Journey of 2'-deoxy-2'-fluoro-5-methyl-1-ß-D-arabinofuranosyluracil (FMAU): from Antiviral Drug to PET Imaging Agent.

BACKGROUND: Developed as an antiviral drug in the 1960s and 1970s, the thymidine analogue 2'-deoxy-2'-fluoro-5-methyl-1-ß-D-arabinofuranosyluracil (FMAU) was translated to clinical application for treatment of herpes simplex virus infection. In phase I clinical trial of FMAU; however, patients experienced neurotoxicity at the pharmacological dose, and FMAU was withdrawn from the trial. More recently, FMAU has been developed as a tracer for positron emission tomography (PET) imaging in early detection of cancer through its binding to human thymidine kinase, which is upregulated in cancer cells. FMAU radiolabeled with 11C or 18F has been examined for PET imaging of tumor cell proliferation and DNA synthesis. Although many reports have been partially published on FMAU, systematic reviews outlining the historic development and imaging probe are lacking. This review is focused on the identification of kinases, the chemistry of FAMU and its application in cancer diagnosis and therapy assessment. OBJECTIVE: The aim of this study was to review the historic development of FMAU, from its synthetic development and antiviral activity studies to its radiolabeling and evaluate it as a PET imaging probe for the early detection of cancer and assessment of treatment response, including published reports on the clinical utility of 18F-FMAU. CONCLUSION: While FMAU was not successful as an antiviral agent, 18F-FMAU is a suitable radiotracer for early detection of cancer and assessment of response to therapy by PET. The process of clinical grade 18F-FMAU production requires further improvement. 18F-FMAU has high potential for clinical application, but further extensive studies are needed to establish this tracer in the diagnosis of various cancers and assessment of their response to therapy.

Microwave-assisted one-pot radiosynthesis of 2'-deoxy-2'-[18F]fluoro-5-methyl-1-ß-d-arabinofuranosyluracil ([18F]-FMAU).

OBJECTIVES: [(18)F]-FMAU is a PET tracer being evaluated for imaging cell proliferation. Current multi-step procedures of [(18)F]-FMAU synthesis are time-consuming, resulting in low radiochemical yield and inconvenient applications for the clinic. We have previously reported the use of Friedel-Crafts catalysts for an improved synthesis of [(18)F]-FMAU. In this study, we investigated the efficiency of microwave-assisted radiosynthesis of [(18)F]-FMAU in comparison with conventional thermal conditions. METHODS: A simplified one-pot synthesis of [(18)F]-FMAU was developed under microwave conditions. Various reaction times, temperatures, and microwave powers were systematically explored to optimize the coupling reaction of 2-deoxy-2-[(18)F]fluoro-1,3,5-tri-O-benzoyl-d-arabinofuranose ([(18)F]-sugar) and bis-2,4-(trimethylsilyloxy)-5-methyluracil (silylated uracil) in the presence of a Friedel-Crafts catalyst, trimethylsilyl trifluoromethanesulfonate (TMSOTf). RESULTS: Microwave significantly enhanced the coupling efficiency of [(18)F]-sugar and silylated uracil by reducing the reaction time to 10 min (6-fold reduction as compared to conventional heating) at 95 °C. Base hydrolysis followed by high-performance liquid chromatography purification produced the desired [(18)F]-FMAU. The overall radiochemical yield was 20 ± 4% (decay corrected, n=3). Radiochemical purity was >99% and specific activity was >400 mCi/µmol. The α/ß anomer ratio was 1:2. The radiosynthesis time was about 90 min from the end of bombardment. CONCLUSIONS: A reliable microwave-assisted approach has been developed for routine synthesis of [(18)F]-FMAU. The new approach affords a simplified process with shorter synthesis time and higher radiochemical yield as compared to conventional heating. A fully automated microwave-assisted synthesis of [(18)F]-FMAU can be readily achieved under new reaction conditions.

Improved synthesis of 2'-deoxy-2'-[18F]fluoro-5-methyl-1-ß-D-arabinofuranosyluracil ([18F]FMAU).

[18F]FMAU is an established PET probe used to monitor cellular proliferation. For clinical applications, a fully automated cGMP-compliant radiosynthesis would be preferred. However, the current synthesis of [18F]FMAU requires HBr activation of the sugar prior to the coupling with silylated uracil. This multiple step procedure makes the development of an automated protocol difficult and complicated. In this study, we report the use of Friedel-Crafts catalysts for an improved synthesis of [18F]FMAU, which also includes a significantly simplified one-pot reaction condition.

A novel technique for the preparation of (125)I-5-trimethylstannyl-1-(2-deoxy-2-fluoro-beta-D-arabino-furanosyl) uracil [correction of urail] and its biodistribution pattern in Kunming mice.

In this study, a novel technique for the preparation of (125)I-5-trimethylstannyl-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl) urail (FIAU) was developed, (125)I-FIAU biodistribution profile was detected in Kunming mice and the possibility of using FTAU radio-labeling for reporter gene imaging was explored. 5-trimethylstannyl-1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl) urail (FTAU) was labeled with radioiodine ((125)I). A rotary evaporation method was used to remove excess methanol. The reactant was purified through a Sep-Pak C18 reversal phase column. The radiochemical purity and in vivo stability were determined using silica gel thin layer chromatography (TLC). The biodistribution of (125)I-FIAU in Kunming mice was also detected. The results showed that (125)I-FIAU could be radiolabeled effectively with FTAU, with mean labeling rate being (81±0.38)% (n =5). The mean radiochemical purity of (98.01±0.40)% (n=5) was achieved after a reversal phase Sep-park column purification. (125)I-FIAU was stable when incubated in normal human serum or in saline at 37°C, with a radiochemical purity >96% during a 0.5-24 h time period. Biological experiments exhibited rapid clearance of (125)I-FIAU from the blood pool. (125)I-FIAU was mostly excreted by kidneys. (125)I-FIAU in myocardium dropped conspicuously after 8 h and there was hardly retention at 24 h. We were led to concluded that the new method of radioiodinization of FTAU for the preparation of (125)I-FIAU is easy, highly effective and stable in vivo. The biodistribution of (125)I-FIAU in Kunming mice showed it can serve as an imaging probe for myocardial reporter genes.

The improved syntheses of 5-substituted 2'-[18F]fluoro-2'-deoxy-arabinofuranosyluracil derivatives ([18F]FAU, [18F]FEAU, [18F]FFAU, [18F]FCAU, [18F]FBAU and [18F]FIAU) using a multistep one-pot strategy.

INTRODUCTION: We and others have previously reported a four-step radiosynthesis of a series of 2'-deoxy-2'-[(18)F]fluoro-5-substituted-1-ß-D-arabinofuranosyluracil derivatives including [(18)F]FAU, [(18)F]FEAU, [(18)F]FFAU, [(18)F]FCAU, [(18)F]FBAU and [(18)F]FIAU as thymidine derivatives for tumor proliferation and/or reporter gene expression imaging with positron emission tomography (PET). Although the radiosynthesis has been proven to be reproducible and efficient, this complicated multistep reaction is difficult to incorporate into an automated cGMP-compliant radiosynthesis module for routine production. Recently, we have developed a simple and efficient one-pot method for routine production of [(18)F]FMAU. In this study, we studied the feasibility of radiosynthesizing [(18)F]FAU, [(18)F]FEAU, [(18)F]FFAU, [(18)F]FCAU, [(18)F]FBAU and [(18)F]FIAU using this newly developed method. METHODS: Similar to the radiosynthesis of [(18)F]FMAU, 5-substituted 2'-[(18)F]fluoro-2'-deoxy-arabinofuranosyluracil derivatives ([(18)F]FAU, [(18)F]FEAU, [(18)F]FFAU, [(18)F]FCAU, [(18)F]FBAU and [(18)F]FIAU) were synthesized in one-pot radiosynthesis module in the presence of Friedel-Crafts catalyst TMSOTf and HMDS. RESULTS: This one-pot radiosynthesis method could be used to produce [(18)F]FAU, [(18)F]FEAU, [(18)F]FFAU, [(18)F]FCAU, [(18)F]FBAU and [(18)F]FIAU. The overall radiochemical yields of these tracers varied from 4.1%±0.8% to 10.1%±1.9% (decay-corrected, n=4). The overall reaction time was reduced from 210 min to 150 min from the end of bombardment, and the radiochemical purity was >99%. CONCLUSIONS: The improved radiosyntheses of [(18)F]FAU, [(18)F]FEAU, [(18)F]FFAU, [(18)F]FCAU, [(18)F]FBAU and [(18)F]FIAU have been achieved with reasonable yields and high purity using a multistep one-pot method. The synthetic time has been reduced, and the reaction procedures have been significantly simplified. The success of this approach may make PET tracers [(18)F]FAU, [(18)F]FEAU, [(18)F]FFAU, [(18)F]FCAU, [(18)F]FBAU and [(18)F]FIAU more accessible for preclinical and clinical research.

Automated synthesis of 2'-deoxy-2'-[18F]fluoro-5-methyl-1-ß-D-arabinofuranosyluracil ([18F]-FMAU) using a one reactor radiosynthesis module.

2'-Deoxy-2'-[(18)F]fluoro-5-methyl-1-ß-D-arabinofuranosyluracil ([(18)F]-FMAU) is an established PET probe used to monitor cellular proliferation. For clinical applications, a fully automated cGMP-compliant radiosynthesis would be preferred. However, the current synthesis of [(18)F]-FMAU requires a multistep procedure, making the development of an automated protocol difficult and complicated. Recently, we have developed a significantly simplified one-pot reaction condition for the synthesis of [(18)F]-FMAU in the presence of Friedel-Crafts catalysts. Here, we report a fully automated synthesis of [(18)F]-FMAU based on a one reactor radiosynthesis module using our newly developed synthetic method. The product was purified on a semi-preparative high-performance liquid chromatography integrated with the synthesis module using 6% EtOH in 10 mM phosphate buffer or 8% MeCN/water. [(18)F]-FMAU was obtained in 12±3% radiochemical yield (decay corrected overall yield based on [(18)F]-F(-), n=4) with 383±33 mCi/µmol specific activity at the time of injection. The α/ß anomer ratio was 4:6. The overall reaction time was about 150 min from the end of bombardment and the radiochemical purity was >99%. This automated synthesis should also be suitable for the production of other 5-substituted thymidine analogues.

Improved synthesis of 2'-deoxy-2'-[18F]-fluoro-1-beta-D-arabinofuranosyl-5-iodouracil ([18F]-FIAU).

An improved synthesis of 2'-[(18)F]-fluoro-2'-deoxy-1-beta-D-arabinofuranosyl-5-iodouracil ([(18)F]-FIAU) has been developed. The method utilizes trimethylsilyl trifluoromethanesulfonate (TMSOTf) catalyzed coupling of 2-deoxy-2-[(18)F]-fluoro-1,3,5-tri-O-benzoyl-d-arabinofuranose with 2,4-bis(trimethylsilyloxy)-5-iodouracil to yield the protected dibenzoyl-[(18)F]-FIAU. Dibenzoyl-[(18)F]-FIAU was deprotected with sodium methoxide to yield a mixture of alpha- and beta-anomers in a ratio of 1:1, which were purified by HPLC. The procedure described in this article eliminates the need for HBr activation of the sugar prior to coupling with silylated iodouracil and is suitable for automation. The total reaction time was about 110 min, starting from [(18)F]-fluoride. The average isolated yield of the required beta-anomer was 10+/-6% (decay corrected) with average specific activity of 125 mCi/micromol.

The design, synthesis and antiviral evaluation of a series of 5-trimethylsilyl-1-beta-D-(arabinofuranosyl)uracil phosphoramidate ProTides.

BACKGROUND: Nucleoside analogues always require phosphorylation to be active. This appears to be a particular limitation for uridine-based nucleosides. Our ProTide method allows the direct use of masked membrane-soluble preformed nucleoside phosphates, bypassing the need for the initial phosphorylation step. We herein applied it to some novel 5-trimethylsilyl arabinosyl uridines. METHODS: 5-Trimethylsilyl-1-beta-D-(arabinofuranosyl)uracil was prepared in six steps starting from uridine, and five phosphoramidate ProTide derivatives were synthesized. These compounds were investigated for activity against a range of DNA and RNA viruses, including herpes simplex virus type-1 and type-2, vaccinia virus and HIV. RESULTS: Overall, these compounds did not show significant antiviral activity against any of the viruses tested. CONCLUSIONS: The inactivity of the ProTides of this nucleoside could correspond with poor ProTide activation in vitro, poor onward metabolism or low activity of the putative monophosphate metabolite.

Phosphoramidates of 2'-beta-D-arabinouridine (AraU) as phosphate prodrugs; design, synthesis, in vitro activity and metabolism.

2'-Beta-D-arabinouridine (AraU), the uridine analogue of the anticancer agent AraC, was synthesized and evaluated for antiviral activity and cytotoxicity. In addition, a series of AraU monophosphate prodrugs in the form of triester phosphoramidates (ProTides) were also synthesized and tested against a range of viruses, leukaemia and solid tumour cell lines. Unfortunately, neither the parent compound (AraU) nor any of its ProTides showed antiviral activity, nor potent inhibitory activity against any of the cancer cell lines. Therefore, the metabolism of AraU phosphoramidates to release AraU monophosphate was investigated. The results showed carboxypeptidase Y, hog liver esterase and crude CEM tumor cell extracts to hydrolyse the ester motif of phosphoramidates with subsequent loss of the aryl group, while molecular modelling studies suggested that the AraU l-alanine aminoacyl phosphate derivative might not be a good substrate for the phosphoramidase enzyme Hint-1. These findings are in agreement with the observed disappearance of intact prodrug and concomitant appearance of the corresponding phosphoramidate intermediate derivative in CEM cell extracts without measurable formation of araU monophosphate. These findings may explain the poor antiviral/cytostatic potential of the prodrugs.

Semiautomated radiosynthesis and biological evaluation of [18F]FEAU: a novel PET imaging agent for HSV1-tk/sr39tk reporter gene expression.

2'-deoxy-2'-[(18)F]fluoro-5-ethyl-1-beta-D-arabinofuranosyluracil ([(18)F]FEAU) is a promising radiolabeled nucleoside designed to monitor Herpes Simplex Virus Type 1 thymidine kinase (HSV1-tk) reporter gene expression with positron emission tomography (PET). However, the challenging radiosynthesis creates problems for being able to provide [(18)F]FEAU routinely. We have developed a routine method using a commercial GE TRACERlab FX-FN radiosynthesis module with customized equipment to provide [(18)F]FEAU. All radiochemical yields are decay corrected to end-of-bombardment and reported as means +/- SD. Radiofluorination (33 +/- 8%; n = 4), bromination (85 +/- 8%; n = 4), coupling reaction (83 +/- 6%; n = 4), base hydrolysis steps, and subsequent high-performance liquid chromatography purification afforded purified [(18)F]FEAU beta-anomer in 5 +/- 1% overall yield (n = 3 runs) after approximately 5.5 h and a beta/alpha-anomer ratio of 7.4. Radiochemical/chemical purities and specific activity exceeded 99% and 1.3 Ci/micromol (48 GBq/micromol), respectively. In cell culture, [(18)F]FEAU showed significantly (P < 0.05) higher accumulation in C6 cells expressing HSV1-tk/sr39tk as compared to wild-type C6 cells. Furthermore, [(18)F]FEAU showed slightly higher accumulation than 9-[4-[(18)F]fluoro-3-(hydroxymethyl)butylguanine ([(18)F]FHBG) in cells expressing HSV1-tk (P < 0.05), whereas [(18)F]FHBG showed significantly higher (P < 0.05) accumulation than [(18)F]FEAU in HSV1-sr39tk-expressing cells. micro-PET imaging of mice carrying tumor xenografts of C6 cells stably expressing HSV1-tk or HSV1-sr39tk are consistent with the cell uptake results. The [(18)F]FEAU mouse images also showed very low gastrointestinal signal with predominant renal clearance as compared to [(18)F]FHBG. The routine radiosynthesis of [(18)F]FEAU was successfully semiautomated using a commercial module along with customized equipment to provide the beta-anomer in modest yields. Although further studies are needed, early results also suggest [(18)F]FEAU is a promising PET radiotracer for monitoring HSV1-tk reporter gene expression.

Growth inhibition of Mycobacterium bovis, Mycobacterium tuberculosis and Mycobacterium avium in vitro: effect of 1-beta-D-2'-arabinofuranosyl and 1-(2'-deoxy-2'-fluoro-beta-D-2'-ribofuranosyl) pyrimidine nucleoside analogs.

The resurgence of tuberculosis and the emergence of multiple-drug-resistant strains of Mycobacteria necessitate the search for new classes of antimycobacterial agents. We synthesized a series of 1-beta-D-2'-arabinofuranosyl and 1-(2'-deoxy-2'-fluoro-beta-D-ribofuranosyl) pyrimidine nucleosides possessing diverse sets of alkynyl, alkenyl, alkyl, and halo substituents at the C-5 position of the uracil and investigated their effect on activity against M. tuberculosis, M. bovis, and M. avium. Among these molecules, 5-alkynyl-substituted derivatives emerged as potent inhibitors of M. bovis, M. tuberculosis, and M. avium. Nucleosides 1-beta-D-2'-arabinofuranosyl-5-dodecynyluracil (5), 1-(2'-deoxy-2'-fluoro-beta-D-ribofuranosyl)-5-dodecynyluracil (24), and 1-(2'-deoxy-2'-fluoro-beta-D-ribofuranosyl)-5-tetradecynyluracil (25) showed the highest antimycobacterial potency against M. bovis and M. tuberculosis. The MIC90 exhibited by compounds 5, 24, and 25 was similar or close to that of the reference drug rifampicin. The most active compounds 5, 24, and 25 were also found to retain sensitivity against a rifampicin-resistant strain of M. tuberculosis H37Rv at similar concentrations. Some of these analogs also revealed in vitro antimicrobial effect against several other gram-positive pathogens.

Synthesis of 5-radioiodoarabinosyl uridine analog for probing HSV-1 thymidine kinase gene: an unexpected chelating effect.

Tumor cells transduced with herpes simplex virus thymidine kinase gene has been intensively applied to the field of positron emission tomography via imaging of its substrate. As a pilot synthesis approach, a facial preparation of 5-[125I]iodoarabinosyl uridine starting from commercial available uridine is reported herein. Interestingly, the tin group in 5-trimethylstannyl arabinosyluridine was easily removed during purification. The destannylation through the formation of a six-ligand coordination involving 2'-hydroxyl and tin was thereby proposed.

Synthesis and evaluation of 2'-deoxy-2'-18F-fluoro-5-fluoro-1-beta-D-arabinofuranosyluracil as a potential PET imaging agent for suicide gene expression.

UNLABELLED: 2'-deoxy-2'-(18)F-fluoro-5-fluoro-1-beta-D-arabinofuranosyluracil ((18)F-FFAU) has been synthesized and evaluated in HT-29 cells as a potential PET agent for herpes simplex virus type 1 thymidine kinase (HSV1-tk) gene expression. METHODS: 2-Deoxy-2-(18)F-fluoro-1,3,5-tri-O-benzoyl-alpha-D-arabinofuranose was prepared by the reaction of the respective 2-triflate with tetrabutylammonium (18)F-fluoride. The fluorosugar was converted to its 1-bromo derivative and coupled with protected 5-fluorouracil. The crude product was hydrolyzed in base and purified by high-performance liquid chromatography to obtain the (18)F-FFAU. In vitro studies were performed in HT-29 cells by incubation at various time points. In vivo studies including biodistribution and microPET were performed in tumor-bearing nude mice. RESULTS: The radiochemical yield was 20%-30% decay corrected with an average of 25% in 4 runs. Radiochemical purity was >99% and average specific activity was 85 GBq/micromol (2,300 mCi/micromol) (end of synthesis). In vitro accumulation of (3)H-FFAU in HSV1-tk-expressing cells was approximately 180-fold (P < 0.001) higher than that in the wild-type cells between 30 and 120 min. In vivo uptake of (3)H-FFAU in HSV1-tk-positive tumors at 2 h was approximately 8-fold (P < 0.001) higher than that in the control tumors. Tumor uptake (percentage injected dose per gram of tissue) and the uptake ratio (tk-positive to wild type) of (3)H-FFAU in tk-positive cells was higher compared with those of our earlier studies using 2'-(14)C-deoxy-2'-fluoro-5-methyl-1-beta-D-arabinofuranosyluracil ((14)C-FMAU) and 9-(4-(18)F-fluoro-3-hydroxymethylbutyl)guanine ((18)F-FHBG) in the same cell lines. microPET on tumor-bearing nude mice also demonstrated a very high uptake of (18)F-FFAU in tk-positive tumors compared with that of the control tumor without significant accumulation in other organs. CONCLUSION: These results demonstrate that (18)F-FFAU has superior biodistribution characteristics and significantly higher in vivo uptake in HSV1-tk-expressing tumor compared with previously studied agents.

Synthesis of pentose-containing disaccharides using a thermostable alpha-L-arabinofuranosidase.

To date, the enzymatically-catalysed synthesis of pentose-containing compounds has been limited to the production of oligo-beta-(1-->3) and oligo-beta-(1-->4)-linked xylopyranosides. To our knowledge, no such syntheses have involved arabinofuranose or, indeed, any other sugars in the furanose configuration. In this report, we describe the use of a thermostable alpha-L-arabinofuranosidase for the synthesis of p-nitrophenyl alpha-L-arabinofuranosyl-(1-->2)-alpha-L-arabinofuranoside, p-nitrophenyl beta-D-xylopyranosyl-(1-->2)-beta-D-xylopyranoside, p-nitrophenyl beta-D-xylopyranosyl-(1-->3)-beta-D-xylopyranoside and benzyl alpha-D-xylopyranosyl-(1-->2)-alpha-L-arabinofuranoside. Importantly, this latter compound is synthesised in a highly regiospecific reaction, which leads to the production of a single disaccharide.

Synthesis and antisense properties of oligodeoxyribonucleotides containing C5-substituted arabinofuranosyluracil.

An oligodeoxyribonucleotide (ODN) containing three C5-substituted arabinofuranosyluracils was synthesized by the post-synthetic modification method from the ODN containing three C5-substituted 2,2'-anhydrouridines. The stability of the modified ODN/DNA duplex was lower than that of the corresponding normal duplex but that of the modified ODN/RNA duplex showed little change. The modified ODN could induce RNase H activity and was resistant against nuclease.

Synthesis of 2'-deoxy-2'-[18F]fluoro-beta-D-arabinofuranosyl nucleosides, [18F]FAU, [18F]FMAU, [18F]FBAU and [18F]FIAU, as potential PET agents for imaging cellular proliferation. Synthesis of [18F]labelled FAU, FMAU, FBAU, FIAU.

An efficient and reliable synthesis of 2'-deoxy-2'-[(18)F]fluoro-beta-D-arabinofuranosyl nucleosides is presented. Overall decay-corrected radiochemical yields of 35-45% of 4 analogs, FAU, FMAU, FBAU and FIAU are routinely obtained in >98% radiochemical purity and with specific activities of greater than 3 Ci/micromol (110 MBq/micromol) in a synthesis time of approximately 3 hours. When approximately 220 mCi (8.15 GBq) of starting [(18)F]fluoride is used, 25 -30 mCi (0.93 -1.11 GBq) of product (enough to image two patients sequentially) is typically obtained.

New synthesis of L-FMAU from L-arabinose.

A new synthesis of 2'-deoxy-2'-fluoro-5-methyl-beta-L-arabinofuranosyl uracil (13, L-FMAU) was achieved in 10 steps from L-arabinose.

Convenient synthesis of arabinonucleoside containing oligodeoxyribonucleotides.

C2 substituted arabinofuranosyluracil derivatives were synthesized and its incorporations into DNA were easily carried out by using post-synthetic modification.

5'-Phosphoramidates and 5'-diphosphates of 2'-O-allyl-beta-D-arabinofuranosyluracil, -cytosine, and -adenine: inhibition of ribonucleotide reductase.

Continuing our studies on ribonucleotide reductase (RNR) mechanism-based inhibitors, we have now prepared the diphosphates (DP) of 2'-O-allyl-1-beta-D-arabinofuranosyl-uracil and -cytosine and 2'-O-allyl-9-beta-D-arabinofuranosyl-adenine and evaluated their inhibitory activity against recombinant murine RNR. 2'-O-Allyl-araUDP proved to be inhibitory to RNR at an IC(50) of 100 microM, whereas 2'-O-allyl-araCDP was only marginally active (IC(50) 1 mM) and 2'-O-allyl-araADP was completely inactive. The susceptibility of the parent nucleosides to phosphorylation by thymidine kinase and 2'-deoxycytidine kinase was also investigated, and all nucleosides proved to be poor substrates for the above-cited kinases. Moreover, prodrugs of 2'-O-allyl-araU and -araC monophosphates, namely 2'-O-allyl-5'-(phenylethoxy-L-alanyl phosphate)-araU and -araC, were prepared and tested against tumor cell proliferation but proved to be inactive. A molecular modeling study has been conducted in order to explain our results. The data confirm that for both the natural and analogue nucleoside diphosphates, the principal determinant interaction with the active site of RNR is with the diphosphate group, which forms strong hydrogen bonds with Glu623, Thr624, Ser625, and Thr209. Our findings indicate that the poor phosphorylation may represent an explanation for the lack of marked in vitro cytostatic activity of the test compounds.

A practical synthesis of L-FMAU from L-arabinose.

A practical synthesis of 2'-deoxy-2'-fluoro-5-methyl-beta-L-arabinofuranosyl uracil (14, L-FMAU) was developed from L-arabinose. L-Arabinose was converted to L-ribose 5, which was used for the synthesis of bromosugar 12 via 2,3,5-O-tribenzoyl-1-O-acetyl-beta-L-ribofuranose 8, which was subjected to condensation with silylated thymine and the resulting protected L-FMAU 13 was deprotected to afford L-FMAU in 14 steps in 8% overall yield.