Bethesda-based self-advised real estate investment trust DiamondRock Hospitality Company announced Tuesday that it prepaid the $201.7 million mortgage loan secured by the Chicago Marriott Downtown Magnificent Mile. The company funded the prepayment with proceeds from the 4.36 percent fixed interest rate, 10-year loan placed on the Boston Westin Waterfront Hotel in October 2015, as well as a portion of a $60 million draw on its senior unsecured credit facility. The mortgage was scheduled to mature in April 2016 and the prepayment will save the company approximately $2.7 million in net interest expense.