I will arriving at Shanghai Huangpu bus station about 2am.

When will you arrive at Shanghai? I mean the date. Well, there seems no train running at that time from Shanghai to Beijing. You can take a taxi from the bus station to Shanghai Hongqiao railway station to wait for the high speed train. The Shanghai-Beijing High Speed train will start to operate from June 28 this year, but the train schedule hasn't open to the public. The first train seems departs at around 6-7am.