Just when it looked as if Yahoo chief Jerry Yang might keep his house in order, billionaire investor Carl Icahn looks set to crash the joint. A source close to the matter said the veteran corporate raider has built up a stake in Yahoo in the last week and plans to run a slate of proxy directors in an effort to force the company back to the negotiating table with Microsoft. It is unlikely that Icahn will join with other hedge funds in the campaign, the source added.

Singapore Airlines has invited offers for its 49 percent stake in Richard Branson’s Virgin Atlantic. The world’s second-biggest airline by market value bought the stake from the British billionaire in 1999 for 800 million pounds ($1.6 billion). “It’s not a secret that we regard it as an underperforming investment. We are still reviewing our plans and are open to all reasonable offers,” Singapore Airlines Chief Executive Chew Choon Seng said. “But as they say in classified ads: No timewasters, please.”

The protracted dispute over the leveraged buyout of U.S. radio operator Clear Channel Communications ended late yesterday as the parties reached agreement to settle the litigation and struck a new deal at a lower price of $17.9 billion. It brings to an end court battles between the private equity buyers, Clear Channel, and the banks which agreed to finance the deal when lending was more lucrative. The new deal will see Thomas H. Lee Partners and Bain Capital pay $36 a share to buy the radio operator, as opposed to the $39.20 they agreed at the peak of the private equity boom last year.

U.S. drugmaker Pfizer is exploring acquisition possibilities in the German biotech sector and has held talks with the management of Munich-based MediGene, two industry sources said. MediGene shares rose 13 percent to 6.3 euros after the news, valuing the group — which specialises in cancer treatment — at around 210 million euros ($325 million). For Pfizer, the world’s biggest drugs company, MediGene would be an easily digested acquisition and the New York-based company has a past history of buying up smaller companies with promising products or technologies. Pfizer Chief Financial Officer Frank D’Amelio said Pfizer’s recent focus was on smaller transactions, and he did not feel obliged to buy mid-size drugmakers, in the $10 billion to $15 billion price range, as some analysts have urged.

TomTom, the world’s biggest maker of car navigation devices, won unconditional permission from the European Commission to buy its main map supplier, Tele Atlas, for 2.9 billion euros ($4.5 billion). U.S. authorities cleared the deal last year.

Tesco, Britain’s biggest retailer, is buying 36 discount stores from South Korea’s E-Land for $1.9 billion — its biggest single acquisition to date. Tesco, like global rivals Wal-Mart and Carrefour, is seeking to expand in fast-growing international markets to offset slowing growth at home. South Korea is Tesco’s second most profitable market after Britain.

Other deals of the day:

* SK Telecom, South Korea’s top mobile operator, said it was holding preliminary discussions with Virgin Mobile over SK’s U.S. mobile business Helio.

* Hunan Nonferrous Metals Corp, China’s top zinc producer, plans to pay up to $77 million for control of Abra Mining, an Australian lead, zinc, gold and silver mining firm in which it already has a 17.8 percent stake.

* Russia’s former electricity monopoly will sell the government’s 29 percent stake in power producer TGK-11 to engineering firm E4 Group, sources close to the sale told Reuters.