BASEL, Switzerland — Syngenta Chief Financial Officer John Ramsay has been named interim CEO of Syngenta AG, Europe’s largest agrochemical company, following the sudden resignation of CEO Mike Mack late last week amid a shareholders’ revolt since Mack turned back a $47 billion offer two months ago by Monsanto Co.

Discontent has been brewing among Syngenta shareholders in recent weeks since St. Louis-based Monsanto withdrew its buyout proposal – a deal that represented a 43 percent premium to Syngenta’s market value at the time. Had the acquisition been successful, it would have created the world’s largest pesticide and seed manufacturer.

"Syngenta urgently needs a leadership that recognizes the realities of the fast-changing markets and draws the right conclusions," said a statement from a shareholder group, the Alliance of Critical Syngenta, backed by private and institutional investors.

Following the news, Monsanto stated: "This action by Syngenta does not fundamentally change anything for us, since they rejected our last proposal and we stepped back from our pursuit of the combination back in August." Monsanto two weeks ago announced a round of 2,600 layoffs and a $3 billion stock buyback plan, claiming it took the action amid a slumping agribusiness economy.

Switzerland-based Syngenta did not respond to emails and telephone calls seeking additional comment for this article. Mack, 55, will leave the company on Oct. 31 after seven years at the helm; he could not be reached for comment either.

Ramsay, who is a United Kingdom national, has spent nearly three decades in the chemicals industry. In 1984, he joined Imperial Chemicals Industries and later moved to overtake finances at Zeneca Agrochemicals that led to the creation of Syngenta AG following the merger.

Mack said Ramsay’s appointment came at an "appropriate time for the company to benefit from the perspectives of a new leader."

Ramsay said in an interview with The Wall Street Journal he would review the Monsanto portfolio and work toward boosting Syngenta’s profits, as well as look at possible partnerships or joint ventures. He added he would consider whether to be a candidate for the permanent CEO post over the coming months.

Investors are calling on the company to appoint a new executive from outside the company. "The new CEO should be an external person who brings a fresh perspective to Syngenta," said Martin Lehmann, a partner from an investor group in Zurich.

Syngenta Chair Michel Demaré said, "This is the time to be open-minded, flexible and ready to jump on opportunities as they come."