Sullivan & Cromwell has guided Alibaba Group Holding on its agreement to buy a controlling stake in Southeast Asian online retailer Lazada Group for about $1 billion. Lazada was advised by Dechert.

Under the deal - Alibaba's biggest overseas investment so far, according to Thomson Reuters data - the firm will buy about $500 million of newly issued Lazada shares. The rest will be bought from current shareholders.

Lazada, founded by Germany's Rocket Internet in 2012, is headquartered in Singapore and also operates in Malaysia, Indonesia, the Philippines, Thailand and Vietnam. The agreement affords Alibaba a chance to tap the region's growth potential, particular as growth slows in China home. In the last three months of 2015, the total value of goods transacted on the company's e-commerce sites rose by its slowest annual rate in more than three years.

The Sullivan & Cromwell team is led by Hong Kong partner Garth Bray and Frankfurt partner York Schnorbus. Meanwhile the Dechert team is led by Munich partner Federico Pappalardo, and also includes New York partners Kristopher Brown, Markus Bolsinger, Christian Matarese and Jay Alicandri, Luxembourg partners Marc Seimetz and Jean-Louis Frognet, and Washington, D.C. partner Jeremy Zucker.