Preliminary evaluation of mesoionic 6-substituted 1-methylimidazo[2,1-b][1,3]thiazine-5,7-diones as potential novel prodrugs of methimazole

Mesoionic heterocyclic compounds as candidate messenger RNA cap analogue inhibitors of the influenza virus RNA polymerase cap-binding activity

BACKGROUND

An unusual feature of influenza viral -messenger RNA (mRNA) synthesis is its dependence upon host cell mRNAs as a source of capped RNA primers. A crucial activity of the influenza polymerase is to steal these primers by binding and cleaving the caps from host mRNAs. The recent structural analysis of the cap-binding fragment of the influenza virus PB2 protein has highlighted the importance of the mesoionic properties of the N7-methylguanine (N(7m)G) component of the mRNA cap in this interaction.

METHODS

A series of mesoionic heterocycles with 5,6-fused ring systems analogous to the N(7m)G component of mRNA cap structures were synthesized and examined for the ability to inhibit the cap-binding activity of the influenza virus RNA polymerase complex using a bead-based in vitro cap-binding assay.

RESULTS

None of the compounds tested were able to significantly inhibit binding and subsequent endonucleolytic cleavage of a synthetic radiolabelled capped mRNA substrate by recombinant influenza virus polymerase in vitro.

CONCLUSIONS

Compounds analogous to the mesoionic N(7m)G component of mRNA cap structures comprise a large class of potential inhibitors of the influenza virus polymerase. Although this preliminary assessment of a small group of related analogues was unsuccessful, further screening of this class of compounds is warranted.

A preliminary investigation of mesoionic xanthine analogues as inhibitors of platelet aggregation

A series of mesoionic xanthines (e.g. mesoionic thiazolopyrimidines, 3, and thiadiazolopyrimidines, 5) and related analogues were examined as inhibitors of human platelet aggregation. Appropriately substituted compounds were found to fully inhibit platelet aggregation, and anhydro-(6-ethyl-8-isopentyl-7-oxo-5-hydroxy-1,3,4-thiadiazolo[3,2 -a]pyrimidinium hydroxide) (5b) was 40 times more potent than the structurally related xanthine theophylline (1). Gel filtration studies suggest that compound 5b irreversibly inhibits aggregation and this might be due to its ability to act as a latent acylation agent.

Contrasting leaf phenotypes control seasonal variation in water loss in a tropical forest shrub

Psychotria marginata, a shrub common to humid tropical forests in Central America, produces leaves in two seasonal flushes with contrasting morphology and physiology. Leaf production is bimodal with a major peak at the beginning of the annual wet season and a secondary peak at the end of the wet season. Together these peaks account for 75-87% of annual leaf production. Leaves produced just prior to the dry season have higher specific mass and, during drought, have lower stomatal conductances and higher water-use efficiencies. Plants irrigated during two consecutive dry seasons continued to produce leaves with these morphological and physiological differences, indicating that this feature has been strongly canalized by some factor other than water availability in this highly predictable yet seasonal habitat. The bimodal leaf production results in acclimation to changing conditions through co-occurring leaves that lack the physiological plasticity usually associated with acclimation. Heterophylly of this form suggests that the moderate drought of the dry season has been a significant selective factor for understory plants.