Using REGEXP_REPLACE in Oracle Am trying to use backreference expression to take out three subexpressions from a search, and reposition each subexpression as follows:

 SELECT REGEXP_REPLACE('AAA 123 ppp','(^[[:alpha:]]+) ([[:digit:]]) ([[:alpha:]]+)','\3 \1 \2') from dual


However am getting the result as AAA 123 ppp where expecting ppp AAA 123
Where am i getting it wrong?
Missing + after [[:digit:]]

select  regexp_replace('AAA 123 ppp','(^[[:alpha:]]+) ([[:digit:]]+) ([[:alpha:]]+)','\3 \1 \2') 
from    dual



  ppp AAA 123