df['timestamps'] = pd.to_datetime(df['timestamps'])
df.set_index('timestamps', inplace=True)

>>> df.resample('5T', how=ohlc_dict)

                         high     close      open       low    volume
timestamps                                                           
2016-08-09 12:35:00  536.7849  536.7849  536.7841  536.6141  0.656000
2016-08-09 12:40:00  536.6749  534.8416  536.6749  534.1801  2.277200
2016-08-09 12:45:00  538.5999  537.7289  534.8131  534.2303  2.971872
2016-08-09 12:50:00  539.2199  539.2199  537.9829  537.9829  1.115219