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Labeling of ( S )‐DES‐4‐amino‐3‐[ 125 I]iodozacopride (DAIZAC), a high‐affinity radioligand for the 5‐HT‐3 receptor
Author(s) -
Mason N. Scott,
Hewlett William A.,
Ebert Michael H.,
Schmidt Dennis E.,
de Paulis Tomas
Publication year - 1996
Publication title -
journal of labelled compounds and radiopharmaceuticals
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.432
H-Index - 47
eISSN - 1099-1344
pISSN - 0362-4803
DOI - 10.1002/(sici)1099-1344(199611)38:11<955::aid-jlcr912>3.0.co;2-#
Subject(s) - radioligand , chemistry , receptor , benzamide , chloramine t , radioligand assay , specific activity , stereochemistry , ligand (biochemistry) , biochemistry , enzyme , organic chemistry
We have prepared ( S )‐5‐chloro‐3‐[ 125 I]iodo‐2‐methoxy‐ N ‐(1‐azabicyclo[2.2.2]oct‐3‐yl)‐benzamide ([ 125 I]DAIZAC, [ 125 I]‐ 3 ) as a radioligand for characterization of the 5‐HT‐3 receptor. Preparation of the 3‐tri‐ n ‐butylstannyl precursor was accomplished from the corresponding unlabeled DAIZAC by reaction with bis(tributyltin). Treatment of the precursor with 5 mCi of Na 125 I and chloramine‐T in dilute HCl gave 2.58 ± 0.22 mCi (52%) of [ 125 I]DAIZAC with >98% radiochemical purity and 1500 Ci/mmol specific activity. Saturation analysis of the binding of [ 125 I]DAIZAC to rat brain homogenates showed a single binding site with a receptor density B max of 0.66 ± 0.03 pmol/g and a receptor affinity K D of 0.15 ± 0.01 nM. Compared to [ 125 I]iodozacopride, we find the 20‐fold higher affinity and easy preparation of [ 125 I]DAIZAC to be advantageous for in vitro identification of brain 5‐HT‐3 receptors.