Generating 500 kHz sine wave using modified PWM
Trying to get 500 kHz sine from PWM seems quite a stretch.

If the frequency is fixed, then look into something resonant, like a class C output stage.  Basically, you start with pulses or a square wave, then use resonance and passive filtering to get rid of the harmonics to make a sine.  This is how radio transmitters work, for example.  They have to produce even higher frequencies at high power levels, and are allowed very little harmonic content.