Tumor Cells Require Thymidylate Kinase to Prevent dUTP Incorporation during DNA Repair

The synthesis of dTDP is unique because there is a requirement for thymidylate kinase (TMPK). All other dNDPs including dUDP are directly produced by ribonucleotide reductase (RNR). We report the binding of TMPK and RNR at sites of DNA damage. In tumor cells, when TMPK function is blocked, dUTP is incorporated during DNA double-strand break (DSB) repair. Disrupting RNR recruitment to damage sites or reducing the expression of the R2 subunit of RNR prevents the impairment of DNA repair by TMPK intervention, indicating that RNR contributes to dUTP incorporation during DSB repair. We identified a cell-permeable nontoxic inhibitor of TMPK that sensitizes tumor cells to doxorubicin in vitro and in vivo, suggesting its potential as a therapeutic option. Cancer Cell 2012, 22, 36-50.

A Practical Synthesis of Zanamivir Phosphonate Congeners
with Potent Anti-influenza Activity

Two phosphonate compounds 4-amino-1-phosphono-DANA and phosphono-zanamivir are synthesized and shown more potent than zanamivir against the neuraminidases of avian and human influenza viruses, including the oseltamivir-resistant strains. For the first time, the practical synthesis of these phosphonate compounds is realized by conversion of sialic acid to peracetylated phosphono-DANA diethyl ester as a key intermediate in three steps by a novel approach. J. Am. Chem. Soc. 2011, 133, 17959-17965.

Intramolecular ion-pair prodrugs of zanamivir and guanidino-oseltamivir

Zanamivir (ZA) is a potent anti-influenza drug, but it cannot be administrated orally because of the hydrophilic carboxylate and guanidinium groups. The ester prodrugs ZA–HNAP was prepared to incorporate a 1-hydroxy-2-naphthoic (HNAP) moiety to attain good lipophilicity in the intramolecular ion-pairing forms. ZA–HNAP resumed high anti-influenza activity (EC₅₀ = 48 nM), in cell-based anti-influenza assays, by releasing zanamivir along with nontoxic HNAP. Bioorg. Med. Chem. 2011, 19, 4796–4802.

A New Drug Design Targeting the Adenosinergic System for Huntington’s Disease: Novel Dual-Action Compounds Targeting Adenosine A_2A Receptor and Adenosine Transporter

A novel compound N⁶-(4-hydroxybenzyl)adenosine isolated from Gastrodia elata, which has been shown to be a potential therapeutic agent for preventing and treating neurodegenerative disease, is found to target both the adenosine A_2A receptor (A_2AR) and the equilibrative nucleoside transporter 1 (ENT1). As A_2AR and ENT1 are proximal in the synaptic crevice of striatum, where the mutant huntingtin aggregate is located, the dual-action compounds concomitantly targeting these two membrane proteins may be beneficial for the therapy of Huntington’s disease. To design the desired dual-action compounds, the pharmacophore models of the A_2AR agonists and the ENT1 inhibitors are constructed. Accordingly, potentially active compounds are designed and then synthesized, if the predicted activity is within acceptable ranges, by chemical modification of adenosine, particularly at the N⁶ and C^5' positions. Indeed, some of the designed compounds exhibit significant dual-action property on both A_2AR and ENT1. In agreement with the competitive ligand binding assay, these compounds also prevent apoptosis of serum-deprived PC12 cells, rendering a crucial function in neuroprotection and potential medical treatment of neurodegenerative diseases. PLoS One 2011, 6, e20934. ChemMedChem 2011, 6, 1390–1400.

Synergistic Effect of Zanamivir–Porphyrin Conjugates on Inhibition of Neuraminidase and Inactivation of Influenza Virus

　　New anti-influenza agents of tetravalent zanamivir on porphyrin scaffold were synthesized. These compounds are ten to hundred times more potent in inhibiting influenza replications, even though they are somewhat less potent in neuraminidase inhibition than the monomeric zanamivir. The enhanced anti-influenza activity is probably attributable to the additional viral inactivation by singlet oxygen due to sensitization of the porphyrin moiety, which is brought in close proximity of virus by the conjugated zanamivir in a manner resembling the “magic bullet” mechanism. J. Med. Chem. 2009, 52, 4903–4910.

A Concise and Flexible Synthesis of the Potent Anti-Influenza Agents Tamiflu and Tamiphosphor

　We report safer and more commercially viable synthetic methods for both anti-influenza drugs Tamiflu and Tamiphosphor using bromobenzene as the starting material. This is an innovative procedure in which the bromine atom is converted to carboxyl or phosphonate groups at the later stage. All reactions are handled without using potentially hazardous intermediates or toxic reagents, and as most of the reactions occurred in a regio- and stereoselective fashion to give crystalline products throughout the synthesis, the isolation procedures were relatively simple and cost effective.
　Like Tamiflu, Tamiphosphor can be taken orally, and functions as an inhibitor of the neuraminidase active site of the H5N1/H1N1 viruses. However, Tamiphosphor proves to be more effective due to its higher enzyme inhibition. Survival rates and recovery rates of infected mice treated with Tamiphosphor both show better results. Angew. Chem. Int. Ed. 2008, 47, 5788-5791.

Structure and Bioactivity of the Polysaccharides in Medicinal Plant Dendrobium huoshanense

　Detailed structures of the active polysaccharides extracted from the leaf and stem cell walls and mucilage of Dendrobium huoshanense are determined by using various techniques, including chromatographic, spectroscopic, chemical, and enzymatic methods. The mucilage polysaccharide exhibits specific functions in activating murine splenocytes to produce several cytokines including IFN-γ, IL-10, IL-6, and IL-1α, as well as hematopoietic growth factors GM-CSF and G-CSF. However, the deacetylated mucilage obtained from an alkaline treatment fails to induce cytokine production. The structure and bioactivity of mucilage components are validated by further fractionation. This is the first study that provides clear evidence for the structure and activity relationship of the polysaccharide in D. huoshanense . Bioorg. Med. Chem. 2008, 16, 6054-6068.

Synthesis of Tamiflu and its Phosphonate Congeners Possessing Potent Anti-Influenza Activity

　Using D-xylose as an appropriate chiral precursor, we have synthesized active neuraminidase inhibitor oseltamivir, antiflu drug Tamiflu, and novel phosphonate congeners that exhibit even stronger antiflu activities by inhibiting the neuraminidases of the wild-type and H274Y mutant of H1N1 and H5N1 viruses. Discovery of such potent neuraminidase inhibitors will offer an opportunity to the development of new anti-influenza drugs. J. Am. Chem. Soc. 2007, 129, 11892–11893.

Discovery of Potent Anilide Inhibitors against the Severe Acute Respiratory Syndrome 3CL Protease

　A diversified library of peptide anilides was prepared, and their inhibition activities against the SARS-CoV 3CL protease were examined by a fluorogenic tetradecapeptide substrate. The most potent inhibitor is an anilide derived from 2-chloro-4-nitroaniline, L-phenylalanine and 4-(dimethylamino)benzoic acid. This anilide is a competitive inhibitor of the SARS-CoV 3CL protease with Ki = 0.03 M. The molecular docking experiment indicates that the P1 residue of this anilide inhibitor is distant from the nucleophilic SH of Cys145 in the active site. J. Med. Chem. 2005, 48, 4469–4473.