Anna Schweifer

NMDA receptor affinities of 1,2-diphenylethylamine and 1-(1,2-diphenylethyl)piperidine enantiomers and of related compounds.

We resolved 1,2-diphenylethylamine (DPEA) into its (S)- and (R)-enantiomer and used them as precursors for synthesis of (S)- and (R)-1-(1,2-diphenylethyl)piperidine, flexible homeomorphs of the NMDA channel blocker MK-801. We also describe the synthesis of the dicyclohexyl analogues of DPEA. These and related compounds were tested as inhibitors of [(3)H]MK-801 binding to rat brain membranes. Stereospecificity ranged between factors of 0.5 and 50. Some blockers exhibited stereospecific sensitivity to the modulator spermine. Our results may help to elucidate in more detail the NMDA channel pharmacophore.

Studies on the biodegradation of fosfomycin: Growth of Rhizobium huakuii PMY1 on possible intermediates synthesised chemically

The first step of the mineralisation of fosfomycin by R. huakuii PMY1 is hydrolytic ring opening with the formation of (1R,2R)-1,2-dihydroxypropylphosphonic acid. This phosphonic acid and its three stereoisomers were synthesised by chemical means and tested as their ammonium salts for mineralisation as evidenced by release of P(i). Only the (1R,2R)-isomer was degraded. A number of salts of phosphonic acids such as (+/-)-1,2-epoxybutyl-, (+/-)-1,2-dihydroxyethyl-, 2-oxopropyl-, (S)-2-hydroxypropyl-, (+/-)-1-hydroxypropyl- and (+/-)-1-hydroxy-2-oxopropylphosphonic acid were synthesised chemically, but none supported growth. In vitro C-P bond cleavage activity was however detected with the last phosphonic acid. A mechanism involving phosphite had to be discarded as it could not be used as a phosphorus source. R. huakuii PMY1 grew well on (R)- and (S)-lactic acid and hydroxyacetone, but less well on propionic acid and not on acetone or (R)- and (+/-)-1,2-propanediol. The P(i) released from (1R,2R)-1,2-dihydroxypropylphosphonic acid labelled with one oxygen-18 in the PO3H2 group did not stay long enough in the cells to allow complete exchange of 18O for 16O by enzymic turnover.

Preparation of nucleosides derived from 2-nitroimidazole and D-arabinose, D-ribose, and D-galactose by the Vorbrüggen method and their conversion to potential precursors for tracers to image hypoxia.

2-Nitroimidazole was silylated using hexaethyldisilazane and then reacted with 1-O-acetyl derivatives of d-arabinose, d-ribose, and d-galactose in acetonitrile at mild temperatures (−20 °C to rt), catalyzed by triethylsilyl triflate (Vorbrüggen conditions). The α-anomer was formed in the former case and the β-anomers in the latter two cases (highly) selectively. When d-arabinose and d-ribose were silylated with tert-butyldiphenylsilyl chloride in pyridine at the hydroxyl groups at C-5 and acetylated at the other ones in a one-pot reaction, mixtures of anomeric 1-O-acetyl derivatives were obtained. These were coupled by the Vorbrüggen method and then deblocked at C-5 and tosylated to give precursors for tracers to image hypoxia in four steps without using Hg(CN)2 necessary for other methods. The Vorbrüggen conditions enable a shorter route to azomycin nucleoside analogues than the previous coupling procedures.

Stereochemical Course of Methyl Transfer by Cobalamin-Dependent Radical SAM Methyltransferase in Fosfomycin Biosynthesis

The methyl groups of [ methyl-( S)]- and [ methyl-( R)]-[ methyl-D,T]-l-methionine fed to Streptomyces fradiae were incorporated into fosfomycin, which was chemically degraded to chiral AcONa. The enzymatic test gave the ( S)-configuration for the chiral AcONa derived from methionine with the ( S)-[D,T]methyl group ( F = 31.7) and ( R) for the one derived from methionine with the ( R)-[D,T]methyl group ( F = 83.0). The radical SAM methyltransferase transfers the methyl group of MeCbl to HEP-CMP with inversion of configuration.

[18F]Fluoro-azomycin-2´-deoxy-β-d-ribofuranoside — A new imaging agent for tumor hypoxia in comparison with [18F]FAZA ☆ ☆☆

INTRODUCTION Radiolabeled 2-nitroimidazoles (azomycins) are a prominent class of biomarkers for PET imaging of hypoxia. [18F]Fluoro-azomycin-α-arabinoside ([18F]FAZA) - already in clinical use - may be seen as α-configuration nucleoside, but enters cells only via diffusion and is not transported by cellular nucleoside transporters. To enhance image contrast in comparison to [18F]FAZA our objective was to 18F-radiolabel an azomycin-2´-deoxyriboside with β-configuration ([18F]FAZDR, [18F]-β-8) to mimic nucleosides more closely and comparatively evaluate it versus [18F]FAZA. METHODS Precursor and cold standards for [18F]FAZDR were synthesized from methyl 2-deoxy-d-ribofuranosides α- and β-1 in 6 steps yielding precursors α- and β-5. β-5 was radiolabeled in a GE TRACERlab FXF-N synthesizer in DMSO and deprotected with NH4OH to give [18F]FAZDR ([18F]-β-8). [18F]FAZA or [18F]FAZDR was injected in BALB/c mice bearing CT26 colon carcinoma xenografts, PET scans (10min) were performed after 1, 2 and 3h post injection (p.i.). On a subset of mice injected with [18F]FAZDR, we analyzed biodistribution. RESULTS [18F]FAZDR was obtained in non-corrected yields of 10.9±2.4% (9.1±2.2GBq, n=4) 60min EOB, with radiochemical purity >98% and specific activity >50GBq/μmol. Small animal PET imaging showed a decrease in uptake over time for both [18F]FAZDR (1h p.i.: 0.56±0.22% ID/cc, 3h: 0.17±0.08% ID/cc, n=9) and [18F]FAZA (1h: 1.95±0.59% ID/cc, 3h: 0.87±0.55% ID/cc), whereas T/M ratios were significantly higher for [18F]FAZDR at 1h (2.76) compared to [18F]FAZA (1.69, P<0.001), 3h p.i. ratios showed no significant difference. Moreover, [18F]FAZDR showed an inverse correlation between tracer uptake in carcinomas and oxygen breathing, while muscle tissue uptake was not affected by switching from air to oxygen. CONCLUSIONS First PET imaging results with [18F]FAZDR showed advantages over [18F]FAZA regarding higher tumor contrast at earlier time points p.i. Availability of precursor and cold fluoro standard together with high output radiosynthesis will allow for a more detailed quantitative evaluation of [18F]FAZDR, especially with regard to mechanistic studies whether active transport processes are involved, compared to passive diffusion as observed for [18F]FAZA.