The present invention relates to a compound of the formula (I), pharmaceutically acceptable salts, hydrolysable esters, isomers and hydrates thereof, and hydrates of the said esters or salts, wherein R1, R2, R3 and are as defined in the description. The present invention further relates to a process for preparing the compounds, to pharmaceutical compositions comprising the compounds, and to the use of the compounds in the manufacture of a medicament for the treatment and/or prophylaxis of infectious diseases.
