Bioactive steroidal glycosides from the marine sponge Erylus lendenfeldi Joel S. Sandler, a, * Susan L. Forsburg b,† and D. John Faulkner a,! a Center for Marine Biotechnology and Biomedicine, Scripps Institution of Oceanography, University of California, San Diego, 8615 Discovery Way, Sverdrup Hall, La Jolla, CA 92037, USA b Salk Institute for Biological Studies, 10010 North Torrey Pines Road, La Jolla, CA 92037, USA Received 5 September 2004; revised 16 November 2004; accepted 16 November 2004 Abstract—Bioassay-guided fractionation of the methanol extract of Erylus lendenfeldi using engineered strains of budding yeast (Saccharomyces cerevisiae) has resulted in the isolation of the known compound eryloside A (1) and two new compounds, erylosides K (2) and L (3). The structures were established based mainly on 1D and 2D NMR data. The absolute stereochemistry of eryloside A, which had never been fully characterized, was determined using the modified Mosher’s method. The absolute stereochemistry of eryloside K was determined by comparison with tetrahydroeryloside A. Compounds 1–3 exhibited selective cytotoxicity against a yeast strain (Drad50) deficient in double strand break (DSB) repair. q 2004 Elsevier Ltd. All rights reserved. 1. Introduction The modern approach to finding new anticancer drugs relies on the discovery of compounds that target the subtle molecular differences between malignant and healthy human cells. 1 The recent integration of genetics and drug discovery has resulted in the engineering of a wide array of molecular alterations in model organisms that can be used to screen for selectively bioactive small molecules. In particular, budding yeast (Saccharomyces cerevisiae) have proven to be an excellent model for discovering novel anticancer agents. 2 In an effort to rapidly identify bioactive marine natural products that target cancer-related pathways, we began screening our collection using an assay 3 to identify extracts that were selectively cytotoxic to budding yeast strains with defined alterations in cell-cycle check- point and DNA-damage repair genes. The methanol extract from the Red Sea sponge Erylus lendenfeldi Sollas, 4 1888 (Demospongiae, Astrophorida, Geodiidae) exhibited selec- tive cytotoxicity against a Drad50 mutant (yMP11406) deficient in DSB repair. Herein, we describe the structure and bioactivity of three steroidal glycosides, erylosides A, K, and L, which were isolated from this extract. 2. Results and discussion 2.1. Isolation and structural elucidation The marine sponge Erylus lendenfeldi was collected in February, 2000 in the Red Sea just north of Hurghada. The methanol extract exhibited selective activity against a Drad50 strain of S. cerevisiae. Bioassay-guided fraction- ation led to the isolation of the known steroidal glycoside, eryloside A (1, 720 mg, 0.4% dry weight), along with two new steroidal glycosides: eryloside K (2, 145 mg, 0.08% dry weight), and eryloside L (3, 90 mg, 0.05% dry weight). The molecular formula of eryloside A (1) was determined to be C 40 H 66 O 12 by high resolution MALDI-MS (m/z 761.4472 ([MCNa] C ). The spectral properties of 1 (Table 1) were identical with the reported values for eryloside A. 5 Thus, 1 is a 3b-O-{b-D-galactopyranosyl-(1/2)-b-D-galactopyra- nosyl}-23b-hydroxy-4a-methyl-5a-cholesta-8,14-diene. 0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tet.2004.11.039 Tetrahedron 61 (2005) 1199–1206 Keywords: Cell-based assay; Double strand break repair; Steroidal glycoside; Modified Mosher’s method; Catalytic hydrogenation. * Corresponding author. Tel.: C1 858 534 2348; fax: C1 858 534 2997; e-mail: jsandler@ucsd.edu † Current address: Molecular and Computational Biology Section, University of Southern California, Los Angeles, CA 90089-1340, USA. ! Deceased.