Blackstone defaulted on the $308 million mortgage on a Manhattan office tower more than a year ago — and the debt is now up for sale at a discount of more than 50%.Special servicer Midland Loan Services was hired by brokerage Jones Lang LaSalle to sell Blackstone’s loan, which is backed by 1740 Broadway, a 26-story Art Deco-style tower between 55th and 56th streets, according to Bloomberg, citing people familiar with the matter.JLL has packaged the debt into a commercial mortgage-backed security for $150 m ...