The description of the Sanctuary spell (PHB p 272) says:
You ward a creature within range against attack. Until the spell ends, any creature who targets the warded creature with an attack or harmful spell must first make a Wisdom saving throw. On a failed save, the creature must choose a new target or lose the attack or spell.
The description of the Sentinel feat (PHB p 169) says:
When a creature within 5 feet of you makes an attack against a creature other than you...you can use your reaction to make a melee weapon attack against the attacking creature.
If a character with the Sentinel feat is also warded by Sanctuary, and an attacker fails the Wisdom saving throw and attacks a different target within 5 feet of the character, will this still trigger the melee attack reaction?