Marit Kristiansen

Iminosugars: potential inhibitors of liver glycogen phosphorylase

The first synthesis of the single isomers (3R,4R,5R); (3S,4S,5S): (3R,4R,5S) and (3S,4S,5R) of 5-hydroxymethyl-piperidine-3,4-diol from Arecolin is reported, including the synthesis of a series of N-substituted derivatives of the (3R,4R,5R)-isomer (Isofagomine). The inhibitory effect of these isomers as well as of a series of N-substituted derivatives of the (3R,4R,5R)-isomer and selected hydroxypiperidine analogues on liver glycogen phosphorylase (GP) showed that the (3R,4R,5R) configuration was essential for obtaining an inhibitory effect at submicromolar concentration. The results also showed that all three hydroxy groups should be present and could not be substituted, nor were extra OH groups allowed if sub-micromolar inhibition should be obtained. Some inhibitory effect was retained for N-substituted derivatives of Isofagomine; however, N-substitution always resulted in a loss of activity compared to the parent compound, IC50 values ranging from 1 to 100 microM were obtained for simple alkyl, arylalkyl and benzoylmethyl substituents. Furthermore, we found that it was not enough to assure inhibitory effect to have the (R,R,R) configuration. Fagomine, the (2R,3R,4R)-2-hydroxymethylpiperidine-3,4-diol analogue, showed an IC50 value of 200 microM compared to 0.7 microM for Isofagomine. In addition, Isofagomine was able to prevent basal and glucagon stimulated glycogen degradation in cultured hepatocytes with IC50 values of 2-3 microM.

Anticonvulsant profile of the imidazoquinazolines NNC 14-0185 and NNC 14-0189 in rats and mice

The anticonvulsant effects of NNC 14-0185 (3-(3-cyclopropyl-5-isoxazolyl)-6-fluoro-5-morpholino-imidazo[1,5- a] quinazoline) and NNC 14-0189 (3-(5-cyclopropyl-1,2, 4-oxadiazol-3-yl)-7-fluoro-5-(4-methyl-1-piperazinyl)-imidazo[1,5- a] quinazoline) in mice and rats were evaluated and compared with those of diazepam, clonazepam and the novel beta-carboline, abecarnil. Following i.p. administration, NNC 14-0185 and NNC 14-0189 prevented audiogenic seizures in DBA/2 mice and the clonic convulsions induced in mice by pentylenetetrazole, DMCM (methyl 6, 7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate), 3-mercaptopropionic acid and a low dose of bicuculline. NNC 14-0185 and NNC 14-0189 prevented seizures induced by pentylenetetrazole in rats and were also effective anticonvulsants in amygdala-kindled rats. In general, the anticonvulsant potencies of NNC 14-0185 and NNC 14-0189 were comparable to those of the reference benzodiazepines. However, like abecarnil, they were not effective against the seizures induced in mice by maximal electroshock and a high dose of bicuculline. The anticonvulsant effects of NNC 14-0185 and NNC 14-0189 against pentylenetetrazole-induced seizures were apparent within 5 min of i.p. injection and persisted for at least 2 h. These effects appeared to be mediated by benzodiazepine receptors since they were inhibited by concurrent administration of flumazenil. Both NNC 14-0185 and NNC 14-0189 showed greater separation between their anticonvulsant and muscle relaxant effects (measured as impaired rotarod performance) than did diazepam. In this respect, their therapeutic windows were similar (NNC 14-0185) to or better (NNC 14-0189) than that of abecarnil. Tolerance did not develop to the anticonvulsant effects of NNC 14-0185 and NNC 14-0189 over a 4-day test. In comparison, the anticonvulsant effects of diazepam and abecarnil were attenuated by repeated drug administration. Thus, NNC 14-0185 and NNC 14-0189 have a promising anticonvulsant and side-effect profile in comparison with diazepam, clonazepam and abecarnil. The potential use of these compounds in the treatment of epilepsy should be explored further.

Differential potentiation of GABAA receptor function by two stereoisomers of diimidazoquinazoline analogues

1 U‐84935, diimidazo[1,5‐a;1′,2′‐C]quinazoline,5‐(5‐cyclopropyl‐1,2,4‐oxidiazol‐3yl)‐2,3‐dihydro, is a ligand of high affinity for the benzodiazepine site of the GABAA receptor composed of α1β2γ2 subunits. 2 The efficacy of its analogues was measured with their ability to potentiate GABA‐mediated Cl− currents in the whole cell configuration of the patch clamp techniques in human kidney cells (A293 cells) expressing the subtype of the GABAA receptor. 3 The analogues displayed various levels of efficacy including agonists, partial agonists and antagonists without marked changes in their affinity for the receptors. 4 The major determinant of their efficacy was the spacial configuration of a methyl substituent of the C2 atom of the rigid and planar diimidazoquinazoline ring: U‐90167, containing the methyl substituent projected below the plane of the ring, markedly enhanced the GABA current with a maximal potentiation of 220 ± 25%, while its stereoisomer, U‐90168, marginally increased the GABA response with a maximal potentiation of 45 ± 10%, to which its methyl group appeared to contribute very little. 5 U‐90167 potentiated the GABA response with an EC50 of 8.1 nm and a Hill coefficient of 1.1 and did not alter the reversal potential for the Cl− current. 6 From computational modelling, the sensitive methyl group of U‐90167 could be assigned to the general region for the 5‐phenyl group of diazepam. The diimidazoquinazoline, because of its rigid and plantar ring structure, may be useful to define further the out‐of‐plane region responsible for agonistic activity and to pinpoint other areas pivotal to the functionality of benzodiazepine ligands.