A New N-Acyl Taurine from the South China Sea Marine Sponge Callyspongia sp.

Abstract

The genus Callyspongia (order Haplosclerida, family Callyspongiidae) is widely distributed and contains various bioactive constituents [1]. In the course of our investigation on the marine sponge Callyspongia species, we have reported some metabolites [2, 3]. Further investigation on the marine sponge Callyspongia species has led to the isolation and characterization of a new N-acyl taurine (1). The sponge Callyspongia sp. was collected off the coast of Hainan Island, South China Sea, in January, 2007. The specimen was identified by Dr. Kyung Jin Lee. A voucher specimen (No. 20070101) was deposited in Natural History Museum, Hannam University, Daejon, Korea and Guangdong Key Laboratory of Marine Materia Medica, South China Sea Institute of Oceanology, Chinese Academy of Sciences, China. The wet marine sponge Callyspongia sp. (10 kg) was extracted with ethanol (90%). The ethanol was evaporated in vacuo to afford a syrupy residue that was suspended in distilled water and fractionated successively with petroleum ether, ethyl acetate, and n-butanol. The n-butanol soluble portion (80.1 g) was subjected to RP chromatography eluted with H2O–MeOH (9:1, fr. A), H2O–MeOH (8:2, fr. B), H2O–MeOH (7:3, fr. C), H2O–MeOH (6:4, fr. D), H2O–MeOH (4:6, fr. E), and H2O–MeOH (0:10, fr. F), to give six fractions. Fraction C (4.12 g) was subjected to silica gel chromatography with CHCl3–MeOH (8:2 to 6:4, gradient) to give three fractions (C1–C3). Fraction C2 (435 mg) was subjected to silica gel chromatography with CHCl3–MeOH (8:2), then purified by Sephadex LH-20 (CHCl3–MeOH, 1:1) to afford 1 (5.0 mg). Compound 1 was obtained as a yellow oil, and its molecular formula was deduced to be C13H25NO4S on the basis of the HR-ESI-MS spectrum at m/z 290.1422 [M – H]– (calcd 290.1426 for C13H24NO4S) and NMR data. The gross structure was determined by the aid of COSY, HMQC, and HMBC experiments. The 1H NMR, 13C NMR, and DEPT data for 1 indicated the presence of two methyls, eight sp3 methylenes, one sp2 methine, and two sp2 quaternary carbons. The sulfur and remaining three oxygens in the molecular formula suggested a sulfonic acid group (SO3H). The 1H NMR signals at 3.63 (2H, t, J = 7.0 Hz, H-1 ) and 3.00 (2H, t, J = 7.0 Hz, H-2 ), and 13C NMR signals at C 174.6 (C-1), 36.6 (C-1 ) and 51.5 (C-2 ), together with the HMBC correlations (Fig. 1) of H-2 with C-1 and H-2 with C-1 and C-1 , indicated the two methylenes C-1 and C-2 to be located between the amide and the sulfonic acid, which revealed a taurine moiety in the structure of 1 [4, 5]. The position of the double bond was ascertained at C-3 and C-4 on the basis of the HMBC correlations of H-4 with C-2 and H-5 with C-3. The methyl group (C-11) was determined to be located at C-3 by the HMBC correlations of H-11 with C-2 and C-4. The geometry of the double bond was deduced to be cis based on the chemical shifts of the allylic carbon C-5 at 29.2, which agreed well with the chemical shift for the allylic carbons of cis-olefins (approximately 29) [6]. Thus, the structure of compound 1 was elucidated as 2-(3-methyl-dec-3-enamido)ethanesulfonic acid. 2-(3-Methyl-dec-3-enamido)ethanesulfonic Acid (1). Yellow oil. 1H NMR (500 MHz, CDCl3, , ppm, J/Hz): 5.36 (1H, t, J = 6.5, H-4), 3.63 (2H, t, J = 7.0, H-1 ), 3.00 (2H, t, J = 7.0, H-2 ), 2.91 (2H, s, H-2), 2.07 (2H, m, H-5), 1.77 (3H, s, H-11), 1.18–1.27 (8H, overlap, H-6–9), 0.93 (3H, t, J = 6.5, H-10). 13C NMR (125 MHz, CDCl3, , ppm): 174.6 (C-1), 131.2 (C-4), 130.2 (C-3), 51.5 (C-2 ), 48.8 (C-2), 36.6 (C-1 ), 29.2 (C-5), 23.7–30.8 (C-6–9), 16.3 (C-11), 14.6 (C-10). HR-ESI-MS m/z 290.1422 [M – H]– (calcd 290.1426 for C13H24NO4S).