$re = '/^(.*?)(?!(?:\(.?\)))END$/m';
$str = 'START OF THE SHOW with some gibberish characters (I) also lots of non-sense things (II) with boring end ()END
START OF THE SHOW with some gibberish characters () also lots of non-sense things () with boring end ()END
START OF THE SHOW with some gibberish characters (I) also lots of non-sense things (II) with boring end (III)END
START OF THE SHOW with some gibberish characters (1) also lots of non-sense things (2) with boring end (3)END
START OF THE SHOW with some gibberish characters (111) also lots of non-sense things (222) with boring end (333)END';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php