Use replaceText to replace groups

[Pierre1234]

Hello,
I would like to do something like that:
put replace("titiTotoHello", "(A-Z)", "_\1") into tmp
to get tmp="titi_Toto_Hello"

But livecode does not understand \1 like other languages like python, perl, (or notepad++ ).
It returns: titi_\1oto_\1ello

Is there simple way to do that? Does Livecode fully implements regex?