The present invention relates to N-[4-(1H-pyrazolo[3,4-b]pyrazin-6-yl)-phenyl]- sulfonamides of the formula I, wherein Ar, R1, R2 and n have the meanings indicated in the claims. The compounds of the formula I are valuable pharmacologically active compounds which modulate protein kinase activity, specifically the activity of serum and glucocorticoid regulated kinase (SGK), in particular of serum and glucocorticoid regulated kinase isoform 1 (SGK-1, SGK1), and are suitable for the treatment of diseases in which SGK activity is inappropriate, for example degenerative joint disorders or inflammatory processes such as osteoarthritis or rheumatism. The invention furthermore relates to processes for the preparation of the compounds of the formula I, their use as pharmaceuticals, and pharmaceutical compositions comprising them.