A novel class of compounds, which act to antagonize the action of the glucagon hormone on the glucagon receptor. Owing to their antagonizing effect of the glucagon receptor the compounds may be suitable for the treatment and/or prevention of any diseases and disorders, wherein a glucagon antagonistic action is beneficial, such as hyperglycemia, Type 1 diabetes, Type 2 diabetes, disorders of the lipid metabolism and obesity.

The present invention relates to 9H-indeno[1,2-b]pyrazin-3(4H)-ones and 9H-indeno[1,2-b]pyrazine-2,3(1H,4H)-diones or tautomeric forms thereof which are useful in treating neurological and psychiatric diseases based on the antagonism of the glycine binding site on the NMDA receptor complex.