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Isolation and Structure Assignments of Rostratins A−D, Cytotoxic Disulfides Produced by the Marine-Derived Fungus Exserohilum rostratum

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journal contribution
posted on 2004-08-27, 00:00 authored by Ren Xiang Tan, Paul R. Jensen, Philip G. Williams, William Fenical
Four new cytotoxic disulfides, rostratins A−D (14), were isolated from the whole broth of the marine-derived fungus Exserohilum rostratum (Drechsler), a fungal strain found associated with a marine cyanobacterial mat. The structures of these cyclic dipeptides were established through chemical degradation and a variety of two-dimensional NMR techniques. The absolute configurations of the rostratins were determined by the modified Mosher method. In the case of the polyhydroxylated compound 1 and the mercaptol 4, regioselective acylation was achieved by modulating the reaction temperature while monitoring the progress of the reaction by 1H NMR. Rostratins A, B, C, and D showed in vitro cytotoxicity against human colon carcinoma (HCT-116) with IC50 values of 8.5, 1.9, 0.76, and 16.5 μg/mL, respectively.

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