Connecticut newsprint magnate and art collector Peter Brant is suing the law firm that handled one of his many business dealings, claiming the lawyers cost Brant tens of millions of dollars by failing to warn him that a company he was selling had an underfunded pension plan.

In the lawsuit filed in Superior Court in Stamford, the Greenwich resident is seeking an unspecified amount in damages from Shearman & Sterling, which is based in New York City. The professional malpractice lawsuit also names Douglas P. Bartner, a Shearman & Sterling partner, as a defendant.