Synthesis of an Anti-hepatitis B Agent, 2'-Fluoro-6'-methylene-carbocyclic Adenosine (FMCA) and Its Phosphoramidate (FMCAP).

2'-Fluoro-6'-methylene-carbocyclic adenosine (FMCA, 12) and its phosphoramidate prodrug (FMCAP, 14) have been proven as a potential anti-HBV agent against both adefovir-resistant as well as lamivudine-resistant double (rtL180M/rtM204V) mutants. Furthermore, in vitro, these agents have demonstrated significant activity against lamivudine/entecavir triple mutants (L180M + S202G + M204V). These preliminary results encourage us for further biological evaluation of FMCA and FMCAP to develop as a potential clinical candidate as an anti-HBV agent, which may overcome the problem of drug resistance in HBV therapy. To support the preclinical exploration, a scalable synthesis of this molecule was needed. In this communication, a practical and scalable synthesis of FMCA, and its prodrug, is reported via ketone 1. The selective opening of the isopropylidene group of 2 led to compound 3. Protection of the allylic hydroxyl group of 3, followed by fluorination and deprotection, afforded the key intermediate 10, which was condensed with a Boc-protected adenine, followed by deprotection, furnished the target nucleoside FMCA (12) in high yield. Further coupling of phosphorochloridate of L-alanine isopropyl ester (13) with FMCA gave its phosphoramidate prodrug FMCAP (14) in good yield.

Design, synthesis and anticancer activity of fluorocyclopentenyl-purines and - pyrimidines.

Based on the potent anticancer activity of 6'-fluorocyclopentenyl-cytosine 2b in phase IIa clinical trials for the treatment of gemcitabine-resistant pancreatic cancer, we carried out a systematic structure-activity relationship study of 6'-fluorocyclopentenyl-pyrimidines 3a-i and -purines 3j-o to discover novel anticancer agents. We also synthesized the phosphoramidate prodrug 3p of adenine derivative 1b to determine if the anticancer activity depended on the inhibition of DNA and/or RNA polymerase in cancer cells and/or on the inhibition of S-adenosylhomocysteine (SAH) hydrolase. All of the synthesized pyrimidine nucleosides exhibited much less potent anticancer activity in vitro than the cytosine derivative 2b, acting as RNA and/or DNA polymerase inhibitor, indicating that they could not be efficiently converted to their triphosphates for anticancer activity. Among all the synthesized purine nucleosides, adenine derivative 1b and N6-methyladenine derivative 3k showed potent anticancer activity, showing equipotent inhibitory activity as the positive control, neplanocin A (1a) or Ara-C. However, the phosphoramidate prodrug 3p showed less anticancer activity than 1b, indicating that it did not act as a RNA and/or DNA polymerase inhibitor like 2b. This result also demonstrates that the anticancer activity of 1b largely depends on the inhibition of histone methyltransferase, resulting from strong inhibition of SAH hydrolase. The deamination of the N6-amino group, the addition of the bulky alkyl group at the N6-amino group, or the introduction of the amino group at the C2 position almost abolished the anticancer activity.

2'-Fluoro-6'-methylene carbocyclic adenosine and its phosphoramidate prodrug: A novel anti-HBV agent, active against drug-resistant HBV mutants.

Chronic hepatitis B (CHB) is one of the major causes of morbidity and mortality worldwide. Currently, clinically approved nucleos(t)ide analogs (NAs) are very efficient in reducing the load of hepatitis B virus (HBV) with minimum side effects. However, the long-term administration of antiviral drugs promotes HBV for potential drug resistance. To overcome this problem, combination therapies are administered, but HBV progressively altered mutations remain a threat. Therefore, optimally designed NAs are urgently needed to treat drug-resistant HBV. Herein, 2'-fluoro-6'-methylene carbocyclic adenosine (FMCA) and its phosphoramidate (FMCAP) have been discovered, which may be utilized in combination therapies for curing drug-resistant chronic hepatitis B. In preclinical studies, these carbocyclic NAs demonstrated potential anti-HBV activity against adefovir, as well as lamivudine (LMV/LAM) drug-resistant mutants. In vitro, these molecules have demonstrated significant activity against LMV/entecavir (ETV) triple mutants (L180M + S202G + M204V). Also, preliminary studies of FMCA/FMCAP in chimeric mice and female Non-obese diabetic/severe combined immunodeficiency (NOD/SCID) mouse models having the LMV/ETV triple mutant have shown a high rate of reduction of HBV DNA levels compared to ETV. In this review, we have summarized preclinical studies of FMCA and its phosphoramidate prodrug (FMCAP).

Asymmetric Synthesis of (-)-6'-ß-Fluoro-aristeromycin via Stereoselective Electrophilic Fluorination.

(-)-6'-ß-Fluoro-aristeromycin (2), a potent inhibitor of S-adenosylhomocysteine (AdoHcy) hydrolase, has been synthesized via stereoselective electrophilic fluorination followed by a purine base build-up approach. Interestingly, purine base condensation using a cyclic sulfate resulted in a synthesis of (+)-5'-ß-fluoro-isoaristeromycin (2a). Computational analysis indicates that the fluorine atom controlled the regioselectivity of the purine base substitution.

Design, synthesis, and anticancer activity of C8-substituted-4'-thionucleosides as potential HSP90 inhibitors.

A series of C8-substituted-4'-thioadenosine analogs 3a-3g, 15, and 17 and their truncated derivatives 4a-4j, 23-25, and 27 have been successfully synthesized from d-ribose and d-mannose, respectively, employing Pummerer type or Vorbrüggen condensation reactions and the functionalization at the C8-position of nucleobase via Stille coupling or nucleophilic aromatic substitution reactions as key steps. All the synthesized compounds were assayed for their HSP90 inhibitory activity, but they were found to be inactive up to 100µM. However, the 8-iodo derivatives 15, 17, and 27 exhibited potent anticancer activity, indicating that different mechanism of action might be involved in their biological activity.

Structure-Activity Relationships of Neplanocin A Analogues as S-Adenosylhomocysteine Hydrolase Inhibitors and Their Antiviral and Antitumor Activities.

On the basis of the potent inhibitory activity of neplanocin A (1) against S-adenosylhomocysteine (AdoHcy) hydrolase, we analyzed the comprehensive structure-activity relationships by modifying the adenine and carbasugar moiety of 1 to find the pharmacophore in the active site of the enzyme. The introduction of 7-deazaadenine instead of adenine eliminated the inhibitory activity against the AdoHcy hydrolase, while 3-deazaadenine maintained the inhibitory activity of the enzyme, indicating that N-7 is essential for its role as a hydrogen bonding acceptor. The substitution of hydrogen at the 6'-position with fluorine increased the inhibitory activity of the enzyme. The one-carbon homologation at the 5'-position generally decreased the inhibitory activity of the enzyme, indicating that steric repulsion exists. A molecular docking study also supported these experimental data. In this study, 6'-fluoroneplanocin A (2) was the most potent inhibitor of AdoHcy hydrolase (IC50 = 0.24 µM). It showed a potent anti-VSV activity (EC50 = 0.43 µM) and potent anticancer activity in all the human tumor cell lines tested.