DEERFIELD, Ill. — Walgreen Co. plans to acquire a 45% equity interest in global pharmaceutical, health and beauty retailer and wholesaler Alliance Boots for $6.7 billion in cash and stock, with the option to buy the remaining 55% of the company in about three years for $9.5 billion in cash and stock.

Walgreens and Alliance Boots on Tuesday called their partnership "the first global, pharmacy-led health and well-being enterprise," noting that the two companies represent the largest retail pharmacy, health and daily living destinations in the United States and Europe. Combined, they would be the world’s biggest purchaser of prescription drugs and a host of other health-related products.

Plans call for the retail and wholesale businesses of Walgreens and Alliance Boots to continue to operate under their brand names. The companies said no job reductions are expected, given their complementary geographic footprints. Walgreens will keep its headquarters in Deerfield, Ill., and Alliance Boots will maintain its support offices in Europe, including in the United Kingdom, as well as the Boots operational hub in Nottingham, England.

Completion of the initial investment, subject to various regulatory approvals, is expected by Sept. 1.

According to Walgreens and Alliance Boots, the chief short- and long-term opportunities of the combination are procurement synergies — including prescription drug, over-the-counter and front-end purchasing, and indirect spend — as well as revenue synergies from introducing Alliance Boots product brands to Walgreens and Duane Reade stores and sharing of best practices, namely in pharmacy operations, health and wellness services, and logistics.

"At Walgreens, our mission is to be America’s first choice for health and daily living — helping our customers to live well, stay well and get well. Today’s announcement represents an exciting opportunity to accelerate our five core strategies and advance that mission — in the United States and now internationally. We are bringing together the strengths and expertise of each company to create a worldwide health care platform for the future that can provide innovative ways to address global health and wellness challenges," Walgreens president and chief executive officer Greg Wasson said in a statement.

Stefano Pessina, executive chairman of Alliance Boots, called the deal a further step in achieving Alliance Boots’ vision of becoming a global health care leader.

"We believe it will bring clear benefits to all stakeholders, creating significant and sustainable industrial value through synergies and the deployment of our joint expertise," Pessina stated. "The fit is natural. Walgreens’ consumer profile in the U.S. is similar to Boots in the U.K. in many ways: a trusted and much-loved pharmacy brand with a strong heritage. Our pharmaceutical wholesale businesses will provide their logistics know-how to Walgreens and are well-placed to be one of the growth engines of the new enterprise.

"Today’s announcement is testimony to the great track record and accomplishments of the Alliance Healthcare and Boots teams that have delivered strong growth since the creation of Alliance Boots six years ago and its subsequent privatization," Pessina added. "I strongly believe that this transaction offers further significant growth opportunities and marks a very positive milestone for the health care industry as a whole."

Walgreens operates 7,890 drug stores in all 50 states and had fiscal 2011 sales of $72 billion. Also, its Take Care Health Systems subsidiary includes more than 700 in-store and work-site health care clinics.

Most of Alliance Boots’ more than 3,300 retail stores contain a pharmacy department.

Alliance Boots, with total sales of about $35.7 billion, has pharmacy-led health and beauty retail businesses in 11 countries and operates over 3,330 health and beauty retail stores, just over 3,200 of which have a pharmacy.

In addition, Alliance Boots has about 625 optical practices, and its pharmaceutical wholesale businesses supply medicines, other health care products and related services to more than 170,000 pharmacies, doctors, health centers and hospitals from over 370 distribution centers in 21 countries.

With the transaction, Walgreens and Alliance Boots together would operate more than 11,000 stores in 12 countries and have the largest global pharmaceutical wholesale and distribution network.

The combined portfolio of retail and business brands would include Walgreens, Duane Reade, Boots and Alliance Healthcare as well as such global health and beauty brands as No7, Botanics and Boots Laboratories.

Upon completion of Walgreens’ initial investment in Alliance Boots, Wasson and Walgreens’ executive vice president and chief financial officer Wade Miquelon, executive vice president and general counsel Thomas Sabatino, and senior vice president and chief strategy officer Robert Zimmerman will join the Alliance Boots board.

Alliance Boots’ Pessina and Dominic Murphy, director and member of investment firm Kohlberg, Kravis Roberts & Co. (KKR), a large stakeholder in Boots, will join the Walgreens board. Through its funds, KKR will be a key shareholder of Walgreens. Alliance Santé Participations S.A., of which Pessina is a director and whose ultimate ownership is a family trust, will also hold a significant stake in Walgreens.

In mid-morning trading, Walgreens’ stock price was down $1.86, or about 5.8%, to $30.10.

Walgreens said it plans to finance the cash payment for the initial investment with existing cash and new borrowings.

The transaction is expected to be accretive to Walgreens net earnings per diluted share in the first year following completion of the initial step of the transaction, by around 23 cents to 27 cents, excluding onetime transaction costs.

During the six-month period starting two-and-a-half years after the closing of the initial investment, Walgreens can choose to proceed to a full combination and purchase the remaining 55% equity interest in Alliance Boots. The companies said that if Walgreens doesn’t exercise that option, under certain circumstances, its ownership of Alliance Boots will decrease from 45% to 42%, in exchange for nominal consideration to Walgreens.

Walgreens said it expects the combined synergies across both companies to be $100 million to $150 million in the first year and $1 billion by the end of 2016.