The present invention relates to compounds of formula I wherein R1, R2 and R3 are defined herein, their pharmaceutically acceptable salts, enantiomeric forms, diastereoisomers and racemates, the preparation of the above compounds, medicaments containing them and their manufacture, as well as the use of the above compounds in the control or prevention of illnesses such as cancer. The frequency converter may be a mixer having a single-ended input and a differential output. The solar energy collection arrangement is for controlling the set of lane markers in centralized manner to ensure sufficient and consistent illumination of the illuminators, and includes a solar energy collector for collecting solar energy, an energy storage, and a central processing circuitry.