Gymnothelignans A–O: Conformation and Absolute Configuration Analyses of Lignans Bearing Tetrahydrofuran from Gymnotheca chinensis

Abstract

Fifteen new lignans, gymnothelignans A−O (1−15), bearing tetrahydrofuran with variable conformations belonging to three potentially related skeletons were isolated from Gymnotheca chinensis Decne. The structures were elucidated by means of detailed spectroscopic analysis. Absolute configurations were assigned using X-ray singlecrystal diffraction and chemical transformations. Moreover, by the homology, compounds 1−11 and eupomatilones were confirmed to have uniform R-configuration at C-5. However, a synthesized congener has long been mistaken as 5-epimer of eupomatilone-6. This work provides guidance for the absolute configuration establishment of the subeupomatilone family with trans-H-4−H-5 configuration.

Two new lignans from Gymnotheca chinensis Decne

“…The correlations of H-6 to CH 3 -17, and H-9 to CH 3 -18 suggested H-6/H 3 -17 and H-9/ H 3 -18 were cofacial. The vicinal coupling constants of H-6/H-7 (J = 2.0 Hz) and H-8/H-9 (J = 5.4 Hz) were in close agreement with those observed in gymnothelignan L (He et al, 2013). Detailed HMBC analysis suggested that the structure of 1 was very similar to Phytochemistry Letters 8 (2014) 38-40 those of gymnothelignan L except for the replacement of the methylenedioxy by two methoxy groups at C-12 and C-13.…”

“…Compound 1 exhibited a greater cytotoxicity than gymnothelignan L against the HepG2 cell line, indicating that the compounds with methoxy groups at C-12 and C-13 possess greater cytotoxicity than the corresponding 6/9 epoxy dibenzocyclooctadiene lignans. All of the gymnothelignans isolated from G. chinensis possess an epoxy bridge (He et al, 2013). The results of the cell viability assay indicated that the epoxy bridge functional group plays an insignificant role in a compound's cytotoxicity.…”

“…In a previous investigation on G. chinensis, we isolated 15 new lignans belonging to the dibenzocyclooctene, eupomatilone and eupodienone series. Only one lignan exhibited moderate activity against HepG2 and Bcl7404 cell lines as demonstrated by a cytotoxicity assay (He et al, 2013). According to the literature, many dibenzocyclooctadiene lignans have been determined to exhibit considerable bioactivities, such as cytotoxicity (Xu et al, 2006a,b;Gao et al, 2013) and anti-HIV activities (Chen et al, 1996;Gao et al, 2008;Yang et al, 2013).…”

Polycyclic Spiro Lignans and Biphenyl Tetrahydrofuranone Lignans from Gymnotheca involucrata

“…In a previous phytochemical investigation on G. chinensis, we isolated 27 new lignans belonging to the dibenzocyclooctene, biphenyl tetrahydrofuran, eupodienone, and norlignan series [3][4][5][6][7][8], while our previous study on the constituents of G. involucrate led to the isolation of a flavonoid glycoside, two sterols, and two lignans [9,10]. In our continuing endeavor to discover unique and new structures from these plants, four rare polycyclic spiro lignans, gymnothespirolignans E, D, C, and F (1)(2)(3)(4), and four new biphenyl tetrahydrofuranone lignans were isolated from the whole plant of G. involucrata. Selected compounds were evaluated for their fungicidal and insecticidal activities.…”

“…1), of which four were rare polycyclic spiro lignans (1)(2)(3)(4), and the other four were atropisomer biphenyl lignans (5)(6)(7)(8) 4.12, 3.84, 3.83 (each 3 H, s); δ C 59.9, 56.6, 56.2], one quaternary carbon (δ C 94.9), and two aromatic ring moieties [δ H 6.71 (1 H, s), 7.45 (1 H, s); δ C 150. 7, 149.6, 148.8, 145.3, 140.2, 139.2, 137.3, 132.8, 125.5, 110.4, 107.6, 99.8].…”