removing spaces between single characters with regual expression

[ciapecki]

I want to remove the spaces in the string only then when they stand
between 2 single characters.
for example: O J Simpson should be translated into OJ Simpson
'A B C' -> 'ABC'
'AB C' -> 'AB C' (no change)
'Teddy Bear A B' -> 'Teddy Bear AB'

how can I do that with regular expression?
Thanks for your help
chris