DEERFIELD, Ill. — Walgreen Co. has taken the second and decisive step toward completing its acquisition of Alliance Boots GmbH, exercising its option earlier this month to acquire the remaining shares of the global pharmaceutical wholesaler and retailer.

Although the form of the merger disappointed many Walgreens investors — mainly with the company’s decision not to realize significant tax benefits by re-domiciling in Switzerland, where Alliance Boots has its corporate base — the deal is expected to close in the first quarter of 2015 pending approval by shareholders and regulators.

The move followed Walgreens’ initial purchase of a 45% equity stake in Alliance Boots in June 2012 for $6.7 billion in cash and stock. The agreement formed then gave Walgreens the option to complete the buyout within three years for an additional $9.5 billion (again, in cash and stock), plus the assumption of Alliance Boots’ debt.

“This is a pivotal moment in Walgreens history as we venture ahead from the best corners in America to the four corners of the world,” said president and chief executive officer Greg Wasson. “In a changing global marketplace with new opportunities and challenges, we will serve our communities, our country and the world in ways we could never have imagined even a few years ago.”

Upon completion of the merger, a new holding company called Walgreens Boots Alliance Inc. will be formed with headquarters in the Chicago area.

It will encompass four divisions: Walgreens, which will retain its base in Deerfield, Ill.; Boots, the leading drug store chain in the United Kingdom and Republic of Ireland, which will remain based in Nottingham, England; Pharmaceutical Wholesale and International Retail, which will include Alliance Healthcare, Europe’s largest pharmaceutical wholesaler; and Global Brands. A cross-divisional global pharmacy market access group will also be formed by the holding company.

Leading the combined entity as president and CEO will be Greg Wasson, who currently holds those titles at Walgreens. Stefano Pessina, executive chairman of Alliance Boots, will become executive vice chairman of the combined company, taking responsibility for strategy and mergers and acquisition. Pessina, who will report to Wasson, will also chair a new strategy committee on the board.

Other key leadership positions, all of whom will be corporate executive vice presidents, include Alex Gourlay, currently president of customer experience and daily living at Walgreens, who will become president of that division. Gourlay moved to Walgreens last year from Alliance Boots, where he was chief executive officer of its health and beauty division since 2009.

Jeff Berkowitz, who is president of Walgreens Boots Alliance Development GmbH, will take on the role of president of pharma and global market access. Ornella Barra, who is CEO of wholesale and brands for Alliance Boots, will be president and CEO of global wholesale and international retail.

Simon Roberts will move from his current position as managing director of health and beauty for the U.K. and the Republic of Ireland at Alliance Boots to become president of Boots. Finally, Ken Murphy, who now is managing director of Health & Beauty International and brands for Alliance Boots, will be president of global brands.

The combined entity will operate more than 11,000 stores in 10 countries and operate the biggest pharmaceutical wholesale and distribution network in the world, with more than 370 distribution facilities supplying over 180,000 pharmacies, doctors, hospitals and health centers in 20 countries.

“The expected creation of the new enterprise will represent the most significant milestone in the history of Alliance Boots and, importantly, a very positive step for the health care industry as a whole,” says Pessina.

Management also unveiled a three-year “Next Chapter” financial plan. In 2012 the companies projected fiscal 2016 revenues of $130 billion and adjusted operating profit of $9 billion to $9.5 billion, with approximately $1 billion in net synergies. The new plan projects revenues of $126 billion to $130 billion for fiscal 2016, with adjusted net earnings of $4.25 to $4.60 per diluted share and more than $1 billion in synergies.