Last summer, Alexander Wang bought the Beaux-Arts HSBC bank on Bowery and Canal for $9.5 million in cash. At the time, the fashion designer declined to say what he was planning to do with the domed 1924 landmark, which HSBC had shuttered a few years earlier. Now, Wang and his mother Ying - one of the co-trustees on the deed - have announced that they will be opening an Asian American cultural center, Wang Contemporary, in the 17,600-square-foot space at 58 Bowery.