The three-year-old online discount-coupon company raised the funds, according to a regulatory filing on Thursday, after reports last month that it was in talks to sell itself to Google Inc for up to $6 billion.

Had the talks been successful, it would have been Google's biggest acquisition.

Groupon did not disclose the names of the investors. Company executives could not be reached for a comment.

The bulk of the funds raised — $344.5 million — will be used to buy back stock from existing shareholders, the company said in a filing with the U.S. Securities and Exchange Commission.

Its shareholders include Chief Executive Andrew Mason and Digital Sky Technologies, which also is an investor in Facebook.

"That is a nice little chunk of change," said Justin Byers, head of business intelligence for VC Experts, a firm that follows investments in private companies.

Analysts estimate it has annual revenue ranging from $500 million to $2 billion. It sends members daily e-mails with discounts from local merchants. The discounts are activated when a certain number of people agree to make a purchase.