ABSTRACT
Four new polyhydroxylated steroids plaksterols A-D (1-4), together with two known related steroids ergost-7,9(11),22-trien-3β,5α,6α-triol (5) and ergosta-6β-methoxy-7,22-diene-3β,5α-diol (6), were isolated from methanol extract of the South China Sea marine sponge Plakortis sp. Their structures were identified by spectroscopic analysis, including NMR, MS, and IR. The cytotoxicity of the polyhydroxylated steroids were evaluated, and compound 6 showed moderate inhibitory activities against K562, HL-60 and BEL-7402 cells.
ABSTRACT
The marine sponge Lamellodysidea herbacea is one of the marine organisms containing unique organobromine molecules polybrominated diphenyl ethers (PBDEs) which have diverse biological activities. Compounds 1−4 have been successfully isolated and their structures were elucidated using nuclear magnetic resonance (NMR) spectroscopy, single-crystal x-ray diffraction, and comparison with data in literature. Compound 1, C12H6 O4 Br6 , was isolated in gram quantity (1.35 g) and elucidated as 2,3,4,5-tetrabromo-6-(3ʹ,5ʹ-dibromo-2ʹ-hydroxyphenoxy)phenol after NMR and X-ray analysis. Compound 1 takes a twist-like conformation with torsion angle ϕ1 = 27.7 (6)°; ϕ2 = 86.5 (5)°, while the angle of the ether bond is 117.5°. Compounds 2−4 were elucidated as 2,3,5-tribromo-6-(3ʹ,5ʹdibromo-2ʹ-hydroxyphenoxy)anisole, 2,3,5-tribromo-6-(3ʹ,5ʹ-dibromomethoxyphenoxy) phenol, 2,3,5-tribromo-6- (3ʹ,5ʹ-hydroxyphenoxy)phenol, respectively. Antibacterial evaluation of 1−4 on Gram-positive and Gram-negative pathogens showed that the potent activity was at 0.08 µg/disk, 12 ± 0 mm (Staphylococcus aureus ATCC 6538); 6.25 µg/disk, 10 ± 0 mm (Klebsiella pneumoniae); and 50 µg/disk, 12 ± 0 mm (ampicillin-resistant Escherichia coli). Compounds 1, 2, and 4 showed ichthyotoxicity (zebrafish embryos, Danio rerio) at a level of LC50 >10 µg/ml [dead, 48 hours postfertilization (hpf)]. This is the first report that compound 4 inhibits the growth of antibiotic-resistant bacteria.