name of film where diamonds turn into sand at the end

[yermaw]

Me and my brother are trying to remember the name of a film we saw as children (i'm 35 just for reference). My brother is sure it has something to do with a futuristic city and a man in white chasing the 3 main characters, 2 of them of asian descent. I'm not too sure on this as he also believes that the word Alpha appears in the title. The one thing we both remember is the theft of some diamonds which were put in a velvet rope bag at round about the halfway point of the movie and at the end they open the bag to see the diamonds and they have turned into sand when they pour them out the bag.

Any help with this will be brilliant as its been doing our heads in since christmas dinner when we were talking about it.

thanks