Walter Wutz

METABOLISM OF THE A1 ADENOSINE RECEPTOR POSITRON EMISSION TOMOGRAPHY LIGAND [18F]8-CYCLOPENTYL-3-(3-FLUOROPROPYL)-1-PROPYLXANTHINE ([18F]CPFPX) IN RODENTS AND HUMANS

Studies of plasma from mice, rats, and human volunteers evaluated methods for the extraction and quantification of the positron emission tomography ligand [18F]8-cyclopentyl-3-(3-fluoropropyl)-1-propylxanthine ([18F]CPFPX) and identification of its metabolites in plasma by thin-layer chromatography and high-performance liquid chromatography (HPLC). Analysis of human, mouse, and rat plasma extracts by HPLC identified four identical radioactive metabolites in each species. The low mass of radioligand administered to humans (0.5 - 5 nmol) prevented direct identification of metabolites. However, incubating liver microsomes with CPFPX and analysis by means of liquid chromatography-mass spectrometry (LC-MS) identified seven compounds, four having the same retention times as the metabolites in human plasma. Analysis of microsomal metabolites by LC-MS identified five [M + H]+ ions of m/z equivalent to hydroxy derivatives, 339, one of m/z equivalent to an oxo derivative, m/z 337, and one of m/z equivalent to a difunctionalized oxo-desaturation species, m/z 335, which is prominent in rat and mouse plasma and is the main metabolite in human plasma. An [M + H]+ ion corresponding to a N-dealkylated derivative was not detected. Thus, like the natural methylxanthines, CPFPX seems to undergo oxidation by liver microsomes but, unlike those methylxanthines, dealkylation did not occur. LC-MS experiments with “in source” fragmentation identified the cyclopentyl moiety to be the most functionalized part of the molecule by liver microsomes and in vivo oxidations. Except for two metabolites, hydroxylated at the N1 propyl chain, all oxidative modifications found took place at the cyclopentyl ring.

Synthesis of 2-benzyl-2H-pyrazole-3,4-diamine dihydrochloride

This report describes a straightforward, high yield synthesis of a previously inaccessible N-protected diaminopyrazole in five steps starting from acrylonitrile, hydrazine and benzaldehyde.

Synthesis of the main metabolite in human blood of the A1 adenosine receptor ligand [18F]CPFPX.

In human blood, the PET radiotracer [(18)F]CPFPX (1) is metabolized to numerous metabolites, one (M1) being the most prominent in plasma 30 min p.i. Because the mass of injected tracer is < or = 5 nmol, concentrations in plasma are too low to analyze. Human liver microsomes generate main metabolites having HPLC retention times identical to those in plasma. HPLC-MS tentatively identified M1 as 2. Synthesis of 2 and identical HPLC-MS spectra of 2 and M1 confirmed that assignment.

Evaluation of radioiodinated 8-Cyclopentyl-3-[(E)-3-iodoprop-2-en-1-yl]-1-propylxanthine ([*I]CPIPX) as a new potential A1 adenosine receptor antagonist for SPECT

8-Cyclopentyl-3-[(E)-3-[(131)I]iodoprop-2-en-1-yl]-1-propylxanthine (2*) was generated by iododestannylation of the tributyl-stannyl-precursor with [(131)I]NaI and chloramine T. The radiochemical yield of 2* was 82 +/- 4%, and the purity exceeded 98%. The specific activity was 33 +/- 19 GBq/micromol. Affinities for rat, pig and human A(1) adenosine receptors (A(1)ARs) were in the low nanomolar range, but poor selectivity for the human A(1)AR over the A(2A)AR was found. Additionally, in vitro and ex vivo autoradiographic studies revealed high unspecific binding which makes this ligand unsuitable for SPECT imaging.