk of trees (Table 2). A previous study had isolated the flavanes myristinins A and D from the trunk of K. elegans (Deng et al., 2005), although the flavanes had also been reported from K. laurina, K. glauca, and K. austrosiamensis (Table 2). In this study, 17 flavanoids were isolated from the twigs and leaves of K. elegans for the first time. These 17 flavonoids belong to five subtypes: chalcone (1–5), isoflavone (6–12), flavonol (16), flavone (13–15), and flavane (17). Among the five chalcones isolated (1–5), two of them were new compounds, and have been named as knemavones A and B (1 and 2). The above results indicate that K. elegans shares some similar chemical characteristics (flavone, flavonol, flavane, and isoflavone) with five other reported species of Knema (Table 2). However, to the best of our knowledge, this is the first report of chalcones from a species of Knema. Therefore, these chalcones, especially the new ones 1 and 2 may serve as potential chemotaxonomic markers for K. elegans and could be used to distinguish among species of Knema.
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Biochemical Systematics and Ecology journal homepage: www.elsevier.com/locate/biochemsyseco
Flavonoids from the leaves and twigs of Knema elegans a
a
b
a
a
a,∗
Zhao Lu , Wen-Chao Wu , Mei Wang , Jia-Qian Zhang , Ye-Gao Chen , Rui Zhan , Li-Dong Shaob,∗∗ a b
T
School of Chemistry and Chemical Engineering, Yunnan Normal University, Kunming, 650050, PR China School of Chinese Materia Medica, Yunnan University of Chinese Medicine, Kunming, 650050, PR China
ARTICLE INFO
ABSTRACT
Keywords: Knema elegans Knemavones Chemotaxonomy
Knema elegans, a tropical evergreen plant, belongs to Myristicaceae family. Phytochemical investigation on the leaves and twigs of K. elegans led to the isolation and identification of two new flavonoids knemavones A and B (1 and 2), along with fifteen known analogues (3–17). These compounds belong to four subtypes of flavonoids, including chalcones, flavanes, flavones, and isoflavones. The structures of 1 and 2 were elucidated by means of spectroscopic techniques, including HRESIMS, 1D, and 2D NMR experiments. Compounds 3–17 are isolated from the title plant for the first time. Moreover, the new chalcones 1 and 2 could serve as chemotaxonomic markers of K. elegans.
1. Subject and source
3. Present study
The genus Knema (Myristicaceae) is comprised of approximately 11 species. Members of genus Knema are tropical evergreen trees, and some species are used to extract industrial oil from the seeds (Sriphana et al., 2016; Wu et al., 2008). This sample was collected in Mengla County, Yunnan Province, China. A voucher specimen (No. 20170712R) has been deposited at the school of Chemistry and Chemical Engineering, Yunnan Normal University.
3.1. Extraction and isolation
2. Previous work To date, only the trunk wood of K. elegans collected in Thailand has been subjected to phytochemical work, which led to the isolation of two flavane derivates (Deng et al., 2005). Previous chemical investigation on other species of Knema genus revealed the presence of acetophenones (Geny et al., 2016; Sriphana et al., 2016; Zeng et al., 1994), lignans (Gonzaléz et al., 1993; Joshi et al., 1978; Pinto et al., 1990; Rangkaew et al., 2009a; Taher et al., 2017), isocoumarins (Kijjoa et al., 1991), flavonoids (Ismail et al., 2015; Gonzaléz et al., 1993; Mei et al., 2000, 2002; Rangkaew et al., 2009a; Zeng et al., 1994), alkyl or acyl resorcinols (Gonzaléz et al., 1993; Pinto et al., 1990), and phenylalkyl phenols (Akhtar et al., 2011; Alen et al., 2000; Geny et al., 2016; Gonzaléz et al., 1996; Kijjoa et al., 1991; Rangkaew et al., 2009b; Spencer et al., 1980; Zahir et al., 1993; Zeng et al., 1994).
∗
The twigs and leaves (17.5 Kg) of K. elegans were extracted with 70% aqueous acetone four times (four days for each time) at room temperature and filtered. The filtrate was evaporated in vacuo. Then the concentrate without acetone (10 L) was partitioned between EtOAc and H2O. The EtOAc portion (325 g) was isolated by CC (silica gel, gradient petroleum ether/acetone 20:1 to 0:1) to yield five fractions AE. Fractions A and E were left untreated. Fraction B (23.0 g) was further repeatedly subjected to CC (Silica gel petroleum ether/EtOAc 50:1 to 1:1; Silica gel CHCl3/acetone 50:1 to 5:1; Sephadex LH-20, CHCl3/MeOH 3:2) to give compounds 2 (5.6 mg), 3 (13.5 mg), and 16 (14.9 mg) (Fig. 1). Fraction C (48.1 g) was applied to a Sephadex LH-20 column eluting with CHCl3/MeOH (3:2) to provide three major fractions (C1–C3). Compound 4 (22.6 mg), 8 (14. mg), and 9 (15.2 mg) were obtained from Fr.C1 (4.1 g) by silica gel CC (CHCl3/acetone 30:1 to 5:1) and Sephadex LH-20 (MeOH). Fr.C2 (15.3 g) was purified on silica gel CC (CHCl3/acetone 20:1 to 2:1) and Sephadex LH-20 (CHCl3/MeOH 3:2) to furnish 5 (24 mg), 10 (30 mg), and 11 (4.1 mg). Fr. C3 (11.6 g) was subjected to silica gel column eluting with petroleum ether/EtOAc (10:1 to 1:1) and Sephadex LH-20 (CHCl3/MeOH 3:2) to give 12 (2.5 mg), 15 (35 mg), and 17 (5 mg) (Fig. 1). Fraction D (26.2 g) was applied to a Sephadex LH-20 column eluting
Corresponding author. Corresponding author. E-mail addresses: [email protected] (R. Zhan), [email protected] (L.-D. Shao).
∗∗
https://doi.org/10.1016/j.bse.2019.103991 Received 3 November 2019; Received in revised form 6 December 2019; Accepted 14 December 2019 0305-1978/ © 2019 Published by Elsevier Ltd.
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Fig. 1. Structures of compounds isolated from K. elegans.
with CHCl3/MeOH (3:2) to provide two major fractions (D1–D2). Compound 1 (4.7 mg) and 7 (13.4 mg) was obtained from Fr.D1 (7.4 g) by silica gel CC (CHCl3/acetone 30:1 to 1:1) and Sephadex LH-20 (MeOH). Fr.D2 (12.3 g) was purified on silica gel CC (CHCl3/acetone 10:1 to 0:1) and then isolated on Sephadex LH-20 with CHCl3/MeOH (3:2) to furnish 6 (14.4 mg) 13 (6.5 mg), and 14 (7.6 mg) (Fig. 1). 3.2. Structure elucidation
Fig. 2. Key 1H-1H COSY and key HMBC (H→C) correlations for 1 and 2.
Compound 1 was obtained as a colorless oil. The HRESIMS pseudomolecular ion [M + Na]- at m/z 325.1056 is consistent with the molecular formula of C17H18O5, indicating 9 indices of hydrogen deficiency. The IR spectrum showed absorption bands for hydroxy group (3423 cm−1) and aromatic moieties (1505 cm−1) (Ma et al., 2014). Analysis of the 1H, 13C, and HSQC NMR data (Table 1) indicated the presence of two phenyl groups (five of those carbons were oxygenated, and four of which were protonated), four methylene groups (including a methylenedioxy group), and a methyl group. Above data suggested that 1 is a diarylpropane (reduced chalcone), similar to horsfielane A
(Du et al., 2017). 2D-NMR spectra highlighted the difference and helped to determine the structure of 1. Key HMBC correlations (Fig. 2) between H-1 and C-2′, H-6′ and C-2'/C-4′, as well as correlations between H-3′-Me and C-2'/C-3′, suggest that the 2′,4′-dihydroxy-3′-methylphenyl moiety is connected to C-1. The only difference was proved to be the connectivity of an additional hydroxy group at C-2″ in 1, which was verified by HMBC correlations from H-3 and H-6″ to C-2″, and further by the HRESIMS data. Therefore, compound 1 was deduced as 1-(2′,4′-dihydroxy-3′-methylphenyl)-3-(2″-hydroxy-4″,5″-methylenedioxyphenyl)-propane, named knemavone A. Indicated by HRESIMS (a [M - H]- peak at 301.1093), compounds 2 and 1 shared the same molecular formula of C17H18O5. Analysis of the NMR data of compound 2 suggested that 2 is also a reduced chalcone, which is similar to 1. Whereas, the assignment of a 2′-hydroxy-4′-methoxyphenyl group at C-1 of 2 was based on HMBC correlations from H-1, H-3′, and H-6′ to C-2′, along with correlations from H-OMe’ to C-4'. Thus, compound 2 was deduced as 1-(2′-hydroxy-4′-methoxylphenyl)-3-(2″hydroxy-4″,5″-methylenedioxyphenyl)-propane, named knemavone B. The structural characterizations of compounds 3–17 were performed by 1D NMR, MS, and comparison with data of those reported in the literature. These compounds were identified as virolane (3) (L. de Almeida et al., 1979), 1-(2′-hydroxy-4′-methoxyphenyl)-3-(4″-hydroxy3″-methoxyphenyl)-propane (4) (Yao et al., 2018), 1-(2′,4′-dihydroxy3′-methylphenyl)-3-(2″,-methoxy-4″,5″-methylenedioxyphenyl)-propane (5) (L. de Almeida et al., 1979), genistein (6) (Hanawa et al., 1991), tectorigenin (7) (Li et al., 2016), 5,7,2′-trihydroxy-4′-methoxyisoflavone (8) (F.O et al., 1976), formononetin (9) (Zeng et al., 1994), 2′,5,7-trihydroxy-4′-metoxyisoflavone (10) (F.O et al., 1976), 7,2′-dihydroxy-4′,5′-methylenedioxyisoflavone (11) (Kaimoyo and VanEtten, 2008), 2′-hydroxypseudobaptigenin (12) (Zhao et al., 2003), 3′,4′,7trihydroxyflavone (13) (Júnior et al., 2008), luteolin (14) (Júnior et al., 2008), quercetin (15) (Krasnov et al., 2006), (2R, 4R)-4′-hydroxy-3′-
Table 1 1 H- (500 MHz) and13C-NMR (125 MHz) data for 1–2 (δ in ppm and J in Hz). No.
1 2 3 1′ 2′ 3′ 4′ 5′ 6′ 1″ 2″ 3″ 4″ 5″ 6″ 3′-Me 4′-OMe OCH2O a
1a
2a
δH (mult. J, Hz)
δC (mult.)
δH (mult. J, Hz)
δC (mult.)
2.49, overlapped 1.71, m 2.49, overlapped
2.55, overlapped 1.79, m 2.55, overlapped
6.52, s 2.03, s
30.8 t 32.0 t 30.9 t 122.1 s 154.3 s 112.9 s 154.8 s 107.9 d 127.6 d 122.2 s 150.1 s 98.7 s 146.9 s 141.7 d 110.2 d 9.0 q
6.57, s
30.3 t 31.8 t 30.8 t 122.3 s 156.9 s 102.4 d 160.2 s 105.6 d 131.3 d 122.7 s 150.3 s 98.6 d 147.0 s 141.7 s 110.2 d
5.74, s
101.7 t
3.72, s 5.80, s
55.6 q 101.7 t
6.27, d, (8.2) 6.67, d, (8.2) 6.33, s
6.43, d, (2.4) 6.34, dd, (8.2,2.4) 6.95, d, (8.2) 6.36, s
Data were recorded in CD3OD. 2
Biochemical Systematics and Ecology 88 (2020) 103991
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Table 2 Flavonoids isolated from Knema genus. Species
Authorities
Parts
Subtypes
Compounds name
K. globularia
(Lam.) Warb.
twigs
flavone flavonol
luteolin quercetin-3-O-β-D-glucopyranoside, kaempferol, kaempferol-3-O-β-Dglucopyranoside, kaempferol-3-O-β-D-rutinoside, kaempferol-3-O-β-Dgalactopyranoside taxifolin catechin proanthocyanidin sulfuretin luteolin (+)-catechin, (−)-catechin 7,4′-dihydroxy-3′-methoxyflavan, 5,7,3′-trihydroxy-4′-methoxyflavan formononetin, biochanin A, 8-O-methylretusin 7,4′- dihydroxy-3′-methoxyflavan, myristinin D, myristinin A myristinins A and D 7,4′- dihydroxy-3′-methoxyflavan
K. laurina
Warb.
stem barks
K. K. K. K.
(Blanco) Merr. Warb. Warb. W.J.de Wilde
stem barks leaves trunk trunk
glomerate glauca elegans austrosiamensis
flavanone flavanol dimeric flavane aurone flavone flavanol flavane isoflavone flavane flavane flavane
Reference
methyl-6,7- methylenedioxy-4-O-2′-cycloflavan (16) (Peng et al., 2016), and 7,4′-dihydroxy-3′-methoxyjauan (17) (Ghosal et al., 1985), respectively.
Mei et al. (2002); Mei et al. (2000)
Ismail et al. (2015) Zeng et al. (1994) Rangkaew et al. (2009a) Deng et al. (2005) Gonzaléz et al. (1993)
CRediT authorship contribution statement Zhao Lu: Investigation, Methodology. Wen-Chao Wu: Investigation, Methodology. Mei Wang: Data curation. Jia-Qian Zhang: Data curation. Ye-Gao Chen: Writing - original draft. Rui Zhan: Writing - original draft, Supervision. Li-Dong Shao: Writing review & editing.
3.3. Knemavones Knemavone A, colorless oil; UV (MeOH) λmax (log ε): 302 (3.0), 204 (3.8) nm; IR (KBr) cm−1: 3532, 3423, 2943, 1620, 1501, 1447, 1176, 1040; 1H and 13C NMR data (CD3OD) see, Table 1; positive HRESIMS m/z 325.1056 [M + Na]+ (calcd for C17H18O5, 325.1046). Knemavone B, colorless oil; UV (MeOH) λmax (log ε): 301 (3.1), 288 (3.1), 203 (3.9) nm; IR (KBr) cm−1: 3508, 3396, 2922, 2856, 1620, 1522, 1175, 1040; 1H and 13C NMR data (CD3OD) see, Table 1; negative HRESIMS m/z 301.1093 [M - H]- (calcd for C17H18O5, 301.1081).
Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements
3.4. Experimental
This project was supported in part by the National Natural Science Foundation of China (31460086 and 31860097), the Science and Technology Program of Yunnan Province (2017FB135), the Start-up Fund of Yunnan University of Chinese Medicine (2019YZG03), and the Discipline Funding of School of Chinese Materia Medica, Yunnan University of Chinese Medicine (2019ZY018).
The IR spectra were obtained by a Tensor 27 spectrophotometer using KBr pellets. The 1D and 2D NMR spectra were recorded on a Bruker DRX-500 MHz spectrometer with TMS as internal standard. Chemical shifts (δ) were expressed in ppm with reference to the solvent signals. The HRESIMS data were recorded on an Agilent G6230 TOF MS.
Appendix A. Supplementary data
4. Chemotaxonomic significance
Supplementary data to this article can be found online at https:// doi.org/10.1016/j.bse.2019.103991.
The genus Knema, an important representative of Myristicaceae family, is comprised of about 11 species. Species of Knema are tropical evergreen trees. Previous phytochemical investigations of six species of Knema led to the isolation of eight subtypes of flavonoids which were not only from the twigs, but also from the stem barks, leaves, and the trunk of trees (Table 2). A previous study had isolated the flavanes myristinins A and D from the trunk of K. elegans (Deng et al., 2005), although the flavanes had also been reported from K. laurina, K. glauca, and K. austrosiamensis (Table 2). In this study, 17 flavanoids were isolated from the twigs and leaves of K. elegans for the first time. These 17 flavonoids belong to five subtypes: chalcone (1–5), isoflavone (6–12), flavonol (16), flavone (13–15), and flavane (17). Among the five chalcones isolated (1–5), two of them were new compounds, and have been named as knemavones A and B (1 and 2). The above results indicate that K. elegans shares some similar chemical characteristics (flavone, flavonol, flavane, and isoflavone) with five other reported species of Knema (Table 2). However, to the best of our knowledge, this is the first report of chalcones from a species of Knema. Therefore, these chalcones, especially the new ones 1 and 2 may serve as potential chemotaxonomic markers for K. elegans and could be used to distinguish among species of Knema.
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