Labelling of octreotide using Br-76-prosthetic groups

A method for labelling the octapeptide octreotide (D-Phe-Cys-Phe-D-TrpLys-Thr-Cys-Thr(ol)) with the positron emitting Br-76 (T-1/2 = 16 h) is presented. epsilon -Boc-protected octreotide was conjugated to N-succinimidyl 4-[Br-76]bromobenzoate 1 and N-succinimidyl 5-[Br-76]bromo-3-pyridinecarboxylate 3 using microwave heating. The conjugates 4 and 5 were isolated in 50-55% radiochemical yield after the removal of the protecting Boc-group. Compound 3 was synthesised from the corresponding trimethylstannyl-precursor in 25% radiochemical yield. The synthesis of methyl-4-[Br-76] bromobenzimidate 8 in 40% radiochemical yield from the precursor methyl -4-trimethylstannylbenzimidate is also described. Experiments were performed to react 8 with Boc-octreotide but no product was obtained. The binding-properties of Br-76-conjugates 4 and 5 to meningiomas were investigated using frozen section autoradiography. Compound 5 showed better binding properties than 4. Copyright (C) 2001 John Wiley & Sons, Ltd.