Boston-based REIT Winthrop Realty Trust has acquired two first mortgage loans, one in California and one in Arizona, for $44 million.

The trust acquired a first mortgage loan secured by a 19-story, 289,000-square-foot office building located at 160 Spear St. in San Francisco and a first mortgage loan secured by a two-building, four-story office complex containing 116,000 square feet in Phoenix. The trust received the mortgages for an aggregate purchase price, after the additional advance of $850,000 on the 160 Spear St. loan, of $44 million.

The 160 Spear loan has an outstanding principal balance of $73.8 million (after giving effect to the $850,000 advance), bears interest at a rate of 6.48 percent, and matures June 9, 2012. The loan is subject to a one-year extension which requires the payment of a $850,000 extension fee.

The Phoenix loan has an outstanding principal balance of $7.2 million, bears interest at 9.8 percent and matures on June 9, 2012. In addition, the borrower has the right to prepay the loan at any time for a discounted payoff amount of $5.5 million.

Winthrop said it acquired both loans from its Concord Debt Holdings joint venture, and financed the purchase from $35 million drawn on its credit line with KeyBank and the balance from its cash reserves.