Chemical Synthesis of (RP)- and (SP)-[16O,17O,18O]Phosphoenol Pyruvate.

Enzymes and chirality are intimately associated. For their mechanisms to be studied, chiral substrates are needed as probes. Here, we report a concise synthesis of (RP)- and (SP)-[16O,17O,18O]phosphoenol pyruvate starting from enantiomerically pure (R)-2-chloro-1-phenylethanol, which was transformed into 18O-labeled 3-methyl-1-phenylbutane-1,3-diol. The diol was reacted with tris(dimethylamino)phosphane and consecutively with H217O to yield a mixture of cyclic H-phosphonates labeled with 17O and 18O. They were silylated and subjected to a Perkow reaction with ethyl 3-chloropyruvate. Two protected-[16O,17O,18O]phosphoenol pyruvates were formed and finally globally deprotected. Their configuration was reassessed by a known enzymatic test in combination with conversion of the formed d-glucose-6-phosphate into mixtures of labeled methyl d-glucose-4,6-phosphates, which were analyzed by 31P NMR spectroscopy. The enzymatic test supported the configuration assigned to labeled stereogenic phosphorus atoms on the basis of synthesis.

Efficient preparation of 2-nitroimidazole nucleosides as precursors for hypoxia PET tracers.

ABSTRACT: 2-Deoxy-D-ribose was converted to α/ß-mixtures of methyl 3-O-acetyl- and methyl 3-O-benzoyl-2-deoxy-5-(p-toluenesulfonyl)-D-ribofuranosides. These were reacted with boron trichloride to generate ribofuranosyl chlorides, which afforded precursors for tracers to image tumor hypoxia on substitution with salts of 2-nitroimidazole. The anomeric ratio of the nucleosides was delicately influenced by the reaction conditions.

Synthesis and preclinical characterization of 1-(6'-deoxy-6'-[18F]fluoro-ß-d-allofuranosyl)-2-nitroimidazole (ß-6'-[18F]FAZAL) as a positron emission tomography radiotracer to assess tumor hypoxia.

Positron emission tomography (PET) using fluorine-18 (18F)-labeled 2-nitroimidazole radiotracers has proven useful for assessment of tumor oxygenation. However, the passive diffusion-driven cellular uptake of currently available radiotracers results in slow kinetics and low tumor-to-background ratios. With the aim to develop a compound that is actively transported into cells, 1-(6'-deoxy-6'-[18F]fluoro-ß-d-allofuranosyl)-2-nitroimidazole (ß-[18F]1), a putative nucleoside transporter substrate, was synthetized by nucleophilic [18F]fluoride substitution of an acetyl protected labeling precursor with a tosylate leaving group (ß-6) in a final radiochemical yield of 12±8% (n=10, based on [18F]fluoride starting activity) in a total synthesis time of 60min with a specific activity at end of synthesis of 218±58GBq/µmol (n=10). Both radiolabeling precursor ß-6 and unlabeled reference compound ß-1 were prepared in multistep syntheses starting from 1,2:5,6-di-O-isopropylidene-α-d-allofuranose. In vitro experiments demonstrated an interaction of ß-1 with SLC29A1 and SLC28A1/2/3 nucleoside transporter as well as hypoxia specific retention of ß-[18F]1 in tumor cell lines. In biodistribution studies in healthy mice ß-[18F]1 showed homogenous tissue distribution and excellent metabolic stability, which was unaffected by tissue oxygenation. PET studies in tumor bearing mice showed tumor-to-muscle ratios of 2.13±0.22 (n=4) at 2h after administration of ß-[18F]1. In ex vivo autoradiography experiments ß-[18F]1 distribution closely matched staining with the hypoxia marker pimonidazole. In conclusion, ß-[18F]1 shows potential as PET hypoxia radiotracer which merits further investigation.

On the configurational stability of chiral, nonracemic fluoro- and iodo-[D(1)]methyllithiums.

Enantiomerically pure fluoro-[D1]methyllithium and iodo-[D1]methyllithiums of up to 92% ee were generated by transmetalation of the corresponding stannanes with MeLi in THF at various temperatures. The intermediate halo-[D1]methyllithiums were trapped with benzaldehyde or acetophenone already present in excess in the reaction mixture to either give halohydrins or to disintegrate to carbene. The fluoro-[D1]methyllithiums were found to be microscopically configurationally stable within the tested range of -95 to 0 °C, but chemically only stable at temperatures below -95 °C due to a rapidly increasing portion disintegrating to carbene. The iodo-[D1]methyllithiums were configurationally labile relative to the rate of addition to PhCHO at all temperatures tested (-95 to -30 °C). Disintegration to carbene interfered as well.

On the Configurational Stability of Chiral Heteroatom-Substituted [D1]Methylpalladium Complexes as Intermediates of Stille and Suzuki-Miyaura Cross-Coupling Reactions.

Enantiomerically pure (S)-tributylstannyl[D1]methanol and (R)- and (S)-tributylstannyl[D1]methyl benzoates were Stille-coupled with bromobenzene and benzoyl chloride in 1,4-dioxane and toluene using [(Ph3P)4Pd] or [(Ph3P)2PdCl2] either alone or in combination with CuCN as cocatalyst at temperatures up to 80 °C. The products were found to be enantiomerically pure. (R)- and (S)-N-(tributylstannyl[D1]methyl)phthalimides gave enantiomerically pure products with benzoyl chloride, but with bromobenzene protected phenyl[D1]methylamines gave products of only 52-69 % ee depending on the solvent used. Tributyl(thio[D1]methyl)stannanes could not be Stille-coupled with benzoyl chloride or with bromobenzene. Similarly, dimethyl phenyl[D1]methylboronate underwent a Suzuki-Miyaura coupling with bromobenzene to give phenyl[D1]methylsilane with 99 % ee. All couplings followed a retentive course and, except in one case, the intermediate [XCHDPdL n ] complexes were found to be microscopically configurationally stable.