Sullivan & Cromwell has been drafted in to advise Microsoft on its landmark $44.6bn (£22.7bn) attempted takeover of internet giant Yahoo! after New York rival Simpson Thacher & Bartlett was conflicted out.

Simpson Thacher last week confirmed that it had been forced to withdraw from the deal due to a conflict that could not be resolved. The firm had initially been handed the lead role for Microsoft, as reported by legalweek.com (4 February).

Sullivan is now fielding a team for the technology giant led by corporate partner James Morphy, and including fellow corporate partners Duncan McCurrach and Alexandra Korry in New York and Eric Krautheimer in Los Angeles.

Simpson Thacher's initial appointment over Sullivan had come as a surprise to some as Sullivan has historically been one of Microsoft's main corporate advisers.

Cadwalader Wickersham & Taft will continue to work alongside Sullivan advising Microsoft on antitrust aspects of the approach. The firm's team is being led by global antitrust chief Rick Rule.

Skadden Arps Slate Meagher & Flom has the lead advisory role for Yahoo!.

Pete Ruegger, chairman of Simpson Thacher's executive committee, said in a statement: "We hold Microsoft and its team in the highest regard. However, in order for us to fulfill our ethical obligations to each of our clients, it became necessary for us to withdraw from this representation."

Microsoft announced on 1 February that it had proposed to the Yahoo! board of directors to buy all outstanding shares of Yahoo!'s common stock as it bids to compete with undisputed online advertising market-leader Google.

The Yahoo! board has yet to accept the Microsoft offer, prompting expectations that the bid could turn hostile.