This is from the perlre manpage. I've not used it before so this is a first stab:
\Q quote (disable) pattern metacharacters till \E

my $pattern = "ABC()DEF";

my $string = "ABC()DEF";

if ($string =~ /\Q$pattern\E/) { print "match 1\n" }
if ($string =~ /$pattern/) { print "match 2\n" }
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You can see that putting your variable between \Q and \E in the regex disables the ( and ) metacharacters in the pattern. (I think!).