Symmetrical divinyl tellurides are prepared by sequential reaction of bis-(triphenylmethyl phosphonium) halotellurate with base or by the reaction of triphenylmethylidene phosphoranes with TeCl
4, ...followed by aldehydes. The products are converted to
E-α,β-unsaturated aldehydes by treatment with
n-BuLi and DMF.
Seleno- and telurocyclofunctionalized furan derivatives were prepared by reaction of phenylselenenyl bromide and p-methoxyphenyl tellurium trichloride with α,γ-diallyl-β-ketoesters in good yield.
Guanosine has been reported to exert neuroprotective effects. We recently reported that, following intraperitoneal (i.p.) injection to rats, it resulted to be widely distributed. Its metabolic ...product guanine also rapidly increased in all the tissues, including brain, after i.p. injection of guanosine and consistently we found a significant enzymatic activity of a soluble purine nucleoside phosphorylase in the plasma of the treated animals. In this study the effect of per os administration of guanosine or guanine to rats submitted to passive avoidance task has been evaluated. Guanosine (4 and 8 mg/kg) administered pretraining impaired retention in the passive avoidance task and was unable to prevent the amnesic effect caused by 100 mg/kg N-omega-nitro-l-arginine methyl ester (L-NAME), an inhibitor of the nitric oxide synthase (NOS) known to reduce the capability of treated animals to acquire or retain informations in several learning tasks. On the contrary, guanine (4 and 8 mg/kg), which per se did not modify the latency to step-trough in the passive avoidance task, when administered pretraining 15 min before L-NAME prevented, in a dose dependent manner, the amnesic effect of the NOS inhibitor. Moreover the nucleobase was able to rescue the memory trace also when administered after training. Neither guanosine nor guanine had effects on locomotor activity. These results indicate that guanine can exert important biological activities which may be different from those mediated by its precursor guanosine, thus this evenience should be taken into account when the biological effects of guanosine are evaluated.
Bakkenolide A
1
is the simplest member of a new class of eremophilane sesquiterpenes isolated a few years ago from
Petasites japonicus.
2
A recent synthesis of
1
3
prompts us to disclose our ...preliminary results which, in a model system, provide an alternative approach to the construction of the novel β-methylene-γ-spirolactone system present in the bakkenolide series.
