Infinity Pharmaceuticals Inc. was downgraded to “neutral’’ from “overweight’’ at Piper Jaffray by analyst Edward Tenthoff. The 12-month target price is now $11.50 per share. On Monday, Cambridge-based Infinity said that it is is ending Phase 2 trials of its experimental drug saridegib as a treatment for bone and cartilage cancers. The results have been disappointing, the company said. Earlier this year, Infinity discontinued its Phase 2 studies of saridegib for the treatment of pancreatic cancer.