regsub -all {[^A-Z,a-z]} $x “” y
ought to do the trick, where x is the input string and y is the output string.
Hope this helps,
Bob
This will also leave commas in the field. If the system barks at anything but alphas you might want to change it to:
regsub -all {[^A-Za-z]} $x {} y
or
regsub -all -nocase {[^a-z]} $x {} y