Bkara, Manssouri and the 17-year-old boy, followed the 75-year-old man and his wife as they left a shop in Long Causeway on September 16.
As they approached Minister Precincts, one of the men sprayed the victim in the face which caused his eyes to sting, distracting him so they could steal his watch.
The victim notified a nearby security guard and the trio were tracked on CCTV removing clothing while heading towards the taxi rank on Broadway.
The taxi was followed by CCTV and later an unmarked police car and pulled over on the Spittals roundabout heading towards Huntingdon where the three were arrested and the victim’s watch located in the vehicle.
They were sentenced at Cambridge Crown Court on Friday (20 November) after previously pleading guilty to robbery.
Bkara, of Alexandra Road, London was sentenced to 51 months in prison. Manssouri, of no fixed abode was sentenced to 49 months in prison and the teenager from Peterborough was given a 24-month detention and training order.
Detective Sergeant Justin Parr said: "This was a planned robbery on a vulnerable individual who was simply going about his daily business. This result was a combination of great work between security, CCTV operators and police. I am pleased that we have taken these violent offenders off the streets of Cambridgeshire."