Simpson Thacher & Bartlett and Homburger have advised state-owned ChemChina on its $43 billion bid to buy over Swiss agribusiness company Syngenta, the biggest overseas acquisition by a Chinese company.

The sellers are being represented by  Bär & Karrer and Davis Polk & Wardwell.

The deal accelerates a shake-up in the global agrochemicals industry and is a setback for U.S. seed company Monsanto, which made an unsuccessful $45 billion move for Syngenta last year.

If completed, it would be China's biggest outbound takeover deal, more than double CNOOC's $17.7 billion purchase of Canada's Nexen in 2012.

In March, Chem China agreed to buy Italian tire maker Pirelli & C SpA, underscoring the company’s interest in Europe.

The deal is expected to receive difficult scrutiny from the U.S. regulators as about a quarter of Syngenta’s sales comes from North America.