Kazuya Tatani

SYNTHESIS OF ADENOPHOSTIN ANALOGUES LACKING THE ADENINE MOIETY AS NOVEL POTENT IP3 RECEPTOR LIGANDS : SOME STRUCTURAL REQUIREMENTS FOR THE SIGNIFICANT ACTIVITY OF ADENOPHOSTIN A

1-O-Tetrahydrofuranyl-α-d-glucopyranose derivatives 5−8 were designed and synthesized as novel IP3 receptor ligands. The glycosidation reactions between fluoroglycosyl donor 23 and tetrahydrofuran derivatives 11−14 as glycosyl acceptors selectively gave the corresponding α-glycosides, which were converted into the target compounds 5−8 via the introduction of phosphate groups using the phosphoramidite method. Among these compounds, 1-O-tetrahydrofuranyl-α-d-glucopyranose trisphosphate derivatives 5 and 8 significantly inhibited the binding of [3H] IP3 to IP3 receptor from porcine cerebella, with IC50 values of 25 and 27 nM, respectively, which were comparable to the affinity of IP3 itself.

Inositol 1,4,5‐trisphosphate and adenophostin analogues induce responses in turtle olfactory sensory neurons

Using the whole‐cell mode of the patch‐clamp technique, we recorded inward currents in response to inositol‐1,4,5‐trisphosphate (IP3) and adenophostin analogues in turtle olfactory sensory neurons. Dialysis of IP3 into the neurons induced inward currents with an increase in membrane conductance in a dose‐dependent manner under the voltage‐clamp conditions (holding potential −70 mV). The application of Ca2+‐free Ringer solution to neurons previously dialysed with IP3 induced inward currents that were reversibly inhibited by application of Na+, Ca2+‐free Ringer solution, normal Ringer solution or 10 μm ruthenium red. Dialysis of the adenophostin analogues, novel IP3 receptor ligands, also induced inward currents with an increase in membrane conductance. The magnitude of the responses to the adenophostin analogues varied among these derivatives. The application of Ca2+‐free Ringer solution to neurons previously dialysed with the adenophostin analogues induced inward currents that were inhibited by the application of normal Ringer solution. The reversal potential of inward currents induced by an adenophostin analogue was similar to that induced by IP3, suggesting that inward currents induced by the adenophostin analogue were generated by a similar ionic mechanism to that induced by IP3. The present study demonstrated that IP3‐mediated transduction pathways exist in turtle olfactory receptor neurons and that adenophostin analogues act as agonists of IP3.

Identification of Adenine and Benzimidazole Nucleosides as Potent Human Concentrative Nucleoside Transporter 2 Inhibitors: Potential Treatment for Hyperuricemia and Gout

To test the hypothesis that inhibitors of human concentrative nucleoside transporter 2 (hCNT2) suppress increases in serum urate levels derived from dietary purines, we previously identified adenosine derivative 1 as a potent hCNT2 inhibitor (IC50 = 0.64 μM), but further study was hampered due to its poor solubility. Here we describe the results of subsequent research to identify more soluble and more potent hCNT2 inhibitors, leading to the discovery of the benzimidazole nucleoside 22, which is the most potent hCNT2 inhibitor (IC50 = 0.062 μM) reported to date. Compound 22 significantly suppressed the increase in plasma uric acid levels after oral administration of purine nucleosides in rats. Because compound 22 was poorly absorbed orally in rats (F = 0.51%), its pharmacologic action was mostly limited to the gastrointestinal tract. These findings suggest that inhibition of hCNT2 in the gastrointestinal tract can be a promising approach for the treatment of hyperuricemia.

Identification of 8-Aminoadenosine Derivatives as a New Class of Human Concentrative Nucleoside Transporter 2 Inhibitors

Purine-rich foods have long been suspected as a major cause of hyperuricemia. We hypothesized that inhibition of human concentrative nucleoside transporter 2 (hCNT2) would suppress increases in serum urate levels derived from dietary purines. To test this hypothesis, the development of potent hCNT2 inhibitors was required. By modifying adenosine, an hCNT2 substrate, we successfully identified 8-aminoadenosine derivatives as a new class of hCNT2 inhibitors. Compound 12 moderately inhibited hCNT2 (IC50 = 52 ± 3.8 μM), and subsequent structure-activity relationship studies led to the discovery of compound 48 (IC50 = 0.64 ± 0.19 μM). Here we describe significant findings about structural requirements of 8-aminoadenosine derivatives for exhibiting potent hCNT2 inhibitory activity.