Thomas and Raymond Kwok, the billionaire brothers and real estate developers charged in one of Hong Kong’s biggest corruption cases, pleaded not guilty Friday.

The brothers, co-chairmen of Sun Hung Kai Properties, were accused by prosecutors last April of participating in a decade-long bribery scheme in which they provided $4.5 million in interest-free loans and other benefits to a longtime senior bureaucrat, Rafael Hui, who was Hong Kong’s chief secretary and head of civil service from 2005 to 2007, in exchange for undisclosed favors.