Five years ago, it would have been "unheard of" for a private equity fund to maintain a substantial minority shareholder position following the sale of one of its portfolio companies, say the leaders of McDermott Will & Emery's corporate practice.

But that's exactly what happened this year when Boston-based client Ampersand Capital Partners rolled over its entire equity stake in biotech provider Vivitide, when KKR-backed Biosynth Carbosyn acquired the company. Lawyers at the firm say Ampersand maintains a "substantial" minority stake in the combined entity, which introduces novel issues related to governance structures and the seller's ability to retrieve its investment by a certain date.