Synthesis and Evaluation of Multisubstrate Bicyclic Pyrimidine Nucleoside Inhibitors of Human Thymidine Phosphorylase

Development of 3'-Deoxy-3',4'-didehydro-nucleoside Prodrug Inhibitors of West Nile and Zika Viruses

The antiviral enzyme viperin catalyzes the formation of 3'-deoxy-3',4'-didehydro-cytidine-5'-triphosphate (ddhCTP). ddhCTP is incorporated into viral genomes and terminates genomic replication to confer broad-spectrum antiviral effects. We have previously utilized phosphoramidate pronucleotide (ProTide) technology to enable metabolic production of ddhCTP in cells from an exogenously dosed 3'-deoxy-3',4'-didehydro-cytidine ProTide, which confers inhibitory activity against West Nile virus (WNV) and Zika virus (ZIKV). Herein, we synthesized 3'-deoxy-3',4'-didehydro-nucleosides containing all native nucleobases (thymine, uracil, adenine, guanine, and hypoxanthine), elaborated each to a ProTide, and measured their activity for controlling WNV and ZIKV infection. In comparison to the ddhC ProTide, we found that the ProTides of 3'-deoxy-3',4'-didehydro-guanosine and 3'-deoxy-3',4'-didehydro-adenosine possess 2- and 4-fold greater antiviral effects against ZIKV, respectively. Collectively, this work advances the development of 3'-deoxy-3',4'-didehydro nucleosides as promising compounds for further development into broad-spectrum antiviral agents.

Design and Synthesis of New α-hydroxy β-fluoro/β-trifluoromethyl and Unsaturated Phosphonates from Carbohydrate-Derived Building Blocks via Pudovik and Horner–Wadsworth–Emmons Reactions

Herein, we present the application of fluorinated carbohydrate-derived building blocks for α-hydroxy β-fluoro/β-trifluoromethyl and unsaturated phosphonates synthesis. Pudovik and Horner–Wadsworth–Emmons reactions were applied to achieve this goal. The proposed pathway of the key reactions is supported by the experimental results, as well as quantum chemical calculations. The structure of the products was established by spectroscopic (1D, 2D NMR) and spectrometric (MS) techniques. Based on our data received, we claim that the progress of the Pudovik and HWE reactions is significantly influenced by the acidic protons present in the molecules as assessed by pKa values of the reagent.

Polycyclic nitrogen heterocycles as potential thymidine phosphorylase inhibitors: synthesis, biological evaluation, and molecular docking study

New polycyclic heterocycles were synthesised and evaluated as potential inhibitors of thymidine phosphorylase (TP). Inspired by the pharmacophoric pyrimidinedione core of the natural substrate, four series have been designed in order to interact with large empty pockets of the active site: pyrimidoquinoline-2,4-diones (series A), pyrimidinedione linked to a pyrroloquinoline-1,3-diones (series B and C), the polycyclic heterocycle has been replaced by a pyrimidopyridopyrrolidinetetraone (series D). In each series, the tricyclic nitrogen heterocyclic moiety has been synthesised by a one-pot multicomponent reaction. Compared to 7-DX used as control, 2d, 2l, 2p (series A), 28a (series D), and the open intermediate 30 showed modest to good activities. A kinetic study confirmed that the most active compounds 2d, 2p are competitive inhibitors. Molecular docking analysis confirmed the interaction of these new compounds at the active binding site of TP and highlighted a plausible specific interaction in a pocket that had not yet been explored.

Synthesis of Phosphonomethyl Tetrahydrofurans via the Mori-Tamaru Reaction of Phosphonodienes

Nickel-catalyzed reductive addition of phosphonodienes to aldehydes (the Mori-Tamaru reaction) gives hydroxy vinyl phosphonates in good yields with excellent control of the relative stereochemistry. Base-induced cyclization of the vinyl phosphonates yields phosphonomethyl-substituted tetrahydrofurans. Inversion of the hydroxyl stereochemistry by Mitsunobu reaction and then cyclization yields a different set of phosphonomethyl-substituted tetrahydrofuran diastereoisomers.

Quantitative and qualitative analysis of the novel antitumor 1,3,4-oxadiazole derivative (GLB) and its metabolites using HPLC-UV and UPLC-QTOF-MS

Fructose-based 3-acetyl-2,3-dihydro-1,3,4-oxadiazole (GLB) is a novel antitumor agent and belongs to glycosylated spiro-heterocyclic oxadiazole scaffold derivative. This research first reported a simple, specific, sensitive and stable high performance liquid chromatography-ultraviolet detector (HPLC-UV) method for the quantitative determination of GLB in plasma. In this method, the chromatographic separation was achieved with a reversed phase C18 column. The calibration curve for GLB was linear at 300 nm. The lower limit of quantification was 10 ng/mL. The precision, accuracy and stability of the method were validated adequately. This method was successfully applied to the pharmacokinetic study in rats for detection of GLB after oral administration. Moreover, the structures of parent compound GLB and its two major metabolites M1 and M2 were identified in plasma using an ultra performance liquid chromatography-electrospray ionization-quadrupole-time of flight- mass spectrometry (UPLC-ESI-QTOF-MS) method. Our results indicated that the di-hydroxylation (M1) and hydroxylation (M2) of GLB are the major metabolites. In conclusion, the present study provided valuable information on an analytical method for the determination of GLB and its metabolites in rats, can be used to support further developing of this antitumor agent.

Synthesis of pyrazolo[1,5-a][1,3,5]triazine derivatives as inhibitors of thymidine phosphorylase

Thymidine phosphorylase (TP) is an enzyme that promotes tumor growth and metastasis and therefore is an attractive druggable target. Using a reported TP inhibitor, 7-deazaxanthine (7DX), as the lead compound; this study was set up to evaluate whether pyrazolo[1,5-a][1,3,5]triazin-2,4-diones and pyrazolo[1,5-a][1,3,5]triazin-2-thioxo-4-ones would exhibit TP inhibitory activity. The pyrazolo[1,5-a][1,3,5]triazine nucleus was constructed using a reaction that annulated the 1,3,5-triazine ring onto a pyrazole scaffold. Among the 52 compounds synthesized and tested, it was found that 1,3-dihydro-pyrazolo[1,5-a][1,3,5]triazin-2-thioxo-4-ones exhibited various extent of inhibitory activity against TP. The best compound 17p, which bears a para-substituted pentafluorosulfur group, showed an IC50 value of 0.04 μM, which was around 800 times more potent than the 7DX (IC50 = 32 μM) under the same bioassay conditions. The results of the study suggested that a substituent with +σ and +π properties inserted at position 4 of a phenyl ring that is attached to position 8 of the pyrazolo[1,5-a][1,3,5]triazin-2-thioxo-4-one scaffold would give excellent TP inhibitory action. In addition, 17p was found to be a non-competitive inhibitor thus suggested that it might interact with TP at a position different from the substrate binding site.

Syntheses of 1-[2-(Phosphonomethoxy)Alkyl] thymine monophosphates and an evaluation of their inhibitory activity toward human thymidine phosphorylase

A series of new monophosphates of 1-[2-(phosphonomethoxy)alkyl]thymines, such as PMPTp(,) 3-MeO-PMPTp, HPMPTp, and FPMPTp, were synthesized and tested for their ability to inhibit human thymidine phosphorylase. Kinetic measurements of enzyme activity were performed using thymidine and inorganic phosphate as the substrates. The data show that some monophosphates provide a considerable increase of the multisubstrate inhibitory effect. The highest inhibitory potency was found with (R)-FPMPTp 4c (K (i) (dT) = 4.09 ± 0.47 μM, K (i)(P(i)) = 2.13 ± 0.29 μM) and (R) 3-MeO-PMPTp 4d (K (i) (dT) = 5.78 ± 0.71 μM, K (i)(P(i)) = 2.71 ± 0.37 μM).

Multisubstrate adduct inhibitors: drug design and biological tools

In drug discovery, different methods exist to create new inhibitors possessing satisfactory biological activity. The multisubstrate adduct inhibitor (MAI) approach is one of these methods, which consists of a covalent combination between analogs of the substrate and the cofactor or of the multiple substrates used by the target enzyme. Adopted as the first line of investigation for many enzymes, this method has brought insights into the enzymatic mechanism, structure, and inhibitory requirements. In this review, the MAI approach, applied to different classes of enzyme, is reported from the point of view of biological activity.

The role of phosphate in the action of thymidine phosphorylase inhibitors: Implications for the catalytic mechanism

The design and synthesis of 5-fluoro-6-[(2-aminoimidazol-1-yl)methyl]uracil (AIFU), a potent inhibitor of thymidine phosphorylase (TP) with K(i)-values of 11nM (ecTP) and 17nM (hTP), are described. Kinetic studies established that the type of inhibition of TP by AIFU is uncompetitive with respect to inorganic phosphate (or arsenate). The results obtained suggest that AIFU and other zwitterionic thymine analog inhibitors of TP act as transition state analogs, mimicking the anionic thymine leaving group, consistent with an S(N)2-type catalytic mechanism, and anchored by their protonated side chains to the enzyme-bound phosphate by electrostatic and H-bonding interactions.

Synthesis of fluorophosphonylated acyclic nucleotide analogues via copper(I)-catalyzed Huisgen 1-3 dipolar cycloaddition

Preparation of several acyclonucleosides containing both a difluoromethylphosphonate group and a triazole moiety is described starting from a difluorophosphonosulfide. The key step of the synthesis involves a copper(I)-catalyzed Huisgen 1-3 dipolar cycloaddition between difluorophosphonylated azides and propargylated nucleobases derived from thymine and 2-amino-6-chloropurine.

Antiangiogenic and antitumor activity of 6-(2-aminoethyl)amino-5-chlorouracil, a novel small-molecule inhibitor of thymidine phosphorylase, in combination with the vascular endothelial growth factor-trap

PURPOSE

Tumors produce multiple proangiogenic factors, making it unlikely that agents targeting a single angiogenic pathway will be sufficient to treat the spectrum of tumors that occur clinically. Platelet-derived endothelial cell growth factor has angiogenic activity in vitro and in vivo and is overexpressed in most human cancers, where its expression has been correlated with increased microvessel density, more aggressive tumors, and poorer patient prognosis. Platelet-derived endothelial cell growth factor is identical to the enzyme thymidine phosphorylase (TP), and unlike other angiogenic factors, the proangiogenic actions of TP are dependent on its enzyme activity.

EXPERIMENTAL DESIGN

A potent and specific small-molecule inhibitor of the catalytic activity of TP, 6-(2-aminoethyl)amino-5-chlorouracil (AEAC), was tested for antiangiogenic and antitumor activity in human cancer xenografts in vivo.

RESULTS

Oral administration of AEAC caused 40% to 50% reductions in the growth of A549 non-small cell lung cancer and PANC-1 pancreatic cancer xenografts, but it was not active against a second pancreatic tumor, BxPC-3. AEAC reduced the microvessel density in the tumors, providing evidence for an antiangiogenic action. Equal or better activity was seen when the mice were treated with the vascular endothelial growth factor (VEGF)-Trap, a soluble VEGF decoy receptor, and the combination of AEAC and VEGF-Trap produced additive antitumor activity that was significantly greater than the VEGF-Trap alone. In the A549 tumors, the combination produced tumor regressions.

CONCLUSION

These studies show antitumor activity for a drug targeting TP and suggest that inhibitors of TP could be used to augment the clinical efficacy of drugs targeting the VEGF pathway.