Phytochemistry of three selected liverworts: Conocephalum conicum, Plagiochila barteri and P. terebrans

2006 ARKIVOC  
2α-Cinnamoyloxy-6β-acetoxybornane (1) has been isolated from the liverwort Conocephalum conicum (Conocephalaceae), while Plagiochila barteri and P. terebrans (Plagiochilaceae) furnished ent-spathulenol, marchantins C and H, 1(10),14-halimadien-13ξ-ol, and trifarienol B. Although the bisbibenzyl-type isoplagiochins have been reported to occur in some Plagiochila species, the presence of marchantins in the genus is very rare. Furthermore, the halimane diterpene usually found in Jungermannia
more » ... Jungermannia species was isolated from Plagiochila sp. for the first time, and the relationship between the two genera Jungermannia and Plagiochila belonging to the Jungermanniales order (suborder: Jungermaniineae) is confirmed. All of the isolated compounds were tested for α-glucosidase inhibitory activity but only marchantin C showed moderate activity. ARKAT novel and biologically active compounds from the moisture-loving plants, we wish to report the isolation and the structure determination of the chemical constituents of three liverworts: Conocephalum conicum, Plagiochila barteri, P. terebrans. The α-glucosidase inhibitory effect of the isolated compounds was evaluated. ARKAT Plant material. C. conicum was collected from Bizan (Tokushima city, Japan) in April 2004, while P. barteri and P. terebrans were collected in Moramanga (near Andasibe), Madagascar in March 2004. After being purified, each sample was air-dried at room temperature. Extraction and isolation procedure. Dried liverworts of C. conicum, P. barteri and P. terebrans were mechanically powdered and extracted with ether at room temperature for one month. The extracts was filtered and concentrated in vacuo to give 69.4 mg extract for C. conicum, 327 mg for P. barteri, and 43.9 mg for P. terebrans. Conocephalum conicum ether extract was divided into three fractions by size exclusion chromatography on sephadex LH-20. The third fraction was rechromatographed on silica gel (hexane: EtOAc; 85:15) to give a fraction rich in compound 1. Preparative TLC on silica gel (hexane: EtOAc; 4:1) resulted the isolation of compound 1 in pure state (1 mg). The ether extract of P. barteri was subjected to a sephadex LH-20 column chromatography to give six fractions. Compound 5 (12.6 mg) was isolated from fraction 3 by a combination of silica gel and ODS flash column chromatography (hexane: EtOAc gradient and 90% MeOH, respectively), while compounds 2 (5 mg) and 3 (0.4 mg) were obtained from fraction 4 by silica gel column chromatography (hexane: EtOAc gradient) and preparative TLC on ODS (80% MeOH), respectively. Silica gel column chromatography (hexane: EtOAc; 6.5:3.5) of the fifth fraction afforded compound 4 (9.2 mg). Size exclusion chromatography of the ether extract of P. terebrans gave five fractions. The fourth fraction was applied to a silica gel column chromatography (hexane-EtOAc, 7:3) to afford compound 6 (1.7 mg). 2α-Cinnamoyloxy-6β-acetoxybornane. Oil ([α] 18 D +18.3 o (c 0.2, CHCl 3 ); IR (KBr) cm −1 : 1731, 1712, 1450; Positive HREIMS: m/z 342.1831 [M] + (C 21 H 26 O 4 , requires 342.4287); 1 H-and 13 C-NMR: see Table 1 . Enzyme inhibition assay. α-Glucosidase inhibitory activity was performed according to the method described by Oki and co-workers 10 with slight modifications. α-Glucosidase was purchased from TOYOBO Co. Ltd, 2-8 Dojima Hama, 2-Chome, Kitaku, Osaka, Japan. Pure Chemical Industries Ltd. The enzyme solution (ES) was prepared by dissolving 0.6 U/ml of αglucosidase in 100 mM phosphate buffer (pH 7) containing 2 g/l bovine serum albumin and 0.2 g/l NaN 3 . p-Nitrophenyl-α-D-glucopyranoside (5 mM) in the same buffer solution (pH 7) was used as a substrate solution (SS). The ES (50 µl) and the test compounds (10 µl) dissolved in dimethyl sulfoxide (DMSO) at a concentration of 1 mM were mixed in each well of the microliter 96-well culture plates and measured spectrophotometrically (Abs 415 nm) at zero time by using a microplate reader (BIO-RAD model 550 Microplate reader). The mixture was preincubated for 5 min at room temperature before SS addition (50 µM) followed by 5 min incubation at room temperature. The increase in absorbance from zero time was measured. The inhibitory activity was expressed as 10 minus relative absorbance difference (%) of test compounds to absorbance change of the control where test solution was replaced by DMSO. Experiences were performed in triplicate and the averages are presented. 1-Deoxynojirimycin
doi:10.3998/ark.5550190.0008.704 fatcat:bkilyijoenasbmjfvlesh7gx24