The head of Chinese developer Soho China (0410.HKG) is partnering with the Safra banking family to buy a 40% stake in the roughly US$3.4 billion General Motors Building in Manhattan, The Wall Street Journal reported, potentially making the property the most valuable office building in the US. According to people involved with the deal, the family of Zhang Xin, CEO of Soho China, and a company under control of Brazilian banking magnet Moise Safra closed the deal on Friday, agreeing to assume debt and pay US$700 million to a group of Middle Eastern sovereign-wealth funds for the stake. The remaining 60% stake is owned by Boston Properties (BXP.NYSE).