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Bioconjugate Chem. 2002, 13, 224−231
Chemical Synthesis of Escherichia Coli STh Analogues by Regioselective Disulfide Bond Formation: Biological Evaluation of an 111In-DOTA-Phe19-STh Analogue for Specific Targeting of Human Colon Cancers Hariprasad Gali,† Gary L. Sieckman,§ Timothy J. Hoffman,†,‡,§ Nellie K. Owen,† Dana G. Mazuru,† Leonard R. Forte,§,⊥ and Wynn A. Volkert*,†,§ Research Service, Harry S. Truman Memorial Veterans’ Administration Hospital, Columbia, Missouri 65201 and Departments of Radiology, Pharmacology and Internal Medicine, University of MissourisColumbia, Columbia, Missouri 65211. Received July 6, 2001; Revised Manuscript Received October 18, 2001
New human Escherichia coli heat-stable peptide (STh) analogues containing a DOTA chelating group were synthesized by sequential and selective formation of disulfides bonds in the peptide. This synthetic approach utilizes three orthogonal thiol-protecting groups, Trt, Acm, and t-Bu, to form three disulfide bonds by successive reactions using 2-PDS, iodine, and silyl chloride-sulfoxide systems. The DOTASTh conjugates exhibiting high guanylin/guanylate cyclase-C (GC-C) receptor binding affinities were obtained with >98% purity. In vitro competitive binding assays, employing T-84 human colon cancer cells, demonstrated the IC50 values of
