A pedestrian was taken to Boston Medical Center with life-threatening injuries last night after being struck by a motorcycle near 622 Massachusetts Ave. around 8:45 p.m., Boston Police said. Police, who did not identify the victim, shut down a section of Mass. Ave. between Washington Street and Harrison Avenue last night while they worked to reconstruct the accident. There were no reports of injury to the motorcyclist. The Police Department’s homicide unit was called to the scene, though no charges have been filed.