It is about 12 km from Belarus Station, the Moscow terminus for trains to/from Belarus (Minsk and Brest), Kaliningrad, Smolensk and international destinations including Vilnius, Warsaw, and Berlin, to the Proton Business Hotel.
By taxi
Depending on the time of day, the journey by taxi will take from 20 to 40 minutes, but should not cost more than $30. If you prefer, you can pre-order a transfer with a driver to meet your train here.
By metro
From Belorusskaya Metro Station (connected to the mainline station concourse), take the brown circle line and travel counterclockwise two stops to Kievskaya. From there travel four stops west to Bagrationovskaya, which is just under twenty minutes' walk from the hotel.