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Proceedings of the 31 st European Peptide SymposiumMichal Lebl, Morten Meldal, Knud J. Jensen, Thomas Hoeg-Jensen (Editors)European Peptide Society, 2010Solid Phase Synthesis and In Depth Analysis of the TumourTargeting Peptide DOTATOC for Clinical ApplicationsSusanne Krämer 1 , Carl von Gall 1 , William Edmund Hull 2 ,Michael Eisenhut 3 , Uwe Haberkorn 1 , and Walter Mier 11 Department of Nuclear Medicine, University Hospital Heidelberg, Heidelberg, 69120,Germany; 2 Deutsches Krebsforschungszentrum, Core Facility: Molecular StructureAnalysis, Heidelberg, Germany, 3 Deutsches Krebsforschungszentrum, Division ofRadiochemistry and Radiopharmacology, Heidelberg, GermanyIntroductionPeptides are useful tools for the targeted delivery of radionuclides and/or chemotherapeuticdrugs to their site of action within an organism. Due to its excellent performance thepeptide derivative (1,4,7,10-tetraazacyclododecane-N,N’,N’’,N’’’-tetraacetic acid)-Tyr 3 -octreotide DOTATOC is the gold standard of peptide radiopharmaceuticals. DOTATOCbinds to somatostatin receptors (receptor subtypes SSTR2 and SSTR5) and can be used forthe diagnosis and therapy of tumours expressing these receptors. Somatostatin receptors areexpressed on neuroendocrine tumours, including carcinoid tumours, pituitary adenoma,pheochromocytoma, and medullary thyroid carcinoma. Somatostatin receptors are alsopositive on the cell surfaces of other types of tumours, such as small cell lung carcinoma,meningioma, astrocytoma, and neuroblastoma. When labelled with 68 Ga DOTATOC allowsthe diagnosis by positron emission tomography (PET), 90 Y labelled DOTATOC has beenproven to be effective for endoradiotherapy. The basis for the clinical application of thispeptide is an efficient solid phase synthesis.Results and DiscussionEven though Tyr 3 -octreotide contains only eight residues, the synthesis is complicated byseveral structural features. The conjugation of the chelator sets further hurdles to obtain aproduct with essentially no side products. Here we describe a synthetic protocol whichallows the solid phase formation and purification of DOTATOC at pharmaceutical quality.The product is characterized in detail by high resolution LC/MS using orbitrap technologyand a complete assignment of its 1 H and 13 C NMR spectra. In addition conformationalfeatures of the peptide were evaluated using 1D and 2D NMR experiments. DOTATOCwas prepared by solid-phase synthesis on a resin loaded with Fmoc-Thr(tBu)-Ol as shownin Figure 1.Fig. 1. DOTATOC solid-phase synthesis strategy using O-tBu-threoninol 2-chlorotrityl resin(grey spheres). Key: (a) stepwise elongation, (b) piperidine, (c) tris(tBu)DOTA, HATU,DIPEA, (d) TFA, H 2 O, phenol, TIS, (e) TFA (f) air oxidation.338