IN-VIVO AUTORADIOGRAPHY OF RADIOIODINATED (R)-3-QUINUCLIDINYL (S)-4-IODOBENZILATE [(R,S)-IQNB] AND (R)-3-QUINUCLIDINYL (R)-4-IODOBENZILATE [(R,R)-IQNB] - COMPARISON OF THE RADIOLABELED PRODUCTS OF A NOVEL TRIBUTYLSTANNYL PRECURSOR WITH THOSE OF THE ESTABLISHED TRIAZENE AND EXCHANGE METHODS

Radioiodinated (R,S)-IQNB and (R,R)-IQNB are prepared either from a tr iazene precursor or using an exchange reaction. In both cases the radi ochemical yield is low. The product of the exchange reaction also suff ers from having a fairly low specific activity. A new method for prepa ring radioiodinated (R,S)-IQNB and (R,R)-IQNB from a tributylstannyl p recursor has recently been developed. This method is more convenient a nd much faster than the triazene and exchange methods, and it reliably results in a high radiochemical yield of a high specific activity pro duct. In rat brain, the in vivo properties of the radioiodinated produ cts of the tributylstannyl method are identical to those of the corres ponding radioiodinated (R,S)-IQNB and (R,R)-IQNB prepared using the tr iazene and exchange methods. Dissection studies of selected brain regi ons show that at 3 h post injection (R,S)-[I-125]IQNB prepared by all three methods have indistinguishable %dose g(-1) values in all brain r egions studied. Autoradiographic comparison of coronal slices through the anteroventral nucleus of the thalamus, through the hippocampus and through the pens at 2 h post injection shows that (R,S)-[I-125]IQNB p repared by the triazene and tributylstannyl methods have indistinguish able patterns of binding. Copyright (C) 1997 Elsevier Science Ltd