The invention relates to cyclic bioisosteres of derivatives of a purine system having a general structural formula R1=—H, —NH2, —Br, —Cl, —OH, —COOH, B=—N═, —CH═, Z=—CH═, —N═, A=—N═ at B=—N═, Z=—CH—, A=—CH═ at B=—N═, Z=—CH—, A=—CH═ at B=—N═, Z=—N═, A=—CH═ at B=—CH═, Z=—CH═, A=—CH═ at B=—CH═, Z=—N═, and their pharmacologically acceptable salts having a normalizing effect on endocellular processes, in particular, it is capable eliminating endocellular metabolic acidosis and capable of binding excessively formed free radicals, in particular, free-radical forms of oxygen, capable of normalizing the nitrergic mechanisms of the cells, and also capable of interreacting with adenosine-sensitive receptors on the membrane of non-nuclear cells and in nuclei-containing cells to decrease the aggregation of thrombocytes. The compounds according to the invention have hepatoprotective effect and can be used for producing pharmaceutical compositions on their base.