UPDATE 1-Turkish discount grocer Sok sees IPO of around 2.6 bln lira -bookrunner

ISTANBUL, April 9 (Reuters) - Turkish discount grocer Sok plans to raise at least 2.6 billion lira ($640 million) in an initial public offering (IPO) to pay down debt, one of the bookrunners said on Monday, the latest in a series of high-profile listings in Istanbul.