Synthesis of three alpha 7 agonists in labeled form.

In support of a program to develop an alpha 7 agonist as a treatment for Alzheimer's disease, three drug candidates, 1, 2, and 3, were prepared in labeled forms. Compound 1 was prepared in C-14 labeled form by lithiation of [2,6-(14)C2]2-chloropyridine and subsequent coupling with spirooxirane-2,3'-quinuclidine. When this same coupling was attempted using [3,4,5,6-(2)H4]2-chloropyridine, alcohol [(2)H6]-6 was the major product indicating that the primary isotope effect for the lithiation step was significant enough to shift the reaction pathway. Therefore, an alternate site of labeling was used to prepare [(2)H4]-1. [(13)C5]-2 was prepared in five steps from [(13)C5 ]2-furoic acid, but the C-14 labeled compound used [(14)C2]-1 as the starting material instead. [(14)C2]-3 was prepared in two steps from [carbonyl-(14)C]nicotinic acid.

Metabolic stability of 6,7-dialkoxy-4-(2-, 3- and 4-[18F]fluoroanilino)quinazolines, potential EGFR imaging probes.

Epidermal growth factor receptors (EGFR), upregulated in many tumor types, have been a target for therapeutic development and molecular imaging. The objective of this study was to evaluate the distribution and metabolic characteristics of fluorine-18 labeled anilinoquinazolines as potential imaging agents for EGFR tyrosine kinase expression. Fluorine-18 labeled fluoronitrobenzenes were prepared by reaction of potassium cryptand [(18)F]fluoride with 1,2- and 1,4-dinitrobenzenes, and 3-nitro-N,N,N-trimethylanilinium triflate in 5min. Decay-corrected radiochemical yields of [(18)F]fluoride incorporation into the nitro-aromatic compounds were 81±2%, 44±4% and 77±5% (n=3-5) for the 2-, 3- and 4-fluoro isomers, respectively. Sodium borohydride reduction to the corresponding [(18)F]fluoroanilines was achieved with greater than 80% conversion in 5min. Coupling of [(18)F]fluoroaniline-hydrochlorides to 6,7-dimethoxy-4-chloro-quinazoline gave the corresponding 6,7-dimethoxy-4-(2-, 3- and 4-[(18)F]fluoroanilino)quinazolines in 31±5%, 17±2% and 55±2% radiochemical yield, respectively, while coupling to the 6,7-diethoxy-4-chloro-quinazoline produced 6,7-diethoxy-4-(2-, 3- and 4-[(18)F]fluoroanilino)quinazolines in 19±6%, 9±3% and 36±6% radiochemical yield, respectively, in 90min to end of synthesis from [(18)F]fluoride. Biodistribution of 2- and 4-[(18)F]fluoroanilinoquinazolines was conducted in tumor-bearing mice (MDA-MB-435 and MDA-MB-468 xenografts). Low tumor uptake (<1% injected dose per gram (ID/g) of tissue up to 3h postinjection of the radiotracers) was observed. High bone uptake (5-15% ID/g) was noted with the 4-[(18)F]fluoroanilinoquinazolines. The metabolic stabilities of radiolabeled quinazolines were further evaluated by incubation with human female cryopreserved isolated hepatocytes. Rapid degeneration of the 4-fluoro-substituted compounds to baseline polar metabolites was observed by radio-TLC, whereas, the 2- and 3-[(18)F]fluoroaniline derivatives were significantly more stable, up to 2h, corroborating the in vivo biodistribution studies. para-Substituted [(18)F]fluoroanilines, a common structural motif in radiopharmaceuticals, are highly susceptible to metabolic degradation.