Global law firm Dorsey & Whitney LLP has entered into a lease agreement with Principal Financial Group Inc. to occupy the 41st floor of 801 Grand Ave. in downtown Des Moines. Dorsey has occupied the skyscraper’s 39th floor since 1992. The firm is expected to relocate by the end of the year to its new space, most recently occupied by the Des Moines Embassy Club. The announcement came as Dorsey celebrates the 20th anniversary of the opening of its Des Moines office.