Article pubs.acs.org/jnp
Bisindole Alkaloids with Neural Anti-inflammatory Activity from Gelsemium elegans Jing Qu,† Lei Fang,† Xiao-Dong Ren, Yunbao Liu, Shi-Shan Yu,* Li Li, Xiu-Qi Bao, Dan Zhang, Yong Li, and Shuang-Gang Ma State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100050, People’s Republic of China S Supporting Information *
ABSTRACT: Three new trace bisindole alkaloids geleganimines A and B (1, 2) and geleganamide (3) were isolated from the aerial parts of Gelsemium elegans. Their structures were elucidated by spectroscopy, particularly from their carbon−proton coupling constants, and electronic circular dichroism. Compounds 1−3 are the first bisindole alkaloids discovered from the genus Gelsemium. Geleganimine B exhibited anti-inflammatory activity indirectly by suppressing lipopolysaccharide-induced proinflammatory factors in BV2 microglial cells with an IC50 value of 10.2 μM. These findings confirm the importance of bioactive trace components in medicinal plant research.
M
quantity (50 kg) of the aerial parts of G. elegans was extracted. The target isolation resulted in three new bisindole alkaloids, geleganimines A and B (1, 2) and geleganamide (3). Their structures were determined by extensive spectroscopic analysis, particularly the carbon−proton coupling constants, and electronic circular dichroism (ECD) experiments. Compounds 1−3 are the first reported bisindole alkaloids from the genus Gelsemium. Herein, we report their structural elucidation, bioactivity, and putative biosynthetic route.
icroglia are endogenous immune cells in the central nervous system that play critical roles in neurodegenerative disorders, such as Parkinson’s disease (PD) and Alzheimer’s disease (AD). Accumulating evidence suggests that activated microglia release neural inflammatory mediators, such as interleukin (IL)-1β, nitric oxide (NO), and TNF-α, and inhibition of microglia may represent a novel pharmaceutical approach for the treatment of PD and AD.1 Indole alkaloids are characteristic constituents of Gelsemium plants. In addition to their analgesic, antitumor, and immunomodulating activities, Gelsemium alkaloids exhibit anti-inflammatory activity in a rat ear edema model.2 In this study, we investigated whether Gelsemium spp. possess new alkaloids with microglial inhibition activity. As a representative plant of the genus Gelsemium, G. elegans Benth. has historically been used in traditional Chinese medicine.3 Its constituents have been widely investigated, and a large number of alkaloids have been isolated.4 Based on the UV spectra and MS data of known Gelsemium alkaloids, chemical screening was performed to investigate new alkaloids from G. elegans using HPLC/UV and HPLC/ESI-MS n techniques. We discovered several trace indole alkaloids with molecular weights approximately twice those of known Gelsemium alkaloids.4 To isolate these trace alkaloids, a large © 2013 American Chemical Society and American Society of Pharmacognosy
■
RESULTS AND DISCUSSION
Geleganimine A (1) was obtained as a white powder. The molecular formula, C39H44N4O8, was determined by HRESIMS [M + H]+ m/z 697.3249 (calcd 697.3232), which indicated 20 indices of hydrogen deficiency. UV absorptions at 214 and 258 nm suggested an indole moiety. The IR spectrum suggested the presence of carbonyl (1725 cm−1), imine (1617 cm−1), and aromatic ring (1465 cm−1) functionalities. 13C NMR data indicated two carbonyls, 12 aromatic carbons, two oxymethines (δC 75.2, 74.8), two N-substituted methines (δC 72.2, 69.0), two oxymethylenes (δC 62.0, 62.0), two methoxy groups (δC Received: July 9, 2013 Published: November 20, 2013 2203
dx.doi.org/10.1021/np4005536 | J. Nat. Prod. 2013, 76, 2203−2209
Journal of Natural Products
Article
C(22)H2; thus, a bond between the additional methylene (C22) and C-19′ was established. The presence of an oxaziridine ring was confirmed by the IR absorption band at 1319 cm−1.6 Hence, the structure of moiety II was determined to be that shown in Figure 1. The linkage between moieties I and II was verified by the HMBC correlations. Moieties I and II accounted for 10 indices of hydrogen deficiency each, indicating an acyclic linkage between moieties I and II. HMBC correlations from H2-22 to C-18 and C-20 revealed a linkage between C-19 and C-22, which was confirmed by the strong correlation from H-19′ to C-19 (Figure 2). Thus, the structure of 1 was elucidated. A crystal of 1 could not be obtained despite many attempts. The configuration of 1 was therefore elucidated based on the NOE correlations, carbon−proton coupling constants, and ECD experiments. The NOE correlations H-3/H2-14, H-5/H16, H-15/H3-18, H-3′/H2-14′, H-5′/H-16′, and H-19′/H-14′a (δH 2.82) indicated that the configurations of moieties I and II at C-3, C-5, C-15, C-16, C-3′, C-5′, C-15′, C-16′, and C-20′ were identical to those of gelsenicine and gelseziridine, respectively. The relative configuration of the acyclic linkage C-19−C-19′ was assigned using carbon−proton coupling constants from an HSQMBC spectrum.7 C-19 and C-19′ were separated by a methylene group (C-22), the diastereotopic protons of which were assigned as H-22a (δH 2.58) and H-22b (δH 2.05), permitting the determination of the relative configuration of C19 and C-19′. The small coupling constant of
Bisindole Alkaloids with Neural Anti-inflammatory Activity from Gelsemium elegans Jing Qu,† Lei Fang,† Xiao-Dong Ren, Yunbao Liu, Shi-Shan Yu,* Li Li, Xiu-Qi Bao, Dan Zhang, Yong Li, and Shuang-Gang Ma State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing 100050, People’s Republic of China S Supporting Information *
ABSTRACT: Three new trace bisindole alkaloids geleganimines A and B (1, 2) and geleganamide (3) were isolated from the aerial parts of Gelsemium elegans. Their structures were elucidated by spectroscopy, particularly from their carbon−proton coupling constants, and electronic circular dichroism. Compounds 1−3 are the first bisindole alkaloids discovered from the genus Gelsemium. Geleganimine B exhibited anti-inflammatory activity indirectly by suppressing lipopolysaccharide-induced proinflammatory factors in BV2 microglial cells with an IC50 value of 10.2 μM. These findings confirm the importance of bioactive trace components in medicinal plant research.
M
quantity (50 kg) of the aerial parts of G. elegans was extracted. The target isolation resulted in three new bisindole alkaloids, geleganimines A and B (1, 2) and geleganamide (3). Their structures were determined by extensive spectroscopic analysis, particularly the carbon−proton coupling constants, and electronic circular dichroism (ECD) experiments. Compounds 1−3 are the first reported bisindole alkaloids from the genus Gelsemium. Herein, we report their structural elucidation, bioactivity, and putative biosynthetic route.
icroglia are endogenous immune cells in the central nervous system that play critical roles in neurodegenerative disorders, such as Parkinson’s disease (PD) and Alzheimer’s disease (AD). Accumulating evidence suggests that activated microglia release neural inflammatory mediators, such as interleukin (IL)-1β, nitric oxide (NO), and TNF-α, and inhibition of microglia may represent a novel pharmaceutical approach for the treatment of PD and AD.1 Indole alkaloids are characteristic constituents of Gelsemium plants. In addition to their analgesic, antitumor, and immunomodulating activities, Gelsemium alkaloids exhibit anti-inflammatory activity in a rat ear edema model.2 In this study, we investigated whether Gelsemium spp. possess new alkaloids with microglial inhibition activity. As a representative plant of the genus Gelsemium, G. elegans Benth. has historically been used in traditional Chinese medicine.3 Its constituents have been widely investigated, and a large number of alkaloids have been isolated.4 Based on the UV spectra and MS data of known Gelsemium alkaloids, chemical screening was performed to investigate new alkaloids from G. elegans using HPLC/UV and HPLC/ESI-MS n techniques. We discovered several trace indole alkaloids with molecular weights approximately twice those of known Gelsemium alkaloids.4 To isolate these trace alkaloids, a large © 2013 American Chemical Society and American Society of Pharmacognosy
■
RESULTS AND DISCUSSION
Geleganimine A (1) was obtained as a white powder. The molecular formula, C39H44N4O8, was determined by HRESIMS [M + H]+ m/z 697.3249 (calcd 697.3232), which indicated 20 indices of hydrogen deficiency. UV absorptions at 214 and 258 nm suggested an indole moiety. The IR spectrum suggested the presence of carbonyl (1725 cm−1), imine (1617 cm−1), and aromatic ring (1465 cm−1) functionalities. 13C NMR data indicated two carbonyls, 12 aromatic carbons, two oxymethines (δC 75.2, 74.8), two N-substituted methines (δC 72.2, 69.0), two oxymethylenes (δC 62.0, 62.0), two methoxy groups (δC Received: July 9, 2013 Published: November 20, 2013 2203
dx.doi.org/10.1021/np4005536 | J. Nat. Prod. 2013, 76, 2203−2209
Journal of Natural Products
Article
C(22)H2; thus, a bond between the additional methylene (C22) and C-19′ was established. The presence of an oxaziridine ring was confirmed by the IR absorption band at 1319 cm−1.6 Hence, the structure of moiety II was determined to be that shown in Figure 1. The linkage between moieties I and II was verified by the HMBC correlations. Moieties I and II accounted for 10 indices of hydrogen deficiency each, indicating an acyclic linkage between moieties I and II. HMBC correlations from H2-22 to C-18 and C-20 revealed a linkage between C-19 and C-22, which was confirmed by the strong correlation from H-19′ to C-19 (Figure 2). Thus, the structure of 1 was elucidated. A crystal of 1 could not be obtained despite many attempts. The configuration of 1 was therefore elucidated based on the NOE correlations, carbon−proton coupling constants, and ECD experiments. The NOE correlations H-3/H2-14, H-5/H16, H-15/H3-18, H-3′/H2-14′, H-5′/H-16′, and H-19′/H-14′a (δH 2.82) indicated that the configurations of moieties I and II at C-3, C-5, C-15, C-16, C-3′, C-5′, C-15′, C-16′, and C-20′ were identical to those of gelsenicine and gelseziridine, respectively. The relative configuration of the acyclic linkage C-19−C-19′ was assigned using carbon−proton coupling constants from an HSQMBC spectrum.7 C-19 and C-19′ were separated by a methylene group (C-22), the diastereotopic protons of which were assigned as H-22a (δH 2.58) and H-22b (δH 2.05), permitting the determination of the relative configuration of C19 and C-19′. The small coupling constant of
