Furanosesterterpenes from the marine sponge Ircinia echinata (Keller, 1889) - Do Thi Trang

Vietnam Journal of Chemistry, International Edition, 54(4): 477-482, 2016 DOI: 10.15625/0866-7144.2016-00350 477 Furanosesterterpenes from the marine sponge Ircinia echinata (Keller, 1889) Do Thi Trang 1 , Duong Thi Dung 1 , Nguyen Xuan Nhiem 1 , Bui Huu Tai 1 , Pham Hai Yen 1 , Hoang Le Tuan Anh 1 , Pham Hai Yen 1 , Do Cong Thung 2 , Chau Van Minh 1 , Phan Van Kiem 1* 1 Institute of Marine Biochemistry, Vietnam Academy of Science and Technology (VAST) 2 Institute of Marine Environment and Resources, VAST Received 24 March 2016; Accepted for publication 12 August 2016 Abstract Four furanosesterterpene, (7E,12E,20Z,18β)-variabilin (1), (12E,20Z,18β)-8-hydroxyvariabilin (2), (7E,11E,3β)- 3,7,11-trimethyl-14-(furan-3-yl)tetradec-7,11-dienoic acid (3), and furoscalarol (4), and one sterol, 3β-hydroxycholest- 5-en-7-one (5) were isolated from the methanol extract of the sponge Ircinia echinata (Keller, 1889). Their structures were elucidated by 1D and 2D-NMR spectra and in comparison with those reported in the literature. Keywords. Sponge, Ircinia echinata, furanosesterterpene, sterol. 1. INTRODUCTION Ircinia is a genus of marine demosponge in the family Irciniidae providing a number of furanosesterterpenoids and steroids. These compounds exhibited a wide spectrum of bioactivities such as anticancer [1-4], antimicrobial [5], and antiviral activities [6]. However, chemical and biological studies of Ircinia echinata have not been studied yet. In this paper, we report the isolation and structural determination of four furanosesterterpenes and one sterol from the Vietnamese sponge, I. echinata (figure 1). 2. MATERIAL AND METHODS 2.1. Animal material The sponge Ircinia echinata was collected at Coto Island, Quangninh, Vietnam in April, 2014. Its scientific name was identified by one of the authors, Prof. Do Cong Thung. A voucher specimen (HM04) was deposited at the Institute of Marine Biochemistry, VAST. 2.2. General experimental procedures Optical rotations were measured on a Jasco DIP- 370 automatic polarimeter. The 1D- and 2D-NMR spectra were recorded on a Bruker AM500 FT-NMR spectrometer. Column chromatography was performed using either silica-gel (Kieselgel 60, 70– 230 mesh and 230–400 mesh, Merck, Whitehouse Station, NJ) or reverse phase (RP-18 resins, 150 μm, YMC Co. Ltd.). Thin layer chromatography (TLC) was carried out using pre-coated silica-gel 60 F254 (0.25 mm, Merck) and RP-18 F254S plates (0.25 mm, Merck). Spots were detected under UV radiation (254 and 365 nm), sprayed with 10% H2SO4 solution followed by heating with heat gun. 2.3. Extraction and isolation Frozen dried sample of I. echinata (10 kg) was ground and ultrasonically extracted with methanol at 40 °C (10 L × three times, 5h each) to give MeOH extract (230.0 g) after removal the solvent in vacuo. Then, MeOH extract was suspended in water and partitioned with dichloromethane to give dichloromethane extract (IED, 90.0 g) and water layer (IEW, 140.0 g). The IED was roughly separated on a silica gel column chromatography, eluting with gradient solvent system of n- hexane/acetone (100/1 to 0/1, v/v) to give six fractions, IED1-IED6. IED2 (19.3 g) was repeatedly subjected to a silica gel column and eluted with n- hexane/acetone (6/1, v/v) to furnish five fractions, IED2A-IED2E. Compound 4 (12.0 mg) was obtained from IED2A by a silica gel column, eluting with n-hexane/ethyl acetate (5/1, v/v). IED2C (1.3 g) was purified on a RP-18 column, eluting with methanol/water (6/1, v/v) to yield compound 3 (8.0 VJC, 54(4) 2016 Phan Van Kiem, et al. 478 mg). IED2D was chromatographed on a silica gel column, eluting with n-hexane/acetone (2.5/1, v/v) to yield compound 2 (11.0 mg). IED3 (12.6 g) was chromatographed on a silica gel column, eluting with n-hexane/acetone (6/1, v/v) to give four fractions, IED3A-IED3D. Compound 1 (30.0 mg) was obtained from IED3A (1.7 g) by a RP-18 column, eluting with methanol/water (5/1, v/v). Compound 5 (20.0 mg) was isolated from IED5A fraction on a RP-18 column, eluting with acetone/water (1/1, v/v). (7E,12E,20Z,18β)-Variabilin (1): colorless oil, 25][ D : -25.9 (c = 0.1, MeOH), molecular formula C25H34O4, 1 H- and 13 C-NMR data, see table 1. (12E,20Z,18β)-8-Hydroxyvariabilin (2): colorless oil, 25][ D : -19.6 (c = 0.1, MeOH), molecular formula C25H36O5, 1 H- and 13 C-NMR data, see table 1. (7E,11E,3β)-3,7,11-Trimethyl-14-(furan-3- yl)tetradec-7,11-dienoic acid (3): colorless oil, optical rotation 25][ D : -21.5 (c = 0.1, MeOH), molecular formula C21H32O3, 1 H- and 13 C-NMR data, see table 2. Furoscalarol (4): colorless oil, 25][ D : +58.2 (c = 0.1, MeOH), molecular formula C27H40O4, 1 H- and 13 C-NMR data, see table 2. 3β-Hydroxycholest-5-en-7-one (5): colorless oil, 25][ D : +45.1 (c = 0.1, MeOH), molecular formula C27H44O2, 1 H- and 13 C-NMR data, see table 2. Figure 1: Chemical structures of 1-5 3. RESULTS AND DISCUSSION Compound 1 was obtained as a colorless oil. The 1 H-NMR spectrum of 1 (in CD3OD) showed six olefinic protons at δH 5.11 (t, J = 6.5 Hz), 5.17 (t, J = 7.5 Hz), 5.30 (d, J = 10.0 Hz), 6.31 (br s), 7.25 (br s), and 7.38 (br s), four methyl groups at δH 1.08 (d, J = 7.0 Hz), 1.58 (s), 1.59 (s), and 1.76 (s). The 13 C- NMR and DEPT spectra of 1 exhibited the presence of 25 carbons, including seven non-protonated carbons (δC 99.01, 126.20, 135.81, 136.52, 144.94, 164.52, and 173.46), seven methines (δC 31.87, 143.73, 112.01, 140.06, 125.21, 125.60, and 115.84), seven methylenes (δC 25.98, 26.81, 27.43, 29.59, 37.62, 40.71, and 40.42), and four methyl groups (δC 6.09, 15.90, 16.11, and 21.06). Analytical 1 H- and 13 C-NMR data of 1 indicated its NMR data were very similar to those of variabilin [7]. The HMBC correlations from H-5 (δH 2.45) to C-2 (δC 112.01)/C-3 (δC 126.20)/C-4 (δC 140.06)/C-6 (δC 29.59)/C-7 (δC 125.21) indicated the furan ring with C-3-substituted. Moreover, the HMBC correlations between H-9 (δH 1.59) and C-7 (δC 125.21)/C-8 (δC 136.52)/C-10 (δC 40.71); H-14 (δH 1.58) and C-12 (δC 125.60)/C-13 (δC 135.81)/C-15 (δC 40.42); H-19 (δH 1.08) and C-17 (δC 37.62)/C-18 (δC 31.87)/C-20 (δC 115.84); H-25 (δH 1.76) C-22 (δC 164.52)/C-23 (δC 99.01)/C-24 (δC 173.46); and between H-20 (δH 5.30) and C-21 (δC 144.94)/C-22 (δC 164.52) suggested the positions of double bonds at C-7/C-8, C-12/C-13, C-20/C-21, and C-22/C-23. In addition, comparison of 13 C-NMR data of 1 to those of variabilin [7] showed the similarity (recorded in the same solvent CDCl3) [8]. Thus, the structure of 1 was determined to be (7E,12E,20Z,8β)-variabilin, a compound was already reported from the sponge Iricinia variabilis [9]. VJC, 54(4) 2016 Furanosesterterpenes from the marine sponge 479 Table 1: 1 H- and 13 C-NMR data of compounds 1 and 2 1 2 C δC # δC a δC b δH b (mult., J, Hz) δC $ δC a δC b δH b (mult., J, Hz) 1 142.4 142.52 143.73 7.38 (br s) 142.7 142.76 143.90 7.39 (br s) 2 111.0 111.13 112.01 6.31 (br s) 110.9 110.91 111.89 6.31 (br s) 3 124.9 125.03 126.20 - 124.8 124.87 126.37 - 4 138.7 138.83 140.06 7.25 (br s) 138.8 138.87 140.08 7.28 (br s) 5 25.0 25.05 25.98 2.45 (t, 7.5) 25.1 25.18 26.19 2.43 (t, 7.5) 6 28.4 28.45 29.59 2.25 (q, 7.5) 24.4 24.42 25.60 1.63 (m) 7 123.7 123.72 125.21 5.17 (t, 7.5) 41.2 41.32 42.17 1.49 (m) 8 135.7 135.79 136.52 - 73.9 73.93 73.23 - 9 16.0 16.06 16.11 1.59 (s) 26.5 26.61 26.87 1.15 (s) 10 39.5 39.55 40.71 2.01 (m) 41.2 41.20 42.62 1.43 (m) 11 26.5 26.57 27.43 2.10 (q, 6.5) 22.5 22.58 23.51 2.00 (m) 12 124.4 124.35 125.60 5.11 (t, 6.5) 124.3 124.35 126.02 5.17 (t, 7.0) 13 134.7 134.88 135.81 - 135.6 135.71 135.74 - 14 15.8 15.83 15.90 1.58 (s) 15.9 16.01 15.81 1.60 (s) 15 39.6 39.69 40.42 2.01 (m) 39.3 39.24 40.41 2.00 (m) 16 25.6 25.72 26.81 1.40 (m) 25.5 25.57 26.78 1.40 (m) 17 36.5 36.66 37.62 1.38 (m) 36.5 36.52 37.62 1.40 (m) 18 30.9 30.87 31.87 2.77 (m) 30.7 30.73 31.79 2.76 (m) 19 20.6 20.66 21.06 1.08 (d, 7.0) 20.5 20.62 21.06 1.08 (d, 6.5) 20 117.1 115.62 115.84 5.30 (d, 10.0) 115.7 115.59 115.61 5.29 (d, 10.0) 21 142.9 142.77 144.94 - 142.0 143.10 145.20 - 22 162.4 n.d. 164.52 - 162.3 n.d. 165.00 - 23 99.0 99.49 99.01 - 99.2 99.31 98.50 - 24 172.5 n.d. 173.46 - 172.1 n.d. 173.60 - 25 6.0 6.17 6.09 1.76 (s) 6.2 6.21 6.09 1.76 (s) a) recorded in CDCl3, b) recorded in CD3OD, #C of (7E,12E,20Z,18β)-variabilin [8], $C of (12E,20Z,18β) 8-hydroxyvariabilin [8], n.d., not determined. Compound 2 was also obtained as a colorless oil. The 1 H-NMR spectrum of 2 showed the signals of five olefinic protons at δH 5.17 (t, J = 7.0 Hz), 5.29 (d, J = 10.0 Hz), 6.31 (br s), 7.28 (br s), and 7.39 (br s); four methyl groups at δH 1.08 (d, J = 6.5 Hz), 1.15 (s), 1.60 (s), and 1.76 (s). The 13 C-NMR and DEPT spectra of 2 exhibited the signals of 25 carbons, including seven non-protonated carbons (δC 73.23, 98.50, 126.37, 135.74, 145.20, 165.00, and 173.60), six methines (δC 31.79, 111.89, 115.61, 126.02, 140.08, and 143.90), eight methylenes (δC 23.51, 25.60, 26.19, 26.78, 37.62, 40.41, 42.17, and 42.62), and four methyl groups (δC 6.09, 15.81, 21.06, and 26.87). Analytical 1 H- and 13 C-NMR data of 2 indicated that its structure was similar to those of 8-hydroxyvariabilin [8]. The HMBC correlations from H-5 (δH 2.43) to C-2 (δC 111.89)/C-3 (δC 126.37)/C-4 (δC 140.08)/C-6 (δC 25.60)/C-7 (δC 42.17); from H-9 (δH 1.15) to C-7 (δC 42.17)/C-8 (δC 73.23)/C-10 (δC 42.62) confirmed the position of 3- substituted furan ring at C-5 and hydroxyl group at C-8. The HMBC correlations between H-14 (δH 1.60) and C-12 (δC 126.02)/C-13 (δC 135.74)/C-15 (δC 40.41); H-19 (δH 1.08) and C-17 (δC 37.62)/C-18 (δC 31.79)/C-20 (δC 115.61); H-20 (δH 5.29) and C- 21 (δC 145.20)/C-22 (δC 165.00); and between H-25 (δH 1.76) and C-22 (δC 165.00)/C-23 (δC 98.50)/C-24 (δC 173.60) confirmed the positions of three double bonds at C-12/C-13, C-20/C-21, and C-23/C-24. Thus, the structure of 2 was defined as (12E,20Z,18β)-8-hydroxyvariabilin, a furanosester- terpene from the sponge Sarcotragus sp. [8]. VJC, 54(4) 2016 Phan Van Kiem, et al. 480 The 1 H-NMR spectrum of 3 showed the signals: five olefinic protons at δH 5.11 (1H, t, J = 7.5 Hz), 5.19 (1H, t, J = 7.0 Hz), 6.31 (1H, br s), 7.26 (1H, br s), and 7.38 (br s); three methyl groups at δH 0.95 (3H, d, J = 6.5 Hz), 1.60 (6H, s)]. The 13 C-NMR and DEPT spectra of 3 exhibited the signals of 21 carbons: four non-protonated carbons (δC 126.20, 136.12, 136.57, and 180.03), six methines (δC 31.95, 112.01, 125.18, 125.29, 143.75, and 140.06), eight methylenes (δC 25.98, 26.54, 27.49, 29.59, 37.79, 40.79, 40.94, and 45.46), and three methyl groups (δC 15.96, 16.11, and 20.32). The 1 H- and 13 C-NMR data of 3 were similar to those of 7E,11E,3β)-3,7,11- Table 2: 1 H- and 13 C-NMR data of compounds 3-5 3 4 5 C δC # δC b δH b (J, Hz) C δC $ δC a δH a (J, Hz) δC ¥ δC a δH a (J, Hz) 1 186.7 180.03 - 1 39.6 39.69 0.62 (m)/ 1.58 (m) 36.4 36.37 1.21 (m)/ 1.95 (m) 2 41.2 45.46 2.00 (m)/ 2.23 (m) 2 18.1 18.13 1.41 (m) 1.60 (m) 31.2 31.22 1.61 (m) 1.94 (m) 3 30.1 31.95 1.94 (m) 3 41.3 41.35 1.08 (m)/ 1.88 (m) 70.6 70.54 3.67 (m) 4 36.2 37.79 1.18 (m)/ 1.31 (m) 4 33.2 33.31 - 41.9 41.83 2.40 (m)/2.50 (m) 5 25.2 26.54 1.43 (m) 5 56.5 56.69 0.83 (m) 165.2 165.04 - 6 39.7 40.94 2.00 (m) 6 18.5 18.50 1.42 (m)/ 1.60 (m) 126.2 126.14 5.68 (s) 7 134.9 136.12 - 7 41.9 42.00 1.15 (m)/ 1.40 (m) 202.4 202.27 - 8 124.3 125.29 5.19 (t, 7.0) 8 36.9 37.00 - 45.5 45.43 2.23 (m) 9 26.6 27.49 2.10 (m) 9 53.0 53.12 1.29 (m) 50.0 49.99 1.35 (m) 10 39.7 40.79 2.00 (m) 10 37.1 37.20 - 38.3 38.29 - 11 135.8 136.57 - 11 21.7 21.73 1.76 (m)/ 1.85 (m) 21.3 21.24 1.59 (m) 12 123.8 125.18 5.11 (t, 7.5) 12 73.5 73.48 5.41 (br s) 38.8 38.73 1.12 (m)/ 2.03 (m) 13 28.5 29.59 2.26 (m) 13 40.7 40.78 - 41.9 43.12 - 14 25.1 25.98 2.45 (t, 7.5) 14 49.8 49.91 1.75 (m) 50.0 49.99 1.50 (m) 3-Me 19.7 20.32 0.95 (d, 6.5) 15 29.3 29.60 1.45 (m)/2.21(m) 26.4 26.33 1.25 (m)/ 2.40 (m) 7-Me 15.9 15.96 1.60 (s) 16 66.5 66.99 4.68 (m) 28.6 28.55 1.29 (m)/ 1.90 (m) 11-Me 16.1 16.11 1.60 (s) 17 120.0 119.96 - 54.9 54.83 1.11 (m) 1′ 142.5 143.75 7.38 (br s) 18 156.6 157.08 - 12.0 11.98 0.68 (s) 2′ 111.1 112.01 6.31 (br s) 19 140.9 141.33 7.19 (d, 2.0) 17.4 17.33 1.20 (s) 3′ 125.0 126.20 - 20 108.1 108.06 6.33 (d, 2.0) 35.8 35.72 1.38 (m) 4′ 138.8 140.06 7.26 (br s) 21 21.3 21.31 0.82 (s) 18.9 18.88 0.92 (d, 6.0) 22 33.2 33.26 0.86 (s) 36.2 36.20 1.21 (m)/ 1.96 (m) 23 15.9 15.93 0.83 (s) 23.9 23.84 1.16 (m)/ 1.33 (m) 24 17.2 17.27 0.94 (s) 39.5 39.49 1.12 (m) 25 22.1 22.17 1.29 (s) 28.0 28.00 1.52 (m) 26 22.6 22.80 0.87 (d, 6.5) 27 22.8 22.56 0.87 (d, 6.5) 1′ 170.0 170.21 - 2′ 21.0 21.14 1.89 (s) a) recorded in CDCl3, b) recorded in CD3OD, #C of (7E,11E,3β)-3,7,11-trimethyl-14-(furan-3-yl)tetradec-7,11-dienoic acid [8], $C of furoscalarol [10], ¥C of 3β-hydroxycholest-5-en-7-one [11]. VJC, 54(4) 2016 Furanosesterterpenes from the marine sponge 481 Figure 2: The key HMBC correlations of 1-5 trimethyl-14-(furan-3-yl)tetradec-7,11-dienoic acid [8]. The positions of functional groups were determined based on analysis HSQC and HMBC spectra, as well as in comparison of similar compound in the literature. Thus, compound 3 was identified as (7E,11E,3β)-3,7,11-trimethyl-14- (furan-3-yl)tetradec-7,11-dienoic acid. This compound was already reported from the marine sponge Sarcotragus sp. [8]. The 1 H-NMR spectrum of compound 4 showed the signals of two olefinic protons at δH 6.33 (d, J = 2.0 Hz) and 7.19 (d, J = 2.0 Hz); two oxymethine protons at δH 5.41 (br s), and 4.68 (m), six methyl groups at δH 0.82 (s), 0.83 (s), 0.86 (s), 0.94 (s), 1.29 (s), and 1.89 (s). The 13 C-NMR and DEPT spectra of 4 exhibited the signals of 27 carbons, including seven non- protonated carbons, seven methines, seven methylenes, and six methyl groups, indicated the presence of furano-tetracyclic sesterterpene. Moreover, the signal of carbonyl (δC 170.21) and methyl [δC 21.14 and δH 1.89 (s)] indicated the presence of acetyl group. The signals of four olefins at δC 108.06 (CH)/ δH 6.33 (d, J = 2.0 Hz), 119.96 (C), δC 141.33 (CH)/δH 7.19 (d, J = 2.0 Hz), and δC 157.08 (C)] featured for 2,3-disubstituted furan. 1 H- and 13 C-NMR data of 4 were identical to those of furoscalrol [10]. The HMBC correlations from H-21 (δH 0.82) to C-3 (δC 41.35)/C-4 (δC 33.31)/C-5 (δC 56.69)/C-22 (δC 33.26); from H-22 (δH 0.86) to C-3 (δC 41.35)/C-4 (δC 33.31)/C-5 (δC 56.69)/C-21 (δC 21.31); from H-24 (δH 0.94) to C-8 (δC 37.00)/C-9 (δC 53.12)/C-11 (δC 21.73)/C-14 (δC 49.91); from H- 23 (δH 0.83) to C-1 (δC 39.69)/C-5 (δC 56.69)/C-9 (δC 53.12)/C-10 (δC 37.20); from H-25 (δH 1.29) to C-12 (δC 73.48)/C-13 (δC 40.78)/C-14 (δC 49.91)/C- 18 (δC 157.08), confirmed the position of two methyl groups at C-4 and the remaining methyl groups at C- 8, C-10, and C-13. The position of acetoxy group at C-12 was confirmed by HMBC correlation from H- 12 (δH 5.41)/H-2′ (δH 1.89) to C-1′ (δC 170.21). Moreover, the HMBC correlations between H-16 (δH 4.68)/H-19 (δH 7.19) and C-17 (δC 119.96)/C-18 (δC 157.08) suggested the position of hydroxyl group at C-16 and furan ring at C-17/C-18. Thus, compound 4 was determined to be furoscalrol [10]. The 1 H-NMR of 5 exhibited the presence of five methyl groups at δH 0.68 (3H, s), 0.87 (6H, d, J = 6.5 Hz), 0.92 (3H, d, J = 6.0 Hz), and 1.20 (3H, s), one oxymethine proton at δH 3.67 (1H, m), and one olefinic proton at δH 5.69 (1H, s). The 13 C-NMR and DEPT spectra of 5 showed the signals of 27 carbons, including 1 carbonyl, 3 non-protonated carbons, 8 methines, 10 methylenes, and 5 methyl groups. Analysis of 1 H- and 13 C-NMR data indicated the strucutre of 5 to be a steroid, a class commonly found in the sponge [11]. The HMBC correlations from H-6 (δH 5.68)/H-8 (δH 2.23)/H-9 (δH 1.35)/to C- 7 (δC 202.27) confirmed the carbonyl group at C-7. In addition, the 1 H- and 13 C-NMR data of 5 were similar to those of 3β-hydroxycholest-5-en-7-one [11]. Acknowledgement. This research was supported by Vietnam Academy of Science and Technology under grant number VAST.TĐ.LDB.01/16-18. REFERENCES 1. S. Xu, X. Liao, B. Du, X. Zhou, Q. Huang, C. Wu. A series of new 5,6-epoxysterols from a Chinese sponge Ircinia aruensis, Steroids, 73, 568-573 (2008). 2. J. H. Su, S. W. Tseng, M. C. Lu, L. L. Liu, Y. Chou, P. J. Sung. Cytotoxic C21 and C22 terpenoid-derived VJC, 54(4) 2016 Phan Van Kiem, et al. 482 metabolites from the sponge Ircinia sp., Journal of Natural Products, 74, 2005-2009 (2011). 3. M. S. Buchanan, A. Edser, G. King, J. Whitmore, R. J. Quinn. Cheilanthane sesterterpenes, protein kinase inhibitors, from a marine sponge of the genus Ircinia, J. Nat. Prod., 64, 300-303 (2001). 4. M. Kuramoto, T. Fujita, N. Ono. Ircinamine, a novel cytotoxic alkaloid from Ircinia sp., Chemistry Letters, 31, 464-465 (2002). 5. D. John Faulkner. Variabilin, an antibiotic from the sponge Ircinia variabilis, Tetrahedron Letters, 14, 3821-3822 (1973). 6. C. J. Barrow, J. W. Blunt, M. H. G. Munro, N. B. Perry. Oxygenated furanosesterterpene tetronic acids from a sponge of the genus Ircinia, Journal of Natural Products, 51, 1294-1298 (1988). 7. W. Balansa, R. Islam, F. Fontaine, A. M. Piggott, H. Zhang, T. I. Webb, D. F. Gilbert, J. W. Lynch, R. J. Capon. Ircinialactams: Subunit-selective glycine receptor modulators from Australian sponges of the family Irciniidae, Bioorganic & Medicinal Chemistry, 18, 2912-2919 (2010). 8. C. J. Barrow, J. W. Blunt, M. H. G. Munro, N. B. Perry. Variabilin and related compounds from a sponge of the genus Sarcotragus, Journal of Natural Products, 51, 275-281 (1988). 9. D. John Faulkner. Variabilin, an antibiotic from the sponge, ircinia variabilis. Tetrahedron Letters, 14, 3821-3822 (1973). 10. G. Cimino, a. F. Cafieri, L. De Napoli, E. Fattorusso. 13 C-NMR spectrum and absolute stereochemistry of furoscalarol, Tetrahedron Letters, 19, 2041-2044 (1978). 11. G. Notaro, V. Piccialli, D. Sica. New steroidal hydroxyketones and closely related diols from the marine sponge Cliona copiosa, Journal of Natural Products, 55, 1588-1594 (1992). Corresponding author: Phan Van Kiem Institute of Marine Biochemistry Vietnam Academy of Science and Technology 18, Hoang Quoc Viet, Cau Giay, Hanoi, Vietnam E-mail: phankiem@yahoo.com.