Pyrrolopyrimidines an agent for inhibiting cysteine proteases

The invention provides compounds of Formula I or a pharmaceutically acceptable salt or ester thereof wherein the symbols have meaning as defined, which are inhibitors of cathepsin K and find use pharmaceutically for treatment of diseases and medical conditions in which cathepsin K is implicated, e.g. various disorders including inflammation, rheumatoid arthritis, osteoarthritis, osteoporosis and tumors.