Orrick Herrington & Sutcliffe and four partners at the firm are the defendants in one suit, with Dorsey & Whitney and six of its partners named in the other.
The amount of profits sought is unknown to the trustee, Ronald Greenspan, according to the suits. He is asking the judge to order the firms and former Brobeck partners to render an accounting of all revenue and expenses related to unfinished business or work done as the result of opportunities that originated at Brobeck.
"When a partner disassociates from a partnership or the partnership dissolves, the net income from all partnership opportunities remains the property of the partnership," the trustee argues in the filing, made on 28 March.
The claim comes after Morgan Lewis & Bockius paid the Brobeck estate $10.2m (£5.11m) in 2004 to settle claims related to its acquisition of 58 Brobeck partners. Morgan Lewis chairman Francis Milone said at the time that the issues were "far from clear" but that the firm settled to avoid protracted litigation.
Magic circle giant Clifford Chance agreed to a similar $3.75m (£1.88m) settlement earlier that year.
Greenspan has also collected an estimated $24m (£12.03m) from some 200 former Brobeck partners for various claims.
The other ex-partners named in the filings are Grady Bolding and Frederick Holden of Orrick; Patrick Arrington, John Baker, Ellen Bancroft, David Hayes and Gabrielle Wirth of Dorsey; James Baker, who moved from Orrick to Jones Day in 2005; and Scott Santagata, formerly of Dorsey.
Brobeck dissolved in February 2003 following the collapse of its core technology market. Although no other law firms are named in the suits, other firms with former Brobeck partners could potentially also face suits.
Orrick is being represented by Howard Rice Nemerovski Canady Falk & Rabkin partners Jonathan Hughes and Pamela Phillips. Greenspan is being advised by Hennigan Bennett & Dorman partner Bennett Murphy.
Dorsey & Whitney declined to comment. A spokesman for Orrick said: "Because this matter involves ongoing litigation, we don't feel it's appropriate to provide our views at this time."
According to the trustee's filing, about 1,145 creditors have filed claims in the case, totaling $258m in potential liabilities.
The Recorder is a US sister title of Legal Week.
