The present invention relates to a compound of formula (I) or isomers thereof, or pharmaceutically acceptable salts or hydrates thereof. The present invention further relates to processes for the preparation of the compounds of formula (I) and optical isomers, and to the use of the compounds of formula (I), or isomers thereof, or pharmaceutically acceptable salts or hydrates thereof as medicaments, in particular as medicaments for the treatment and prevention of Hepatitis B.