# http://perlmonks.org/?node_id=1180396
use strict;
use warnings;

my $sa = 'random,junk no,one,cares about(I,Want,This,stuff) but, (not,this) stuff which&might have-random characters';

my $new= $sa =~ s/
           (?: ^ .*? \( )? # swallow start till first opening paren
           ( [^,)]+ )      # match words (non-delimiters)
           ,?              # swallow delimiter
           (?: \) .* $  )? # swallow first closing paren till EOL

        / $1 #/xgr;

print "#$new";