Amazon.com Inc, in keeping with a strategy of building up its services and brand name instead of looking for near-term profits, said Monday that it made three acquisitions at a total cost of $645m in stock. The online retailer bought Exchange.com Inc, a Cambridge, Massachusetts-based company that offers hard-to-find, antiquarian, and used books at www.bibliofind.com, and hard-to- find recordings and music memorabilia at www.musicfile.com.

Bibliofind is said to offer more than nine million items, while MusicFile has more than three million items for sale. Amazon said the acquisition will greatly increase its selection of rare and obscure goods, while giving the independent dealers who use the two services access to its estimated eight million online shoppers.

Amazon has also agreed to buy Redwood City, California-based Accept.com Inc, which is described as an e-commerce company that is developing technology to simplify person-to-person and business-to-consumer transactions on the internet. Amazon was no more specific about the company’s offerings or how they would be integrated into its business.

The third company being acquired is Alexa Internet Inc, which offers a free advertising-supported web navigation service that works with internet browsers to provide users with information about sites being viewed and make suggestions on related sites. Again, Amazon declined to elaborate on its plans for the San Francisco-based company.

Amazon said it is acquiring all of the outstanding shares and assuming all outstanding options of the three companies and the deals are expected to close before June 30. All three transactions will accounted as purchases and are subject to customary closing conditions, including shareholder and regulatory approval. No further financial details were disclosed.