Glycolipids from the Formosan Soft Coral Lobophytum crassum

Abstract

During the course of our investigation on the bioactive chemical constituents from marine invertebrates, [1][2][3][4][5][6] we have investigated a soft coral Lobophytum crassum collected from Taiwanese waters. Earlier studies of the genus Lobophytum have led to the isolation of terpenoids, of which some have shown cytotoxic, [7][8][9][10] anti-HIV, 11) and antibacterial 12) activities. In this paper we report the isolation and structural elucidation of three new glycolipids 1-3 (Fig. 1) from this organism. The absolute configurations of 1-3 were determined by the comparison of specific optical rotations of sugar and aglycon moieties with known compounds, chemical conversions, and the application of Mosher's method. Cytotoxicity of metabolites 1-3 against the growth of a limited panel of cancer cells of HepG2, Hep3B (human liver carcinoma), MDA-MB-231 (human breast carcinoma), and Ca9-22 (human gingival carcinoma) is also discussed. Results and Discussion(2R)-1-Hydroxy-3-hexadecyloxy-propyl-b -D-arabinopyranoside (1) was isolated as amorphous white solid. Its HR-ESI-MS exhibited a pseudomolecular ion peak at m/z 471.3296 [MϩNa] ϩ (Calcd for C 24 H 48 O 7 Na, 471.3298), corresponding to the molecular formula C 24 H 48 O 7 , indicating one degree of unsaturation. The 1 : 2 ratio of carbon and proton atoms and high oxygen content in its molecular formula and strong absorption bands at n max 3391, 1142, 1075, and 1007 cm Ϫ1 in IR spectrum suggested that 1 might be a glycolipid. An anomeric glycoside proton resonance was observed at d 5.67 (1H, d, Jϭ3.3 Hz), corresponding to a carbon resonance at d 100.4 (d) in the HMQC spectrum. Except for the above carbon (C-1Ј), the 13 C-NMR spectrum of 1 exhibited eight oxygenated carbons, including four oxymethylenes at d C 71.7 (t), 71.1 (t), 64.5 (t), and 63.0 (t), and four oxymethines at d C 78.5 (d), 71.0 (d), 70.8 (d), and 70.1 (d) ( Table 1). Above data together with the methyl group resonanting at d H 0.85 (3H, t, Jϭ6.6 Hz) and methylenes at d H 1.26 (br s) revealed the structure of 1 to be a glycoside with a long aliphatic chain.The gross structure of metabolite 1 was further established by the 2D-NMR studies, particularly in 1 H-1 H COSY, HMQC and HMBC experiments. The correlations of 1 H-1 H COSY revealed proton-proton sequences, from H-1Ј to H-5Ј, H 2 -1 to H 2 -3, H 2 -1Љ to H 2 -2Љ, and H 2 -15Љ to H 3 -16Љ, as shown in Fig. 2. The HMBC correlations from H-1Ј to C-5Ј and C-2, as well as other correlations illustrated in Fig. 2, established a pyranose and a glycerol ether moiety. The pyranose was identified as b-arabinopyranose by analysis of coupling constants of the related protons (Table 1). HR-ESI mass spectrum and the above 2D-NMR spectroscopic analysis led to the establishment of the aglycon to be chimyl alcohol.The absolute configurations on the sugar portion and lipid aglycon were determined on the basis of methanolysis, chemical transformation and the application of the modified Mosher's method. As shown in Chart 1, methanolysis of 1 with 1 N HCl (aq) -MeOH...

Chemical components from the Vietnamese soft coral Lobophytum sp.

“…Previous chemical investigation on Lobophytum species resulted in the identification of various cembranoid diterpenes and several steroids, glycolipids, and alkaloids; some of which showed cytotoxic and anti-inflammatory activities (Uchio et al, 1981;Chang et al, 2000;Radhika et al, 2004;Muralidhar et al, 2005;Chao et al, 2007;Fattorusso et al, 2008;Cheng et al, 2009). In continuation of our search for bioactive products from Vietnamese marine organisms (Dang et al, 2007;Minh et al, 2007aMinh et al, , 2007bMinh et al, , 2008Tung et al, 2009), the present study on the soft coral Lobophytum sp.…”

Cembranoids from the Dongsha Atoll Soft Coral Lobophytum crassum

“…Soft corals belonging to the genus Lobophytum (Alcyoniidae) have been well recognized as a rich source of secondary metabolites endowed with a range of structural diversity and various biological activities [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21]. Previous bioassay results of some cembraniods and their analogues have demonstrated remarkable pharmacological potential such as in vitro cytotoxicity against various cancer cell lines [2,3,4,5,6,7,8,9], anti-inflammatory properties [10,11,12], antimicrobial activities [10], and HIV-inhibitory activity [13].…”

Antibacterial and cytotoxic properties of isoprenoids from the red sea soft coral, <i>Lobophytum</i> sp

“…In a continuing efforts at studying marine metabolites, collected from Red Sea Saudi Arabia, with biological activity, we have previously isolated several bioactive secondary metabolites from Sarcophyton trocheliophorum and S. glaucum [2][3][4][5] Recently, our interest in allcyonaria coral, led us to isolate several secondary metabolites from Lobophytum sp. Literature survey showed that metabolites of Lobophytum sp exhibited various biological activities, such as antitumor [6][7][8][9][10][11][12][13], antibacterial [14], anti-inflammatory activities [14][15][16] and antiviral [17]. Our investigation led to the isolation and characterization of four sesquiterpenes: alismol (1), nardol (2) aristol-9-ene (3), alismoxide (5), one cembranoid type diterpene, cembrene A (4), and two steroid type compounds, Chalinasterol (6) and Nephalsterol C (7).…”