DEERFIELD, Ill. — Activist investor Barry Rosenstein, managing partner of hedge fund JANA Partners LLC, has stepped down from the Walgreens Boots Alliance (WBA) Inc. board after reducing his investment in the company.

WBA said late Friday that Rosenstein, who has been a director since September 2014, was slated to end his service on the board once JANA’s stake in Walgreens fell below a certain threshold, based on the Nomination and Support Agreement that the companies had signed at that time.

Barry Rosenstein (Photo courtesy WallStreetWeek.com)

“I could not have dreamed up a better example of the value of constructive and positive engagement between a company and its shareholders, and I am proud of the work this board has done since 2014 to put Walgreens on the path to delivering maximum value for all of its shareholders,” Rosenstein said in a statement.

Under the Nomination and Support Agreement, Rosenstein would resign from the Walgreens board if JANA and its affiliates’ holdings of Walgreens common stock fell below 6.25 million shares. According to a Securities and Exchange Commission filing on May 18, Rosenstein disposed of 6 million shares of WBA common stock, leaving JANA with about 4.579 million shares of the company.

“We thank Barry for the new perspectives and experience he brought to the board during his tenure,” WBA chairman James Skinner stated. “He played a valuable role at an important time for the company as Walgreens and Alliance Boots combined in 2014 to transform into a global company.”

Rosenstein had joined the board shortly after Walgreens and Alliance Boots unveiled their plan to form the Walgreens Boots Alliance holding company, which consisted of four divisions: Walgreen Co.; the Boots pharmacy, health and beauty chain; Pharmaceutical Wholesale and International Retail; and Global Brands.

At the time, JANA held 12.5 million shares, or 1.3%, of Walgreens common stock and had agreed to cap its interest in Walgreens at 4.9% while Rosenstein served on its board.

“I sincerely appreciate, and want to personally thank, Barry for the tremendous insight he has provided to our board to help create value for our shareholders,” Stefano Pessina, executive vice chairman and chief executive officer of WBA, said in a statement Friday. “His talent and expertise have made a significant contribution to the success of our company and its future.”

Earlier this month, WBA said affiliates of investment firm Kohlberg Kravis Roberts & Co. L.P. (KKR) plan an underwritten secondary offering 15 million shares of WBA common stock. The underwriter, Citigroup, also is slated to be granted a 30-day option to buy up to an additional 1.5 million shares of WBA stock.

WBA reported that it had issued approximately 52.46 million shares to KKR in connection with the Alliance Boots merger, which closed at the end of 2014. The shares to be sold by KKR represent about 29% of their current stake in WBA, or 31% if Citigroup exercises its option in full.

Dominic Murphy, a member of KKR and the head its United Kingdom operations and European health care industry team, will remain a member of the WBA’s board after the secondary offering is completed, WBA added. Murphy had joined the Walgreens board when the drug chain completed the first part of the merger transaction with Alliance Boots in August 2012.