Two functions, used together, can convert non-alpha characters to blanks, then remove the blanks from the string.
Given a field called X that has a value of - "a!b@c#d$e" - first use TRANSLATE to replace the non-alpha characters with blanks like so:
This results in - "
a b c d e".
The second function - STRIPX - is used to remove multiple occurrences of a character from a string. In this case, the blanks created by the TRANSLATE function are removed. Add STRIPX to the calculation above to achieve the final result of "
STRIPX(TRANSLATE(X," ","!@#$")," ")